Mounting Evidence Suggests Coronavirus is Airborne
Authentic Wein® Air Purifiers Can Help
Now that Covid-19 is being recognized as a potential airborne hazard- with micro droplets under 5 microns in size that can remain airborne and travel great distances- you must not only wear a mask but make sure you are in a well ventilated area to avoid inhaling an infectious dose. In a recent article from the New York Times by Apoorva Mandavilli, “It’s Not Whether You Were Exposed to the Virus. It’s How Much.”
“It’s clear that one doesn’t have to be sick and coughing and sneezing for transmission to occur,” said Dr. Dan Barouch, a viral immunologist at Beth Israel Deaconess Medical Center in Boston.
Larger droplets are heavy and float down quickly — unless there’s a breeze or an air-conditioning blast — and can’t penetrate surgical masks. But droplets less than 5 microns in diameter, called aerosols, can linger in the air for hours.
“They travel further, last longer and have the potential of more spread than the large droplets,” Dr. Barouch said. Three factors seem to be particularly important for aerosol transmission: proximity to the infected person, air flow and timing.
A windowless public bathroom with high foot traffic is riskier than a bathroom with a window, or a bathroom that’s rarely used. A short outdoor conversation with a masked neighbor is much safer than either of those scenarios.”1
Online you can find hundreds of wearable air purifiers that claim to protect you from Covid-19. However, cheaply manufactured air purifiers, sold by mail order companies in the United States for a significant markup, can actually deposit Covid-19 on exposed skin, hair and clothing, leading to infection. Without production of ion wind, as well as an electrostatic exclusion zone, these devices are not addressing the three factors mentioned in the article that should be considered to avoid transmission of an infectious dose of Covid-19.
Wein® is the inventor and originator of the advanced Air Supply® AS-300R personal air purifier! This rechargeable air purifier, with 28 hours of run time per charge, is ultra lightweight, wearable and propels cleaner, fresher and healthier air into your personal breathing zone. Created especially to help sufferers who want to breathe more easily when they travel. Ounce for ounce the AS-300R outperforms the competition and is top of the line in personal air purification. With an advanced plasma discharge design, the AS-300R comes with solid platinum emitter and stainless steel grid. This Air Supply® Rechargeable also comes with a breakaway strap for user safety.
In addition to wearing a mask, Wein® products including the Air Supply and two Minimate models, can substantially counter all three hazards. The air purifiers create an intense ion wind to provide effective isolation distancing, lowering the concentration of Covid-19 exposure. Wein® Viramask, an antibacterial face mask, plus the electrostatic charging and exclusion zone, tends to counter exposure time. Ventilation and covid concentration reduction is one of the key factors in lowering the risk of airborne viral infection!
In the same article, Dutch researchers at the University of Amsterdam found that even the smallest breeze is effective at lowering Covid concentration and infectious doses. By using a special spray nozzle to simulate the expulsion of saliva droplets, then tracking their movement, “the scientists found that just cracking open a door or a window can banish aerosols.” The Air Supply AS300R produces over 90 ft/min. in counter airflow against airborne pathogens.
Observations from two hospitals in Wuhan, China, published in April in the journal Nature, determined much the same thing: more aerosolized particles were found in unventilated toilet areas than in airier patient rooms or crowded public areas.1
Wein® wearable air purifiers can provide critical ventilation around the mouth, nose and eyes, including on the mask’s surface, of more than 50 ft/min. of purified ionizing airflow against airborne Covid virus anywhere you go. None of the inferior air purifiers can do this because they don’t have the dynamic, cleansed airflow of the Wein® units. Some of these units actually require you to place a conductive neck cord around your neck that makes you part of the electrical circuit. This is not safe!
Wein Products is Pleased to Announce the Introduction of Kovidex Coming Soon!
Kovidex table top electrodynamic plasma virus remover and air cleaner, available first quarter 2021
Virologists believe Viruses are transmitted to others in sneezes and coughs and even normal breathing and talking. These exchanges can release large short range droplets containing viruses greater than 10 microns in aerodynamic diameter, and also release much longer range semi evaporated smaller droplets called droplet nuclei which are semi desiccated evaporated droplets less than 10 microns. These droplets can become airborne depending on prevailing air drafts. Fomites which can also land on surfaces that are touched and find their way onto mucous membranes in the mouth nose and eyes.
Depending on air currents which can cause reintrainment of fromites on surfaces into the air; these aprticles are the most worrisome, as transmission is long range airborne droplet nuclei that can remain airborne indefinitely and travel though air ducts and throughout a facility. Virologists presently think that the Coronavirus COVID -19 is also airborne.
The Kovidex table top plasma room virus concentration reducer and air cleaner is here to save the day!
The Kovidex operates 24/7, under 50 watts, and silently vacuums room virus, bacteria, mold spores, and toxic allergenic pollutants and contaminants. These particles pass through a very intense plasma chamber of 13.5 trillion ions per cc, ozone dissociated into singlet oxygen reactive oxygen species, intense ionizing wind, and electron impact decomposition. The air flow then transits a super efficient ozone catalyst exit grill. Ozone levels are below .05 parts per million with fanless, noiseless, electrodynamic airflow of greater than 200 CFM.
Kovidex is a technology whose time has come as a weapon against airborne viruses and droplet transmission by coughing, sneezing, talking, and exhalation. Kovidex lowers the concentration of toxic and infectious respiratory challenges in the air we breathe and thereby lowers the risk of inhalation according to respiratory protection authorities.
Attractive ABS plastic aesthetic table top cabinet.
50 watt continuous service dc universal worldwide adapter.
Dim 14" x 12" x 6".
Internal high efficiency permanent ozone catalytic grill.
Ozone output less than .05 twa ppm.
wt. 7 pounds
Fanless silent electrodynamic ionic wind.
Suggested retail $450.
Kovidex electrodynamic technology is not a conventional electrostatic air purifier!
It is much more than that! Firstly the technology has been designed specifically to combat microbes, including airborne bacterial mold spores and especially viruses of all kinds including the Coronavirus (SARS MERS and COVID-19). This is done by targeting their aerodynamic size ranges of .01 to 20 microns and depends on if they are desiccated or in droplet form. There are no mechanical fans or noise but pure soundless laminar air flow streaming out of the KOVIDEX. Noise and beating fans stir up dust and further exacerbate virus dispersal and can reentrant virus deposited on surfaces into the air making them airborne.
After years of innovative research and development, Wein Products has invented a silent air-motor that produces laminal air flow to drive room circulation through our 13.5 trillion ions per cubic centimeter, 20KV plasma chamber, which can destroy most virus and bacteria continuously with every air exchange.
The Kovidex also produces a safe level of ozone. There is no known virus that ozone cannot destroy. Using ozone is much better than UV light, as it is not line of sight, and creeps into every crevice. Ozone has also been shown to be one of the best oxidizers known to man.
Ozone is heavier than ambient air and sinks to the floor to increased concentration; this destroys or inactivates droplet containing viruses (that also sink to the floor in 4 to 6 feet). Ozone concentration levels never exceed EPA standards on inhalation, as the human breathing zone is essentially 100% relative humidity which destroys Ozone molecules.
From Inventor Stan Weinberg:
KOVIDEX is NOT AN AIR PURIFIER OR CLEANER BUT AN AIRBORNE COVID-19 DISSINFECTION MACHINE THAT WAS DESIGNED AND VALIDATED SPECIFICALLY TO DISSINFECT A LARGE ROOM OF COVID -19.
IT DOES SO BY CONTINUOUSLY RECYCLING ROOM AIR EXCHANGES THROUGH A HIGH ENERGY PLASMA FIELD OF 13TRILLION IONS PER SECOND THAT MUST BE THE MOST PATHOGEN LETHAL ENVIRONMENT KNOWN TO MODERN SCIENCE OF REACTIVE OXYGEN SPECIES (ROS), INTENSE ELECTRON IMPACT DECOMPOSITION, OZONATION, ULTRA VIOLET RADIATION, OXIDATION SPECIES , SINGLET OXYGEN AND TREMENDOUS IONIZATION!
THE KOVIDEX CONTINOUSLY RECYCLES EXISTING ROOM AIR SO THE PATHOGEN ULTIMATELY IS INACTIVATED ACCORDING TO THE LATEST VALIDATION STUDIES AS SHOWN IN THE GRAPHICAL PRESENTATION.
THE KOVIDEX HAS NO FILTERS TO REMOVE OR SERVICE THUS PREVENTING ROOM REINTRAINMENT OF COVID-19 FROM BECOMING AIRBORNE AGAIN. AFTER A FEW MINUTES OF OPERATION SOPHISTICATED OPTICAL PARTICLE COUNTERS AT KOVIDEX EXIT GRILL SHOWS VIRTUALLY ZERO PARTICULATES EXITING IN THE 300 CFM SOUNDLESS , FANLESS ELECTRONIC PLASMA WIND.
MOST ORDINARY AIR PURIFIERS OPERATING AT 300CFM ARE MUCH TO NOISY TO BE USED FOR ANY LENGTH OF TIME IN RESIDENTIAL , MEDICAL OR COMMERCIAL SETTINGS.
KOVIDEX WILL BE AVAILABLE AFTER BETA TESTING IN FIRST QUARTER 2021 MSRP WHITE ONLY $450. QUANTITY DISCOUNTS AVAILABLE.
OTHER BIG ADVANTAGES: AIRBORNE COVID-19 DISINFECTION OF LARGE ROOMS WITH FULL HUMAN CONTINUAL OCCUPANCY! SAFE FOR HUMAN OCCUPANCY DURING DISSINFECTION! USES LESS THAN 60 WATTS
ALL OTHER ROOM DISSINFECTION METHODS RESTRICT HUMAN OCCUPANCY WHILE THE DISSINFECTION AGENT DISSIPATES OR INTENSE UVC IS SHUT OFF. Also ECONOMIC COSTS ARE A FRACTION OF THE COST OF CONVENTIONAL DISSINFECTION.METHODS USING TRAINED PERSONNEL USING SPECIALIZED PERSONAL PROTECTIVE EQUIPMENT . EXPENSIVE EXTREMELY LOUD AIR PURIFIERS ARE A MAINTENANCE FILTER REPLACEMENT HAZARD AND MAY JUST FILTER AND STORE THE COVID-19 VIRUS . WITH MOOD AND SLEEP DEPREVATION BECAUSE OF LOUD MOTOR FAN NOISES. KOVIDEX IS COMPLETELY SILENT!
Note these first of its king KOVIDEX are BETA TESTING DEVICES AND Please send any comments or performance issues back to the factory to improve any deficiencies. We do know that multiple Validation studies by world authorities in respiratory protection show that the KOVIDEX is extremely efficient in removing Virus sized particles from room air quickly. If Kovidex produces and static sounds simply clean the internal PLASMA ARRAY CHAMBER BY INVERTING KOVIDEX A DOZEN TIMES WITH POWER OFF. You well hear glass beads inside sliding up and down and cleaning the ARRAY TUNGSTEN WIRES inside. The static noise also helps clean the array wires.
KOVIDEX has a permanent but removable Ozone/Virus servicing filter by inverting unit, turning Kovidex off and sliding up the front foot of the Kovidex you can spray bleach on the metal filter and rinse with water and dry with hair dryer . Servicing required only every month or so but use PPE or facemask to remove Ozone / Virus filter before spraying with bleach and drying.
Caution USE ONLY THE PROVIDED ADAPTER for AC 100 to 240 volts AC to 26 volts 2A
plug in AC adapter and adapter light should glow green and activate rocker switch to ON. Blue light should turn on above rocker switch showing plasma field is active. and large ion wind will be emitted from front grill of KOVIDEX. Leave on 24/7
Unit is now processing over 100 cubic feet per minute and removing 99% of Virus and droplet sized particulates from ambient air in the room SILENTLY In 30 minutes almost 100% are removed from room air. The KOVIDEX is selectively designed to remove from .01 to 2.5 microns Virus sized fractions which only the best HEPA filters can match and do it silently. HEPA FILTRATION by contrast is extremely noisy and will not permit restful sleep.
The USER FRIENDLY KOVIDEX has only one speed setting at maximum efficiency. So set and forget and BREATHE AGAIN WITH CONFIDENCE!!
It is exciting to see a removal efficiency of 98 to 99+ % which your Kovidex unit achieves. A very substantial removal level for particles in the size range of COVID-19 novel corona virus. I am very excited about the performance evaluation data obtained! Reducing airborne particle concentrations in this size range is a direct and powerful way to decrease health risk in humans.
— Sergey A Grinshpun, Ph.D. Professor, Director, Center Health related Aerosol Studies
Department of Environmental & Public Health Sciences, University of Cincinnati. www.eh.uc.edu/aerosol
Figure 1 presents the decay of the total non-dimensional concentration (C/C0) of aerosol particles in the range of 0.01 – 2.5 µm as measured by the P-Trak CPC. The particle physical removal effect is strong. E.g., in 10 min of operation of the KOVIDEX Ion Purifier, the aerosol concentration dropped by a factor of 3-8 while the natural decay produces only 15% decay. In 30 min, the total aerosol concentration is about 3% of the initial level (on average) while the natural decay is responsible for only 1/3 of the decrease. Finally, a 50-min operation decreases the total concentration to the value <1% of the initial level (the natural decay would decrease it only twice).
Figure 2 presents the natural and purifier-enhanced decays of the total non-dimensional concentration measured with the GRIMM system (nano + optical) in about the same size range. The results are generally similar.
Figure 3 shows non-dimensional fractional concentrations (natural decay and purifier-enhanced decay) measured with the GRIMM system in three particle size ranges selected from the menu of channels available in this measurement system. The first one, 0.052-0.140 µm, approximately represents the coronavirus size range with a peak of ≈ 0.10-0.13 µm (a single virion diameter); this size range is rather inclusive reflecting a variety of methods utilized for measuring coronavirus (e.g., cryo-electron tomography and cryo-electron microscopy on substrates, particle mobility analysis in aerosol, etc.) as well as the GRIMM measurement capability. The second, 0.19-0.58 µm, represents relatively small virus-carriers or agglomerates. The third, 1.0-2.5 µm, represents larger (super-micrometer) particles that may carry these viruses.
Figure 4 presents the physical removal efficiency, ɛ, of the total Grimm-measured aerosol. It took 30 min to achieve a 90% efficiency, and 40 min to achieve a 95% efficiency. In approximately 50 min, the efficiency of the total aerosol removal reached 96-97% and stayed at that plateau level for the entire test time (till the measurement stopped at 90 min).
Figure 5 presents the results of the same experiment, but the data were recorded for the three above-listed particle size ranges. It was observed that aerosol particles of the range, which includes the coronavirus size, as well as larger 1.0-2.5 µm particles are almost fully removed (ɛ ≈ 98-99.7%) in 50 min of the purifier operation. The fraction of 0.19-0.58 µm was removed at an efficiency of ≈98-99% and then ɛ saturated at this level. Based on the findings shown in Figures 4 and 5 it was hypothesized that a certain particle background, perhaps associated with the particles generated by the Purifier or the GRIMM system in the range between ≈ 0.15 and 1.0 µm may affects the results preventing us from seeing the efficiency levels in excess of ≈99% for this size fraction. This phenomenon needs a separate investigation.
In addition to the data reported above, we calculated the Clean Air Delivery Rate (CADR) for different times of operation and for different aerosol fractions (total and the coronavirus range). Table 1 presents the results. The CADR ranged from 60 to 73 CFM for the total and from 67 to 92 CFM for the coronavirus-representing sizes.
Table 1. CADR, CFM (calculated, approximated)
We also observed that the KOVIDEX Purifier operated at a very low noise level.
No excessive ozone generation was observed (the ozone level was continuously monitored downstream of the Purifier; however, we did not conduct a full-scale study that aimed at measuring ozone at different distances from the purifier).
One may ask: "Why wasn't the actual Covid-19 live virus not used to test?"
Covid-19 is not alive but an inert lifeless particle, and obeys the same forces of gravitation electrostatics draft currents. These include: brownian motion, diffusion as any other particle while airborne, in droplet dessicaterd nuclei or large droplet encasement.
Testing with Covid-19 endangers research personnel needlessly. Also virus testing is usually a simulant and the actual virus is never used!
The exact same result of percent elimination is achieved using inert stable particles of the same size and density.
Actual test results can apply universally to all Coronaviruses like MERS and SARS without having to test for different mutations or other Coronaviruses.
How our air purifiers help destroy viruses, including COVID-19
In 1996 Wein Products invented the Minimate Air Supply AS150MM and filed 4 US patents. Since then, Air Supply wearable Minimates have been there to help consumers during the SARS outbreak, Birdflu, Swine Flu, and other pandemic challenges. The Air Supply Minimate also helps with allergies, toxic molds, chemical sensitivities and other airborne contaminant and pollutants.
There have been many copiers and infringers, but none have succeeded in reducing harmfull concentrations of inhalable allergenic pollutants or infectious airborne toxic contaminants in the breathing zone. Nor have these copiers succeeded in reducing unsafe Ozone levels. Air Supply wearable technology has been validated by world authorities in respiratory protection. Many peer reviewed and published studies have shown significant reductions in airborne pathogen sized particulates in the breathing zone by ionization.
Air Supply emits an acceptable level of ozone (.03PPM, EPA, OSHA, NIOSH) that helps destroy pathogens, such as COVID-19 by diffusing through the protein coat into the nucleic acid core in seconds. COVID-19 is an enveloped virus and is usually much more sensitive to short exposure ozone than other viruses.1
In addition to the Air Supply ionization wind that physically helps lower the concentration of the the coronus sized pathogen, Dr. J Cann in his book Principles of Molecular Virology states:
Most damage to human cells during virus infection occurs very early, often before clinical symptoms of viral disease appear. This makes treatment of virus infection very difficult. Therefore in addition to being cheaper prevention of virus infection, is undoubtably better than the cure. In summary the microbe shielding effect is quite effective and can help prevent human airborne pathogenic infection.
— COVID-19 is a perfect example of this.
UCLA testing has also confirmed that Air Supply technology is far superior to any known air cleaner in wearable personal airspace for destruction of both biological and chemical pollutants! Air Supply as a preventative, is far superior therefore to drugs for the following reasons:
No side effects.
Zero microbe resistance or mutations adaption multiple drug resistance.
Fast pathogen destruction.
No recuperation period required.
Bilateral prevention destroys incoming pathogens from infected people helps stop outgoing. Pathogens from infected wearers preventing infection of those nearby.
See Covidex testing results graphs for virus removal efficiency, as the Air Supply is a miniature version of of this, working in a smaller volume of the breathing zone. Also the 5 year study books one and two at University of Cincinnati School of Health Related Aerosol Studies/ Professor Dr. Sergey Grinshpun who has worked with most federal agencies such as CDC, EPA, NIOSH, OSHA, NASA, etc.
Also look at ozone levels chart which monitors basically real life ozone inhalation environments by monitoring levels on inhalation ozone that human inhalation actually experiences instead of artificial contrived ozone chambers that have nothing to do with real world human lung inhalation conditions. Please see ozone solutions website for all ozone answers!
Underwriters Laboratories (UL) and other nationally recognized test laboratories have decided to test our wearable Air Supply as though they were large room air purifiers and cord connected to AC high voltage. They test in accordance with UL 867 for electrostatic air purifiers with an artificial 25º F and with relative humidity of 50% without a person wearing it at a human inhalation position. Even though they don’t test the Air Supply next to the nose at 90º F and 100% relative humidity, under real world conditions, we still pass all safety testing for human safe levels at .03ppm! We are in talks with UL to exclude us from UL 867 as Plenum and Duct testing is excluded now!
Are air ionizers safe for the environment? What should I avoid?
What is ozone?
Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule-- the oxygen we breathe that is essential to life. The third oxygen atom can detach from the ozone molecule, and re-attach to molecules of other substances, thereby altering their chemical composition. It is this ability to react with other substances that forms the basis of manufacturers’ claims for air purification.
What are positive and negatives of ozone?
The phrase "good up high - bad nearby" has been used by the EPA to distinguish between ozone in the upper and lower atmosphere. Ozone in the upper atmosphere, or "stratospheric ozone," helps filter out damaging ultraviolet radiation from the sun. Though ozone in the stratosphere is protective, ozone in the atmosphere (the air we breathe) can be harmful to the respiratory system. Harmful levels of ozone can be produced by the interaction of sunlight with certain chemicals emitted to the environment (such as automobile emissions and chemical emissions of industrial plants). These harmful concentrations of ozone in the atmosphere are often accompanied by high concentrations of other pollutants, including nitrogen dioxide, fine particles and hydrocarbons. Whether pure or mixed with other chemicals, ozone can be harmful to health.
What are air purifiers with ozone?
HEPA/Ionic air purifiers with built-in ozone generating devices use a filter, or electrostatic plates, as their primary means of filtration but utilize ozone to remove odors and freshen the air. There are consumer and commercial grade ozone generators that produce relatively high concentrations of ozone, but otherwise they are ineffective at removing airborne allergens like mold and pollen. While there is nothing “wrong” with ozone generators in controlled applications, they absolutely should not be sold for residential use. When used in the home, these types of air cleaners can be very hazardous to your health.1
What are safe levels of ozone exposure with air purifiers?
Wein Products, Inc. latest air purification system features ionic air purifiers that are filterless, virtually ozoneless and excel at cleaning the air of particles that comparable air filters may miss, such as smoke, fumes, bacteria, viruses and odors wherever you travel. What does virtually ozoneless mean? The Food and Drug Administration (FDA) requires ozone output of indoor medical devices to be no more than 0.05 ppm. Ozone output for the Minimate™ Ionic Air Purifier AS180i and Air Supply® Rechargeable Ionic Air Purifier AS-300R personal air purifiers are both less than .028 ppm, which is well under the standard. In addition, based on extensive scientific evidence about the effects of ozone on public health and welfare, in 2015 the Environmental Protection Agency strengthened the ground-level ozone standard to 0.070 ppm.
What are the differences between Wein Minimate and Air Supply?
Both the Minimate and Air Supply personal air purifiers are meant to be worn, are tested down to virus size range of .04 microns to defend against the coronavirus (Covid-19) and both are filterless, hence maintenance free. So what are the differences in the two wearable devices? First, the Minimate comes with a Lithium CR123A battery that lasts up to 40 hours. The Air Supply is rechargeable and comes with a USB cable for 28 hours of run time per charge. Both are designed to be portable, come with a neck cord and their measurements are similar, though the Minimate is more compact. The Air Supply weighs 2.12 oz. and the Minimate is 1.5 oz.
Coronavirus: What is it and How to Reduce the Risk of Infection
Help combat airborne viruses with the Wein® Air Supply® Rechargeable and Minimate.
The United States recently issued the highest level travel advisory for China over the rapidly spreading outbreak of coronavirus. Delta and United airlines have halted all flights to mainland China. For those who must travel internationally, using a personal ionic air purifier like the Wein® Air Supply® Rechargeable can help (see more about this below).
The World Health Organization (WHO) declared the virus a global public health emergency, requiring states to ramp up their responses. Almost 12,000 people have been diagnosed with the rapidly spreading virus and more than 200 have died, with all fatalities occurring in China.
Coronaviruses are a large family of viruses that range from the common cold to much more serious diseases, according to the World Health Organization. They can infect both humans and animals. The newly emergent strain in China is related to two other coronaviruses that have caused major outbreaks in recent years: MERS, or Middle East respiratory syndrome, and SARS, or severe acute respiratory syndrome. The new virus hasn’t been named yet; it’s referred to as “a novel coronavirus."1
The new virus is believed to have originated from a live animal market in Wuhan. Health authorities say that now the virus is spreading from person to person through coughing, sneezing or touching a surface that is infected, then touching the face or coming into contact with contaminated fecal matter.
Antibiotics are not effective for viruses and there is no medication for this new coronavirus. Health-care professionals are focusing on providing “supportive care,” including ensuring patients get plenty of liquids and oxygen.
In the United States, the Centers for Disease Control and Prevention (CDC) recommend that the best precaution against contracting the virus are to avoid touching your face, stay away from people who are sick, and wash your hands frequently. The CDC also says that Americans shouldn't wear face masks to prevent the spread of the coronavirus. Even though this is counter to the rise in face masks sales, they say masks don't work and give the user a false sense of protection and can lead to a higher rist of coronavirus infection. Face masks effectiveness depends on the type of germs people want to avoid and the type of masks they wear, in addition to having the mask properly fitted.
There are two main types of face mask. N95 respirators, which are generally used to combat smoke or heavy pollution, block out particles as small as 0.3 microns in diameter – but the coronavirus is 0.12 microns wide. Surgical masks, which rarely filter particles smaller than 5 microns, are more common but far less effective.2
Aside from the precautions mentioned, for those who are travelling internationally, wearable ionic air purifiers like the Wein® Air Supply® Rechargeable and Minimate, have shown significant and substantial reductions of airborne, breathable particles from .04 to 3 microns in size. Filterless ionic air purifiers operate by sending out electrically charged ions into the air that bond with harmful impurities. Once a bond is made, these particles become too heavy to stay in the air. This results in the contaminants falling out of the air or grounded object, where they are attracted to the positively charged collection plate and later cleaned off by the owner. In addition to practicing the precautions outlined by the WHO, these devices may help combat airborne germs, bacteria and viruses anywhere you go by lessening the concentration of inhaled airborne infectious contaminants. Lessening the particle concentration reduces the probability of inhaling an infective dose thereby lowering the probability of becoming infected.*
In addition to using a personal ionic air purifier, WHO’s standard recommendations for the general public, to reduce exposure to and transmission of a range of illnesses, are as follows:
Frequently clean hands by using alcohol-based hand rub or soap and water;
When coughing and sneezing cover mouth and nose with flexed elbow or tissue – throw tissue away immediately and wash hands;
Avoid close contact with anyone who has fever and cough;
If you have fever, cough and difficulty breathing seek medical care early and share previous travel history with your health care provider;
When visiting live markets in areas currently experiencing cases of novel coronavirus, avoid direct unprotected contact with live animals and surfaces in contact with animals;
The consumption of raw or undercooked animal products should be avoided. Raw meat, milk or animal organs should be handled with care, to avoid cross-contamination with uncooked foods, as per good food safety practices.
WHO also warned that people of any age can become infected by the virus and that older people and those with pre-existing medical conditions seem to be more vulnerable to becoming severely ill with the virus.
How do HEPA air purifiers compare to filterless ionic air purifiers?
Researching which air purifier to buy can be a tedious task. There are multiple types, a wide variety of prices and consideration of the space you will be using it in. We will give you some information about two of the most popular air filters available today: HEPA filters and ionic air purifiers.
How It Works
High Efficiency Particulate Air (HEPA) filter works by using a fan to force air through a fine mesh that traps harmful particles such as pollen, pet dander, dust mites and tobacco smoke. Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.97% of particles whose diameter is greater than or equal to 0.3 μm. A HEPA filter actually traps airborne contaminants, but can lose any effectiveness once it becomes clogged with debris. Once saturated, the filter can release pollutants trapped on the filter surface back into the air. A HEPA filter also has a greater footprint than filterless air purifiers, since the HEPA filter needs to be replaced approximately every 6-8 months.
A filterless ionic air purifier operates by sending out electrically charged ions into the air that bond with harmful impurities. Once a bond is made, these particles become too heavy to stay in the air. This results in the contaminants falling to the floor or grounded object (depending on the device and placement), where they are attracted to the positively charged collection plate and later cleaned off by the owner. Products that include a collection plate or placed in a neutral location are better at avoiding the chance that particles can be kicked back up into the air when people walk through the room. For example, the Wein® Products Vortex Ionic Air Purifier ion emitter stimulates airflow by discharging ions in a rapid, spiral vortex motion- actually drawing airborne pollutants to the device, instead of waiting for them to randomly pass near the unit. The “on” and “off” feature of the device is beneficial because it regulates the high ion output by intermittently discharging ions. Negatively charged ions are beneficial to the environment because they attract the positive ions found in dust, pollen, bacteria, cigarette smoke and mold spores--and pull these microscopic hazards to the earth using electrostatic forces. This ionic air purifier can filter particles as small as 0.01 μm, including certain viruses, bacteria and fumes.
How big is the space you’re purifying?
The largest space an air purifier with a HEPA filter can purify is about 1,560 sq. ft. This is fine for most home applications, but for a large business space this may not be sufficient. In comparison, some ionizers can purify an air space up to 3,500 sq. ft.
Noise level is another feature to consider when comparing HEPA air purifiers and ionic air purifiers. HEPA air purifiers are designed to circulate air in the room and remove contaminants, dust and allergens by trapping them in filters. Unlike ionic purifiers, HEPA purifiers always use a fan – it’s not possible for a product to work without one. Ionic air purifiers are usually fanless, therefore silent.
Do you want a portable air purifier or one that is stationary? Since ionic purifiers are filterless and fanless they can be much smaller than their counterpart, hence more portable! This allows for the possibility to have a personal air purifier like the Wein® Products Air Supply® Rechargeable that you wear to clean pollutants from the air wherever you go, like doctor appointments, driving, in the office or when traveling.
What about ozone emission safety?
You may have heard about the danger of ozone air purifiers, which use ozone to clean the air. Due to the serious health effects that ozone can have on people, federal agencies have established the following set of health standards for what are considered safe levels of exposure for ozone:
Healthy Amount = 0 to 0.05 ppm
Moderate Concern = 51 to 100 ppm
Hazardous Amount = 100+ ppm
With such standards in place, the Food and Drug Administration (FDA) now requires that ozone output for indoor medical devices is no more than 0.05 parts per million. Any higher and the product would be considered unsafe for continuous home use. Ionic air purifiers, like Wein® Products air purifiers, are ozone-safe and certified by OSHA standards to produce ozone emission concentrations less than 0.050 ppm. Ionic air purifiers should not be confused with ozone air purifiers. Unlike ionizers, ozone generators produce a lot of ozone molecules in the air and don’t internally collect contaminant particles. The idea is for ozone to bond with airborne particulates which then fall from the air. They are commonly used to quickly remove airborne contaminants and odors, however the same thing that makes them efficient is what makes them harmful to humans because of the high ozone output.
The EPA announces nearly 100 Million People are breathing particulates daily.
Regarding Second Hand Smoke:
Second Hand Smoke has been classified by the EPA as a "Group A" human carcinogen meaning there is no safe level of exposure! We at Wein Products support the efforts by Americans For Nonsmokers' Rightsto bring this important safety message to you.
DISCLAIMER: "No air filtration or air purification system has been designed that can eliminate all the harmful constituents of secondhand smoke. A reduction of the harmful constituents of secondhand smoke does not protect against the disease and death caused by exposure to secondhand smoke. The U.S. Surgeon General has determined secondhand smoke to cause heart disease, lung cancer, and respiratory illness."
Position Statement on Second Hand Smoke
Dear Mr. Alpert,
Wein Products has been at the forefront of innovating safe and effective environmental technologies for many years In this effort we have been assisted by Dr. Sergey Grinshpun's excellent team of dedicated scientists at the University of Cincinnati School of Environmental Health Sciences who have tested and validated our products in their toxic aerosol risk assessment laboratories. The studies have been peer reviewed and published in respected journals worldwide . Two new studies completed last year on the respiratory mask enhancement effects of using our equipment have also been accepted for publication. His laboratories are used by most Federal Environmental, Occupational Health and Safety Agencies and he has been a keynote speaker at Homeland Defense Conferences.
Our ionic air purification equipment has been comparison tested against other manufacturers in Dr. Grinshpun's laboratories and in some notable cases is ten times more effective than a leading national brand.
Even so, while air purification technology is rapidly gaining ground and while our systems have been shown in Dr. Grinshpun's laboratories to substantially (98%) reduce the concentrations of all aerosols from .04 (virus sized) to 3 microns. This includes a large portion of the components in second hand smoke.
This reduction cannot protect users of our equipment nor anyone else's from this environmental toxic carcinogen since any exposure is dangerous to human health.
Classification of second hand smoke as a type "A" aerosol toxin makes this a very tough nut to crack but we are working on it.
Please let me know how we can support your humanitarian efforts .
Cordially, Stan Weinberg
Chairman & CEO
Wein Products Inc.
Weinberg Family Charitable Trust
Many people think Influenza is just a seasonal nuisance. It is not just a nuisance . It is ONE OF THE WORST VIRAL INFECTIONS KNOWN TO MAN!
Even with modern Man's advanced medical technology, it kills over a million people world wide every year with over 200,000 birth defects and with over 35,000 deaths in the US alone! For some unfathomable reason it is not A REPORTING DISEASE as designated by the CDC. No accurate records are kept. The worldwide economy also loses over a TRILLION....that is a thousand BILLION dollars a year in unrealized productivity yearly.
If H5N1 mutates to become the next pandemic ( this has happened three times in the last hundred years ) it could destroy the entire world economy for years.
It remains one of the top ten causes of death in the United States. During an ordinary flu season in the USA, over 25% of the population is infected with ordinary type A Influenza in spite of Flu shots . That is in a good year. The shots are only 50% effective for Americans 50 or older and that is if the yearly vaccine components are accurately gauged against the prevalent strains coming from Asia. The chicken egg vaccine production is also outmoded and incapable of ramping up for any extraordinary Public Health threat such as human to human transmissible Avian Influenza like H5N1. This ancient vaccine formulation method developed about 50 years ago, depends on GUESSES by the epidemiologists and is composed of a cocktail of three or four dominant strains based on the viral coatings of these strains which change each year. If they guess wrong as has happened then there is minimal protection.
None of these Methods are applicable to N5N1 as Humans have no resistance to this new emerging disease.
H5N1 virus has over 52% mortality. It can become airborne and it is rapidly mutating to become the next worldwide PANDEMIIC. There is now a raging scientific/medical controversy whether in fact any of the anti viral medicines work against this killer virus.
Avian flu struck in 1918 and wiped out over 50 million people in less than six months. This was the worst epidemic in human history and it happened in the 20th century. It was far worse than the BLACK DEATH in Europe. Sars has a mortality of about 10%, 1918 flu about 15%. H5N1 about 52%.
If it happens again as most epidemiologist say it will , we will be almost defenseless. WE ARE RIPE FOR ANOTHER PANDEMIC RIGHT NOW.
VIRULENT INFLUENZA MUTATIONS CAN KILL IN HOURS!
In 1918 a person could wake up feeling fine and be dead that evening and turning blue.
The Mask Controversy Prevention Is The Key!
The H5N1 Viral particle is spherical and from 50 to 180 nanometers in aerodynamic size. Millions are aerosolized in water droplets and deposited on surfaces or become airborne by coughing or sneezing, Evaporation in low humidity can reduce the active viral particle to below .5 microns in less than a fraction of a second which can easily get through leaky and ill fitted surgical and respiratory N95 masks
NIOSH Rated Disposable Respiratory Protection Masks. The N R or P series masks are all excellent respiratory protection if fitted properly and IF they maintain that fit.
Everyone has an individual facial structure, so universal fit is problematic and indeed NIOSH and the CDC is now developing standards to minimize TOTAL INWARD LEAKAGE AND TEST PERFORMANCE UPGRADES to address this ongoing problem.
Fit factor testing presently only addresses the leakage for a particular style shape or grade of mask and DOES NOT TEST the working, donned mask for actual protection on the job! Some leakage testing even done by the CDC reports leakage factors greater than 12% using N95 under real world conditions.
The N95 NIOSH tests actually GLUE the mask being tested to a test plate to prevent leakage during the test. In real world use only rubber bands are used to try to seal the mask to faces which are constantly breathing talking and using facial muscles that can dislodge any attempt at a viral seal.
ID 50 for Influenza H5N1 if it is like ordinary type A is less than 1,000 particles. This is the number estimated by scientists in which 50% of those susceptible will come down with the disease . It can easily be seen that a 12% mask penetration would not stop the virus from being inhaled by the mask user.
How To Increase The Protection Factor Provided By Existing Facepiece Respirators Against Airborne Viruses: A Novel Approach
SER GEY A. GRINSHPUN, BYUNG UK LEE, MJKHAlL YERMAKOV, and ROY MCKAY
Center for Health-Related Aerosol Studies, Occupational Pulmonary Services Department of Environmental Health,
University of Cincinnati, Cincinnati, OH 45267-0056, U.S.A.
Keywords: RESPIRATOR, PARTICLE PENETRATION, PROTECTION FACTOR, ION EMISSION
Adverse health effects associated with airborne particles, including microbial and non-microbial aeroallergens, have recently gained considerable attention, especially due to increased reporting of respiratory symptoms in some occupational and residential indoor environments. The latest outbreaks of emerging diseases and the threat of bioterrorism have added some fuel to the problem. Although the transmission routes for some emerging diseases are still to be identified (e.g., SARS), many virus-induced health effects are known to be spread in the aerosol phase. Reducing the concentration of inhaled airborne particulates should reduce the risk of infection, as the number of cases among susceptible population is proportional to the average concentration of infectious droplet nuclei in a room and the probability that the particles will be inhaled. There is a special demand to increase the efficiency of existing respiratory protection devices, which otherwise may not provide an adequate protection against aerosol agents. Responding to this demand, we have developed and tested a new concept that allows to drastically enhance the protection factor provided by conventional facepiece filter respirators against submicron airborne particles (e.g., viruses). The concept is based on the continuous emission of unipolar electric ions in the vicinity of a respirator.
The new concept was tested in a non-ventilated indoor chamber (24.3 m3). An R95 respirator (3M 8247, 3M Company, St. Paul, MN, USA) was sealed to a manikin with silicone and petroleum jelly and connected to a breathing machine that operated at a constant air flow rate of 30 L/min. (inhalation). Prior to the start of data collection, leak tests (between the mask and the face of the manikin) were conducted with a bubble producing liquid (Trubble Bubble, New Jersey Meter Co., Paterson, NJ, USA). This experimental design allowed us to evaluate the enhancement effect of continuous emission of unipolar electric ions on the protection provided by the respirator filter (assuming that the particle penetration through the leaks was negligible). The viral-size particles (mid-point aerodynamic size da = 0.04-0.20 µm) were aerosolized into the chamber using a smoke generator. An Electrical Low Pressure Impactor (ELPI, TSI Inc./Dekati Ltd, St. Paul, MN, USA) was used to determine the concentration and aerodynamic particle size distribution in real-time. Aerosol sampling from outside and inside the respirator was alternated. Sampling lines and flow rates were identical up- and down-stream of the ELPI. The time resolution was adjusted to 10 seconds. The respirator protection factor was determined as a ratio of the measured aerosol concentrations outside (COUT) and inside (CIN) the respirator in 3 min. increments during a period of 12 min. The set-up is schematically presented in Figure 1. The background tests were performed in the absence of air ion emission. Then, a unipolar ion emitter (VI-3500*, Wein Products, Inc., Los Angeles, CA, USA) was turned on at 20 cm from the respirator, and the protection factor was determined in 3 min. increments during 12 min. of its operation. The emitter was characterized by measuring the air ion density at 1 m from the emission point using an Air Ion Counter (AlphaLab Inc., Salt Lake City, UT, USA). In addition, to the manikin-based experiments with a sealed respirator, human subject testing was also performed. In this phase of testing, the same model R95 filtering facepiece was worn by a test subject who was previously fit tested to this respirator using a TSI model 8020 Portacount (TSI, Inc). The fit testing protocol included standard head and breathing maneuvers required in the U.S. (normal and deep breathing, moving the face and the body left and right and up and down, talking, etc.).
The protection factor measured with the respirator sealed on the manikin face was 73±6.0. We expected that it would exceed 20 since the R95 device should have at least 95% collection efficiency in the worst-case scenario. The emitter characterization tests showed that the density of negative air ions in the chamber increased rapidly, once it was turned on. It reached (1.340±0.037)x106 cm·3 during 5 sec., remained approximately at that level during a 30 min. continuous ion emission, and dropped to the initial level within 3 min. after it was turned off (Figure 2). Therefore, it was concluded that the experiments with respirators in the presence of the emitter were conducted at a constant air ionization level.
Figure 3 shows the particle size integrated data as a function of the ion emission time (time t = 0 represents the protection factor determined without emission of air ions, while t > 0 represent the data obtained when the emitter was continuously operated during 3, 6, 9, and 12 min., respectively.) It is seen that the respirator protection increased to 512±65 (enhancement of 7) as a result of a 3 min. ion emission in the vicinity of the respirator. Further ionization did not significantly change the enhancement of the respirator performance (p= 0.06). It is believed that since the particles and the filter fibers charged unipolarly by the ions, the repelling forces decreased the particle flow toward the filter. This reduced the number of particles that could potentially penetrate through the mask and be inhaled. The protection (fit) factors of the R95 respirator measured on the human subject ranged from 110 to 278, depending on the breathing procedure, with an average of 152, when no air ion emission was introduced. When the ion emitter was turned on, the fit factors ranged from 311 to 1380, with an average of 611, showing a 4-fold enhancement. The data suggest that faceseal leakage may somewhat reduce, but not eliminate, the effectiveness of respirator performance enhancement achieved due to the unipolar ion emission.
Continuous unipolar ion emission in the vicinity of a filtering facepiece respirator has the potential to drastically enhance performance against virus-size aerosol particles.
The authors are thankful to Wein Products, Inc. (Los Angeles, CA, USA) for helping initiate this research.
*This document originally pertained to VI-2500, Wein Products, Inc.
Shu-An Lee, Atin Adhikari, Sergey A. Grinshpun, Roy McKay, Rakesh Shukla, Haoyue Li Zeigler, and Tiina Reponen
University of Cincinnati, Department of Environmental Health, Cincinnati, Ohio
A new system was used to determine the workplaceprotectionfactors(WPF)fordustandbioaerosolsinagricultural environments.Thefieldstudywasperformedwithasubject wearinganN95filteringfacepiecerespiratorwhileperforming animalfeeding,grainharvestingandunloading,androutine investigationoffacilities.Asexpected,thegeometricmeans (GM) of the WPFs increased with increasing particle size rangingfrom21for0.7–1µmparticlesto270for5–10µm particles (p < 0.001). The WPF for total culturable fungi (GM35)wassignificantlygreaterthanfortotalculturable bacteria (GM 9) (p 0.01). Among the different microorganismgroups,theWPFsof Cladosporium,culturablefungi, andtotalfungiweresignificantlycorrelatedwiththeWPFsof particlesofthesamesizes.AscomparedwiththeWPFsfordust particles,theWPFsforbioaerosolswerefoundmorefrequently below10,whichisarecommendedassignedprotectionfactor (APF)forN95filteringfacepiecerespirators.Morethan50% oftheWPFsformicroorganisms(meanaerodynamicdiameter <5 µm) were less than the proposed APF of 10. Even lower WPFswerecalculatedaftercorrectingfordeadspaceandlung deposition. Thus, the APF of 10 for N95 filtering facepiece respirators seems inadequate against microorganisms (mean aerodynamic size <5 µm). These results provide useful pilot data to establish guidelines for respiratory protectionagainst airborne dust and microorganisms on agricultural farms. The method is a promising tool for further epidemiological and intervention studies in agricultural and other similar occupational and nonoccupationalenvironments.
Farmers are at high risk of exposure to airborne dust and microorganisms. These exposures can cause respiratory diseases. According to the U.S. Bureau of Labor Statistics, around 13 million people gain some earnings from farming in the United States. Of these, 6 million people are family members living and working on the farms.
The application of engineering controls for preventing farmers and their family members from exposure to airborne particles, including microorganisms, is limited because of the diverse nature of the dust and bioaerosol sources in agricultural settings. Personal protection by respirators is often the only feasible option for farmers to minimize their exposure to airborne dust and microorganisms. However, the Respiratory Protection Standard (29 CFR Part 1910.134) is not applicable to many agricultural environments, and there is limited guidance for respiratory protection against biological particles.
Respirators used by agricultural workers should be certified by NIOSH in accordance with 42 CFR Part 84. Under these certification guidelines, N95 filtering facepiece respirators have the filtration efficiency of at least 95% for the most penetrative particle size of 0.3 µm. These respirators have been recommended by the Centers for Disease Control and Prevention (CDC) for health care workers to protect them from infectious aerosols, which can cause diseases such as SARS (severe acute respiratory syndrome) and tuberculosis. Qian et al. found that the filtration efficiency of some N95 filtering facepiece respirators is 99.5% or higher for the NaCl and PSL particles in the size range of 0.75 to 1 µm as well as for Bacillus subtilis (the mean aerodynamic diameter 0.8 µm) and Bacillus megatherium (the mean aerodynamic diameter 1.2 µm). The aerodynamic sizes of most bacteria and fungal spores are between 0.7 and 10 µm and thus the filtration efficiency by N95 filtering facepiece respirators should be even higher than 99.5%. However, these contaminants enter the respirator cavity not only through the filter material but also through the faceseal leaks, which is the primary pathway for contaminants to penetrate inside negative pressure respirators (especially those that have poor respirator fit). N95 filtering facepiece respirators are relatively comfortable for workers because they are lightweight and do not obstruct vision or hinder communication as much as elastomeric respirators. Therefore, in the present study, the N95 filtering facepiece respirator was investigated for its field performance in protecting farmers against airborne dust and microorganisms.
The workplace protection factor (WPF) is commonly used to assess respirator performance in the workplace. The WPF, which is defined as a ratio of the particle concentration outside the respirator to that inside the respirator, is a measure of the protection provided in the workplace under the conditions of that workplace, by a properly selected, fit tested, and functioning respirator that is correctly worn and used. In our previous study, we developed a new personal sampling system for determining the protection provided by respirators against airborne dust and microorganisms. This personal system was tested for its capability of measuring and reflecting the nearly instant changes in the aerosol concentrations inside and outside the respirator through laboratory and field evaluation. Both laboratory and field studies showed this system to be a promising tool in determining the protection provided by respirators against particles and microorganisms. The objective of the current study was to use the newly developed personal sampling system in agricultural environments to determine the protection provided to farmers by N95 filtering facepiece respirators against airborne dust and microorganisms of different particle size ranges. Our concurrent article will characterize exposures, whereas this article focuses on respiratory protection.
Materials And Methods
Field Study Design
Field samples were collected using a personal sampling system previously described in detail by Lee et al. In short, the sampling system consisted of two sampling lines (in-facepiece and ambient sampling lines) that were used to collect particle samples inside and outside the respirator. N95 filtering facepiece respirators (model 8210, 8110S; 3M, St. Paul, Minn.) were used in the field experiments. Airborne dust and microorganisms were sampled through the sampling probes at a flow rate of 10 L/min and drawn through Tygon tubing to a metal sampling chamber at the end of each sampling line. A portion of each aerosol flow (2.8 L/min) was sampled from the chamber into an optical particle counter (OPC, model HHPC-6; ARTI Inc., Grants Pass, Ore.) for dust measurement. The rest of the aerosol flow (7.2 L/min) passed through a filter sampler that collected the airborne microorganisms.
The selected flow rate of 10 L/min is five times the conventional in-facepiece sampling flow rate used for fit testing. As described in Lee et al., a higher flow rate was selected to decrease the respirator purge time and the potential sampling bias for nonhomogenous distributions of the particle concentration inside the respirator. In addition, the high flow rate decreases the detection limit of particle measurements when measuring for a specific sampling period, which is especially important for evaluating the respirator performance against low concentrations of airborne microorganisms. This high flow rate, however, may lead to the overestimation of particle penetration into the mask particularly at low respiration flow rate.
Our field measurements were conducted in six farms—three types of animal confinements (swine, poultry, and dairy), and three grain farms. Detail information on farming activities and farm characteristics, as well as on the methods for enumeration of airborne dust and microorganisms, are presented in Lee et al.
All subjects recruited in the study had to pass the medical clearance evaluation and fit test before participating in field testing. The medical clearance evaluation was conducted using the questionnaire, specified in OSHA standard 1910.134, Appendix C. The medical clearance was authorized by a licensed physician. Before starting the field test, subjects signed an Institutional Review Board consent form, where the possible risks of the field test were addressed. All study subjects were required not to have beard or stubble on their face and not to smoke 1 hour before the test.
The respirator fit test was performed once for each subject prior to his or her involvement in the field testing. Before fit testing, each subject was trained and instructed to wear the respirator properly. The instructions followed the manufacturer’s guidance on the use of the respirator. Fit testing was conducted with a TSI Portacount Plus in connection with N95 companion (TSI, Inc., St. Paul, Minn.) in compliance with the 6-exercise protocol. With the quantitative fit test, a fit factor of 100 or above constituted a pass. The subject then donned the respirator equipped with the personal sampling system. In each farming environment, one to four subjects were involved in the experiment that lasted for 30 to 60 min. The testing time covered the time it took the subject to complete the specific work task under investigation. Subjects were recruited primarily from agricultural farms, while students and staff of the University of Cincinnati also participated.
Correction on WPF Data Based on the Respirator Dead Space and Lung Retention
Several studies have shown that respirator dead space and lung retention decrease the concentration inside the respirator during inhalation, resulting in the overstating of the WPF. Hinds and Bellin developed a model to predict the average true concentration inside the respirator after accounting for the effects of lung retention and respirator dead space. In their study, the ratio of an average full breathing cycle concentration to an average inhalation concentration (Cfull/Cin) was related to the ratio of the respirator dead volume to the tidal volume (Vds/Vt). The association was described in detail for five values of fractional particle depositions in the respiratory tract (Fdep) in the absence of faceseal leakages. Based on the information obtained for Vds/Vt and Fdep in our study, the ratio of Cfull/Cin can be interpolated from a figure presented in Hinds and Bellin’s paper. Thus, the corrected WPF (WPFcorr) can be calculated as following:
where the WPF value is measured during the full breathing cycle.
To use this model, information is needed on the respirator dead space volume, tidal volume, and fractional deposition of particles in the respiratory tract. For an N95 filtering facepiece respirator, the respirator dead volume was measured by immersing a human face into an N95 respirator filled with water and measuring the remaining water volume inside the respirator. The average of three repeats was of 123 mL. Tidal volume of 1250 mL was selected to represent an adult male performing light work.
The respiratory deposition of particles was calculated using an existing computer-based deposition model. These calculations were performed separately for each microorganism group/species and for dust particles in the five OPC particle size classes. All of the physiological data, which were required for the respiratory deposition model, were specified for an average height of American adult male (176 cm) under light workload.
The data analysis was performed by analysis of variance (ANOVA), t-test, and correlation model by Statistical Analysis System (SAS) version 8.0 (SAS Institute Inc., Cary, N.C.). P-values of <0.05 were considered significant. Intra- and intersubject variability in WPFs was investigated by repeated measure analysis using PROC MIXED procedure in SAS. Two different models were considered for both dust and microorganisms. The first model was one-way random effect model used to examine the between-subject and within-subject variability without including the covariate of particle size and microbial type in the model. The second model was a two- factor mixed-effect model, in which one additional covariate (particle size for nonbiological particles, and microbial type for biological particles) was included. Particle size had two levels: 0.7–2 µm and 2–10 µm, and microbial type had two levels: culturable fungi and culturable bacteria.
The between-subject and within-subject variability were estimated by the restricted maximum likelihood (REML) method due to the unbalanced nature of data. In addition, the difference in mean WPFs among five particle sizes as well as among the predominant fungal spores were examined by ANOVA followed by pair-wise comparison using Tukey’s studentized range (HSD) test. The t-test was used to examine the difference in the protection factors for biological and nonbiological particles, specifically comparisons between culturable fungi and culturable bacteria and comparisons between two particle size ranges: 0.7–2 µm (bacteria) versus 2–10 µm (fungi). The correlation coefficient was obtained to examine the association between the WPF for airborne microorganisms and the WPF for dust of similar particle sizes. All WPF data used for statistical analyses were log-transformed to achieve normal distribution. When the concentration inside the respirator was undetectable, one-half of the detection limit was used to calculate the WPF.
Results And Discussion
Figure 1 presents the percentile and mean values of the WPFs, determined as a ratio of the concentration outside the respirator to that inside the respirator. The WPFs provided by N95 filtering facepiece respirators against airborne dust were found to be associated with the particle size. The geometric means (GM) of the WPFs were 24 for the particles in the range of 0.7 to 2 µm and 75 for the particles of 2 to 10 µm. With specific size fractions, GM 21 for 0.7–1 µm particles, 28 for 1–2 µm particles, 51 for 2–3 µm particles, 115 for 3–5 µm particles, and 270 for 5–10 µm particles. The difference in WPFs for particles in the five size classes was statistically significant (p < 0.001). The WPF for the particle size fraction of 2–10 µm, representing the size of most airborne fungi, was significantly higher than that for 0.7–2 µm, representing the size of most bacteria (p 0.01). Correspondingly, the WPF for total culturable fungi (GM 35) was significantly greater than for total culturable bacteria (GM 9; p 0.01).
For the most common fungal genera or groups, the geometric means of the WPFs were 5 for Aspergillus/Penicillium, 6 for Ascospores, 15 for Basidiospores, 68 for Cladosporium, 15 for smut spores, 15 for Epicoccum, and 22 for Alternaria. Their corresponding calculated mean aerodynamic sizes were 3.7, 5.6, 6.8, 8.1, 9.7, 14.5, and 18.9 µm. Thus, similarly to the situation with nonbiological particles, the WPF increased with an increase in the microorganism size with the exception of Cladosporium.
When the individual fungal genera and groups were inves- tigated, Cladosporium had a wide range of WPF values com- pared with other fungi. The large variability in the spore size of Cladosporium can explain this phenomenon. The physical size and aerodynamic size of Cladosporium cladosporioides are 3.6 0.7 µm and 1.8 0.7 µm, respectively, as reported by Reponen et al. The size of Cladosporium spp. measured in our study ranged from 7.8–16.6 µm in length and 4.3–
9.2 µm in width, while Ellis reported wider ranges of the spore size (3–40 µm [in length] 2–13 µm [in width]) that reflect different species of Cladosporium. In addition, the agglomeration of the Cladosporium was observed under the microscope for the air samples. The abovementioned factors were attributed to a decrease in the penetration of Cladosporium through the faceseal leaks and a greater variation in the WPFs.
Fungal spores as large as Cladosporium are not able to remain suspended in the air for a long time. Most of them will settle down on the ground before they reach the sampling probe. The concentration of spores in the air may not rise to considerable levels as long as there is no continuous aerosolization source in the environment. As reported in our concurrent study, most of the concentrations of individual fungal genera and groups outside the respirator were close to the detection limit in animal confinements. This caused the concentration of these spores inside the respirator to remain below detection limit in several cases. In these cases, the WPFs were calculated by using one-half of the detection limit for the concentration inside the respirator. This might introduce a bias in estimating the respiratory protection against fungal spores as large as Cladosporium.
In addition, if the leak size is close to particle size, the shape of the fungal spores, as well as the shape and size of faceseal leaks, might affect the penetration of spores through the faceseal leaks. For example, nonspherical fungal spores, such as Cladosporium, penetrate differently when the large end of a spore encounters a small faceseal leak, compared with when it encounters a large faceseal leak. Likewise, penetration is different when the large end of a spore encounters a slit shape faceseal leak compared with a circular faceseal leak. Thus, large variation in the WPF was expected for nonspherical fungal spores.
Figure 1 also shows the proposed assigned protection factor (APF) and the pass/fail criterion for N95 filtering facepiece respirators, which are 10 and 100, respectively, for N95 filtering facepiece respirators. Among 19 observations, 68% of the WPFs for particles in the lowest size range of 0.7–1 µm were above 10, whereas for large particles, this percentage was greater. However, more than 50% of the WPFs for microorganisms, such as culturable bacteria (62%), culturable actinomycetes (64%), Aspergillus/Penicillium (65%), and Ascospores (64%), were below 10. The mean aerodynamic diameter of these microorganisms was estimated to be below 5 µm. Most of the WPF values for larger fungal spores were higher as discussed above: 59% of smut spores, 78% of Alternaria, and 67% of Epicoccum in WPF values were
above 10. Although the WPF for dust and microorganisms showed similar increasing trend with increasing particle size, the WPF for particles were found to be higher than that for microorganisms of the same size range. This might be due to differences in the particle losses occurring in the faceseal leaks due to different shape and density of biological and nonbiological particles.
Another reason could be related to the measurement bias of the OPC in size-selective count of dust particles. The optical particle counter operates by projecting light on particles and detecting light scattering from particles; thus, factors such as shape and color of particles interfering light scattering can affect the instrumental measurement on particles. When the air samples were analyzed under the microscope, dust particles with irregular shape and different colors were ob- served. Unlike the dust particles, fungal spores have close- to-regular shapes. The difference in reflective index and shape of the dust particles is expected to cause significant variability of the measured particle sizes and number con- centrations in a specific environment when using the OPC. Furthermore, the irregular shape of dust particles increases particle losses through the faceseal leaks due to the interception mechanism.
The density of particles may also play a role. The aerodynamic sizes of dust particles and fungal spores were calculated based on the assumption that ρ 1 g/cm3. However, the density of dust particles, such as sand and clay, can be higher than 1 g/cm3 whereas for many fungal spores the density is smaller than 1 g/cm3. This is likely to result in the underestimation of the aerodynamic size of dust particles and the overestimation of the aerodynamic size of fungal spores. Following this logic, the aerodynamic sizes of dust particles may be underestimated whereas those for fungal spores may be overestimated. When the physical sizes of dust particles and fungal spores are about the same and their Stokes numbers are close to 1, even small variation in the density of particles can have a pronounced effect on the dust particle losses in the faceseal leaks due to the impaction mechanism. The concentration of the dust particles inside the respirator was lower than that of the fungal spores, resulting in the higher protection factor. These findings deserve further research. Since there are no OSHA required guide- lines for respiratory protection against biaerosols, and OSHA has proposed to change the APF for filtering facepieces, the results obtained in this study provide important pre- liminary information to consider for respiratory protection against airborne dust and microorganisms in agricultural farms.
Nearly all the WPF studies used to justify the APF = 10 for half-mask respirators have involved particulate contaminants, and many of these studies have been done with large particles. However, large particles, which comprise most of the total mass, were found to be less penetrative than small ones. Thus, by determining the total mass concentration inside and outside respirator, one may lead to underestimate the WPF values for small particles, which would result in the overestimation of the APF values. Our data show that the particle size should be taken into account when assigning APF values.
Since the WPF for both airborne dust and microorganisms was found to be associated with the particle size, we
investigated whether the WPF of airborne microorganisms and the WPF of dust of the same size range correlate with each other. Table I shows the correlation between the WPF of dust and the WPF of fungal spores for predominant groups and genera. The WPF for Cladosporium, total fungi, and culturable fungi showed a significant association with the WPF for total dust (0.7–10 µm) as well as with the WPF of dust in the corresponding size range: 5–10 µm for Cladosporium (r 0.61, p 0.02), 2–10 µm for total fungal spores (r 0.50, p 0.03) and culturable fungal spores (r 0.61, p 0.01). Although the WPF of Aspergillus/Penicillium did not significantly correlate with the WPF of dust, the best correlation between the WPF for Aspergillus/Penicillium and dust was observed with the particles in the size range of 2–3 and 3–5 µm, which coincides with the size of Aspergillus/Penicillium spores. The WPFs obtained for other microorganisms were found to have much lower correlation with those obtained for the particles.
As mentioned above, the variation in the shape and re- flection index of nonbiological particles may play a role in the measurement of their size and may explain the poor correlation between the WPF of airborne microorganisms and the WPF of dust. In addition, the mean aerodynamic size of Alternaria (14.5 µm) and Epicoccum (18.9 µm) were greater than 10 µm, which exceeded the upper limit of the particle sizes that the OPC can measure at about 10% efficiency. Thus, for further study involving these two large fungi or similar ones, the OPC should be customized to measure particle sizes up to 20 µm. Moreover, the sampling losses through the sampling line should be carefully addressed for these large particles.
Figure 2 presents the regression plots for the associations that were found to be significant: WPF of Cladosporium, total fungi, and culturable fungi vs. the WPF of dust particles for the corresponding size range. The equations provided in Figure 2 can be used to estimate the WPF of these microorganisms when only dust measurement is performed. It means the WPFs of microbes can be obtained by import- ing the WPFs of particles of the same aerodynamic size in the equation. Considerable time and expense could be saved for the microbiological analysis. However, as we found significant correlations for only a few microbial types, our data indicate that the WPFs for most of the microorganism genus/groups cannot be estimated utilizing WPFs measured for particles.
Several subjects recruited among students and staff at the University of Cincinnati repeated the experiment in different farming environments. This allowed us to investigate the difference in WPFs between and within subjects. Table II shows the variability of the WPFs between subjects and within subjects for airborne dust and microorganisms. The Appendix shows the raw data used in these calculations. The first model (without covariates) shows that the between-subject variability was 1.08 for dust and 0.13 for microorganisms, while the within-subject variability was 1.43 and 3.9, respectively. This demonstrates that the within-subject variability in WPFs was greater than the between-subject variability for half-mask respirators when there were no other covariates included in the model. The findings support the results presented by Nicas and Neuhaus.
However, when the covariate, such as particle size or microbial type, was included in the model, the within-subject variability decreased as seen in Table II. This may result
in the within-subject variability being equal to or smaller than the between-subject variability at least for nonbiological particles. Table II also shows that the fraction of the between- subject variability versus the total variability for dust increased from 43% to 52% when the particle size was accounted for in the model. Note that the between-subject variability in microorganisms was much smaller than the within-subject variability. Also, the latter for biological particles was two to three times larger than that for nonbiological ones. It is likely that different farming activities involved different particle size distributions, different microbial composition, and different faceseal leakage.
When comparing the within-subject and between-subject variability in WPFs for airborne dust and microorganisms, other covariates such as particle size, microbial types, and farming activities should be carefully addressed, and the effect of these factors on WPF measurements in agricultural environments should be further investigated. From our small-scale study results, it appears that the WPF distributions between biological and nonbiological particles are very different from each other. Therefore, more detailed research will help to better characterize WPFs.
Previous studies showed that respirator dead space and lung retention decrease the concentration inside the respirator
during inhalation, resulting in overestimation of the WPF. So far, only a few WPF studies have investigated the effects of respirator dead space and lung retention because the information on the distribution of the particle size inside the respirator was not readily available. In this study, the OPC provided the size distribution of particles inside the respirator for five different size fractions in the particle size range of 0.7 to 10 µm. In addition, the size information for fungal spores was obtained from the data presented by Lee et al.
Table III presents the differences in the WPF data before and after accounting for the lung deposition and respirator dead volume. As seen from the table, the total deposition in human respiratory tract (Fdep) ranged from 39 to 96% for particles in the size range of 0.7 to 10 µm, and from 63% to 95% for fungal spores, which cover the particle size range from 3.7 to 18.9 µm in mean aerodynamic size. The measured WPF values were corrected by accounting for respirator dead space and lung retention using Hind and Bellin’s approach. The bias was calculated by dividing the difference between the protection factors before (WPF) and after correction (WPFcorr) by the protection factor after correction. For particles in the size range of 0.7 to 10 µm, the WPFs before correction were overestimated by 22% to 75%. For fungal spores in the mean aerodynamic size of
3.7 to 18.9 µm, the protection factors before correction resulted in the overestimation ranging from 41% to 75%. This information provided the possible bias caused by respirator dead space and lung retention when we evaluated the respiratory protection against airborne dust and microorganisms in agricultural farms. As compared with the WPF values presented in Figure 1, the percentage of WPF values less than 10 would be increased after correction for dead respirator space and lung retention. For example, the percent- age of WPF values less than 10 for Aspergillus/Penicillium was increased from 65% to 71% resulting from the correction.
The protection provided by N95 filtering facepiece respirators against dust and airborne microorganisms varied with particle size, shape, and density. The WPFs for microorganisms were smaller than those for nonbiological (dust) particles of the same size range measured by OPCs. This may be due to pronouncedly irregular shape and higher density of dust particles as compared to biological particles. More than 50% of the measured WPFs for microorganisms (mean aerodynamic size <5 µm) were less than the proposed APF of 10. Even lower WPFs were calculated after correcting for respirator dead space and lung deposition. As a consequence, the APF of 10 for N95 filtering facepiece respirators against microorganisms (mean aerodynamic size <5 µm) seems to be inadequate for more than 50% of wearings. Our data shows that particle size and the nature of particles (nonbiological/biological) should be taken into account when computing APF values
for particulate respirators. In order to establish respiratory protection guidelines against airborne microorganisms in agricultural farms, more field data must be obtained. The present results provide preliminary data toward developing such guidelines, and the method developed can be used for further epidemiological and intervention studies in agricultural and other environments with considerable bioaerosol contamination.
The authors are grateful to farm owners for providing access and help in field measurements.
The authors also thank students and staff members who volunteered to be human subjects in the field testing when needed.
Special thanks go to Mike Brugger and LingYing Zhao (Ohio State University) for helping us find field sites.
This research was supported by the National Institute for Occupational Safety and Health (NIOSH R01 OH04085) and through the Pilot Project Research Training Program of the University of Cincinnati Education and Research Center.
Allertech Laboratory, INC. Gives Opinion on Operational Characteristics of Air Supply® Ionic Technology Products
Allertech Laboratory, INC.
I have been asked to render my opinion on studies examining the operational characteristics of Air Supply ionic technology products, including the AS180i Minimate* personal wearable device and the Vortex VI-3500* room air purifier. I have reviewed these studies from the standpoint of their potential effectiveness in the management of allergies and asthma.
Avoidance of airborne allergens remains the cornerstone of management of inhalant allergies and asthma. Individuals sensitized to airborne allergens will experience manifestations of allergic inflammation in the upper airways (sinuses and nasal passages) and/or the lower airways. The severity of allergic sinusitis, allergic rhinitis and allergic asthma is, in large part, a function of levels of allergen exposure. A reduction in exposure levels is generally accompanied by a commensurate reduction in symptoms of allergic disease and the need for treatment. Interventions that reduce the levels of airborne allergens may be therefore be expected to result in symptomatic improvement.
Allergy & Asthma: Information and Technology: Meeting the Challenge
I have reviewed studies performed by Dr. S.A. Grinshpun of the Aerosol Research and Exposure Assessment Laboratory in the Department of Environmental Health of the University of Cincinnati. Dr. Grinshpun has authored 79 publications in leading peer-reviewed journals as well as 59 book chapters and full-length papers and proceedings. The results of studies of studies on Air Supply technologies have been published in the Journal of Aerosol Science 32 (SI), 2001.
The studies of this technology have addressed several relevant aspects, namely (i) the degree to which the devices remove airborne particles of varying diameters (ii) the effect of ionic perturbation of micro-organisms as expressed by viability and (iii) the adjuvant effect of the Air Supply devices on protection afforded by standard filtration masks.
Using aerosolized liquid polystyrene particles and sodium chloride test particles as universally accepted airborne pathogenic simulants, the Wein® AS180i* reduced close to 95% of particle mass concentrations after 1.5 hours in both calm air conditions and mixing air conditions. Test particles ranged in size from 0.4 – 1.0 um, representing the aerodynamic size range of microbial fragments, single bacteria, most of the fungi and their aggregates.
Studies of the AS180i* unit were undertaken in a setting designed to replicate the aircraft seating microenvironment. Using a 2.6M³walk-in chamber at 33 cfm of air mixing, the particle removal efficiency for particles in the range of 0.3 -3.0 um was found to be 50% within 15 minutes, 80% at 30 minutes and about 90% at 40 minutes.
A second Air Supply unit, the Vortex VI-3500* showed extremely high particle removal efficiency of 90% in 40 – 50 minutes, reaching about 95% in 60 minutes for all the tested particle size fractions.
Ionic air purifiers produce high electric charges on viable airborne microorganisms, leading to microbial stress, which may reduce the viability of microbes in the breathing zone. The bactericidal effect of the AS180i* unit was tested on representative gram-negative and gram-positive bacteria, namely pseudomonas spp., E.coli and S. epidermidis. At a relative humidity of 17 ± 5% and temperature of 26±2ºC, mean bacterial inactivation values at one minute (as measured by CFU/ml on nutrient agar plates) were: S. epidermidis: 53 ± 20%; Pseudomonas spp.: 71 ± 11% and Escherichia coli: 93 ±2%.
In studies performed by Dr. Donald Dennis (Head, Atlanta ENT Centre) using the Air Supply Vortex VI-3500* unit, airborne mold spore counts dropped over the course of 6 days from “too numerous to count” to zero in a mould colony count room.
Further studies undertaken by Monitoring Instruments for the Environment (MIE Inc.) on the AS180i* device assessed efficiency of airborne allergen removal by nephelometry. Results showed that under standardized conditions 85 – 91% of cat epithelium, 85 – 86% of alternaria and cladosporium (major outdoor moulds) and 71% of dust mite allergen were removed from an 8 ft³walk-in chamber in one minute.
The filtration performance of surgical masks operating with or without the Air Supply Vortex VI-3500* units was assessed. The initial protection factor of the 3M-1838 surgical masks was in the range of 3.5 – 4.0. The protection factor incressed to 30 at 9 minutes when the Vortex VI-3500* unit was operating. The effective filtration of the surgical mask, used in conjuction with the Vortex VI-3500* unit, was comparable to that of an N95-level respirator in terms of collection characteristics.
In my opinion, these data suggest that the Air Supply technology used in the AS180i* and Vortex VI-3500* units will remove airborne allergens (including animal danders, dust mite allergens and moulds) therby reducing exposure in sensitized individuals. This reduction in allergen exposure should be reflected by a corresponding improvement in symptoms and a reduction in the need for treatment.
The Bactericidal effect of the Air Supply ionic technology on airborne bacteria and the marked enhancement of the filtration efficiency of standard surgical masks by adunctive use of the Vortex VI-3500* unit should afford significant protection against airborne pathogens in bioaerosols.
*This document orginally pertained to the Vortex VI-2500 and AS150GXB Minimate, Air Supply products, Wein Products, Inc.
Manikin-Based Performance Evaluation of N95 Filtering-Facepiece Respirators Challenged with Nanoparticles
ANNA BAŁAZY1,2, MIKA TOIVOLA1, TIINA REPONEN1, ALBERT PODGÓRSKI2, ANTHONY ZIMMER3 and SERGEY A. GRINSHPUN1
1Department of Environmental Health, Center for Health-Related Aerosol Studies, University of Cincinnati, Cincinnati, OH 45267-0056, USA; 2Department of Chemical and Process Engineering, Warsaw University of Technology, Warsaw, Poland; 3Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH 45226, USA
Protection of the human respiratory system from exposure to nanoparticles is becoming an emerging issue in occupational hygiene. The potential adverse health effects associated with particles of 1–100 nm are probably greater than submicron or micron-sized particles. The performance of two models of N95 half-facepiece-filtering respirators against nano-sized parti- cles was evaluated at two inhalation flow rates, 30 and 85 l min-1, following a manikin-based protocol. The aerosol concentration was measured outside and inside the facepiece using the Wide-Range Particle Spectrometer. Sodium chloride particles, conventionally used to certify N-series respirators under NIOSH 42 CFR 84 regulations, were utilized as the challenge aerosol. The targeted particle sizes ranged from 10 to 600 nm, although the standard certification tests are performed with particles of 300 nm, which is assumed to be the most penetrating size. The results indicate that the nanoparticle penetration through a face-sealed N95 respirator may be in excess of the 5% threshold, particularly at high respiratory flow rates. Thus, N95 respirators may not always provide the expected respiratory protection for workers. The highest penetration values representing the poorest respirator protection conditions were observed in the particle diameter range of 30–70 nm. Based on the theoretical simulation, we have concluded that for respirators utilizing mechanical filters, the peak penetration indeed occurs at the particle diameter of 300 nm; however, for pre-charged fiber filters, which are commonly used for N95 respirators, the peak shifts toward nano-sizes. This study has confirmed that the neutralization of particles is a crucial element in evaluating the efficiency of a respirator. The variability of the respirator’s performance was determined for both models and both flow rates. The analysis revealed that the coefficient of variation of the penetration ranged from 0.10 to 0.54 for particles of 20–100 nm in diameter. The fraction of N95 respirators for which the perform- ance test at 85 l min-1 demonstrated excessive (>5%) penetration of nanoparticles was as high as 9/10. The test results obtained in a relatively small (0.096 m3) test chamber and in a large (24.3 m3) walk-in chamber were found essentially the same, thus, suggesting that laboratory-based evalua- tions have a good potential to adequately represent the respirator field performance.
Filtering-facepiece respirators are commonly used for personal protection from exposures to respirable aerosol particles. Fine particles are known to cause various respiratory health effects, including allergic alveolitis, asthma, pneumoconioses, cancer and others (WHO, 1999), as well as infectious diseases transmitted by bioaerosol particles, e.g. tuberculosis, Legionnaires’ disease, Q fever, mumps, measles and influenza (McCullough et al., 1997). Nanoparticles are believed to be particularly detrimental to human health since the inflammatory response depends on the surface area of deposited particles rather than their mass (Tran etal., 2000). Other observations reviewed by Churg (2000) indicate that the inflammatory response closely matches the number of ultrafine particles reaching the airways and alveoli. Once deposited into the respiratory tract, nanoparticles can cross the epithelial and endothelial cells into blood and lymph circulation and reach other target sites, such as bone marrow, lymph nodes, spleen and heart. Furthermore, there is increasing evidence that nano- particles, if deposited in the upper airways, can be translocated to the central nervous system and ganglia along axons and dendrites of olfactory neurons (Oberdo¨rster et al., 2005). The N95 half-mask filtering-facepieces are widely used to reduce the inhalation exposure to particles, as these respirators are inexpensive, convenient and highly efficient if properly fitted. They are recommended against solid and liquid aerosols that do not contain oil. The N95 facepieces are certified according to the National Institute for Occupational Safety and Health (NIOSH) regulations, 42 CFR 84 (NIOSH, 1997), after passing the tests performed using charge- neutralized sodium chloride (NaCl) aerosol with the particle size of 300 nm in diameter. The certification criterion for N95 half-facepiece respirators is that the total momentary particle penetration, P, through the respirator cannot exceed 5% at 85 l min-1, i.e. the filtration efficiency, defined as h = 1 P, should be at least 95%. The value of 300 nm is pres- ently accepted as the most penetrating particle size (MPPS) for particulate filters. However, numerous investigations have demonstrated that the MPPS can vary considerably from one filter model to another and is dependent on the operational conditions. For non-charged fibers, while the MPPS increases with increasing fiber diameter (Grafe et al., 2001) and decreasing flow rate (Howard, 2003), it lies primarily within the range of 100– 300 nm. The data collected by Brown (1993) indicate that the MPPS may be even as high as 700 nm for very low (0.001 m s-1) air velocity through the filter. For pre-treated respirator filter media, the MPPS dependence on the fiber charge (Martin and Moyer, 2000) suggests greater uncertainty with respect to the most penetrating aerosol fraction.
To achieve high particle capture efficiency while maintaining relatively low breathing resistance, the N95 respirator filters are typically manufactured with charged (pre-treated) fibers. These are further referred to in this paper as electret filters. The certification tests for N-series filters are carried out until minimum efficiency is achieved or until an aerosol mass of >200 mg has contacted the filter, since, in contrast to mechanical filters, the particle capture efficiency of electret filters decreases initially with the filter loading (Baumgartner and Lo¨ffler, 1987; Martin and Moyer, 2000; Ji et al., 2003). This effect depends on the properties of aerosol particles, and, according to Baumgartner and Lo¨ffler (1987), can be attributed to the neutralization of fiber charges by the charges of opposite polarity that are carried by aerosol particles collected on the fiber. Walsh and Stenhouse (1996) suggested an alternative explanation related to the reduction of electrostatic effect as the layer of particles covering the fiber increases, which, in turn, causes shielding of the electric field. Barrett and Rousseau (1998) attributed the decrease of the electret filter efficiency with loading to the chemical interaction between fibers and aerosol. Once the loading has achieved a certain level, an electret filter begins acting as a mechanical filter and its efficiency increases. The pressure drop across the filter increases during loading. Walsh and Stenhouse (1997) studied how this increase is affected by the particle size, charge and material properties, as well as by the filter face velocity and the fiber charge. They developed the computer simulation of the dendrite formation in two dimensions utilizing the Kuwabara flow field (Kuwabara, 1959). The theoretical study by Walsh and Stenhouse (1997) suggests that the particle deposition on the fiber surface is more uniform when it is primarily driven by the electrostatic mechanism than by inertia. Moreover, they found that more uniform deposition is also associated with an increased fiber charge. Similar results were obtained by Oh etal. (2002) using Brownian dynamics simulation. The Kuwabara flow field was also used by Lathrache et al. (1986b) to calculate the penetration of charged particles through charged fibers. The investigators observed that under the charge equilibrium conditions the particle charge distribution considerably affects the particle deposition onto charged fibers and the dependence of the penetration on the particle size is bimodal. The results of theoretical study by Kanaoka et al. (2001) indicate that charged particles tend to form taller dendrites that concentrate on a more limited area on the fiber surface than uncharged particles. The performance of filtering-facepiece respirators has been extensively tested using non-biological par- ticles (Chen and Willeke, 1992; Qian etal., 1997b, 1998; Barrett and Rousseau, 1998; Huang etal., 1998; Han, 2000; Martin and Moyer, 2000) as well as biological particles (Brosseau etal., 1997; McCullough etal., 1997; Qian etal., 1997a, 1998; Reponen etal., 1999; Wang etal., 1999; Lee etal., 2004a). However, these studies primarily addressed the particle sizes >100 nm. Owing to increasing con- cern about health effects associated with the production of nanomaterials and other issues involving nanoparticles, and because N95-type respirators are widely recommended and used in occupational environments, there is a clear need to evaluate the performance of these respirators in the nano-sized range. Other aspects of testing filtering-facepiece respirators remain unresolved. Although, it seems important to know the variability of the performance characteristics of filtering-facepiece respirators of the same model, we have not found any specific information on this topic in the literature devoted to N95 respirators. Also, while manikin-based protocols have been used for testing of the respirators’ performance in various test chambers (Lee etal., 2004b, 2005), the size of the test chamber needed to accurately predict the field performance of the respirator has not been adequately investigated. In this study, the performance characteristics of N95 respirators operating at different inhalation flow rates were tested at the initial moment of filtration (no loading factor was considered) using nano-sized and submicron NaClparticles(10–600nm). The particle penetration was determined as a function of the particle size. The within-respirator-model variability was also determined. In order to validate the manikin-based testing protocol, similar measurements were conducted in small and large test chambers.
Materials and Methods
The aerosol particle penetration through the N95 respirator filter was measured following a manikin- based protocol, in which the filtering-facepieces were sealed on the manikin face so that no leakage occurred between the face and the inner filter surfaces. To assure this, the leakage test was conducted using a bubble-producing liquid. The experiments were carried out in a test chamber utilizing sodium chloride aerosol (used by NIOSH in certification testing of N-series filtering-facepieces).
Figure 1 presents a diagram of the experimental set-up for measuring the particle penetration through an N95 respirator. Aspirated by fan (1), the ambient air was purified in the HEPA filter (2) and then supplied to the aerosol generator (3) (a six-jet Collison nebulizer, BGI Inc., Waltham, MA). The generated aerosol was diluted with the clean air supplied by pump (4), passed through dryer (6) and a 85Kr electrical charge equilibrator (7) (Model 3054, TSI Inc., Minneapolis, MN), and directed to the top part of the ‘small’ (0.096 m3) test chamber (8). The design enabled us to achieve a good uniformity of the challenge aerosol in the test chamber. The manikin (9) was placed inside the chamber, and the test respirator (10) was sealed on its face by a silicone sealant. The manikin was equipped with a probe to sample the aerosol inside the facepiece. The outside aerosol was sampled at 5 cm from the respirator outer surface with a probe of approximately the same diameter and length as the in-facepiece sampling probe. The experiments were performed with a manikin at an inhalation air flow provided by a pump (13). The flow rate was controlled by a flow meter (12) (Model 4043, TSI Inc., Minneapolis, MN). In this study, two flow rates were tested: 30 l min-1 representing light workload and 85 l min-1 representing heavy work load (the latter is used in respirator certification tests). The inside and outside aerosol sampling probes operating at 1 l min-1 were connected to the Wide-Range Particle Spectrometer (14) (WPS, model 1000 XP, Configuration A, MSP Corp., Shoreview, MI).
The WPS combines three measurement principles: the differential mobility analyzer (DMA), the con- densation particle counter (CPC) and laser particle spectrometer (LPS). This allows measuring the dia- meter and the number concentration of aerosol particles in a wide size range, namely from 10 to 10 000 nm particle diameter. The DMA and CPC cover the range of 10 to 500 nm in up to 96 channels, whereas the LPS has a measurement capability from 350 to 10 000 nm in 24 channels. In order to remove
the particles larger than 500 nm from the DMA air stream, the instrument is equipped with the single- stage impactor. A built-in aerosol charge equilibrator (210Po radioactive alpha source) imparts the Boltzmann charge distribution on the particles. After passing through the impactor and the charge equilibrator the aerosol enters the DMA where the particles of a narrow electrical mobility are extracted. The DMA operates in two modes: with the DMA voltage stepped (DMS mode) or scanned exponentially (SMS mode). The particles classified by the DMA according to their electrical mobility are subsequently transported to the CPC for counting. The CPC is of the thermal diffusion type, where butanol condenses on the sampled particles, making them grow to a size that is easy to detect with a light scattering detector (MSP, 2004). The aerosol concentration and particle size distributions measured by WPS inside and outside the respirator, respectively, was analyzed by the personal computer (15) and plotted against the particle size, dp, represented by the mobility diameter for particles up to 350 nm and optical diameter in the size range of 350–600 nm.
For the method validation, selected experiments were repeated using a large (24.3 m3), walk-in test chamber that simulates the field conditions in indoor work environments. In this case the manikin was placed in the center of the chamber and the challenge aerosol was evenly distributed in the chamber volume by a centrifugal fan.
Test N95 respirators
Two models of N95 filtering-facepiece respirators, commercially available from different manufacturers (further referred to as A and B) were selected for this study. Both of them consist of the charged fibers (electret media), and they are widely used in occupational environments. Respirator A is characterized by high fit factor value, while Respirator B has considerably lower fit factor (Coffey et al., 2004). Tables 1 and 2 summarize the physical parameters of respirators A and B, determined by the authors of this study (with the exception of the information on the fiber materials that was provided by manufacturers). The thickness of each layer, L, was measured using a vernier caliper. The fiber diameter, df, was determined by analyzing the micrographs obtained under an optical microscope, connected to a digital camera and a personal computer. The surface density, rSF, was obtained by weighing the samples of filters with a known surface area. Using these parameters and the available density of the fiber material, r, the packing density was calculated as:
After deducting the areas covered by the silicon sealant, the overall surface area was determined for each facepiece. The above area was 0.0110 m2 for Respirator A and 0.0134 m2 for Respirator B. The face air velocities, U0, calculated as the ratio of the volumetric flow to the surface area, were also differ- ent: at Q = 30 l min-1, U0 = 4.5 cm s-1 for Respirator A and 3.7 cm s-1 for Respirator B; at Q = 85 l min-1, U0 = 12.9 and 10.6 cm s-1 for Respirators A and B, respectively.
The aerosol penetration through the N95 respirator was determined particle-size-selectively, as a ratio of the aerosol concentrations recorded in each WPS channel inside, cin(dp), and outside, cout(dp), the facepiece:
The measuring cycle included three samples upstream of the filter, three samples downstream of the filter and then again three samples upstream of the filter (the last allowed us to assure that the aerosol concentration outside the respirator was consistent during each experiment). The fractional penetration,
P(dp), was calculated based on the mean values of the aerosol concentration recorded in specific channels that were reckoned taking into account the second and the third samples of each cycle. The first samples were excluded as they could be contaminated by the aerosol remaining in the tube after prior measurement.
The measurement data were recorded in 48 channels of the DMA and 24 channels of the LPS. However, when the particle count in a channel was <50, the numbers from two or more channels were combined to achieve statistically representative data. The penetration of aerosol particles >600 nm was not calculated, because there were too few of those outside the respirator.
This study was initiated to primarily address the respirator protection against nanoparticles. The test particle size distribution is shown in Fig. 2. The highest aerosol concentration was observed in the particle diameter range of 20–40 nm. Overall, the test particle size range extended to as much as 600 nm, which allowed us to include dp = 300 nm that is currently adopted for the respirator certification.
To determine the within-respirator-model variability of the penetration, 10 identical facepieces of each model were evaluated for both inhalation flow rates tested in this study. The mean value, standard deviation and the coefficient of variation of P(dp) were calculated for each flow rate and each N95 respirator model using the complete data set obtained from ten experiments. The fraction of identical respirators that did not pass the N95 criterion (i.e. those that demonstrated the particle penetration in excess of 5%) was also determined.
To compare the penetration of sodium chloride particles through the N95 respirators obtained in the small and large chambers, the paired t-tests were run using Origin 6.0 (OriginLab Corp.).
Experimental Results and Discussion
The test chambereffect
Similar to other manikin-based laboratory studies of N95 half-facepiece respirators, our tests were con- ducted in a relatively small test chamber (much smaller than a typical setting in which a worker wears the respirator). As part of the method of validation, we examined whether the performance characteristics obtained in this 0.096 m3 test chamber represent those expected in the field. Figure 3 depicts the comparison of the particle penetrations obtained for Respirator A using small and large (24.3 m3) chambers. The comparison was made for both inhalation flow rates used in this study. As it is difficult to achieve sufficiently high aerosol concentration level in a large volume, a greater number of the WPS channels were combined when analyzing the data collected in a large chamber. For consistency, the same channel-combining strategy was applied for the data obtained in the small chamber when applying the statistical testing. The paired t-tests ran for Respirator A revealed P-values of 0.397 and 0.053 for the inhalation flow rates of 30 and 85 l min-1, respectively. This indicates that the respirator efficiency values determined in two test chambers were not significantly different. A similar conclusion was made for Respirator B.
The above finding suggests that the respirator performance tests carried out in a chamber of relatively small volume can be successfully used to predict the respirator performance in a workplace (this conclusion deals with face-sealed respirators and, thus, does not address the particle penetration through the leakage).
Size selective penetration curve and variability of the respirator performance
The within-respirator-model variability of the respiratory protection provided by Respirators A and B
at inhalation flow rates of 30 and 85 l min-1 is demonstrated in Fig. 4. Table 3 presents the values of the coefficient of variation that is defined as the ratio of the standard deviation to the mean and calculated in the particle diameter range of 20–100 nm. For the particles <20 nm and >100 nm, the penetration was close to zero (suggesting the respiratory protection level of almost 100%) so that there was no need to assess the N95 respirator performance variability. It is seen that at Q = 85 l min-1 the mean values of the penetration through Respirator A reached the 5% threshold for nanoparticles of 41 nm. Furthermore, for Respirator B, the mean penetration was >5% for dp = 33–73 nm, although it is expected to be below this level for all respirable particles (as B is an N95- certified respirator). It is acknowledged that N95 facepieces are certified on the basis of the total instantaneous penetration of 300 nm particles, and for this particle size our experiments showed the mean penetration values considerably <5%. How- ever, the data presented in Fig. 4 revealed that the maximum particle penetration through both N95 facepieces tested in this study occurred not at dp = 300 nm but in the nano-sized range (when the particles mobility diameter is between 40 and 50 nm). Table 3 also presents the fraction of identical respirators, among the 10 tested (n = 10), which had the particle penetration in excess of 5% for some particle sizes. It is seen that at 30 l min-1, the particle penetrations through Respirators A and B were always <5% for all measured particle sizes. The increase of the inhalation flow rate to 85 l min1 decreased the protection level provided by both respirators against particles of 20–100 nm. As a result, 6 of the 10 tested A-facepieces and 9 of the 10 tested B-facepieces showed penetration >5%. Further increase of the inhalation flow rate is anticipated to decrease the protection of N95 respirators against nanoparticles to an even greater extent. Although Q = 85 l min-1 is a relatively high breathing flow rate (simulating human breathing at a heavy work load), much higher rates are believed to be achievable in the workplace. Janssen (2003) refers to the suggestion that respirators should be tested at flow rates exceeding 350 l min-1. The concern in this case is potentially excessive penetration of very small particles; thus, the higher penetration would be represented by the particle number rather than by the particulate mass. One could argue that the mass of penetrated nano- particles is not sufficient to cause health problems. However, the health effects associated with nano- particles may not necessarily relate to the particulate mass. Similarly, the effects caused by the human exposure to biological particles, such as viruses and bacteria, often depends on the number of inhaled bioparticles, for some of which the infectious dose is very low (McCullough and Brosseau, 1999).
With respect to the real life situation, the above findings represent the best-case scenario as the tested respirators were sealed to the manikin so that no particles penetrated through the face-seal leakage. The actual respiratory protection level provided by these respirators may be even lower if the respirator does not have a perfect fit. Coffey et al. (2004) evaluated the fitting characteristics of 18 models of N95 half-facepiece respirators and determined the effect of the fit-testing on their protection level. They showed that respirator wearer cannot expect to achieve the desired level of protection without a proper fit-testing. Moreover, the face-seal leakage increases with the filter loading owing to the pressure drop increase. According to Moyer and Bergman (2000), the penetration of NaCl particles through the face-seal leakage of N95 respirators can increase beyond 5% even at a low-level loading. Thus, given that the loading effect and a poor fit may increase the particle penetration above the levels found in this study, we conclude that the N95 respirators may not be efficient in providing the expected respiratory protection for workers exposed to nanoparticles.
Comparison Of The Theoretical Calculations With The Experimental Data
Mathematical model of the particle penetration through an electret filter
In addition to the experimental data reported above, the theoretical calculations of the particle penetration through respirator filters were conducted using the classic theory of depth filtration (Pich, 1966; Lee and Mukund, 2001):
where Ef is the collection efficiency of a single fiber. Since the N95 respirator facepieces are usually multilayered, the total penetration through the respirator was determined as a product of the penetrations of each layer, calculated from equation (3).
The capture of particles ranging from 10 to 1000 nm by a mechanical fibrous filter is driven primarily by the diffusion and interception mechanisms. Assuming that these mechanisms are independent, the single- fiber collection efficiency can be obtained from the following equation:
where ED is the single-fiber efficiency due to diffusion and ER is the single-fiber efficiency due to interception. The single-fiber efficiency for the diffusion mechanism can be calculated (Payet et al., 1992; Gougeon et al., 1996) as:
Here Ku is the Kuwabara hydrodynamic factor calculated as
and Pe is the Peclet number defined as
where U0 is the face velocity and D is the particle diffusion coefficient
kB is the Boltzmann constant (1.3807 · 10-23 J K-1), m is the fluid viscosity, T is the fluid absolute temperature, and CC is the Cunningham slip correction factor. The latter is calculated as
where Kn is the Knudsen number defined as the ratio of the gas free path (that is equal to 65 nm under normal conditions) to the particle radius. The single-fiber efficiency for the interception mechanism was calculated as:
where NR is the interception parameter defined as the ratio of the particle diameter to the fiber diameter. Figure 5 presents the results of the penetration calculated at U0 = 12.9 cm s-1 (Respirator A at Q = 85 l min-1) for the filter with characteristics, such as L, df, a and rSF, identical to those of Respirator A for two situations: when the fibers were not initially charged (mechanical filter, dotted curve) and when the fibers have a charge density, q, of 13 nC m-1 (electret filters, solid curve). The particle deposition is assumed to be driven by diffusion and interception for mechanical filter, with additional electrostatic interaction for electret. The difference between the two curves is clearly seen. The theory indeed predicts that if the filter fibers of Respirator A were not charged, the MPPS would be 300 nm. In that case, however, the particle penetration peak would reach as high as 80% (which considerably exceeds the experi- mental values). As the commercially available N95 half-facepiece respirators are made of fibrous electret filter media, the electrostatic mechanism plays an important role significantly enhancing the filter cap- turing efficiency. Below we describe the model that was employed to determine the particle penetration curve for the Respirator A with electret filter.
Neutral particles passing through the media made of charged fibers are polarized by the electric field and dipole charges are induced on the particles. The magnitude of the charge is proportional to the particle volume. The theoretical quantification of the par- ticle deposition on charged fibers due to polarization forces is difficult because of uncertainty in the fiber charge density determination. We have failed to find
any specific information about ‘typical’ values of q in the literature with few exceptions. The value of q = 34.2 nC m-1 was referred to by Brown (1979) and later used by Kanaoka et al. (1987) in their calculation of the polarization force. Much lower values, q = 0.5 nC m-1 (Walsh and Stenhouse, 1996) and q = 0.06 nC m-1 (Lathrache etal., 1986b) were predicted theoretically with no experimental confirmation.
To calculate the single-fiber collection efficiency due to polarization force, Kanaoka et al. (1987) used the following semi-empirical equation:
The parameter NQ0 defined as the ratio of the electrostatic attraction force to the drag force is given for the case of a uniformly (unipolarly) charged fibers by:
where ep is the relative permittivity of the fiber and e0 is the permittivity of the vacuum. In the present work, the efficiency of collection of neutralized particles on bipolarly charged fibers due to polarization force was calculated from the equation proposed by Lathrache and Fissan (1986a):
In the equation (13) the parameter NQ0 for a line- dipole charged fiber is defined as follows:
where ef is fabric dielectric constant and q denotes the charge of each sign per unit length of the fiber. The empirical constant B is introduced to allow for
deviation of real filters structure from the ideal geometry of the Kuwabara cell model. At B = 0.21, the theoretical data on the particle penetration through the filter of Respirator A have a best fit with the experimental data. We found that for the above B-value, the single-fiber efficiencies predicted by equations (13) and (11) were not significantly different. The overall collection efficiency of uncharged particles by a single charged fiber can be calculated based on the modified equation (4) as
As the fiber charge density was not known for Respirator A, we used q = 13 nC m-1 as the best fit for the theoretical and experimental data. Figure 6 depicts the comparison of experimental data and theoretical curves obtained for Respirator A at the flow rate of 85 l min-1 (the shaded area is bracketed by q of 13 and 14 nC m-1). It was assumed that only the middle layer of the respirator is charged since the structures of two other layers indicated that they serve as supported layers rather than highly efficient filters. A slight discrepancy between experiments and theoretical prediction may be caused by several fac- tors. One is non-homogeneity of the respirator fiber structure (Huang etal., 1998). Another is the shad- owing of the fibers that occurs as the downstream fibers are in the shade of upstream ones, which induces collection of fewer particles on the down- stream fibers [this effect is not included in the above theoretical model (Podgo´rski, 2002)]. The third possible reason for the discrepancy is limitations of the model owing to the lack of specific information about the procedure used for the fiber electrization. The theoretical modeling for an electret filter clearly indicates that charging of fibers tremendously decreases the number of particles that penetrate through the filter. For example, at fiber charge density of 13 nC m-1, the polarization force results in the penetration decrease from 80% to 5% for Respirator A. Furthermore, the MPPS shifts towards much smaller particle sizes (40–50 nm) compared with the conventional (mechanical) filter. The pos- sibility of this shift was reported by Martin and Moyer (2000) who investigated the initial penetration of dioctyl phthalate (DOP) aerosol through different models of the particulate respirator filters including N95-type. Based on the experiments with charged and uncharged media, the authors suggested that the maximum penetration of particles through the fiber- charged filters occurs at dp <300 nm (specifically, between 50 and 100 nm).
Although the electret filter looses its initial high efficiency during the aerosol loading, the application of the fiber charging is useful to enhance the filter performance. Other alternatives have limitations. For instance, to achieve the same protection level when using Respirator A with non-charged fibers, one would need to increase the thickness of its middle layer over 20 times or decrease the fiber diameter of this layer 4-fold. The increase of the filter thickness would considerably increase the pressure drop; the decrease of the fiber diameter does not seem to be an easy option either, since production of very fine fibers is technologically challenging.
Neutralization of particles
The certification test of an N95 filtering-facepiece respirator is carried out utilizing charge-neutralized particles in order to examine respirators’ performance under ‘worst-case’ scenario, representing the maximum penetration. Neutralization of aerosol particles is particularly important when testing electret filter.
In case both the fibers and the particles are charged, an emerging Coulombic force significantly enhances the capture of particles and, thus, reduces the penetra- tion. The comparison of penetration values obtained with and without the particle charge equilibrator is shown in Fig. 7. For Respirator A operated at Q = 85 l min-1, the penetration decreased over 3-fold once the 85Kr source was removed.
A similar experiment was conducted for a low efficient mechanical filter, in which case no signifi- cant difference between penetrations of electrically- neutralized and non-neutralized particles was observed. A charged particle polarizes the uncharged fiber and experiences an image force; however, unless the particle carries very high charges, this force is not strong compared with Coulombic or polarization forces.
Our results on the effect of the particle charge on the filter performance are in line with the findings of Chen and Huang (1998) and Fjeld and Owens (1988), who reported that the particle charging decreased the penetration through both the charged and non- charged filters. Kanaoka et al. (1987), who experi- mentally studied the particle collection by an electret filter media with rectangular fibers, achieved the maximum penetration at dp = 30–40 nm for uncharged particles, whereas singly charged particles showed the peak at much larger sizes. These results are fully applicable when attempting to predict the performance of N95 filtering-facepiece respirators against nanoparticles.
The conventional wisdom is that the N95 filtering half-facepiece respirators are highly efficient for protecting the human respiratory tract against fine and ultrafine airborne particles if properly fitted. However, our manikin-based tests revealed that the penetration threshold of 5% established for N95 facepieces could be exceeded when used against nanoparticles in the size range of 30–70 nm. At the same time, the penetration of 300 nm particles (utilized as the most penetrating size for the certification of N95 respirators under 42 CFR 84 NIOSH regulations) was found to be considerably <5% for two N95 respirator models and two inhalation flow rates, 30 and 85 l min-1, tested in this study. The shift of the MPPS towards nano-sized particles is attributed to the electret filter media, which is conven- tionally utilized by the respirator manufacturers nowadays (the application of charged fibers consid- erably increases the filter efficiency, while the breath- ing resistance remains unchanged). The theoretical modeling of the particle penetration through mech- anical and electret filters confirmed the experiment- ally observed shift. The modeling also confirmed that the particles captured by fibers only due to diffusion and interception go through the filter much more readily than those, which—in addition—are subjec- ted to polarization force. It was quantitatively demon- strated that the particle electrical neutralization is a crucial element during testing the electret filters. If not neutralized, the particles can also be attracted to charged fibers owing to Coulombic force that significantly decreases the penetration, thus, resulting in the overestimation of the respirator protection characteristics.
The variability of the respirators’ performance was determined for both N95 models and both inhalation flow rates. The analysis revealed that the coefficient of variation of the penetration ranged from 0.10 to 0.54 for particles of 20–100 nm in diameter. At 85 l min-1, the fraction of N95 respirators for which the performance test demonstrated excessive (>5%) penetration of nanoparticles was as high as 9/10.
The test results obtained in a relatively small (0.096 m3) test chamber and in a large (24.3 m3) walk-in chamber were found essentially the same, suggesting that laboratory-based evaluations have a good potential to adequately represent the respirator field performance.
S. A. Grinshpun, G. Mainelis, M. Trunov, A. Adhikari, T. Reponen, K. Willeke
Center for Health-Related Aerosol Studies, Department of Environmental Health; University of Cincinnati, Ohio, USA. Present address Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey, USA. Present address Mechanical Engineering Department, New Jersey, USA. Institute of Technology, Newark, New Jersey. USA.
Numerous techniques have been developed over the years for reducing aerosol exposure in indoor air environments. Among indoor air purifiers of different types, ionic emitters have gained increasing attention and are presently used for removing dust particles, aeroallergens and airborne microorganisms from indoor air. In this study, five ionic air purifiers (two wearable and three stationary) that produce unipolar air ions were evaluated with respect to their ability to reduce aerosol exposure in confined indoor spaces. The concentration decay of respirable particles of different properties was monitored in real time inside the breathing zone of a human manikin, which was placed in a relatively small (2.6 m³) walk-in chamber during the operation of an ionic air purifier in calm air and under mixing air condition. The particle removal efficiency as a function of particle size was determined using the data collected with a size-selective optical particle counter. The removal efficiency of the more powerful of the two wearable ionic purifiers reached about 50% after 15 min and almost 100% after 1.5 h of continuous operation in the chamber under calm air conditions. In the absence of external ventilation, air mixing, especially vigorous one (900 CFM), enhanced the air cleaning effect. Similar results were obtained when the manikin was placed inside a partial enclosure that simulated an aircraft seating configuration. All three stationary ionic air purifiers tested in this study were found capable of reducing the aerosol concentration in a confined indoor space. The most powerful stationary unit demonstrated an extremely high particle removal efficiency that increased sharply to almost 90% within 5-6 min, reaching about 100% within 10-12 min for all particle sizes (0.3-3 µm) tested in the chamber. For the units of the same emission rate, the data suggest that the ion polarity per se (negative vs. positive) does not affect the performance but the ion emission rate does. The effects of particle size (within the tested range) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria) as well as the effects of the manikin's body temperature and its breathing on the ionic purifier performance were either small or insignificant. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when used inside confined spaces with a relatively high surface-to-volume ratio.
Ionic air purifiers have become increasingly popular for removing dust particles, aeroallergens and airborne micro organisms from indoor air in various settings. While the indoor air cleaning effect, resulting from unipolar and bipolar ion emission, has been tested by several investigators, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. Among the five tested ionic air purifiers (two wearable and three stationary) producing unipolar air ions, the units with a higher ion emission rate provided higher particle removal efficiency. The ion polarity (negative vs. positive), the particle size (0.3-3 µm) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria), as well as the body temperature and breathing did not considerably affect the ionization-driven particle removal. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when they are used inside confined spaces with a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms and animal confinements). Based on our experiments, we proposed that purifiers with a very high ion emission rate be operated in an intermittent mode if used indoors for extended time periods. As the particles migrate to and deposit on indoor surfaces during the operation of ionic air purifiers, some excessive surface contamination may occur, which introduces the need of periodic cleaning these surfaces.
Inhaled airborne particles and microorganisms can cause adverse health effects, such as asthma and allergic diseases (Burge, 1990; Koskinen et al., 1995; Miller, 1992; Spengler et al., 1993) as well as airborne infections (Burge, 1990). Exposure to indoor aerosol pollutants has become a growing public and occupational health concern (American Lung Association, 1997; Gammage and Berven, 1996; Samet and Spengler, 1991). The outbreaks of emerging diseases and the threat of bioterrorism have generated special needs in indoor air cleaning against respirable particles, especially those of biological origin. Strategies developed for protecting building environments from deliberately used aerosol agents require efficient air filtration and air cleaning systems [National Institute for Occupational Safety and Health (NIOSH), 2003]. Conventional indoor air purifiers include mechanical filters, electronic air cleaners, hybrid filters, gas phase filters and ozone generators. Among various mechanisms, the emission of ions, also referred to as air ionization, has shown considerable promise. Emission of bipolar ions enhances the agglomeration of smaller particles into larger ones, which then gravitationally settle and thereby purify the air. Ionization may also cause attraction between particles and grounded surfaces resulting in electrostatic deposition.
The physical and biological effects of small air ions on indoor air quality as well as various health benefits and implications of air ionization have been discussed in the literature (Daniell et al., 1991; Kondrashova et al., 2000; Krueger and Reed, 1976; Soyka and Edmonds, 1977; Van Veldhuizen, 2000; Wehner, 1987). The ion emitters, which meet health standards (e.g. by not generating ozone above the established thresholds), have been incorporated in commercial air purification devices that utilize either bipolar or unipolar ion emission. These devices are currently produced by several manufactures worldwide (Sharper Image Inc., Little Rock, AR, USA; Topway Electronic Factory Co., Guangzhou, China; Wein Products, Inc., Los Angeles, CA, USA; etc.) and used in residential and occupational settings for removing dust particles, aeroallergens, and airborne microorganisms from the air. The ion emission has been tested by several investigators for its ability to reduce the indoor aerosol concentration (Bigu, 1983; Bohgard and Eklund, 1998; Grabarczyk, 2001; Harrison, 1996; Hopke et al., 1993; Khan et al., 2000; Kisieliev, 1966; Li and Hopke, 1991). The bactericidal effect of air ionization has also been assessed (Lee, 2001; Marin et al., 1989; Seo et al., 2001; Shargavi et al., 1999). However, the mechanisms involved in the ionic purification of inhaled air in the breathing zone remains poorly understood. Furthermore, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. This controversy reflects a lack of quantitative data on the purifiers’ efficiency in peer-reviewed scientific journals.
Ionic air purifiers are available as stationary and wearable devices. The latter have been specifically developed for personal respiratory protection by targeting particles in the human breathing zone. Some models are designed to operate in confined spaces, such as automobiles, aircraft cabins, bathrooms, office cubicles, and small animal confinements. Our pilot study has demonstrated that unipolar ion emission by corona discharge may considerably reduce the aerosol concentration in the breathing zone (Grinshpun et al., 2001). We concluded that the concentration decrease, during the air ionization, occurs as air ions impart electrical charges of the same polarity on aerosol particles, and the unipolarly-charged particles then repel each other out of the breathing zone towards nearby surfaces, where they are deposited. More recent investigation by our group (Lee et al., 2004) has shown that a high-density emission of unipolar ions has a good potential for air cleaning across room-size indoor spaces uniformly contaminated with fine and ultrafine aerosol particles. Another recent work - an extensive theoretical study of Mayya et al. (2004), which was awaiting publication when the present paper was being completed - has identified and analyzed several physical factors affecting the airborne particle removal by unipolar ionization and developed advanced computational model to quantify the process.
In this study, we determined the particle removal efficiencies of five ionic air purifying devices - two wearable and three stationary units - that produce unipolar ions (either positive or negative). The concentration decay of respirable particles (0.3- 3 μm) was monitored in real time inside the breathing zone of a human manikin placed in a chamber that simulated a confined indoor environment. The role of air mixing in the chamber as well as the breathing effect and the body temperature effect on the performance of the ionic air purifiers were also investigated.
Study design and methods
The tests were conducted in a walk-in chamber made of wood (painted) with interior dimensions of L x W x H = 1.2 m x 1.0 m x 2.2 m ≈ 2.6 m³. A standard size human manikin was placed inside facing the chamber center, see Figure 1. The manikin’s nose was located 0.3 m from the back of the chamber, 0.5 m from the side walls, and 1m from the floor (sitting position). This configuration was used in our previous studies on evaluations of respirators (Willeke et al., 1996).
Aerosol generation and flow patterns
Polydisperse NaCl particles and monodisperse poly styrene latex (PSL) spheres, as well as bacterial cells of Pseudomonas fluorescens were used as test aerosols. Both types of biologically inert particles (NaCl and PSL) and P. fluorescens bacteria have been extensively utilized in earlier studies for evaluating sampling devices and respirators (Grinshpun et al., 1999; Mainelis et al., 2002a,b; Stewart et al., 1995; Terzieva et al., 1996; Wang et al., 2001; Willeke et al., 1996). Gram-negative P. fluorescens bacteria are commonly found in air environments. A standard Collison nebulizer (BGI Inc., Waltham, MA, USA) operated at a flowrate of 6 1/min was employed to aerosolize the test particles from a liquid suspension. The liquid content of the aerosolized droplets was evaporated by mixing the aerosol flow with 80 1/min of dry filtered air. The combined airflow entered the test chamber through an air laminarizing and distributing unit. The air exhaust, positioned at the bottom of the chamber, was connected to an external pump through a HEPA filter.
Most of the tests were performed with NaCl aerosol generated from a solution prepared by dissolving 20 g of reagent quality NaCl (Fisher Chemical, Fair Lawn, NJ, USA) into 400 ml of deionized and sterilized water. After drying, the particles had a broad size spectrum, including the range of interest [0.3- 3 μm as measured by an optical particle counter (OPC)]. This range represents a wide variety of aeroallergens and microbial agents (Reponen et al., 2001).
Two size fractions of PSL spheres (Bangs Laboratories, Inc., Fishers, IN, USA), with median count diameters of 0.44 µm (ag = 1.07) and 0.95 µm (ag = 1.1), were used for selected experiments. Prior to aerosolization, the suspension of PSL particles was deagglomerated for 5 min in an ultrasonic bath (model 220, Branson Cleaning Equipment Co., Shelton, CT, USA). Bioaerosols of P. fluorescens (ATCC 13525; American Type Culture Collection, Rockville, MD, USA), rod-shaped bacterial cells of dₚ ≈ 0.8 µm, were also used for selected experiments. Standard microbial preparation procedures utilized in our previous studies (Mainelis et al., 2002a,b; Stewart et al., 1995; Wang et al., 2001) were followed prior to aerosolizing the P. fluorescens cells. The tests with PSL and P. fluorescens were performed to study the effect of the physical material and biological status of particles on the particle removal by continuous air ion emission.
During each test, the concentration and size distribution of the airborne particles were monitored in real time with an OPC (model 1.108; Grimm Technologies Inc., Douglasville, GA, USA). It enumerated aerosol particles every minute in 16 detection channels within the particle size range of 0.3 to about 30 µm. The range of interest was represented by the following eight channels (the size fractions are listed by their channel mid-points): < dp > = 0.35, 0.45, 0.58, 0.73, 0.90, 1.3, 1.8 and 2.5 µm.
A wearable air purifier was positioned on the manikin’s chest so that the ion emission point would be in line with the manikin’s nose, which was 0.2 m above the purifier. The OPC inlet was positioned directly above the purifier’s outlet, perpendicular to the line between the purifier and the manikin’s nose. The aspiration efficiency of the OPC inlet is approximately l00% regardless of its orientation since the test particles (0.3-3.0 µm) are virtually inertialess (Grinshpun et al., 1990, 1993). At first the OPC measurements were performed at three locations: 1, 10 and 19 cm above the ion emission point. Although the variability of the aerosol concentration near the ionizer was very high, the aerosol concentrations measured at 10 cm (upper chest level) and 19 cm (nose-mouth area) were essentially the same with a variability ranging from 10 to 20% for the entire tested particle size range. We concluded that it would be sufficient to measure the aerosol at the point representing inhaled air.
When evaluating the performance of stationary air purifiers, aerosol sampling was also performed in the breathing zone, while the tested unit was placed either on the floor or on the table (in accordance with its operational function). Overall, the inhalation point seems the most appropriate location for the OPC inlet as the ultimate objective is to characterize the air purification effect of ionic emitters in terms of respiratory exposure to airborne contaminants. Our preliminary study revealed no significant effect of the distance from the emission point to the walls of the test chamber on the aerosol concentration as long as this distance exceeded 0.45 m. Stationary air purifiers were evaluated at equal distance between the manikin’s face and the opposite wall.
Determination of the particle removal efficiency
The size-specific aerosol concentration, C (dp), was measured as a function of monitoring time, t. The natural decay was measured for 10 h as a baseline test. In the experiments involving air ion emission, the time varied from 1 to 3 h, depending on the emission rate of the ionic air purifier being tested. For each purifier, two concentration decay curves were obtained: the natural decay, i.e. when the ion emitter was ‘off’ [Cnatural (dp, t)], and the one with the ion emitter ‘on’ [Cionizer (dp, t)]. The particle removal efficiency was determined as follows:
The natural decay depends on the air mixing conditions in the chamber. Therefore, separate baseline tests were conducted in calm air as well as with the fan operating at 33 and 900 CFM.
It should be noted that the above definition is different from the ratio of the initial to the final aerosol concentration levels, which is referred to as the ‘concentration reduction factor (CRF)’ and often used in the literature. Mayya et al. (2004) acknowledged the limitation of CRF indicating that it ‘is not a primary index of ionizer performance.’ The particle removal efficiency used in this study allows comparing the ionization-driven concentration decrease to the natural decay occurring because of gravitational settling, diffusion and other mechanisms.
Prior to each experiment, the test chamber was ventilated by supplying particle- and ion-free air for about 1 h, until the total particle concentration inside the chamber was below 10³ particles per liter of air. At that time, the ventilation was turned off and the aerosol generation system was activated. The fans operated at two points inside the chamber to achieve uniform aerosol concentration across the volume. Once the total concentration reached about 10⁶ particles per liter of air, the aerosol generator and the fan were turned off. After waiting for 5 min to allow the concentration to stabilize, the test began (t = 0). When using a non-breathing manikin under calm air-conditions, the only device that was operating inside the chamber at t > 0 was the OPC, which ran at a very low flow rate (1.2 1/min) so that no considerable air movement occurred. When testing with a breathing manikin or under air mixing conditions, the breathing simulation machine or/and the air mixing fan produced significant air movement inside the chamber. The tests involving the breathing manikin were conducted to determine whether the inhalation-exhalation cycle affects the particle removal efficiency of the tested ionic air purifier. The air flow was supplied by a breathing simulation machine located outside the test chamber. The aerosol concentration decay solely resulting from the breathing simulation was compared with the natural aerosol decay in the chamber. The tests were also conducted with the manikin pre-heated to an average temperature of T = 40°C. These experiments were carried out for 1 h to assess whether the body temperature affects the performance of the ionic purifier. The aerosol concentration decay measured with the preheated manikin was compared with the results obtained with a non-heated manikin (T = 23°C). The manikin was made of non-conductive material and dressed in a laboratory coat (not shown in Figure 1), which was washed between the tests.
A separate set of experiments was performed with the manikin placed in a partial enclosure built inside the test chamber. This confined space was restricted by front, side and overhead panels. The configuration simulated a passenger seating section in an aircraft (front panel = front seat, side panels = nearby passengers, overhead panel = overhead compartment). The volume of the partially enclosed air space was about 0.275 m³ consisting of about 0.250 m³ of open space in the front and on the sides of the manikin and about 0.025 m³ of open space between the manikin’s head and the overhead panel. Gaps of 7.5 cm between the panels allowed air exchange. To evaluate the effect of indoor air volume on the particle removal efficiency, one wearable unit placed in a very small Styrofoam chamber-box (L x W x H = 0.31 m x 0.30 m x 0.28 m ≈ 0.026 m³ = 1/100 of the main test chamber). The purifier was located at the midpoint of the bottom surface (the small dimensions of the chamber-box did not allow using the manikin inside the box). The OPC inlet was positioned 10 cm above the ion-emission point.
Tested air purifiers
Two models of wearable ionic air purifiers, provided by Wein Products, Inc. (Los Angeles, CA, USA), were tested in this study. One was equipped with a metal grid acting as an electrostatic precipitator, the Minimate prototype* (further referred to as W1), and the other had no grid, the Minimate prototype*(further referred to as W2). Both units emitted positive ions with the production rate of W2 being five- to l0-fold higher than that of W1. The estimated ion densities produced by these devices (based on the measurement data reported by the manufacturer) were in the range of ~0.5 x l0⁵ to ~5 x 10⁵ ions per cm³ at a distance of 1 m from the emission point, assuming calm air conditions. Three stationary units (also by Wein Products, Inc.) were the AS250B* (further referred to as S1) with an estimated ion density of ~2 x 10⁵ positive ions/cm³ at 1 m from the emission point, the AS1250B* (referred to as S2) with ~5 x l0⁵ positive ions/cm³ and the VI-3500 (referred to as S3) with ~30 x l0⁵ negative ions/cm³. For each set of conditions, three replicate tests were performed. Although the variability of the measured aerosol concentration was almost 20% for NaCl and PSL particles and about 25% for bacteria, the removal efficiency showed very low variability (usually < 5%). The data were statistically analyzed by using the Microsoft Excel software package (Microsoft Co., Redmond, WA, USA).
Results and discussion
Natural decay of airborne particle concentration
In the absence of ion emission, the aerosol concentration in the test chamber slowly decreased with time.
The natural air cleaning mechanisms in calm air contaminated with fine particles (about 0.1- 2 µm) are primarily gravitational sedimentation and diffusion. For the tested particle size range of 0.3- 3 µm, the natural aerosol concentration decay is driven mainly by sedimentation. The measurement data showed that the concentration of 2- 3 µm NaCl particles in the test chamber naturally decreased by 50% in about 2 h, while for 1 µm particles of NaCl and P. fluorescens cells, the 50% decrease took over 10 h. The concentration of 0.3-0.4 µm particles of NaCl showed < 10% decrease during a l0-h period. Most of our experiments involving ionic air purifiers were conducted within much shorter time periods (1-3 h), because our pilot data showed that the air ionization can significantly reduce the aerosol concentration during about an hour (Grinshpun et al., 2001).
Wearable ionic air purifiers
Figure 2 shows the particle removal efficiency as a function of time for the W1 and W2 wearable ionic air purifiers operating in calm air. The top two figures show the size-selective measurement data obtained with NaCl particles and recorded in the first eight OPC channels. The bottom figures show the size-integrated data for the entire measured particle size range of 0.3-3 μm. The data suggest that the removal efficiency did not have a clear trend with the particle size (within the tested range). The particle removal efficiency of W1 increased gradually from 5-15% at t = 15 min to about 30-40% at t = 1 h. The size-integrated data demonstrate that the air cleaning provided by this purifier reached considerable levels after it had continuously operated in the chamber for more than an hour: the aerosol concentration of NaCl in the breathing zone decreased by a factor of 2 (removal efficiency = 50%) after 1.5 h and almost fivefold (removal efficiency = 80%) after 3 h. The particle size-specific removal efficiency values lay within a 15% corridor from each other at each specific time point.
The purifier labeled as W2 provided much more efficient air cleaning as compared with W1, which can be attributed to a higher ion production rate. The particle removal efficiency of W2 reached approximately 50% during the first 15 min and continued increasing with the time. As a result of its 1.5-h continuous operation on the manikin’s chest, almost 100% of the initially airborne particles were eliminated from the breathing zone. Comparison of the performance characteristics of W1 and W2 under calm air conditions confirms that the air cleaning provided by a unipolar ion emission becomes more efficient at a higher ion production rate.
When the fan was operated in the test chamber at 33 CFM, it produced an air velocity level equivalent to the air exchange rate of about 20 AEH (no external ventilation was actually introduced during the tests). At this air mixing rate, the particle removal efficiencies of both wearable ionic air purifiers were slightly higher than under calm air conditions. However, the difference was not statistically significant (t-test: P > 0.05). Once vigorous air mixing (900 CFM) was introduced, the air cleaning became much more rapid. The air currents intensify the ion propagation in the chamber and enhance the ion-particle interactions. This makes the
particle charging by air ions more efficient and consequently increases the removal efficiency.
Figure 3 presents the data obtained with W2 operating under air mixing conditions of 33 and 900 CFM. It is seen that during the first 15 min about 50-60% of the airborne particles were removed at 33 CFM and about 65-80% at 900 CFM. The ion emission appeared to be sufficient to clean the chamber air of essentially all the test particles in about 1 h of operation when it was enhanced by a 33 CFM fan in the chamber: the size-integrated aerosol concentration determined for dp = 0.3- 3.0 µm decreased to almost 1% of its initial level. At 900 CFM, all particle size fractions, except the two largest ones, dp = 1.6-2.0 µm (< dp > = 1.8 µm), and 2.0-3.0 µm (< dp > = 2.5 µm), showed the aerosol concentration reduction by a factor of ~10² –10³ in about 40 min. The curves representing < dp > = 1.8 and 2.5 µm show excessive variability because intensive air mixing removed the larger particles from the air very quickly making the baseline concentration measurement statistically unreliable in about 30-40 min. Consequently, the size integrated efficiency at 900 CFM is shown only for dp = 0.3-1.6 µm.
Compared with a typical air exchange rate in an indoor environment (Abt et al., 2000), the air mixing rate of 900 CFM creates rather excessive air movement (especially when it is applied to confined spaces), while 33 CFM seems more reasonable. As the data collected with both wearable purifiers show that the increase from 0 to 33 CFM did not significantly affect their performance, further experiments were performed at 33 CFM. Thus, on one hand, by introducing some air mixing we made our experimental conditions more representative of a typical small room or cabin, and, on the other hand, we kept the air mixing rate below the level at which it begins to significantly affect the particle removal efficiency.
Stationary ionic air purifiers
The particle removal efficiency curves for the three stationary ionic air purifiers are shown in Figure 4. The curves represent the size-selective monitoring data obtained with NaCl particles under air mixing conditions (33 CFM). Each of the three devices demonstrated considerable air cleaning efficiency. The particle removal efficiency of SI shows some dependence on particle size, although this effect was not very pronounced. The size-specific curves are similar to those obtained for the wearable W2 unit, which reflects the fact that their ion production rates are approximately the same. Surprisingly, S2 that has a higher ion production rate than S1 does not show greater particle removal efficiency.
The third stationary purifier, S3, demonstrates extremely high particle removal efficiency: it increased sharply to almost 90% within 5-6 min, reaching about 100% within 10-12 min for all tested particle sizes. This is attributed to its very high ion production rate. When this air ionizer was operating in the test chamber for a prolonged period of time, such as 1 h, the high number of ions emitted in the relatively small volume of 2.6 m³ produced considerable electric fields that resulted in charging of objects inside the chamber, subsequently causing electrostatic discharges. Our observations suggest that these occasional undesirable electrostatic discharges during human activity represent a limitation for the long-term continuous use of powerful ionic devices in confined spaces. The related safety issue may be resolved by introducing a time limit for their continuous operation. Indeed, as the particle removal efficiency of S3 reaches a plateau of about 100% in 10-12 min, there is no need to keep this purifier operating continuously for an hour in an air volume as small as 2.6 m³. We examined the performance of S3 operating in an ‘on-and-off’ alternating mode for a period of 1 h, during which ions were periodically emitted for 10-min with a subsequent 10-min interruption. It was found that the overall particle removal efficiency exceeded 98% after an hour of its operation in this intermittent mode. Although the purifier’s performance remained very high, the electrostatic discharge problem was reduced. We believe that the above strategy can be used in the field if the device is equipped with a timer allowing it to emit air ions in an intermittent mode.
Effect of properties of the test aerosol particles
For all five ionic air purifiers evaluated in this study, the tests performed with PSL spheres and P. fluorescens bacteria confirmed the findings obtained with the NaCl aerosol. When testing with PSL particles (dp = 0.44 and 0.95 µm), the removal efficiency was approximately the same as that of NaCl particles of the same sizes and operational time. However, some difference was observed when testing with airborne bacteria. For instance, the data generated with P. fluorescens cells using W1r were about 15% lower (on average) than those obtained with NaCl and PSL particles and had considerable variability.
Pseudomonas fluorescens cells are rod-shaped and thus can be charged by air ions differently than the spherical PSL particles or close to spherical salt particles. Furthermore, the initial particle charge levels of P. fluorescens cells are likely to be different from the initial charge levels of the nonbiological test particles used in this study. Gittens and James (1963) and Sherbet and Lakshmi (1973) have shown that Gram-negative water-borne bacteria have an overall net negative surface charge because of the presence of ionizable amino (NH₂) and carboxyl (COOH) groups of proteins exposed at the cell surface. The data reported in our earlier publications (Mainelis et al., 2001, 2002c) suggest that the aerosolized P. fluorescens bacteria can carry significant electrical charges (up to 10⁴ elementary charges per individual cell), which sharply contrasts with the low electrical charges carried by airborne NaCl particles.
Effect of microenvironment
In addition to the above-described experiments conducted in our 2.6 m³ walk-in test chamber, the air purifiers were also tested on a manikin placed inside the partial enclosure (0.275 m³) that was placed inside the walk-in chamber to simulate aircraft seating. Figure 5 compares the performances of W1 and W2 in the walk-in chamber (with no enclosure built inside) to those inside the enclosure. The particle removal efficiencies shown here are the size-integrated data obtained with the NaCl aerosol during a 90-min experiment at 33 CFM. The reduction in aerosol concentration was found to proceed at a similar pace with and without the partial enclosure. The particle removal efficiency was somewhat higher inside the enclosure for the W2 unit, although the difference between corresponding size-integrated values for the two typed of enclosure was mostly below 10%. The particle removal efficiency of W2 reached about 40% after 10 min of continuous operation, and about 70%after 20 min. After 40 min it exceeded 90%, and was in the range of 95- 98% between 60 and 90 min. For W1, the particle removal efficiency measured on the manikin inside the partial enclosure was lower than that of the more powerful W2, similar to the results that were obtained in a walk-in chamber with no enclosure.
The performance of an ionic air purifier in a specific microenvironment is believed to depend on the volume of this microenvironment. Given that the air volume inside the partial enclosure is about an order of magnitude lower than that of the full-size walk-in chamber, it was somewhat surprising to find such a small difference between the data obtained in these two settings. At the same time, it can be explained by the fact that the partial enclosure has sizable gaps allowing the ‘enclosed’ air to exchange with the air in the chamber (representing passenger aircraft seating, which is also not fully separated from the air in the cabin). An additional experiment conducted in a very small chamber-box (0.026 m³ revealed that the particle concentration in that box decreased much more rapidly than in the 100-times larger walk-in chamber. For example, when W1 was operated inside this box, the particle removal efficiency reached 50% in about 2 min and 90% in about 8 min. The data collected in the two fully-enclosed microenvironments (0.026 and m³) confirm that the time needed to remove a certain percentage of particles from a fully enclosed microenvironment by unipolar ion emission is greater for the larger air volume. The ion emitter operating in a specific air volume creates a charged aerosol cloud, in which the particles (i) repel each other towards the chamber walls where they subsequently deposit and (ii) create ‘image charges’ (same magnitude, but opposite polarity) in the surrounding non-conductive surfaces so that they are attracted to these surfaces and deposited on them. The wall surfaces of the small box (made of dielectric Styrofoam) promote higher electrostatic deposition of the particles charged by air ions than the painted wooden walls of the walk-in chamber. In addition, the top of the small chamber, which was close to the ion emitter, deflected the ion wind of ~ 0.5 m/s. Resulting from this deflection, the ions were quickly and uniformly distributed throughout the small chamber air volume, causing considerable particle deposition on the wall surfaces.
Effects of breathing and body temperature
One would expect that when a breathing simulator is used with the manikin, the air in the chamber would slowly be cleaned because of the inhalation-exhalation process itself (some inhaled particles will be lost inside the machine). At breathing rate of 30 1/min (medium work load), the entire air volume of 2.6 m³ would circulate through the machine during about 1.5 h, assuming that no air molecule will move in and out twice. At 85 1/min (heavy work load), this would occur during about half an hour. The natural aerosol concentration decays in the breathing zone, measured respectively with and without the breathing machine operating with the manikin, allowed determining the relative contribution of the breathing effect to the particle concentration reduction as a function of time. At 30 1/min, this contribution gradually increased from 0 to about 20-40% in 1 h (with the time-integrated contribution of approximately 15%). At 85 1/min, it reached about 40-60% in an hour (time-integrated contribution 25%). Thus, the aerosol concentration reduction occurring because of the manikin breathing is smaller than the air cleaning effect provided by ion emission. It was concluded that the operation of the breathing machine attached to the manikin has little effect on manikin-based performance evaluation of ionic air purifiers.
To explore the potential effect of body temperature on the ion and particle movement and thus on the particle removal from the breathing zone, we compared the data obtained with non-heated and pre-heated manikins. Pre-heating was chosen over continuous electrical heating since the electric heating system affected the behavior of the airborne ions near the manikin during the test and, thus, the air purifier’s performance. The particle removal efficiencies of the W2 purifier plotted as a function of time were compared for a non-heated manikin maintained at 23°C and a manikin that was pre-heated to maintain its average body temperature at about 40°C for an hour. The size-specific data show that the body temperature has no significant effect on the performance of the ionic air purifier, regardless of particle size (t-test: P > 0.05).
Conclusions and future work
All five tested unipolar ionic air purifiers were shown capable to significantly reduce the aerosol concentration in the breathing zone of a human manikin, especially in a confined space. Air mixing, especially vigorous one (900 CFM), established in a non-ventilated chamber enhanced the air cleaning effect. While observing most efficient air cleaning with the most powerful unipolar ion emitter, we found that its long term (~1 h) operation in a confined space can excessively charge objects in the vicinity causing occasional electrostatic discharges. As the latter may limit long term continuous use of ionic devices in low-volume environments, we propose that purifiers with a very high ion production rate should be operated in an ‘intermittent mode.’ Our test confirmed the feasibility of this approach. Additionally, the use of ionic emitters in an intermittent mode may reduce the ozone level that may be of concern when a powerful ionizer operates during a prolonged period of time (Niu et al., 2001). Another (rather obvious) limitation comes from the fact that the aerosol particles, which migrate to indoor surfaces and eventually deposit there, contaminate these surfaces (extreme cases are referred to as ‘the black wall effect’). Thus, from the practical stand point, the air purification based on the continuous air ion emission adds the need of cleaning of the surfaces periodically to avoid an excessive particle accumulation. In this light, it seems important to investigate the effect of wall materials on the ionization-based aerosol particle removal as well as on the subsequent cleaning of indoor surfaces.
The data suggest that the ion polarity does not affect the performance, but the ion emission rate does. The effects of particle size (within the tested range) and properties (NaCl, PSL, P. fluorescens bacteria) as well as the effects of the manikin’s body temperature and breathing on the ionic air purifier performance were either small or insignificant. It seems that the role of particle size should be further investigated. Experimental study of Grabarczyk (2001) and theoretical work of Mayya et al. (2004) indicate that the CRF of an ionic air purifier is particle size dependent. On the other hand, in contrast to CRF, the particle removal efficiency defined by Equation 1 may have shown a suppressed size effect because both of its components, [Cionizer (dp, t)] and [Cnatural (dp, t)], are particle size dependent.
The unipolar ionic air purifiers seem to be more efficient in reducing aerosol exposure in the breathing zone when used in confined spaces characterized by a small volume and -- as a result -- by a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms, and animal confinements). More data are needed to better predict the performance of ionic purifiers in rooms with different surface-tovolume ratios.
Another issue that deserves further investigation is a situation when continuous particle generation occurs in indoor air environment during ion emission. Our tests presented in this paper were conducted when the aerosol concentration was not sustained by a particle source; therefore, the concentration depleted essentially to zero after certain time. However, if the particle source is present, the concentration should attain a steady-state level, which is generally different from zero (Mayya et al., 2004). This level can be determined from the balance equation accounting for the velocity of the particle migration to indoor surfaces and the particle production rate by the source. In this work, we did not “intend” to study the effect of initial aerosol concentration on the performance of ionic air purifiers. Thus, the initial concentration was not a subject of considerable variation in our tests. However, theoretical modeling conducted by Mayya et al. (2004) for the background levels covering a six order of magnitude range has revealed that the particle charging process depends on the initial aerosol concentration. As a result, at high initial concentration, the concentration reduction should occur rapidly in the beginning (because of a considerable space charge effect) and then attain near linearity as the concentration further decreases. At relatively low initial concentrations, a constant removal rate should be expected resulting in approximately linear reduction in a log-linear scale (Mayya et al., 2004). More experiments are needed to address this issue.
The authors are grateful for the cooperation of Wein Products, Inc., which helped initiate this research and made available various air purifying devices to the project. The technical assistance provided by Mr. Dainius Martuzevicius during the manuscript preparation is also appreciated.
*The tested units are prototypes of the currently available Minimate Personal Air Purifier AS150MM that has an ion production rate of 1.2 x 10¹⁴ ions per second as reported by the manufacturer.
Filtering Efficiency of N95- and R95-Type Facepiece Respirators, Dust-Mist Facepiece Respirators, and Surgical Masks Operating in Unipolarly Ionized Indoor Air Environments
Byung Uk Lee, Mikhail Yermakov, Sergey A. Grinshpun
Center for Health-Related Aerosol Studies Department of Environmental Health, University of Cincinnati 3223 Eden Avenue, PO Box 670056, Cincinnati, Ohio 45267-0056, US.A
Present address: Environment & Process Technology Division, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul, Korea.
The emission of unipolar air ions in the vicinity of a filtering facepiece respirator has been recently shown to considerably enhance its respiratory protection efficiency. The effect is driven by the electric repelling forces that develop between the unipolarly charged mask and the aerosol particles, thus creating a shield for the incoming particles and consequently decreasing the penetration efficiency through the filter. The manikin-based preliminary evaluation of this concept has been performed with a very limited number of variables. In this study, four types of half-mask facepiece filtering devices (N95, R95, and dust-mist respirators, as well as surgical masks), operating at two different breathing flow rates, were tested with unipolar air ion emitters exhibiting different emission rates and polarities. The particle penetration efficiency through the facepiece filter was determined in a room-size indoor test chamber by a real-time particle size selective aerosol monitoring performed inside and outside of the mask, which was face-sealed onto a manikin. Three commercially available ionic air purifiers were utilized as air ion emitters. For the targeted particle size range of ~0.04 - 1.3 µm, a 12- minute air ionization in the vicinity of a manikin enhanced the respiratory mask performance by a factor ranging from 1.61 to 3,250, depending on the respirator type, breathing flow rate, and the ion emission rate. The effect was achieved primarily within the first 3 minutes.
The facepiece filtering respirators has been widely used to reduce human exposure to the aerosol particles. The respirator performance has been extensively studied over the years (Brosseau et al., 1989· Chen et al., 1994· Hinds et al., 1988· Huang et al., 1998; Johnson et al., 1994; Johnston et al., 2001· Lee et al., 2004c; Nicas et al., 2003; Oestenstad et al., 1990; Qian et al. 1997; Qian et al. 1998· Weber et al. I 993; Willeke et al., 1996). A wide variety of the disposable particulate respirators have been characterized with respect to their protection factor. The ational Institute for Occupational Safety and Health (NIOSH)-instituted respirator certification program (Federal Register 60:110 (1995)) has affected millions of workers that routinely use respirators in their workplaces. Based on the collaboration of NIOSH , the U.S. Army Soldier Biological and Chemical Command (SBCCOM) , and the National Institute for Standards and Technology (NIST), appropriate standards and test procedures are being developed for all classes of respirators that should provide respiratory protection from various inhalation hazards , including chemical, biological, radiological, and nuclear aerosol agents .
Although the effort towards the performance evaluation and standardization of conventional disposable particulate respirators and health-care masks have been rather successful , very little progress has been made during the last decade on the improvement of the filtering efficiency of these devices . The outbreaks of emerging respiratory diseases, such as the Severe Acute Respiratory Syndrome (SARS), as well as growing concerns about a deliberate release of the aerosolized biological warfare agents , such as bacteria and viruses , have triggered an urgent demand for improving the performance of existing respiratory protection masks, especially in the fine and ultrafine particle size ranges.
We have recently developed a novel concept, which dramatically enhances the performance of a conventional facepiece filtering respirator/mask against fine and ultrafine particles (Lee et al., 2004a). The concept is based on the charging of aerosol particles by the corona-produced unipolar air ions (Adachi et al., 1985; Hernandez-Sierra et al. 2003; Wiedensohler et al., 1994) in the vicinity of a respirator. The continuously emitted ions impose significant electric charges of the same polarity on the airborne particles and the mask surface. The repelling forces create an "electrostatic shield" against incoming particles, thus decreasing the penetration efficiency through the filter. The newly-developed concept was pilot-tested with two masks , face-sealed on a manikin operated at a fix breathing flow rate of 30 L/min and one ion emitter (Lee et al., 2004a).
In the present study, we investigated several factors, which affect the ion-emission-driven enhancement of the protection efficiency of a conventional facepiece filtering mask when they are face sealed to the test manikin. These factors include the type of respirator, the breathing (inhalation) flow rate , as well as the ion emission rate and polari ty.
We targeted the particle aerodynamic diameter range of da ~ 0.04 - 1.3 µm. Numerous bioaerosol agents that can cause emerging diseases or may be potentially used in the event of bioterrorism belong to this particle size range: e.g., da ~0.1 µm for coronavirus (the etiological agent of the SARS) and da ~ 1 µm for Bacillus anthracis (bacteria causing anthrax).
The experiments were conducted in an unventilated indoor test chamber (L x W x H = 3.78 m x 2.44m x 2.64 m = 24.3 m3). This facility has been extensively used in our previous studies (Choe et al., 2000; Grinshpun et al., 2002; Lee et al., 2004a; Lee et al., 2004b). Figure 1 demonstrates the schematic diagram of the experimental setup. A breathing manikin with a face-sealed filtering mask was exposed to a polydisperse test aerosol. The leakage tests were conducted prior to the experiments with a detergent based leakage-detecting liquid (Trubble Bubble, New Jersey Meter Co. Paterson , NJ, USA) to identify possible mac ro-leaks (> 1 µm) between the mask and the face of the manikin. The manikin was located in the center of the chamber. The particle concentrations inside (Cin) and outside (Cout) the mask were measured by the electrical low pressure impactor (ELPI, TSI Inc./Dekati Ltd. St. Paul, MN, USA). This cascade impactor has a real-time measurement capability that provides data on the airborne particle number concentration and size distribution in one-minute time increments. The aerosol particles are charged by the corona charger, which is located downstream of the impactor's sampling inlet , and then detected by the electrometers inside the instruments. The data were recorded in 12 ELPI channels, from 0.04 to 8.4 µm. The latter sizes represent the midpoint diameters of the 1st and the 12th impaction stages, respectively (the midpoint = the geometric mean of the stage ' s boundaries).
The penetration efficiency of the respiratory mask, Ep , was calculated from the measured concentration values by the following equation:
The penetration efficiency was determined as a function of the particle aerodynamic diameter. For each set of condition, the test was conducted, respectively, with no air ionization and with a commercial ionic air purifier continuously operating in the chamber for 12 minutes (since the effect was usually achieved during the first 3-6 minutes, we selected the 12-rnin interval as sufficient for the testing). When the ELPI was used in the presence of air ion emission, the aerosol sampling inlet of the instrument was equipped with the Kr85 charge equilibrator (3M Company, St. Paul, MN, USA), which allowed us to avoid the effect of highly charged aerosol particles on the performance of the ELPI' s electrometers. A control experiment was conducted in the chamber (without the manikin and respirator) to demonstrate the satisfactory performance of the charge equilibrator upstream the ELPI. The penetration efficiencies of a face-sealed mask obtained with and without air ion emission were compared at the following time points: t = 3, 6, 9, and 12 min. As the concentration outside the mask decreases with the time due to the particle unipolar charging and their subsequent repelling and migration to indoor surfaces (Lee et al., 2004b), the time dependence Cout (t) in the chamber was accounted for using the linear interpolation. The ratio of the above efficiencies (calculated at a specific time point) was defined as a respirator performance enhancement factor.
The background aerosol concentration m the test chamber was not sufficient for an accurate measurement inside the mask because the filter removed a considerable number of airborne particles. To increase the background concentration, we used a custom-built smoke generator that aerosolized particles in the submicro meter and micrometer size ranges (Cheng et al., 1995). This was particularly suitable to simulate airborne bacteria and viruses, as well as droplet nuclei that often serve as carriers for the air transmission of infectious agents.
Four types of half-mask filtering facepieces were tested, including the NIOSH-certified N95 and R95 respirators, disposable dust-mist respirators, and surgical masks. All of them are commercially available from a major manufacturer. The tests were conducted at two inhalation flow rates: 30 L/min (breathing under light work load) and 85 L/min (breathing under heavy work load). The lower flow rate was established by the ELPI pump that normally operates at 30 L/min. For the higher flow rate, an additional pump operating at 55 Umin was employed.
Three commercially available ionic air purifiers (Wein Products Inc, Los Angeles, USA) were utilized to produce unipolar air ions in the chamber. These included one stationary unit, *VI-3500 (L x W x H = 20 cm x 16.5 cm x 8.5 cm), which emitted negative ions at a rate of ~ 2x l014e-/s (e stands for the elementary charge unit), and two wearable units, *AS180i Minimate (+) and *AS180i Minimate (-) (L x W x H = 6.5 cm x 4 cm x 2.2 cm), which emitted positive and negative ions, respectively, at the same rate of - 7x1013e±/s. (Wein Products Inc, Los Angeles, CA. Personal Communication (2002)). To standardize the ion emission rate characteristics of these ionic air purifiers, the ion concentration were measured with the Air Ion Counter (AlphaLab Inc, Salt Lake City, UT, USA) at the same distance from the source during the test. The *VI-3500 Vortex stationary unit produced an air ion concentration of (1.34 ± 0.04) x 106 e-cm-3 at 1 m from the emission point, while less powerful *AS180i Minimate wearable units (positive and negative) produced (3.62 ± 0.18) x 105 e + cm-3, and (3.91 ± 0.22) x 105 e-cm-3, respectively (Lee et al., 2004b). In each test, a unipolar ion emitter was turned on at a distance of 20 cm from the mask. Once the emitter was turned on in the chamber, the ion concentration rapidly increased to the saturation level (specified above for each device). It occurred in less than 10 seconds, after which the concentration of air ions remained at that level while the device was operating. Once the emitter was turned off, the ion concentration decreased to the initial level in about 3 minutes.
The test chamber was operated at an air temperature of 23± 1c0 and a relative humidity of 42 ± 9%, which were monitored during each test by a thermometer/hygrometer (Tandy Co, Fort Worth, TX, USA). The average value and the standard deviation were calculated for each set of conditions as a result of at least three replicates.The data were statistically analyzed using software package Microsoft Excel (Microsoft Co, Redmond, WA, USA).
Results and Discussion
Original Characteristics of the Face-Sealed Respiratory Protection Masks (No Air Ion Emission)
First, the respirators tested in this study were characterized with respect to their original penetration efficiency (with no air ionization in the vicinity of the mask). The size-specific (fractional) concentrations of test aerosol particles measured in the chamber by the ELPI (Cout at t = 0) are presented in Figure 2. The aerosol generator was adjusted to reproduce the initial concentration and size distribution in each test with the coefficient of variation below 50% (determined from 30 replicate tests). It is seen that the aerosol particles were primarily within a range of da ≈ 0.04 - 0.5 µm, with the concentration decreasing by more than an order of magnitude when the particle size exceeded 1 µm.
The particle penetration efficiency through the N95 respirator, face-sealed on the manikin inhaling at a flow rate of 30 L/min, was originally - 2%. Although the average efficiency values showed a slight decrease with increasing particle size in the submicrometer range, this effect was rather low. With a flow rate increased to 85 L/min, we found a higher penetration than at 30 L/min. The primary difference was observed for da < 0.3 µm (Figure 3). The increase in the flow rate through the respirator filter resulted in the decrease in the residence time, which reduced the efficiency of the diffusional and electrostatic particle deposition inside the filter (the mechanism applies to the respirators equipped with electret filters). Thus, more submicrometer particles were allowed to penetrate through the electret medium of the N95 filter at higher flow rates. Similar results were obtained with the R95-type respirator operated at 30 and 85 L/min, respectively.
For the dust-mist respirators operated at 30 L/min, the original penetration efficiency decreased approximately from 11.0% (da = 0.04 µm) to 6.0% (da = 1.3 µm). Under the same breathing regime, the surgical masks showed the highest penetration (>20%) for da = 0.04 µm and the lowest (<15%) for da = µm. No tests were performed with these two respirators at flow rates exceeding 30 L/min.
The impaction-, interception-, and diffusion-based filtration models predict that the peak penetration is reached at da between 0.1 and 0.3 µm, and the particles below 0.1 µm should be collected more efficiently as their size decreases (diffusion regime) (Halvorsen, 1998; Hinds, 1999; Lee and Mukund, 200l). This tendency is not clearly seen from our experimental data. The discrepancy can be partially attributed to additional mechanisms, not considered by the above models. For example, image forces, associated with the initially charged fibers (e.g., the N95 filtering facepieces are usually pre-treated), may shift the penetration efficiency curve toward smaller particles. In addition , the penetration of ultrafine particles may occur through undetected facial micro-leaks, as well as submicrometer leaks between the core filter material and the elastic peripheral support (Lee et al., 2004a). Another factor could be associated with the spatial variations in fiber diameter, orientation, packing density, as well as initial fiber electrostatic charge level (Huang et al., 1998). The influence of the above factors on the original respirator penetration efficiency was considered to be beyond the scope of this study, as the study focused on the effect of unipolar air ion emission. Further experiments are needed to address the limitations of the manikin-based respirator evaluation protocol for ultrafine particles.
Penetration Efficiency of Different Masks Affected by the Continuous Unipolar Air Ion Emission
Figure 4a demonstrates the effect of continuous negative ion emission produced by a powerful *VI-3500 Vortex ionic air purifier on the filtering efficiency of a face-sealed dust-mist respirator. The latter operated at 30 L/min. It is seen that the penetration efficiency decreased from 6-11% to almost 0% for the entire test particle size range. Figure 4b shows that the penetration efficiency of the face-sealed N95 respirator at the same inhalation flow rate also dramatically decreased due to the ion emission (the data were originally reported in our earlier paper (Lee et al., 2004a) and are presented here for comparison). Continuous operation of the *VI-2500 Vortex emitter for 12 minutes resulted in about a SO-fold enhancement the N95 respirator protection.
The enhancement factors achieved after 12-minute air ionization were calculated for the N95, R95 and dust-mist respirators, as well as the surgical mask, using the penetration efficiency values integrated over the entire tested particle size range (weighted by the number of particles at each size fraction):
The data are presented in Table I. All the facepiece :filtering masks demonstrate a considerable enhancement effect, from about 20-fold to over 3000-fold. The dust-mist respirator exhibited almost no penetration as a result of the air ion emission. The difference in the enhancement factors observed for different masks exposed to the same air ion concentration can be attributed to their filter materials. As very little information on the properties of the filter materials used for commercial respirators is available from the manufacturer, no further discussion can be offered at this point.
Effect of the Air Ion Polarity and EmissionRate
The continuous emission of unipolar ions at the same rate caused approximately the same enhancement effect, irrespective whether the emitted ions were positive [AS150MM (+)] or negative [AS150MM (-)]. The effect of the polarity of air ions is shown in Figure 5 for the R95 respirator (a and b) and surgical mask (c and d) operated at 30 L/min.
Table 2 shows the enhancement factors provided by the *VI-3500 Vortex ionic air purifier (higher emission rate) and the AS150MM purifiers (lower rate). The data show that the higher concentration of air ions in the vicinity of the respirator resulted in a stronger enhancement of the respirator performance.
Effect of the Inhalation Flow Rate
The penetration efficiency curves, obtained for the N95-type respirator operated at a flow rate of 85 L/min, are shown in Figure 6. Continuous emission of negative ions by the *VI-3500 Vortex ionic air purifier during 12 minutes decreased the penetration efficiency of ultrafine particles through the respirator filter from about 3.5% to <0.1%. For larger particles (da ~ 1 µm), the penetration efficiency decreased from approximately 1.9% to 0.3%. Table 3 compares the enhancement factors determined for N95 and R95 respirators face-sealed on the manikin and operated at two inhalation flow rates (the values are particle size integrated within the test range of da = 0.04 - 1.3 µm). The change in the flow rate seems to have no significant effect on the particle penetration through the N95 respirator. The role of the inhalation rate appeared to be more prominent for the R95 respirator as the enhancement factor increased almost 3-fold with the flow rate increasing from 30 to 85 L/min. The difference between the data obtained for the R95 and N95 respirators, with respect to the flow rate effect on their performance enhancement, is likely caused by different properties of the filter materials (electret media of N95 versus carbon-based media of R95).
Effect of the Ion Emission Time
Resulting from the tests conducted for 3-, 6-, 9-, and 12-minute time intervals, the penetration efficiency values integrated over the tested particle size range showed some decrease with the time. Although observed for all masks, this trend was not statistically significant (p-values of all t-tests were greater than 0.05). The findings suggest that the major enhancement of the respirator performance is achieved within the first 3 minutes of ion emission. The actual "characteristic" time of the enhancement effect is likely to be shorter than 3 minutes since the air ion concentration reaches its saturation level during the time interval as short as l0 seconds after the emitter is turned on. However, the study design limitations and the measurement precision criteria did not allow us to conduct tests at t<<3 min.
Continuous emission of unipolar air ions by corona-ionizing air purifiers in the vicinity of a disposable half-mask respirator enhanced its protection characteristics against fine and ultrafine particles of bacterial and viral size ranges. In this study, the effect was proven for four types of face-sealed respiratory protection devices, including N95, R95, and dust-mist respirators, as well as surgical masks, with the particle penetration efficiency reduction up to about 3000-fold. The enhancement of the respirator filtering efficiency does not appear to depend on the particle size (within the size range tested in this study). While a higher ion emission rate is strongly associated with greater respirator performance, the ion polarity (negative versus positive) was found to have no effect on the performance enhancement factor. The findings hold true for two inhalation flow rates tested in this study: 30 and 85 L/min. It was concluded that the major enhancement effect occurred in the first 3 minutes of the ion emission. Overall, a dramatic improvement of the aerosol filtering efficiency of a disposable respirator due to continuous unipolar ion emission is achievable under various conditions. It should be noted that our experiments presented in this paper utilized a manikin-based protocol with a respirator/mask, which was face-sealed on the manikin, so that we addressed primarily the aerosol penetration through a filter material; the respirator fit remains beyond the scope of this study and should perhaps be investigated more appropriately through tests involving human subjects and a fit-testing protocol.
The participation of Dr. Byung Uk Lee in this study was supported in parts by the Korea Science & Engineering Foundation (KOSEF) and Korea Institute of Science and Technology (KIST). The authors wish to thank Wein Products, Inc. for the equipment and resources that the company made available to this project. The authors extend their appreciation to Ms. Alexandra-Sasha Appatova for her help in prepa1ing and editing this paper.
Reference to any companies or specific commercial products does not constitute or imply their endorsement, recommendation, or favoring by the University of Cincinnati or by the investigators conducting this study.
*This document originally pertained to Vortex VI-2500 and Minimate AS150MM, Wein Products, Inc.
CDC Workshop on Respiratory Protection for Airborne Infectious Agents
Agenda and Abstracts
Respirator Performance with Infectious Agents
Center for Health-Related Aerosol Studies, University of Cincinnati, Cincinnati, OH.
Respirators are widely used to reduce the human exposure to aerosol particles, including airborne microorganisms. Respiratory protection against biological aerosols has recently gained a special attention due to the bioterrorism threat and several outbreaks of emerging diseases. There is an increasing need to evaluate the performance of existing facepiece respirators (including health-care and industrial masks, NIOSH-certified N95/R95 respirators, and other devices), especially with biological aerosols. Bioaerosol particles associated with health effects are primarily within a range of approximately 0.04-5 µm and include viruses, bacteria (vegetative cells and spores), and fungi.
We have developed and built a sophisticated laboratory facility for evaluating respiratory devices with bioaerosol particles and their surrogates using the manikin-based protocol. Several indoor test chambers are now available in our laboratories including a 25 m3 indoor chamber with a close-loop air purification system. The aerosol concentrations are measured in real time inside and outside the mask, which is worn by a manikin. The measurements can be conducted by several different particle size selective aerosol spectrometers that allow covering the particle size range of 0.03-20 µm. The penetration efficiency is determined as a ratio of these concentrations for specific particle size fractions at different breathing flow rates. We have tested numerous respirators in this facility with non-biological particles-simulants as well as with six bacterial species. In addition to the aerosol penetration studies, we have investigated the re-aerosolization of microbial agents from the mask's outer surface during exhalation as well as the survival of viable bacteria on respirators. The data obtained in these studies will be discussed in the presentation.
A new personal sampling system for assessing the respirator protection factor directly in the field has been recently developed and evaluated under controlled laboratory conditions and in occupational environments. The system is designed for a real-time measuring the aerosol inside and outside the respirator with two portable optical particle counters and the simultaneous collection of microorganisms into two filter samplers for subsequent microscopic analysis and/or cultivation. Using the newly-developed system, we have determined the protection provided by the N95 filtering facepiece respirators against biological aerosol particles ranging from 0.7 to 10 µm. The data will be discussed.
As our findings revealed I imitations of existing respirators for reducing inhalation exposure to airborne bioagents, we have developed a novel concept for enhancing the collection efficiency of conventional filtering masks against bacterial particles and virions. The emission of unipolar electric ions in the vicinity of the mask was found to decrease the
particle penetration through the filter by one to two orders of magnitude. Since the infectious dose of many agents is ~ 101 to 103 particles, we concluded that the ion emission effect should make a crucial difference with respect to the exposure and health risk.
Dr. Gabor Lantos Supports Ionic Technology For Avoiding Airborne Allergens and Asthma
I wish to bring to your attention an effective and inexpensive physical modality to reduce the risks from airborne respiratory pathogens and allergens.
A year ago I was asked by Jorley Distributing Inc., the Canadian Distributor for Wein Products Inc., manufacturer of Air Supply® Ionic Air Purifiers, to provide a professional (engineer’s) opinion regarding the plausibility of the underlying physics of ionic air purifiers and their ability to reduce the concentrations of inhaled microorganisms and harmful inanimate particles.
The reports in recent peer-reviewed journals demonstrate the efficacy of these purifiers in significantly reducing the concentrations of ambient Viral and Bacterial sized particulates within an individual’s breathing zone.
I have rendered my opinion in regards to infectious particles, as has Dr. Peter Vadas, Allergist and Immunologist, regarding allergens and irritants. Both of these Opinion Letters are posted on Jorley's web site. I have also enclosed highlighted segments from the latest peer-reviewed publications.
You might like to consider the prophylactic benefits of the room-size unit *(the Vortex VI 3500) or personal, wearable unit *(the Mini-Mate AS180i) for asthmatic and allergic patients/employees, and for individuals at risk of exposure to respiratory pathogens.
Dr. Gabor Lantos
*This document originally pertained to VI-2500 and Mini-Mate AS150MM, Wein Products, Inc.
Respiratory Protection Against Airborne Biological Agents
Presented by: City of Cincinnati
University of Cincinnati U. S. Environmental Protection Agency Veterans Affairs (VA) Medical Center
Sergey A. Grinshpun and Tiina Reponen
Department of Environmental Health, University of Cincinnati, Cincinnati, Ohio, U.S.A.
Facepiece respirators are widely used to reduce the human exposure to with biological warfare or emerging diseases are primarily within the range of 30 run to 3 µm. Due to the threat of bioterrorism, the need to evaluate the performance of existing health-care masks and NIOSH certified N95 respirators and the demand to improve their efficiency have significantly grown. We have developed and built a sophisticated laboratory facility for evaluating various respiratory devices with bioaerosol particles and their surrogates using a manikin based protocol in a 25 m3 indoor chamber. The aerosol concentrations are measured real-time inside and outside the mask worn by a manikin. The measurements are conducted by a particle size selective aerosol spectrometer. The penetration efficiency is determined as a ratio of these concentrations for specific particle size fractions at different breathing flow rates. The data obtained with biological particles and their non-biological surrogates showed the limitations of existing respirators for reducing inhalation exposure to airborne spores and virions. We developed a novel concept for enhancing the collection efficiency of conventional filtering masks. The emission of unipolar electric ions in the vicinity of the mask was found to decrease the particle penetration through the filter by one to two orders of magnitude. Given that the infectious dose of many agents is· in order of 101 to 103 particles, the ion emission effect should make a crucial difference with respect to the exposure and health risk.
S. A. Grinshpun, A. Adhikari, B. U. Lee, M. Trunov, G. Mainelis, M. Yermakov & T. Reponen
Center for Health-Related Aerosol Studies, Department of Environmental Health, University of Cincinnati, USA
Current affiliation: Mechanical Engineering Department, New Jersey Institute of Technology, USA
Current affiliation: Department of Environmental Sciences, Rutgers University, USA
Various health effects are associated with or directly caused by respirable airborne particles and microbial agents. To reduce the hunan exposure to these indoor pollutants, numerous techniques have been developed over the years. In this study, we have investigated the effect of unipolar air ionization on airborne dust particles and microorganisms in indoor environments. The concentration and particle size distribution were measured in real time using optical and aerodynamic particle counters with a special focus on the bacterial particle size range of 0.5 to 2 µm. The tests were conducted in three indoor chambers of different volumes (ranging from 26 L to 24.3 m3) at different ion emission rates (producing air ions at ~104 to ~l05ions/cm3 as measured at ~1 m from the source). The concentration decay occurring due to ionic emission was compared to the natural decay for four types of challenge aerosols. Resulting from the interaction with unipolar air ions, airborne particles exhibited considerable electric charges of the same polarity as the emitted ions. Due to electrostatic repelling forces, the particles migrated toward the indoor surfaces and rapidly deposited on these surfaces. Two small, battery operated ionic emitters tested in this study showed significant air cleaning efficiency for respirable (sub- and super-micrometer) particles. This effect was more pronounced in smaller air volumes. The efficiency of ion emission in reducing the viability of airborne microorganisms in indoor air was also evaluated in a specially designed set-up. Two species of Gram-negative bacteria (Pseudomonas fluorescens and Escherichia coli) and one species of Gram-positive bacteria ( Staphylococcus epidermidis) were tested. It was found that a significant percentage of airborne viable bacteria could be inactivated by the ion emission: up to 92% of E. coli was inactivated during a one-minute exposure in dry air. It was concluded that the ion-driven decrease in the aerosol concentration combined with the bactericidal effect can significantly reduce human exposure to indoor air pollutants, such as particles and microorganisms.
Respirable airborne particles, including airborne dust, microbial agents and aeroallergens, may cause adverse health effects, such as asthma, allergic diseases (2, 7, 10, 14] and airborne infections . Although health effects associated with biological aerosols have been of a special concern for decades, recent outbreaks of emerging infections as well as the growing concern about bioterrorism have drawn additional attention to the development of control methods against indoor air pollutants, particularly against viable bacterial cells and spores.
The deposition and retention of particles larger than 0.5 µmin upper and lower parts of the respiratory tract (and subsequently the health effects associated with these particles) depends on the aero.dynamic particle size (dae). For most of the airborne bacterial species, dae ranges from 0.5 to 2 µm. For example, our earlier measurements of aerosolized bacteria using aerodynamic particle counters have shown dae=0.7-0.8 µm for Pseudomonas fluorescens [15, 17], 0.9 µm for Bacillus subtilis , and 1.10 µm for Micrococcus luteus . The optical particle size of bacterial particles is usually close to the aerodynamic one (within ±20%) [l]. Bacteria aerosolized from liquids (e.g., saliva or mucus) may initially be carried in or by larger droplets. However, the water content is likely to evaporate rapidly, thus decreasing the particle size to 1-2 µm. This is almost always true in indoor air environments (as long as the atmosphere is not close to the saturation level).
Among several air cleaning techniques currently used for reducing the aerosol concentration in indoor air settings (e.g., residential and office rooms, as well as aircraft and automobile cabins), the air ion emission has been explored and shown a promise [3, 4, 6]. The data obtained in two latest studies conducted by our research team [5, 8] helped to better understand the mechanisms involved in indoor air purification due to unipolar ion emission. The principle is schematically shown in Figure 1. Resulting from their interaction with unipolar air ions, the airborne particles carry considerable positive or negative electric charges, depending on the polarity of the emitter. Due to electrostatic repelling forces, the particles migrate toward the indoor surfaces and rapidly deposit on these surfaces.
The air ionization has been incorporated into commercial air purification devices manufactured by Ionair, Inc. (Midland, Ml, USA), Sharp Corporation (Osaka, Japan), Topway Electronic Factory Company (Guangzhou, China), Wein Products, Inc. (Los Angeles, CA, USA) and other companies. Most of the ionic air purifiers, including unipolar ion emitters, have been originally designed to reduce the exposure to all types of aerosol particles, irrespective of their biological properties. Since viable airborne bacteria represent a specific hazard, it is important to determine the physical and biological efficiencies of ionic air purifiers against these air contaminants. Toe physical efficiency of ionic air purifiers represents their ability to reduce the concentration of bacterial particles in the air, whereas the biological (bactericidal) efficiency represents their ability to reduce the microbial viability by inactivating viable microorganisms that remain airborne. The overall air cleaning efficiency is a product of the physical and bactericidal efficiencies of the ionic air purifier. In this study, we evaluated both the physical and bactericidal effects of unipolar ion emission against viable bacterial cells.
Experimental design and method
The air cleaning process was experimentally investigated by measuring the aerosol concentration and particle size distribution in real time inside indoor test chambers of three different air volumes. These included a large walk-in chamber that simulated a residential room (24.3 m3), a small walk-in chamber that simulated a small office area or an automobile cabin (2.6 m3), and a "box" that simulated a small enclosure (26 L). Polydisperse NaCl aerosol monodisperse PSL spheres of three sizes, polydisperse smoke aerosol, and vegetative cells of Pseudomonas fluorescens bacteria (ATCC 13525) were used as the challenge aerosols in the experiments. The sodium chloride and PSL particles, as well as bacterial cells were generated by 3-jet Collison nebulizer (BGI, Inc., Waltham, MA, USA) operated at a pressure of 12 psi. Smoke particles were generated by a custom-built smoke generator. The challenge aerosol was delivered into the test chamber with a clean, laboratory-filtered air at a specific temperature (T = 22°C) and relative humidity (RH= 28±5%).
Two types of instruments were used for the particle size selective measurements. The Grimm optical particle counter (OPC, model 1.108, Grimm Technologies Inc., Douglasville, GA, USA) served as an optical size spectrometer in all three test chambers. The Aerosizer (API/TSI, Inc. St. Paul, MN, USA) and the Electrical Low Pressure Impactor (ELPI, TSI Inc./Dekati Ltd, Tampere, Finland) served as aerodynamic particle sizers (Aerosizer operated in parallel to the Grimm OPC in the small walk-in chamber, whereas the ELPI was used in the large walk-in chamber). Although the operational particle size ranges of the Grimm OPC, Aerosizer and ELPI are distinctly different, all three are capable of accurately measuring the particle concentration within the size range of bacterial particles, i.e., 0.5 - 2 µm.
The experimental facility used to study the physical efficiency of ion emitters is schematically shown in Fig. 2. Table 1 describes the characteristics of the test chambers and lists the challenge aerosols and the instrumentation involved in the tests.
The concentration decay occurring due to ionic emission was compared to the natural decay. The nondimensional particle concentration was determined as a ratio of the concentration measured at a specific time point, t, to the initial one (measured at t = 0). The tests were performed under calm air conditions.
In this paper, we report the data obtained with two portable (wearable) ion emitters available from Wein Products, Inc.: Minimate, AS180i and AS150MM*. The y produce positive air ions at essentially different ion emission rates. To quantify these rates in terms of the volumetric ion density, the air ion concentration created inside the 24.3 m3 chamber was determined with an Air Ion Counter (AlpbaLab Inc., Salt Lake City, UT, USA) at specific distances from the ion source.
Figure 3 schematically . shows the experimental facility developed for investigating the effect of air ions emitted by an ionic air purifier on the viability of airborne bacteria. The setup consisted of the following major elements: autoclavable bioaerosol test chamber (LxWxH = 60x30x30 cm3) made of metal, source of HEPA filtered air, air temperature and humidity control system, Collison nebulizer, Grimm OPC, and BioSampler (SKC Inc., Eighty Four, PA, USA). The dimensions of the chamber represent the breathing zone. The Collison nebulizer, commonly used for aerosolizing bacteria from liquid suspensions, simulated the aerosolization of viable bacteria by human coughing and sneezing. The OPC monitored the particles throughout the chamber air volume to assure a uniform aerosol concentration pattern. The BioSampler provided accurate and representative collection of viable bacteria from the air into liquid for subsequent total counting and colony forming unit (CFU) enumeration [18). In these experiments, the bacteria were airborne for approximately one minute between the microbial aerosolization and the sampling. Based on our preliminary studies, this time was sufficiently short to minimize the effect of desiccating air on bacterial viability.
The entire setup was housed in a Class II, Type B2, biological safety cabinet (Sterilchem GARD, Baker Company, Sanford, ME, USA). This allowed us to maintain sterile conditions during the experiments and to ensure that all airborne bacteria were properly exhausted after passing through the bioaerosol test chamber. The ionic air purifier under the test was placed at the chamber entry point, downstream of the nebulizer outlet. The ions produced by the air purifier were carried by the temperature- and humidity-controlled sheath air flow (36 L/min) that entered the chamber at the same point. The OPC, the BioSampler, and the humidity/temperature meter (portable thermohygrometer pen, Fisher Scientific, Pittsburgh, PA, USA) were placed downstream, close to the outlet of the chamber. The walls of the chamber and all the equipment units were grounded to avoid any electric charge build-up inside the experimental setup.
Similar to the evaluation of the physical efficiency, two models of Wein wearable ionic air purifiers, Minimate, AS180i and AS150MM*, were tested with respect to the bactericidal efficiency.
Two species of Gram-negative bacteria (Pseudomonas fluorescens and Escherichia coli) and one species of Gram-positive bacteria (Staphylococcus epidermidis) were utilized in this part of the study as challenge aerosols. Cultures of P. fluorescens (ATCC 13525) and S. epidermidis (ATCC 14990) were obtained from the American Type Culture Collection (ATCC, Rockville, MD, USA). A laboratory culture of E. coli (strain DH 5oc) was used.
P. fluorescens, S. epidermidis, and E. coli have been utilized as challenge microorganisms in many studies reported in the literature. The first two species are common in indoor air environments and relatively easy to handle under laboratory conditions, which helps ensuring accurate and credible experimental data. The selected specie of Pseudomonas and Staphylococcus have relatively low pathogenicity as compared to many other species of the same genus. Generally, there are many microorganisms with limited pathogenicity that have the same (or similar) aerodynamic and/or biochemical characteristics as highly pathogenic agents. Simulants are widely used for evaluating the bactericidal effects. For instance, Bacillus subtilis var niger (BG) spores are well-known simulants of Bacillus anthracis (causing Anthrax) and have been utilized in many studies conducted by the, US Department of Defense and other agencies. The third bacterium selected for the tests, E. coli, is a very sensitive Gram negative bacterium, known to cause various health problems and widely used as a test microorganism in microbial studies [9, 11]. E. coli species used in this study is not pathogenic although it has physiological properties similar to its well-known "cousin" food-borne E.coli O1S7:H7. Some E.coli strains produce enterotoxins. Airborne E. coli have been found in occupational air environments. e.g., in farms . Since a recent study implicated airborne spread of E.coli O1S7:H7 during an outbreak investigation  we believe that inclusion of E.coli bacteria as a test microorganism is particularly timely.
Vegetative cells of P. fluorescens and S. epidermidis were cultured by incubating them in Trypticase Soy Broth at 28°C for 18 hours and at 37°C for 24 hours, respectively. Vegetative cells of E. coli were cultured for 18 hours in Luria Bertani (LB) broth at 37°C. After incubation, the vegetative cells were washed three times with sterile deionized water by vortexing (Vortex Touch Mixer, model 231, Fisher Scientific, Pittsburgh, PA, USA) followed by centrifugation at 7,000 rpm for 7 minutes at room temperature (Sorval RC-SB, Sorval Co., Newtown, CT, USA). Before using the bacterial suspension for aerosolization, the concentration of bacteria in the suspension was adjusted to 108 - 109 bacteria/mL, as determined by microscopic counting. After the second washing, the cells were stored at room temperature for up to 3 hours. One more washing was done when refilling the nebulizer with bacterial suspension prior to each subsequent experiment.
The Collison nebulizer aerosolized bacteria-containing water droplets ofup to 3 µm in aerodynamic diameter. Thus, bacterial cells were first encapsulated in water droplets. This simulates the way in which infectious microorganisms often enter the air environment from their sources, such as human saliva and mucus during coughing or sneezing. Then the effluent aerosol was diluted and dried immediately by the temperature- and humidity-controlled sheath air flow. Finally, the dry airborne bacterial cells entered the bioaerosol test chamber at T = 26:!:2°C and RH=l7±5% (dry indoor air). While the bactericidal efficiency was determined primarily under dry air conditions, one experiment with AS150MM and P. fluorescens was conducted at high humidity (RH=89±3%.)
The same bacterial suspension was used for less than 35-40 minutes. This allowed us to minimize the effect of aerosolization time on the initial viability, so the latter remained the same throughout the test.
Once the bioaerosol concentration reached the desirable level inside the chamber and remained at that level for at least 3 min (as measured by the OPC), the collection of airborne bacteria into the BioSampler began. The sampling time was 10 min. Each experiment was performed with three replicates using the same bacterial species with and without running the tested ionic air purifier.
The concentration of viable bacteria in the sample (CFU/mL) was determined by cultivation of the liquid collection medium on nutrient agar plates. Three dilutions (10’1, 102 and 10 -3 were prepared from the original sample. Aliquots of 100 µL from the original suspension and the dilutions were cultivated on agar plates in triplicate. P. fluorescens and S. epidermidis were cultivated on Trypticase Soy Agar, whereas E.coli was cultivated on LB agar (using the following amounts: LB Broth= 10 g; Agar = 7.5 g; Distilled water = 500 mL). The inoculated culture plates were then incubated at 28°C for 40 hours for P. fluorescens, at 37°C for 24 hours for S. epidennidis and at 37°C for 18 hours for
E.coli. The colony forming units (CFU) in each culture plate were counted from the diluted sub-samples that had about 30-300 colonies. The concentration of culturable bacteria in the BioSampler liquid, CCFU (CFU/mL), was calculated as follows:
where NCFU is the average CFU number determined from three repeats, n is the dilution factor and v0 is the volume of the suspension spread on each agar plate (0.1 mL).
Total (viable plus non-viable) bacterial count was conducted by epifluorescence microscopy (Leitz, Laborlux S, W. Nuhsbaum Inc., McHenry, IL, USA). To determine the total bacterial count in each sample collected by the BioSampler, an aliquot from that sample was filtered and analyzed using acridine orange staining and epifluorescence microscopy.
Prior to filtering the bioaerosol sample suspension through a black polycarbonate filter (Millipore GTBP 0250; pore size 0.2 µm, diameter 25 mm), each filter was equilibrated by filtering 5 mL of sterile phosphate buffer through it Then 5 mL of acridine orange solution (0.1 mg/mL) was added to the bioaerosol sub-sample (taken from the original sample and three dilutions: 10 -1, 10-2 and 10-3) and mixed thoroughly by shaking. The volume of the bioaerosol sub-sample to be enumerated (ranged from 0.2 to 2 mL) was chosen after preliminary tests conducted at various dilution ratios. The volume that resulted in the number of counts ranging from 4 to 40 per microscopic field was selected. After adding the acridine orange stain to the sub-sample the suspension was allowed to stand for 5 minutes and then filtered by vacuum suction. The filter was mounted on a microscopic slide with light mineral oil and a cover slip.
The microorganisms on the filter were counted by the epifluorescence microscope at a magnification of 1000X. For each test, we counted either 40 randomly chosen microscopic fields or a total of 400 bacteria. In the latter case, at least 20 fields were counted. The total bacterial count, CTOTAL, (Number/mL) in the BioSampler suspension was determined as follows:
where NTOTAL is the average bacterial count per microscopic field, R is the effective radius of the filter (10 mm), A is the area of the microscopic field (0.02351 mm2) and v is the volume (in mL) of the original bacterial suspension analyzed.
The liquid samples were collected from the Collison nebulizer before and after aerosolization. These samples were analyzed for culturable and total counts of bacteria as described above. Five dilutions of the samples (10-3 to l0 -7) were used for these analyses.
After analyzing the culturable and total counts in each sample, we determined the bacterial viability, V, as a ratio of Ccru/CTOTAL The bactericidal effect of the ionic air purifier was quantified as the bacterial inactivation (in percent), calculated by using the bacterial viability data as follows:
Here VOFF was the bacterial viability fraction obtained when the ionic air purifier was not operating, and VON was the bacterial viability fraction when the ionic air purifier was operating. The average values of the bacterial inactivation and standard deviation from three different experiments were calculated. It is important to stress that our study design accounted for the natural viability loss due to desiccation, thus allowing us to distinguish the loss of viability due to the air ionization.
Results and discussion
Figure 4 shows the air ion concentration measured in the large walk-in chamber at a distance of 1 m from the emission point of Minimate, AS180i*. It is seen that the ion concentration increased very rapidly to approximately 3.5x105 ions per cm3 and remained approximately at that level during the entire operation time. Once the ion emitter was turned off, the air ion concentration decreased almost as rapidly as it had increased and reached the initial level. The data suggest that the process of particle charging by ions is homogeneous, which is important for the validation of experimental protocol. The Minimate AS150MM* unit showed similar results, except the "saturation" level was much lower. approximately 2x I04 ions per cm3
Figure 5 presents the time evolution of the nondimensional concentrations of three particle size fractions (smoke particles) in the large walk-in chamber, as measured by the ELPI. The upper curves represent natural decay, and the lower curves represent the decay when the Minimate AS180i/AS150MM ion emitter operated in the chamber. The data obtained with the Grimm OPC for these particle sizes confirmed the ELPI data within ±30%. We found this agreement acceptable given the accuracy of the two instruments and the difference between the aerodynamic and optical sizes of the particles. The data collected with airborne bacteria and NaCl bad the same trends. Quantitatively, the removal rate of bacterial cells followed the one obtained for 1-µm smoke particles (Fig. 5b) with an average deviation of ±18%. The results obtained for smoke and NaCl were as close as ±7%. It is seen that the ion emission results in much more rapid particle removal from the air than the natural air cleaning (due to gravitational sedimentation). For instance, the ion emission decreased the concentration of 0.5 µm particles by a factor of 5 during an hour whereas the respective decrease caused by the natural decay was only 25% (Fig. 5a). The effect of ion emission is rather high, given that it is achieved by a small, battery operated unit (about 10 cm in size) inside an air space as large as 24.3 m3. As the lower curves in Figures 5a-c are almost identical the data suggest that the physical efficiency is about the same for particles in the entire bacterial size range (0.5-2 µm).
The air volume was found to be a factor affecting the physical efficiency of the ionic air purifiers. Figure 6 demonstrates the nondimensional aerosol concentration as a function of the test chamber volume and the time of ion emission. The graphs are based on the particle size integrated data obtained with smoke particles (large walk-in chamber) and NaCl (small walk-in chamber) particles. The aerosol measurements performed with the NaCl using the Aerosizer and Grimm OPC in the small walk-in chamber revealed similar trends. The difference between the data provided by these instruments did not exceed ±20%. Therefore, further tests that involved PSL particles and P. fluorescens bacteria were conducted using the OPC only. The ion emission by AS180i* during the time as short as 3 min does not seem to be sufficient to provide substantial air cleaning even in relatively small air volumes. The data obtained at t = 15 min show about l :5-fold decrease of the initial aerosol concentration of bacterial or bacteria-size particles in the large walk-in chamber (24.3 m3) and 2-fold decrease in the small walk-in chamber (2.6 m3). The ion emission in a very small air space (26 L box) creates tremendous air cleaning effect so that the number of particles that remains airborne in 15 minutes does not exceed few percent of their initial number in that space. The physical efficiencies of AS150MM obtained in the small and large walk-in chambers, respectively, were considerably different at t = 30 and 60 min.
Although the physical efficiency of AS150MM demonstrated the same trends, the decay caused by the ion emission by AS180i* was not as rapid as that obtained with AS180i*, which reflects the difference in their ion emission rate.
The mean bacterial inactivation values (in percent) and the standard deviations for three species tested in this study at RH=17±5% were: S. epidermidis: 53±20%; P. fluorescens: 71±11% and E. coli: 93±2% (see Fig. 7). The viability of all three microorganisms was affected even by a short exposure to the air ion flow (texp ≈ l min). The bactericidal effect was found to be higher for the two Gram-negative bacteria (P.fluorescens and E.coli) than for the Gram-positive S. epidermidis. The difference between the average inactivation values observed for S. epidermidis and P. fluorescens is relatively small, whereas the average inactivation for E. coli is significantly higher than for the two other species. The data reflect the individual bacterial responses to the stress resulted from the interaction of air ions with bacterial cells and suggest that P. fluorescens and E.coli are more sensitive to injuries caused by electrical charges than S. epidermidis. The lower bacterial inactivation of S. epidermidis cells can be explained by high resistance of Gram-positive bacteria to various types of stresses. The cell wall of Gram-positive bacteria is rigid  and thick, thus protecting the bacterial cells from environmental stresses. In contrast, Gram negative bacteria of P. fluorescens and E. coli have very thin sheet-like cell envelopes  that offer less protection against environmental stresses. The difference in bacterial responses to unipolar electric charges found between the Gram-negative and Gram-positive cells might also have been caused by the chemical differences in their cell wall structure. The cell wall of Gram-negative bacteria has more lipid content, whereas Gram-positive bacteria have more peptidoglycans in the cell wall. This may differently affect the charge-related orientation of metabolically linked proteins and other cell membrane components. Figure 8 presents the comparative bactericidal effect of the Minimate AS180i/AS150MM* ionic air purifiers obtained with P.fluorescens cells at RH = 17±5% (texp ≈ 1 min). With the bacterial inactivation of 69±20% for ASlSOG and 71±11% for AS150MM, no stastically significant difference (t-test: p>0.05) was observed for these ion emitters, although they produce significantly different ion concentration levels. The data suggest that while the difference in the ion emission rate did affect the physical (particle removal) efficiency, it appeared to have: no effect on the bactericidal efficiency under our experimental conditions.
The bactericidal effect caused by the air ions on viable airborne cells of P. fluorescens after the I-min exposure decreased when the humidity level increased from 17±5% to 89±3%. The average value of the bacterial inactivation dropped more than 3-fold and the data variability increased considerably.
Thus, the bactericidal effect of the air ion emission is more pronounced at low air humidity, typical for indoor environments. Since the bacteria may become coated by a thin layer of water when exposed to a high humidity environment, we hypothesize that this layer could shield the bacterial cell wall from the air ions.
The data on the physical and bactericidal efficiencies of the air ion emission suggest that the reduction in the indoor aerosol concentration combined with the bacterial inactivation can sjgnificantly reduce the human exposure to indoor air pollutants, such as.particles and microorganisms.. The.following estimate was made based on the data obtained with AS150MM* operated during 30 minutes in. the small walk-in chamber: as about 80% of viable airborne bacteria have been removed from indoor air (Fig. 6) and.at least 71% of the cells remaining in the air have lost their viability during the same time (P. fluorescens, t > l min, Fig. 7), the overall efficiency of the ion emission against the viable bacterial agent is 1- (1 - 0.8)(1 - 0.71) = 0.942, i.e. 94.2%. This corresponds to an almost 20-fold exposure reduction.
Reference to any companies or specific commercial products does not necessarily constitute or imply their endorsement, recommendation, or favoring by the group of authors or by the University of Cincinnati.
*This document originally pertained to the AS150G and AS150MM, Wein Products, Inc
Evaluation of the Ionic Purification Efficiency by the Electrical Low Pressure Impactor (ELPI)
Byung Uk Lee, Mikhail Yermakov, Sergey A. Grinshpun
Center for Health-Related Aerosol Studies, Dept. of Environmental Health, University of Cincinnati, Cincinnati, OH, USA
Introduction and Objective
The ion emission has been shown to reduce the concentration of airborne dust particles and microorganisms in indoor environments. The aerosol particles, charged unipolarly by the emitted ions, repel and migrate toward the surfaces, which results in their rapid deposition. Those ion emitters, which meet health standards (e.g., do not generate ozone above the established thresholds) have been incorporated in commercial air purification devices. The ionic air purifiers are being increasingly used in indoor environments.
In this study, three ionic air purifiers, VI-3500*, Air Supply/Minimate* (+) positive and Air Supply/Minimate* (-) negative (Wein Products Inc., Los Angeles, CA), were evaluated with respect to their indoor air cleaning efficiency.
Since some airborne biological agents are primarily represented by submicrometer and micrometer particles (e.g., isolated airborne viruses range from 0.04 to about 0.2-0.3 μm and bacterial spores are about 1 μm in their equivalent optical/aerodynamic diameter), the targeted particle size range was 0.04 to 2 μm.
Indoor test chamber of ~ 25 m³
Smoke particle generator
Electrical low pressure impactor (ELPI, TSI Inc./Dekati Ltd, St. Paul, MN)
The particle-size-specific concentrations recorded in 12 channels of the ELPI, dₐ= 0.04 to 10 μm
The particle charge distribution measurement
The ELPI sampling inlet is ~ 0.2 m from the purifier
Air temperature = 23±10°C
Relative humidity = 42±9%
Original charges of particles generated in our experiments were very low (less than 1 elementary charge per particle, on average). When an ionic air purifier operated, the airborne particles exhibited considerable positive or negative electric charges, depending on the polarity of the purifier (e.g. the average charge of 1 μm particles reached ~10²e + in 3 minutes when the Air Supply/Minimate (+) operated). The experimental results are in good agreement with the theoretical data obtained using the diffusion charging model.
Ionic air purifiers demonstrate significant air purifying efficiency. A 30-minute operation of the VI-3500* in a room-size chamber removed about 97 % of 0.1 μm particles and about 95% of 1 μm particles from the air, in addition to the natural decay effect. A 60-minute operation of the Air Supply/Minimate (+) and Air Supply/Minimate (-) moved about 83% and 84% of 0.1 μm particles and about 79% and 83% of 1 μm particles from the air, respectively.
*This document originally pertained to VI-2500, AS180i and AS150MM.
Removal of fine and ultrafine particles from indoor air environments by the unipolar ion emission
Byung Uk Lee, Mikhail Yermakov, Sergey A. Grinshpun
Department of Environmental Health, Center for Health-Related Aerosol Studies. University of Cincinnati, 3223 Eden Avenue, P.O. Box 670056, Cincinnati OH 45267-0056 USA
The continuous emission of unipolar ions was evaluated in order to determine its ability to remove fine and ultrafine particles from indoor air environments. The evolution of the indoor aerosol concentration and particle size distribution was measured in real time with the ELPI in a room-size (24.3m³) test chamber where the ion emitter was operating. After the results were compared with the natural decay, the air cleaning factor was determined. The particle aerodynamic size range of ~0.04- 2 pm was targeted because it represents many bioaerosol agents that cause emerging diseases, as well as those that can be used for biological warfare or in the event of bioterrorism. The particle electric charge distribution (also measured in the test chamber with the ELPI) was rapidly affected by the ion emission. It was concluded that the corona discharge ion emitters (either positive or negative), which are capable of creating an ion density of 10⁵--10⁶ e± cm⁻³, can be efficient in controlling fine and ultrafine aerosol pollutants in indoor air environments, such as a typical office or residential room. At a high ion emission rate, the particle mobility becomes sufficient so that the particle migration results in their deposition on the walls and other indoor surfaces. Within the tested ranges of the particle size and ion density, the particles were charged primarily due to the diffusion charging mechanism. The particle removal efficiency was not significantly affected by the particle size, while it increased with increasing ion emission rate and the time of emission. The performance characteristics of three commercially available ionic air purifiers, which produce unipolar ions by corona discharge at relatively high emission rates, were evaluated. A 30-minute operation of the most powerful device among those tested resulted in the removal of about 97% of 0.11m particles and about 95% of 1 μm particles from the air in addition to the natural decay effect.
Keywords: indoor air environment; air purification; aerosol concentration; unipolar ion emission; electric charge
Numerous epidemiological studies have established an association between the indoor aerosol contaminants, including airborne dust, bioaerosols and aeroallergens, and adverse health effects. Most respiratory problems are closely associated with fine (≤ 2 μm, Baron and Willeke, 2001) and ultrafine (≤ 0.1 μm, Hinds, 1999) particle size fractions. Given that people spend a significant percentage of their time indoors (Klepeis et al., 2001), there is a high demand for efficient methods for indoor air cleaning against fine and ultrafine aerosol particles. Conventional techniques for controlling indoor aerosol pollutants, including mechanical filtration and electrostatic precipitation, have been incorporated into commercial devices of various capacities and efficacies (Ludwig and Turner, 1991). While being widely and successfully used in indoor air environments, the mechanical devices and electrostatic precipitators are often criticized for their considerable size and power consumption, excessive noise level and the need to be routinely maintained (e.g. routine filter replacement and the plate cleaning). Electrostatic filters have also been used for air cleaning but there have been very few studies that characterized their efficiency with a particular focus on fine and ultrafine particles (Jamriska et al., 1998).
As an alternative method, the emission of air ions that charges aerosol particles have been evaluated as to its capability to reduce the concentration of airborne dust and microorganisms in indoor environments (Grabarczyk, 2001; Grinshpun et al., 2001; Krueger and Reed, 1976; Niu et al., 2001). Among several particle charging methods, corona ionization is particularly effective in charging small aerosol particles, including the fine and ultrafine fractions (Adachi et al., 1985; Buscher et al., 1994; Wiedensohler et al., 1994; Hernandez-Sierra et al., 2003). Recent experiments conducted in a 2.6 m³ test chamber with a manikin have demonstrated that the aerosol concentration in the breathing zone may decrease considerably due to unipolar ion emission with a corona ionizer (Grinshpun et al., 2004). In these experiments, the concentration and the size distribution of 0.3-3 μm particles aerosolized by a Collision nebulizer (BGI, Inc., Waltham, MA, USA) were measured in real time using an optical particle counter. It was concluded that the aerosol particles, charged unipolarly by the emitted ions, repel and migrate toward the indoor surfaces, which results in their rapid deposition on these surfaces. Thus, it is anticipated that the efficiency of air cleaning in an indoor environment depends on its volume.
Those ion emitters, which meet health standards (e.g., do not generate ozone above established thresholds), have been incorporated in commercial air purification devices. The air purifiers that apply either open or shielded corona ionizers are being increasingly used in indoor environments. Nevertheless, there is a lot of controversial information about the performance of these devices, and the claims made by some manufacturers have not been substantiated by credible scientific investigations. Available ionic air purifiers differ by the emission rate, ion polarity (either unipolar or bipolar), and other characteristics.
The data reported earlier by our research group (Grinshpun et al., 2001, 2004) revealed that a high-density unipolar ion emission has a good potential for air cleaning in confined spaces, such as a very small room or car cabin (volume ~1-10 m³). However, the efficiency of this method for larger volumes (e.g., a typical room of 20-40 m³) has not been quantitatively characterized. Furthermore, no information has been reported on the efficiency of the unipolar ionic air purification against the particles of ≤0.3 μm, which includes the ultrafine fraction and the lower end of the fine fraction.
In this study, we investigated the effect of continuous unipolar ionization on the evolution of the indoor concentration and particle size distribution of fine and ultrafine aerosols. We targeted the particle aerodynamic diameter range of dₐ~0.04-2 μm, which is of special public interest because of its health relevance. Many bioaerosol agents that cause emerging diseases, as well as those that can be used for biological warfare or in the event of bioterrorism, belong to this particle size range. For example, dₐ~0.1 μm for coronavirus (the etiological agent of the SARS) and dₐ~1 μm for Bacillus anthracis (bacteria causing anthrax). Three ion emitters, VI-3500*, AS150MM (+), and AS150MM (-), which produce unipolar ions by corona discharge at different emission rate and polarity (all are available from Wein Products, Inc., Los Angeles, CA, USA), were evaluated in a room-size indoor chamber. The aerosol concentration and aerodynamic particle size distribution in the chamber were monitored in real-time. The particle electric charge distribution was also measured to relate the ion emission rate to the particle removal efficiency.
The tests were conducted in a non-occupied, unventilated test chamber (L x W x H = 3.78 m x 2.44 m x 2.64 m = 24.3 m³). This facility was developed in the Center for Health-Related Aerosol Studies at the University of Cincinnati and used in our previous studies (Choe et al., 2000; Grinshpun et al., 2002). A closed loop air ventilation system with two HEPA filtration units was utilized to clean the chamber between experiments. A small fan was used to achieve a uniform aerosol concentration pattern inside the chamber.
The electrical low-pressure impactor (ELPI, TSI Inc./Dekati Ltd., St. Paul, MN, USA) was used to determine the concentration and aerodynamic particle size distribution in real-time. This instrument utilizes the cascade impaction principle and also has a direct-reading capability. When performing the concentration and size distribution measurements, the particles were directed to the ELPI inlet through the Kr⁸⁵ charge equilibrator (3M Company, St. Paul, MN, USA). The ELPI is also capable of measuring the charge distribution of the collected particles. When the instrument was used in the charge-detection mode, the Kr⁸⁵ charge equilibrator was detached from the system. The time resolution of the ELPI was adjusted to 10 s. The data were recorded in 12 ELPI channels (each channel = impaction stage), from 0.04 to 8.4 μm. The latter sizes represent the midpoint diameters of the respective impaction stages (the midpoint = the geometric mean of the stage’s boundaries). The ELPI operated in the center of the chamber.
The natural aerosol concentration in the chamber was not sufficiently high for accurate direct-reading measurements, especially after the first 5-10 min. of the operation of an ion emitter, which removed a considerable number of airborne particles. To increase the initial background aerosol concentration, we used a smoke generator. The generated smoke particles primarily covered a sub micrometer aerodynamic size range (Cheng et al., 1995). Overall, the data recorded in the first 9 measurement channels of the ELPI (dₐ= 0.04-2.0 μm) were sufficient.
Three ion emitters were tested: a stationary negative ionic air purifier, VI-3500 (L x W x H = 20 cm x 16.5 cm x 8.5 cm), as well as two portable purifiers, positive AS150MM (+) and negative AS150MM (-) (L x W x H = 6.5 cm x 4 cm x 2.2 cm). The ion density produced by the non-thermal corona discharge in the chamber was measured in our experiments for each device with the Air Ion Counter (AlphaLab Inc., Salt Lake City, UT, USA) continuously every 10 s during about an hour. This device is capable of measuring within the range of 10¹-2 x 10⁶ ions cm⁻³.
First, the natural decay of the aerosol concentration was determined. Prior to the test, the smoke aerosol was generated and mixed in the chamber for 20 min so that it was uniformly distributed, and the average total particle concentration exceeded the level of ~1.3 x 10⁵cm⁻³. Then the ELPI began recording the data (t = 0) starting from the initial concentration Cinitial (da, t = 0). It operated continuously for 1 h, and the aerosol concentration Cnatural (da, t) was measured. To quantitatively characterize the natural decay, the non-dimensional fractional concentrations were determined every 10 s.
After this, the test aerosol was generated and mixed in the chamber again to reach the same initial concentration level. At t = 0, the ion emitter located in the center of the chamber was turned on and Cinitial ionizer (da, t = 0) was determined (the distance from the ion emitter to the inlet of the ELPI was approximately 0.2 m). Then the aerosol concentration, Cionizer (da, t), was measured with the ELPI in 10-second time intervals during 1 h, until the particle count decreased below the limit of detection.
The chamber was cleaned by a close-loop ventilation system at 10 air exchanges per hour for about 4 h to ensure that the ions generated during the test had been removed and the initial natural aerosol concentration in the chamber had been restored. Then the experimental procedure was repeated for the next ion emitter under the test program.
The air temperature was 23± 1°C and the relative humidity was 42± 9% during each experiment as monitored with a Thermometer/hygrometer (Tandy Co., Fort Worth, TX, USA).
To quantify the efficiency of the particle removal exclusively due to the ion emission, the air cleaning factor (ACF) was determined. For every particle size, ACF is defined as the ratio of the concentration measured at a specific time point during the natural decay due to the concentration measured at the same time point when the ion emitter was operating:
The data on ACF were presented as a function of the particle aerodynamic size and the duration of the ion emission. The aerosol concentrations Cionizer (da, t) were also compared to Cinitial ionizer (da, t = 0), and the decay was characterized by the non-dimensional concentration
In addition to the particle size and concentration measurements, the particle charges were measured with the ELPI that operated in its electrical charge detection mode. The data were revealed using the software made available by Dekati, Ltd., Tampere, Finland. The particle charge distribution was also assessed using the diffusion charging model (Hinds, 1999):
where n(t) is the number of elementary charges acquired by a particle during a time t due to the diffusion charging; dp is the particle physical diameter; k= 1.38 x 10-23 J K-1 is the Boltzmann’s constant; T is the air temperature (K); KE = 9.0 x 109N m2C-2 is a constant proportionality of the Coulomb’s electrostatic equation: e= 1.6 x 10-19C is the elementary charge; ci is the mean thermal speed of ions; and Ni is the ion density in the air. In our calculations, we assumed that dp≈da since the particles were close-to-spherical and their density was 1 g cm-3 (Cheng et al., 1995).
The average values and the standard deviations were calculated for each set of conditions as a result of at least 3 replicates. The data were statistically analyzed using the Microsoft Excel software package (Microsoft Co., Redmond, WA, USA).
Results and discussion
Fig. 1 shows the initial particle size distribution. The data represent the average of 9 tests. It is seen that the particles of da≈ 0.04-0.5 µm were dominant (ΔC/Δlog da ranged from ~104 to >105 cm-3), while larger particles of da ≈1-2 µm were present at lower concentration levels (ΔC/Δlog da~102 -103cm-3). The initial (t = 0) aerosol concentration of each measured particle size fraction was reproducible with the variability not exceeding 40% for 9 replicates.
The evolution of the non-dimensional particle fractional concentration due to the natural decay is shown in Fig. 2. The non-monotonic fractional decay curves reflect the variety of physical mechanisms involved in the aerosol transport even if no ventilation is introduced in the indoor environment (Vincent, 1995). The particles of smaller (da<0.2 µm) and larger (da>0.8 µm) fractions demonstrated greater decay than those of an intermediate range. The smaller particles are naturally removed from the air through depositing on indoor surfaces primarily due to the effect of diffusion, which becomes more pronounced with the decreasing particle size. In addition, the aerosol concentration of smaller particles decreases due to their coagulation with larger ones. The larger particles are subjected to the inertial deposition and gravitational sedimentation, which both increase with the increasing particles size. The above effects are relatively weak in the intermediate size range of ≈0.2-0.8 µm. The available gravitational settling models [tranquil or stirred (Hinds, 1999)] cannot accurately predict the natural decay rate observed in this study (in the absence of air ionization by an emitter). Our experimental data demonstrated that the concentration decay was twice as rapid as had been predicted by the above models for larger particles. This difference may be attributed to the intrinsic flow instability associated with the ELPI operation and other factors that enhance the particle deposition on surfaces. Also, the experimental equipment inside the chamber introduced some extra indoor surfaces, in addition to the floor, thereby increasing the natural particle deposition rate as compared to the gravitational settling models.
Although the natural decay shown in Fig. 2 for the fine and ultrafine particles is sharper than it is predicted by theoretical models, it is still very slow for effective air cleaning: it takes 30 min to achieve a concentration decrease by about 10-30% and an hour to achieve approximately 20-50% drop.
The unipolar ion emission may accelerate the aerosol concentration decay significantly. The air cleaning factors are presented in Table 1a for VI-3500 and Table 1b for AS150MM (+) and AS150MM (-). Resulting from a 15-minute operation of the VI-3500 (which has the highest emission rate among the tested ionic air purifiers), the particles were removed from indoor air at the rate, which is greater than the natural decay rate by a factor of 5.0 ± 1.1 to 6.8 ± 0.7. A 30-minute operation of VI-3500 surpassed the natural decay rate by a factor ranging from 15.3 ± 2.6 to 33.6 ± 5.5. This resulted in the removal of about 97% of 0.1 μm particles and about 95% of 1 μm particles from the air, in addition to the natural aerosol concentration decrease that occurred during the same time. The positive ion emission produced by AS150MM (+) and the negative ion emission produced by AS150MM (-) also significantly cleaned indoor air from the particles of 0.04-2 μm, but the ACF-values were not as high as those obtained for the more powerful VI-3500 (see Table 1). The difference between the data obtained for AS150MM (+) and AS150MM (-) was statistically insignificant. The arithmetic average of the
p-values that represented each particle size fraction was p = 0.19. In a 30-minute operation of AS150MM, the air cleaning rate surpassed the natural decay by a factor ranging from 2.1 ± 0.4 to 3.4 ± 1.6. A 60-minute operation of both AS150MM devices allowed reaching about twice greater ACF-values than their 30-minute operation. No statistically significant effect of the particle aerodynamic size on the air cleaning factor was observed p = 0.18.
The evolution of the non-dimensional particle fractional concentration with the time of ion emission is shown in Fig. 3 as a function of da: VI-3500 (Fig. 3a), AS150MM (+) (Fig. 3b), and AS150MM (-) (Fig. 3c). To standardize the ion emission rate characteristics of different emitters, we measured Ni with the Air Ion Counter at a distance of 1 m from the source during the test. The ion densities provided by VI-3500, AS150MM (+) and AS150MM (-) were (1.34 ± 0.04) x 106 e¯cm-3, (3.62 ± 0.18) x 105 e+cm-3, and (3.91 ± 0.22) x 105 e- cm-3, respectively. The numbers in parenthesis in Fig. 3 indicate an average value of the measured Ni (in elementary chargers per cm3). For each device, the ion emission during the first 3 min resulted in a statistically significant decrease of the aerosol concentration across the tested particle size range (p = 0.03). Continuous ion emission [an “ion shower” as referred to by Grabarczyk (2001)] makes the particle removal effect time-dependent. Resulting from the continuous operation of VI-3500, the aerosol concentration decreased more than 2-fold in 6 min, ~3-fold in 9 min, ~5 to 10-fold in 15 min, and >20-fold in 30 min. Both the positive and negative AS150MM ion emitters also efficiently removed particles from indoor air, but not as rapidly as the more powerful VI-3500. The above decrease of the particle concentration was observed for the entire test particle size range. No significant effect of the particle size on the efficiency of air cleaning was found (p = 0.17).
It was found that the particle electric charges of the initially generated aerosol were very low. On average, the ELPI measured less than one elementary charge per particle. In contrast, when an ion emitter operated, the airborne particles exhibited considerable charges (either positive or negative, depending on the polarity of the emitter). The particle charge distributions measured experimentally by the ELPI and calculated using Eq. (4) are presented in Fig. 4 in a logarithmic scale. The graphs represent the data obtained after the ionizers were operated for 3 min. It is seen that the average particle charge increases sharply with its size. The ion emission from VI-3500 increased the initial particle electric charges to ~101 negative elementary charges per particle of 0.1 μm and to ~102 negative elementary charges per particle of 1 μm. The ions emission from the AS150MM devices resulted in a lower, but still significant particle charge enhancement. The average deviations between the experimental results and the theoretical data across the entire test particle size range were about 31%, 23%, 24% for VI-3500, AS150MM (+), AS150MM (-) ion emitters, respectively.
The theory underestimated the electric charge level for larger particles and overestimated it for smaller ones. The theoretical calculations utilized exclusively the diffusion charging model, as no external electric field was applied in our experimental setting. However, the ion densities produced by the emitters were so high that the ion flux itself could have generated a significant space electric field. The ion-induced space field might have resulted in additional charging of particles. For our experimental condition, we estimated that the field charging becomes significant relative to the diffusion charging when the particles are larger than ~1 μm are greater than their calculated values. The difference between the experimental and theoretical values is more pronounced at higher ion emission rates (this difference was greater for VI-3500 than for AS150MM). This also can be attributed to the ion-induced space field, which should increase with increasing ion emission rate. The overestimation of the measured data by the diffusion charging model observed for ultrafine particles can be explained by the limitation of the theoretical model.
Indeed, while the model includes the ion concentration, it is insensitive to the particle concentration, assuming that the latter is much lower than the former. However, the concentration of ultrafine particles (~105cm-3) established in our tests was comparable to the ion density (~105-106e± cm-3). This could affect the particle-ion collision efficiency because some particles were not surrounded by a sufficient number of ions. Therefore, these particles had lower electric charges than is predicted by the diffusion charging model.
The real-time measurement of air ions showed that the ion density rapidly increased when the emitter began operating in the chamber. After reaching the saturation level within 10 s, it stayed at that level while the continuous ion emission supplied new ions in to the indoor air environment. For VI-3500 and AS150MM once the ion emitter was turned off, the ion density dropped by a factor of 10-20 during about 10 s and essentially reached the initial (background) level in 3 min. This reflects a very high electric charge dissipation caused by the interaction of air ions with indoor surfaces in the chamber.
The particle removal efficiency, which can be achieved by a corona discharge unipolar ion emitter, depends on the particle electric mobility, Z, and the electric field strength, E, created by the unipolar air ions. The mobility was calculated for the three ionic air purifiers tested in this study. The ELPI-measured particle size and electric charges were incorporated to the following equation (Hinds, 1999):
where Cc is the slip correction factor; q(dp) is an average electric charge of a particle that has a diameter dp (q = ne); and ƞ is the air viscosity. Table 2 lists the electric mobility values, which were determined based on the particle charge distribution measured at t = 3 min. The mobility changes very slowly with the time of ionization following the logarithmic function of the diffusion charging model.
From Eq. (4), if the air is ionized by the most powerful VI-2500 emitter, the particle electric charges increase on average only by approximately 34% while the ionization time increases 100-fold (from t = 3 min to t = 300 min = 6 h). Being proportional to the particle charge [see Eq. (5)], the mobility would also change by 34% in 6 h. Since in our experiments t = 1 h, we concluded that the particle charge distribution measured at t = 3 min is representative of the particle electric mobility during the entire 1-hour test.
It is seen from Table 2 that the particle electric mobility was not dependent on the particle size. This can be attributed to the combination of the space field charging (effective for larger particles) and the diffusion charging (effective for smaller ones). The suppressed effect of the particle size on their electric mobility can help explain why the decay of the non-dimensional fractional concentration was not dependent on the particle size (see Fig. 3).
To relate the particle electric mobility and the ion-induced electric field to the particle removal from the air, the particle drift velocity was calculated using the equation for the terminal particle electrostatic velocity VE, (Hinds, 1999):
According to Grabarczyk (2001), the ion emission density levels achieved in our experiments should create a field strength of ~103 to ~104V m-1. The particle drift velocity, calculated assuming that the field is spatially uniformed, allowed estimating its drift time from the center of the test chamber to the wall (the chamber’s characteristic dimension). With the ion density provided by the VI-3500 emitter, the drift time is ~12 min. For the AS150MM units, it is ~45 min. Thus, ideally, the operation of the VI-3500 unit should make the entire volume of the chamber particle-free in about 12 min, and the operation of AS150MM should result in the particle-free environment in approximately 45 min. This theoretical estimate of the particle removal efficiency is in a reasonable agreement with the experimental values, although no 100% air cleaning was actually achieved in our experiments. The measurement data suggested the following: a 12-minute operation of VI-3500 removed about 80-90% of particles and a 45-minute operation of AS150MM removed almost 80% of particles (see Fig. 3).
Overall, we concluded that the ionic air purifiers, which are capable of producing unipolar ion density levels of 105-106e± cm-3, can be efficient in controlling fine and ultrafine aerosol pollutants in indoor air environments. The efficiency depends on the ion emission rate, as the latter affects the particle mobility. The air volume of the microenvironment (or, to be more precise, its surface-to-volume ratio) is also an important factor affecting the particle removal efficiency. This becomes apparent when the data obtained in this study in a 24.3 cm3 chamber are compared to those measured in our previous study (Grinshpun et al., 2004), where the same ionic air purifiers were evaluated in a 10-fold smaller chamber (the particle size ranges tested in these two studies have an overlap between 0.3 and 2 μm). The data suggest that with increasing air volume, more time is needed to reach a certain air cleaning level. Thus, unipolar ionic air purifiers are especially efficient in confined spaces.
It should be acknowledged that continuous injection of air ions of a single polarity (unlike bi-polar ions) into an enclosed environment leads to the charge accumulation of insulating surfaces, which may cause occasional electrostatic discharges or other “static”- related problems, especially at low humidity levels. Certain treatments of indoor surfaces may help address this issue (to be tested in future studies). Another phenomenon that limits the use of some unipolar ion emitters for the indoor air purification is a production of by-products. For example, negative ion generators may produce excessive concentration of ozone and nitrogen oxides. Several methods (e.g., a soft-corona discharge technique) have been developed to keep the concentration of these by-products in the air below conventionally accepted thresholds.
Continuous emission of unipolar ions (either positive or negative), which is capable of creating an ion density of 105-106e± cm-3, can be efficient in controlling fine and ultrafine aerosol pollutants in indoor air environments, such as a typical office or residential room. The particles are charged primarily by the diffusion charging mechanism. At a high ion emission rate, the particle mobility becomes sufficient so that the particle migration results in their deposition on the walls and other indoor surfaces. Within the experimental conditions, the particle size effect on the mobility is suppressed and thus the particle removal efficiency is about the same for the fine and ultrafine particles size ranges. The particle removal depends on the ion emission rate and the time of emission. The indoor air volume is also a factor affecting the performance of an ion emitter.
Three ionic air purifiers, which produce unipolar ions by corona discharge at relatively high emission rates, were tested in this study through a real time aerosol monitoring and found efficient to remove fine and ultrafine aerosol particles from the air of a typical room. A 30-minute operation of the most powerful ion emitter (VI-3500) removed about 97% of 0.1 μm particles and about 95% of 1 μm particles from the air in addition to the natural decay effect. A 60-minute operation of two other emitters [AS150MM (+) and AS150MM (-)] in the same environment removed about 83% and 84% of 0.1 μm particles, respectively.
*This document orginally pertained to the Vortex VI-2500 , Wein Products, Inc.
Unipolar Ion Emission Enhances Respiratory Protection Against Fine and Ultrafine Particles
Byung Uk Lee, Mikhail Yermakov, Sergey A. Grinshpun
Department of Environmental Health, Center for Health-Related Aerosol Studies, University of Cincinnati
We developed a novel concept that allows to considerably improve the performance of conventionally used filtering-facepiece respirators against fine and ultrafine aerosols including viral and bacterial agents. The concept is based on the continuous emission of unipolar ions. The effect was evaluated through the real-time monitoring of the concentration size distribution of fine and ultrafine aerosol particles. The measurements were conducted inside and outside of a respiratory mask that was face sealed on a breathing manikin. A commonly used Type N95 respirator and surgical mask were utilized for the tests. The manikin was placed in a 24.3-m3 indoor test chamber and exposed to polydisperse surrogate aerosols simulating viral and bacterial particles with respect to the aerodynamic size. The particle penetration through the mask was found to decrease by one-to-two orders of magnitude as a result of continuous unipolar ion emission in the chamber. The flux of air ions migrated to the breathing zone and imparted electrical charges of the same polarity to the aerosol particles and the respirator filter surface. This created an electrostatic shield along the external surface of the filter, thus enhancing the protection characteristics provided by the respirator. The above performance enhancement effect is crucial for minimizing the infectious risk in the cases when the conventional filtering-facepiece respirators are not able to provide an adequate protection against airborne viruses and bacteria.
The outbreaks of emerging diseases (e.g. SARS) and the threat of bioterrorism have triggered an urgent demand for adequate respiratory protection against bioaerosol agents, including airborne viruses and bacteria. Particular interest has been directed towards increasing the efficiency of existing respiratory protection devices.
The filtering-facepiece masks, including Type N95 respirators, are frequently used in indoor air environments to prevent or considerably reduce inhalation of droplet nuclei that can potentially carry viable microorganisms. Millions of workers, including health-care personnel, routinely use respirators in their workplaces (United States Department of Labor, 1995). In case of bioterrorist attach in a major urban area, there may be a need in millions readily available respiratory protection devices. The existing respirators have been extensively evaluated against fine particles (e.g., Brosseau, Evans, Ellenbecker, & Feldstein, 1989; Chen, Ruuskanen, Pilacinski, & Willeke, 1990; Chen & Willeke, 1992; Huang, Willeke, Qian, Grinshpun, & Ulevicius, 1998; Johnston, Myers, Colton, Birkner, & Campbell, 2001; Qian, Willeke, Grinshpun, Donnelly, & Coffey, 1998; Halvorsen, 1998) and microorganisms (Centers for Disease Control and Prevention, 1994; Lee, Slavcev, & Nicas, 2004a; Qian, Willeke, Grinshpun, & Donnelly, 1997; Qian et al., 1998; Reponen, Wang, Willeke, & Grinshpun, 1999; Willeke, Qian, Donnelly, Grinshpun, & Ulevicius, 1996). At the same time, the protection efficiency of existing facepiece respirators have not been well characterized with respect to ultrafine particles, i.e. those below 0.1 µm (Hinds, 1999).
The respirators differ from one another by their filtration efficiency, which is dependent on the filter properties and the particle size. For example, a Type N95 respirator may allow up to 5% penetration in “a worst-case scenario,” when most-penetrating sodium chloride particles of 0.3 µm mass median aerodynamic diameter are drawn through the filter at a flow rate of 85 1 min-1 (Federal Register, 1995). The penetration efficiency of larger Mycobacterium tuberculosis bacteria (Mtb, 0.8 µm) through a face-sealed N95 respirator at strenuous workload is as low as about 0.5% (Qian et al., 1998). The face-sealed filter of a conventional health-care mask, which ensures relatively low pressure drop and consequently good comfort level, allows approximately 15% of airborne Mtb surrogate bacteria to penetrate, thus providing 85% protection against these bacteria (Willeke et al., 1996).
If the bacterial concentration in the air is 1000 m-3, an unprotected individual breathing at 30 1 min-1 inhales 1800 microorganisms per hour, whereas the one wearing a perfectly fit N95 respirator inhales up to 90 microorganisms per hour. If the infectious dose of a bioaerosol agent of interest is less than 90, the N95 respirator may not provide an adequate respiratory protection once the exposure time exceeds one hour. The use of an improperly fit-tested tight-fitting respirator may further decrease the respiratory protection level because of the additional particle penetration that occurs through the face-seal leaks (Chen et al., 1990; Chen & Willeke, 1992; Oestenstad, Dillion, & Perkins, 1990a; Oestenstad, Perkins, & Rose, 1990b). Based on the above considerations, it seems very useful if the filtration efficiency of existing respirators can be increased while the comfort level provided by these devices would remain the same.
With respect to the respiratory exposure and protection, the particle aerodynamic diameter range of da~ 0.04-2 µm is of special public interest because of its health relevance. Many bioaerosol agents, including viruses and bacteria that cause emerging diseases as well as those that can be used for biological warfare or in the event of bioterrorism, belong to this size range. For example, according to the National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov), the dimension of the coronavirus virion (the etiological agent of the SARS) are (60-120) x (160-200) nm, which corresponds to da~ 0.1 µm. For Bacillus anthracis (bacteria causing anthrax), da~ 1 µm. As the above range is broad and includes both the fine and the ultrafine particle fractions (Baron & Willeke, 2001; Hinds, 1999), the particle penetration efficiency through the filter media can be affected by several mechanisms and is generally characterized by the particle aerodynamic size. This allows testing the performance of respirator filters against pathogenic agents using non-pathogenic aerosol surrogates that simulate the aerodynamic characteristics of the particles of interest.
In this study, we developed and evaluated a novel concept that drastically enhances the performance of conventional filtering-facepiece respirators against fine and ultrafine aerosol particles. The concept is based on the continuous emission of unipolar ions into the air in the vicinity of the respirator. The aerosol particles are unipolarly charged by air ions primarily due to the diffusion charging mechanism (Adachi, Kousaka, & Okuyama, 1985; Frank, Cederfelt, & Martinsson, 2004; Hernandez-Sierra, Alguacil, & Alonso, 2003; Wiedensohler et al., 1994). The ion-filter interaction and the deposition of unipolarly charged particles on the external surface of the filter impose significant unipolar charge on the filter. This creates a shield for the incoming particles (as they carry charges of the same polarity), which decreases the penetration efficiency through the filter.
The new concept was experimentally evaluated in a non-occupied, unventilated indoor test chamber (L x W x H = 3.78 m x 2.44 m x 2.64 m = 24.3 m3). This facility, developed in the Center for Health-Related Aerosol Studies at the University of Cincinnati, has been used in our previous studies (Choe et al., 2000; Grinshpun et al., 2002, 2004).
The experimental setup is schematically shown in Fig. 1. A breathing manikin with a face-sealed respiratory mask was exposed to the airborne polydisperse surrogate aerosols that simulated viral and bacterial particles with respect to their aerodynamic size. The leakage tests were conducted between the mask and the face of the manikin with a bubble-producing liquid (Trubble Bubble, New Jersey Meter Co., Paterson, NJ, USA). The manikin operated at a breathing flow rate, 30 1 min-1, representing human breathing during light workloads (Mineral Resources, 1994; Johnson, Weiss, & Grove, 1992).
The electrical low-pressure impactor (ELPI, TSI Inc./Dekati Ltd., St. Paul, MN, USA) was used to determine the concentration and aerodynamic particle size distribution in real-time. This instrument utilizes the cascade impaction principle and – in addition— has a direct-reading capability. The aerosol particles are charged by the corona charger downstream of the ELPI inlet and subsequently detected by the electrometers inside the cascade impactor.
The particles were collected by the ELPI inside and outside the respirator using identical sampling lines. For these measurements, a 10-mCi Kr85 charge equilibrator (3M Company, St. Paul, MN, USA) was installed upstream of the ELPI inlet to neutralize the particles to Boltzmann charge equilibrium. This allowed us to avoid the influence of high electric charges, imparted by the particles as a result of their interaction with air ions, on the ELPI performance. The time resolution of the instrument was adjusted to 10 s. The data were recorded in 12 ELPI channels (each channel = impaction stage), from 0.04 to 8.4 µm. The latter sizes represent the midpoint diameters of the first and the 12th impaction stages (the midpoint = the geometric mean of the stage’s boundaries).
The natural aerosol concentration in the indoor test chamber was not sufficient, particularly for the measurement inside the mask, because the filter removed a considerable number of ambient airborne particles. To increase the initial background aerosol concentration, we used a smoke generator. The smoke particles covered primarily the submicrometer aerodynamic size range (Cheng, Bechtold, Yu, & Hung, 1995) with a sharp decrease in the particle number at da > 1.5-2 µm. Thus, the data recorded in the first 8 measurement channels of the ELPI (da = 0.04-1.3 µm) were used for the analysis.
The measured aerosol concentrations inside (CIN) and outside (COUT) the mask were incorporated into the equation for the respirator penetration efficiency, Ep:
which was determined as a function of the particle aerodynamic diameter. Ep is actually the inversed protection factor that is frequently used as a respirator performance index.
Initially, the background tests were conducted by measuring the penetration efficiency of the mask with no ion emission. Then, a unipolar ion emitter was turned on at a distance of 20 cm from the mask, and Ep(da) was determined in 3-min time intervals during 12 min. The continuous air ion emission in the chamber decreased COUT as the particles, charged by ions to the same polarity, repelled and subsequently migrated toward the chamber’s walls and deposited on these walls (Grinshpun et al., 2004). The change in the COUT-value that occurred during each 3-min time interval due to ionic air purification in the chamber was taken into the account through the linear interpolation of COUT(t).
In this study, we used a negative ion emitter (VI-3500*, Wein, Inc., Los Angeles, CA, USA) producing an air ion concentration of Ni ~ 1.3 x 106 elementary charges per cm3 as determined at a distance of 1 m from the source. The ion concentration was measured by the Air Ion Counter (AlphaLab Inc., Salt Lake City, UT, USA) that operates within the range of 10 – 2x106 ions per cm3.
Two types of filtering-facepiece respiratory masks commercially available from a major manufacturer were tested in this study. One was the NIOSH (US National Institute for Occupational Safety and Health) certified N95 respirator and the other one was a conventional disposable surgical mask. The N95 respirator consists of inner and outer cover webs made of rayon. Its filter made of polyester and polypropylene with the electrostatically charged microfibers providing relatively high filtering efficiency. In the surgical mask, the polypropylene filter is sandwiched between inner and outer webs made of rayon. The filter of a surgical mask has lower filtration efficiency as compared to the one of an N95 respirator. Thus, the effect of ion emission on the respirator filter efficiency was tested for the masks having two distinctly different original performance characteristics.
The average values and the standard deviations of the penetration efficiency were calculated for each set of conditions as a result of at least three replicates. The data were statistically analyzed using the Microsoft Excel software package (Microsoft Co., Redmond, WA, USA).
Fig. 2 shows the normalized initial aerosol concentration measured outside the respirator mask. Each data point represents an average of six replicates. It is seen that the aerosol particles were primarily within a range of da ≈ 0.04-0.5 µm (the concentration ΔN/Δlog da was between > 104 and > 105 cm-3), while fewer micron-size particles were detected (ΔN/Δlog da ~ 103 cm-3). For each measured particle size, the initial aerosol concentration was reproducible with the variability (the coefficient of variation) not exceeding about 50% for six replicates.
Fig. 3 presents the data obtained with two types of face-sealed respirators: N95 respirator and a surgical mask. When no air ion emission was introduced, the Ep-value, averaged over the test range of da, was about 1.8% for the N95 respirator. The particle size did not considerably affect the penetration through the N95 respirator filter, although some decrease of Ep with increasing da was observed for da ≈ 0.04-0.5 µm. Once the negative ion emission began, the penetration decreased to 0.27% during the first 3 min. At t = 12min, it further decreased to about 0.11%, enhancing the N95 respirator filter performance approximately by a factor of 17 (Fig. 3a). For the surgical mask, the initial penetration efficiency ranged from 18.7% (da = 0.04 µm) to 11.1% (da = 1.3 µm). Resulting from the emission of negative ions, the average penetration efficiency through the surgical mask dropped from 15.4% (t = 0) to 0.19% (t = 12 min), demonstrating an 80-fold enhancement (Fig. 3b). The data in Fig. 3 show that the most pronounced effect occurred within the first 3-min interval.
4.1 Baseline test
It was surprising to observe that the initial penetration efficiency (t=0) of ultrafine particles through both masks slightly increased with decreasing particle size. In contrast, the available filtration models predict that the peak penetration is reached at da between 0.1 and 0.3 µm, and the particles below 0.1 µm should be collected more efficiently as their size decreases (diffusion regime) (Halvorsen, 1998; Hinds, 1999; Lee & Mukund, 2001). The following considerations explain the results of our baseline test for the ultrafine particles. These models (and the laboratory-generated experimental data that support them) characterize the particle penetration through a homogeneous perfectly sealed fibrous filter material but not through a respirator mask. The design of a filtering-facepiece respirator does not assure a perfect peripheral connection of the assembly, so micro-leaks may be present between the core filter material and the elastic peripheral support. These leaks can contribute to the penetration of the ultrafine particles. In addition, although the mask was “glued” on the manikin, some very small, micrometer- or sub micrometer-size leaks may still remain. Most of soap-bubble-based air leak detection methods are capable to identify micro-leaks greater than 1 µm. If da is much lower than the characteristic size of the micro-leaks (⪡ 1 µm), the particles may penetrate through these remaining sub micrometer micro-leaks, thus affecting the overall aerosol penetration efficiency through the filtering mask. One more possible factor is associated with the spatial variations in fiber diameter, orientation, packing density, as well as initial fiber electrostatic charge level (for those masks utilizing electret filter media). These variations have been shown to significantly affect the respirator performance increasing the penetration efficiency of particles of ~ 0.1 µm (Huang et al., 1998).
4.2 Enhancement due to the unipolar air ion emission
The enhancement of the respirator performance, observed almost immediately after the ion emitter started operating, can be attributed to the electrostatic effect. The emitted negative ions as well as the particles charged by these ions in the air, impose significant negative charge on the respirator filter. This forms the “electrostatic shield” against the particles moving toward the mask. The repelling forces decrease the number of particles that can approach the filter. The above-described effect works outside of the respirator, as opposite to the aerosol filtration by diffusion, impaction, interception, and electrostatic deposition (Lee & Mukund, 2001) that takes place inside the filter. Therefore, the ion-induced decrease in the particle penetration efficiency does not cause the pressure drop increase through the filter providing the enhanced performance with the same comfort level.
To quantitatively characterize the effect, we calculated the velocity of particle migration induced by the electrostatic interaction in the vicinity of the filter. It was then compared to the velocity of the air flow through the filter caused by inhalation. In this calculation, we used information about the airborne particle electric charges and the air ion density, obtained by the ELPI and the Air Ion Counter, respectively. The particle size of da = 0.1 µm was chosen, as it represents the dominant size range used in our experiments. Furthermore, this value is at the borderline between the fine and ultrafine particle size ranges. In addition, many viral particles have an aerodynamic diameter of ~ 0.1 µm. Two main assumptions were made. First, the aerosol particles and air ions that interacted with the respirator were assumed to give all their electric charges to the respirator filter. Second, the charged filter was assumed to act as a point-charge located at the center of the respirator’s surface. As the ion emission level produced in our experiment, a 0.1 µm particle carries, on average, 10 elementary charges (Lee, Yermakov, & Grinshpun, 2004b). The calculation showed that the total electric charge acquired by the respirator filter, as a result of a 3-min continued emission from the VI-3500 ion source, is abut 1.5 x 1013 elementary charges, if the breathing flow rate is 30 1 min-1. The ion concentration at the center of the respirator was determined to be approximately 1.6 x 108 cm-3 (this point located 20 cm from the ion emission source). Thus, the particle migration velocity was found to exceed the air flow velocity, created by the inhalation in the breathing zone, approximately by a factor of 75. This suggests that the effect of the repelling force between the unipolarly charged particles and filter surface is much stronger than the aerodynamic force. Therefore, although our assumptions may not be sufficiently conservative, the above assessment demonstrates that the enhancement of the respirator performance by the unipolar ion emission is governed by the electrostatic “shield” mechanism.
The drastic decrease of the particle penetration through the respirator filter due to continuous unipolar ion emission may be critical in providing additional respiratory protection by existing masks against viral and bacterial particles. For example, an individual exposed to the influenza virus concentration of 10,000 m-3 inhales approximately 4500 x 0.18 = 810 viruses during 15 min when breathing through a conventional surgical mask at 30 1 min-1 in the absence of ion emission (Ep ≈ 18% for 0.1 µm particles). The continuous emission of negative air ions (Ni ~ 106 e- cm-3) in a 25-m3 room would reduce the indoor viral concentration by a factor of 9 during that 15-min interval (Lee et al., 2004a, b). In addition, it would enhance the surgical mask protection reducing Ep from 18% to at least 0.19%. Thus, only about (4500/9) x 0.0019 =0.95 ≈ 1 virus would be inhaled in 15 min. Given that the infectious dose of influenza A2 is 790 viruses (Lawrence Berkeley National Laboratory), the ion emission effect would make an important difference with respect to the health risk.
While this study is limited to the negative ion emission, we anticipate that the respirator performance enhancement effect can be achieved also by generating positive air ions, as long as the ion concentration in the vicinity of the mask (breathing zone) is sufficiently high. Future studies will address the effects of polarity and the ion emission rate on the particle penetration efficiency through respirator filters.
Generally, the mask protection factor depends not only on its filter penetration efficiency but also on its face fit (in practice, the facepiece mask is not sealed to the human face allowing the particles to penetrate through the leak). This pathway may become especially apparent when the filter material is highly efficient. Therefore, future tests involving human subjects, different fit factors, and other experimental conditions (flow rates and different masks) are needed to better characterize the enhancement effect, discovered in this study, and link it to the exposure.
The experimental evaluation part of this investigation was supported by the Wein Products Inc., Los Angeles, CA, USA. The participation of Dr. Lee in this study was partly due to the Post-doctoral Fellowship Program and the Advanced Environmental Monitoring Research Center (ADEMRC) Program of the Korea Science & Engineering Foundation (KOSEF). The authors are thankful for this support.
*This document originally pertained to the Vortex VI-2500, Wein Products, Inc.
The Premier Conference and Exposition for Occupational and Environmental Health and Safety Professionals
American Industrial Hygiene Conference & Expo 2004
Droplet Deposition In Industrial Duct Bends
T. Peters, D. Leith, University of North Carolina, Chapel Hill, NC.
A study of droplet deposition in industrial duct bends is presented. Factors investigated were: (1) flow Reynolds number (Re= 203,000, 368,000]; (2) particle Reynolds number [l0 ≤ Re ∞ 200]; (3) particle Stokes number (0.08 ≤ Stk ≤ 16); (4) bend angle (0 =45°, 90°, 180°]; (5) bend curvature ratio [1.7 ≤ R0 12]; (6) orientation [horizontal-to-horizontal and horizontal-to-vertical]; and (7) construction technique [smooth, gored, segmented]. Measured deposition was compared with mod els developed for bends in small diameter sampling lines (Re < 20,000; Rep ∞ < 13).
Whereas deposition measured in this work generally agreed with that estimated with mod els for particles smaller than 30 µm (Stk < 0.7), it was significantly lower than that estimated for larger particles. As the flow around larger particles became increasingly turbulent, the models progressively under-represented drag forces and over estimated deposition. For particles larger than 20 µm, deposition was slightly greater in the horizontal-to-horizontal orientation than that i.n the horizontal-to-vertical orientation due to gravitational settling. Penetration was not a multiplicative function of bend angle as theory predicts due to the developing nature of turbulent flow in bends. Deposition in a smooth bend was similar to that in a gored bend; however, a tight radius segmented bend (R0 = 1.7) exhibited much lower deposition. For more gradual bends (3 ≤ R0 ≤ 12), curvature ratio had negligible effect on deposition.
A new model was constructed to explain these results and is applicable to a broad range of industrial situations. Using this model, engineers can optimize ventilation systems to better protect workers-increased protection from harmful contaminants, reduction of duct fires, and/or reduced explosion risks-at reduced operating costs and/or less-frequent system maintenance intervals. Moreover, this model will enable health officials to evaluate bioterrorist threats, such as deposition of anthrax in ducts.
Indoor Air Purification By Ionic Emission
S. Grinshpun, B. Lee, M. Yermakov, University of Cincinnati, Cincinnati, OH.
Among various techniques that reduce the indoor concentration of respirable particles, ionic emitters have been increasingly used in office, industrial, and residential environments. Some ionization-type air cleaners incorporate corona effect to the airborne particles that make the unipolarly charged particles repel and migrate toward the indoor surfaces. In this study, five ionic air purifiers were evaluated in a 25-mJ nonoccupied, unventilated room. The study was conducted with the particles of typical virus and bacteria sizes (aerodynamic diameter = 0.04 to 2 µm). The particle concentration and size distribution were measured as a function of time with the electrical low pressure impactor that has a real-time measurement capability. The aerosol concentration decay occurring due to the ionic emission was com pared to the natural decay. It was found that the ion flow in the tested air environment increased the electric charge of aerosol particles by one to two orders of magnitude, depending on the particle size. The operation of the unipolar ion emitter producing about 106 e-/cm3 reduced the aerosol concentration by a factor of 5 in 15 minutes and by a factor ranging from 15 to 30 in 30 minutes. The ionic air purification efficiency was found to be primarily dependent on the ion emission rate and the indoor air volume.
Aerosol Generation By Blower Motors As A Blas In Assessing Aerosol Penetration Into Cabin Filtration Systems
W. Heitbrink, S. Collingwood, University of lowa, Iowa City, IA.
Cabin filtration systems use blower motors to pressurize a vehicle's cab with clean, filtered air and to recirculate air through the heater and air conditioner evaporator cores. These systems reduce operator exposure to aerosols, such as pesticides, respirable crystalline silica, and bioaerosols, by a factor of 10--50. To evaluate compliance with product performance specifications, optical particle counters are used to measure size-dependant aerosol concentration inside and outside the cab. The ratio of inside to outside concentration is termed penetration. Blower motors use stationary carbon brushes to transmit electricity to a rotating armature, creating dust. Emissions from four blowers used in agricultural vehicles were measured in a test chamber. The blower motors were operated at 12 and 13.5 volts direct current. A vacuum cleaner moved 76 m3/hr of air through HEPA filters, the test chamber, and into a 5-cm diameter pipe. An optical particle counter drew air through an isokinetic sampling probe and measured the size-dependent particle concentrations from 0.3 to 15 µm. The blower motor aerosol concentrations were between 200 and 1800 particles per liter. Aerosol penetration into three stationary agricultural vehicles were measured at low concentrations (outside in the winter) and high concentrations (inside repair shops with burning incense sticks). The data was analyzed to estimate the concentration of cab-generated aerosol. In the 0.3- 1 µm range, estimated blower motor aerosol concentration and the measured concentration in the cab during low concentration testing were approximately the same. For two used vehicles, other sources of aerosol generation were present for particles larger than 1 µm. For an unused vehicle, the in-cab aerosol concentration during low concentration testing and the estimated concentration of blower motor aerosol were similar over the particle size range 0.3--4µm. Aerosol generated by the blower motor and other sources affect penetration measured with optical particle counters.
Search For The Optimal Pleat Count From The Perspective Of Filter Quality
C. Chen, T. Hsiao, National Taiwan University, Taipei, Taiwan, Republic of China; C. Chen, S. Huang, Institute of Occupational Safety and Health, Taipei, Taiwan, Republic of China.
Pleated filter panels have been used in a variety of industrial sectors. The present optimization of pleat filter design is based on minimizing the pressure drop at a certain approaching velocity. However, the filtration efficiency, an equally important indicator, is rarely being con templated together with the air resistance in the optimization process.
In this work, filter quality, instead of pressure drop, is used as the optimization criterion. Dioctylphthalate was used as the test agent to challenge fibrous polypropylene.filters. The filter media were dipped in isopropyl alcohol to remove possible electrostatic charges. Nine customarily made filter holders were fabricated to hold just one pleat of tilter with different spacing, simulating different pleat count range from 0.25 to 5.0 pleat/cm. The approaching velocity was fixed at 100 cm/sec. A scanning mobility particle sizer was used to measure the aerosol number concentrations and size distributions upstream and downstream of the pleat ed filter. The pressure drop across the filter media was monitored by using an inclined manometer.
The results showed that filter quality curve (as a function of pleat count) is almost independent of aerosol size. For submicrometer sized particles, aerosol penetration decreased with increasing pleat count because more filter ing materials were available for aerosol deposition. For micrometer-sized particles, aerosol penetration decreased with decreasing pleat count due to higher inertial impaction. For the filter tested in the present study, the optimal pleat count for filter quality was always slightly higher than that for pressure drop. For example, the optimal pleat count was 1.88 pleat/cm from the standpoint of pressure drop, but to have the highest filter quality, the pleat count needs to increase to 2.23 pleat/cm.
Dr. Gabor Lantos Introductory Letter for Ionic Technology Reducing Risks of Airborne Respiratory Pathogens and Viruses
Dr. Gabor Lantos MD.P.ENG.MBA Head of Occupational Health Management Services Inc. Toronto, Barries, London, Vancouver
Dear Mr. Weinberg:
You have asked me for my professional opinion regarding the potential use of the Wein Air Supply Ionic Air Purifiers as adjunctive self-protection for healthcare workers and for other individuals who might be contacts of the SARS virus or other infectious agents.
As an Occupational Health consultant to many of Toronto’s teaching hospitals I have been much involved with containing the recent SARS outbreaks and have made both private and public submissions to the Ontario Commission to Investigate the Introduction and Spread of SARS in Ontario (www.sarscommission.ca My own submission of November 17th begins on page 165 of the transcript).
For the reasons that follow, it is my professional opinion, both as a professional engineer and as an occupational physician, that both the room-size and the neck-worn air purifier can be of significant benefit in mitigating the risks from SARS, as well as from other common airborne pathogens such as the “common cold” coronaviruses, tuberculosis, and Influenza A & B.
Current medical knowledge about SARS is not adequate for prevention and is not reliable for treatment. Immunoprophylactic means do not yet exist and early therapeutic trials for the afflicted have been ineffective and even harmful. Until such time as effective immunizations and/or therapies are developed and readily available, the emphasis must be on preventative measures.
The successful containment of the SARS outbreaks was predicated on Public Heath interventions, Environmental Controls, and Personal Protection Equipment. Traditional Infection Control policies and procedures were insufficient. As per a recent CDC publication (Emerging Infectious Diseases Vol. 9, No. 10, October 2003): “To prevent the spread of SARS we implemented strict respiratory and contact precautions”.
The World Health Organization's investigation of Hong Kong's Amoy Garden Apartments revealed how the infection was spread via interconnected airstreams throughout the building.
The rationale for the use of Ionic Air Purifiers is that ion emission reduces the concentration of airborne particles. Aerosolized pathogens and contaminated airborne droplets become charged and precipitate on nearby surfaces: no longer to be inhaled. Early studies conducted by the UCLA Department of Microbiology simulated the airstream characteristics of human breathing, “mimicking real-life usage” of the neck-worn instrument. They showed a “consistently reproducible”, 90% reduction of airborne bacteria. Dr. Spira, the medical director, by virtue of the experiments we have conducted, the results suggest that we could significantly reduce the risk of pneumonia especially those contracted in hospitals.
This last statement is particularly noteworthy given the fact that at least half of the SARS cases in Toronto were acquired in hospitals (nosocomially).
Later research conducted at the University of Cincinnati Medical Center's Division of Environmental and Industrial Hygiene/Health Related Aerosol Studies were published in the peer-reviewed Journal of Aerosol Science Vo.32, SI, September 2001, and subsequently presented at the European Aerosol Conference in Germany. It was found that depending on particle size, operational time, and other variables, anywhere from 79-97% of particles were removed from room air. This size range includes particles of bacteria, molds, and viruses. The most recent Summer 2003 studies by the lead authors Drs. Grinshpun and MacKay showed that whereas a surgical mask alone reduces by 75% the total number of inhaled organisms, the combination of a surgical mask and the VI3500 Vortex* room air purifier resulted in a 99.5% reduction of inhaled infectious particles.
Respirators(masks) and ionic air purifiers used together created a synergistic system. Not only does the air purifier reduce the upstream concentration of particles, but it also enhances the filtering performance of the respirator because charged particles are more effectively filtered than are electrically neutral ones. There are well known difficulties with the sourcing, securing, fitting, and wearing of N95's. The effectiveness of a standard surgical mask together with an ionic air purifier is equal to or greater than that of an N95 alone.
Reducing the concentration of airborne particulates reduces the risk of infection. As per Nardel E.A., and Macher J.M., (Respiratory Infection Transmission and Infection Control Chapter 9, Bioaerosols: Assessment and Control ACGIH 1999) “the expected number of cases among a given number of susceptible persons is proportional to the average concentration of infection droplet nuclei in a room, and the probability that the particles will be inhaled”.
In summary, it is my professional opinion that the use of the air purifier alone, or in high risk settings as adjuncts to masks, respirators, and other PPE, will significantly reduce the risk of contracting airborne infections.
— Dr. Gabor Lantos P.Eng MBA MD
Occupational Physcian & Professional Engineer
*This document orginally pertained to the VI2500 Vortex, Wein Products, Inc.
University of Cincinnati Medical Center Report On the Performance of Surgical Masks Operating with the Wein Air Purifiers
Environmental Health Foundation
Department of Environmental Health University of Cincinnati
Dear Mr. Weinberg
This memo is to summarize the results of the Phase 1 tests that have recently been performed with surgical masks sealed to a manikin (with an absolute fit, i.e., no leakage). In this memo, I would also like to inform you about some preliminary findings of Phase 2, which was initiated to test the masks worn on a subject (the Phase 2 study design enables us to address the leakage issue).
This phase included the following:
the indoor air cleaning efficiency evaluation of your five products, such as Vortex VI-3500*, Minimate AS180i (positive and negative)*, Automate AS1250B*, and Sanimate AS250B*, conducted with the ELPI in a virus-size range;
the filter performance tests conducted with N95/R95 respirators sealed on a manikin when operating in the presence of high ion flows emitted by your products; and
the latter tests conducted with surgical masks.
The indoor air cleaning efficiency data for all the Wein ionic purifiers tested with the ELPI have been submitted to you earlier. The indoor aerosol concentration decreased significantly due to the ionization, especially when using the Vortex VI-3500* air purifier: a 30-minute operation of this air purifier in a typical room (volume = 25 m3) removed about 97% of 0.1 µm particles and about 95% of 1 µm particles from the air. You have also received the data on the performance of the N95/R95 respirators sealed to a manikin, which demonstrated an ionizer-driven improvement of the filter collection efficiency by a factor ranging from 1.6±0.1 (Automate AS1250B*) to 4.5±0.7 (Vortex VI-3500*).
My report below is focused on the performance of surgical masks operating with the Wein air purifiers.
First, we tested a 3M surgical mask (Model 1838, widely used, very popular) that was perfectly sealed on the manikin face and operated at the inhalation flowrate of 30 L/min. The collection efficiency was about 80% for submicron particles, including the virus-size range of 0.04 to 0.21 µm that was specifically targeted. This 80% efficiency translates into a protection factor of 5. The protection factor (also referred to as the fit factor, American National Standard – Fit Testing Method, ANSI Z88.10-2001, p.1) is the ratio of the aerosol concentration in the breathing zone outside the mask to that inside the mask. The factor is generally particle size dependent. The most penetrating particle size range is about 0.1 to 0.3 µm. Once the Vortex VI-3500* was switched on, the protection factor started increasing and exceeded the level of 70 in about 3 minutes of the ionizer’s operation (the average value during this time interval). It jumped to about 400 in 6 min and continued further increasing with the time (although at a lower rate). The above effect exclusively represents the enhancement of the performance of the respirator filter material. The rapid decrease of the ambient concentration due to the Vortex VI-3500* was taken into account when determining the protection factor. The Minimate™ AS180i* units (positive and negative) have also demonstrated a considerable enhancement effect: the protection factor increased from about 5 at t=0 to over 70 at t=3 min and was relatively stable at the level of 70 to130 at t = 6-12 min. The Automate AS1250B* showed some enhancement as well; however, the effect was weaker (the reason was previously discussed with you).
Overall, we are excited to see the filter performance effect of this magnitude, although it is understood that Phase 1 was set to test the masks in a perfect fit condition while the surgical masks have generally a very poor fit potential.
This phase was initiated to address the leakage issue. Indeed, in a real life the protection factor depends on the particle penetration through the respirator filter material as well as on the particle penetration through the leakage. The leakage of some size always exists between the face surface and the filter. The face/body movement increases the potential of the particle penetration through the leakage. The standard fit test is performed to determine an individual’s ability to obtain an adequate seal with a specific respirator. For instance, the fit test performed with the N95/R95 facepiece respirators using the Portacount (TSI, Inc.) is supposed to check whether these respirators fit well enough so their overall collection efficiency exceeds the 95% threshold (protection factor >20). If the filter material is very efficient and creates a good barrier, the aerosol tends to flow through a leak, especially if the pressure drop through the filter is high. Once the collection efficiency of a filter material significantly increases (e.g., >>95%), the potential of the particle penetration through the leakage may increase tremendously (as the pressure drop change may result in a rerouting of the aerosol flow). Under certain conditions, this pathway may become a primary one. Therefore, it is important to run the tests not only with a manikin with a sealed mask but also with a human subject, using the Portacount as the standard method. The exploratory part of Phase 2 was performed in collaboration with Dr. Roy McKay who actually conducted the fit testing of the 3M-1838 mask on me since I volunteered to be a subject. The standard fit testing protocol, which utilized the Portacount, included numerous procedures (normal and deep breathing, moving the face and the body left and right and up and down, talking, etc.).
The initial protection factor of the 3M-1838 surgical masks was found to range from 3.5 to 4. These values are slightly lower than those obtained in our Phase 1 experiments carried out with the mask sealed on the manikin. The difference points to the leakage effect. The protection factor determined increased to about 30 (t ≈ 9 min) when the Vortex VI-3500* was operating, thus turning a surgical mask with a poor fit and relatively low filter efficiency into an N95-level respirator in terms of its collection characteristics. Indeed, the collection efficiency of the surgical mask exceeded 95% due to Vortex VI-3500*. The Minimate™ AS180i* unit demonstrated the ionizer-driven improvement of the efficiency from 3.5 to about 9. The enhancement of the mask overall performance was lower than that observed with a more powerful Vortex VI-3500* but still significant: almost 3-fold.
The data suggest that the leakage represent a clear limitation of the respirator performance enhancement effect, which could have been over an order of magnitude greater if the mask’s fit was perfect. We did not observe any fit improvement due to the ionization. Thus, we could not expect a perfect fit from a surgical mask because of its design. We anticipate that the average leak size remained about the same while the filter material exhibits a much better protection due to the ionization. It is believed that since the particles and the filter fibers charged unipolarly by the ions, the repelling forces decreased the particle flow toward the filter. This consequently reduced the number of particles that could potentially penetrate through the mask and be inhaled. In spite of the fit factor limitations, the overall performance of a surgical mask against virus-size particles seems to drastically improve due to the constant ion flow produced by the Vortex VI-3500* and Minimate™ AS180i*.
In addition to our tests with the surgical masks on a human subject, we conducted one run with the R95-type respirator that fits to the face much tighter than a surgical mask. Due to its rigid periphery, it can be easily adjusted to a specific shape and thus has a better fit potential. When operating the Vortex VI-3500* located at a distance of 40 cm from the human face, the overall protection factor demonstrated a 4-fold increase, exceeding 1000 for certain procedures (normal breathing and deep breathing). The above improvement of the respirator performance agrees well with our Phase 1 results obtained with this respirator sealed on a manikin (4.5±0.7). The slight difference can be attributed to the leakage. The leakage effect was not as significant for the R95 respirator as the one observed for a surgical mask.
It is understood that the above-described Phase 2 findings are preliminary and we are interested in continuing this phase beyond the exploratory level.
The above-summarized data are being further analyzed from the statistical viewpoint and presented in a non-dimensional graphical form. The detailed data report on Phase 1 and the above- summarized data on Phase 2 will be submitted to you within a week.
All the objectives and specific aims proposed for Phase 1 and the exploratory stage of Phase 2 have been met. Two issues were addressed beyond the work scope, originally outlined for Phases 1 and 2 (see below).
Air cleaning, exposure to infectious agents and overall risk reduction:
We have concluded that an ionic air purifier exhibits two mechanisms, which decrease the number of infectious particles inhaled by a person wearing a respirator mask: the reduction of the indoor concentration upstream of the respirator and the enhancement of the respirator performance. The sample estimate presented below exemplifies the cumulative effect resulting from these two mechanisms. The calculations were performed based on the data obtained with the Vortex VI-3500* unit. Please keep in mind that this is only estimation but not a full-fledge risk assessment!
After the Vortex VI-3500* air purifier operates continuously for 15 min in a 25 m3 room, the concentration of submicron particles in this room decreases by a factor of 6. The overall protection factor of a surgical mask, enhanced by the ionic purifier, is about 30 (this takes into account the finding that the considerable improvement of the filter characteristics was partially suppressed by the leakage effect, see Phase 2 results). Thus, the number of submicron particles inhaled by a person is reduced by a factor of 6x30=180, instead of about 3.5 - 4 provided by a surgical mask alone. Let us assume that the concentration of influenza virus in an indoor environment is 1000 m-3. Its infectious dose, ID, is 79 viruses (inhaled). The air volume inhaled during one hour is 1.8 m3 assuming that the breathing rate is 30 L/min. Thus, an unprotected person will inhale 1,800 viruses (> ID50); the person wearing the surgical mask will receive 1,800/4=450 viruses (> ID50); and a person walking into a room where the Vortex VI-3500* was operating for about 10 min will inhale about 1,800/180=10 viruses (< ID50). This example shows the potential of the ionic air purifiers for the exposure reduction when they are used together with respirator masks. More comprehensive assessments that include infectious characteristics of other viruses/bacteria can be performed upon your request.
The ion emission rate and the aerosol particle mobility (or how much should the ion production rate be increased?). The particle charges were measured in our experiments with the ELPI in its charge distribution mode (the software was obtained from Dekati, Inc., Finland). The particle charge distribution was also assessed using the diffusion charging theory (described by Hinds in his “Aerosol Technology” book, 1999, Chapter 15). The experimental and theoretical data are in a good agreement. It was found that the particle charging level is close to the highest possible. In my opinion, this aspect deserves to be further investigated. There is a saturation charge level for every particle size. The performance of ionic air purifiers depends on the particle mobility, which is a complex function of their size and charge. Ideally, any newly-developed ionic air purifier should be evaluated as to its ion emission rate. If this rate is too low, it may be insufficient to drastically affect the particle mobility. On the other hand, starting from a certain level, any further increase in the ion production will probably not affect the air cleaning performance since the aerosol particle charging has essentially reached a plato. In the latter case, a constant supply of ions is needed to maintain the air cleaning efficiency level, but the performance would not improve if the ion concentration increases. Thus, it is important to know how much effort should be devoted to the increase of the ion flow emitted by a specific model.
Please let me know if you have any questions. We are certainly excited about our findings and look forward to working with you further on Phase 2. Dr. McKay has agreed to continue collaborating on the project if so requested.
Sergey A. Grinshpun, Ph.D.
Surgical Mask (3M 1838) enhancement factor
*This document orginally pertained to the Vortex VI-2500, Minimate™ AS150MM, Automate™ AS1250, and Sanimate™ AS250B Air Supply products, Wein Products, Inc.
Alexander Zakhartchouk and Marat Khodoun Give Their Opinion On How to Reduce the Spread of SARS
Dear Mr. Weinberg:
This letter is written in response to your request and expresses our professional opinion regarding physical and biological properties of the coronavirus, its infectious pathways, and possible methods to decrease the risk of infection in indoor environments. In March 2003, a novel coronavirus was discovered in association with cases of severe acute respiratory syndrome (SARS).
Both of undersigned (AZ and MK) were trained in virology, molecular biology and infectious diseases. Dr. A. Zakhartchouk has an extensive expertise in virology. He has published 19 peer-reviewed papers on various aspects of virology and is currently engaged in research on SARS vaccine development at the Vaccine and Infectious Disease Organization, University of Saskatchewan, Saskatoon (Canada). Dr. M. Khodoun has 7 years of experience in molecular diagnostic research and is currently employed at the Children’s Hospital Medical Center in Cincinnati (USA).
Coronavirus virions are spherical, enveloped virus particles, ranging from 80 to 160 nm in diameter. They may become airborne through the aerosolization of the body fluids and transmitted in the air while being carried by larger droplets (for example, with saliva aerosolized during cough and sneeze). Similar to the previously known coronaviruses, the newly-emerged SARS-associated coronavirus is also transmitted by droplet spread. The combination of a surface contamination and, possibly, an airborne spread may play a role. Recent data suggest that the virus may remain viable for considerable periods on a dry surface (up to 24 hours).
The discovery of a novel SARS-associated coronavirus provides a dramatic example of an emerging disease in humans caused by a coronavirus family. Although previously discovered and characterized human coronaviruses cause up to 30 percent of colds, they rarely cause a lower respiratory tract disease. In contrast, animal coronaviruses cause devastating epizootic of respiratory or enteric diseases in livestock and poultry. However, phylogenetic analyses and sequence comparisons showed that SARS-associated coronavirus is not closely related to any of the previously known coronaviruses.
Since the coronavirus, like many other viruses, can be transported in the air as aerosol particles, the risk of infection spread is proportional to their aerosol concentration. Depending on the ID50 and other factors, this risk can be drastically decreased if the viral particle concentration in indoor air is reduced. The use of indoor air cleaners and personal respirators is believed to be an adequate measure for the risk reduction.
We hope this information will be of your assistance.
Alexander Zakhartchouk, Ph.D., D.V.M. Research Scientist (II) Vaccine and Infectious Disease Organization, University of Saskatchewan
Marat Khodoun, Ph.D Research Fellow, Cincinnati Children's Hospital Medical Center, Research Foundation, Division of Developmental Biology
Prepared by Dr. Sergey A. Grinshpun, July 29, 2003
After the VI-3500* air purifier operates continuously for 15 min in a 25 m3 room, the concentration of submicron particles in this room decreases by a factor of 6. The overall protection factor of a surgical mask, enhanced by the ionic purifier, is about 30 (this takes into account the finding that the considerable improvement of the filter characteristics was partially suppressed by the leakage effect, see Phase 2 results). Thus, the number of submicron particles inhaled by a person is reduced by a factor of 6x30=180, instead of about 4, provided by a surgical mask alone. The air volume inhaled during a one-hour exposure is 1.8 m3 assuming that the breathing rate is 30 LPM. Some examples are presented below. The green color indicates that the estimated number of bioagent particles is below ID50; the red color indicates that the estimated number is above ID50.
*This document originally pertained to the VI-2500, Wein Products, Inc
Sergey A. Grinshpun Letter Affirming Effectiveness of Ion Generating Equipment on SARS, Anthrax and Smallpox
University of Cincinnati Medical Center
Department of Environmental Health University of Cincinnati
Mr. Stanley Weinberg Wein Products Inc.
Dear Mr. Weinberg,
You have requested a letter expressing my opinion as to whether the findings on the efficiency of your ion generating equipment, which has been tested in our laboratory, can be extrapolated to the SARS virus, the Anthrax bacterial spores, and the Smallpox virus. As I understand it, your request relates to two issues: (1) whether the aerosol concentration decrease observed in our tests with non-pathogenic particles is expected to occur with the above biological agents and (2) if so, would your air purifying equipment provide any meaningful degree of protection against airborne microorganisms causing SARS, Anthrax, or Smallpox.
With respect to the first question, it is my opinion that the aerosol concentration reduction, which we found earlier for test particles ranging from about 0.3 to 3 microns, can be extrapolated to any particles of this aerodynamic size range, regardless of their infectious characteristics.
Furthermore, our recent preliminary study has shown that the above particle size range may be extended to lower sizes: below 0.04 µm (as measured by the ELPI). Thus, the entire tested particle size range covers the sizes of most airborne viruses and bacteria.
The next question relates to the evaluation of the protection efficiency against SARS and other diseases for which the airborne transmission has either been identified or anticipated. It is presently anticipated that the SARS-causing virus can potentially be transmitted via airborne routes, i.e. with the droplets from a human sneeze or cough. Generally, the sizes of single viruses range from about 0.04 to 0.3 µm. Aerosolized saliva droplets containing viruses may be one or two orders of magnitude greater. However, as some water content of these droplets evaporates rapidly, most of the virus-carrying particles fall into the size range of about 0.1 to 3 µm. This range has been tested in our experiments. Our data show that your ion generating equipment,
including the tested Vortex VI-3500* (stationary) and Minimate™ AS180i* (wearable), should significantly reduce the concentration of droplets of 0.1 to 3 µm in the vicinity of the ionic air purifiers (at least, under the conditions tested of our laboratory). This reduction in the aerosol concentration should occur in the breathing zone of a person using your wearable ionic purifier and in a room in which your stationary unit is operating. The effect was found to be time-dependent and indoor air volume- dependent. The aerosol concentration reduction is especially pronounced in confined spaces and may vary considerably from one model/manufacturer to another, depending on the ion emission rate and other factors.
It should be understood that ionic air purifiers are not generally viewed as a way to replace personal masks or respirator filters. However, under certain conditions, the utilization of ionic devices may offer the same or comparable air purification efficiency as achievable with surgical masks and respirators while providing a greater comfort level for the wearer/user. It should be also understood that no claims must be made that your ionic air purifiers can fully eliminate the risk of inhaling airborne particles or prevent the transmission of infectious agents in indoor air. The reductions in airborne particle concentrations that we observed would, in my opinion, be useful in providing some degree of risk reduction against any disease for which the aerosol transmission is one of the infectious pathways. As a general principle, if the airborne concentration of a virus or bacteria is substantially reduced, the risk of contracting the disease through inhalation is also substantially reduced. In fact, for this very reason the conventional personal protective devices, such as personal masks and N95 respirators, are recommended by the US Centers for Disease Control and Prevention (CDC) and other agencies. The personal masks reduce the number of particles inhaled from the air contaminated with microorganisms (not aiming necessarily to achieve a zero-penetration). The airborne precautions were specified in the CDC document of May 1, 2003, entitled “Updated Interim Domestic Infection Control Guidelines in the Health-Care and Community Settings for Patients with Suspected SARS” (www.cdc.gov).
In the case of SARS, it is believed that aerosol transmission is one of the infectious pathways. During the CDC Telebriefing of May 15, Dr. Gerberding, the agency Director, stated: “there were opportunities for SARS virus to become airborne … it is imperative that we practice extreme vigilance in infection control precautions, that airborne contacts and standard procedures are appropriate in situations where patients with SARS are housed and that the droplet precautions that have been the primary focus need to be continue as well.” She also stated: “we can’t rule out the possibility of aerosol or airborne transmission, and so … we are emphasizing the extreme importance of vigilance to all levels of airborne protection” (CDC Telebriefing Transcript: Update on SARS, www.cdc.gov). The CDC recommended that the N95 respirator be used to protect against SARS transmission by the airborne route (Updated Interim Domestic Infection Control Guidelines in the Health-Care and Community Settings for Patients with Suspected SARS, www.cdc.gov).
The N95 respirator works by trapping at least 95% of airborne particles, thereby reducing the concentration of inhaled microorganisms. While based on a different principle and providing a time- and room-volume-dependent efficiency, the Wein ion generating equipment also reduces the concentration of aerosol particles in the breathing zone, thus providing a decrease in the exposure to indoor infectious aerosol agents.
Our ongoing manikin-based laboratory study addresses the situation when the respirator is being used in combination with an ionic air purifier operating in its vicinity. The aerosol concentration measurements are being conducted inside and outside the mask. The particle penetration
efficiency is determined as a function of time within the particle size range of 0.04 to about 3 microns. Among viruses and bacteria within this size range are coronavirus (SARS), which is between 0.06 to 0.22 µm, Variola major virus (Small pox), which is about 0.2 to 0.3 µm, and Bacillus anthracis bacteria (Anthrax), which is about 1 µm. The experiments have been set up in a room-size (25 m3) indoor test chamber utilizing “physical” particles. The natural aerosol concentration decay is taken into account in our study design. The preliminary data obtained with an inhalation rate of 30 liters of air per minute revealed that a unipolar ion emission near the respirator significantly enhances its performance, especially for small submicrometer particles.
The protection factor (the inverse of the particle penetration) of the N95 respirator with a perfect face fit was found to increase by about 50% due to the enhancement provided by the Automate™ AS1250B* unit. When a more powerful Vortex VI-3500* ion emitter was operating near the manikin’s face, the N95 protection factor increased more significantly allowing <1 % of aerosol particles to penetrate through the filter (instead of the 5% penetration threshold of the certified N95 respirator). Based on our preliminary data, I believe that the added electrostatic charges on the N95 fibers cause a significant enhancement effect (about 5-fold for the Vortex VI-3500* ionic purifier). I would expect this fiber-charge-driven enhancement effect to also manifest itself with other facemasks (e.g., with the common surgical mask that has lower collection efficiency than the N95 respirator). This statement needs to be experimentally verified. The laboratory tests involving surgical masks combined with ionic emitters are now in the planning stage with results expected in about two months.
I believe that when both effects (the indoor air concentration reduction and the respirator filter performance enhancement) are combined, the concentration of particles inhaled by a person wearing both a respirator mask and a Wein ionic air purifier would be reduced to a greater degree than if the person used the mask alone. This applies to all airborne particles in the tested size range.
Based on the currently available data, I would conclude that the aerosol concentration reduction, which results from operating the Wein ion emitters in indoor environments should further reduce the infection risk of airborne viruses or bacteria as compared to either completely unprotected breathing or to the inhalation protection provided by the N95 respirator alone. Depending on the infectious dose of a specific organism and its indoor aerosol concentration level, the risk reduction may be achieved for any agent within the size range of 0.04 to 3 microns, including coronavirus, Smallpox-causing virus and Anthrax-causing B. anthracis spores. I anticipate that the best results can be obtained when all the people in a room use ionic purifiers and wear personal protective mask. This should increase the overall efficiency for each individual exposed to an indoor air contaminant and minimize the cross-contamination effect
I recognize that although the major transmission route for SARS is still to be identified, it is presently thought to be spread by touch as well as by the aerosol transmission. Thus, reducing the concentration of airborne particulates should reduce the risk of infection. According to E.A. Nardell and J.M. Macher (Respiratory Infections – Transmission and Environmental Control – Chapter 9; IN: Bioaerosols: Assessment and Control, ACGIH, 1999), “the expected number of cases among a given number of susceptible persons is proportional to the average concentration of infectious droplet nuclei in a room and the probability that the particles will be inhaled” (p. 9- 6). Among the measures that can prevent or reduce airborne infection, the above experts list the control of the concentration of infectious agents in potential sources and maximizing removal rates of airborne infectious aerosols through dilution ventilation and use of air cleaners (p. 9-11). Numerous recently published documents, including the WHO (www.who.int) and CDC (www.cdc.gov) guidelines and recommendations, some of which were already quoted in this letter, as well as other materials (e.g., the SARS Clinical Information Sheet issued by the Johns Hopkins University on April 24, 2003), support this viewpoint.
I understand that the ions emitted from your purifiers charge aerosol particles and these particles move toward indoor surfaces and deposit on them. This suggests that the surface cleaning issue should be properly addressed when the equipment is used. As I have previously stated, the surface decontamination seems to be a less complex task than the air cleaning when the latter is done at very high efficiency levels. Although the particle resuspension from surfaces is generally acknowledged as a potential air contamination source, the efficiency of reaerosolizing viruses and bacteria is believed to be very low because of their small size. For infectious aerosols, “particles that contact a surface are assumed to adhere to it” (Nardell and Macher, p.9-10). The charged particles are especially difficult to resuspend. From my perspective as an aerosol scientist, it is of a primary importance to significantly reduce the aerosol concentration of infectious particles, which will subsequently decrease the probability that these particles would be inhaled and – as a result – will reduce the risk of adverse health effects.
Let me know if you have further questions. Sincerely,
Sergey A. Grinshpun, Ph.D.
Director, Center for Health-Related Aerosol Studies
*This document orginally pertained to the Vortex VI-2500, Minimate™ AS150MM, and Automate™ AS1250 Air Supply products, Wein Products, Inc.
Effect of Wearable Ionizers on the Concentration of Respirable Airborne Particles and Microorganisms
Volume 32, Supplement 1
Journal of Aerosol Science
Abstracts of the European Aerosol Conference 2001
S.A. GRINSHPUN. G. MAINELIS. T. REPONEN. K. WILLEKE. M.A. TRUNOV and A. ADHIKARY
Center for Health-Related Aerosol Studies. Department of Environmental Health. University of Cincinnati, Ohio, 45267-0056, USA
Keywords: IONIZER, ELECTROSTATIC PRECIPITATION, BIOAEROSOLS, INDOOR AIR
Health effects associated with respirable biological and non-biological particles are of special concern. Numerous techniques have been developed over the years to reduce bioaerosol concentrations in indoor environments. Some of these techniques target viable microorganisms, while others aim at the overall reduction of the bioaerosol concentration. Indoor air purifiers include mechanical filters, electrostatic precipitators (ESP), ionizers, hybrid filters, gas phase filters and ozone generators. Although most of the conventional air purifiers are stationary devices, several models of portable wearable ionizers have recently become available to clean the air in the human breathing zone (e.g., AS180i and AS150MM*, Wein Products Inc., Los Angeles, CA, USA). The ion wind produced by corona discharge inside these small, battery-operated devices emits ions into the air environment where they charge airborne particles. Some ionizers have an electrostatic precipitation section designed to collect charged particles. While these devices are commercially available and widely used, their air cleaning mechanisms are not well understood. In this study, we investigated the effect of a portable ionizer on the aerosol concentration measured in the vicinity of a human manikin placed in a 2 m3 walk-in environmental chamber.
Three types of respirable particles were used for testing: polydisperse NaCl particles ranging from dp=0.3 to 3.0 µm, monodisperse PSL spheres of the same size range, and Pseudomonas fluorescens bacteria of dp=0.8 µm. The test particles represent the size range of microbial fragments, single bacteria, most of fungal spores and microbial aggregates. Aerosolized with a standard Collison Nebulizer (BGI Inc., Waltham. MA, USA) and mixed with dry filtered air, the test particles were carried through a 10 mCi 85 Kr particle charge neutralizer into the environmental chamber through an air laminarizing and distributing unit. An external pump, whose inlet was positioned at the very bottom of the chamber, removed the air from the test chamber.
The airborne particle concentration and size distribution were monitored in real time at various locations of the chamber using an Optical Particle Counter (OPC) (model 1.108, Grimm Technologies Inc., Douglasville, GA, USA). A nephelometer (model pDR-lOOOAN. \OE. Inc., Bedford. MA, USA) was used in parallel to measure the airborne particle mass concentration.
In most of the experiments, the air purifier was positioned on the chest of a manikin so that the unit's outlet would be in line with the manikin's nose. The experiments were conducted under calm air conditions with breathing and with non-breathing manikins, as well as in mixed air. Ionizer AS-150 (Wein Products Inc., operating voltage = 5 V, nominal current = 70 mA) generating positive ions was tested in two regimes: (i) with a metal grid acting as an ESP and (ii) without the ESP section. The ion density measured in the nose/mouth region (19 cm above the ionizer located on the chest) ranged from 5x10° to 2x10° ions, cm3: the maximum velocity of the ion jet in front of the device was about 400 eras. The evolution to the aerosol concentration was determined during two 3-hour periods: first with the ionizer turned off (to account for the natural decay) and, second, when the device was continuously operating.
The particle removal efficiency (defined as the relative aerosol concentration decrease) was determined as
where C is the aerosol concentration for a specific particle size. Each experiment was repeated three times.
The results of selected experiments are presented in Figure 1. The particle removal efficiency was not significantly affected by the particle size within the size range tested, nor by the particle type (NaCl versus PSL, biological versus non-biological). Thus, the data shown in Figure 1 hold true for all the tested particles. The particle removal efficiency was found to increase with time. It moderately depended on the distance from the ionizer (19 cm above the unit = nose/mouth region; 10 cm above the unit = upper chest level). When the ionizer operated with the ESP section, it removed about 50% of particles under the nose in 1.5 hours of continuous operation without air mixing. The ionizer without the ESP section operating in calm air performed better than the one with the ESP: the particle removal efficiency in the breathing zone reached about 80% in 30 minutes of operation and about 100% in 1.5 hours.
Air mixing increased the particle removal efficiency. The effect of inhalation and exhalation on air cleaning was marginal (the data were not significantly affected by the manikin's breathing). The particle removal mechanisms, due to their charging as well as the ESP effect, are discussed.
*This document orginally pertained to the Air Supply/Minimate, Wein Products, Inc.
Treatment of Allergic Fungal SinusItis by Decreasing the Environmental Air Fungal Load
By Donald P. Dennis, M.D., F.A.C.S.
In September 1999 Mayo Clinic published an article that pegs 93% of all chronic sinusitis as being caused by mold. The mechanism of formation of sinusitis is, you breathe particles (mold in most cases) in the air to which you have an allergic reaction. This reaction causes small pits to form in the lining membranes of the sinuses. These pits trap mucous so that the mucous cannot drain. The stagnant mucous gets infected which causes nasal polyps and thickening of the lining which obstructs the outflow of mucous . The polyps cause more infection and the infection causes more polyps and then there is a viscous cycle which perpetuates itself.
This reaction is most likely a type 2 hypersensitivity reaction. All type 2 hypersensitivity reactions stop when the antigen (mold in this case) is removed. We knew from 20 years of experience that when patients cleaned their environmental air their sinusitis improved. The air mold level required for health was discovered by testing the one hour gravity plate exposure inside each chronic sinusitis patient's home and following them by endoscopic photo graphs as remediation of mold was done. Over 300 patients homes were done and it was discovered that a mold count of 0-4 colonies with a one hour gravity plate exposure was required for the sinus mucosa to clear by endoscopic photography.
Many different ways of mold remediation were tested and a protocol was developed that was easy for the patient to implement and cost effective.
The Wein ionizers model 2500 and 150mm were tested in a know mold contaminated room.
One hour gravity plate samples were taken in the room at different interval before and during the test. All of the plates taken before the ionizer test were too numerous to count colonies (TNTC). The Wein room unit 2500 model caused the mold count to drop to zero by day six in a TNTC mold colony count room.
The Wein neck 150mm unit was tested with a mannequin head with a hose through the nose. A suction pump was attached to the hose. The hose was placed in a jar with a mold plate in the bottom of the jar. Samples were taken by turning on the suction pump and allowing the plate inside the jar to be exposed for 1 hour. All of the plates done before and during the test showed a TNTC mold colony counts. Then the last plate was removed and new plate inserted and the Wein neck 150mm unit was turned on in the factory set power position. At 1 hour there was zero mold colonies. At 2 hours there was 1 colony. The 2 hour plate was a new plate.
Sinus health occurs at 0-4 colonies per 1 hr. plate exposure and the Wein neck 150mm unit reduced the mold load to 1 colony in 2 hours. 2 hour exposure would allow 8 colonies and the Wein unit allows l colony so it is 8 times better or 800% better than required to achieve sinus health.
EPA “Introduction to Indoor Air Quality: A Reference Manual" uses 50 CFU/m3 as a beginning concern and 10.000 as a problem amount using an Anderson sampler. The equivalents of Gravity feed to Anderson Sampler for 3 minutes @ 28.3 L/min are:
‘Dateline’ and Good Housekeeping put a Wein® Minimate™ to the Test
In a "Dateline NBC"/Good Housekeeping exclusive, Hoda Kotbe reports on some of the wacky products you can buy today.
It’s hard to resist those high-tech gizmos you see in some catalogs. You know, those strange-looking gadgets that promise to ease your aches and pains, help you look younger, or even make your clothes fit better. Sometimes they work, but some of these “miracle cures” can turn out to be snake oil. So we put a few of them to the test, and you might be surprised by the results. Hoda Kotbe reports with a “Dateline NBC”/Good Housekeeping exclusive.
A LIP PUMP, a peppermint inhaler, a toe stretcher? Welcome to the world of weird catalog products. You know, the ones most of us wouldn’t dare own up to ordering? But with billions of dollars in catalog sales every year, someone is buying this stuff — even a beeper-like gadget to clean your personal breathing space.
“You wear it around your neck,” says Sharon Franke of the Good Housekeeping Institute. “It sucks in the air. It cleanses it and then discharges it in a stream up to your face. Sounds really ridiculous right?”
Intrigued and more than a tad skeptical, the Good Housekeeping Institute ordered the air purifier for an evaluation of catalog products that seem too good to be true.
“We thought why would this work?” says Franke. “How could this work?” The Institute put a variety of products selected from eight different catalogs to the test, including an odd-looking device for toning your face, masks for sinus pain, even a pants stretcher for those who are “fat.” The products were evaluated by a team of Good Housekeeping staffers who tried them out, along with a panel of doctors, then given a “reality check” rating of zero to five stars.
“We were surprised that some of them work,” says Franke.
So which products made the cut? First, the cho-pat knee strap, which sells for $14.50. Can a simple strap with a velcro fastener really relieve pain? An old knee injury had forced Tracy, a Good Housekeeping employee, to give up kneeling in church. But with the kneestrap on, she even gets right down on the floor.
“I knelt on the marble floor without a kneeler and I had no discomfort whatsoever,” says Tracy. “I love it. It’s great.”
The manufacturer cautions it won’t help all knee problems and Good Housekeeping’s medical experts, who do prescribe the very same strap for their patients, say you should still consult a doctor before ordering from a catalog. The Good Housekeeping reality check? Three out of five stars.
And what about gel-soles? They sell for $15.95, and the catalog claims slipping one into your shoe lets you “say goodbye to hot, sore, miserable feet.” The manufacturer also says the gel-soles have medical endorsements. So how do they stand up?
“It kind of felt uncomfortable because it felt like there was something in my foot that was strange and squishy,” says Dana, a Good Housekeeping staffer.
“They do make it softer and easier to walk on your feet,” says Tony.
The Good Housekeeping staffers gave the gel-soles mixed reviews and orthopedist Dr. William Levine says you can buy over-the-counter insoles that will provide more cushioning.
“I’d be fairly skeptical about recommending this to any of my patients,” says Dr. Levine. So the gel-soles get a Good Housekeeping reality check of just two stars.
The instructions do clearly warn that the suction device may cause bruising and the manufacturer maintains with proper use, it will keep your lips full for up to 12 hours. But plastic surgeon Dr. Bob Tornambe says you might as well go a few rounds with Mike Tyson.
“In my opinion you could accomplish the same thing by getting punched in the mouth,” says Dr. Tornambe. “That causes a fat lip also.” The lip enhancer gets a Good Housekeeping reality check of zero stars. And wouldn’t it be nice if you could sniff your appetite away? For $30, the Aroma Works Suppress Inhaler is supposed to “fool the stomach into thinking your stomach is full.”
“Nobody reported that this works,” says Franke. “And none of the doctors that we consulted knew of any reason why it should work.” In fact, the manufacturer admits it has no medical evidence to support its claims, and told “Dateline” that like anything else, it won’t work for everyone. The Good Housekeeping reality check? Another zero.
And finally, the personal air purifier, and it promises to “eliminate airborne pollutants, allergens and viruses from your breathing space.”
“My eyes would be itching,” says Carol. “My nose would be this extreme tickle, I could be sneezing.”
Normally, cats make Good Housekeeping staffer Carol Wapner downright miserable. But to put the purifier to the test, she agreed to wear it to this adoption center, where she was surrounded by the furry felines. “I feel fine,” says Carol. “I do smell the cat litter I must say.”
Remarkably, even after 25 minutes, Carol didn’t sneeze once. Was it really the purifier? Or could it have been mind over matter? Wein Products, the company that makes the air purifier, insists it really works thanks to what it calls a “revolutionary technology” that destroys pollutants in the air. The company says it has done extensive testing, but makes no medical claims and says this is not a medical device. Instead, it says the proof is in the use, telling “Dateline” it has hundreds of satisfied customers.
Still skeptical, Good Housekeeping turned to its engineers for help. They devised a “smoke test” to see if the air purifier could clear out a tank of smoke. First, they lit a cigarette and allowed it to burn inside the tank, building up a lot of smoke.. Then they put the air purifier in the tank:
“If you look in here you will see that there is no more streams of smoke,” says Jamey. “To our astonishment, it did help the people who wore it,” says Franke, “and it did clear out a tank of smoke. And it’s something that we could recommend to people with a few caveats about the downsides.”
The downside? The price for one — nearly $100. Plus, testers complained it is heavy and unattractive. So, the purifier gets a reality check of three stars. But it gets a gold star from Carol Wapner who never thought she could spend this much time up close and personal with one cat, much less 18!
“No reaction,” says Wapner. “It’s amazing. Thirty minutes, half an hour.” The manufacturer of the air purifier says it now sells a smaller, lighter model that is 20 dollars cheaper (unit is actually more actually, error by dateline).
Is There Finally a Replacement for Mercury Cells? It Looks that Way, But it Sure Took Some Doing
Finally! Wein develops a replacement for mercury cells.
No subject that I’ve written about lo these many years has raised the hackles of so many readers of this column as the imminent demise of mercury button batteries. The reasons are obvious. Many expensive vintage cameras and exposure meters–from Leica CLs to Gossen Lunasixes to Nikon Photomic meter prisms to Konica Autoreflexes–in order to function properly, depend on the steady voltage supplied by mercuric oxide cells. And, as we’ve discovered in testing them, alkaline batteries are a poor substitute, even if they’re the same size and deliver a similar initial output.
Several readers, and many electronics experts, have suggested using zinc-air batteries, the kind often found in hearing aids, as a replacement for mercury cells. Certainly, the zinc-air chemistry offers one of the few viable alternatives to mercuric oxide in terms of delivering steady voltage and having a high energy storage capacity. Also, the voltage level supplied by unmodified zinc-air cells designed for hearing aids is acceptably close to that provided by mercury cells. Indeed, several experimenters, including yours truly, have used them successfully (albeit with jury-rigged adapters and spacers) in mercury-powered cameras and meters.
However, running promising experiments is one thing; producing a commercially successful replacement for mercury cells is quite another. Fortunately, one company, Wein Products, Inc. of Los Angeles, California, decided to take up the challenge. As you’ll soon see, they faced some formidable obstacles.
The main problem Wein’s engineers confronted is that a zinc-air battery starts producing electricity in usable quantities as soon as you remove the adhesive seal from the back of the cell. This lets oxygen into the cell through tiny holes in the back, which feeds the chemical reaction.
The reaction continues to produce current even when you’re not drawing any–but at a somewhat slower rate. As a result, the zinc air button cells used in hearing aids and similar devices have an unusually short life compared with other battery types. Their lifespan is further curtailed by moisture evaporating through the air holes.
Most zinc-air button cells designed primarily for use in hearing aids are well suited to this application. They’re much lighter in weight than mercury button cells, provide a steady voltage output, and have sufficient energy capacity. They also contain far less toxic material than do mercury cells, which makes their disposal more environmentally friendly.
The fact that they can dry out and run down in a couple of months or less is of little consequence when they’re used in hearing aids. Hearing aids draw far more current than do exposure meter circuits, so the cells inevitably run down quite a bit sooner than that. In photo applications, the current draw is so low, however, that zinc-air cells could theoretically last as long as mercury cells.
Conventional zinc-air button cells produce 1.4 volts each. The chemical mix in Wein’s newly developed MRB625’s has been altered, so they put out a nominal 1.36 volts when the cells are activated. Also, the Wein cells have only two air holes, compared with three or four in hearing aid cells, which helps slow down drying out and lets less oxygen into the cell.
According to Wein, the majority of photo exposure meters and cameras designed for mercury cells draw no more than 200 microamperes of current–even in bright sunlight. Thus, not much oxygen is needed to keep the cells working briskly enough to power photo equipment. Since hearing aid cells need to supply over one milliampere (1000 microamperes), they need more air–hence, more air holes.
Wein estimates, on the basis of lab tests and field trials, that a set of their cells should give about three months of service once the seals are removed. They should last several years if kept sealed.
But do the Wein cells deliver power at as constant a rate as mercury cells? To compare their voltage stability, we placed two different post-production versions of the Wein cells, one Rayovac zinc-air hearing aid cell, and a 625 mercury button cell on 200 microampere loads on the lab bench. During two months of continuous current drain, none of the cells’ output dropped more than a few thousandths of a volt. However, the Wein cells dropped only about half as many millivolts as the hearing aid cell did–an impressive performance.
But how well do these Wein cells actually work in exposure meters? To find out, we tested two different pre-release versions in our lab. One type put out about 1.325 volts; the other, about 1.314 volts. Wein will be producing only one of the two types when the new batteries are officially released at the 1995 Photo Marketing Association show. Based on our tests, the difference between them appears insignificant.
In our trials using a Gossen Luna-Pro exposure meter, we got the same readings whether we used brand-new 625 mercury cells, a set of mercury cells that had been in the meter for about three years, or either set of Wein cells. The readings among all four sets varied less than a third of a stop.
Out of curiosity, we also tried a set of Rayovac Pro Line 675A zinc-air hearing aid batteries in the Luna-Pro. We got just about the same readings using these cells as well.
As we mentioned in a previous column (September ’94, page 144), you shouldn’t leave spent zinc-air cells in your camera equipment for more than a couple of months. We’ve been advised by hearing aid battery manufacturers that old cells could leak chemicals out of the vent holes. The risk is said to be greatest if the cells are completely run down.
To check the validity of this admonition, we placed a 675A hearing aid battery, with its seal removed, on top of our desk, for one month. Afterwards, to kill it off, we shorted it out with a bent paper clip for 48 hours. We then removed the paper clip. After a second month on my desk the cell still didn’t leak. Of course, just because this particular cell hasn’t leaked to date doesn’t mean you shouldn’t heed the manufacturers’ advice. After all, these folks have examined and tested more batteries than any of us ever will.
By the way, we were astonished to find that after two months and the paper clip trick, a subsequent test of the hearing aid cell showed that it was still putting out over 1.3 volts. Even more interesting, it pushed the needle of a mercury battery tester far into the green! The meter itself draws about one milliampere when set for testing mercury batteries.
One drawback of both the 675A and the prototype Wein cells we tested is that they’re too small to serve as direct replacements for the most commonly used mercury cells – the 625’s. Both are the same diameter as the tiny 675 mercury button cells.
To help them fit the Gossen Luna-Pro, we fashioned a cylinder of thin cardboard cut from a file card. The strip was ⅜-inch wide. We coated the strip with glue and rolled it into a cylinder ½ inch in diameter on the inside. When the glue was dry, we slipped a pair of cells into the cylinder and put the combination into the meter. We also found it necessary to pry up the battery-compartment lid’s spring a bit to get a better contact with the cells since they’re also a tiny bit shorter than 625 cells. Once we had done these things, the cells stayed in place and worked just fine.
We’ve saved the best news for last. By the time you read this, Wein should be marketing their new cells in the larger 625 size. This will make them much easier to use, without any adaptations needed, in a much wider variety of photo equipment. They’re packaged individually at $5.95 per cell, a relatively small price to pay to keep your costly vintage equipment operational. They’ll also be sold to service centers in packs of ten.
While we haven’t yet evaluated the production versions of any Wein cells, our hunch, on the basis of preliminary testing, is that they should, during their shorter life, work as well as mercury cells in most cameras and meters. They also may be even less prone to leaking than conventional zinc-air cells and may last far longer in photographic applications. As soon as we can get our hands–and measuring devices–on over-the-counter Wein cells, we’ll definitely put ‘em through their paces and report our findings in detail.
In the meantime, herewith some suggestions for potential users. To prevent corrosion, we strongly recommend that you remove Wein or zinc-air cells from your equipment after they’ve been in service for three months or so. In fact, Wein suggests that you can increase the cells’ useful lifespan by removing them from your meter or camera and replacing the peel-off seals if you don’t intend to use your equipment for a few days or longer. This should help keep the cells from drying out. A final energy-saving tip: Don’t activate fresh cells until you actually plan to use the equipment; leave their original seals intact.
It goes without saying that we’re very interested in hearing from our readers about their experiences – both positive and negative – with these new batteries. Just drop a line (snail mail only, please) to Cell Mates, c/o Popular Photography, 1633 Broadway, New York, NY 10019.