CDC Workshop on Respiratory Protection for Airborne Infectious Agents
CDC | UofC | CHRAS | Aerosol Science | Lab Test
November, 2004

CDC Workshop on Respiratory Protection for Airborne Infectious Agents

Agenda and Abstracts

Respirator Performance with Infectious Agents

 

SA Grinshpun
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.