Selecting respirators for control of worker exposure to infectious aerosols.

A method for selecting respirators for protection in infectious aerosol environments was developed, building on a procedure used to choose respiratory protection for environments containing nonbiological contaminants. Modifications in the traditional respirator selection method are proposed for situations where information on occupational exposure limits, toxicity, and airborne concentrations is absent. Toxicity is determined from risk rankings proposed by a variety of organizations. The nature of the activity allows assessment of source generation, which is combined with room volume and airflow to obtain a ranking of airborne concentration. Finally, concentration and toxicity ranks determine a minimum assigned protection factor, which corresponds to a respirator class. Case studies are presented to illustrate the proposed decision logic. For each situation, the procedure yielded choices that were both protective and reasonable. These results suggest that the procedure will be applicable to a variety of settings for a range of infectious organisms.

Improved methods for generation, sampling, and recovery of biological aerosols in filter challenge tests.

In preparation for filter efficiency tests and sampler comparison studies, methods of biological aerosol generation, sampling, and filter recovery were modified from previous studies. Methods described include (1) techniques for generating aerosols that reduced nuisance particles to negligible levels and increased the cell culturability of Mycobacterium abscessus by 30%, (2) sampling techniques that lowered the detectable range of biological particle size from 0.65 to 0.45 micron and reduced the sampling flow from the chamber from 28.3 to 1.5 L/min, and (3) development of methods to remove culturable organisms from respirator filter media. These methods were developed for filter challenge tests with M. abscessus and were applied to two other bacteria. They may also have application to a wider variety of organisms and bioaerosol assessments.

Collection of three bacterial aerosols by respirator and surgical mask filters under varying conditions of flow and relative humidity.

A variety of respirator filters and surgical masks were challenged with three aerosolized bacteria: Mycobacterium abscessus (M.a.) (a rod), Staphylococcus epidermidis (S.e.) (a sphere), and Bacillus subtilis (B.s.) (a rod). Tests were conducted at two flow rates (45 and 85 l./min) and two humidity levels (30 and 70%). Aerosols were measured with a total-particle, direct-reading, spectrometer and a viable particle cascade impactor. Measurements up- and downstream of the filter or mask were used in determining aerosol penetration; respirator or surgical mask fit was not evaluated. Bioaerosol penetration measured with two aerosol sampling instruments was found to correlate. Additionally, bioaerosol test parameters were evaluated with respect to their effect on penetration. Increasing flow resulted in increased penetration of all organisms while an increase in relative humidity did not exert a consistent effect on all organisms. Of the respirators approved by the National Institute for Occupational Safety and Health (NIOSH), filter efficiency was as expected with dust/mist respirators having the lowest and HEPA filters the highest efficiency. Surgical masks were the least efficient of all filters tested; these are not certified by NIOSH. Bioaerosol penetration was compared to that of a polystyrene latex sphere (PSL) aerosol. Penetration of the test aerosols was predicted on the basis of particle aerodynamic diameter and was expected to be in this order: PSL > M.a. > S.e. = B.s. The PSL aerosol was the most penetrating, as predicted. However, results showed that B.s. was more penetrating than S.e. The aerodynamic diameter may not be the best parameter for predicting aerosol penetration of non-spherical particles in these filters.