Comparisons of two common bioaerosol samplers were made after sampling and enumeration of airborne fungal propagules in several office structures on a university campus in Southern California. Data collected on five occasions throughout the year showed that a Surface Air Systems (SAS) high flow portable sampler recovered consistently lower levels of colony forming units (cfu) than an Andersen N6 single stage impactor. There was no difference statistically between the samplers when concentrations of Cladosporium were compared. Compared to the Andersen N6, the SAS sampler recovered about half the number of cfu for three other fungal categories, i.e. non-sporulating species, Aspergillus and Penicillium and others. Differences in sampler efficiencies are discussed in terms of effective particle diameters. Counts of culturable airborne fungal spores obtained with the SAS sampler should be interpreted with caution when genera other than Cladosporium predominate.
Exhalation valves are a critical component of industrial respirators. They are designed to permit minimal inward leakage of air contaminants during inhalation and provide low resistance during exhalation. Under normal conditions, penetration of aerosol through exhalation valves is minimal. The exhalation valve is, however, a vulnerable component of a respirator and under actual working conditions may become dirty or damaged to the point of causing significant leakage. Aerosol penetration was measured for normal exhalation valves and valves compromised by paint or fine copper wires on the valve seat. Penetration increased with increasing wire diameter. A wire 250 microns in diameter allowed greater than 1% penetration into the mask cavity. Dirt or paint accumulated on the exhalation valve allowed a similar level of penetration. Work rate had little effect on observed penetration. Penetration decreased significantly with increasing aerosol particle size. The amount of material on the valve or valve seat necessary for significant (greater than 0.5%) inward leakage in a half-mask respirator could be readily observed by careful inspection of the exhalation valve and its seat in good lighting conditions.
A performance model for half-mask and single-use respirators is presented. It represents a possible alternative to field measurements of respirator performance. Experimental data on filter and leak performance given in Part I were used to develop a model that allows one to predict 1) the overall respirator penetration as a function of particle size for any work rate and 2) overall total mass penetration for any work rate and exposure aerosol-size distribution for a known respirator filter and facial seal leak condition. A simplified method based on general regression equations is presented that allows one to estimate these quantities based on QNFT (quantitative fit testing) measurements and a knowledge of the exposure aerosol-size distribution. Example calculations are given for a situation in which QNFT gives a fit factor of 50 for a half-mask with dust, fume and mist filter cartridges, but predicted protection factors for various use conditions range from 20 to 81 depending on exposure particle-size distribution and work rate of the wearer.
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