Classification and Use of HEPA Filters in Respiratory Protection Equipment

Filter Classification and Efficiency

The National Institute for Occupational Safety and Health (NIOSH) classifies HEPA filters as air-purifying respirators of type P-100 (or N-100, R-100), representing the highest level of protection with a filtration efficiency of 99.97% for particles of 0.3 microns 1
HEPA filters correspond specifically to the P-100 category (or its equivalents N-100, R-100), placing them at the highest level of respiratory protection against particles 1
A P-100 respirator allows for a maximum penetration of 0.03%, whereas an N95 respirator allows for a penetration of 5% 1
Therefore, a P-100 filter is more than 100 times more effective than an N95 filter for removing biological agents such as viruses 1

HEPA filters can be installed in reusable respirators with replaceable filters 2
When used in particulate air-purifying respirators, the efficiency of the HEPA filter is so high (effectively 100%) that leakage through the filter is not a consideration 2
Practically all inward leakage of droplet nuclei occurs at the facial seal of the respirator, not the filter 2
Powered air-purifying respirators (PAPR) equipped with HEPA filters provide the highest level of protection against aerosols 1, 3
PAPR with fitted facepieces have less than 2% leakage at the facial seal under routine conditions 2
PAPR with loose-fitting facepieces, hoods, or helmets have less than 4% leakage at the facial seal 2

The Occupational Safety and Health Administration (OSHA) regulations state that "where workers are exposed to a hazard that would require the use of a respirator with HEPA filtration, the appropriate class of respirator under the certification 42 CFR Part 84 is the Type 100 (N-100, R-100, or P-100)" 1
The National Institute for Occupational Safety and Health (NIOSH) recommends a filter efficiency of P-100, consistent with their recommendations for emergency response to biological incidents 1
Respirators must be certified by NIOSH and marked with the manufacturer's name, part number, level of protection, and "NIOSH" 4

A respirator, regardless of type, only traps the COVID-19 virus, it does not destroy or inactivate it 1
There are no known safe exposure levels for biological aerosols; respirators can reduce inhalation exposures but cannot eliminate the risk of infection 1
Disposable respirators must have elastomeric components that improve the seal (foam, rubber, or plastic), and two or more adjustable suspension straps to maintain a proper fit 1