A Guide to Air-Purifying Respirators 

Air-purifying respirators (APRs) work by removing gases, vapors, aerosols (airborne droplets and solid particles), or a combination of contaminants from the air through the use of filters, cartridges, or canisters. These 

respirators do not supply oxygen from other than the working atmosphere, and therefore cannot be used in an 

atmosphere that is oxygen-deficient1 or immediately dangerous to life or health2 (IDLH). The appropriate respirator for a particular situation will depend on the environment and the contaminant(s).

Filtering Facepiece Respirators

Filtering facepiece respirators (FFRs) remove particles from 

the inhaled airstream of the wearer. They may be referred to 

as “N95 respirators”. They are also sometimes called disposable respirators because the entire respirator is discarded 

when it becomes unsuitable for further use because of 

hygiene, excessive resistance, or physical damage. 

FFRs are divided into classes based on their filtration capabilities. “N95” is a term referring to the N95 filter class, which 

removes at least 95% of airborne particles using a “most-penetrating” sized particle during “worst case” NIOSH testing. 

The FFR classes include N (not resistant to oil), R (somewhat resistant to oil), and P (strongly resistant to oil) 

series, which are available at 95, 99, and 100 filtration efficiency levels. 

FFRs provide protection against particles, but not gases or vapors, and should not be used for respiratory protection to protect against hazardous gases or vapors. These classes and oil-resistant designations are applicable to 

all types of air-purifying respirators. 

FFRs form a tight seal against the user’s face, covering the nose and mouth. As 

the user inhales air through the facepiece, particulate material collects on the 

fibrous material of the filter, which removes the particulate contaminant from 

the airstream. An FFR may have an exhalation valve located on the filter, which 

reduces breathing resistance during exhalation. 

Photo courtesy of Shutterstock 

1

 OSHA CFR 1910.134(b) defines oxygen-deficient as an atmosphere with an 

 oxygen content below 19.5% by volume.

2 IDLH values can be found at: https://www.cdc.gov/niosh/idlh/intridl4.html

N95, N99, N100 – Filters at least 95%, 99%, 99.97% of airborne particles. Not resistant to oil.

R95, R99, R100 – Filters at least 95%, 99%, 99.97% of airborne particles. Somewhat resistant to oil.

P95, P99, P100 – Filters at least 95%, 99%, 99.97% of airborne particles. Strongly resistant to oil.

Photo courtesy of Shutterstock
Elastomeric Half Facepiece Respirators

Elastomeric half facepiece and quarter facepiece respirators are reusable 

devices with exchangeable cartridges or filters. The facepiece is made of 

rubber or silicone that forms a seal against the user’s face. The facepiece 

of the elastomeric respirator must form a tight seal against the user’s 

face, covering the nose and mouth just like the disposable FFRs; therefore, fit testing is required. The attached filters and cartridges are replaceable and can be easily changed. Elastomeric respirators can be used to protect against 

gases, vapors, and/or particles if equipped with the appropriate filters and/or cartridges. 

When cleaning and sanitizing a respirator, the manufacturer’s guidelines should always be followed. Check the 

manufacturer’s website if guidance is not included with the packaging of the respirator. If guidance isn’t available, OSHA provides general cleaning and sanitizing guidelines. Elastomeric half facepiece respirators have an 

APF of 10.

OSHA Definitions of Filter and Cartridge/Canister, CFR 1910.134(b)

Filter or air-purifying element means a component used in respirators to remove solid or liquid aerosols from the 

inspired air. 

Canister3

 or cartridge means a container with a filter, sorbent, catalyst, or combination of these items, which 

removes specific contaminants from the air passed through the container.

Elastomeric Full Facepiece Respirators

Like the elastomeric half facepiece respirator, the elastomeric full facepiece respirator is a reusable device. This type of respiratory protective device uses exchangeable 

cartridges, canisters, or filters. It is also made of rubber or silicone, but the elastomeric full facepiece has a clear plastic lens that covers the face and provides eye 

protection. The full facepiece covers roughly from the hairline to below the chin. 

These types of respirators tend to provide a more reliable face seal than FFRs or 

elastomeric half facepiece respirators. Since these respirators cover the user’s face 

and eyes, they can also be used to protect against liquid splashes and irritating vapors. 

Annual fit testing is still required. Elastomeric full facepiece respirators have an APF of 50.

Photo courtesy on Shutterstock 

Photo courtesy of Honeywell 

International Inc

3 A canister on a tight fitting full facepiece or PAPR can be used for escape from unknown concentrations of gas or vapor hazards whereas a 

cartridge based system cannot be used in this capacity. 

Because the effectiveness of this type of respirator relies upon the breathing air travelling through the filter, a 

tight seal to the user’s face is very important. Therefore, the Occupational Safety and Health Administration 

(OSHA) (29 CFR 1910.134) requires an annual respirator fit test to ensure that users receive the expected level 

of protection by minimizing any leakage of unfiltered contaminant through gaps between the face and facepiece. 

When used with a respiratory protection program, including annual fit-testing, an FFR will reduce exposures by 

1/10th. Another way to express this is that the OSHA Assigned Protection Factor (APF) is 10. For proper donning (putting on) and doffing (taking off) techniques of this type of respiratory protection, refer to the manufacturer’s instructions. 

Filtering Facepiece Respirators (continued)
Powered Air-Purifying Respirator

Powered Air-Purifying Respirators (PAPRs) are battery-powered devices that 

use a blower to pull air through attached filters (for particles) or cartridges 

(for gases or vapors) to clean it before delivering it to the breathing zone of 

the wearer. High-efficiency (HE) filters are the only class of particulate filters 

available for powered air-purifying respirators. The benefits of PAPRs include 

a low breathing resistance with a high level of protection. PAPRs can be used 

to protect against gases, vapors, or particles, if equipped with the appropriate 

cartridge, canister, or filter. PAPRs are generally more protective than non-powered half mask respirators because the blower creates positive pressure inside 

the facepiece under most work conditions, which reduces inward leakage of 

potentially contaminated air. A half facepiece PAPR has an APF of 50, and a full 

facepiece PAPR has an APF of 1,000.

A PAPR may have a tight-fitting half or full facepiece or a loose-fitting facepiece, 

hood, or helmet. The loose-fitting PAPR does not require fit testing. Loose-fitting 

PAPRs may be an alternative for users who have facial hair or are otherwise not 

able to pass a fit test with a tight-fitting respirator. However, OSHA does require fit 

testing for a tight-fitting PAPR3

. Loose-fitting PAPRs have an APF of 25. Loosefitting PAPRs with a helmet or hood can have an APF up to 1,000 if supported by 

manufacturer-supplied test evidence.

 References

 Occupational Safety and Health Administration (OSHA) CFR 1910.134 https://www. 

 osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=12716 

 National Institute for Occupational Safety and Health (NIOSH): NIOSH Guide to Industrial 

 Respiratory Protection. DHHS (NIOSH) Publication No. 87-116. Cincinnati, Ohio: NIOSH, 1987. 

 http://www.cdc.gov/niosh/docs/87-116/ 

 National Institute for Occupational Safety and Health (NIOSH): Hospital Respiratory Protection Program 

 Toolkit. DHHS (NIOSH) Publication No. 2015-117. Pittsburgh, Pennsylvania: NIOSH, 2015. https://www.cdc.gov/ 

 niosh/docs/2015-117/pdfs/2015-117.pdf?id=10.26616/NIOSHPUB2015117 

4

 OSHA CFR 1910.134(f)(8) states that fit testing of tight-fitting atmosphere-supplying respirators and tight-fitting powered air-purifying respirators shall be accomplished by performing quantitative or qualitative fit testing in the negative pressure mode, regardless of the mode of operation 

(negative or positive pressure) that is used for respiratory protection.

This document is in the public domain

and may be freely copied or reprinted. 

DOI: https://doi.org/10.26616/NIOSHPUB2018176

DHHS (NIOSH) Publication No. 2018-176

August 2018

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Photo courtesy of Honeywell 

International Inc. 

Photo courtesy of MSA