Using an Air-Purifying Respirator (APR)

Air purifying respirators purify the surrounding air and prevent inhalation of airborne dusts or chemicals through disposable cartridges.


Respirators are a last resort when engineering and work practice methods have already been used to control harmful exposures to the extent feasible or while those methods are being implemented.  Respirator use must be part of a complete respiratory protection program. The employer must determine that respirators users are medically cleared to wear a respirator and trained in the proper donning, doffing, use and maintenance of the assigned device. Reusable respirators must be properly maintained, cleaned and stored.  Fit testing is an essential part of a respiratory protection program.

A respirator must be selected based on the type and level of hazard exposure.

A respirator must either be supplied with air that meets OSHA standards or be fitted with air purifying cartridges or filters that are matched to the exposure.  This solution addresses only air purifying respirators. 

Respirator use is a last resort when feasible engineering and work practice methods are not fully effective in controlling harmful airborne exposures to below allowable limits.   Even if respirators will still be necessary:

  • use chemical products that produce the lowest hazard levels while meeting specifications;
  • use the best available ventilation;
  • limit unnecessary access to the contaminated area to the extent feasible;
  • avoid entering areas of elevated exposure to materials used by other workers whenever feasible; and
  • use respiratory protection to control the remaining exposure when air contaminants are still not adequately controlled even when following these and other engineering and work practice methods.

If you work as an independent contractor you can obtain respirator selection and use information from the manufacturer of the respirator that you are using. Some safety supply companies also offer expert guidance. With regards to selecting the appropriate respirator and filters/cartridges, information is available from NIOSH and all manufacturers.  You must know what you are exposed to and what the level of exposure is to properly select a respirator and appropriate filters or cartridges.


Do not use an air purifying respirator in an Immediately Dangerous to Life or Health (IDLH) environment, including oxygen deficient atmospheres (less than 19.5% ).


The following information applies to the use of an air purifying respirator (APR). If you wear an air purifying respirator at work:

  • Use only a model and size for which you have been successfully fitted.  Unfitted respirators may not provide effective protection.
  • Ensure that there is no beard or hair in the respirator sealing area. Even a light beard can break the seal and does not act as an effective filter.
  • Fit check the respirator after each donning and adjust the straps until you have a reliable seal.
  • Make sure that you install the correct cartridge for the exposure. Refer to the product SDS if you are not sure about what's in the materials that you are using. Compare your exposure to the respirator manufacturer's cartridge selection chart or web tool. Respirator bodies and filters/cartridges are certified as a unit - do not mix component from different manufacturers.
  • Follow your employer’s cartridge change schedule, but if you smell the contaminant or feel irritation or other symptom of exposure while wearing the respirator, there may be a break-through.  Leave the exposure area and change the cartridges even if it is before the specified change time. 
  • If you experience difficulty in breathing, the filters may be overloaded and should be changed.
  • If there is evidence of deterioration, the filters or cartridges may not work effectively anymore and should be changed.
  • Start the day with a fresh chemical cartridge. Do not reuse a chemical cartridge on a second day.
  • When you finish for the day, clean and properly store the respirator. Remove and discard the cartridges or filters.

Filters remove solid particles and aerosols but not vapors or gases. They are rated for three levels of oil resistance and three levels of filtration efficiency.  The classification of "N" means the filter is not resistant to oil; "R" means the filter can resist oil and "P" means that the filter is oil-proof. A "P" or "R" filter must be used when oil mists are present.  Filters are rated at 95%, 99% or 99.97% efficiency.  99.97% efficient filters are labeled at 100. An N95 filter (commonly used in general construction) is acceptable if you only need to remove 95% of particles in an oil free environment.  Higher rated filters are needed in more extreme situations.  Filter efficiency must also be factored when calculating the maximum use level of a respirator.  For a half-face respirator with an N95 filter, the total leakage is calculated as 10% (around the face piece) + 5% (through the filter).

For workers exposed to engineered nanomaterials, NIOSH has concluded that N95 and P100 particulate filters provide the expected filtration efficiency according to their efficiency ratings (Rengasamy, et al 2009). However, both OSHA and NIOSH recommend that N100 or P100 filters be used when workers are exposed to high levels of airborne engineered nanomaterials (OSHA Fact Sheet FS-3634; NIOSH blog post December 7, 2011). Surveys have shown that the most common respirators that are in use against engineered nanomaterials are P100 filters on elastomeric half mask or filtering facepiece respirators (Conti, et al 2008).

For chemical cartridges, a qualified person must establish a cartridge change schedule. It is essential to know the nature and level of all contaminants that will or may be in the workplace air to select a respirator and filter and to establish a cartridge change schedule.  Work level, humidity and altitude will also effect respirator selection and performance.  For painting tasks, a combination particle and organic vapor cartridge may be required and a pre-filter may also be used to limit filter overloading.

E-tools are available that can provide expert guidance in determining medical clearance to wear a respirator, selecting respirators and cartridges, and in establishing cartridge change schedules.

OSHA provides a compliance guide for small employers with references to applicable standards and Cal OSHA provides an extensive guide to respirator selection and use, including fit checking, cleaning and storage. For work with lead, asbestos, or methylene chloride workers and their employer must adhere to additional specific requirements for respirator selection.  If you elect to voluntarily wear a respirator, even though you are not legally overexposed, you may do so, but your employer must include you in the respiratory protection program unless the respirator that you select is a filtering face piece.  If you voluntarily wear a filtering face piece your employer only needs to provide you with a copy of Appendix D of the respiratory protection standard.  Surgical masks, bandanas or other non-certified filters do not provide reliable protection and they are not permitted by OSHA to be used to protect workers from inhalation hazards. For reliable protection, OSHA requires the use of a NIOSH-certified filtering face piece.

Risks Addressed:

Airborne toxic dusts, mists, vapors, mists, and fumes, including airborne engineered nanomaterials. Air purifying respirators filter but do not provide breathing air and are not reliably effective against most gases, especially carbon monoxide.

How Risks are Reduced:

Air purifying respirators form a tight seal around the face.  Solid contaminants are removed by the filters, including, for example, airborne nanoparticles generated from activities on nano-enabled construction products.  Vapors are removed by packing material inside the cartridge that physically or chemically causes the contaminant to adhere to the filtering media. 

Air-purifying respirators work by either filtering particles from the air or chemically cleaning (purifying) the air.  Solid contaminants, including particles of engineered nanomaterials, are removed by filters when the user breathes in through the respirator.  Likewise, vapors are removed by the chemical media, located inside cartridges that can physically or chemically cause the contaminant to adhere. The ability of a chemical cartridge to remove contaminants is limited by the attraction between the packing material and the contaminant and by the amount of surface areas within the packing for adherence by all vapors in the air, including water.  Also, to ensure that a particular respirator performs as the manufacturer claims, NIOSH established the National Personal Protective Technology Laboratory (NPPTL) as one of the research laboratories to help certify these APRs under NIOSH 42 CFR Part 84.

Effects on Productivity:

Respirators may slow the work process and reduce productivity.


Jean Christophe Le, MPH, Buck Cameron - CPWR - The Center for Construction Research and Training

Bill Kojola – CPWR – The Center for Construction Research and Training

Hazards Addressed:


Respirators are available at local safety supply stores and online. Please visit our related solutions below for the appropriate APF level.

Return on Investment

To calculate the return on investment (ROI) for your specific application, please visit our Return on Investment Calculator. While a specific ROI example has not been developed for this particular solution, the ROI Calculator provides a useful tool and guidance on how to generate your own on investment analysis.