Selecting Respirators with Confidence

You must meet OSHA's PELs, but you may decide to meet other, stricter exposure recommendations as a good practice.

HAVE you ever cringed to see someone wearing a filtering facepiece for protection from exposure to organic vapors? The worker probably thought one respirator was as good as another. Misunderstandings in respirator selection can lead to overexposures and illness.

Identify the Contaminants
Selecting the correct respirators to protect employees from exposures to air contaminants starts with meeting the requirements of OSHA's Hazard Communication standard (29 CFR 1910.1200). Before employees can be protected, the air contaminants have to be identified. Material Safety Data Sheets provide valuable information.

Closely observe work practices to complete the picture of how employees are exposed. How do operations generate dust, mist, fumes, vapors, or gases? Pin down the sources of exposure, the length of time workers are exposed, the amount of physical exertion and movement required during the job, and other factors that influence respirator selection.

Review Exposure Limits
Once you know the identities of the chemicals to which employees are exposed, you can review information on exposure limits. Meeting OSHA's permissible exposure limits (PELs) outlined in the air contaminants standard (29 CFR 1910.1000) is mandatory; however, there are other sources of exposure recommendations to consider, too.

Acting under the authority of the Occupational Safety and Health Act of 1970 (OSH Act), the National Institute for Occupational Safety and Health develops recommended exposure limits (RELs). To formulate these recommendations, NIOSH evaluates medical, biological, engineering, chemical, trade, and other information relevant to the hazard. NIOSH transmits these recommendations to OSHA and publishes them in a variety of documents, including the NIOSH Pocket Guide To Chemical Hazards. More information is available from the NIOSH Web site at:

The American Conference of Governmental Industrial Hygienists (ACGIH®) publishes Threshold Limit Values (TLVs®) for Chemical Substances and Physical Agents and Biological Exposure Indices (BEIs®) each year, as ratified by the organization's Board of Directors. ACGIH® Worldwide is a member-based organization that advances worker health and safety through education and the development and dissemination of scientific and technical knowledge. The TLVs® and BEIs® are health-based values established by committees that review existing published and peer-reviewed literature in various scientific disciplines.

Based on the available information, ACGIH® formulates a conclusion on what level of exposure the typical worker can experience without adverse health effects. There is no consideration given to economic or technical feasibility. TLVs® and BEIs® are guidelines to be used by professionals trained in the practice of industrial hygiene. More information is available from

You must meet OSHA's PELs. However, other exposure recommendations may be more stringent. You may decide to meet these stricter exposure recommendations as a good practice.

If OSHA hasn't set a PEL for a contaminant, you still have to meet the OSH Act's Section 5(a)(1) (the "general duty clause") requirements to provide a safe workplace. These other exposure recommendations, along with the OSHA PELs promulgated in 1989 that were subsequently vacated by court action in 1992, can guide you to meet general duty clause obligations.

Measure Employee Exposures
Don't rely on a novice to measure employee exposures. OSHA's air contaminants standard states at 1910.1000(e) that "a competent industrial hygienist or other technically qualified person" needs to approve administrative or engineering controls or protective equipment used to meet exposure limit requirements.

Work with the person conducting your exposure monitoring to ensure you get the most reliable results and best recommendations. Exposure monitoring should be done to capture information on employees' greatest exposures. Employee protection is most assured when control measures are implemented to address the highest anticipated levels of exposure.

Implement Control Measures
As noted in both OSHA's air contaminants and respiratory protection standards, the use of respiratory protection is appropriate only after you have determined and implemented feasible administrative or engineering controls (see 1910.1000(e) and 1910.134(a)(1)).

Respirators should be the last defense from harmful exposures to air contaminants. OSHA would rather see employers enclosing or confining the source of contaminants, using general and local ventilation, and substituting less toxic materials to control exposures than requiring employees to wear respirators. You can identify effective control measures only when you have information on employee exposures, exposure limits, and employee work practices. Experts, such as industrial hygienists, can recommend effective control measures.

Review APFs and MUCs to Select Respirators
Effective Nov. 22, 2006, employers are to use the assigned protection factors (APFs) and maximum use concentrations (MUCs) to select respirators that meet or exceed the required level of employee protection as outlined in the revision to the respiratory protection standard published in the Aug. 24, 2006, Federal Register.

Revised 1910.134(b) states: "Assigned protection factor means the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program."

Use APFs to select the appropriate type of respirator based upon the exposure limit of a contaminant and the level of the contaminant in the workplace. Select respirators by comparing the exposure level found in the workplace to the maximum concentration of the contaminant in which a particular type of respirator can be used (the maximum use concentration, or MUC). In general, you can determine the MUC by multiplying the respirator's APF by the contaminant's exposure limit. If the workplace level of the contaminant is expected to exceed the respirator's MUC, you must choose a respirator with a higher APF.

Examples of OSHA's Assigned Protection Factors

Type of respirator


Filtering facepiece


Half-mask air-purifying respirator with elastomeric facepiece


Full-facepiece air-purifying respirator with elastomeric facepiece


Powered air-purifying respirator with tight-fitting half-mask facepiece


Powered air-purifying respirator with tight-fitting full-facepiece


Powered air-purifying respirator with a loose-fitting facepiece


For example, a full-facepiece air-purifying respirator has an APF equal to 50. The chemical dimethylformamide has a PEL of 10 parts per million (ppm) as an eight-hour time weighted average. Multiplying the APF by the PEL gives a MUC equal to 500 ppm for this application. The workplace level of dimethylformamide is expected to reach 30 ppm. In this example, the respirator is expected to offer enough protection--30 ppm is less than the MUC of 500 ppm.

Note NIOSH Approvals
OSHA requires employers to select NIOSH-certified respirators (see 1910.134(d)(1)(ii)). NIOSH evaluates and approves respirators per the requirements of 42 CFR part 84. The manufacturer of a NIOSH-certified respirator provides a copy of the NIOSH approval with the respirator. The NIOSH approval indicates those contaminants and airborne concentrations for which use of the respirator is approved. Use only a respirator that is approved for the contaminants and exposures in your workplace.

If the calculated MUC exceeds the NIOSH-approval performance limits of a respirator's cartridge or canister, the MUC must be recognized as the lower limit based on the approved performance limits. For example, an employee will wear a full-facepiece air-purifying respirator with an APF equal to 50 while exposed to methyl ethyl ketone vapor. The PEL for methyl ethyl ketone is 200 ppm as an eight-hour TWA. The MUC would calculate to 10,000. However, because NIOSH approved the respirator's cartridge for a maximum of 1,000 ppm of organic vapor, the MUC must be recognized as the lower 1,000 ppm.

Complete the Program
Even though you're ready to provide respirators, you don't yet know that your employees are medically qualified to use them. The physician or other licensed health care professional has to have information on the type of respiratory protection to be provided in order to make the determination it will be safe for the employees' health to wear the protection.

Once you know the employee is medically able to wear the selected respirator, you need to make sure an employee using a respirator with a tight-fitting facepiece has a good fit. OSHA's respiratory protection standard outlines accepted qualitative and quantitative fit test protocols. The appropriate fit test depends on factors including:

  • The type of respirator,
  • The contaminant, and
  • The expected concentration of the contaminant in the workplace.

The respiratory protection program isn't complete until you include, as applicable, provisions for:

  • Chemical cartridge/canister change-out schedules,
  • Procedures to use respirators in environments immediately dangerous to life and health,
  • Supplied air breathing quality and use,
  • Respirator maintenance and care,
  • Employee training, and
  • Program evaluation and recordkeeping.

When OSHA finalized the respiratory protection standard in 1998, the agency's best estimates were that the rule would avert more than 4,000 work-related injuries and illnesses and more than 900 deaths each year. This goal can be achieved when respirator selection involves matching a careful assessment of the hazards to the capabilities and limitations of the respirator.

This article appeared in the November 2006 issue of Occupational Health & Safety.

This article originally appeared in the November 2006 issue of Occupational Health & Safety.

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