Editor’s note:
This article introduces recently revised performance terms for respiratory protection. The revision was a project of the AIHA Respiratory Protection Committee. A complete list of new and revised definitions follows this article.​

Health and safety practitioners, program administrators, and users of respiratory protection are likely familiar with the term “protection factor,” which has been in comm​on use since the mid-1970s. The term was originally intended to express the level of protection a given type of respirator would provide when worn. Mathematically, the protection factor was expressed as the ratio of challenge agent outside a respirator (Co) to that which would penetrate into the wearer’s breathing zone (Ci). The “original” protection factors used in the United States were based on quantitative fit-testing studies performed at Los Alamos National Laboratory (formerly Los Alamos Scientific Laboratory).​

In the early 1980s it was recognized that respirator performance is a function of where and how the measurements are made. For example, Co and Ci measurements made in workplaces using integrated sampling methods were found to differ from measurements made on the same type of respirator in laboratories with quantitative fit-testing systems, as explained in a 1986 paper published in the
Journal of the International Society for Respiratory Protection
. Furthermore, researchers sometimes controlled one or more of the factors that affected respirator performance to better understand and characterize the influence of each factor.
Thoughtful discussions
began in the
AIHA Journal
and eventually became a project for AIHA’s Respiratory Protection Committee. The terms in use today—quantitative fit factor, workplace protection factor, assigned protection factor, and so on—were formalized by the Respiratory Protection Committee and published in the
AIHA Journal
in 1985. The committee later revised the terms for clarity and republished them in 2002. The latest revision was undertaken to clarify and refine minor issues, account for new measurement technology, and add terms for research that did not fit neatly into any of the previous terms. Three new terms were added to define laboratory performance measurements conducted with respirators mounted to manikins. The revised and newly added terms are intended to expand and clarify the meaning of measurements made under a wider variety of conditions. The terms are applicable to all respirator types. They are appropriate regardless of the instruments or analytical methods used for the measurements, and are unaffected by statistical analysis or other mathematical treatment. In general, the performance terms have no legal standing, but several of them have been incorporated into OSHA regulations, NIOSH publications, and ANSI standards. Researchers are strongly urged to properly use these terms in their publications. These terms are necessary to properly depict where, how, and under what circumstances respirator performance is measured or described. As noted earlier, it has long been known that fit measurements (now called quantitative fit factor, QNFF) differ from protection measurements (now designated workplace protection factor, WPF). The same limitation should be applied to every term: each is discrete, and no measurement has been shown to accurately predict another. While the original term “protection factor” has served our profession well, it lacks the precision to describe all scenarios in which respirator performance is discussed. It should not be used without the proper modifier as described in these definitions.
is an industrial hygiene consultant in Stillwater, Minn. He can be reached at (651) 430-0815 or

is director of Occupational Pulmonary Services at the University of Cincinnati in Ohio. He can be reached at (513) 558-1234, ext. 88 or
Authors’ note:
Reader feedback is welcome. Comments can be directed to the authors or to Jessica Hauge, chair of the Respiratory Protection Committee, at

In the 1980s, the
AIHA Journal
published several letters to the editor that discussed the importance of standard terminology for respiratory protection. The letters appeared in three issues: December 1982, page A16; March 1983, pages B24–25; and March 1983, pages B25–26.
AIHA Journal
also published previous versions of the Respirator Performance Terminology as letters to the editor. The first version appeared in the May 1985 issue, page B22, and the second version​ appeared in the March/April 2002 issue, page 132.
Additional sources of information on respiratory protection terminology include:
    Journal of the International Society for Respiratory Protection
    : “Field test of powered air purifying respirators at a battery manufacturing facility” (January 1986).
  • Los Alamos Scientific Laboratory: “Respirator Protection Factors,” Report No. LA-6084-MS (1976).
​New Terminology for Respiratory Protection
What's in a
The following terms were developed by the AIHA Respiratory Protection Committee to represent respirator performance in various contexts. They should be used properly in research studies, publications, and all other discussions of respirator performance to ensure clarity of meaning. In each term, Co represents the measured or estimated concentration of contaminant in the air outside the respirator. Ci represents the measured or estimated concentration of contaminant in the air inside the respirator. The comments clarify, and are considered to be a part of, their respective definitions.
​Assigned Protection Factor (APF)
The minimum expected workplace level of respiratory protection that would be provided by a properly functioning and used respirator or class of respirators to properly fitted and trained wearers when all elements of an effective respirator program are established and are being implemented.
When sufficient data exist, APF is based on statistical analysis (usually the lower 5th percentile) of a population of workplace protection factor measurements. The APF should be achieved at least 95 percent of the time a respirator is properly worn. APFs have also been established using simulated workplace protection factors or other infor​mation. The APF takes into account all potential sources of facepiece penetration (for example, face seal penetration, filter penetration, valve leakage). It does not account for factors that degrade protection such as poor maintenance, failure to follow manufacturer’s instructions, and failure to wear the respirator during the entire exposure period.
Effective Protection Factor (EPF)
A measure of the protection provided by a properly selected, fit-tested, and functioning respirator when it is worn for only some fraction of the total exposure period in the workplace.
EPF is the ratio of the contaminant concentration outside the respirator to that in the air actually inhaled. It is determined by sampling outside the respirator and in the breathing zone during the total exposure period, regardless of whether the respirator is being worn. While the respirator is worn, breathing zone sampling is done from within the respirator. EPF is strongly influenced by non-wear time, regardless of the respirator’s workplace protection factor (WPF). EPF may also be estimated by correcting appropriately measured WPFs for the time that the respirator is not worn during the exposure period using the following formula. It can be validly applied only if the air contaminant concentration is relatively constant over the exposure period, where:
Ts = shift or exposure duration (hours) Tw = number of hours respirator is worn Tnw = number of hours that respirator is not worn
Fit Factor
A numeric expression of how well a tight-fitting respirator fits a wearer during a fit-test.
Fit factor represents the ratio of a challenge agent outside the respirator to the challenge agent that leaks into the respirator. Fit factors are most commonly aerosol or gas concentration ratios expressed as Co/Ci, but can also be derived using air flows or other challenges. This definition is not meant to preclude the use of novel methods.
Laboratory Protection Factor
A laboratory measurement of respirator performance on test subjects when one or more of the conditions for a simulated workplace protection factor (SWPF) is not met.
These studies can be used to examine individual aspects of respirator performance. Examples include evaluation of particle penetration through improperly selected filters, performance of tight-fitting respirators that are not fit-tested, and improper airflow to atmosphere-supplying respirators.
Program Protection Factor (PPF)
An estimate of the respiratory protection provided to a worker in the context of a specific respirator program.
PPF represents the contaminant concentration that the wearer would inhale if the respirator were not worn (Co) divided by the contaminant concentration inside the respirator as the respirator is used in the context of the existing respirator program (Ci). The inside of the respirator concentration may be estimated indirectly from biological monitoring as the airborne concentration expected to produce the measured biological index (except for contaminants with significant risk of skin absorption or ingestion, or if there is a substantial background level in body fluids from non-occupational sources).
The program protection factor is a measure of the effectiveness of the site’s respirator program. Factors that may affect the program protection factor are the activity of the wearer in that setting, the motivation of the wearer, the fit of the respirator, respirator selection, the respirator design, training, maintenance, storage, supervision, program administration and monitoring, and any other variable that affects program effectiveness. If any of these program elements are deficient, the program protection factor will be adversely affected.
Qualitative Fit Factor (QLFF)
An estimate of the minimum fit factor for a specific tight-fitting respirator to a specific individual when a validated qualitative fit-test is passed—that is, the test agent is not detected by the subject’s senses.
A validated qualitative fit-test is one that meets the sensitivity criteria of ANSI standard Z88.10 or is listed in 29 CFR 1910.134. For example, currently accepted qualitative fit-tests provide an estimated fit factor of 100.
Quantitative Fit Factor (QNFF)
The fit factor established during a quantitative fit-test for a specific tight-fitting respirator to a specific individual.
QNFF is intended to represent facepiece-to-face-seal leakage. Leakage from other sources (for example, air purifying elements, damage, and so on) is intended to be essentially zero. QNFF is measured with specialized instrumentation while the subject performs prescribed test exercises.
Simulated Workplace Protection Factor (SWPF)
A measure of respirator performance that is done in a laboratory using test exercises designed to simulate work. The respirator must be properly selected, fit-tested, worn, and used.
SWPF is determined by simultaneously measuring a test atmosphere concentration outside (Co) and inside (Ci) a properly functioning respirator. Immediately sequential Co and Ci samples are acceptable. If the test atmosphere concentration is well controlled, Co samples may be shorter than Ci samples. Filter and/or cartridge penetration may or may not contribute to the Ci measurement. It may also be desirable to match the exposure and environmental conditions (for example, temperature, humidity, and so on) to those of the workplace.
Workplace Protection Factor (WPF)
A measure of the protection provided in the workplace, under the conditions of that workplace, by a properly selected, fit-tested, and functioning respirator while it is correctly worn and used.
WPF is a direct measurement of respirator performance in a specific work environment. It represents the workplace contaminant concentration outside the respirator (Co) divided by the contaminant concentration inside the respirator (Ci). Co and Ci must be measured simultaneously, only while the respirator is properly worn and used during normal work activities. Immediately sequential Co and Ci samples of similar duration are acceptable when integrated sampling methods are not available, but must be used with caution. Filter and/or cartridge penetration may or may not contribute to the Ci measurement. Ci measurements made using respirators that are poorly maintained, improperly used, or not worn during the entire exposure period are inappropriate for WPF determination.
New Terms: Respirator Performance Measurements Made Using Manikins

Manikin Filter Efficiency Factor (mFEF)
The concentration of an airborne challenge outside a respirator divided by the concentration of the challenge that enters the respirator through its filter media. Airflow rate, airflow pattern (continuous, sinusoidal, and so on) and environmental conditions must be specified. It is measured with the respirator sealed to a manikin.
Manikin Fit Factor (mFF)
An expression related to the amount of leakage measured through the face or neck seal of a respirator mounted to a manikin under specified airflow and environmental conditions. If the challenge to the seal is an airborne substance, mFF is the ratio of its airborne concentration outside the respirator divided by the concentration that enters the respirator through the seal. If the challenge is airflow or air pressure, conditions and assumptions for quantifying leakage must be specified. Leakage from other sources (for example, air purifying elements) must be essentially zero. The respirator may be mounted to the manikin without sealants; be partially sealed to the manikin; or be sealed to the manikin with artificially induced leaks.
Manikin Total Penetration (mTP)
The fraction of an airborne challenge that enters a respirator mounted to a manikin from any source. Common sources of penetration include, but are not limited to, the face seal and the filter medium. Airflow rate, airflow pattern, and environmental conditions must be specified. The respirator is not sealed to the manikin.

AIHA's Director of Government Affairs, Aaron Trippler, reported in October that OSHA is working on an updated compliance directive for workplace violence. The updated directive is expected to be released in February 2016.
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The first definitions for respiratory protection terms appeared in a letter to the editor published in the December 1982 issue of the AIHA Journal. Alan Hack, Chuck Fairchild, and Barbara J. Skaggs of the Los Alamos National Laboratory Industrial Hygiene Group proposed definitions for four terms: Fit Factor, Protection Factor, Field Performance Factor, and Worker Use Factor. The letter noted that published industrial hygiene studies referred to "several different measurements of respirator efficiency or performance, with 'Protection Factor' being used to refer to each of them." A response from NIOSH staff in the March 1983 AIHAJ introduced additional terms, including Assigned Protection Factor.