Respirator Fit Testing, Assigned Protection Factors and Maximum Use Concentrations 

The respiratory protection standard includes a requirement for a medical clearance for required use of tight-fitting respirators and for some specific respirators even with voluntary use.

• By Gregory Boothe
• Aug 02, 2021

In my experience, respiratory protection is one of the more common forms of PPE used by employers in the United States. In many cases, employers may decide to use respiratory protection to reduce employee exposures to health hazards without trying to reduce personal exposures using more effective engineering or administrative controls. Because the consequences of being exposed to high concentrations of some chemicals can result in severe health effects or death, it is very important that respirators are properly chosen and worn in the workplace.

OSHA published a respiratory protection standard, 29 CFR 1910.134 in 1998. The respiratory protection standard is designed to help employers establish and maintain a highly effective respirator program when respirators are required to be used in a workplace. To discuss all of the requirements of the standard would take more space than we have in this article. Therefore, I will focus on fit testing and the use of assigned protection factors (APFs) and the calculation and use of maximum use concentrations (MUCs). These are areas where I see some employers struggle with comprehension and implementation.

The respiratory protection standard includes a requirement for a medical clearance for required use of tight-fitting respirators and for some specific respirators even with voluntary use. The medical evaluation is designed to determine if an individual has any medical conditions that might preclude them from being able to safely wear a respirator in the workplace. You would not want an individual donning a respirator and having a heart attack because of the respirator use.

Another requirement of the standard is to perform a fit test prior to the original use of a respirator and annually thereafter. The fit test is designed to determine which type, model and size of respirator properly will fit each individual. An employee using a respirator that does not fit properly can have little to no protection from the hazardous environment present in the workplace. You do not want an individual to don a respirator and think that adequate protection is provided only to have the worker experience a severe health reaction because the respirator is not providing the protection that it was supposed to.

There are two basic methods that OSHA has approved for determining if a respirator fits properly. These methods are referred to as quantitative fit testing (QNFT) and qualitative fit testing (QLFT). The names tell you that the QNFT method provides a quantitative result while the QLFT provides a qualitative result. Basically, the QNFT provides you with a numerical fit factor indicating quantitatively how the respirator fits the individual while the QLFT just ask if the respirator fits. Of the two methods, my experience has been that a majority of employers utilize the QLFT because it carries a lower initial investment and is easier to perform. OSHA has published the instructions for performing fit tests for the QNFT and QLFT methods in Appendix A to the regulation.

OSHA developed the assigned protection factors (APFs) to assist you with the determination of maximum protection for different respirators. The APFs are listed in Table 1 of 29 CFR 1910.134. When using one of the QNFT methods the respirator is attached to the machine and the result is displayed as a number called the fit factor. Positive pressure respirator facepieces must be converted and tested in the negative pressure mode. The fit factor and the APF are related by a factor of 10. The fit factor must be 10 times higher than the APF to correspond with the APF. Therefore, the fit factor must be at least 500 for all full-face piece respirators and at least 100 for all quarter- and half-mask respirators in order to pass the fit test. When using the QLFT methods, the individual just has to indicate they do not detect the challenge agent in order to pass the fit test and use the designated APF. The obvious question is: when can I use the QLFT method and when do I have to use the QNFT method?

First, we must look at the different types of respirators that could be used in a hazardous environment. There are two basic types of respirators, air-purifying respirators (APRs) and atmosphere-supplying respirators (ASRs). Basically, air passes through some filter in an APR which removes hazardous compound from the air prior to the air entering the wearer’s respiratory system. An important variable is ensuring the filter that is being used is specific for the hazardous chemical that is present in the work environment. In other words, you need a particulate filter for particulates and a specific gas or vapor cartridge for gases and vapors. Unlike the APR, the ASR provides “clean” air to the wearer that is separate from the air in the working environment. With a supplied-air respirator (SAR), the air comes from a tank sitting in the neighboring work area or from a compressor, hopefully operating in a clean environment. The air might also come from a tank the wearer carries on their back (a self-contained breathing apparatus or SCBA). With all ASRs, the type of regulator will have a huge impact on the protection the respirator can provide. Some regulators will maintain a positive pressure inside the respirator face piece at all times which does not allow outside air to enter the face piece. This is especially important if the worker is in an area that is or might become immediately dangerous to life and health (IDLH).

APRs and ASRs can also have different face pieces. The most common are half-mask and full-face piece. You can find quarter-mask, but they are very uncommon. Some respirators use a loose-fitting face piece where the face piece does not come into contact with the wearer’s face. The powered air purifying respirator (PAPR) is a special positive pressure APR using a battery powered fan to pull the air through the filter and then blow the air into the face piece. As you can see from Table 1, whether you use an APR or ASR and the type of face piece you use determines the level of protection that can be expected while using the respirator. In general, positive pressure respirators have higher APFs than negative pressure respirators and regulators that maintain a positive pressure inside the face piece have the highest APFs. APFs can then be used to calculate a maximum-use concentration (MUC). The MUC represents the highest concentration of a chemical for which you can use a particular respirator. To calculate the MUC, you must know the APF and the PEL (or the TLV or REL if you want) for the chemical. You simply multiply the APF by the PEL to obtain the MUC. For example, the OSHA PEL for Methyl Ethyl Ketone (MEK) is 200 ppm. If you wanted to use a half-mask APR with the proper chemical cartridge the MUC would be 10 X 200 ppm = 2,000 ppm. That means you should be able to safely use a half-mask APR with the appropriate cartridges in an atmosphere up to 2,000 ppm MEK. If the concentration exceeded 2,000 ppm, you would have to use a respirator with a higher APF.

However, there is one other variable you must consider, the IDLH concentration. If the concentration in the work environment exceeds the IDLH concentration, 29 CFR 1910.134 requires you to use specific types of ASRs and the MUC would then be set below the IDLH. The National Institute for Occupational Safety and Health is one organization that publishes IDLH values for many compounds. The published IDLH for MEK is 3,000 ppm so your MUC is less than the published IDLH value. For gases and vapors, there is also a requirement to use a cartridge with an end-of-service-life indicator (ESLI) or develop a change out schedule. This is a requirement that many employers forget about. Another example would be if you wanted to use a half-mask APR with appropriate cartridges for an atmosphere containing hydrogen sulfide. The OSHA PEL for hydrogen sulfide is 20 ppm as a ceiling concentration. With the proper cartridges, the MUC would be 10 X 20 ppm = 200 ppm. However, the published IDLH concentration is 100 ppm, so you would have to reduce the MUC to 100 ppm.

How does this relate to when you can use QLFT methods and when you have to use QNFT methods? OSHA has stated that QLFT methods can only be used for negative pressure APRs when they will be used in concentrations less than 10 times the PEL. This is because current studies do not validate the protocols higher than that level. So, if you are going to use a negative pressure APF (half- or full-mask) in an atmosphere that is less than 10 times the PEL, you can use one of the QLFT protocols. If you want to use a negative pressure APR in an atmosphere greater than 10 times, the PEL you must use one of the QNFT methods.

OSHA allows the use of any of the QLFT or QNFT methods for all positive-pressure ASRs because they are almost always used in the positive pressure mode in the workplace. The ASRs are tested in the negative pressure mode so the facepiece must be modified for the fit testing. Once the positive pressure ASR passes any QNFT or QLFT test, OSHA allows the use of the higher APF for that respirator.

This article originally appeared in the July/August 2021 issue of Occupational Health & Safety.