Under the Occupational Safety and Health Administration’s (OSHA) Respiratory Protection Standard (29 CFR 1910.134), APFs and MUCs are used in the proper selection of respiratory protection equipment for non-IDLH (immediately dangerous to life and health) atmospheres.

Employers must select respirators using Table 1.0: Assigned Protection Factors. They also must consider MUC’s before respirator selection. Selection of respirators should be based on the actual airborne contaminant level found in the workplace. Determining the actual airborne contaminant level typically requires industrial hygiene monitoring.

In addition, for the APFs and MUCs to be properly applied, all respirators must be fit-tested and used in accordance with all local and federal regulations. The APF/MUC will not be accurate for employees that are not clean shaven, have hair that interferes with the fit of a tight-fitting respirator, have a poor fitting respirator, or an improperly selected cartridge. Employees wearing tight-fitting respirators with facial hair that interferes with the fit is a common deficiency found during potent compound safety gap assessments.

What is an Assigned Protection Factor?

An APF is a term used by OSHA to determine how well a respirator/filter combination will protect an individual from external contaminants. It is an estimate of the level of protection a respirator provides. APFs are used to select the appropriate class of respirators that will provide the necessary level of protection. There are certain levels used for different types of masks. The APF is based on the type of mask and size.

An APF of 10 means that no more than one-tenth of the contaminants to which the worker is exposed will leak into the inside of the mask. An APF of 100 means only an one percent leakage.

Example: If the airborne concentration of an airborne contaminant such as the highly potent compound Compound X is 20 ug/m3, then a properly-fitted half-face mask with an APF of 10 would reduce the exposure inside the mask down to 2 ug/m3. A properly-fitted full-face mask with an APF of 50, would reduce the exposure inside the mask down to 0.4 ug/m3.

What is a Maximum Use Concentration?

The MUC is a term used by OSHA for the upper limit at which the class of respirators is expected to provide protection. The MUC can be calculated by multiplying the APF in Table 1.0, by the permissible exposure limit (PEL), short-term exposure limit (STEL), or ceiling limit of the contaminant.

APF × PEL = MUC

If an exposure ever approaches the MUC, then the employer should select the next highest level of respirator. The respirator can be used up to this concentration as long as the MUC does not exceed the immediately dangerous to life or health (IDLH) level. When no OSHA PEL is available for a hazardous substance, the MUC must be determined using available information and professional judgement.

Example: If the permissible exposure limit for a contaminant such as Toluene* is 200 ppm, then a half-faced mask with an APF of 10 should protect the employee up to 2,000 ppm. 10 APF × 200 ppm = 2,000 ppm (MUC)

Caution: Since the IDLH for Toluene is 500 ppm, you cannot use an air purifying respirator. You must use positive pressure supplied air or self-contained breathing apparatus.

Selection of Respiratory Protection in the Pharmaceutical Industry

The use of respiratory protection in the pharmaceutical industry presents many challenges.

First, prior to relying upon respirators as a means of employee protection, the company should implement engineering and administrative controls. After these controls have been installed, containment validation should be performed to determine the effectiveness of these controls. Containment validation can be performed using either a surrogate compound, such as lactose or naproxen sodium, or a compound-specific air sampling and analytical method. If the containment validation monitoring indicates that engineering and administrative controls by themselves do not reduce the airborne concentration to below the occupational exposure limit (OEL), then the company will need to select the proper respiratory protection.

The second major challenge with the use of respirators in the pharmaceutical industry is that many active pharmaceutical ingredients (APIs) do not have established OELs. Fortunately, Affygility Solutions has developed OELs for many generic APIs. Our current catalog listing of OEL Fastrac monographs can be found at oelfastrac.com. One of the many advantages of OEL Fastrac monographs are that they also contain the permitted daily exposure (PDE) value (a.k.a the acceptable daily exposure) . The PDE is used in the risk assessment process for preventing cross-contamination in multi-product facilities, which is an EMA, PIC/s, ANVISA, and WHO requirement.

The third challenge in using respiratory protection in the pharmaceutical industry is you must determine what the APF is for the specific make and model of your respiratory protection. OSHA has made is very clear that if you are applying an APF of 1000 for a powered air-purifying respirator (PAPR), you must have documentation from either the manufacturer or internal study documentation that support the use of the 1000 APF.

Conclusion

In order to prevent employee exposures to active pharmaceutical ingredients, solvents, or other hazardous chemicals, engineering and administrative controls should be first applied. Then, if these controls by themselves are not sufficient enough to lower potential exposures to below the OEL, then it will be necessary for the company to implement an effective respiratory protection program. Having a thorough understanding of APF and MUC concepts is critical is the proper selection of respiratory protection.

And when in doubt, always refer to the Respiratory Protection Standard 29 CFR 1910.134.

Table 1.0 Assigned Protection Factors ⁵

Notes

1. Employers may select respirators assigned for use in higher workplace concentrations of a hazardous substance for use at lower concentrations of that substance, or when required respirator use is independent of concentration.
2. The assigned protection factors in Table 1 are only effective when the employer implements a continuing, effective respirator program as required by this section (29 CFR 1910.134), including training, fit testing, maintenance, and use requirements.
3. This APF category includes filtering facepieces, and half masks with elastomeric facepieces.
4. The employer must have evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protection of 1,000 or greater to receive an APF of 1,000. This level of performance can best be demonstrated by performing a WPF or SWPF study or equivalent testing. Absent such testing, all other PAPRs and SARs with helmets/hoods are to be treated as loose-fitting facepiece respirators, and receive an APF of 25.
5. These APFs do not apply to respirators used solely for escape. For escape respirators used in association with specific substances covered by 29 CFR 1910 subpart Z, employers must refer to the appropriate substance-specific standards in that subpart. Escape respirators for other IDLH atmospheres are specified by 29 CFR 1910.134 (d)(2)(ii).

Definitions

• APF - Assigned Protection Factor (APF) 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 as specified by this section.
• IDLH – Immediately Dangerous to Life and Health (IDLH) is defined by the US National Institute for Occupational Safety and Health (NIOSH) as exposure to airborne contaminants that is "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment.
• MUC - Maximum Use Concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator, and is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance

References

• OSHA – Assigned Protection Factors for the Revised Respiratory Protection Standard. OSHA Respiratory Protection standard – 29 CFR 1910.134

Published October 19, 2017 / Updated July 8, 2021

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