Interpreting OSHA's New APF Proposal

Once promulgated, it puts to rest many questions about the protective capabilities of different respirator types.

RESPIRATOR Assigned Protection Factors (APFs) represent a critical aspect of respirator performance and are an essential part of any respiratory protection program. APFs are used to determine the Maximum Use Concentrations (MUC) for each type of respirator. The MUC, which is the maximum airborne concentration of a hazardous substance from which an employee can expect to be protected when wearing a respirator, is usually determined by multiplying the APF times the exposure limit of the hazardous substance. The Occupational Safety and Health Administration emphasizes in the APF proposal that MUCs must not be applied for immediately dangerous to life or health concentrations (IDLH); only SCBAs can be used at these concentrations.

On June 6, OSHA published the proposed rule to amend the Respiratory Protection Standard to incorporate new APFs for respiratory protection programs. This proposal fills the gap left by the exclusion of APFs from OSHA's 1998 revision of the respiratory protection rule, 1910.134. OSHA said the new rule, together with another proposal on fit testing, is expected to prevent approximately 4,000 injuries and illnesses, as well as preventing about 900 deaths annually from cancer and other chronic diseases.

The long-awaited proposal contains OSHA's APF Table, definitions for APFs and MUC, and amendments to replace the existing APF requirements in OSHA's substance-specific standards. If promulgated as a final rule, this would mean that in most cases, the same APF numbers would be used for every substance. Written comments from interested parties were to be submitted by Sept. 4, 2003. OSHA leaders planned to hold an informal public hearing on the APF proposal in Washington, D.C. in the late summer or early fall of 2003. The final rule would presumably be published sometime thereafter and include an effective date allowing the public time to become familiar with the changed regulation.

This article provides an overview of the proposed rule, including APF recommendations for specific classes of respirators and brief historical context for APFs in each category.

OSHA's Proposed APFs
Air Purifying Respirators (APRs)

Half Mask APRs

OSHA states in the preamble to the proposed rule that half mask respirators, including the sub-classes of filtering facepieces and elastomeric facepieces, vary widely in design and construction. However, an analysis by OSHA of available workplace protection factor (WPF) and simulated workplace protection factor (SWPF) studies could not differentiate between these sub-classes, which justifies combining them into a single class. OSHA determined the WPF data shows nearly 96 percent of the data in these combined studies to be at or above an APF of 10.

Full Facepiece APRs
The 1992 American National Standard on Respiratory Protection, ANSI Z88.2-1992, assigned an APF of 100 to full facepiece APRs. OSHA believes this number is too high, based on studies conducted after 1992. As a result, OSHA is proposing an APF of 50 for this type of respirator, which regulators point out is consistent with the 1987 NIOSH Respirator Decision Logic. OSHA is requesting comments and new information to be submitted in response to this proposal.

Table I.--Assigned Protection Factors [PROPOSED]*

Type of respirator1,2

Half mask

Full facepiece


Loose fitting facepiece

1. Air-Purifying Respirator

3 10



2. Powered Air-Purifying Respirator (PAPR)



4 1,000


3. Supplied-Air Respirator (SAR) or Airline Respirator:


Demand mode




Continuous-flow mode



4 1,000


Pressure-demand or other positive-pressure mode




4. Self-Contained Breathing Apparatus (SCBA):


Demand mode





Pressure-demand or other positive-pressure mode (e.g., open/closed circuit)

5 10,000 (maximum)

5 10,000 (maximum)



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 I apply only when the employer implements a continuing, effective respirator program as specified by OSHA's Respiratory Protection Standard at 29 CFR 1910.134, including training, fit testing, maintenance, and use requirements.

3. This APF category includes quarter masks, filtering facepieces, and half masks.

4. Previous studies involving Workplace Protection Factor (WPF) and Simulated Workplace Protection Factor (SWPF) testing on helmet/hood respirators show that some of these respirators do not provide a level of protection consistent with an APF of 1,000. Therefore, only helmet/hood respirators that ensure the maintenance of a positive pressure inside the facepiece during use, consistent with performance at a level of protection of 1,000 or greater, receive an APF of 1,000. All other helmet/hood respirators are treated as loose-fitting facepiece respirators and receive an APF of 25.

5. Although positive-pressure SCBAs appear to provide the highest level of respiratory protection, a SWPF study of SCBA users concluded that all users may not achieve protection factors of 10,000 at high work rates. When employers can estimate hazardous concentrations for planning purposes, they must use a maximum assigned protection factor no higher than 10,000.

[From Federal Register, Vol. 68, No. 109, Friday, June 6, 2003, Proposed Rules, page 34115]

* Added by authors

Powered Air-Purifying Respirators (PAPRs)
Full facepiece, hoods and helmets

OSHA is proposing an APF of 1,000 for full facepiece PAPRs and PAPRs used with hoods or helmets. This number agrees with the 1992 ANSI standard but is higher than the NIOSH RDL. OSHA believes WPF and SWPF studies demonstrate these respirators can achieve these levels. The one exception OSHA has added to the table of APFs is a footnote that states, "only helmet/hood respirators that ensure the maintenance of a positive pressure inside the facepiece during use, consistent with performance at a level of protection of 1,000 or greater, receive an APF of 1,000."

In other words, OSHA is proposing to separate within the category of hoods and helmets those respirators that are documented to support an APF of 1,000 versus those that do not have such documentation. Other hoods and helmets for which the manufacturer cannot provide supporting data justifying an APF of 1,000 would be treated as loose-fitting facepiece respirators and would receive an APF of 25.

OSHA decision-makers are approaching this class of respirators differently than respirators in other categories because of the results of the Organization Resources Counselors study and other similar studies. While these studies verified that many NIOSH-approved respirators in this category are capable of affording the wearer an APF of 1,000, they also identified certain powered air purifying and supplied air respirators with hoods and helmets may not have designs capable of providing APFs of 1,000. OSHA states that "this level of performance can best be demonstrated by performing a WPF (Workplace Protection Factor) or SWPF (Simulated Workplace Protection Factor) study."

Regarding the issue of who should perform the testing of these respirators to attempt to justify an APF of 1,000 and how these tests should be performed, OSHA states: "In this regard, while the respirator manufacturer most likely would perform the required testing, it would be incumbent on the employer to ensure that the respirators they selected for employee use received this testing."

Therefore, it would appear OSHA has determined that testing by respirator manufacturers is acceptable, and it is left to the employer to determine the acceptability of the manufacturer's data and results.

Loose Fitting Facepieces
A loose fitting facepiece has a partial seal to the face. OSHA is proposing an APF of 25 for this class of respirators after examining the WPF and SWPF studies and concluding the highly variable data supports their conclusion to propose this conservative APF.

Supplied Air Respirators (SARs)
Half Mask, Continuous Flow or Pressure Demand Mode

Based on the performance of half mask PAPRs in WPF and SWPF studies, OSHA is proposing an APF of 50 be assigned to this class. OSHA points out the NIOSH RDL rated these respirators at 1,000, but that the more conservative APF of 50 is warranted because of the lack of WPF and SWPF data for these respirators.

Full Facepiece, Continuous Flow or Pressure Demand Mode
OSHA is proposing an APF of 1,000 for this class based on an SWPF study and on the similarity of this type of respirator to that of a full facepiece PAPR. NIOSH had rated these models at 50 in the RDL.

Hoods and Helmets
SARs with hoods and helmets are given an APF of 1,000 in this proposal, with the same footnote about the need for supporting APF data as for PAPRs with hoods and helmets.

Loose Fitting Facepieces
According to OSHA, no WPF or SWPF studies were available for this class of respirator, so OSHA is proposing an APF of 25 based on studies of loose fitting facepiece PAPRs.

Self-Contained Breathing Apparatus (SCBA)
For tight fitting full facepiece SCBAs used in the pressure demand or other positive pressure modes, OSHA is proposing an APF of 10,000. This number is supported by the NIOSH RDL, the ANSI Z88.2-1992 standard, and WPF and SWPF studies. A footnote has been added to alert users that "a SWPF study of SCBA users concluded that all users may not achieve protection factors of 10,000 at high work rates. When employers can estimate hazardous concentrations for planning purposes, they must use a maximum assigned protection factor no higher than 10,000."

One important caveat to this proposal is that APFs can only be used when the employer implements a continuing, effective respirator program as specified in 1910.134.

The new proposal from OSHA clarifies much of the longstanding confusion about the protection factor ratings of the respirators that employers and workers rely upon for protection in hazardous atmospheres. Almost irrespective of its final content, this new rule, once promulgated, will become the authoritative source for respirator Assigned Protection Factors and ease the burden of health and safety professionals who for many years have had to reconcile conflicting protection factor data from substance-specific regulations, NIOSH recommendations and consensus standards.

It puts to rest many questions about the protective capabilities of different respirator types by putting forth recommendations that rely on scientific methods and validation studies. In the end, the new OSHA proposal should result in improved worker protection by ensuring proper and consistent selection, use, enforcement, and administration of respiratory protection in the workplace.

This article originally appeared in the November 2003 issue of Occupational Health & Safety.

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