OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

December 18, 1989

                     REGIONAL ADMINISTRATOR

                     OFFICE OF FIELD PROGRAMS


SUBJECT:              Respiratory Protection Table

This is in response to your memorandum of September 12, 1989, concerning the respiratory protection tables in standard 29 CFR 1910.1028 for benzene and standard 29 CFR 1910.1025 for inorganic lead.

The fundamental information conveyed by each table is the protection factor assigned various respiratory protection devices. The protection factor for a respirator indicates the maximum amount a respirator may be assumed to reduce exposure in actual workplace situations. For example, if a respirator has a protection factor of 10 and an employee wears the respirator for 8 hours in an atmosphere where the 8-hour, time-weighted average (TWA) airborne concentration of an air contaminant is 80 parts per million (ppm), the respirator may be assumed to have reduced the employee's exposure to an 8-hour TWA concentration of 8 ppm, i.e, 80 ppm divided by 10. If there were also a 15-minute period where the TWA concentration of the air contaminant were, for example, 300 ppm, the respirator may be assumed to have also reduced this 15-minute TWA exposure to 30 ppm, i.e., 300 ppm divided by 10.

In the reverse situation, where one knows the protection factor for a respirator and the PEL or PEL's for an air contaminant, one can determine the maximum concentration(s) of the air contaminant in which the respirator may be used. For example, if a respirator has a protection factor of 10 for an air contaminant having an 8-hour TWA PEL of 2 ppm and a short term exposure limit (STEL) of 10 ppm, the maximum concentrations of the air contaminant in which the respirator may be used are 8-hour TWA concentrations of 20 ppm and 15-minute TWA concentrations of 100 ppm, i.e., 2 ppm times 10 and 10 ppm times 10.

Table 1 in the benzene standard relates the protection factor for benzene for various respiratory protective devices indirectly by stating at what maximum 8-hour TWA airborne benzene concentration each device may be used for protecting employees. This value divided by the 8-hour TWA PEL for benzene is the protection factor of each device for benzene.

Looking at Table 1 one notes that the maximum 8-hour TWA airborne benzene concentration in which a full facepiece respirator with organic vapor cartridges may be used is 50 ppm. Since the 8-hour TWA PEL for benzene is 1 ppm, the protection factor for that respirator is 50, i.e., 50 ppm divided by 1 ppm. Benzene also has a 15-minute STEL of 5 ppm. Therefore, there is also a maximum 15-minute TWA benzene concentration in which the respirator may be used for protecting employees. It is 50 times 5 ppm 250 ppm. Moreover, an approval limitation for organic vapor cartridges by the National Institute For Occupational Safety and Health (NIOSH) prohibits using the respirator for protecting employees from atmospheres having any benzene concentration peaks above 1,000 ppm.

Table II in the inorganic lead standard relates the protection factor against inorganic lead aerosols for various respiratory protective devices directly by stating the maximum inorganic lead aerosol concentrations in which various respirators may be worn in terms of multiples of the 8-hour TWA PEL. For example, a full facepiece, air-purifying respirator with high-efficiency filters may be worn in 8-hour TWA lead aerosol concentrations not exceeding 50 times the 8-hour TWA PEL. The statement indicates that the respirator's protection factor for inorganic lead is 50 and it may be used in 8-hour TWA inorganic lead aerosol concentrations not exceeding 2.5 milligrams per cubic meter.

September 12, 1989

                   Directorate Of Compliance Programs

                   Office of Field Programs

FROM:               LINDA R. ANKU
                   Regional Administrator

SUBJECT:            Respiratory Protection Tables

Attached is a letter written to Dr. Richard F. Boggs concerning the respiratory protection table of the benzene standard, 29 CFR 1910.1028, as well as a memorandum to this office concerning the respiratory protection table of the lead standard, 29 CFR 1910.1025.

The letter to Dr. Boggs states the airborne concentrations in the respiratory protection table for benzene are time weighted averages. The memo to this office states that the airborne concentrations in the respiratory protection table for lead are maximum concentrations. although the correspondence refers to two different standards, there is inconsistency in the responses.

It should be noted that the NIOSH approval for dust, fume and mist cartridges states that the cartridges are approved for "dusts, fumes, and mists having an exposure limit measured as a time weighted average. Organic vapor cartridges are approved as "respiratory protection against not more than 1000 parts per million organic vapors by volume." The NIOSH approvals tend to indicate that cartridges for organic vapors should not be used if exposures exceed a maximum level whereas for dust or fume the use of cartridges should be compared to a time weighted average.

Clarification is requested concerning the apparent difference in the interpretation of the respiratory protection tables for the benzene and lead standards.

April 6, 1989

Dr. Richard F. Boggs
Vice President
Organization Resources Counselors, Inc.
1910 Sunderland Place, N.W.
Washington, D.C. 20036

Dear Dr. Boggs:

This is in response to your letter of September 29, 1988, requesting clarification on several issues relating to compliance with the Occupational Safety and Health Administration's (OSHA) final rule on occupational exposure to benzene. Please accept my apology for the delay in response.

I will respond to your questions in the order in which they were raised:

Question 1:

Table I - Respiratory Protection for Benzene (52 PR 34564) does not indicate whether the airborne concentrations listed in the left column are time-weighted-averages (TWAs) or instantaneous exposure levels. Are the levels indicated in Table I TWAs?


Yes. The levels stated in the left column of Table I of 29 FR 1910.1028(g) represent airborne concentrations of benzene for which the specific respirator type(s) stated in the right-hand column are meant to provide protection. The levels in Table I are arrived at by multiplying the permissible exposure limit (PEL) by the protection factor assigned a specific type of respirator (half-mask, negative pressure respirators are usually assigned a protection factor of ten; ten tines the PEL of one ppm is ten ppm; etc.). This is consistent with the values found in the respirator tables of other previously promulgated OSHA standards such as OSHA's lead standard, which allows the use of,as an example, half-mask negative-pressure respirators for concentrations of lead up to "ten times the PEL." Ten ppm benzene is ten times the PEL of one ppm benzene (ten times the 8-hour, time-weighted average permissible exposure limit of one ppm).

Question 2:

Table 1 referred to in question 1 above does not address respiratory protection for short term exposure levels (STELs). Consequently, according to Table 1 the use of half-mask respirators against STELs exceeding 10 ppm is prohibited. Typically, a half-mask respirator is assigned a protection factor of 10 and considered protective against STELs less than or equal to 50 ppm. Is it correct to assume that OSHA will permit the use of half-mask respirators for STELs less than or equal to 50 ppm?


OSHA standards promulgated prior to the final benzene standard to rely on the assignment of a protection factor of ten (10) when permitting the use of half-mask, negative pressure respiratory protection for exposures up to ten times the PEL. OSHA allows the use of a half-mask, negative pressure respirator with air-purifying cartridges when airborne concentrations of benzene are 10 ppm or less, which is ten times the PEL of 1 ppm, measured as an 8-hour time-weighted average exposure. OSHA refers to the STEL as a "PEL" (see 1910.1028(c)). Ten times the STEL of 5 ppm is 50 ppm. Assuming the respirator provides a protection factor of ten, the use of this respirator in concentrations of up to 50 ppms would reduce the in-mask concentration to 5 ppm, the STEL, which is not to be exceeded for more than 15 minutes. The use of a half-mask respirator would therefore comply with the respirator selection requirements where STEL exposures to benzene are 50 ppm and below, and as long as the worker's overall time-weighted average exposure during the 8-hour shift does not exceed 10 ppm.

Question 3:

Technology in the area of respirator fit testing is changing. Portacount, a relatively new effective methodology for quantitative fit testing does not fulfill all the requirements of the mandatory Appendix regarding respirator fit testing for two reasons: a) the test agent atmosphere is not generated within a chamber; and b) in-mask samples are taken for less than 1 minute. OFC does not believe that in developing the appendix, OSHA intended to discourage innovative effective approaches to fit testing. How does OSHA intend to address this issue?


On November 8, 1988, a memorandum was sent to all OSHA Regional Administrators in order to clarify Agency compliance policy on the use of the Portacount device for quantitative fit testing. A copy of that memo and attachments is enclosed for your reference.

I hope the answers provided above have been responsive to the concerns you raised. If we can be of further assistance, please feel free to contact us again or you may contact Ms. Melody Sands of the Office of Health Compliance Assistance at (202) 523-8036.


Thomas J. Shepich, Director
Directorate of Compliance Programs