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 http://www.osha.gov.

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 1- Respiratory Protection for Benzene (52 FR 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 1 TWAs?


Yes. The levels stated in the left column of Table I of 29 CFR 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 were 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 times the PEL of one ppm in 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 do rely on the assignment or 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 up to 50 ppm 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 E 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. ORC 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.

[This document was edited on 03/22/99 to strike information that no longer reflects curent OSHA policy.]

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