Noise action levels for work shifts over eight hours

March 26, 1982
Mr. Jonathan A. Jacoby
Supervisor, Industrial Hygiene
Ethyl Corporation
Toxicology and Industrial Hygiene Department
[Recipient address omitted]
Dear Mr. Jacoby:
This is in response to your inquiry of January 8, 1982, to Ms. Debra Feldman concerning OSHA's noise standard (29 CFR 1910.95). Please accept my apology for our delay in giving you written confirmation of the information MaryAnn Garrahan conveyed to you over the telephone on February 11, 1982.
Specifically, your question is whether the noise standard is adjusted for workshifts greater than 8 hours. The answer is no for provisions which reference Table G-16 of 1910.95, and yes whenever the standard refers to the 85 decibel (dB) time-weighted average (TWA) "action level".
Table G-16 is used for determining when engineering or administrative controls (1910.95(b)(1)) are required, and — where there is no significant threshold shift — when mandatory hearing protectors (1910.95(a)) are required to reduce noise levels. This table does not go below 90 dB; thus, it does not adjust for exposures greater than 8 hours in a workshift. For any 8-hour period of exposure within the extended workshift, exposures are required to be limited to a TWA of 90 dB.
On the other hand, Appendix A of 1910.95 is used to determine the "action level" of an 8-hour TWA of 85 dB referred to in 1910.95(c)-(s). Table G-16a of this Appendix is adjusted for workshifts greater or less than 8 hours. Thus, the "action level" could be greater than 85 db for exposures less than 8 hours, or less than 85 dB for exposures greater than 8 hours in a workshift.
I hope this information is helpful.
Sincerely,
Glen R. Williamson
Agency Coordinator of Noise Projects
[Directorate of Science, Technology, and Medicine]
[Corrected 5/22/2013. For clarity, the calculation used above is as follows.]

AL=90+16.61log[50/12.5(hours)]