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.

November 17, 1989

Mr. Stephen Gee
System Designer
Formerly Environmental Health Associates
ENSR Health Sciences
1320 Harbor Bay Parkway Suite 100
Alameda, CA 94501

Dear Mr. Gee:

This is in response to your letter of October 12, 1989, addressed to MaryAnn Garrahan, concerning the identification of a standard threshold shift (STS) in hearing ability for individuals with a very poor sense of hearing.

An STS is defined at 29 CFR 1910.95(g)(10) in the occupational noise exposure standard as "... a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear." This definition applies regardless of the hearing threshold values in the baseline audiogram. Therefore, if, for example, an employee's baseline audiogram showed hearing thresholds of -10 dB at all three frequencies and the employee's first annual audiogram showed hearing thresholds of O dB at all three frequencies, the employee has had a change in hearing threshold of an average of 10 dB relative to the baseline audiogram and has suffered an STS.

In the case of an employee whose baseline audiogram shows hearing thresholds of 90 dB at all three test frequencies, the determination of an STS would have to be done with an audiometer having an output of at least 100 db at all three frequencies. Only persons qualified to do clinical audiological evaluations should make such determinations.

I appreciate the opportunity to clarify this matter for you. If you require more information please do not hesitate to contact me.


Thomas J. Shepich, Director
Directorate of Compliance Programs