February 23, 1996

Dean A. Harris, Ph.D.
Industrial Audiologist
Dean H. Harris Associates, Inc.
Post Office Box 1498
Estes Park, Colorado 80517-1498

Dear Dr. Harris:

This is in response to your letter of October 10, 1995, concerning baseline audiograms.

You said that another audiologist recommended to one of your client companies that they use a separate baseline for each ear and that they revise each of the baselines independently as each ear shows a Standard Threshold Shift (STS). The company asked you to obtain from the Occupational Safety and Health Administration (OSHA) an opinion on this procedure for revising baseline audiograms.

In OSHA's view, this procedure is acceptable and more protective because it provides a clearer indication of how each ear is affected by noise and could provide for the reporting of more STSs. The procedure in OSHA's Noise Standard, 29 CFR 1910.95, permits the baselines for both ears to be revised together even when only one ear shows an STS.

You also said that the audiologist recommended revising the baseline if the hearing showed a 5 dB average improvement at 2000, 3000, and 4000 Hz. You stated that in clinical audiology, a 5 dB change is considered normal day to day variation of the human hearing threshold. You contend that a 10 dB average hearing improvement should be used for revising a baseline. The company asked you to obtain OSHA's opinion on this matter.

Rule 29 CFR 1910.95(g)(9)(ii) states that the audiogram may be revised when, in the judgement of the audiologist, otolaryngologist, or physician who is evaluating the audiogram, the hearing threshold shown in the annual audiogram indicates significant improvement over the baseline audiogram. Thus, there is no specific amount of improvement in hearing threshold that an annual audiogram must indicate before it can be substituted for the current baseline audiogram. OSHA relies on the professional reviewing the annual audiogram to judge when the substitution may be made. If the professional reviewing the annual audiogram judges that the audiogram indicates a significant improvement in hearing threshold over that indicated by the baseline audiogram, then the annual audiogram may be substituted for the baseline audiogram.

We appreciate the opportunity to clarify this matter. If you have further questions please contact Gail Brinkerhoff at (202) 219-8036.

Sincerely,



Ruth McCully, Director
Office of Health Compliance Assistance




October 10, 1995

Ruth McCully
Director of Health Compliance
OSHA
200 Constitution Ave., N.W.
Washington, D.C. 20210

Dear Ms. McCully:

I serve as a consultant in hearing conservation to several companies around the country. Recently another audiologist recommended to one of my client companies that they change the method of revising baselines on hearing tests. They suggested using separate baselines for the two ears. For example, when one ear shows an STS, only the baseline for that ear would be revised, while the unchanged ear would retain its separate baseline. It is my contention that to use two different tests from different dates to serve as baselines for the two ears would be rewriting the OSHA noise Standard as the standard did not infer such use of revision procedures.

The same audiologist recommended revising the baseline if one ear showed a 5 dB average improvement at 2000, 3000, and 4000 Hz in either ear. In clinical audiology, a 5 dB change is considered normal day to day variation of the human hearing threshold. I content that a 10 dB average change should be used for improving a baseline.

The company has asked me to get an opinion from OSHA to assist them in determining what to do on baseline revisions. I have been in contact with the Dallas office and was referred to you for your feelings.

I would appreciate your opinion as soon as possible as we have a meeting scheduled with the company to make a decision in this matter.

Thank you very much for your assistance.

Sincerely,



Dean A. Harris, Ph.D.
Industrial Audiologist