March 13, 1984

Mr. W. William Ament
Organization Resources Counselors, Inc.
1625 I Street, N.W.
Washington, D.C. 20006

Dear Mr. Ament:

This is in response to your letter of January 16 concerning OSHA Instruction CPL 2-2.35A, which provides internal Agency guidelines for enforcing 29 CFR 1910.95(b)(1) a provision of the occupational noise standard applying to general industry and maritime employment. 29 CFR 1910.95(b)(1) requires that feasible administrative or engineering controls be utilized to correct employee overexposure to noise.

The term "laboratory-based noise reduction" that is used at l.a. of Appendix A of CPL 2-2.35A means the noise attenuating effectiveness allotted to the hearing protectors using test data that has been obtained in a laboratory following ANSI S3.19-1974 or ANSI Z24.22-1957 procedures. A mathematical resolution of the laboratory test data is required to arrive at the noise attenuating effectiveness for a hearing protector. The method of resolving the data may be the one developed by the Environmental Protection Agency to provide what is termed the Noise Reduction Rating (NRR), or it may be one of the three developed by the National Institute for Occupational Safety and Health (NIOSH). The NIOSH methods are described in the "List of Personal Hearing Protectors and Attenuation Data," HEW Publication No. (NIOSH) 76-120, 1975, pages 21-37.

The examples given on the enclosed page illustrate the application of a 50 percent safety factor to the "laboratory-based noise reduction" for a hearing protector.

We appreciate the opportunity to provide assistance in this matter. If we may serve you again in the future, we shall be glad to do so.

Sincerely,



John B. Miles, Jr.
Director
Directorate of Field Operations