Audiometer calibration and hearing conservation tests

June 8, 1983

Carl D. Bohl, Sc.D.
Department of Medicine and
Environmental Health
Monsanto Company
[Recipient address omitted]
Dear Dr. Bohl:

Thank you for your letters of April 28, 1983, to Assistant Secretary Auchter, Gary Strobel, John Martonik, James Foster and myself regarding the audiometer calibration requirement of the March 8, 1983, hearing conservation amendment.

The hearing conservation amendment requires that audiometric tests as pure tone, air conduction, hearing threshold examinations, with test frequencies including, as a minimum, 500, 1000, 2000, 3000, 4000, and 6000 Hertz. This requirement can be met by using a wide range audiometer, limited range audiometer, or a narrow range audiometer that has the required test frequencies.

Audiometers must be calibrated according to the procedures contained in Appendix E, and in accordance with sections 4.1.2, 4.1.3, 4.1.4.3, 4.4.1, 4.4.2, 4.4.3, and 4.5 of the American National Standard Specification for Audiometers, S3.6-1969.

Wide range audiometers and some limited range audiometers can meet the requirements of 4.1.3 for an output hearing threshold level of 100 decibels (dB). Since limited range audiometers, according to the ANSI 2.1.2 definition, are only required to have an output level of at least 70 dB, these audiometers are calibrated at their maximum output level or the 100 dB level required in 4.1.3., whichever is smaller.

The requirements in Appendix C apply to pulse tone and self-recording audiometers that interrupt the tone signal automatically. This automatically pulsed tone must have an on-time of at least 200 milliseconds. Audiometers of this type are generally available. As an example, the Beltone 100 series audiometers have a pulse on-time of 230 milliseconds. The manufacturer's technical specifications for the audiometer being used must be examined to be sure that the pulsed tone meets the specifications of Appendix C. If your pulse tone audiometer does not meet the requirements of Appendix C, it must be modified or replaced. Any modifications should be discussed with the manufacturer.

The linearity check requirements of Appendix E are based on those contain in ANSI S3.6-1969. Paragraph 4.1.4.1 of S3.6 gives the range of allowable variation.

"The measured difference between two successive designations of hearing threshold level shall not differ from the dial-indicated difference by more than (1) three-tenths of the dial interval measured in decibels, or (2) 1 dB, whichever is larger."

The manufacturer's specifications for attenuator linearity should be taken into account when determining linearity since these may be stricter than those contained in S3.6.

A discussion of the exhaustive calibration trigger level of 15 dB or greater is contained in the preamble to the final hearing conservation amendment (48 FR 9768). The requirement contained in paragraph (h)(5)(ii) is correct: deviations of 15 dB or greater require an exhaustive calibration. The trigger level of greater than 10 dB contained in Appendix E is incorrect, since it could be interpreted as requiring an exhaustive calibration for 11 dB deviation. An exhaustive calibration is necessary when an acoustic calibration results in deviations of 15 dB or greater.

I hope this has clarified the audiometer calibration requirements of the final hearing conservation amendment for you. If you have any further questions, please do not hesitate to contact us.

Sincerely,
R. Leonard Vance, Ph.D.
Director
Health Standards Programs