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.

April 28, 2021

Ms. Renée Lefrançois
Director of Audiology
Shoebox Inc.
80 Aberdeen Street, Suite 301
Ottawa, ON K1S 5R5, Canada

Dear Ms. Lefrançois:

Thank you for your letter to the Occupational Safety and Health Administration (OSHA). Your letter was referred to the Directorate of Enforcement Programs for a response. You requested clarification on certain elements addressed in the OSHA Occupational Noise Exposure standard (noise standard), 29 CFR § 1910.95, Appendix D, in regards to the sound level meter requirements for measuring ambient room noise levels in a hearing testing environment. This letter constitutes OSHA’s interpretation only of the requirements discussed and may not be applicable to any questions not delineated within your original correspondence. Your specific questions are paraphrased below, followed by OSHA’s response.

Background: OSHA’s noise standard at 29 CFR § 1910.95(h) states the requirements for audiometric testing. Section 1910.95(h)(4) states that audiometric examinations shall be administered in a room meeting the requirements listed in Appendix D, Audiometric Testing Rooms. Appendix D provides that rooms used for audiometric testing shall not have background sound pressure levels exceeding those in Table D-1, the Maximum Allowable Octave-Band Sound Pressure Levels for Audiometric Test Rooms, measured in decibels (dB). The American National Standards Institute (ANSI) also specifies maximum permissible ambient noise levels (MPANLs) allowed in audiometric test rooms that are more stringent than those required by OSHA at 29 CFR § 1910.95 Appendix D.1

Appendix D further states that equipment used to measure ambient noise levels in testing rooms conform at least to the Type 2 requirements of American National Standard Specification for Sound Level Measurements, S1.4-1971 (R1976), and to the Class II requirements of American National Standard Specification for Octave, Half-Octave, and Third-Octave Band Filter Sets, S1.11-1971 (R1976).

Question 1: Is it adequate to use equipment for measuring ambient room noise levels in a hearing testing environment that supports Z-weighted measurements, but not A- or C-frequency weighting?

Response: Yes. Most sound level meters have three built-in filters called A, C, and Z (zero) weighting networks that filter out sound frequencies to different degrees. The very low frequencies are discriminated against (attenuated) quite severely by A-weighting (dBA), similar to the frequency response of the human ear. C-weighting (dBC) slightly attenuates low frequencies, and Z (zero) weighting (dB) does not apply any attenuation or weighting to any frequency.2 Table D-1 does not specify a weighting scale, therefore, it is adequate to use equipment that supports Z-weighted measurements, but not A- or C-frequency weighting.

Question 2: Is it appropriate to use slow or Leq time weighting? Would it be adequate to use equipment that supports slow or Leq time weighting but not fast or impulse time weighting?

Response: Yes. The slow response time setting on a sound level meter measures the sound at one-second intervals and is appropriate to use for measurement of the ambient noise in audiometric testing rooms. The equivalent sound level (Leq) is a way to express the average sound level over time on the readout of sound level meters. It is adequate to use the Leq measured sound level for purposes of ambient noise measurements in audiometric testing rooms.3

Question 3: Would it be adequate to use equipment that supports octave-band filtering but not half or one-third octave-band filtering?

Response: Yes. 29 CFR § 1910.95, Appendix D, Table D-1, specifies the maximum allowable sound pressure levels in the 500, 1000, 2000, 4000 and 8000 Hertz (Hz) frequency bands. While some instruments have the capability to measure using one-half or one-third octave-band filtering, the level of detail provided by one-third octave bands, however, is rarely required for occupational noise evaluation and control and therefore is not required to comply with Appendix D.3

In addition to meeting background noise level requirements in Appendix D, the OSHA noise standard, at 29 CFR § 1910.95(g) Audiometric testing program and (h) Audiometric test requirements, contains specific requirements for audiometric testing including:

  • Audiometric tests shall be conducted with audiometers that meet American National Standard Specification for Audiometers, S3.6-1969 (ANSI S3.6-1969);

  • All audiograms obtained pursuant to this section shall meet the requirements of Appendix C: Audiometric Measuring Instruments;

  • Audiometric tests shall be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000, and 600 Hz, separately for each ear;

  • The functional operation of the audiometer shall be checked before each day’s use;

  • Audiometer calibration shall be checked acoustically at least annually in accordance with Appendix E: Acoustic Calibration of Audiometers;

  • An exhaustive calibration shall be performed at least every two years in accordance with ANSI S3.6-1969; and,

  • Audiometric tests shall be performed by a licensed or certified audiologist, otolaryngologist, or other physician, or by a technician who is certified by the Council for Accreditation in Occupational Hearing Conservation. A technician who performs audiometric tests must be responsible to an audiologist, otolaryngologist, or physician.

Please note, OSHA does not register, certify, approve, or otherwise endorse commercial or private sector entities, products, or services.  In addition, Canadian occupational noise standards may have different requirements than the United States’ OSHA standards.  You may find the Canadian standards for your territory on the Government of Canada, Canadian Center for Occupational Health and Safety webpage at www.ccohs.ca.

Thank you for your interest in occupational safety and health.  I hope you find this information helpful.  OSHA’s requirements are set by statute, standards, and regulations.  Letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances.  This letter constitutes OSHA’s interpretation of the requirements discussed.  From time to time, letters are affected when the agency updates a standard, a legal decision impacts a standard, or changes in technology affect the interpretation.  To assure that you are using the correct information and guidance, please consult OSHA’s website at www.osha.gov.  If you have further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190.


Patrick J. Kapust, Acting Director
Directorate of Enforcement Programs


[1] ANSI S3.1-1999 (R2018)

[2] OSHA Technical Manual, Section III, Chapter 5, Noise, II.B.10, Loudness and Weighting Networks.

[3] Ibid., Appendix A, Glossary.