In teaching many CAOHC-approved Hearing Conservationist Training courses over the years, I have observed many a student surprised to learn that OSHA does not require a sound booth for audiometric testing.  OSHA simply requires that the environment in which testing occurs meet the ambient background noise levels specified in Appendix D of the OSHA Noise Standard 29 CFR 1910.95(h)(4).

Those maximum background noise levels are as follows:

A higher-quality testing environment produces higher-quality testing results.

Open-room testing is permitted as long as the noise levels in the room do not exceed the maximum values specified above.  Nevertheless, sound booths are widely used throughout industry and by medical clinics because of the primary drawback of open-room testing – the likelihood of spikes in background noise negatively affecting test results.  The phone rings, people walk by, laughter in the hallway, a noisy ventilation system – all can make a person’s hearing appear worse than it actually is.  Sound booths, while not immune to this, significantly reduce the likelihood of fluctuating ambient noise affecting test results.  A higher-quality testing environment produces higher-quality testing results.

OSHA requires measurements be taken to determine whether the test environment at least meets the maximum ambient noise levels given above, whether testing is conducted open-room or in a sound booth.  The test environment must be in compliance every time an audiometric test is performed.

How often should this ambient noise level evaluation occur?  1910.95(h)(4) only states that the background noise not exceed the maximum levels; it does not state how often such evaluation should occur.  For many years, this was interpreted to mean that OSHA required ambient noise evaluation once and then again if something changed.  For instance, if one switched rooms for open testing, or moved the sound booth to a different location, or if it appeared that background noise levels might have increased perhaps due to a noisy ventilation system…then it was time to re-evaluate.  As a practical matter, professional hearing conservationists usually recommended re-evaluation every 3 years or so if for no other reason than aging of the booth itself, and especially the ventilation fan, might be expected to increase background noise levels.  Actual industry practice varied widely with more proactive companies evaluating their sound booth every 1-3 years with others waiting a decade or more.

What is little recognized is that OSHA revised its policy on this issue.  On 14 February 2005, OSHA issued a letter of interpretation specifically addressing how often the audiometric test room must be evaluated.  The letter specifies different criteria for stationary sound booths, open-room testing, and mobile audiometric testing.  This letter can be viewed here.

Stationary Sound Booth
With regard to a stationary sound booth, the letter states the following:  “For a sound booth that never moves once it is stationed, the ambient noise levels may not need to be measured more than once a year.  However, an evaluation should also be done if there are changes in the outside environment that could have changed the internal ambient background levels.”  In other words, OSHA requires an ambient noise level evaluation at least annually for a stationary sound booth.

Mobile Audiometric Testing
For mobile testing, OSHA did not issue a change in this letter.  Mobile testers must continue to do a background noise check whenever the van is relocated to a new location. OSHA advises to check ambient noise levels at least daily – a good practice – and to consider relocating the van as necessary.

Open-Room Testing
In the letter, OSHA acknowledges that open-room testing is subject to constantly changing noise levels.  OSHA states that, “In this situation, background noise levels may need to be monitored whenever an audiometric test is administered.”  In practice, this is difficult without an audiometer which performs constant background noise monitoring to automatically pause testing when noise levels exceed what is permissible.  Without such an audiometer, the tester must be vigilant in manually pausing and restarting the test based upon noise levels.

In the letter, OSHA emphasizes that “every audiometric test must be performed in rooms meeting the requirements listed in Appendix D so that measured thresholds between tests reflect real hearing change rather than measurement error.”  It is the duty of the Audiometric Technician to ensure that hearing tests are accurate and valid, and part of this duty ensuring that background noise does not negatively affect test results.