The Acoustical Society of America (ASA) has published a new standard that specifies laboratory-based procedures for measuring, analyzing, and reporting the passive noise-reducing capabilities of hearing protection devices. The consensus standard, Methods for Measuring the Real-Ear Attenuation of Hearing Protectors, ANSI/ASA S12.6-2008, published in December 2008, significantly revises the 1997 edition of the standard.
One of the hearing protector fitting procedures described in the new standard, Method A, is expected to be the procedure specified by the U.S. Environmental Protection Agency (EPA). The EPA will spell out the procedure for testing hearing protectors to determine the noise reduction rating (NRR) when EPA publishes proposed changes to the federal regulation on labeling for hearing protectors (40 CFR 211) this year.
ASHA is a member of the American National Standards Institute (ANSI) S12 Committee on Noise, and is represented by Laura Wilbur. The working group that developed the revised standard—S12/WG11 Hearing Protector Attenuation and Performance—included technical experts and interested parties from research and military organizations, hearing protector manufacturers, and users of hearing protection devices (HPDs). ASHA members Amanda Azman, Elliott Berger (chair), Doug Ohlin, Theresa Schulz, Brad Witt, and I participate in WG11.
Since 2004 EPA officials have actively solicited suggestions from WG11 and organizations, agencies, manufacturers, and individuals as to how the NRR and other information on packages of HPDs should be modified to communicate more clearly and accurately how well those devices work.
In 2007, WG11 completed work on a related standard, Methods for Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn, ANSI/ASA S12.68-2007. That standard was developed in response to an EPA request for a consensus standard describing new methods for calculating number ratings for hearing protectors.
Real-ear attenuation at threshold (REAT) is the test procedure used around the world to measure the performance of HPDs worn by human subjects in the laboratory. The procedure measures the change in sound-field hearing threshold for narrow bands of noise that occurs when HPDs are worn. REAT testing measures not only the capability of the device to block sound from entering the ear, but also the degree to which the device fits the ears of the subjects and how well the subjects fit the device relative to the manufacturers' instructions.
Hearing Protection Fit Methods
Like the 1997 version of the standard, S12.6-2008 describes the general conditions and procedures for conducting REAT tests in the laboratory and provides two different methods of fitting the hearing protectors: Methods A and B.
Method A: Trained-Subject Fit
Previously known as the Experimenter Supervised Fit, Method A is intended to measure the capabilities of HPDs when fitted by thoroughly trained users. Significant changes were made to Method A to clarify the level of involvement of the person conducting the test and minimize variability of the test between laboratories. This method allows a training period with each subject, during which the test administrator provides the subject with instruction and coaching on the fitting procedure specified by the HPD manufacturer. However, when the training period is completed and the REAT test is to begin, the subject must don the hearing protector without assistance.
Method B: Inexperienced-Subject Fit
Intended to approximate the protection that can be attained by groups of informed users in workplace hearing conservation programs, Method B specifies that only inexperienced, "novice" hearing-protector wearers be used as subjects. This method was referred to as the Subject Fit method in the 1997 version of the standard.
As in the previous standard, the influence of the person conducting the test is extremely limited. The results obtained when using this fitting procedure are expected to be affected to a great extent by the human factors related to the wearers' experience, training, and motivation. This method is useful for estimating the upper limits of attenuation of a hearing protector that can be achieved, on average, by groups of workers in hearing conservation programs.
To stay informed about pending changes to the Noise Reduction Rating and related technical issues, visit ASHA's online Resource Guide for Hearing Conservation/Occupational Audiologists on the ASHA Web site. Copies of ANSI/ASA S12.6-2008 may be purchased from the ASA online standards store at or 800-874-6383.