Revised ANSI Hearing Protector Test Methods Likely to Affect How NRR is Determined
By Ted Madison,
10/31/2008
Indianapolis, IN: Experts in the field of hearing protection have reached consensus on a revised American National Standard, "Methods for Measuring the Real-Ear Attenuation of Hearing Protectors, ANSI/ASA S12.6-2008." It contains significant changes to the previous edition of the standard, published in 1997.
One of the hearing protector fitting procedures, Method A, described in the new standard, is expected to be the procedure specified by the United States Environmental Protection Agency (EPA) for testing hearing protectors to determine the Noise Reduction Rating (NRR) when EPA publishes proposed changes to the federal regulation on labeling hearing protectors in late 2008.
The ANSI working group that developed the revised standard, S12/WG11, included technical experts and interested parties from research and military organizations, hearing protector manufacturers, and users of hearing protection devices (HPDs). The group was chaired by Elliott Berger, Senior Scientist for Aearo Technologies.
Since 2004, EPA officials have been actively soliciting suggestions from WG11, along with other organizations, agencies, manufacturers, and individuals, as to how the NRR and other information on packages of HPDs can be modified to communicate more clearly and accurately how well those devices work.
In 2007, WG11 completed work on a related standard, ANSI/ASA S12.68-2007, "Methods for Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn." That standard was developed in response to a request by the EPA for a consensus standard describing new methods for calculating number ratings for hearing protectors.
Background
Real-Ear Attenuation at Threshold (REAT) is the test procedure used around the world to measure the performance of HPDs when they are fit properly on human subjects in the laboratory. The procedure measures the change in the sound level entering subjects' ears that occurs when HPDs are worn. REAT testing is used to measure not only the capability of the device to block sound from entering the ear, but 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.
Revisions
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 in order 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 interacts with the subject, providing 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 on his or her own 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. It is expected that the results obtained when this fitting procedure is used will be affected to a great extent by the human factors related to the experience, training, and motivation of the wearers. It provides a useful method for estimating the upper limits of attenuation of a hearing protector that is achievable, on average, by groups of workers in hearing conservation programs.
Additional Information
To stay informed about pending changes to the Noise Reduction Rating and related technical issues, visit www.NRRUpdate.com and sign up to receive periodic technical updates from Aearo Technologies.
Copies of ANSI/ASA S12.6-2008 are available for purchase from the Acoustical Society of America (ASA) online standards store at asastore.aip.org or by calling ASA at 1-800-874-6383.