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Methods for Estimating the Adequacy of Hearing Protector
I. For employees who have experienced a standard threshold shift, hearing protector attenuation must be sufficient to reduce employee exposure to a TWA of 85 dB. Employers must select one of the following methods by which to estimate the adequacy of hearing protection attenuation.
II. The most convenient method is the Noise Reduction Rating (NRR) developed by the Environmental Protection Agency (EPA). According to EPA regulation, the NRR must be shown on the hearing protector package. The NRR is then related to an individual worker's noise environment in order to assess the adequacy of the attenuation of a given hearing protector. This Appendix describes four methods of using the NRR to determine whether a particular hearing protector provides adequate protection within a given exposure environment. Selection among the four procedures is dependent upon the employer's noise measuring instruments.
III. Instead of using the NRR, employers may evaluate the adequacy of hearing protector attenuation by using one of the three methods developed by the National Institute for Occupational Safety and Health (NIOSH), which are described in the "List of Personal Hearing Protectors and Attenuation Data," HEW Publication No. 76-120, 1975, pages 21-37. These methods are known as NIOSH methods #1, #2 and #3. The NRR described below is a simplification of NIOSH method #2. The most complex method is NIOSH method #1, which is probably the most accurate method since it uses the largest amount of spectral information from the individual employee's noise environment. As in the case of the NRR method described below, if one of the NIOSH methods is used, the selected method must be applied to an individual's noise environment to assess the adequacy of the attenuation. Employers should be careful to take a sufficient number of measurements in order to achieve a representative sample for each time segment.
NOTE: The employer must remember that calculated attenuation values reflect realistic values only to the extent that the protectors are properly fitted and worn.
IV. When using the NRR to assess hearing protector adequacy, one of the following methods must be used:
(a) When using a dosimeter that is capable of C-weighted measurements:
(1) Obtain the employee's C-weighted dose for the entire workshift, and convert to TWA (see Appendix A).
(2) Subtract the NRR from the C-weighted TWA to obtain the estimated A-weighted TWA under the ear protector.
(b) When using a dosimeter that is not capable of C-weighted measurements, the following method may be used:
(1) Convert the A-weighted dose to TWA (see Appendix A).
(2) Subtract 7 dB from the NRR.
(3) Subtract the remainder from the A-weighted TWA to obtain the estimated A-weighted TWA under the ear protector.
(c) When using a sound level meter set to the A-weighting network:
(1) Obtain the employee's A-weighted TWA.
(2) Subtract 7 dB from the NRR, and subtract the remainder from the A-weighted TWA to obtain the estimated A-weighted TWA under the ear protector.
(d) When using a sound level meter set on the C-weighting network:
(1) Obtain a representative sample of the C-weighted sound levels in the employee's environment.
(2) Subtract the NRR from the C-weighted average sound level to obtain the estimated A-weighted TWA under the ear protector.
NOTE: Authority and reference cited: Section 142.3, Labor Code.
1. Amendment filed 10-3-83; effective thirtieth day thereafter (Register 83, No. 41).