The most convenient method to use when evaluating the type of hearing protection needed is the noise reduction rating (NRR) developed by the Environmental Protection Agency (EPA). According to the 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. The NRR was developed for use in evaluating hearing protection from environmental sources measured with C-weighting.

The following methods must be used to calculate protected occupational exposure using A-weighted data as required under this rule.

• In general, it is best to fit hearing protection with a protected exposure sufficiently below the PEL to provide a safety factor. However, excessive protection, where the protected exposure is below about 70 dBA may interfere with communication and the employee’s ability to hear activity or alarms around them.
  
  

  Examples:

  - Hearing protection example: 90 dBA exposure using earplugs with an NRR of 20 dB. The effective protection for the plugs is 13 dB and the protected exposure is 77 dBA, which is below the PEL.

  - Dual hearing protection example: 105 dBA exposure using earplugs with an NRR of 33 dB and earmuff with a NRR of 29 dB. The effective protection is 31 dB and the protected exposure is 74 dB, which is below the PEL.

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 No. 1, No. 2 and No. 3. The NRR described here is a simplification of NIOSH Method No. 2. The most complex method is NIOSH Method No. 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 above, 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.

The employer must remember that calculated attenuation values reflect realistic values only to the extent that the protectors are properly fitted and worn.

More information on NRR:

• The 7 dB reduction is based on the typical difference between industrial noise as measured using A-weighting and the noise used in the laboratory to measure attenuation when the hearing protector is evaluated for determination of the NRR.

• If a value other than 7 dB would appear appropriate, the employer should use one of the alternate evaluation methods rather than using the NRR method.

• Similarly, the estimated NRR for dual hearing protection is based on typical results for such systems. Where a NRR specific to the dual protection system worn is available or other data allows use of the alternate evaluation methods, the employer choose to do so.

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