Help your employees make the most of the hearing protection devices (HPDs) they wear by verifying that the noise reduction provided is adequate and that the HPDs are properly used, maintained and replaced.
The Noise Reduction Rating (NRR) is a description of how much noise reduction was measured on a group of well-trained hearing protection users who wore the HPD correctly in a laboratory test. As the science has evolved in hearing protection, it is becoming generally recognized that the best way to ensure the adequacy of a hearing protector for any specific worker is to the conduct fit testing to confirm that the expected level of attenuation is achieved (i.e., the proper type of protector was selected and is being used correctly). 3M strongly recommends the fit testing of hearing protectors. Although U.S. regulations do not yet address fit testing, OSHA regulation 29 CFR 1910.95 specifies that the NRR may be used to determine whether a particular hearing protector provides adequate protection within a given noise exposure in one of the following ways:
If your company uses A-weighting to measure the TWA noise exposure of employees, the OSHA method for determining adequacy of hearing protection using the NRR is shown below.
In the U.S., OSHA has provided guidance on how employers are to use the NRR to estimate the noise reduction obtained by employees. These examples are based on information in the OSHA Technical Manual section III, chapter 5, appendix E.
If your company uses A-weighting to measure the TWA noise exposure of employees, the OSHA method for determining adequacy of hearing protection using the NRR is shown in Example 1 above.
In Example 1, the protected exposure for a group of employees who wear this hearing protector is estimated to be 71 dBA. This protected exposure level is well below the OSHA PEL of 90 dB TWA so the hearing protector attenuation would be considered adequate for this exposure.
NOTE: When C-weighting is used to measure the TWA of employees, OSHA does not require use of the 7 dB correction to the NRR.
The practice of reducing the NRR value, or derating, is done to account for the difference between the NRR and the attenuation workers get when on the job. Since the 1980s, OSHA enforcement policy in the U.S. has been to apply a 50% derating to the NRR as a safety factor when employers use hearing protectors as a substitute for noise controls. See Example 2 to learn how to apply the OSHA 50% derating.
In Example 2 above, the protected exposure for a group of employees who wear this hearing protector is estimated to be 83 dBA. This protected exposure level is below the OSHA PEL of 90 dB TWA so the employer who uses this hearing protector as a substitute for noise controls would likely be considered to be in compliance with OSHA noise control requirements.
Wearing earmuffs together with earplugs provides between 5-10 dB more noise reduction than either device worn by itself. The extra protection provided varies depending on the frequency of the sound.
In the U.S., OSHA allows employers to add 5 dB to whichever device has the highest NRR to estimate the combined protection when dual protection is worn. In most cases, this 5 dB adjustment is factored in after the NRR has been corrected for A-weighting and derating has been applied. See Example 3 above.
Always follow the User Instructions provided with the hearing protectors for fitting, cleaning & storage, and replacement of HPDs. In general, replace hearing protectors when they are damaged or no longer provide an effective noise-blocking seal.
Care: Headband and outside of cups are washable. Foam inserts inside cups are not. Replace bands when: damaged or they no longer provide enough tension to hold cups tightly over ears. Replace cushions and foam inserts: every six months or sooner if they are damaged or are no longer soft and pliable.
IMPORTANT NOTE: This information is based on selected current national requirements. Other country or local requirements may be different. Always consult User Instructions and follow local laws and regulations. This website contains an overview of general information and should not be relied upon to make specific decisions. Reading this information does not certify proficiency in safety and health. Information is current as of the date of publication, and requirements can change in the future. This information should not be relied upon in isolation, as the content is often accompanied by additional and/or clarifying information. All applicable laws and regulations must be followed.