What Is an NRR Rating on Hearing Protection?

by Jackie Lohrey; Updated September 26, 2017
Ear Protectors

The Occupational Safety and Health Administration standards require businesses to implement a hearing-conservation program whenever workplace noise exceeds OSHA permissible noise levels. Although the preferred solution is to reduce noise levels permanently, providing employees with hearing protection that meets OSHA noise-reduction standards is an acceptable alternative solution.

What Is Excessive Noise?

OSHA defines excessive noise as sound levels that exceed a minimum sound intensity for a specific time. These range from sound levels rising above 115 decibels for 15 minutes or less to levels rising above 85 decibels over an eight-hour period. NRR, an acronym for noise-reduction rating, is a unit of measurement that determines the effectiveness of hearing-protection devices used to decrease excessive sound exposure in a noisy working environment.

NRR Explained

The highest NRR rating for earplugs is 33, and the highest rating for earmuffs is 31. Although the higher the NRR number associated with a device the greater the potential for noise reduction, the stated NRR is the maximum protection expectation if the device fits perfectly and is worn correctly. In many situations, actual noise reduction is about 50 percent of the listed NRR. For example, if the NRR is 30 for a device, it most likely reduces the noise about 15 decibels.

Improving Hearing Protection

Wearing both earplugs and earmuffs increases hearing protection -- not by the sum of both ratings, but by five decibels. For example, when wearing NRR 20 earplugs and NRR 26 earmuffs, the combined NRR rating is 31, not 46.

About the Author

Based in Green Bay, Wisc., Jackie Lohrey has been writing professionally since 2009. In addition to writing web content and training manuals for small business clients and nonprofit organizations, including ERA Realtors and the Bay Area Humane Society, Lohrey also works as a finance data analyst for a global business outsourcing company.

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