The noise reduction rating (NRR) is a decibel value that shows how much noise a hearing protector can block under laboratory conditions.
The noise reduction rating (NRR) is a single number, in decibels, that shows how much a hearing protector such as an earplug or earmuff can reduce noise exposure. It is measured in a laboratory under ideal fitting conditions and printed on the product packaging. Most hearing protectors sold in the United States have NRRs between about 20 and 33 decibels.
The U.S. Environmental Protection Agency requires hearing protectors to carry an NRR label under 40 CFR Part 211. Employers use the NRR, together with workplace noise measurements, to estimate whether a hearing protector will reduce a worker's exposure to a safe level under OSHA's occupational noise standard, 29 CFR 1910.95.
The NRR is a useful starting point, but it is widely known to overstate the protection most workers actually get. Real-world fit, comfort and how consistently the protector is worn usually reduce performance well below the laboratory number.
The NRR is measured against C-weighted noise, while workplace noise exposures are usually measured in A-weighted decibels (dBA). It also reflects ideal fitting by trained test subjects. For both reasons, OSHA and NIOSH recommend adjusting, or derating, the NRR before relying on it.
Example: a worker is exposed to 100 dBA and wears earplugs with an NRR of 29. (29 − 7) ÷ 2 = 11. Estimated exposure with protection = 100 − 11 = 89 dBA.
When earplugs and earmuffs are worn together, the combined protection is not the sum of the two NRRs. A common rule of thumb is to add 5 dB to the protection provided by the higher-rated device.
More protection is not always better. Protectors that block too much sound can make it hard to hear alarms, warnings and coworkers, which leads some workers to remove them. Many programs aim for protected exposures between about 70 and 85 dBA.
Hearing protection is the last line of defense under the hierarchy of controls. Quieter equipment, enclosures, barriers and other engineering controls should come first. See noise-induced hearing loss for why this matters.
A sawmill issued earplugs with an NRR of 33 to all workers and assumed this solved its noise problem. Annual hearing tests, however, showed several workers with standard threshold shifts. A noise survey found exposures of 102 dBA at the debarker. Using OSHA's derating method, the earplugs were expected to reduce exposure to about 89 dBA, not the 69 dBA the label seemed to suggest.
The mill built a sound-insulated control booth for the debarker operator, added fit testing for earplugs and found that several workers were inserting them only partway. After hands-on training and offering three earplug styles, measured personal protection improved significantly, and no new threshold shifts appeared in the following year's tests.
It depends on the noise level. In most workplaces, a properly fitted protector with an NRR in the mid-20s or higher is enough, but the right choice depends on measured exposure and real-world fit.
Not in practice. After adjusting for measurement differences and real-world fit, actual reduction is usually much less than the label value.
No. Combining them typically adds only about 5 dB of extra protection to the higher-rated device.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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