It could take only a few minutes of exposure to certain sounds for hearing loss to occur.  Data compiled from the CDC/NIOSH website contains the following information in regard to hearing protection numbers:

  • Each year, 30 million people are exposed to harmful noise at work.
  • Noise-induced hearing loss is the second most-often reported occupational injury.
  • It only takes a few minutes of exposure to certain sounds for damage to occur.
  • Hearing loss is permanent and irreversible.

Here are some scary statistics:  a newspaper press (97dB) can cause permanent hearing damage in just 30 minutes.  A chain saw (110 dB) can cause permanent damage in less than 2 minutes.  A simple hand drill (98 dB) or a tractor (96dB) can cause permanent damage in less than 30 minutes.

Noise Reduction Rating is a number that appears on the labels of all hearing protection products sold in the U.S.  In theory, the NRR equals the level of noise reduction (in decibels) provided by the earplug or earmuff, in laboratory conditions.  These conditions can be very different from actual working conditions.  Earplugs may be inserted incorrectly or earmuffs may not completely cover ears of workers, therefore the products may not furnish the level of protection listed on the package.

NIOSH has recommended that NRR data be adjusted to account for these differences.  For real world working conditions, NIOSH recommends that the NRR for earmuffs should be reduced by 25%, the NRR for formable earplugs reduced by 50%, and for all other earplugs should be reduced by 70%.  For example, a pair of earplugs with an NRR of 29 would be adjusted according to the NIOSH recommendations to 14.5 (29 dB x 50% = 14.5 dB).

Whenever the time-weighted average noise is greater than 85dB, OSHA requires the use of hearing protection.  By adjusting the NRR of a hearing protector according to NIOSH’s recommendations, and subtracting that number from the actual time-weighted noise level, it is possible to get an idea of how much noise is actually entering the ear.

An example is: a worker in a factory who experiences a time-weighted average noise level of 97 dB would need a hearing protector that provides at least 12 dB of protection.  That worker would need earmuffs with an NRR of at least 16 or formable earplugs with an NRR of at least 24, based on the ratings on the packaging.

NRR data can be misleading without a proper understanding of its usefulness as a tool.  If it is used correctly, however, it can provide valuable information to help workers choose the correct hearing protection device.

Gateway Safety


  1. The greatest danger that my hearing gets is not at work. I’m a sports fan and certain team sports tend to have very noisy crowds. Obviously, the noise is something that one doesn’t want to prevent in that setting but getting apair of earplugs might not be a bad idea (though I haven’t tried it).

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