@Tenna,
@Ken219,
@alifalijohn,
@ampumpkin, and
@Grace, all hearing protection devices are required to be tested in a laboratory to determine their noise reduction rating (NRR).
@attheedgeofscience writes (quite incorrectly) that the "effective noise reduction [of a hearing protection device] in a real environment is somewhat less (approximately 50% of NRR ..." In other words, he believes earplugs provide about half the protection in a real-world environment that they do in a laboratory. For example, in his opinion, an earplug with a 32 NRR would attenuate only 16 dB when using dBC noise levels.
He is incorrect.
The noise reduction provided by a hearing protection device in a laboratory is identical to the protection it provides in any other environment.
The OSHA recommendation to use 50% reduction when estimating field attenuation in the workplace is called
de-rating. This guideline has
nothing to do with earplugs and everything to do with the people who wear them. When an earplug is not correctly inserted into the ear, it provides considerably less protection. Studies performed in workplaces have shown that some people know how to properly insert earplugs and some do not. These studies indicate in a number of cases the attenuation achieved in the workplace is identical to the NRR rating shown on the packaging; but they also show in a number of other cases attenuation can be much lower than that which is achieved in a laboratory.
Due to the wide variation in the amount of protection achieved by people who wear a hearing protection device in the workplace, OSHA wrote a guideline to de-rate the NRR of hearing protection devices by 50% to take into account people who do not know how to correctly insert or fit a hearing protection device.
The bottom line is that earplugs provide the same amount of protection shown on the packaging
provided we know how to correctly insert them.
A side note: When using two hearing protectors (i.e., earplugs and earmuffs), OSHA recommends adding 5 dB to the NRR of the hearing protection device with the higher NRR rating.
*****
While I was editing my post,
@Grace asked a key, cut-to-the-chase question. If she is wearing properly-fitted earplugs with a 33 NRR, and is in a 95 dB setting, will her hearing protection result in her being exposed to 62 dB?
The short answer is "yes". The longer answer is your earplugs may enable you to be exposed to less than 62 dB
at certain frequencies. (For more information, see the details on the packaging for your earplugs.)
In the example I used earlier in the thread, Flents Soft Foam Ear Plugs have an NRR of 33. These ear plugs attenuate sound by 33 dB at 125 Hz and provide protection in the mid-to-high 30s in the frequency range of 250 Hz to 2 kHz. Surprisingly, the maximum attenuation provided at 6 kHz and at 8 kHz is 45.4 dB and 46 dB, respectively.
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