ELECTRONIC EARMUFFS
ITEM 46798
The EPA has selected the NRR as the measure of a hearing protector’s noise reducing capabilities.
Harbor Freight Tools makes no warranties as to the suitability of the NRR as a measure of actual
workplace protection since such protection is highly dependent on user training, motivation, and utilization.
A better estimate of workplace protection can be obtained by derating the labeled NRR by 50%.
The NRR calculated from this attenuation data is 24. Improper fit of this device will reduce its effectiveness
in attenuating noise. Consult instructions for proper fit.
The level of noise entering a person’s ear, when a hearing protector is worn as directed, is closely
approximated by the difference between the A-weighted environmental noise and the NRR.
ATTENUATION DATA ANSI S3.19-1974
Test
Corrected
NRR
NRR (without
125 250
500 1000 2000 3150 4000 6300 8000
40CFR211 correction)
Frequencies (Hz)
Mean
Attenuation (dB)
2.9
2.0
17.1 27.8 36.7 45.3 41.9 45.6 37.5 39.2
1.4 1.2 3.6 2.6 1.3 1.8 2.5 2.1
27
24
Sandard
Deviation (dB)
Example:
1.) The environmental noise level as measured at the ear is 92 dBA.
2.) The NRR is 24 decibels (dB).
3.) The level of noise entering the ear is approximately equal to 68 dBA.
For noise environments dominated by frequencies below 500 Hz, the C- weighted
environmental noise level should be used.
The NRR used in the above example was achieved under laboratory conditions.
Although hearing protectors can be recommended for protection against harmful effects of
impulsive noise, the Noise Reduction Rating (NRR) is based on the attenuation of continuous
noise and may not be an accurate indicator of the protection attainable against impulsive noise
such as gunfire.
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