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You need to know the
approximate noise level of the environment you are seeking protection
against. The decibel (dB) level can be measured with a sound level
meter. This works fine in professional environments, but homeowners and
consumers can use estimates and common sense. Most equipment and
machinery used by homeowners, such as lawn mowers, chain saws, line
trimmers and similar devices do not produce sounds in excess of 100dB.
In addition the exposure time is usually limited to a couple of hours.
If you use a tool
that produces 100 dB, and plan to use it for an hour or two, and you use
an average hearing protector with a 25 dB Noise Reduction Rating, you
will be more than adequately protected. Of course, if you also are
exposed to noise at work, you must take this into consideration, since
it is your total daily dose that matters. To calculate your exposure the
EPA noise regulation advises that you deduct the NRR from the noise
level.
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Example, the tool
and hearing protector discussed above: 100 dB - 25dB = 75 dB at the
ear.
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For professional
applications, OSHA advises that the NRR be reduced by 7 dB:
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Example: 100dB -
(25 - 7)dB = 82dB at the ear.
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OSHA may also
require a 50% reduction of the NRR after the above reduction:
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Example: 100dB -
(25 - 7) x 0.5 = 91dB at the ear.
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