Etymotic ER•200DW8 Personal Noise Dosimeter with Data Logging - Manual (Page 16)

16
What Dose % Means
Noise dose is a measurement of noise exposure. It is the
combination of the amount of sound and the amount of
exposure time. While sound levels may fluctuate over time,
noise dose never decreases over time; it either remains
stable or increases. Think of 100% dose as the exposure
limit for an entire day. Note, however, that dose limits
are based on a 5-day work week and assume quiet the
rest of the time; therefore 500% is the exposure limit
for an entire week. The risk of hearing impairment grows
with increasing noise dose.
The limits of safe exposure to high sound levels are not
absolute, since people differ in their degree of susceptibility
to noise-induced hearing loss. Dose limits are based on
average susceptibility. A small fraction of the population
is more susceptible than average, and for these people
a 100% dose per day (or 500% per week) may be
enough noise exposure to cause hearing loss over
time. Likewise, a small fraction of the population is less
susceptible than average, and these people may be able
to tolerate noise exposures exceeding 500% in a week
without developing significant hearing problems. Most
people will fall somewhere between the two extremes.
Since noise-induced hearing loss is irreversible and there
is no way to determine individual susceptibility beforehand,
a conservative approach would be to monitor the noise
dose and use hearing protection whenever the noise
dose exceeds 50%. By doing this, the risk of over-exposure
is minimized.