Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 423

Noise —Noise is any unwanted sound.
Noise dose —The noise exposure expressed as a percentage of the allowable daily exposure.
For OSHA, a 100% dose would equal an 8-hour exposure to a continuous 90-dBA noise;
a 50% dose would equal an 8-hour exposure to an 85-dBA noise or a 4-hour exposure to a
90-dBA noise. If 85 dBA is the maximum permissible level, then an 8-hour exposure to a
continuous 85-dBA noise would equal a 100% dose. If a 3-dB exchange rate is used in con-
junction with an 85-dBA maximum permissible level, a 50% dose would equal a 2-hour
exposure to 88 dBA, or an 8-hour exposure to 82 dBA.
Noise dosimeter— An instrument that integrates a function of sound pressure over a period of
time to directly indicate a noise dose.
Noise hazard area— Any area where noise levels are equal to or exceed 85 dBA. OSHA
requires employers to designate work areas, post warning signs, and warn employees when
work practices exceed 90 dBA as a “noise hazard area.” Hearing protection must be worn
whenever 90 dBA is reached or exceeded.
Noise hazard work practice —Performing or observing work where 90 dBA is equaled or
exceeded. Some work practices will be specified; however, as a rule of thumb, whenever
attempting to hold a normal conversation with someone who is 1 foot away and shouting
must be employed to be heard, one can assume that a 90-dBA noise level or greater exists
and hearing protection is required. Typical examples of work practices where hearing pro-
tection is required are jack hammering, heavy grinding, heavy equipment operations, and
similar activities.
Noise-induced hearing loss —A sensorineural hearing loss that is attributed to noise and for
which no other etiology can be determined.
Noise level measurement— Total sound level within an area. Includes workplace measure-
ments indicating the combined sound levels of tool noise (from ventilation systems, cool-
ing compressors, circulation pumps, etc.).
Noise reduction rating (NRR) —The NRR is a single-number rating method which attempts
to describe a hearing protector based on how much the overall noise level is reduced by
the hearing protector. When estimating A-weighted noise exposures, it is important to
remember to first subtract 7 dB from the NRR and then subtract the remainder from the
A-weighted noise level. The NRR theoretically provides an estimate of the protection that
should be met or exceeded by 98% of the wearers of a given device. In practice, this
does not prove to be the case, so a variety of methods for “de-rating” the NRR have been
discussed.
Ototoxic —A term typically associated with the sensorineural hearing loss resulting from
therapeutic administration of certain prescription drugs.
Ototraumatic —A broader term than ototoxic. As used in hearing loss prevention, refers to
any agent (e.g., noise, drugs, or industrial chemicals) which has the potential to cause per-
manent hearing loss subsequent to acute or prolong exposure.
Presbycusis —The gradual increase in hearing loss that is attributable to the effects of aging,
and not related to medical causes or noise exposure.
Real ear attenuation at threshold (REAT) —A standardized procedure for conducting psycho-
acoustic tests on human subjects designed to measure sound protection features of hearing
protective devices. Typically, these measures are obtained in a calibrated sound field, and
represent the difference between subjects' hearing thresholds when wearing a hearing pro-
tector vs. not wearing the protector.
Real-world attenuation —Estimated sound protection provided by hearing protective devices
as worn in “real-world” environments.
Sensorineural hearing loss —A hearing loss resulting from damage to the inner ear (from any
source).
Sociacusis —A hearing loss related to non-occupational noise exposure.