Environmental Engineering Reference
In-Depth Information
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 work-
place measurements indicating the combined sound levels of tool noise
(from ventilation systems, cooling compressors, circulation pumps, etc.).
Noise reduction rating (NRR)
—The NRR is a single-number rating method
that 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 preven-
tion, refers to any agent (e.g., noise, drug, industrial chemical) that has the
potential to cause permanent hearing loss subsequent to acute or prolonged
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.
Sensorineural hearing loss
—Hearing loss resulting from damage to the inner
ear (from any source).
Sociacusis
—Hearing loss related to non-occupational noise exposure.
Sound intensity (I)
—At a specific location, it is the average rate at which sound
energy is transmitted through a unit area normal to the direction of sound
propagation.
Sound level meter (SLM)
—A device that measures sound and provides
a readout of the resulting measurement. Some SLMs provide only
A-weighted measurements, others provide A- and C-weighted measure-
ments, and some can provide weighted, linear, and octave (or narrower)
band measurements. Some SLMs are also capable of providing time-inte-
grated measurements.
Sound power
—The total sound energy radiated by a source per unit time.
Sound power cannot be measured directly.
Sound pressure level (SPL)
—A measure of the ratio of the pressure of a sound
wave relative to a reference sound pressure. Sound pressure level in decibels
is typically referenced to 20 mPa. When used alone (e.g., 90 dB APL), a
given decibel level implies an unweighted sound pressure level.
Standard threshold shift (STS)
—(1) OSHA uses the term to describe a change
in hearing threshold relative to the baseline audiogram of an average of
10 dB or more at 2000, 3000, and 4000 Hz in either ear. It is used by OSHA
to trigger additional audiometric testing and related follow-up. (2) NIOSH
uses this term to describe a change of 15 dB or more at any frequency,
5000 through 6000 Hz, from baseline levels that is present on an immediate
