| Attenuation: Real Ear Attenuation at Threshold (REAT) |
A standardized procedure for conducting psychoacoustic 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 protector vs when not wearing the protector. |
| Attenuation: Real-World |
Estimated sound protection provided by hearing protective devices as
worn in "real-world" environments. |
| Baseline Audiogram |
A valid audiogram against which subsequent audiograms are compared
to determine if hearing thresholds have changed. The baseline audiogram
is preceded by a quiet period so as to obtain the best estimate of the
person's hearing at that time. |
| Continuous Noise |
Noise of a constant level as measured over at least one second using
the "slow" setting on a sound level meter. Note, that a noise which is
intermittent, e.g., on for over a second and then off for a period would
be both variable and continuous |
| Controls: Administrative |
Efforts, usually by management, to limit workers' noise exposure by
modifying workers' schedule or location, or by modifying the operating
schedule of noisy machinery. |
| Controls: Engineering |
Any use of engineering methods to reduce or control the sound level
of a noise source by modifying or replacing equipment, making any physical
changes at the noise source or along the transmission path (with the exception
of hearing protectors). |
| dB (Decibel) |
The unit used to express the intensity of sound. The decibel was named
after Alexander Graham Bell. The decibel scale is a logarithmic scale in
which 0 dB approximates the threshold of hearing in the mid frequencies
for young adults and in which the threshold of discomfort is between 85
and 95 dB SPL and the threshold for pain is between 120 and 140 dB SPL. |
| Dosimeter |
When applied to noise, refers to an instrument that measures sound
levels over a specified interval, stores the measures, and calculates the
sound as a function of sound level and sound duration and describes the
results in terms of, dose, time-weighted average and (perhaps) other parameters
such as peak level, equivalent sound level, sound exposure level, etc. |
| Equal-Energy Rule |
The relationship between sound level and sound duration based upon
a 3 dB exchange rate, i.e., the sound energy resulting from doubling or
halving a noise exposure's duration is equivalent to increasing or decreasing
the sound level by 3 dB, respectively. |
| Ergonomics |
The study or measurement of how work is done as it relates to worker
fatigue, discomfort or injury. |
| Exchange Rate |
The relationship between intensity and dose. OSHA uses a 5-dB exchange
rate. Thus, if the intensity of an exposure increases by 5 dB, the dose
doubles. Sometimes, this is also referred to as the doubling rate. The
U.S. Navy uses a 4-dB exchange rate; the U.S. Army and Air Force use a
3-dB exchange rate. NIOSH recommends a 3-dB exchange rate. Note that the
equal-energy rule is based on a 3 dB exchange rate. |
| Hazardous Noise |
Any sound for which any combination of frequency, intensity, or duration
is capable of causing permanent hearing loss in a specified population. |
| Hazardous Task Inventory |
A concept based on using work tasks as the central organizing principle for collecting
descriptive information on a given work hazard. It consists of a list(s) of specific tasks
linked to a database containing the prominent characteristics relevant to the hazard(s) of
interest which are associated with each task. |
| Hearing Damage Risk Criteria |
A standard which defines the percentage of a given population expected
to incur a specified hearing loss as a function of exposure to a given
noise exposure. |
| Hearing Handicap |
A specified amount of permanent hearing loss usually averaged across
several frequencies which negatively impacts employment and/or social activities.
Handicap is often related to an impaired ability to communicate. The degree
of handicap will also be related to whether the hearing loss is in one
or both ears, and whether the better ear has normal or impaired hearing. |
| Hearing Loss |
Hearing loss is often characterized by the area of the auditory system
responsible for the loss. For example, when injury or a medical condition
affects the outer ear or middle ear (i.e. from the pinna,
ear canal, and ear drum to the cavity behind the ear drum - which includes
the ossicles) the resulting hearing loss is referred to as a conductive loss.
When an injury or medical condition affects the inner ear or the auditory nerve
that connects the inner ear to the brain (i.e., the cochlea and the VIIIth cranial
nerve) the resulting hearing
loss is referred to as a sensorineural loss. Thus, a welder's
spark which damaged
the ear drum would cause a conductive hearing loss.
Because noise can damage the tiny hair cells located in the cochlea, it
causes a sensorineural hearing loss. |
| Hearing Loss Prevention Program Audit |
An assessment performed prior to putting a hearing loss prevention
program into place or before changing an existing program. The audit should
be a top-down analysis of the strengths and weaknesses of each aspect of
the program. |
| HTL (Hearing Threshold Level) |
The hearing level, above a reference value, at which a specified sound
or tone is heard by an ear in a specified fraction of the trials. Hearing
threshold levels have been established so that 0 dB HTL reflects the best
hearing of a group of persons. |
| Hz (Hertz) |
The unit measurement for audio frequencies. The frequency range for
human hearing lies between 20 Hz and approximately 20,000 Hz. The sensitivity
of the human ear drops off sharply below about 500 Hz and above 4,000 Hz. |
| Impulsive Noise |
Used to generally characterize impact or impulse noise which is typified
by a sound which rapidly rises to a sharp peak and then quickly fades.
The sound may or may not have a "ringing" quality (such as a striking a
hammer on a metal plate or a gunshot in a reverberant room). Impulsive
noise be repetitive, or may be a single event (as with a sonic boom). Note: if impulses
occur in very rapid succession (such as with some
jack hammers), the noise would not be described as impulsive. |
| Loudness |
The subjective attribute of a sound by which it would be characterized
along a continuum from 'soft' to 'loud'. Although this as a subjective
attribute, it depends primarily upon sound pressure level, and to a lessor
extent, the frequency characteristics and duration of the sound. |
| Material Hearing Impairment |
As defined by OSHA, a material hearing impairment is an average hearing
threshold level of 25 dB HTL at the frequencies of 1000, 2000, and 3000
Hz. |
| Noise |
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 conjunction 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-Induced Hearing Loss |
A sensorineural hearing loss that is attributed to noise and for which
no other etiology can be determined. |
| NRR (Noise Reduction Rating) |
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 permanent hearing loss subsequent to acute or prolonged
exposure. (See also acoustic trauma.) |
| Permissible Exposure Limit |
OSHA-permissible limits; presently 90 dBA. A time-weighted average
exposure that must not be exceeded during any 8-hour work shift of a 40-hour
work week |
| Presbycusis |
The gradual increase in hearing loss that is attributable to the effects
of aging, and not related to medical causes or noise exposure. |
| Sensor-Neural 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. |
| Sound Level Meter (SLM) |
A device which measures sound and provides a readout of the resulting
measurement. Some provide only A-weighted measurements, others provide
A- and C-weighted measurements, and some can provide weighted, linear,
and octave (or narrower) band measurements. Some SLMs are also capable
of providing time-integrated measurements. |
| SPL (Sound Pressure Level) |
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 µPa. When used alone, (e.g., 90 dB SPL) a given
decibel level implies an unweighted sound pressure level. |
| STS |
Standard Threshold Shift: 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. Used by OSHA to
trigger additional audiometric testing and related follow up.
OR
Significant Threshold Shift: NIOSH uses this term to describe a change
of 15 dB or more at any frequency, 500 through 6000 Hz, from baseline levels
that is present on a retest in the same ear and at the same frequency.
NIOSH recommends a confirmation audiogram within 30 days with the confirmation
audiogram preceded by a quiet period of at least 14 hours. |
| TLV (Threshold Limit Value) |
A guideline provided by the American Conference of Governmental Industrial
Hygienists to denote the exposure, which when reached or exceeded, may
be hazardous. For noise the TLV is 85 dBA and the exchange rate is 3 dB. |
| TWA (Time Weighted Average) |
A value, expressed in dBA, which is computed so that the resulting
average would be equivalent to an exposure resulting from a constant noise
level over an 8-hour period |
| Threshold Shift |
Audiometric monitoring programs will encounter two types of changes
in hearing sensitivity, i.e. threshold shifts: permanent threshold shift
(PTS) and temporary threshold shift (TTS). As the names imply,
any change in hearing sensitivity which is persistent is considered a PTS.
Persistence may be assumed if the change is observed on a 30-day follow-up
exam. Exposure to loud noise may cause a temporary worsening in hearing
sensitivity (i.e., a TTS) that may persist for 14 hours (or even longer
in cases where the exposure duration exceeded 12 to 16 hours). Hearing
health professionals need to recognize that not all threshold shifts represent
decreased sensitivity, and not all temporary or permanent threshold shifts
are due to noise exposure. When a permanent threshold shift can be attributable
to noise exposure, it may be referred to as a noise-induced permanent threshold
shift (NIPTS). |
| Weighted Measurements |
Two weighting curves are commonly applied to measures of sound levels
to account for the way the ear perceives the "loudness" of sounds.
A-weighting: A measurement scale that approximates the "loudness"
of tones relative to a 40 dB SPL 1000 Hz reference tone. A-weighting has
the added advantage of being correlated with annoyance measures and is
most responsive to the mid frequencies, 500 to 4000 Hz.
C-weighting: A measurement scale that approximates the "loudness"
of tones relative to a 90 dB SPL 1000 Hz reference tone. C-weighting has
the added advantage of providing a relatively "flat" measurement scale
which includes very low frequencies. |
Appendix F is also available in