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Definitions (Section 4)

Audiometer. An instrument for gauging and recording acuity of hearing

Audiometric test. A clinical evaluation of a person's hearing capability, using a calibrated pure-tone audiometer and performed in accordance with 29 CFR 1910.95 (g) and (h). At SLAC, such tests are provided on site by the Medical Department.

Casual visitor. Individual coming to the SLAC campus for a period of no more than 30 days per visit, whose visit does not involve unescorted entry to industrial/accelerator or other areas where unique SLAC hazards warrant limited access, and whose visit is for the following types of purposes: attending public lectures, public tours, or other activities open to the public; attending workshops, conferences, and collaboration meetings; use of the Linear Cafe (SLAC cafeteria); use of the Stanford Guesthouse; and meetings with SLAC personnel.

Decibels-A-weighted scale (dBA). The unit in which sound levels are measured for expressing the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 130 for the average pain level in humans

Designated noise area. A work area with an eight-hour TWA of 85 dBA or higher, or with periodic impact noise of 115 dBA or higher as surveyed and posted by the SLAC hearing conservation program

Hearing protection/protectors. Devices worn in or on the ears to reduce exposure to noise. May include disposable earplugs, reusable earplugs (banded and corded), and earmuffs.

Impact noise. A noise that occurs at intervals of greater than one per second; for example, the noise made by a metal shear. Personnel must not be exposed to impact noises exceeding 140 dBA peak sound pressure.

Noise dosimetry. The process or method of measuring a person's individual exposure to noise over a given time period

Noise reduction rating (NNR). Measure of the estimated attenuation capacity of a hearing protector to represent the approximate noise reduction, in dBA

Otological. Relating to otology, the branch of medicine that deals with the structure, function, and pathology of the ear

Permissible noise exposure. At SLAC, an eight-hour time-weighted average of 85 dBA

Sound level. Ten times the common logarithm of the ratio of the square of the measured A-weighted sound pressure to the square of the standard reference pressure of 20 micropascals. Units in decibels (dB).

Sound level meter. A hand-held, direct-reading instrument with a microphone, an electronic-filter network, and a visual display such as a meter or digital readout. Because sound-level meters provide a real-time indication of noise intensity, they are typically used to survey an area.

Standard threshold shift. 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

Threshold limit value (TLV). Recommended health-based guidelines for occupational exposure to noise levels published by the American Conference of Governmental Industrial Hygienists (ACGIH). TLVs for noise represent the sound pressure levels and durations of exposure that represent conditions under which it is believed that nearly all workers may be repeatedly exposed without adverse effect on their ability to hear and understand normal speech.

Time weighted average sound level (TWA). That sound level, which if constant over an eight-hour exposure, would result in the same noise dose as is measured

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