Environmental, Health and Safety Services

Hearing Loss Prevention Definitions

Action Level The noise level (85 dBA), calculated as an eight-hour, time-weighted average, at which OSHA requires exposed employees be included in the Hearing Loss Prevention Program.

Administrative controls when OSHA PEL exposure levels are exceeded, feasible administrative (i.e. worker-machine rotation, breaks from noise) or engineering controls shall be utilized. If administrative or engineering controls fail to reduce sound levels within OSHA PEL exposure levels, personal hearing protective devices shall be provided to the employee by the employer, and used to reduce sound levels to within the levels of OSHA PEL exposure levels.

Attenuation is the reduction in sound pressure level in dB which occurs as a person moves further and further away from a noise source (i.e. moving out-of-doors or down an air-conditioning duct system).

Audiogram The chart, graph, or table showing hearing threshold level as a function of frequency; a method of measuring degree of hearing loss.

Audiologist A professional, specializing in the study and rehabilitation of hearing, who is certified by the American Speech-Language-Hearing Association or licensed by a state board of examiners.

Audiometry A baseline audiogram must be obtained for each employee at the beginning of employment or within 6 months of the first noise exposure. An annual audiogram is required thereafter.

Baseline audiogram The audiogram against which future audiograms are compared.

CFR Code of Federal Regulation.

Continuous noise type of constant, unchanging noise which is generated by turbines, air conditioners or fans.

Criterion sound level The dB level at which permissible exposure level is reached; for OSHA, criterion is 90 dBA (which will result in a maximum dose of 100%).

dB(A) unit of measurement of sound level in dB using a weighting network of the A scale on a SLM. A-weighting is a pitch/frequency response filter adjustment which makes its reading conform, very roughly, to the human ear response at a loudness level of 40 phons.

dB(B) unit of measurement of sound level in dB using a weighting network of the B scale on a SLM. B-weighting is a pitch/frequency response filter adjustment which simulates the human ear response at a loudness level of 70 phons.

dB(C) unit of measurement of sound level in dB of the C scale on a SLM. In this case, the SLM reading contains no weighting network in the circuit (i.e. it is flat).

Decibel (dB) Unit of measurement of sound level.

Dose percentage representation of exposure level, based on an 8 -hour criterion.

Dosimeter a special battery-powered sound level meter that is worn by the worker being monitored for noise exposure. It continuously computes TWA and noise dose using a specified exchange rate for trading sound level and exposure duration. The rate for OSHA is 5 dB increase per halving of time.

Engineering controls when OSHA PEL exposures are exceeded, feasible engineering controls (i.e. quieter machinery, noise path absorbers or barriers, mufflers, or equipment isolation) or administrative controls shall be utilized. If such controls fail to reduce sound levels within OSHA PEL exposure limits, personal hearing protective equipment shall be provided to the employee by the employer and used to reduce sound levels to within OSHA PEL limits. The preferred method of noise control is engineering to reduce the noise at its source by engineering controls.

Exchange or doubling rate defined as how dB value and exposure duration are exchanged or traded. (Dosimeters use 3 or 5 dB rate). OSHA recommends using a 5 dB rate.

Frequency the measure of the rapidity of alterations of a periodic acoustic signal, expressed in cycles per second, or Hz. Commonly known as pitch.

Hearing Loss Prevention Program (HCP) is required by the Hearing Conservation Amendment (1983) which requires that a hearing conservation program be administered when employee noise exposures are 85 dBA TWA on slow meter response. This corresponds to a 50% noise dose. This is called the OSHA action level.

Hertz (Hz) Unit of measurement of frequency, numerically equal to cycles per second.

Impact-type noise type of noise impact noise generated by the impact of drop hammers and punch presses on another surface. This type of noise is described as "transient" as it is less than one second in duration, which may be repeated after a delay of more than one second.

Intermittent noise a type of noise exposure that an employee is exposed to if he/she makes trips from one type of noise to another several times during a normal working day (i.e. the inspector or facility supervisor who periodically makes trips from a relatively quiet office into noisy production areas may be subject to this type of noise).

Noise dose The ratio, expressed as a percentage, of (1) the time integral, over a stated time or event, of the 0.6 power of the measured SLOW exponential time-averaged, squared A-weighted sound pressure and (2) the product of the criterion duration (8 hours) and the 0.6 power of the squared sound pressure corresponding to the criterion sound level (90 dB).

Noise Dosimeter An instrument that integrates a function of sound pressure over a period of time in such a manner that it directly indicates a noise dose.

Noise Reduction Rating (NRR) This is the HPD manufacturer's single number attenuation rating based on idealistic laboratory measurements across a range of frequencies.

Noise-Induced Permanent Threshold Shift (NIPTS) Hearing loss suffered as the result of noise exposure, all or part of which is permanent.

Octave-Band Analyzer a sophisticated instrument used to determine where the noise energy lies in the pitch/frequency spectrum. Most commonly used when engineering control of noise problems is planned, because industrial noise is made up of various sound volumes/intensities at various pitches/frequencies.

Peak sound level OSHA requires that accurate sound level measurements be made of true peak SPL (i.e. OSHA requires that peak noise exposures be kept below 140 dB for impulse sound). True peak SLM readings must adequately measure a pulse of 100 microseconds in duration.

Permissible Exposure Limit (PEL) This is the eight-hour, time-weighted average noise level that must not be exceeded. The OSHA PEL is 90 dBA per 8-hour day with a 5 dB exchange rate.

Projected Dose projects an 8-hour dose from the sample obtained in less than 8 hours. Most accurate if noise levels are constant.

Representative exposure Measurements of an employee's noise dose or 8-hour time-weighted average sound level that the employers deem to be representative of the exposures of other employees in the workplace.

Sound level a level of sound in dBA, dBB or dBC of sound waves in the air which are referenced above the standard sound pressure level of 20 µPa.

Sound Level Meter (SLM) This is the basic instrument used to measure sound pressure variations in air.

Sound Pressure Level (SPL) Measured in decibels, it is 20 times the logarithm to the base 10 of the ratio of the pressure of a sound to the reference pressure of 20 m Pa.

Temporary Threshold Shift (TTS) Hearing loss suffered as the result of noise exposure, all or part of which is recovered a period of time after removal from the noise source.

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

Training program is required annually, concerning effects of noise on hearing, use of hearing protective devices, and the purpose/necessity of audiometric testing.