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| Module 1: Occupational Hygiene - Section 5: Instrumentation |
| OH5.6: Workplace Noise Measurents |
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| Module 1: Occupational Hygiene - Section 5: Instrumentation |
| OH5.6: Workplace Noise Measurents |
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Where it is considered that workers may be exposed to noise exceeding the equivalent noise level of 85 dB(A), such a workplace should be assessed. The purpose of such assessment would be to:
A number of instruments for measuring sound levels are commercially available. These include sound level meters (SLM), integrating sound level meters (ISLM), noise dosimeters and sound frequency analysers. 7
The Sound Level Meter is the basic instrument used for measuring noise. It consists of a microphone which converts sound waves into electrical impulses; electric circuitry which modifies and amplifies the signal according to demands of the user; and an output section to display the signal in units of sound as required.
SLMs are categorised by their precision, ranging from the most precise (type 0) to the least (Type 3). Type 0 is usually used in the laboratory, Type 1 is used for noise surveys, Type 2 is a general purpose meter. Type 3 is not recommended for workplace noise measurement. A standard SLM takes only instantaneous noise measurements. This is sufficient in workplaces with continuous noise levels which do not vary substantially. In workplaces with impulse, intermittent or variable noise levels, the SLM makes it difficult to determine a person's average exposure to noise over a work shift.
The Integrating Sound Level Meter integrates sound energy over a measurement period and divides the measured values by the period of measurement to provide a direct reading of the average sound energy over that period. An integrating SLM is most convenient to use for measuring non-steady noise exposure. The ISLM can simultaneously measure the equivalent, peak and maximum sound levels. The equivalent noise level Leq valueis defined as the continuous noise level which, over a given period, has the same total energy as the actual fluctuating noise.
Workers sometimes move around a lot and are thus exposed to varying noise levels. In such a situation it is difficult to accurately determine the worker's exposure with the aid of environmental readings taken from the stationary devices above. For this reason portable personal dosimeters have been developed which give a more accurate reflection of the individual's exposure to noise. The noise dosimeter is carried in the worker's pocket with the microphone attached to his/her lapel for all or part of the shift. The dosimeter then directly measures personal noise exposure, expressed as a percentage of the acceptable exposure. The percentage can be mathematically converted, by means of a nomogram, to a corresponding Leq value. .
