Module 1: Occupational Hygiene - Section 5: Instrumentation

OH5.7: Noise Survey and Noise Control

Noise survey:

Noise surveys provide useful information which enable identification of:

• areas where employees are likely to be exposed to harmful level of noise;
• machines and equipment which generate harmful levels of noise;
• employees who might be exposed to unacceptable noise levels; and
• noise control options to reduce noise exposure.

A noise survey is conducted in areas where noise exposure is likely to be hazardous (>85 dB(A)). A noise survey involves measuring noise level at selected locations throughout the plant or sections to identify noisy areas. It is important to make sure that noise measuring instruments are always properly calibrated. This means checking the instrument's calibration acoustically before and after each day's use, as well making appropriate electronic assessments at appropriate intervals.

A reasonably accurate sketch showing the locations of workers and noisy machines is drawn.

SABS Code 083-1996 gives detailed information on how to conduct a noise survey (it is in the process of being revised ). ⁶

According to the Environmental Regulations for Workplaces a noise survey, for compliance purpose, must be conducted by an Approved Inspection Authority. Also the noise assessment should be repeated when:

• there is a change in production process
• on installation of new equipment; or at least once every two years.

 Recently promulgated Noise Regulations under the OHSAct

Noise control:

The noise survey should produce a map of sound levels in the workplace, and focus attention on areas that contribute the most to the problem. Options available for controlling these sources and reducing noise levels at the worker's ear are threefold: ⁸

• Control at source - reduce noise output of machines and should be first line of defense.
• Control of noise path - placing shields and baffles between noise source and operator, and is the second line of defense.
• Enclosure of operator - only when all else fails, enclose operator either in a sound proof booth or protect by means of ear protection.

Exposure to noise is generally controlled by engineering techniques, administrative measures, and personal protective equipment.

Engineering controls entail eliminating excessive noise during the design stage of a new plant or during revision of processes in an existing plant. One of the strategies available is to substitute noisy machinery / process / material with less noisy equivalents. If substitution is not economically feasible, then it is necessary to consider modifying machinery. Some noise control techniques can be applied easily and cheaply by staff in the plant (balancing, lubricating and adjusting machines). Other techniques, for example use of baffles and partitions, the muffling of vibration, and the use of acoustically soft materials are more expensive and complicated to install.

Administrative control measures include change in production programmes, rotating workers in the plant to ensure acceptable noise dose, and limiting amount of continuous exposure (eg time) to high noise levels.

Administrative measures are easy to implement, and also have the additional advantage that few additional costs are attached. However, this does not necessarily mean that they are cost-effective. This needs to be determined on a case-by-case basis accounting for all the costs.

Use of personal protective equipment is often regarded as a cheap and quick way to solve the noise problem. However, it is expensive to implement in the long run. One of the reasons noted by workers for resisting use of hearing protection devices is the discomfort this causes.

Play the video clipNot much control going on here! The hooter is used to communicate with workers over the background noise which itself is more than 85dB(A).

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