As with any occupational hazard, control technology should aim at reducing noise to acceptable levels by action on the work environment. Such action involves the implementation of any measure that will reduce noise being generated, and/or will reduce the noise transmission through the air or through the structure of the workplace. Such measures include modifications of the machinery, the workplace operations, and the layout of the workroom. In fact, the best approach for noise hazard control in the work environment, is to eliminate or reduce the hazard at its source of generation, either by direct action on the source or by its confinement.

Components And Working

In existing facilities, quantification of the noise problem involves identification of the source or sources, determination of the transmission paths from the sources to the receivers, rank ordering of the various contributors to the problem and finally determination of acceptable solutions.

To begin, noise levels must be determined at the locations from which the complaints arise. Once levels have been determined, the next step is to apply acceptable noise level criteria to each location and thus to determine the required noise reductions, generally as a function of octave or one-third octave frequency bands (see chapter 1).

Once the noise levels have been measured and the required reductions determined, the next step is to identify and rank order the noise sources responsible for the excessive noise. The sources may be subtle or alternatively many, in which case rank ordering may be as important as identification. Where many sources exist, rank ordering may pose a difficult problem.

When there are many sources it is important to determine the sound power and directivity of each to determine their relative contributions to the noise problem. The radiated sound power and directivity of sources can be determined by reference to the equipment manufacturer's data (ISO 4871) or by measurement, using methods outlined in chapter 1. The sound power should be characterized in octave or one third octave frequency bands (see chapter 1) and dominant single frequencies should be identified. Any background noise interfering with the sound power measurements must be taken into account and removed.

Often noise sources are either vibrating surfaces or unsteady fluid flow (air, gas or steam). The latter are referred to as aerodynamic sources and they are often associated with exhausts. In most cases, it is worthwhile to determine the source of the energy which is causing the structure or the aerodynamic source to radiate sound, as control may best start there.

Having identified the noise sources and determined their radiated sound power levels, the next task is to determine the relative contribution of each noise source to the noise level at each location where the measured noise levels are excessive. For a facility involving just a few noise sources, as is the case for most occupational noise problems at a specific location, this is usually a relatively straightforward task.

GENERAL SOURCE NOISE CONTROL CAN INVOLVE:

- replacement or adjustment of worn or loose parts;

- balancing of unbalanced equipment;

- lubrication of moving parts;

- use of properly shaped and sharpened cutting tools.

Substitution of materials (e.g., plastic for metal), a good example being the replacement of steel sprockets in chain drives with sprockets made from flexible polyamide plastics.

- electric for pneumatic (e.g. hand tools);

- stepped dies rather than single-operation dies;

- rotating shears rather than square shears;

- hydraulic rather than mechanical presses;

- presses rather than hammers;