Design and lay out the workplace for reduced noise exposure
When considering a new workplace or modifying an existing one, noise emissions and noise exposure can be limited by careful choice of design, layout and the construction materials used for the building. For example, the appropriate use of absorption materials within the building can reduce or limit the effects of reflected sound (specialist help will be needed to put this into effect).
Noise risk management is a lot easier if you limit the number of employees exposed. Careful planning could segregate noisy machines from other areas where quiet operations are carried out, reducing the need for noise control after the workplace is in operation (see also the section on screens and barriers). The number of employees working in noisy areas should be kept to a minimum.
When considering using noise-absorbing materials to change the acoustic characteristics of a work area remember:
- environmental and workplace factors: absorption materials are available in forms which are designed to withstand physical impacts, and can be adapted to hygienic environments or where absorption of oil, water etc may be a problem;
- there may be a reduction in the natural light if absorption is placed in the roof;
- adding absorbent materials to walls and ceiling areas will only affect the reflected, reverberant sound – not the direct path of sound.
Screens and barriers - placing an obstacle between the noise source and the people
Screens, barriers or walls can be placed between the source of the noise and the people to stop or reduce the direct sound. Barriers should be constructed from a dense material, eg brick or sheet steel, although chipboard and plasterboard can be used.
Screens and barriers work best when they are placed close to the noise source or close to the people you are trying to protect. The higher and wider they are, the more effective they are likely to be. They work best in rooms with either high or sound-absorbent ceilings.
Covering the barrier or screen with noise-absorbing material on the side facing the noise source will have the added advantage of reducing the sound reflected back into that area containing the noise source. Those workplaces which have already been treated with sound-absorbing material will help to create conditions which will allow the screen or barrier to perform to its maximum potential, since in these cases the direct noise is likely to be the dominant source.
CAUTION: Be aware of the following when using screens or barriers:
- Screens and barriers may not work well for low frequencies.
- They are best at reducing the direct noise, and may not affect reflected noise.
- Always place the screen or barrier as close to the noise source or employee position as possible.
- The screen or barrier should be made of a dense material, and should be lined with absorptive material facing the noise source.
- Always consider other health and safety risks, such as safe movement of people and vehicles, when placing barriers in the workplace.
Refuges - noise-reduced enclosures for people
Noise refuges can be a practical solution in situations where noise control is very difficult, or where only occasional attendance in noisy areas is necessary. The design of refuges will be similar to that of acoustic enclosures, although since the purpose is to keep noise out rather than in, lining the inner surfaces with acoustic absorbent material will not be necessary.
If machine controls are brought into the refuge, and thought is given to allowing remote monitoring or viewing of machinery and processes, it should be possible to minimise the amount of time that workers have to spend outside the refuge – so maximising the benefit of having the refuge. For example, a refuge that is used for only half a shift will achieve no more than 3 dB reduction in noise exposure.
Refuges must be acceptable to employees. This means they must be of a reasonable size, well lit and ventilated and have good ergonomic seating.
CAUTION: Check your refuge design for:
- adequate ventilation;
- good door and window seals;
- self-closing doors;
- dense construction materials, with plenty of acoustically double-glazed windows;
- isolation from the floor to reduce structure vibrations;
- size – is it large enough?
Distance - increase the distance between the source of the noise and the people
Increasing the distance between a person and the noise source can reduce noise exposure considerably. Some examples of this are:
- direct the discharge from exhausts well away from workers, eg by fitting a flexible hose to discharge exhaust several metres away from the operator. Similarly, on a mobile machine powered by an internal combustion engine the exhaust can be kept well away from the driving position;
- use remote control or automated equipment to avoid the need for workers to spend long periods near to machines;
- separate noisy processes to restrict the number of people exposed to high levels of noise, eg test engines in test cells which need to be entered only occasionally, make arrangements for quiet inspection tasks to be carried out away from noisy manufacturing areas, and locate unattended air compressors and refrigeration plant in separate rooms.