Noise in Quarries
What is Noise?
Noise means unwanted sound or loud discordant or disagreeable sound or sounds. The effect of noise on hearing can be temporary or permanent. Temporary deafness is often experienced after leaving a noisy place. Although hearing recovers within a few hours, this should not be ignored as it is a sign that continued or regular exposure to such noise could cause permanent damage. Hearing loss is usually gradual due to prolonged exposure to noise. it may only be when damage caused by noise over the years combines with normal hearing loss due to ageing that people realise how deaf they have become. Hearing damage can also be caused immediately by sudden, extremely loud noises, though this is not common. Exposure to noise may also cause tinnitus, which is a sensation of noises (such as ringing or buzzing) in the ears. This can occur in combination with hearing loss
Noise measurements are necessary to assess employee noise exposure and to prepare an effective noise reduction programme. Because the sensitivity of the ear varies with the frequency of sound received, meters used to measure noise levels according to the decibel scale incorporate weighting filters which mimic the response of the human ear. The resultant readings are expressed as ‘A-weighted decibels’ dB (A).
Chapter 1 of Part 5 of the Safety, Health and Welfare at Work (General Application) Regulations 2007 (S.I. No. 299 of 2007) as amended sets down the minimum requirements for the protection of workers from the health risks associated with noise in the workplace.
Reducing Noise Exposure in Quarries
General Good Practice
Well-planned preventative maintenance schemes will have beneficial effects on noise control. Examples of the causes of excessive noise are worn bearings, air leaks, cover/enclosures not properly fitted, loose materials on platforms, loose bolts, rattles and worn chute linings etc.
Many of the larger and more modern machines have integral control cabins for the operator, from which all of the machine functions can be controlled. These cabins also provide protection from dust and the elements. There are significant noise reduction benefits by fitting a silencer to the rotation motor on a down the hole drilling machine particularly where it is on the mast. Diesel powered compressors should have silencers and covers and doors should be closed.
On new machines, the noise levels in the cabins need not be a problem. On older machines, soundproofing and physically dividing the engine from the driver’s cab may be necessary to reduce the noise to acceptable levels. Successful noise level reductions can only be maintained if the equipment is kept in good order and the doors and windows fit properly and are kept closed.
Insulation and covers around engines and fans can greatly reduce noise levels. Engines should be fitted with suitable intake silencers. Retrofitting can be worthwhile but is seldom easy.
All cabs that are sound-proofed are likely to have or should have the following features:
a. anti-vibration mountings;
b. complete enclosure with any openings (for ventilation) fitted with an acoustic attenuator;
c. vibration damped panels;
d. acoustic lining of the cab.
Depending upon the location, installation and particular type of crusher, high levels of noise are involved. Resilient mountings, chute linings, acoustic curtains, lagging, covers etc. can bring about useful reductions in noise levels. However it is difficult to reduce noise below the second action level. In many cases this can only be achieved by housing the operator in a control cabin. If remotely situated, the use of closed-circuit television (CCTV) can ensure adequate operation.
The use of synthetic screen mats or cloths to replace the traditional metal plate or woven wire has immense benefits and, coupled with chute linings, enclosures or complete encapsulation, further reductions can be achieved. If a complete screen house is considered to be an enclosure, personnel should only be allowed to enter if suitable PPE is used. Entry to such enclosures should be avoided when the equipment is in use and the use of control techniques including bin level indicators and CCTV should be considered.
The larger the product, then generally the greater the problem. The use of ‘stone’ baffles and/or chute linings can reduce both noise and wear. Efficient maintenance can reduce ‘squeal’ from conveyor idlers. By reducing the drop height and by preventing material impacting onto empty bins/hoppers can restrict noise levels and the use of spiral chutes or lined cascade towers will lower noise levels.