Metal manufacturing noise control

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Noise-induced hearing loss (NIHL) is still a cause of reduced quality of life for many metal workers. High noise levels with potentially damaging impact occur in many operations like grinding, punching, shearing, forming etc. Significant impact noises are also produced when handling material such as dumping sheared rods into racks, stacking sheet metal and dropping metal offcuts into metal recycling bins. 

What does the law say?

Employers must, so far as is practicable, ensure that noise to which a person is exposed at the workplace does not exceed the exposure standard for noise (Occupational Safety and Health Regulation 3.46), namely an exposure equivalent to 85 dB(A) for 8 hours a day or a peak noise of 140 dB(C). 
Like any other hazards at the workplace, noise hazards should be controlled by following the 3 basic steps: 

  • hazard identification
  • risk assessment 
  • risk control 

Hazard identification

If you have to raise your voice to a shout to be understood by others one metre away, then the employer, in consultation with occupational safety and health representatives and other employees, should list all the machines and activities that produce high noise levels. At this stage it can be decided if all those activities/machines are necessary and if they can be replaced by other, less noisy ones. 

If it is not possible to eliminate all the noise sources from the workplace then a risk assessment should be undertaken. 

Risk assessment

The risk assessment should be done by a competent person using methods and instrumentation described in Australian Standards. The assessment should detail the levels present, items causing the most noise and people affected by the noise, so that a noise control plan can be prioritised. 

Risk control

Once you have assessed the risks, you need to introduce changes to reduce the risk of NIHL. The best way of controlling noise is to eliminate the sources of noise from your workplaces. This can be done by introducing a 'buy quiet' purchasing policy or by designing a workplace in a way that separates noisy processes and machines from people. 

For existing workplaces the best way to handle noise control is to follow the following steps or a combination of them. 

  • elimination: eg. high quality welding eliminates or significantly reduces the need for grinding. 
  • substitution: eg. hydraulic pressing instead of stroke forming. 
  • isolation: eg. by doubling the distance from the source inside a workshop the noise level decreases by about 2 - 4 dB(A) or in the open by 6 dB(A). 
  • engineering noise control 
  • controlling noise at the source: eg. Installing vibration isolation fittings reduces significantly noise radiated by vibrating parts of the machine. 
  • controlling engine noise - eg. Installing an appropriate silencer reduces noise emitted by an engine. 
  • controlling noise - transmission path: eg. enclosing machines, separating noisy and quiet areas by barriers, using sound absorbing material, placing machines away from hard-surfaced walls. 
  • controlling noise by maintenance: eg. replacing worn or chipped gear teeth, balancing machines. 
  • using quieter work practices: eg. using bending instead of hammering, lowering materials instead of dropping, lining benches.
  • administrative control: eg. rotating operators, scheduling noisy activities for outside of normal hours, providing quiet refuge rooms. 
  • personal hearing protectors: eg. suitable muffs, plugs or combination of both. 

Once controls have been implemented, you need to check that they: 

  • are being used correctly 
  • have solved the problem 
  • are not causing further problems 

Training

Everyone exposed to high noise levels at the workplace needs training. This training should cover the effect of exposure to noise on health, the noise exposure present in the workplace and steps taken to control it. Every employee should know which hearing protectors should be used and for which jobs, how to look after ear muffs, when to replace them, how to insert earplugs properly. 

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