Generally hearing loss occurs over a period of time and because that there is not an immediate injury it can be viewed as low risk, and it’s a risk that is hard to see. It’s not until you lay in bed at night and start to notice that annoying ringing in your ears or are always saying WHAT?! to the grandkids that you realise the damage is done.
Whether the exposure standard of 85 dB(A) averaged over eight hours is exceeded depends on the level of noise involved and how long workers are exposed to it. Peak noise levels greater than 140 dB(C) usually occur with impact or explosive noise such as sledge-hammering or a gun shot. Any exposure above this peak can create almost instant damage to hearing. Decibels are not like normal numbers. They can’t be added or subtracted in the normal way. The decibel scale is logarithmic. On this scale, an increase of 3 dB therefore represents a doubling or twice as much sound energy. This means that the length of time a worker could be exposed to the noise is reduced by half for every 3 dB increase in noise level if the same noise energy is to be received.
Table 1: Equivalent Noise Exposures LAeq,8h = 85 dB(A)
Noise Level dB(A) Exposure Time Example Sound Source
80 16 hours[i] Kerbside Heavy Traffic
82 12hours1
85 8 hours Front end loader
88 4 hours
91 2 hours Lawn Mower
94 1 hour
97 30 minutes
100 15 minutes Sheet Metal Workshop
103 7.5 minutes
106 3.8 minutes
109 1.9 minutes Chainsaw
112 57 seconds
115 28.8 seconds
118 14.4 seconds
121 7.2 seconds Angle Grinding
124 3.6 seconds
127 1.8 seconds
130 0.9 seconds Rivet Hammer
When purchasing equipment the operators manual will have the sound power level listed and this will tell you how many decibels the equipment will produce when operating. Some equipment will have a sticker on the equipment itself with the power sound level (decibel rating) e.g. Stihl farmboss MS311 chainsaw has a sound power level of 106 dB (A), this means damage to your hearing will occur after 3.8 minutes if no hearing protection is used. The other way to identify noise levels is to use a noise (dose) meter to measure the noise level. Ongoing monitoring of potential noise hazards by reviewing the audiometric tests of the workers to see if the provided Personal Protective Equipment (PPE) is appropriate.
Effective risk control may involve a single control measure or a combination of two or more different controls. Eliminate the risk The most effective control measure is to eliminate the source of noise completely, for example by ceasing to use a noisy machine, changing the way work is carried out so hazardous noise is not produced or by not introducing the hazard into the workplace. Obviously, this won’t get the job done. Minimise the risk If it is not reasonably practicable to eliminate the source of noise, you must minimise the risk associated with hearing loss so far as is reasonably practicable. This includes ensuring that the noise does not exceed the exposure standard by choosing one or more of the following measures:
  • substitute the hazard with plant or processes that are quieter
  • modify plant and processes to reduce the noise using engineering controls
  • isolate the source of noise from people by using distance, barriers, enclosures and sound-absorbing surfaces.
If there is a remaining risk, it must be minimised so far as is reasonably practicable by implementing administrative controls, and if a risk still remains, then suitable personal protective equipment must be provided and used. These two types of control measures, when used on their own, tend to be least effective in minimising risks because they rely on human behaviour and supervision.

Substituting plant or processes to reduce noise

Buy ‘quiet’ One of the most cost-effective and long-term ways of reducing noise at work is choose the quietest plant for the job. This can be done by obtaining information on noise emission (for example, data on sound power level or sound pressure level at the operator position) from the manufacturer, importer or supplier of plant and comparing it to determine the quietest plant. Using engineering controls A good understanding of the operation of the plant or process is necessary when considering ways of minimising noise at its source. Examples of engineering control measures include:
  • fitting exhaust mufflers on internal combustion engines
  • fitting silencers to compressed air exhausts and blowing nozzles
  • isolating a vibrating noise source to separate it from the surface on which it is mounted using rubber mounts and flexible connections
  Maintenance Regular maintenance of plant and equipment is essential as it will deteriorate with age and can become noisier. Check for changes in noise levels – badly worn bearings and gears, poor lubrication, blunt blades, loose parts, unbalanced rotating parts and steam or air leaks all create noise that can be reduced with good maintenance. Engineering controls such as vibration mountings, impact absorbers, gaskets, seals, silencers, barriers and other equipment should be regularly inspected and maintained. Reduce the amount of noise exposure by reducing the time they are exposed to it. Using personal hearing protectors Regulation 44: If personal protective equipment (PPE) is to be used at the workplace, the person conducting the business or undertaking must ensure that the equipment is:
  • selected to minimise risk to health and safety
  • suitable for the nature of the work and any hazard associated with the work
  • a suitable size and fit and reasonably comfortable for the person wearing it
  • maintained, repaired or replaced so it continues to minimise the risk
  • used or worn by the worker, so far as is reasonably practicable.
Regulation 46: A worker must, so far as reasonably able, wear the PPE in accordance with any information, training or reasonable instruction. Personal hearing protectors should be selected and maintained in accordance with AS/NZS 1269.3 Occupational noise management hearing protector program. Suppliers of hearing protectors should provide the full information on the attenuation likely to be provided including the SLC80 ratings, class and octave band attenuation values. The attenuation values should be derived from attenuation measurements made in accordance with AS/NZS 1270 Acoustics – hearing protectors. Selection When selecting personal hearing protectors you should consider:
  • the degree of attenuation required in the worker’s environment. Do not provide protectors that overprotect by cutting out too much sound – this can cause difficulties hearing verbal instructions and other sounds needed to work safely
  • the suitability for the type of working environment and the work tasks. For example, ear-plugs are difficult to use hygienically for work that requires them to be inserted with dirty hands and in these circumstances, ear-muffs are more appropriate, but ear-muffs can be uncomfortable to wear in hot environments and can make it difficult for the wearer to enter a confined space or to wear a helmet
  • the comfort, weight and clamping force of the personal hearing protector.
Recommended Class of hearing protector
Measured exposure LAeq,8h dB(A) Class
Less than 90 1
90 to less than 95 2
95 to less than 100 3
100 to less than 105 4
105 to less than 110 5
Individual fit of personal hearing protectors is critical for optimum protection. Several devices are available to assist with this. Wearing work equipment—such as hard hats, dust masks and eye protection—may affect the performance of the protector. The fit of hearing protectors should be checked while the user is wearing regular work equipment. Workers wearing spectacles should be fitted with hearing protectors while wearing the spectacles. Maintenance Personal hearing protectors must be regularly inspected and maintained to ensure they remain in good, clean condition. The inspections should check that:
  • ear-muff seals are undamaged
  • the tension of headbands is not reduced
  • there are no unofficial modifications
  • compressible ear-plugs are soft, pliable and clean.
If disposable ear-plugs are used, they should only be worn once. This content has been abbreviated from one of our O H & S articles, written by AST Group.