One of the main effects of noise at work is noise-induced hearing loss. This can happen in two ways: 

• noise of very high peak levels (more than about 135-140 decibels (dB)) can cause immediate damage to the structures of the inner ear; or 
• noise of a lower level over an extended period of time can cause gradual damage.

People vary in their susceptibility to noise damage.  A 'safe' level to protect the most noise-sensitive people from any hearing loss during a working lifetime, would be an average over the work shift of about 75 dB(A).  For more information see Section 1.2 of the Code of practice, Managing noise at workplaces.

Noise can also contribute to other health effects such as increased blood pressure, stress and tinnitus (ringing in the ears).  Safe levels to guard against these effects have not yet been determined and research is continuing.  As a guide, stress can be reduced by keeping levels below 50 dB(A) in areas where people need to do work requiring concentration. 

Another effect of noise is difficulty communicating and hearing warning signals or other sounds needed to work safety.  A 'safe' level in these situations will vary depending on the level of the signals and the hearing capabilities of the listeners. 

Reducing noise levels at the source provides the most effective way of protecting workers' hearing.

Because noise is measured on a logarithmic scale, a reduction in noise of 3 dB(A), which seems small, is in fact the equivalent of halving the intensity of the noise. This would mean that the person could work for twice as long at the reduced level and have the same daily personal noise exposure as before.

The various types of hearing protectors (earmuffs, ear plugs, semi-inserts) are not the best forms of protection because they rely on individual workers being able and willing to use the equipment correctly.  Failure to wear the hearing protectors correctly 100% of the time in excessive noise will significantly decrease the effective protection.  Their effectiveness  is also reliant on their condition and whether they fit correctly, which is particularly difficult if other protective equipment also needs to be worn.  They can also fail or be inefficient without this being visibly obvious.

For all these reasons, hearing protectors are regarded as a last resort risk reduction measure, to be used only when all other practicable steps to reduce excessive noise have been taken. 

Depending on the source, noise can be reduced in several ways, as follows:

• buying quiet machinery and equipment; 
• maintaining machinery and equipment routinely; 
• reducing machinery and equipment vibration; 
• muffling engine and compressed air noise; 
• isolating the noise source in an insulated room or enclosure; 
• placing a barrier between the noise source and the employee; or 
• isolating the employee from the source in an insulated booth or room. ​