A variety of sources contribute to the generation of noise on timber processing sites. Woodworking machinery is of central importance, but other contributors include extraction equipment, chippers, air tools, vehicles and stereos.

Noise assessments are a legal requirement on sites where the daily personal noise exposure is likely to be above the first action level (see below). Despite the fact that these requirements have been in place since 1989, it is still common to find companies that have employees exposed to significantly more than the first action level, which have conducted no assessments.

Furthermore, many employees have not been educated about the dangers of noise – accepting it as ‘part of the job’. Consequently, they do not bother with hearing protection or they wear it in an incorrect manner – leading to hearing deteriorating much more rapidly than it would naturally.

Other problems with uncontrolled noise in the workplace are that it can distract operators from their task or prevent them from hearing warnings.

Noise is often described as unwanted sound, with the latter being transmitted through vibration in the air. Such vibrations are converted into mechanical energy by the ear drum which is connected to three small bones, which in turn are attached to the inner ear. There are around 30,000 highly sensitive hair cells in the latter which convert physical movement into details which are sent to the brain.

Exposure to excessive noise levels can lead to a gradual reduction in hearing sensitivity over and above that which occurs with age. In addition, tinnitus can occur, leading to a constant ringing in the ears.

The ear is sensitive to loudness – a reflection of the intensity of the sound. However, the intensity is strongly affected by the frequency. The ear is most sensitive to sounds in the 1-4kHz range. A given sound pressure (measured in decibels) will be perceived as being less loud the further above or below this range the sound is.

Consequently, sound will often be corrected to reflect the sensitivity of the human ear through the use of the ‘A’ weighted scale – giving a level of noise in terms of dB(A). It should be noted that an increase of 3dB doubles the sound intensity – ie 83dB is twice as loud as 80dB.

Daily action levels

The damaging effects of noise are related to the amount of sound energy received. This dose depends upon the level of the noise and the duration of the exposure. Thus, a long exposure to a low level of noise may cause comparable hearing damage to a short exposure to a high level of noise.

Consequently, the Noise at Work Regulations 1989 concentrate upon eight hour daily action levels expressed as ‘equivalent continuous daily personal exposure levels’ or LEP,d.

The regulations place a general duty upon employers to reduce the risk of hearing damage to the lowest level reasonably practicable. The preferred option for noise reduction is prevention at source, for example through the proper specification and maintenance of equipment. Consideration should then be given to attenuation, ie reducing the transmission of noise before it can reach the worker. This may involve blanketing walls, ceilings and partitions with noise-absorbing materials.

Personal protection such as ear plugs are a last resort which should be used only if neither of the first two approaches leads to a satisfactory solution. The problem with personal protection is that it protects only the individual wearing it. Furthermore, this protection is only as good as the equipment, its maintenance and the way it is worn. It is rare to enter a hearing protection zone and find that all employees and visitors have remembered to wear their protection.

Finally, exposure time to excessive noise may be reduced by allowing rest periods in areas away from noise and by the rotation of tasks. Thus, an operator may spend four hours working on machinery followed by four hours in assembly areas.

If the daily personal noise exposure is likely to be 85dB(A) or above, a noise assessment must be conducted by a competent person.

Within the timber industry, at least some employees will be exposed to more than 85dB(A) in the vast majority of woodworking areas. Consequently, employers should ensure that they have conducted noise monitoring. This need not be repeated every year, especially if there has been little in the way of change in the workplace.

If the level of noise is between 85-90dB(A), the employer must undertake training and awareness raising to ensure that the employees are aware of: the risks to hearing associated with the workplace; how to minimise the risk; consequences of not controlling the risk; how to obtain hearing protection; and how to use, maintain and store hearing protection.

Hearing protection must be provided to those that request it. However, where noise levels are between 85-90dB(A), it is a matter of individual choice whether to wear hearing protection. The awareness raising allows individuals to make an informed choice based on the nature of their typical working day.

If the level of noise is above 90dB(A), the employer must take more stringent action. Ear protection zones must be marked, hearing protection must be provided and it must be worn by all who enter the zone.

Management must play an active role in hearing protection, being seen to be wearing the appropriate equipment at all times and ensuring that all others do so on a continuing basis.

Different types of personal protective equipment (PPE) are available to protect hearing and these have their relative merits and problems.

Expanding polyurethane foam ear plugs are relatively cheap and fit a wide range of individuals. No maintenance is required and they are generally comfortable. They have fairly good attenuation properties across the aural frequency range yet allow some degree of speech communication. However, the plugs do not reduce the sound intensity transmitted through the bone structure around the ear. They are also relatively difficult to see from the perspective of managers ensuring that everyone is wearing the required PPE.

Consequently, disposable ear plugs tend to be used on a temporary basis – for visitors and contractors or where there is a high turnover of staff.

Ear defenders

Ear defenders are designed to cover the ears with large external cups held in position with a headband. They provide the best attenuation across the aural frequency range and reduce the transmission of sound through the bone structure around the ear. Furthermore, it is easy to see if they are being worn.

However, defenders are more expensive and some employees object to them because of their bulk, heat and general discomfort. In addition, protection may be reduced for spectacle wearers or those with a lot of hair.

It should be noted that the EU recently proposed a tightening of the levels of controls on noise and vibration – with thresholds being reduced by 5dB(A). Companies should also be aware of the increasing number of civil actions being brought against employers by former employees claiming that their hearing has been damaged as a result of work. Consequently, more organisations are conducting hearing tests on new and existing employees, as well as ensuring that they have written records of relevant training conducted and working procedures.