It is easy to become complacent about noise in the timber industry. Noise is an unavoidable consequence of working wood with machines, so the problem may be accepted as just being “part of the job”. Where hearing protection is worn, its effect is often limited by incorrect use. In addition, the resulting hearing loss tends to occur very gradually and may not be noticed by the sufferer for some time.
As a result of these problems, companies need to be proactive on the issue. The starting point is to understand exactly how much noise is being generated, via a noise survey. This is a legal requirement on any site where employees might be exposed to more than 85dB. At a level of 85dB it would be necessary to raise your voice to talk to a person two metres away. From April 2006, this level will be reduced to 80dB. In terms of noise, a change of 5dB is extremely significant. The noise scale is logarithmic and an increase of just 3dB represents a doubling in the level of sound energy.
Noise survey
A noise survey involves the use of high specification noise monitoring equipment to record the level of noise in the workplace. It should also assess the suitability of hearing protection. Key elements of the survey might include:
The noise survey will calculate two main levels of noise to which site personnel are exposed: personal daily exposure and peak levels.
Personal daily exposure is the noise dose to which an individual is exposed during the course of the working day. The associated thresholds will be reduced from April 2006. Dose is a function of loudness and duration. For example, an operator exposed to 15 minutes at 105dB is exposed to the same noise dose as one spending eight hours in a 90dB environment. The table below summarises the current and future requirements.
The peak level is the highest sound pressure level to which an individual is exposed. This may last for just a fraction of a second.
Noise limits
A new feature of the revised regulations will be the introduction of noise limits for the first time. The limits represent the maximum level of noise to which an employee may be exposed after taking into account the effect of hearing protection. Calculations are required to ensure that hearing protection is suitable for the type of noise to which workers are exposed both in terms of its frequency and loudness.
Some companies assume that if they specify the heaviest ear muffs available, this will make their employees as safe as possible. However, it is possible to over-specify the level of hearing protection leading to employees being cocooned in a quiet vacuum. This can lead to health and safety problems due to isolation and detachment from the working environment – for example, we are less conscious of the danger of a saw blade if we cannot hear it. In addition, employees may not be able to hear warnings such as fork lift truck horns or shouts from other workers. Therefore, part of the noise survey should ensure that noise exposure is reduced to around 60-70dB(A) for employees after taking into account the effect of their hearing protection.
Exposure to the noise limits can be calculated in a number of ways. The most accurate involves “octave band analysis” to break down noise into its component frequencies. Hearing protection manufacturer data can then be subtracted from these frequencies to give the actual level of exposure with protection.
Expanding polyurethane foam ear plugs fit a wide range of individuals. No maintenance is required and they are generally comfortable. They have fairly good attenuation properties yet allow some degree of speech communication.
However, the plugs are relatively difficult to see from the perspective of a manager who is ensuring that everyone is wearing the required protection. In addition, there are hygiene concerns about rolling ear plugs between the fingers as dust, oil and solvents and so on can be transferred into the ear. This problem can be reduced by the use of foam plugs incorporating insertion sticks as these do not need to be rolled. In addition, disposable plugs can be expensive if they are replaced several times each day. 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 a range of attenuation levels according to the model which is specified and it is easy to see if they are being worn. However, defenders are more expensive and some employees object to them due to their bulk, heat and general discomfort. In addition, protection may be reduced for spectacle wearers.
A compromise is available in the form of ear plugs with plastic bands. These have the benefits of longevity and cost. They are not bulky or hot and can be worn around the neck when not required, encouraging staff to keep the hearing protection with them at all times.
There is no simple answer to the question of which type of hearing protection is best. Ideally, companies might choose one model of each of these three different products – appropriate to the required level of attenuation – and let employees decide which they prefer.
