Control of noise in the workplace - Part 2

When performing a noise survey, an accurate representation of a person’s exposure to noise with a sound level meter (SLM) or noise dosimeter is required. An SLM is a handheld device, which enables measurements to be taken at the ear (within 10-15 cm) with the instrument pointing at the noise source, measuring both ears. By repeating this exercise for all the operations that an employee performs during the day, it’s possible to then calculate their daily exposure (LAEP,d).

Employees should ordinarily be informed they’re being measured; however, it may not be possible to do so in certain situations (eg, forklift drivers) or for individuals that have a complex work pattern and are exposed to many different noise levels. In these situations, it’s best to use a noise dosimeter worn on the person, preferably for their entire shift.

So, which device is best? A common misconception is that if you have to measure noise dose, you use a dosimeter. In fact, the preferred method of measurement for noise surveys is to use an SLM. There are several reasons for this, primarily because when performing a noise survey with an SLM, the operator is present and measuring the noise of the employee. This ensures good quality measurements that are repeatable.

With an SLM, a representative measurement is made for each job function and the exposure time for each, and from there the eight-hour exposure can be calculated. The more complex the work pattern of an employee becomes, the more difficult it is to assess the noise dose using an SLM, because more measurements would need to be taken to calculate noise dose. It may, at times, not be possible to measure the noise with an SLM because it’s not practical or safe, say for people like forklift drivers or individuals with complex work patterns. This is when a noise dosimeter is the best way of getting a noise dose. Where the selection of hearing protection is required, it may be necessary to measure the frequencies of the noise that are present to ensure the hearing protection is giving the adequate attenuation.

A noise dosimeter can be started at the beginning of the shift and run until the end of the working day; then the LAEP,d can be directly read from the instrument or downloaded without the need for calculations. Noise dosimeters will also ‘log’ the noise data so that, when downloaded to a PC, the time history of the noise can be viewed. This gives the ability to analyse when and where high noise exposures occur. This can be even more useful when the dosimeter can be placed on an employee who is prepared to make a diary of what times and jobs he or she was performing throughout the day. This enables employers to directly see which operations most need noise control in order to reduce noise exposure.

When it is applicable to use a noise dosimeter, it is important to know the pitfalls in order to get reasonable results. The inherent problem with a dosimeter is that it is unlikely that you are going to be present to watch the employee and what they are doing. This means that they can be left to their own devices and the novelty of having a noise monitor is too much for many to resist. For example, people shout into it and try to press buttons etc. In order to try and get good data when you first get a dosimeter, you must firstly place it on a responsible employee and explain thoroughly the importance of the measurements. Secondly, ignore the first few days’ worth of data that you get and get the dosimeter out on site every day so that the novelty will wear off.

By having a noise dosimeter where you can see the time history of the noise, it’s possible to instantly see from the downloaded graphs if there are any ridiculous spikes of noise that you know the employee couldn’t have been exposed to and check any results you get by going out with an SLM to verify them. It’s also possible for employees to keep a diary of their working day, which can be correlated to any exposure graph. This will allow you to see exactly what activities are contributing the most to an employee’s exposure and therefore concentrate any noise control on these particular activities.

Part 3 will consider how to get the most out of noise measurement surveys.