The regulations are designed to protect individuals from damage to their hearing, both from exposure to sustained levels of noise over a working life, and from very high impulses of noise, which can give instant damage. With this in mind, measurements are taken which assess the average exposure an individual is subjected to throughout the day and also measure any ‘peaks’ of noise which could result in instant hearing damage.

In order to compare different industries and shift times in a way that the same action levels can be used, noise exposure is standardised to an eight hour working day value called LAEP,d (‘daily personal noise exposure). When measuring the LAeq it is important to measure for a period of time that is representative of the employees’ exposure and what the exposure time is for that noise. If an employee performs different jobs (and hence experiences differing noise levels) it will be necessary to repeat this for each different job, noting the exposure time for each.

If people are likely to be exposed to high levels of impulsive noise, such as noise emitted from heavy pressing operations or sheet metal working, then the peak noise must be measured.

The two main methods for the measurement of noise are either to use a sound level meter or a noise dosimeter. A sound level meter is  primarily designed as a hand held meter, whereas the noise dosimeter is worn by an employee for his or her working shift. A common misconception is that if you have to measure noise dose, you use a dosimeter. In fact the HSE’s preferred method of measurement for noise surveys is to use a sound level meter.

There are several reasons for this, primarily because when performing a noise survey with a sound level meter the operator is present and measuring the noise of the employee. This ensures there are good quality measurements that are repeatable. With a sound level meter, 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 the difficulty to assess the noise dose using a sound level meter is increased because more and more measurements would need to be taken in order to calculate noise dose. This is when a survey would include the use of dosimeters. At RSA we use small dosebadges that employees can wear on their lapel or collar. The dosebadge can then be started at the beginning of the shift. Another useful feature of noise dosimeters is that they will ‘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 through a shift. 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 will give the employer the ability to directly see which operations most need noise control in order to reduce noise exposure.

Although it is always the last resort, where the selection of hearing protection is required it may be necessary to measure the frequencies of the noise that are present (octave bands) to ensure that the hearing protection is giving the correct attenuation:

	as opposed to
Octave band measurement		Broadband time history

If you feel that you may need a noise assessment within your workplace, your first step should be to ring us for an informal chat. This will help us to understand the issues within your workplace and enable us to suggest an assessment programme to satisfy both the current legislation, as well as your own needs. Any noise at work risk assessment involves a consultant spending some time at your site, taking noise measurements, and then writing the report.