Control of noise in the workplace - Part 3

All instruments have a minimum level of accuracy required for measurements. This is primarily down to the two types of microphone that can be used: Class 2, (the minimum required), or Class 1 (more precise). Note that ‘Class’ is also referred to as ‘Type’, in certain instrument standards but uses the same numbering system. Both dosimeters and SLMs are manufactured to a specific standard. Any SLM used should preferably be manufactured to IEC 61672, but the older standards of IEC 60804 and IEC 60651 are still acceptable. Noise dosimeters should meet the requirements of IEC 61252.

Any noise-monitoring equipment should be field calibrated prior to use, as stipulated by the regulations. This means you should use a ‘field’ calibrator prior to use. Field calibrators produce a noise signal, normally a tone of 1 kHz at 114 dB, allowing you to verify if the noise monitor is measuring the same level. It’s also recommended to place the calibrator on the noise monitor after the measurement as well to ensure there has been no significant deviation. Regulations require instruments and acoustic calibrators to be returned to the manufacturer for full calibration every two years to ensure they remain within specification.

Windshields should always be used on all noise measurements, even if inside. They not only prevent wind affecting the results, but provide some protection for the microphone from dust, moisture and knocks.

If exposed to high levels of noise, it may be necessary to calculate the effectiveness of the hearing protection provided to employees. This involves matching the frequency of noise an employee is exposed to, with a hearing protector that provides good attenuation at those frequencies. The recommended method for doing this is by the ‘octave-band’ method. This involves measuring the frequencies of noise that a person is exposed to using an octave-band SLM. A calculator to then determine how effective the hearing protection provided is can be found at www.hse.gov.uk/noise/calculator.htm.

A noise survey involves much more than taking measurements. Noise exposure is as much about how long the employee is exposed to the noise as the noise level itself. Therefore, it is just as important to look and ask questions of what employees are doing and how long for, as well as their managers, in order to get an accurate idea of an employee’s exposure time. However, performing a good noise survey is as much about using your eyes and ears and knowing employees’ work patterns and responsibilities as it is about using the instrument.

For example, someone whose job role it is to drill holes in metal plates may be performing that job role all day. So if you ask him or her ‘How long every day to you spend doing this job?’ you are likely to get the response ‘All day’ from the employee. Hence, if you used the noise level of when the drill is on in your exposure calculation then an incorrect dose would be calculated. What needs to be done instead is to look at the operation as a whole and analyse how long the drill spends on and off. By measuring the noise with the drill off as well as on, you will be able to use both these values and times, together with their quiet times during breaks to achieve an accurate dose calculation. It is important to remember that the LAeq,8h is a personal value for each employee in their work environment, not an area value. Just measuring noise at points around a site is inadequate.

Conclusion

By using modern noise level meters and dosimeters backed by acoustic calibrators, employers can survey their workplace to assess the element of risk. The cost of a good-quality SLM is a wise investment in this respect. If a problem is found then consultants can be engaged to rectify the problem. This means with some knowledge and understanding of noise measurements and terminology it is possible to achieve a good-quality noise survey without the need to rely on a consultant in the first instance.