Seeking sound solutions
October 1st 2007

Complying with the EU Directive on the control of noise in the workplace has been eased over the last decade, as some noise measuring equipment has become simpler to use and at the same time, far more capable, explains Alan Wallis of the IEC working group for sound level meter standard and chief scientific advisor to Scientific Measurements and Pulsar Instruments

Most meters now feature some form of computer control, giving capabilities unheard of by previous generations. In some designs, this increase in power has been targeted towards even simpler operation, while in others it has been used to give new complex information. This mix of capabilities has given rise to three distinct measuring methods.

Simple Survey Many industrial premises do not have noise levels anywhere near the First Action level of 80dBA or 135dBC peak and if you are fairly sure that you fall into this category, the use of an entry level simple digital sound level meter may be adequate. By selecting F-time-weighting and MAX hold, a walk-round survey can be done and if no levels are found above say 74dBA, you can be reasonably sure you are in compliance. However, you cannot be absolutely sure and if there is doubt, or you are near to or over the First Action level, there are two alternatives; measuring the whole area, or individual worker exposure measurements.

Whole area 'Whole area' measurements are the more traditional and an integrating sound level meter with a second peak channel is needed. Traditionally, the meter was set up on a tripod and a long period measured; long enough to be sure the noise was representative of normal conditions.

With some modern instruments, they can be set to make the global measurements you need for compliance, but in parallel can also take a new measurement every minute, storing a 'time history' of the noise which is very valuable in finding the location of the highest levels. One vital matter however in using both the above methods is instrument calibration.

If your meter is not calibrated before and checked after each measurement, you cannot use your data with confidence.

Individual workers Noise Dosimeters have been around for 25 years; they were traditionally big and clumsy devices and had a cable from the belt mounted device to a shoulder worn microphone – no longer.

Several manufacturers have produced devices so small that they can be shoulder worn without affecting the worker's actions and with no risk of the cable catching on machinery.

Usually known as dosebadges, some of these devices have no controls, no display and are operated by a remote control unit rather like a TV remote. In use, a badge is fitted to the worker and set running by the remote. At the end of the working day, it is stopped by the same method and then the data from it is downloaded by the same remote and the only way to tell if the device is in operation is often a tiny flashing LED. The advantage of the 'individual' method is that wherever the worker goes and whatever he does, both their true noise exposure and true peak level are measured and stored. In fact some of these devices, just like an area monitor, can take a time history of both the LAeq – or average level and the dBC peak – the two parameter that must be controlled. As the remote reader has a computer chip to operate it, this can give a data readout in almost any form to meet local or national standards such as LEP,d and LEX,8h as required for example in the UK. As all these exposure metrics are calculated from a combination of level and time, any one is easy to generate with a computerised device. These devices, now formally known as Personal Sound Exposure Meters or PSEM have their own international standard IEC 61252.

The equipment Choosing the best device for your needs is not easy.

However, there are International standards to guide us. In 2003, IEC published a new standard IEC 61672 that superseded the older ones. For measurements for the EU Directive, any new meter should comply with this standard. IEC 61672 and IEC 61252 both include the concept of 'Pattern Approval'; in other words a meter should be tested and approved by a proper independent laboratory. Further they should have 'Routine Verification', in ordinary words, they should be fully re-calibrated at least every two years.

It would therefore not seem sensible to buy from a manufacturer who cannot demonstrate that he has Pattern Approval for at least some of his instruments. "No manufacturer can Pattern Approve all his range – it is just too expensive," says Wallis.

"But in the UK there are three different manufacturers who have such approval; however, none of the very low cost imported devices have ever been proven to comply, despite their sales claims," concludes Wallis.

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