Health and Safety
| Choosing the right tools for the noise at work regulations |
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| Written by James Tingay, Group Marketing Manager, Cirrus Research plc, 2008 | |
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James Tingay of Cirrus Research provides advice on how to choose the best noise measurement tools to suit your needs, and outlines some issues for consideration after the equipment has been purchased.
Noise legislation, designed to protect hearing and prevent noise nuisance, is becoming tougher and more widespread. Choosing a noise measurement instrumentNoise measurement instruments, and sound level meters in particular, can vary hugely in cost as well as in complexity. It is possible to find instruments, usually via the Internet, for little as £20 and it is possible to spend well over £5,000 on a sound level meter. Deciding which to buy can therefore be confusing, and expensive if the wrong choice is made. A simple instrument may require less training to operate, but might not give the measurement parameters needed. An expensive instrument may provide the data required, but the level of training and understanding needed to use it could turn it into an expensive bookend. Although there are many professionals who are using noise measurement instruments every day, the majority of users are those for whom noise is just a part of their jobs. For this type of user, there is a strong case to be made for choosing an instrument that meets the practical requirements of any regulations, standards or guidelines whilst keeping the instrument as simple as possible. Before choosing a supplier or instrument, consider a few points. 1. What measurements are required? As a rule of thumb, the more expensive the sound level meter, the more functions the instrument will provide. However, these functions should not get in the way of making the noise measurements needed to comply with regulations and guidelines. The level of training and experience required to operate complex sound level meters can often get in the way of making good-quality noise measurements. For example, the Control of Noise at Work Regulations 2005 requires the following measurements for compliance:
Most sound level meters that can provide these measurements will also be able to display the basic sound level, which can be useful for quick noise level checks. As sound level meters become more sophisticated, other functions will be available in addition to these two basic parameters. These may be useful for other measurement applications and to deal with more complex noise risk assessments. One of the most useful of these additional functions is data logging or storage of measurements in the instrument. Downloading measurements to a software program allows measurements to be stored for later reference, to be used in risk assessment reports or for more detailed analysis and noise exposure calculations. It is becoming increasingly common for those responsible for occupational noise measurements also to be charged with the recording of environmental noise. So an instrument that provides additional measurement parameters such as Lmax, L10 and L90 may be appropriate provided, of course, that the user understands the difference between these functions and those required for occupational noise measurements. And I would stress once again that for occasional users, an instrument that provides a large number of functions and features may not be the best solution, due to the high degree of training and understanding required. 2. Noise dosemeters There are many situations where using a handheld sound level meter is not possible for both practical and safety reasons. For example, assessing the noise exposure of forklift truck drivers or employees with complex working patterns would be problematic using a sound level meter and this is where a noise dosemeter becomes the ideal measurement tool. A major advantage of using a noise dosemeter is that if they are worn for the whole working shift, then the noise dose will have been measured in full and no further calculations will be required. One of the most useful features that a noise dosemeter can provide is a display of the noise level throughout the day. Although the overall noise exposure is the most important data, and the one that is used to check against any regulations and noise limits, being able to see the times when the noise was high and to be able to identify unusual or unexpected noise levels can be vital in understanding the pattern of noise recorded. 3. What accessories are required? It is always advisable to purchase a sound level meter or noise dosemeter as a complete kit. This typically contains the instrument, a suitable acoustic calibrator, a windshield and a protective carrying case. By purchasing a kit, you will have all of the accessories needed to use the equipment in the way specified by the manufacturer. One of the most important accessories is an acoustic calibrator. Without this, the noise measurement instrument cannot be calibrated and therefore any measurements made would have to be considered questionable. All noise measurement standards, regulations and guidelines will state that an instrument must be calibrated before and after each use. 4. Can the equipment be serviced and recalibrated? One aspect of noise measurement that is often overlooked is the question of service and calibration. All measurement standards, regulations and guidelines require that an instrument is calibrated before and after each use using an acoustic calibrator. For example, the Control of Noise at Work Regulations 2005 states that: "A sound calibrator should be used to check the meter each day before and after making measurements." It also states that, "Some meters have an internal electronic calibration. The internal calibration only checks the instrument's electronics and does not provide a check of the microphone." The accuracy of low-cost noise measurement instruments can vary dramatically with ±2dB often quoted as the accuracy. Calibrating this level of sound level meter also using a low-cost acoustic calibrator with ±1dB accuracy could allow the instrument to be 3dB away from the true noise level. Using this type of sound level meter without calibrating it first would introduce an unknown level of error. Calibration and recalibrationNoise measurement instruments are precision tools and the level of accuracy required from them is very high. Manufacturers spend considerable time and effort to ensure that their instruments meet these standards. Calibration and recalibration are an important part of using a noise measurement tool. Every noise measurement instrument should be calibrated both before and after every measurement and also on a regular basis by an external source. A good-quality sound level meter should be either sold with a suitable acoustic calibrator or one should be available from the manufacturer. If an instrument is supplied without a certificate of calibration from the manufacturer or if there is a charge for a calibration certificate, then this should be viewed with caution. An instrument produced by a reputable manufacturer, and especially one that meets the latest standards, will have been calibrated and verified and so this information should be provided, as standard, with the instrument. This applies to all types of noise measurement equipment. If this is not the case then the question should be asked, "Does this instrument meet the standards that are required for me to meet my regulations and guidelines?" Two questions that are commonly asked are:
If a sound level meter, noise dosemeter or acoustic calibrator is to continue to provide the same performance that it did when it was new, regular servicing and recalibration is essential. The calibration information supplied with a new instrument states that at a point in time, usually at the end of the manufacturing process, the instrument was verified and that it met the specifications claimed. Noise measurement instruments are sensitive and knocks, impacts or tampering can affect the measurements and over a period of time. Components such as the microphone, for example, can alter in performance over long periods. Regular servicing and recalibration can help in monitoring these issues and ensure that the equipment continues to operate reliably and accurately. When an instrument is recalibrated, the performance of both the microphone and the electronics of the instrument should be checked against the original specifications and standards. Simply using an acoustic calibrator to do this does not provide enough information about the performance of the instrument. To carry out a full verification, the microphone capsule must be removed from the sound level meter and this is often where low-cost instruments fail. Many low-cost instruments have microphones that cannot be removed and so cannot be subjected to a full calibration. As the microphone capsule is probably the single most important part of a sound level meter or noise dosemeter, this type of calibration should be considered as insufficient and possibly inaccurate. If in doubt, ask for information about what standards the instrument will be tested to, and request a certificate of calibration that states that the instrument was tested to the appropriate noise instrument standards. Checklist
Further informationJames Tingay, Group Marketing Manager, Cirrus Research plcTel: +44 1723 891655 Email: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it www.cirrusresearch.co.uk |
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