Choosing noise measurement equipment for Noise at Work
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Noise legislation, designed to protect hearing and prevent noise nuisance, is becoming tougher and more widespread. It’s a response to our increased understanding of the damage that noise can do to hearing, and the negative impact it can have on quality of life in the wider community. It has resulted in a growing need to measure noise and rising demand for noise measurement equipment. However in order to gather accurate and meaningful information about noise levels in your workplace, or the impact you might be having on your neighbours, it is essential that you invest in the right measurement equipment for the task in hand. This article aims to provide advice on how to choose the best noise measurement tools for your application, and outlines one or two issues for consideration after the equipment has been purchased.
So we need to look at the following factors:
1. Does the instrument give the measurement functions needed to comply with any Standards, Regulations or Guidelines? » For the Noise at Work Regulations in the UK and Europe, the essential measurements are LAeq,t and LCPeak
2. Is the instrument available with all of the accessories needed to operate it according to the manufacturer’s instructions? » A Sound Level Meter should be supplied with a suitable Acoustic Calibrator, Windshield and Protective Case
3. Does the instrument meet the specifications required by the Standards, Regulations or Guidelines? From the 2005 Control of Noise at Work Regulations: » Your sound level meter should meet at least Class 2 of BS EN 61672-1:2003 (the current instrumentation standard for sound level meters), or at least Type 2 of BS EN 60804:2001 (the former standard). » Your dosemeter should meet the requirements of BS EN 61252:1997. » Your calibrator should meet at least Class 2 of BS EN 60942:2003.
4. Can the equipment be recalibrated and serviced according to both the manufacturer’s recommendations and the requirements of any Standards, Regulations or Guidelines?
So lets explain in a little more detail!
Choosing a noise measurement instrument
Choosing a noise measurement instrument Noise 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, 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.
What measurements are required?
As a rule of thumb, the more expensive the Sound Level Meter, the more functions the instrument will provides. 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:
1. The equivalent continuous A-weighted sound pressure level (LAeq)
2. The maximum C-weighted peak sound pressure level (LCPeak)
There may also be a need to measure other metrics such as the equivalent continuous C-weighted sound pressure level (LCeq), or the Leq in octave frequency bands, if there is a need to provide suitable hearing protection, but the basic measurements needed are the LAeq and LCPeak values. 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 ogging 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 details 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 which provides a large number of functions and features may not be the best solution, due to the high degree of training and understanding required.
Noise Dosemeters Measurements made using a Sound Level Meter would typically be short term LAeq and LCPeak values which would then be used to calculate a daily or weekly exposure value in terms of an LAEP,d or LEX,8h.
However, 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 fork lift 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. Noise dosemeters typically measure both the overall LAeq and LCPeak values as well as calculating the daily exposure value in terms of LAEP,d or LEX,8h. 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.
For example, the Control of Noise at Work Regulations 2005 which is in force in the UK uses a 3dB Exchange Rate (Q) and requires no threshold time weighting to be used, whereas the OSHA Regulations in force in the US, as well as a number of other countries, uses a 5dB Exchange Rate, an 80dB Threshold and Slow time weighting. Whilst these may seem to be relatively small differences, they can produce significantly different results.
The most obvious difference is that the US OSHA configuration records the noise exposure as 75% of the daily level whilst the UK configuration records the same noise as being 511% i.e. over 5 times the daily exposure limit. It is vital therefore to ensure that if a noise dosemeter is to be used, that it has been configured and calibrated correctly so that you record the measurements you need.
What accessories are required?
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.
Acoustic calibrators are designed to work with specific microphone capsules and using a combination of units from different manufacturers can introduce unknown errors to the calibration of the instrument. As the microphone capsule on the instrument is the most delicate part and is easily damaged, special care should be taken when carrying a sound level meter. It is common for microphone capsules to cost many hundreds of pounds and so damaging this part of the instrument can be very costly indeed. Using the windshield supplied with the instrument, even when the measurements are being made indoors, will help to protect the microphone from accidental damage. Noise dosemeters are usually more robust as their microphone capsules are either housed inside the instrument or are protected by a windshield or cover. This helps to protect the unit from damage as well as stopping dust and other contaminants getting on to the microphone. Again, as with Sound Level Meters, it is advisable to purchase a dosemeter as a complete measurement kit which would include the accessories needed.
Does the equipment meet the required standards?
The performance of sound level meters, noise dosemeters and acoustic calibrators are set out in national, European and international standards. These standards are produced initially through the International Electro-technical Commission (IEC), before being adopted as European and then as National Standards.
For example, the current standard for Sound Level Meters is IEC 61672-1:2002. This has been adopted as a European Harmonised standard, an EN, which is then adopted as a British Standard with the title BS EN 61672-1:2003. The date at the end of the standard shows when it was adopted and this may be different from the original IEC standard. Similarly, the IEC standard is adopted in Germany as a DIN-EN standard, France and as NF-EN standard and Spain as an UNE-EN standard.