Types of noise meter - hand-held, wearable or area meters in a noise assessment?
The two main types of noise meter used in a noise assessment.
There are two basic types of noise meter:
Hand-held - the name says it all
Wearable - also called dosimeters or dosimeters.
You can also use each as static area meters too.
Wearables are a small device which can be placed on the shoulder of a person. It takes a reading on a pre-determined schedule, e.g. every five seconds, so builds up a trend over time.
Wearables have a use but a great deal of care is needed with them and they really shouldn’t automatically be used as the primary means of gathering data in every case. For some cases they are indeed best, but for most workplaces not so much.
How long to measure noise for?
Noise assessments do not have to be done over many hours, indeed for as lot of workplaces it is a waste of time and once you have a level for a job it will be the same whether you measure for four minutes or four hours. That means a noise survey done with a hand-held gives exactly the same result as a wearable.
Wearable noise meters are ideal for some people
The person is really mobile, e.g. a forklift driver. It’s not going to work having an unfit middle aged chap trotting after the forklift waving a hand-held meter around and looking primed for a heart attack.
The job has a long cycle.
But that’s about it.
One of my noise kits, a hand-held meter and ten wearable noise meters (dosimeters).
Problems with wearable noise meters in noise assessments
I treat them with a bucket-load of caution as experience has shown over the years that dosimeters / dosimeters are extremely susceptible to error.
You lose control of the noise assessment
Firstly, the second someone walks away wearing a noise meter you have lost control of that noise assessment. You have no idea what it is measuring, no idea what causes any peaks, and no idea if there is any interference with it. One of the purposes of a noise assessment is to identify causes of high noise levels but if you are not there to see it you don’t know what caused it - a collar rubbing on the meter or someone dropping a pallet can both look the same on a downloaded trace.
Deliberate interference
I bet the mortgage with 100% certainty that if I put fifteen wearable noise meters on people in a noise assessment and they walk away, within two minutes someone has bellowed down the end of at least one, and probably several. Not the wearer usually but their mates seem unable to help it - as soon as they see a noise meter being worn people can’t help shouting at it as it is seemingly hilarious. The poor dears never seem to twig that in a noise assessment lower noise levels would be better and mean maybe less hearing protection needed, or even none, not higher.
You can end up with huge peaks and high averages but which have no cause in the work being done which you can link to it as they walked off wearing the meter.
Accidental interference
As people move around clothing moves, meters move, and inevitably at some point clothing rubs on the meter. No matter how carefully they are placed it always happens with at least one or two. A collar rubbing a meter may not be loud to us, but to the meter that will be a hellishly loud noise and will be recorded as such.
Or I have seen people get cold and put a coat on over the top of the meter, both rubbing against it and muffling it at the same time.
Recording speech as a critical noise generating false high levels
This is a very real issue with wearable noise meters. I did a noise assessment recently where the background levels were around 82 dB(A), so reasonably loud but not so loud it is dangerous. I placed some of the wearable meters on the line to get the general noise, (using them as static area meters) and some on people standing at the same line, and also did hand-held measurements.
The meters placed on the line and the hand-held meter all gave levels around 81 to 82 dB(A), but there wearable meters all came back in the high 80s and even low 90s dB(A).
The issue was chatting. As they worked they all talked and the wearable meters placed on their shoulders were getting full blast of the wearer’s own voice. The voice was directed away from their ears but the meter was picking it up. The meters placed on the line itself were measuring the noise of the line and the general chat noise, but were not quite so influenced by the wearer’s own voice.
The wearable meters would give a noise assessment result showing a serious noise risk, and that hearing protection is needed and also hearing testing, whereas the line and hand-held measurements showed the levels were much more reasonable.
The wearable noise meters were just wrong.
Summary
A good noise assessment will use the most appropriate noise meters for the job, but that is not automatically wearable noise meters and they have to be used, and viewed, with caution.
Also, although the limits are phrased as eight hour averages, that doesn’t mean you have to measure for eight hours and always measure with wearable meters.
Wearable dosimeters do have a use, but only where the work justifies it.
