Types of noise meter used in a noise assessment
Key points on types of noise meter which may be used in an industrial noise assessment
Noise assessments will use noise meters which are either hand-held, wearable (placed on the shoulder of a person) or area (long-term measurement in a static area).
No one type of noise meter is always better than the others, all have their strengths.
Not every noise assessment needs to use wearable noise meters (dosemeter), it depends on the specific jobs.
Care is needed with wearable noise meters as they can have a lot of interference, both accidental and deliberate, which will skew the results.
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 / dosemeters.
You can also use each type as static area noise meters too.
Wearables / Dosimeters are a small device which can be placed on a person’s shoulder. 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 a lot of 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.
Read more: How long to measure for in a noise assessment
Wearable noise meters are ideal for some people
Wearable dosimeters do have a function and can be the best way to get a noise assessment result for some people. For example:
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.
The person uses multiple tools or machines as part of the cycle of their work.
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
They must be treated with a bucket-load of caution as experience has shown over the years that 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 the dosimeter was actually measuring, no idea what caused any peaks, and no idea if there has been 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. If someone is static and working on a machine, with a hand-held you are physically there to measure it, you know exactly what causes peaks within the cycle.
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 a few 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 hilarious. The poor dears never seem to twig that in a noise assessment lower noise levels would be better for them and could mean maybe less hearing protection needed, or even none at all, but they always seem to want to get the reading 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 and 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.
As a side note, I have come across another consultancy who will place the wearable noise dosimeter on the back of the person’s shoulder, facing behind them, to get around the speech issue. No, no and thrice no - now the meter is pointing away from the noise (people are almost always facing the noise) and shielded by their body. It may not sound much but that will drop the reading by a few dB and give an inaccurate result.
Summary on dosimeters in noise assessment
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. Dosimeters are not automatically the best way to get the correct results.
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.
Back when I was first getting trained in noise assessment, my tutor was vehemently opposed to wearable noise meters / dosimeters. His comment was that they should always be used for at least a week first. You put the dosimeters on people and leave them every day for a week, then take that data and delete it all, just bin it, and only then do you start to take the readings seriously. He was somewhat extreme on it but his point was solid - after a week people have got bored and stopped fiddling with them or shouting at them, anything less and the data is often too unreliable to be any use. Clearly this is entirely impractical in reality, but his point was well made.
FAQ: Types of noise meter used in a noise assessment
If the Control of Noise at Work Regulations 2005 say the noise limits are an eight hour limit for noise experienced by people, then don’t wearable noise meters have to be used for every noise assessment?
No, what is most important is accuracy. If someone does a job cycle which is say five minutes, you can easily measure a few of those with a hand-held meter and get a result for it, and that result won’t change if you measure for 15 minutes or 15 hours. The hand-held has fewer points where inaccuracy can creep in compared to a wearable.
Why not just do all noise assessments with a load of wearable noise meters?
That is kind of possible but there are a couple of issues. One is cost, the doseBadges I use cost about £400 per meter and I have 15 of them currently. If I doubled up to 30 then that is a massive chunk of cash needed, plus ongoing calibration costs. With 15 of them I already have more than most noise consultants do. And the second one is accuracy. I need to know what I am measuring in a noise assessment and while a wearable noise meter will tell me what noise that person experienced, it doesn’t tell me what caused that noise. Measuring with a hand-held noise meter means I am there to see what is creating the noise.
Are you not being a bit cynical is saying how often people interfere with a wearable noise meter?
No. On any given noise assessment I will put out 15 wearable noise meters, and for every person they go on I tell them not to fiddle with them, cover them up, tap them, shout into them and so on. Almost without fail, every single day at least one comes back with a massive reading which bears no relation to the noise on the site. Sometimes it is accidental, but often it is some numpty (usually not the person actually wearing it) shouting into the end of it as making it as loud as possible is hilarious. They seemingly have never twigged that a lower result is better and would mean less hearing protection!
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