NOISE ASSESSMENT AT WORK
Advice on managing noise risks

Reasons why hand-held meters are used in place of dosimeters 

Interference - deliberate or accidental

If you are doing a noise assessment and pop a wearable dosemeter on someone and send them on their merry way, the second they walk away you have lost control of that assessment. You have no idea if their mates are shouting down it (they will, without a shadow of a doubt) or whether it has moved slightly and their collar is now rubbing against the microphone which will cause a massive spike in the results.

In an assessment in March 2022 I had a mobile operator I needed to measure so stuck a dosemeter on him as I couldn’t do it any other way as he was on and off vehicles. I walked past him ten minutes later and saw him and another chap both bellowing down the end of it. This is absolutely normal, and inevitable - they always do that, without fail, no matter how much you tell them not to. Conversely, a few weeks ago I had a mobile chap wearing a dosemeter and came back to find he had put a coat on over the top of it as he had got cold. I have had collars of coats move and rub against them and everything else you can think of. Interference has a huge impact.

Talking has a huge impact on dosemeter results

Even something as simple as the person wearing the meter talking to other people will impact the result, sometimes massively. By necessity the microphone is placed close to their face as it needs to be close to their ear, but it is closer still to their mouth and the volume of their own voice will have a disproportionate impact on the readings obtained from the dosemeter. If you aren't there to see the data being gathered then for all you know most of what you've measured is a few hours of someone chatting to their colleagues.

Again, I have had this in the past. I used to use dosemeters more and on one memorable job had a wearable meter come in at about 92 dB(A), but there was nothing in the facility making anything remotely close to that noise. It turned out the wearer spent all day bellowing at everyone else and I had just recorded the sound of his own rather impressive voice.

Identifying noise sources is one of the points of noise assessment

A noise assessment is not just about measuring a number of decibels but also seeing what can be done to control noise. If they have wandered off wearing a meter then you don't know what caused the result so identifying potential controls is impossible.

You also have no idea what job they were doing. They may supposed to be on a particular machine but you don't know if they've had a breakdown (the machine, not them personally), gone off to help a mate out, moved to another machine for a bit, etc. 

You also don’t know how they did their job - out of six people doing nominally the same work, one or two may do something small but different, possibly even just how they sit or stand when working, which has an impact on their noise exposure.

Basically, once they walk away all you get back is the exposure pattern with little confidence in how it was obtained.

With a hand-held noise meter you know what caused the noises you are measuring and know that there was no interference, deliberate or accidental.

What about the whole 8-hour average - don’t you need to wear meters for a long time for that?

Nope - just because the noise limits are given in terms of an 8-hour average doesn’t mean you have to measure for 8 hours.

You can easily get the figures you need to calculate a daily exposure from a hand-held meter, or from a dosemeter worn for a short time. For example, if someone does the same job all day and you measure the noise levels, after a few minutes the meter will have settled to a steady figure. From that point on the reading won’t change no matter how long you measure so measuring for many more hours makes absolutely no difference at all.

Often jobs are cyclical and with a hand-held noise meter you just measure each part of the cycle and them combine it into a daily result, or with a wearable you measure for a few cycles, for example for an hour, and then use that to calculate a daily exposure.

If jobs are not running at the time you can easily measure all the parts separately, using sample runs if necessary, then manually calculate an eight hour exposure from that.

There are very very few cases where the only way to get a daily average exposure is to measure for a full shift. Although when I say ‘very very few cases’ I mean that in 30 years of noise assessments I’ve never come across one.

Summary on noise dosemeters / dosimeters

One of the esteemed and rarified beings who taught Institute of Acoustics courses once told me that personal wearable meters should never be used for less than three weeks for any one measurement. Within that, you do one week of measurements and then throw those results away as the individuals concerned are certain to have fiddled with the meter or their mates will have pratted about with it, usually by shouting at it.

Once those results are binned then use it for another two weeks to iron out any other errors from their work routine.

He is rather extreme in his dislike of personal dosemeters but the point stands, they are very unreliable.

• Results can be calculated as 8-hour doses using component parts measured for short durations, and done that way are probably more accurate than a dosemeter worn all day.

• Wearable noise meters have a much higher risk of incorrect results than hand-held meters.

• Wearable noise meters hinder the assessor doing the most important part of the job - identifying what is causing the noise.

• Wearable dosemeters have a use and play a part in a noise assessment, but they are not the ‘gold standard’ and are often inferior to a decent hand-held measurement.