Using dosimeters and time on site
(or 'dosemeters' or 'dosebadges')

We use both dosimeters in the form of dosebadges (which are small cable-free electronic meters clipped to a shoulder), and hand held meters in our noise assessments, but priority is always given to hand held noise measurements as dosimeters are very much a ‘false friend’. Our old noise teacher who is now one of the senior examiners at the Institute of Acoustics always said dosimeters should never be used for a period shorter than three weeks, and after the first week that data should be thrown away as it is too unreliable and then just the last two weeks of data used. He is a little extreme on this but the root of his point is good, namely that dosimeters are hugely unreliable.

There are a few reasons for this:

  • People pratting about – they seem unable to resist bellowing down each other’s meters which can give a massive spike in the noise levels and affect the complete noise assessment result, not only by pushing the dB(A) average up but also by possibly exceeding the dB(C) peak level. The same is true for them just tapping on the top of the meter, which again is something they seem unable to resist. No matter how much they are told not to, they can’t seem to stop themselves.
  • Once someone wanders off they may adjust their overall or coat and part of it such as their collar starts to rub against the microphone, which again can create massive peaks and chance the noise assesment result. The use of dosebadges rather than the older dosimeters which have a microphone at the shoulder and are then connected to a belt unit by cable stops some of this error as there is less to get caught, but it can still happen.
  • A huge part of a noise assessment is analysing the job to see what particularly is causing peaks and pushing averages up and then to see what engineering controls are possible, which is mandatory before hearing protection is considered. If someone has wandered off wearing a dosimeter or dosebadge the assessor has no idea what is causing those peaks and therefore has their ability to identify critical parts of the job much reduced.
  • Dosimeters don’t give octave band results which are important for assessing the suitability of hearing protection.
  • Dosimeters give a result for that particular person but how different people do the same job can make a big difference to their exposures. With a nice long dosimeter reading for one person the tendency is that the assessor is not there for a large part of the measurement period and this becomes the standard noise exposure for the job and possible variations between people are overlooked.

Dosebadge used in HSMC noise assessmentsDespite all this, we do have a suite of seven dosebadges which we use in a noise assessment but they are in effect the tools used to gain an overview of the job, which is then used to highlight tasks which need specific measurement with the hand held meter, and it is the data from that which is of most importance on from which the daily exposures are calculated. They are good for identifying trends and also for assessing mobile employees though as otherwise the noise consultant is sprinting around after them which given our general levels of fitness is not good!

Dosimeters and measurement time in noise assessments

This also impacts exposure time and the measurement period used in the noise assessment. All reports should be job or task based so personal exposures are highlighted rather than simple dB(A) levels per machine but to calculate that it is not always necessary to be there for a full shift if the jobs are reasonably routine or the same tools and equipment are used all shift. Therefore we would be on site for as long as is necessary to get a good suite of results with that varying depending on how routine or complex the noise assessment is for that site.

As an example of this - if somone is using Machin A for 2 hours, then machine A+B for 3 hours, then machine A again for the remaining 3 hours of the shift, that is very easy to measure with a hand-held meter. Each part is measured for long enough to get the reading settled and confirmed, and then we can manually calculate their daily exposure by combining the various measurements. This also has the advantage that if this combination changes on other days we can easily calculate the impact on their exposure and potentially include data in the report for the noise assessed on the day, but also the noise levels which may be present on other days for other combinations of work.

The hardest jobs to measure are actually the non-routine tasks undertaken by things such as joinery workshops and engineering or maintenance departments where what they are doing on one day is often completely unrepresentative of what they will do the following day. In such cases, using dosimeters or dosebadges for their entire shift not only gives unreliable results for that day but that day itself is of little value in understanding exposures on other days. In these cases it comes down to getting a good suite of measurements for the various tools and jobs which are possible and then talking to the people doing the job to get an idea of how the job varies and what the most common changes in the jobs are. This means in the report we can then give exposures for say “2 hours Job A + 2 hours job B + 4 hours Job C”, and also other combinations such as “3 hours of A, B and C plus 2 hours of Job D”, etc. That is far more useful to the employer than just the dosimeter result for one specific day.

Example of it going a bit wrong

HSMC All-Knowing Chief Adam was doing a noise assessment on a packagin line in a food plant up near Manchester and had a dosebadge running for about 90 minutes. The line was pretty quiet and was not a current hearing protection area, so when he stopped the measurment and downloaded the result he was surprised to see peaks exceeding 145dB(C), which instantly made the entire area a hearing protection zone.

So, while another noise measurement was being done, he then went from station to station down the line using the hand-held meter to try and find the cause of these peaks, looking for short-terms bangs or high-volume noises such as compressed air releasing, worn equipment, etc. After over a hour nothing remotely close to the peaks could be identified and the person who had worn the badge confirmed they had not gone anywhere else, meaning the only assumption could be that someone had interfered with the meter and shouted down it, tapped it, etc. The net result therefore was to ignore the dosebage result and rely on the hand-held meter data for the noise assessment, meaning hearing protection was no needed in the area.

No boom-boom meters

We do have a couple of intrinsically safe dosebadges which can be used in potentially exposive atmospheres meaning we can do noise assessments in areas where flammable or explosive vapours may be present.

Back to top

designed by hampton-smith