Are noise-sensing illuminated signs any use for noise safety?
The short answer is no, illuminated noise safety signs are not useful, and in many cases simply mislead. They have no part in a noise assessment.
The noise signs are instant but the Regs are averages
The best way to explain this is using the example of a site I went to for a noise assessment.
They had an area where average noise levels were about 77 to 78 dB(A) so perfectly fine, but there were very brief periods where the noise jumped to about 88 dB(A) for a few seconds.
Including these slightly higher-noise peaks, the daily exposure levels for the staff were around 79 to 80 dB(A) so well below the limit where hearing protection is mandatory. Hearing protection was just about meeting the limit for it to be optional here - it should be provided but people can choose if they want to wear it.
Fundamentally the sign was wrong - it was saying hearing protection is needed based on the instantaneous levels, whereas the known daily average proved there was no requirement for mandatory hearing protection at all, by some margin.
They quickly just become wallpaper
Companies sometimes have a policy that when these illuminating noise signs light up hearing protection is then needed - people are expected to then put it on. The problem in an area with intermittent noise is that the signs flash away merrily to themselves and quickly become just light-up wallpaper as everyone ignores them.
By the time people have got their hearing protection on then the sign goes back to saying all is OK again so they inevitably, and understandably, ignore it.
Meanwhile, if noise is consistently high and over the limits then hearing protection is needed anyway so the sign being illuminated adds nothing.
The illuminated noise signs are uncalibrated
Noise meters are fickle beasts and their accuracy wanders, sometimes quite considerably. They have a very delicate thin sensor at their head, the sensitivity of which changes depending on things like temperature or humidity. A tiny particle of dust or moisture getting into there can impact it.
This is why noise meters are calibrated on the day before and after every occasion they are used. If I do noise assessments on three successive days the calibration of the noise meters will almost inevitably change a little every single day as humidity and temperature varies.
The illuminated noise signs on the other hand are never calibrated so their accuracy will just wander around all over the place with no checks on accuracy.
Summary on illuminated noise signs
The main issue is that the Noise Regs are interested in the average noise level for a day, not the peak dB(A), and an occasional peak over 85 dB(A) in an otherwise quiet job is pretty much irrelevant and often has no material impact on people’s daily exposures.
Noise signs where the noise is intermittent like this are pretty useless. If they only light up briefly then everyone ignores them, and they indicate hearing protection as needed when in reality it isn’t.
Conversely, if the noise is consistently high then hearing protection should be mandatory anyway so the illuminating sign adds nothing.
There are no checks on accuracy which will change over time.
Illuminating noise signs seem like a nice idea but to be honest are a waste of time.
