NOISE ASSESSMENT AT WORK
Hearing protection

How to use SNR to calculate hearing protection suitability

To use SNR, take your measured noise level and simply subtract the SNR figure for the hearing protector.

There is one mildly complicating factor in that the ‘noise level’ is the average dB(C), not the average dB(A), peak dB(A) or peak dB(C). If that sounds like gibberish then what I’m waffling about is that you need to look at your average noise exposures over time (a cycle, a day, whatever is appropriate) not the highest levels you see.

Your ‘normal’ average figures are in dB(A), that’s the one which has the 85dB(A) limit at work, but there is a second way to measure noise called dB(C). dB(C) is normally used for instant bangs, noises where duration doesn’t matter, such as dropping a pallet, but we also use average dB(C) for calculating how good hearing protection is.

This can be important as average dB(C) figures may vary a bit from average dB(A) figures for a given job. However, if you only have dB(A) measurements though then so be it, you won’t be a million miles out, but to be accurate you really should use dB(C).

Just remember though, do not use ‘worst case’ decibel figures, so not the highest ones you see; you need the averages which will probably be much lower.

What is the ideal range to aim for under the protector?

This refers to the noise the wearer actually hears after the effects of the hearing protection are taken into account.

• Ideally, aim for 65 to 75 dB under the protector - 75 is about ‘spot-on-perfect.

• 60 to 65 dB is acceptable if the protector is also ideal for other jobs, although it is very much at the lower end of acceptability.

• 76 to 80 is also acceptable if the protector is ideal for other jobs, although it is getting towards the upper end where only a slight mis-fitting could lead to exceeding the limits.

• Avoid protectors where the calculation shows them to be below 60 dB or over 80 dB.

Styles of hearing protection to make available

Once you have done the noise assessment and have calculated the suitability of hearing protectors, how do you go about choosing which one(s) to issue to the staff? Firstly - have a few approved and available forms of hearing protection. Don’t just have one.

An employer needs to have a few types of hearing protector available for employees to choose from. Some people loathe putting things in their ears, and many of those may feel some form of pain as the plug pushes against the delicate ear canal. Also, not everyone has the same sized ear canals. Ear canals keep growing with age so for example one plug may fit perfectly in your 60 year old long-serving Production Manager who has lug-holes you could drive a train through, but the young apprentice may have tiny tubes that the plug is just too big for.

I would always recommend that an employer has, as a minimum, two approved forms of ear plug at least one approved form of muff/defender. That way an employee can choose the best one for them, the compliance with using it will be better and everyone wins.

You may also find that some specific people or groups need another different for of hearing protection, for example fork lift truck drivers may need something different - they still have to wear hearing protection, but you need to take care not to over-protect.