How do I calculate noise exposure to determine what ear protection is needed when working with machinery?

The European directive controlling noise levels at work — the Physical Agents Directive (Noise) — came into force earlier this year. It works in a similar way to the vibration directive in that there are levels at which action must be taken and a limit beyond which exposure is not allowed. And, just as with vibration, you need to calculate exposure levels for each machine you use. Note the new levels are lower than those in the previous Control of Noise at Work Regulations.

The first action level kicks in at 80dBA. At this level employers must assess employees’ exposure, provide information about the risks and make hearing protection available. The second action level starts at 85dBA. At this level employers must introduce health surveillance, ensure hearing protection is worn and introduce a programme of control measures along with designated hearing protection zones.

The limit value is 87dBA and refers to exposure at the operator’s ear. It permits the reduction afforded by hearing protection and exposure can be averaged over one week instead of the previous eight hours in the Control of Noise regulations. To calculate exposure you must know the sound pressure leve of the machine — you’ll find this stated in the manufacturer’s manual for the machine and is based on the noise at the operator’s ear at a set distance from the machine. You also need to know the amount of time that piece of equipment is used.

From these two figures, you can calculate exposure to noise using the interactive Noise Calculator on the HSE website (www.hse.gov.uk). HSE suggests a hierarchy of actions be taken to limit exposure to noise, such as using quieter kit where possible. Manufacturers have been busy developing quieter engines and increasing sound-proofing on a range of machines.

Ear defenders should be viewed as a last resort when other means are eliminated. You’ll find they have a SNR value indicating the sound pressure reduction afforded by them. The HSE suggests derating this figure by 4dB to allow for imperfect fitting and degradation due to age and condition.


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