We explain a strategy to adopt when measuring loud event type noises, and how to use the results to predict the contribution to your employees’ daily personal noise exposure. A convenient table to use as a tool for the prediction is included
There might be loud, potentially harmful noises that exist in your workplace which appear in the form of events such as bursts, impulses, explosions, and impacts (e.g. from sources such as air jets, riveters, firearms, forge hammers, and nail guns). When carrying out a risk assessment, It may be desirable to assess such events separately for predicting the contribution of these types of noises to your staff’s daily personal exposure, LEP,d.
So what measurement strategy could you adopt for these types of noise events? How can you use the results to determine the contribution to the LEP,d in your workplace? Employers are duty bound to reduce the LEP,d to as low as reasonably practicable to comply with the Control of Noise at Work Regulations (2005).
Sound Exposure Level
One strategy that you could adopt would be to measure a quantity known as the sound exposure level (LAE) of the noise. By definition, the LAE is a measure of the acoustic energy in an event, or a given number of discrete events which would have the same amount of acoustic energy as a constant noise level lasting for 1 second. Put simply, the LAE is mathematically equal to an averaged sound level, LAeq, normalised to 1 second. Most ‘professional’ sound level meters used for carrying out measurements in the workplace should be capable of measuring the LAE.
Once the LAE is measured for an event or series of events, and knowing the likely number of these daily events, it is possible to predict their contribution towards the LEP,d .This prediction may be conveniently expressed in the form of the HSE ready reckoner noise exposure points. A useful table to have at hand is provided below to make this prediction relatively easy, and a worked example further below demonstrates how to use this table.
As a reminder, the regulations state that the Lower Exposure Action Value (LEAV) is equivalent to 32 HSE exposure points (LEP,d = 80dB), and the Upper Exposure Action Value (UEAV) is equivalent to 100 HSE exposure points (LEP,d = 85dB).
Below is a time history plot of a series of impact like events generated by a carpenter hammering nails into a wood panel. The objective is to measure the LAE of the events and use this value to predict the noise exposure points contributing to his LEP,d. , using the table above.
A noise measurement of the 10 hammer blow events was carried out and the LAE measured 118dB.
The carpenter estimated making 100 blows daily in total. From the ready reckoner table above, the ratio of the number of events during the day/the number of events during the measurement equates to 100/10 = 10. This value ‘intersects’ with an LAE of 118dB in the table giving 70 noise exposure points which contribute towards his LEP,d. He would only need to be subjected to an additional 30 exposure points (perhaps originating from other noise sources) to reach 100 points, and hence be exposed to the UEAV.
So providing noise containing high noise events are assessed in this manner, it is possible to predict the contribution of these noise events towards a person’s LEP,d.
Point of note:
If you choose to predict the contribution to the LEP,d of events using this method, then do ensure the exclusion of these events when measuring the LAEQ of other types of noise in proximity. Failure to do so will inevitably run the risk of overestimating the LEP,d as you will duplicate the contributions from the events.
What do you need to consider when carrying out a competent noise risk assessments in a workplace? Find out by clicking here to download a free guide. This guide also includes how to identify hearing protection overprotection, which may be a hazard in the workplace.