How long should a noise assessment take?

This a common, and understandable, question people looking for a noise assessment often ask - how long will it take.

Eight hour daily averages in noise assessment

The Noise Regs talk about an employer having a reasonable estimate of the daily noise exposure levels for employees and the standard way to calculate that is over an eight hour working day. But, that doesn’t mean a noise assessment has to last for eight hours.

To take two scenarios:

• Bob works on a press, doing the same thing roughly every 30 seconds. If we measure for a few minutes the noise reading will settle at say 91 dB(A). From that point on it doesn’t matter if you measure for five minutes or five hours, the result will be exactly the same.

• Steve works on the press for three hours and then on a robotic welder five hours. If you measure the press and the welder separately you will get a noise reading for each. Then some maths magic can add the two exposures together, including their respective exposure times, and give you an eight hour daily average figure.

In both, you don’t need to measure for eight hours to get a daily noise exposure figure. Once a reading has settled for a job, measuring for longer doesn’t change it.

Number of noise meters makes a big difference.

Back when I started doing noise assessments, most noise assessments were done with one noise meter whereas now I am using up to fifteen noise meters at once. That means I can gather the same data now in one hour which would have taken two days to do in the past.

Machines running times influence the noise assessment

One of the biggest influences on a noise assessment duration is whether the machines are actually running as a lot of sites have machines which only run at certain times of day. That is no problem for a noise survey and I would just make sure I am there for it as needed.

Size of site is less important than you may think

What is crucial for a noise assessment is not really the number of people or square footage of a site but what is the variation in the work.

If you have a food factory with say 250 employees, often most do the same jobs on the same production lines so from a noise assessment perspective it is very simple. Conversely, if you have a joinery workshop with 20 employees, that can be far more complex as the variation in their work from day to day can be enormous.