The mistakes people make when managing noise

Phil Chambers BSc, CMIOSH  Strategic Safety Systems Ltd

I quite often come across companies who have received incorrect advice about noise and have got into difficulties when trying to enforce the wearing of hearing protection. This goes against one of the key approaches to effective health and safety management, which is that you can “sell” the control measures to those affected. So where are the mistakes being made?

Noise level and noise exposure

In most cases, the legal requirements relate to noise exposure and not noise level.  The only time this is not true is where you have high peak noise levels, say from nail guns. Noise exposure is the combination of noise level and the time to which you are exposed to it. Because noise is measured using a logarithmic scale, dB, you cannot multiply noise level by the exposure time, as you would multiply electrical power by time to get energy in kWh.

What we have instead is a daily equivalent noise exposure (L_ep,D) which is specified in dB, ie exactly the same units as noise level.  And that is where the confusion arises.  An L_ep,D of 80 dB is a pattern of exposure to maybe different levels for different times which gives you the same noise ‘dose’ as a continuous level of 80 dB for 8 hours.

Mistake No. 1: Noise level

This leads us to the first mistake: people will take the worst-case noise level on a machine and base their requirements on this.  One recent case I came across was a hopper that had a noise level of 85 dB(A) when standing next to it.  But once it was loaded, you didn’t need to go anywhere near it. The other parts of the extensive machine were much quieter, but following the consultant’s advice, the company had a mandatory hearing protection requirement on the whole line because of the hopper noise.

Mistake No. 2: Duration

Another case had an 85 dB(A) noise level when next to one part of the machine which was never accessed when it was running.  What actually happened was that it took 10 minutes to set up the machine, at about 75 dB(A), and then a very short run length of about 20 minutes during which the operators were exposed to about 81 dB(A). The run lengths and noise levels in different positions were not taken into account by the assessor and the company were having difficulties enforcing their mandatory hearing protection policy.

So how do we measure noise exposure?

There are two ways of doing this.

Sampling monitors

These may be a badge type that operators wear over a significant period, say a complete shift.  Data from these can then be downloaded to a PC which will give you both an L_ep,D value and a graph.  They give a very accurate snapshot during that shift, but are limited in their ‘what if?’ capability.

Level measurement and calculation

The other approach is to measure noise levels for different activities or positions on the machine and then use these and the exposure times to calculate the noise exposure.

This is less accurate than sampling monitors as it does depend on getting the exposure durations correct, but it has the big advantage of being able to ask questions like, “What is the effect of short or longer production runs?”

You can either use the ‘ready reckoner’ process[1] or spreadsheets to calculate the exposure.  I created the Strategic Safety Systems spreadsheet[2] many years ago for this purpose, but the HSE have recently introduced their own[3].

By far the best approach is to use both methods. Use the level measurement/calculation method to test the sensitivity of the noise exposure to different conditions and take samples for the snapshot and use these to cross-reference your calculations.

Mistake No. 3 Reliance on hearing protection

As with all risks, personal protective equipment is the least preferred control measure.  However, some organisations fail to take even simple measures to control noise at source.

One recent example was a continuous waste stream from a roll label press which passed down a tube made from 40mm plastic pipe. The noise it made as it rubbed on the edge of this pipe was amplified by the pipe’s megaphone effect and caused a noise level of 86 dB(A). Preventing this pipe rubbing action by a bit of coat hanger wire reduced the noise level to 78 dB(A).  The operators had complained but the company had not taken this action.

Mandatory hearing protection areas

In some cases, noise assessments will conclude that an area is one where the wearing of hearing protection is mandatory.  There are several questions you must address:

Does the high noise exposure occur only when the machine is running? 

If so, you need to put a statement under the mandatory signs saying “only when machine is running”.

If there are short-term visitors, do they need to wear PPE? 

Technically, their exposure is low, but in my opinion, the only way you can “police” your control measures is to require everyone to wear hearing protection.

Is there an exception to this?

The one exception to this is where the exposure of some people is low and the wearing of PPE increases other risks.  I have one client who has equipment that requires mandatory PPE for operators but forklift trucks deliver material occasionally. The forklift truck drivers have a low noise exposure and, were they to wear hearing protection, then other risks would increase.  What they have done is make it clear to all people by methods including notices, that short-term visits by forklift trucks do not require the wearing of hearing protection.

Noise can be a major health hazard, but if it is approached sensibly, then the risks can be controlled.

References:

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