Effectiveness of enclosures and curtains as a noise control method following a noise assessment
When you do a noise assessment, it is tempting to reach straight for the hearing protection but there are some steps all employers need to follow first, ranging from a need to eliminate the noise risk, through various minimisation steps before finally landing at hearing protection.
The logic is that if the noise risk is eliminated then everyone is protected permanently, whereas with hearing protection ongoing compliance is needed every day, with each person being protected individually.
Somewhere in the middle sits physically separating the person from the noise, either by enclosing the machine to contain the noise, or enclosing the person (e.g. in an operator cabin) so they are protected in there.
Plastic curtains
Noise assessments need follow up action to control noise exposures, and a standard plastic curtain can be a very effective control method.
Part of that can be physical screens or barriers which help to stop the noise reaching people, and the humble plastic curtain can be very effective for that. By these I mean those translucent thick plastic strips which hang down.
These curtains are typically seen between different rooms within a factory, or where one area is more tightly controlled than another, for example due to temperature or vehicle movement but they can also be used for noise control after a noise assessment.
I have measured many of these during noise assessments and typically they can give a reduction in the noise of anything from 10 to 14 dB or so, which given 3dB is a doubling of the noise energy, is quite a significant change.
In the video above, you can watch the impact of the plastic curtain on the noise meter, where it changed from ≈73 dB(A) on one side of the curtain, and then jumps immediately to ≈87 dB(A) on the other side. That curtain is very effectively containing the noise and means one area can stay below the limits and no hearing protection is needed.
Partitioning a site with these doesn’t hinder passage of goods or personnel through them, but they are an effective and simple noise control measure.
Acoustic enclosures
Enclosing a high-noise machine can be very effective at minimising noise. I have done noise assessments on a few of these over the years and even if not used entirely properly the noise reduction can be good.
For example, I did a noise assessment on a machine which was generating levels of ≈92 dB(A) and an enclosure had been put around it. The operators had got into the habit of leaving the door through the enclosure open but even with the door open, levels immediately outside the enclosure where the operators are based were ≈81 dB(A), well back below the noise limits. With the door closed noise levels fell to ≈74 dB(A).
On another machine, levels inside an acoustic enclosure were ≈90dB(A) but less than half a metre away on the other side of the enclosure where staff were based most of the time noise levels were ≈73 dB(A), a dramatic reduction in noise level.
As personnel in these cases spent almost all their time outside the enclosures, it meant hearing protection was only needed for going in for brief times and only then as a precaution. In addition, based on how often they went into the enclosure their daily exposures were ≈81 dB(A), so they didn’t meet the limit for hearing testing and the employer also avoided the costs of health surveillance.
Acoustic enclosure around a press
In another example, I did a noise assessment recently in an engineering company with multiple presses. To their credit they had enclosed a lot of the presses and the impact on the noise levels was impressive.
Inside the enclosure levels were averaging around 90 dB(A), while outside it noise levels were around 80 to 81 dB(A), even with the door open.
The operator had brief periods of noise as he entered the enclosure, but all other staff nearby were dropped back below the 85 dB(A) limit completely.
