Reducing Hearing Damage through Noise Control

noise sign

The Noise at Work Regulations 2005 place obligations on employers to find and implement ways of reducing hearing damage through effective noise control. There are various ways in which noise induced hearing loss can be reduced without reducing the profitability or effectiveness of a business. Most of these methods can be put in place for a reasonable cost and will become apparent when a proper noise risk assessment is carried out.

Fan Installations

Axial flow or centrifugal fans will produce the lowest levels of noise when they are running at maximum efficiency. This means that when a fan is installed and is not running efficiently, it will produce higher than necessary levels of noise, so increasing the risk of noise induced hearing loss

To ensure maximum efficiency and reduction of noise, there should be at least 2-3 duct diameters of straight duct between any feature that may disturb the flow and the fan itself.

Adequate and regular maintenance of fans in this way should produce noise reductions of between 3db and 12db.

Fan Speed

Fan Speed

Fan noise is generally to the 5th power of the fan speed, so high levels of noise reduction can be achieved by a small drop in fan speed. The speed of an industrial fan can be reduced by changing control systems, pulley sizes and dampers.

This will have a significant impact in reducing hearing damage and the following levels of noise reduction can be achieved:
 

Fan Speed Reduction Noise Reduction
10% 2dB
20% 5dB
30% 8dB
40% 11dB
50% 15dB

Electric Motors

Electric motors are used widely in workplaces for fans, pumps, machine tools and more. Many general duty motors are available which are up to 10dB quieter than older models and by replacing these motors, this reduction in noise can be easily achieved.

In order to reduce the economic impact of replacing all motors in one go, companies could adopt the approach of introducing new motors as part of their regular maintenance. This process will reduce incidences of hearing damage in the work force.

Chain and Timing Belt Drives

Noise reductions of between 6dB and 20dB can be achieved by replacing noisy chain drives with quieter timing belts. There are a number of quieter timing belts which use different tooth profiles to reduce the noise produced by their operation. In particular, a chevron tooth pattern is able to produce very quiet timing belts. Noise induced hearing loss will be reduced when these steps are taken.

chain belt drive

Damping

Damping can be used to reduce hearing damage for workers who stand near chutes, hoppers, machine guards, panels, conveyor belts, loud tanks and many other noisy items of machinery.

There are 2 methods of applying damping to machines in the workplace.

Unconstrained layer damping uses a layer of bitumastic high damping material and sticks it to the surface.

Constrained layer damping takes place when a laminate is created and applied to the surface.

Constrained layer damping is generally felt to be more effective as it is tougher and more rugged.

Sound deadened steel guards, panels or other components can be used for dampening or self-adhesive steel sheet can be used too. This can simply be stuck onto existing components to reduce the noise. When 80% of the flat surface area is covered, noise reduction of 5dB to 25dB can be produced. This will have a massive impact on the noise in a workplace and will significantly reduce the risk of noise induced hearing loss.

The damping process does have some limitations and will not produce these results in every case – when the sheet thickness is greater than 3mm, it becomes much harder to produce substantial noise reduction.

Ductwork

Extraction, ventilation and cooling devices or openings in walls can create high levels of noise in a workplace.

A reduction of 10dB to 20dB can be achieved from this airborne noise y lining the last bend in the duct with an acoustic absorbent such as foam, rockwool or fiberglass. As an alternative, fit a simple absorbent lined right angled bend to fit on the opening to reduce the sound produced. To achieve the best results, either side of the bend should be lined along a length that is at least twice the duct diameter.

In some cases, duct vibration will cause noise, but this can be treated with damping.

ductwork

Vibration Isolation Pads

Placing motors, pumps, gearboxes and similar machines onto rubber bonded cork pads will have the effect of reducing the transmission of vibration and noise that is emitted. In cases where the machine is bolted to the floor or a steel support, this method is especially effective in reducing hearing damage.

It is important to note that in cases where a bolt is present, additional pads must be placed underneath the bolt. Otherwise, the process is not as effective as it should be.

Lots of anti-vibration mounts are available, often rubber, neoprene or spring types. The level of noise reduction is difficult to estimate as much depends on the size of the plant and the frequency of vibration to be isolated.

Existing Machine Guards

Many machines already have guards on them which can be used to reduce the level of noise created.

Firstly, it is necessary to minimise the gaps in the guards. By reducing half the gap / open area in a set of guards, the noise can be reduced by 3dB. When the gaps are reduced by 90% through flexible seats or additional close fitting panels, a 90dB noise reduction can be obtained.

Secondly, by lining the inside of the guards with an acoustic absorbent material like foam, rockwool or fibreglass, the noise that is trapped by the guards is reduced.  This is because less noise can escape from the gaps that have been reduced.

Guard vibration can also be reduced with damping as described above.

Before carrying out the changes to the machine guards, a mock up can be made using cardboard and wide tape to see what the likely effect of reducing the gaps and lining the guards will make to the noise emitted.

Modification of existing machine guards is a very effective way of reducing the risk of noise induced hearing loss within a workplace.

machinery guards

Pneumatic Exhausts

Pneumatic exhaust noise can be reduced by 10dB to 30dB by fitting effective silencers. There are some practical points to note though.

Where back pressure exists, a large coupler and silencer should be used.

Then clogging is an issue, a straight through silencer than cannot clog and has no back pressure should be used.

In cases of multiple exhausts, manifold them into a single, large diameter pipe fitted with the rear silencer from virtually any make of car. This is readily available from any tyre and exhaust fitter.

The level of noise reduction available from this technique will have a great impact on reducing hearing damage for workers near the exhaust.

Pneumatic nozzles

Existing copper pipe nozzles for cooling, drying and blowing machines can be replaced with quiet, higher efficiency entraining units, often reducing noise output by 10dB. They also have the benefit of using less compressed air.

Reducing Hearing Damage through Noise Control

As can be seen from the examples above, there are many simple methods that can be taken by employers to reduce the levels of noise that their workers are exposed to.

These ought to be identified by a robust noise risk assessment system to reduce the risk of noise induced hearing loss. Most of the methods described will bring a workplace to within the safe limits required by the Noise at Work Regulations 2005. This is especially true when used in conjunction with a system for the use of appropriate personal protective equipment.

These measures will have the benefit of reducing the risk of hearing damage and increase efficiency and productivity.

(This article was produced with reference to the helpful “top 10 Noise Control Techniques” produced by the Health and Safety Executive)