In industrial places that are normally full of machineries or mechanical systems, noise is definitely inevitable, and in fact, very loud. This can sometimes be harmful to the workers hence causing occupational health and safety hazard. Therefore, in this article, we will look into noise control measures that can be used to overcome industrial noise in workplace.
Noise sources
Let’s begin with a recap on how noise is being produced:
Sound in general, is produced by vibration, or sometimes due to aerodynamic systems. Vibration-induced noises can be caused by multiple reasons, for example:
- Mechanical shocks and friction between machinery parts like hammering, rotating gears, bearings, cutting tools etc.
- Moving parts that are off-balanced
- Vibration of large and heavy structures
As for aerodynamic noises, they are caused by air or fluid flows through pipes, fans, or pressure drops in air distribution systems as well. Typical examples of aerodynamic noise sources are:
- Steam released through exhaust valves
- Fans
- Combustion motors
- Aircraft jets
- Turbulent fluid flow through pipes
Steps to control noise in workplace
To properly control the noise in the workplace, these steps should be carried out:
- Identify the sound sources (i.e., vibrating sources or aerodynamic flow)
- Identify the noise path from source to worker
- Determine the sound level of each source
- Determine the relative contribution to the excessive noise of each source and proceed to rank the sources accordingly. The dominant source should always be prioritised and controlled first in order to obtain significant noise attenuation.
- Understand the acceptable exposure limits as written in the health and safety legislation and find out the necessary sound reduction.
- Find out solutions while taking the degree of sound attenuation, operation, productivity restrains and cost into consideration.
To reduce exposure to noise
In general, noise exposure can be reduced by the elimination of noise source if possible, otherwise substitution of source with a quieter one or the application of engineering modifications works too.
The most effective way to minimise the exposure of noise is to engineer it out at the very beginning: the design stage. It is suggested to always choose equipment features that can reduce noise level to an acceptable level. For new installations, again select a quiet equipment, and make sure to have a procurement policy that opts for using quiet equipment, and finally eliminate any design flaws that may lead to noise amplification.
Engineering modifications refer to changes that can affect the source, or the sound path. This is usually the preferred solution for noise control in already-established workplaces (those without noise protection measures during design stage). This is because engineering modifications are known to be more cost effective, especially to control the noise at the source than along the path.
Administrative controls and the use of personal protective equipment (PPE) are also effective as measures of noise control applicable on workers themselves. A combination of both may be taken into consideration when the noise exposure would not justify the implementation of engineering solutions that are more expensive. However, it is important to always note that administrative control and PPE may not be as effective as implementing engineering noise control during the starting stage or modifications of sound path. Therefore, they should be categorised as the last resort.
Engineering solutions to reduce noise
Different solutions can be applied for vibration-induced noise and aerodynamic-noise.
For vibration-induced noise, the key point is to reduce the amount of vibration at the source. The typical solutions include modification of the energy source such as lowering the rotating speed of fans, or reducing the impact force of hitting tools etc. Adding damping materials onto vibrating surfaces due to mechanical forces can help to reduce vibrational effects too, especially for thin structures. To prevent unwanted damage due to friction or impact, the damping material may be sandwiched between the surface of equipment and another material that is resistant to abrasion. This treatment is called the constraint layer treatment.
Other methods to reduce vibration-induced noise include minimising gaps in machine guards and cover them with acoustic-absorbent material, replacing metal parts with plastic parts whenever possible, and replacing motors with quieter ones.
On the other hand, to treat aerodynamic-induced noise, specialists recommended to implement engineering practices that are capable of reducing noise associated with unstable fluid flow, for example minimising fluid velocity, increasing pipe diameter or minimising turbulence by utilising large and low speed fans with curved blades.
Besides those mentioned above, there are also passive noise control measures that can be used. These include using enclosures and isolations by storing noisy equipment in enclosed spaces/rooms that have special acoustic features like isolation, louvres or sealings. Installations of acoustic barriers (sound-absorbing panels) in workplaces, or silencers inside ducts and exhausts works well in attenuating unwanted noise too.
General measures to keep in mind
Finally, here are some general methods that one can take to ensure that workplace noise is under controlled.
Regular maintenance should always be performed, where the focus should be on identifying and replacing any worn-off or loose parts, lubricating any moving parts, and make sure that the rotating equipment does not get off balance to avoid vibration-induced noise.
Noisy processes should be taken note about and be substituted with quieter ones. Sound reverberation in the room should be reduced. Reverberation is when sound produced in an enclosure hits reflective surfaces and reflects back into the room in addition to the original noise paths. In some cases, reverberated sounds may dominate the original sound. A good method to help in such conditions will be to add padding onto the reflective surfaces with sound absorbing materials so that noise level can be reduced. Another way will be to arrange the equipment in the room so that they are not too close to too many reflective structures.
Conclusion
In conclusion, always take measures to identify the sound sources in the industrial workplace and find out suitable ways to solve the noise issues to achieve noise limits in accordance with exposure limits set in the health and safety legislation published by the local authorities. It is utmost important to obey the noise exposure limits to ensure the hearing health of workers in the workplace.
Reference
https://www.ccohs.ca/oshanswers/phys_agents/noise_control.html
https://www.who.int/occupational_health/publications/noise10.pdf
