Noise at work: The Hierarchy of Control

Responsibilities of Employers and Employees

In the previous write-up, the legal requirements regarding noise limits set by the Department of Occupational Safety and Health Malaysia (DOSH) were discussed (DOSH, 2018). The Factories & Machinery (Noise Exposure) Regulations, 1989, should be always obeyed by industrial workers and employers to ensure the safety and health at work for all employees (Lee, 1989).

In this article, we will further discuss about the noise control methods based on the Hierarchy of Control to improve workplace from noise hazard. Before we begin, here is a quick recap from previous topics:

One should not be allowed to be exposed over:

  • 90 dBA for 8 hours/First Schedule/Daily noise dose of 1.0
  • 115 dBA at any time
  • 140 dB for impulsive noise

As a responsible employer, it is important to know that “the occupier shall reduce and maintain exposure to noise level below the limits by engineering control as far as reasonably practicable”, as stated in Regulation 15. As such, employers should conduct exposure monitoring that includes Area Monitoring and Personal Monitoring.

To ensure that noise control can be achieved efficiently, the following key actions should be taken account of:

  • Prioritising and tackling the immediate risks
  • Identifying possible methods
  • Assessing the reduction levels that can be achieved by introducing cumulative controls
  • Assigning responsibilities
  • Monitoring controls and performance

In Area Monitoring, noise mapping is a very common method to identify major noise sources in a specific area. The noise sources can be shown in the form of noise contours, where noise sources with the higher noise level can be determined hence action to be prioritised there. More attention will be given to higher machines or processes that emit higher noise levels.

Before deciding on solutions for noise control, the employers should take a few factors into consideration. They include:

  • The scale of the noise problem and its impact on the business, including workers
  • The cost and effort required to reduce noise exposure
  • The effectiveness of planned control measures
  • The number of individuals who would benefit from the control measures

The basic strategy of noise control

Strategy

Example

Control at Source

Control at design stage (Modify, Redesign, Relocate)

Reduction at Path

Adding barriers/enclosing the equipment

Adding sound-absorbent materials

Reduction at Receiver

Relocating the employee from the sound field

Limiting employee’s working time in the noise area

Using hearing protective devices

Adding enclosures/absorptions

These basic treatments by using engineering controls can typically achieve noise reduction effects as listed here:

Source Control

Path Control

Receiver Control

6 – 8 dB

Direct

Indirect

10 – 25 dB and above

10 – 25 dB and above

4 – 6 dB

Noise Control at Source

Noise control at the source can be implemented at the very beginning: the design stage. During the planning process, it is best to include noise control methods if noise sources are already identified here. Suitable modifications or replacement can be done, otherwise the applications of enclosures and vibration damping methods can be used to minimize the noise produced. Most importantly, proper maintenance should be done frequently once the project/object is completed to ensure the effectiveness of noise control measures.

Noise Control at Path

To reduce the noise at the path, the most effective method would be to absorb the sound along the path by using suitable absorbent materials. It is also possible to deflect the sound in other directionss by utilizing reflecting barriers in the noise path. If both methods still do not work as expected, sound enclosures can be used to contain the sound by placing the source in the enclosure.

Noise Control at Receiver

To protect the receiver (in our case, the employees), the techniques that can be applied are mainly using Hearing Protective Devices (HPD) like earmuffs, or by altering the work schedule to limit the exposure to hazardous noise.

Hierarchy of Control

Elimination

According to the Hierarchy of Control, the elimination method is the most effective way for noise control. Elimination means physically removing the hazard, which can be done by changing a work process such that it achieves the goal of getting rid of the hazard. Despite its effectiveness, this method may be very time consuming and costly. Therefore, it is always necessary to ask yourself a few questions before proceeding with the elimination method:

  • Is the process necessary?
  • Can we achieve what we want in a different way?
  • Can we get another option to do it?

Substitution

This is the second-best way to control noise hazards. Substitution method is rather similar with elimination, but instead of fully removing a hazard source, you replace it with something that does not produce a hazard. For it to be an effective control, it is important for the new product to not produce another hazard. Substitution can be done in a few ways:

  • Change of process – Same outcome, but different mechanism
  • Change of technique – Same objective, but different way of getting there
  • Change of equipment

Engineering Control

As the next best approach if a hazard cannot be eliminated or substituted, engineering control is defined as “Methods that reduce noise exposure by decreasing the amount of noise reaching the employee through engineering design approaches. Engineering controls isolate the noise from the worker through noise reduction” (NIOSH, 1996a).

By using engineering controls, employers can do physical changes to the work area or process that can effectively minimize a worker’s exposure to noise hazards. The control methods should be focused on eliminating or reducing the actual hazard source.

The key principles of engineering control include:

  • Absorption
  • Insulation
  • Distance
  • Silencer
  • Vibration isolation
  • Damping

Administrative Control

As defined by NIOSH, administrative controls mean “Methods that reduce exposure by limiting the time a worker is exposed to noise through administrative approaches. Administrative controls isolate the worker from the noise by reducing exposure” (NIOSH, 1996a).

Examples of administrative controls include:

  • Organizing schedules wisely such that noisy work is carried out when the number of workers is fewer.
  • Inform workers and everyone involved in advanced to limit their exposure.
  • Prepare quiet areas for breaks.
  • Set a time limit for workers staying in noisy areas, as per the schedule below (Noise Exposure Regulation):

Hearing Protective Device (HPD)

HPD should be the last resort when all other control methods are impractical for application. There are various types of HPD in the market for different applications, like earmuffs or earplugs with different noise reduction rating (NRR) and SNR.

More information regarding the use of HPD, including wearing methods, how to choose the suitable HPD, and why you need HPDs, will be posted in the upcoming article. The take home message in today’s article is: “the occupier shall reduce and maintain exposure to noise level below the limits by engineering control as far as reasonably practicable.” In the case of industrial venues, employers and employees must work together to implement noise control measures, hence preventing occupational hearing damage.

References

DOSH, 2018. Introduction of Noise & Legal Requirement, s.l.: Department of Occupational Safety And Health Malaysia.

Lee, K. S., 1989. Factories and Machinery Act 1967, s.l.: Federal Subsidiary Legislation.

Written by Khei Yinn Seow

Posted on September 11, 2020

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