Protecting employees from exposure to noise
Employers have a duty to protect the health and safety of their employees. This duty includes protecting employees from exposure to noise. The Occupational Health and Safety Regulations 2017 (OHS Regulations) set a noise exposure standard measured in units called decibels (dB). The noise exposure standard is an 8-hour average of 85 dB(A) and a peak noise level of 140 dB(C) at the employee's ear position.
Exposure to noise that exceeds the standard is considered dangerous to employees' hearing. Employers must ensure employees' exposure to noise does not exceed the noise exposure standard.
If there is uncertainty about whether noise exposure exceeds or may exceed the standard, employers must determine an employee's exposure to noise in the workplace. When determining noise exposure, employers must not take into account the effect of any hearing protectors employees may be using.
Employers must take into account:
- the level of noise to which employees are exposed
- the duration of the exposure
- plant and other sources of noise at the workplace
- systems of work at the workplace
- any other relevant factors
Information about employers' duties is available on the WorkSafe website, including the Noise compliance code. The Noise compliance code provides practical guidance on how to comply with obligations under Victoria's occupational health and safety legislation to manage risks associated with workplace noise exposure.
Controlling impact or vibration noise
Materials handling in a workplace can generate high levels of noise. Sources of noise include objects colliding or dropping from height onto hard surfaces, such as metal hoppers or collection bins. The level of noise depends on the size and type of materials and the weight and speed of the object. For example, reducing the drop height of an object from 5m to 5cm can reduce noise by about 20 dB(A).
To control impact and vibration noise:
- eliminate or reduce the force of impact
- dampen or stiffen surfaces
- isolate mechanical vibration
- reduce operating speeds or pressures
Use the hierarchy of control
The hierarchy of control is a step-by-step approach to eliminating or reducing risks. It ranks risk controls from the highest level of protection and reliability through to the lowest.
Employers must control noise in line with the following hierarchy of control measures:
- eliminate the source of noise
- substitute noisy plant with quieter plant or processes, isolate the plant or use engineering controls
- use administrative controls
- provide hearing protection
Employers must apply each level of the hierarchy so far as reasonably practicable before moving down to the next control measure. This means employers cannot go straight to hearing protection to control the noise without applying the higher-level control measures, so far as reasonably practicable.
It is often necessary to use a combination of control measures to effectively control noise.
Noise reduction examples
Specific examples of how to reduce impact or vibration noise are as follows:
- reduce drop heights
- change the angle of impact to reduce the force of impact
- use resilient rubber-type materials to absorb the impact of falling objects
- use resilient mats on the floor below work benches or guillotines. This will reduce the noise of falling cut-offs
- fit rubber buffers to stop points
- apply a progressive cutting edge to punch tooling on power presses. This will reduce impact noise
- use conveyor belts rather than rollers which rattle
- use conveyors with spacers to prevent components striking against each other during transportation
- reduce the speed of the conveyor belt
- use wire mesh guards if solid panels vibrate
- use brass or helical-type gears that are dampened and mesh together better
- apply a layer of damping or ‘deadening’ material to vibrating panels. For example, bituminous or rubber material
- apply temporary damping panels to sheet metal during fabrication, cutting and machining
- stiffen/brace surfaces to reduce vibration
- use perforated plates or woven metal mesh instead of sheet metal
- use materials with inherent damping, for example, plastic instead of steel
- clamp work-pieces with rubber-lined clamps to reduce vibration
- dampen or increase the mass of work benches to reduce general impact noise
Figure 1: Plates falling from a roller conveyor on to a collection table cause intense impact noise. A self-levelling or adjustable table or container reduces the fall height and reduces the noise.
Figure 2: Materials falling from a conveyor belt cause impact noise. Reducing the drop height and lining the hopper with impact-absorbing material and damping material will reduce the noise.
Figure 3: Panels on machinery, motors or pumps are prone to vibration and are therefore a source of radiated noise. Using a laminated panel with damping properties can reduce noise significantly.
Figure 4: Using a wire mesh bin instead of one made from sheet metal reduces impact noise. Fitting resilient polyurethane-type wheels to the bin can also reduce rattling on uneven flooring.
Damping, or sound deadening
Vibrating structures can resonate, or 'ring' depending on the size, type and thickness of the material or panel. The resonance, or 'ringing', amplifies the noise from the vibrating surfaces.
Damping vibrating surfaces can reduce the noise, see figure 5.
Figure 5: When a wine glass is struck, it resonates for some time. If the glass is touched with the tip of a finger, the resonance is dampened and the ringing stops.
Damping, or sound deadening, involves applying a viscoelastic or bituminous-type material, such as mastic or asphalt, to reduce the vibration and the radiation of noise from large thin vibrating surfaces such as metal chutes, hoppers and machine guards. Damping can be applied as a single layer or a sandwich layer, which is usually more effective and rugged.
Damping materials can be painted, sprayed, trowelled or glued onto the vibrating surface. Self-adhesive dampening sheets are also available and can be stuck on the inside or outside of a surface. It is possible to reduce noise by 5 to 25 dB(A) by covering most of the surface with a damping layer that is at least half as thick as the panel being treated.
Constrained or sandwich damping involves sticking a rigid second layer, such as sheet metal or foil, over the viscoelastic damping layer as shown in figure 6.
Figure 6: Unconstrained, or single-layer, damping and constrained, or sandwich, damping.