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.
Circular saws are used in workplaces to cut metal, plastic, wood and masonry. They can be:
- portable saws, for example, drop saws
- hand-held and fixed saws, for example, panel saws
- docking saws
- beam saws
Noise levels from circular saws can vary from 80 dB(A) up to 120 dB(A). Noise levels vary depending on the type of saw and the material being cut. Other variables include:
- saw blade diameter and thickness
- number of teeth
- tooth design
- gap between teeth, called the gullet
- level of damping
- speed of blade
- feed rate
- condition of the saw
Different types of circular saws
Figure 1: Beam saw
Figure 2: Panel saw
Figure 3: Pendulum saw
Figure 4: Mitre saw or drop saw
Circular saw noise
Circular saws produce noise while idling, cutting and due to vibration of the work-piece.
Idling or free-running noise
Idling or free-running noise is associated with air turbulence from the saw teeth and the gaps, or gullets, between teeth. The larger the gullet, the more noise created. The air turbulence also causes the saw to vibrate and produce a ringing or hissing sound.
An idling saw can produce noise levels of around 90 to 95 dB(A). It can contribute significantly to employee exposure to noise without any material being cut.
Cutting noise is a result of the impact of saw teeth on the material being cut. The impact also causes the saw to vibrate and generate noise. Less noise is produced if there are more and smaller teeth on the saw blade. This is because the impact force per tooth is reduced.
Work-piece vibration can be a significant source of noise when cutting plastic or metal if the work piece is not suitably clamped or damped. Cutting aluminium extrusions generates particularly high levels of noise. The noise levels vary with the profile of the extrusion.
To identify the dominant noise source of a saw, measure or assess noise levels at each stage of the work cycle, for example, idling and cutting. Once dominant noise sources are identified, apply the most appropriate control measures.
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.
A wide range of noise control measures can be applied to circular saws to reduce noise from 3 to 20 dB(A) or more. Suitable control options may include the following:
Eliminate the use of saws
Eliminate the need to use saws by:
- buying pre-cut or pre-fabricated materials, for example, timber, metal, stone, to eliminate the need to use a circular saw
- using a quieter cutting process such as a guillotine or power hacksaw
Substitute noisy circular saws for quieter ones
If elimination not reasonably practicable, an employer may choose a saw with a quieter motor and a saw blade that has:
- the greatest number of teeth and the smallest teeth suitable for the job
- the smallest possible gullets
- built-in vibration damping such as laser-cut slots or laminated blade construction, see figure 5.
- tungsten carbide tipped (TCT) teeth which stay sharper longer and can reduce cutting noise by up to 14 dB(A)
Figure 5: Tips for choosing a quiet saw blade
If elimination and substitution controls are not reasonably practicable, the employer may use engineering controls such as:
- full or partial acoustic enclosures
- barriers, partitions or screens to shield nearby employees
- damping collars on existing blades to reduce vibration
- installing isolation mounts and positioning the saw on a stable surface, such as concrete
- placing a rubber mat under bench-mounted saws, such as portable cut-off saws, to minimise vibration of the bench
- firmly bolting the saw in place to minimise vibrations
- using foam inside guarding panels on pendulum cross-cut saws
- minimising gaps, dampening or isolating panels and lining them with sound absorbing materials on beam saws
- using manual or pneumatically operated padded clamps on either side of the cutting point
- lining the feed table with foam or mineral wool
If elimination, substitution and engineering controls are not reasonably practicable, an employer may use administrative controls, for example:
- do not leave saw idling unnecessarily
- use a lower operating speed. A 25% reduction in rpm may reduce noise levels by 6 to 8db(A) and a 50% reduction in rpm may reduce noise levels by up to 15 dB(A)
- schedule noisy cutting work at times when the least number of employees are in the area
- use job rotation to reduce duration of employee exposure
- ensure employees do not use excessive pressure when cutting
- keep cut depth to a minimum
- locate saws in a separate room or in an isolated area to minimise exposure to other employees. Doubling employees’ distance from a saw can reduce noise up to 6 dB.
Maintenance is critical to the reduction of circular saw noise. Therefore:
- keep blades sharp. Noise reductions of up to 10 dB(A) have been reported by sharpening a blade or using sharp tungsten carbide teeth
- tighten any loose parts, for example, belts and blade covers, to ensure they do not rattle or vibrate
- maintain saws, including the motor, in good condition. Schedule regular servicing and replacement of worn bearings, brushes and belts
- test the main shaft bearings for wear by twisting the blade from side to side
Damping saw blade vibration
Damped blades can significantly reduce noise while the saw is idling and in use. Effective damping of saw blades may achieve reductions of 6 to 17 dB(A). Damping collars should be at least one-half of the blade diameter to be effective. Saw blade damping can be in the form of:
- deep slots built into the saw, missing teeth or deeper gullets, see figures 6 and 7
- internal damping layers built into the blade (sandwich laminate blades)
- damping material sandwiched between concave steel plates, see figure 8
Figure 6: Saw blade with deeper gullets
Figure 7: Widening gullets by removing teeth. Reference: WorkSafe New Zealand, Noise abatement for circular saws
Using two parallel sheets of 18mm particleboard as close as possible to each side of the blade can reduce noise. This method has reduced idling noise up to 17 dB(A) and has also reduced cutting noise.
Figure 8: Saw blade damping
The following table shows the effect of different saw blade features on sound levels at operator position.
|Saw blade parameter||Sound Level (reduction dB(A))|
|Smaller and more teeth. Cutting lengths of aluminium using tungsten blade (350mm)|
|84 teeth, 3.5 mm wide||97|
|108 teeth, 3.2 mm wide||91|
|Vibration damping. Cutting brick using 350mm masonry blade (20 teeth)|
|Idling noise (free running) – more smaller gullets|
|84 gullets, 10mm x 7mm||91|
|108 gullets, 8mm x 4mm||84|
Circular saw enclosure
The following diagrams show a circular saw enclosure designed for rapid access during operation and extensive access for cleaning and maintenance.
Figure 9: Rapid access during operation
Figure 10: Extensive access for cleaning and maintenance
Legend for circular saw enclosure images
- Workpiece clamps.
- Sound-deadening table.
- Small apertures.
- Light-gauge perforated steel sheet.
- Sound-absorbing material.
- Solid outer skin of 12mm timber board.
- Sheet steel, 1-2mm or similar.
- Noise abatement for circular saws – WorkSafe New Zealand
- Engineering Noise Control Reports ENC-2-93, ENC-4-93 – WorkSafe WA