Noise is sound that is loud, unpleasant, or undesired. Sound is vibration energy that passes through air (or other media) and is received by the ear, stimulating the auditory nerves and producing the sensation of hearing.
The energy produced when something vibrates produces sound waves that have a definite pattern.
The wavelength determines the pitch of the sound. Long, slow waves are a low pitch (like a foghorn). Short, fast waves are a high pitch (like a whistle). Frequency is measured in hertz (Hz), or waves per second. The slowest, lowest sound a human can hear is approximately 20 Hz. The highest sound a human can hear is approximately 20,000 Hz (or 20 kilohertz – kHz).
The strength or loudness of a sound is determined by the amplitude or height of the sound waves. Tall waves are loud; short waves are quiet. Tall, fast waves are a rattle. Short, long waves are a hum.
Loudness is measured in decibels (dB). The scale runs from 0 which is the threshold of hearing to 140 which is the threshold of pain.
The decibel scale is logarithmic in nature. This means that a 10dB increase is actually 10x louder, so 80dB is 10x louder than 70dB, and a 3dB increase is a doubling in loudness, so 73dB is twice as loud as 70dB.
Health Effects of Noise
Noise at work can cause hearing loss that can be temporary or permanent.
Temporary deafness is often experienced after leaving a noisy place. Although hearing typically recovers within a few hours it should not be ignored. Continued exposure to high levels of noise can permanently damage hearing.
Permanent hearing damage can be caused in two ways:
- Sudden, extremely loud, explosive noises, e.g. from cartridge-operated machines can cause immediate permanent damage. This is often referred to as blast deafness or acoustic trauma.
- Usually hearing loss occurs gradually because of prolonged exposure to noise. It may only be when damage caused by noise over the years combines with hearing loss due to ageing that people realise how deaf they have become.
Tinnitus (ringing, whistling, buzzing or humming in the ears), may also be caused as a result of exposure to workplace noise.
Noise Action Levels
There are three noise action levels defined in the Noise at Work Regulations. At each level the employer is required to take certain steps to reduce the harmful effects of noise on hearing.
| Noise Action Levels | Daily / weekly average | Employers Duties |
| Lower exposure action value | 80 dB(A) | Provide information and training Make hearing protection available |
| Upper exposure action value | 85 dB(A) | Take reasonably practicable measures to reduce noise exposure (engineering controls / technical measures Provision of mandatory hearing protection pending engineering controls and, where necessary, after engineering controls |
| Exposure limit value | 87 dB(A) | This level must not be exceeded, taking hearing protection into account |
Control Measures
Noise control strategies involve controls at
- the source,
- the pathway and
- the receiver.
- Replace the machine with one with lower noise emissions;
- Move the machine to an area with fewer employees;
- Ensure the machine is being properly maintained; and
- Modify parts of the machine, e.g. by replacing components with ones designed to operate more quietly:
- Isolate panels or add damping materials to them;
- Isolate the machine from the building with isolation mounts or isolated foundations; and
- Fit appropriate silencers to air inlets and exhausts.
Control the path of the noise:
- Fit a suitably designed enclosure around a machine if it does not require ‘hands-on’ operation;
- Provide a noise haven for employees supervising the operation of large machines where enclosing the whole machine would be difficult;
- Erect barriers or screens between different elements in the production process, separating quiet operations from noisy ones; and
- Add absorptive materials to the building to reduce reverberant noise (echoes).
Control noise at the receiver:
The receiver can be protected from the effects of noise by positioning (distance); reduction of the time exposed; or provision of PPE.
- Position the worker further away from the source of noise (Doubling the distance can reduce the effect of the noise by 3 to 6 dB).
- Except for very loud noises (130dB+), it is the accumulated dose that causes hearing loss. Halving the time exposed will reduce the dose received by half (3dB).
- Personal hearing protection (PHP) should be provided quickly on discovering a risk to health due to noise. It is not an alternative to technical and organisational noise controls but a means of managing the immediate risk pending the development of other control measures. Longer-term, it should be used where there is a need for additional protection beyond what has been achieved through noise control. Hearing protectors should be CE marked, in good condition, the correct size and worn properly.