CAW National Council 4000
Occupational Health and Safety

Physical Hazards:  Industrial Noise

The effects of loud industrial noise on workers are numerous. Deafness is the most noticeable effect. The stress produced by
excessive noise can contribute to heart, circulatory and digestive problems. In addition, equilibrium, metabolic and nervous system
disturbances can result.

Noise is measured in decibels. The softest sound we can hear is 0 decibels . Ordinary conversation is about 65 decibels. A loudness
of about 130 decibels causes acute pain in the ear.

Exposure to loud noise can damage the hearing organs and can result in deafness. Even a brief exposure to loud noise can give a
temporary hearing loss. This can be a ringing or other noises in the ear, can give a ‘muffled’ quality to speech, and results in an
inability to hear high-pitched sound.

If the exposure period is very brief or the noise is not too loud, this temporary deafness goes away in a few hours after you leave
the loud noise.

But, if the noise is very loud and the exposure period is long, the temporary deafness may not disappear entirely. You may slowly
develop a permanent hearing loss. Both ears are effected. There is neither pain nor bleeding. No operation, no drugs, no hearing
aid will restore this lost hearing. The nerve cells in the hearing organ have been destroyed and will not grow back. The damage is

This permanent hearing loss begins at the 80 decibel level for most people.

Here are some common noise levels in industries:

  1. General office (two bookkeeping machines
  2. Road grader
  3. Weaving loom
  4. Wire rope stranding machine
  5. Chain saw
  6. Welder

80 Decibels
95 Decibels
97 Decibels
104 Decibels
114 Decibels
95 Decibels

DEAFNESS .......... SLOWLY .......... SURELY

Permanent deafness comes on very slowly. You don’t notice it at first because only your ability to hear high pitched sounds is
affected. If you like to listen to music you might notice a change in your enjoyment. Certain parts of the music would not be heard.

With continued over-exposure to loud noise, the deafness gradually spreads to lower pitched sounds like those of human speech.
You find it hard to understand what someone is saying if the room is noisy or crowded. You start to depend more and more on lip
reading or other clues to ‘get what you can’t hear.’

Frustration becomes very strong - perhaps so strong that ordinary activities, meetings or parties where communication is important
only annoy you.


As with all kinds of pollution, the best way to control noise and vibration (a common cause of noise) is at the source. If machines
were designed in the first place to minimize noise, much of the problem would be eliminated.

Re-design of equipment for noise control often does not require a great deal of inventiveness. For instance, if the noise is due to
one piece of metal hitting against another, a thin film of polypropylene or a felt gasket placed between the parts may solve the
problem. Where feasible, plastic may be substituted for metal. If a machine or a fan is not set on level ground or it vibrates against
the floor, it can be mounted on springs or other vibration isolators to reduce the noise from this source. Such vibration-isolating
techniques are also available for punch presses and similar equipment. Sound-absorbing floor material may also help.

One source is air rushing from jet streams on air pressure lines. The noise from these lines is often high pitched, damaging, and
extremely irritating, and eliminating it can make a great deal of difference in the plant environment. To quiet this source of noise,
inexpensive mufflers are available, both as air-inlet filters and as air-discharge mufflers. Mufflers can also be installed on all motor
vehicles, such as fork-lift trucks, and on other motored equipment.

Design for noise control should not be added on as an afterthought but should be included in the original design of equipment.
Where this has not been done and where it is impossible to re-design of equipment, the next best step is to isolate noisy
equipment or processed from the people who work with or around them. Noise travels many paths within a building, through
openings or thin walls, and off non-absorbent surfaces. To avoid exposing workers to noise, the paths it travels must be rerouted
or the sound must be absorbed. Noise-absorbing partitions or walls can surround equipment, or else equipment can be operated by
remote control with the operator in a soundproof room or booth. If only one piece of equipment or process on the shop floor is
noisy, it should be acoustically isolated from the other workers and operations. Distance is an effective sound reducer, since the
intensity diminishes with the square of the distance. That is, doubling the distance cuts the sound down by one-quarter;
quadrupling the distance reduces the sound 16 times.

Sometimes equipment is noisy because it is not maintained properly. As with all other aspects of industrial health and safety,
preventive maintenance is essential for keeping a plant a safe place to work in. Even the best-designed machinery will become
noisy and dangerous if it is not maintained. Unfortunately, shutting down machines and operations for preventive care is not always
monetarily profitable to companies, so machines are allowed to wear down and become hazardous as long as they can still keep up
production. Workers must insist on proper preventive maintenance as a regular part of the production schedule.

If all other measures fail to bring the noise in the plant down to an acceptable level, protective devices can be used as a last resort.

Earplugs, Bilsom wool, and earmuffs cut down on noise from 8 to 40 decibels depending on the brand.

Unfortunately, protective devices are not really a solution to the problem but only a compromise. All protective devices, whether for
the ears, mouth, or whatever, are uncomfortable to wear, especially if the plant is hot. Some workers develop fungus infections in
their ears form constantly keeping them covered.

It is important that Health and Safety Committee members do their utmost to see that noise is controlled at its source. Companies
nearly always prefer to have workers wear hearing protection rather than controlling noise at its source, since its cheaper. We must
fight against this tendency.


ACGIH TLV 85 d BA (decibels - A scale)

Source:  CAW Health, Safety & Environment Department