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Reg No : 2014/216213/07, SANAS Accredited : OHO033, DOL Accreditation No. : CI024
OCCUPATIONAL HEALTH AND HYGIENE
G R Dekenah: Managing Director/ Occupational Hygienist
Sound is defined as any pressure variation in air, water or some other medium that the human ear can detect. ‘Noise, on the other hand, is generally defined as ‘unwanted’ sound’. Noise can be a nuisance at common law and under statute law, resulting in disturbance and loss of enjoyment of life, loss of sleep and fatigue. Secondly, it can distract attention and concentration, mask audible warning signals or interfere with work, thereby becoming a causative factor in accidents. Finally, exposure to excessive noise can result in hearing impairment, the condition known as ‘noise-induced hearing losses or occupational deafness’. However, provided the intensity and duration of exposure are sufficient, even ‘wanted sound’, such as loud music, can lead to hearing impairment. Occupational deafness is a prescribed occupational disease.
Effects of Exposure
- Temporary Threshold Shift: Is the short-term effect, that is, a temporary reduction in hearing acuity, which may follow exposure to noise. The condition is reversible and the effect depends to some extent on individual susceptibility.
- Permanent Threshold Shift: Takes place when the limit of tolerance is exceeded in terms of time, the level of noise and individual susceptibility. Recovery from permanent threshold shift will not proceed to completion, but will effectively cease at some particular point in time after the end of the exposure.
- Acoustic Trauma: Is quite a different condition from occupational deafness (noise-induced hearing loss). It involves sudden aural damage resulting from short-term intense exposure or even from one single exposure. Explosive pressure rises are often responsible, such as exposure to gunfire, major explosions or even fireworks.
For the steadiest types of industrial noise, intensity and duration of exposure (dose) are the principal factors in the degree of noise-induced hearing loss. Hearing ability also deteriorates with age (presbycusis), and it is sometimes difficult to distinguish between the effects of noise and normal age deterioration in hearing.
In any strategy to reduce or control noise two factors must be considered, that is, the actual source of the noise, and the transmission pathway taken by the noise to the recipient. Personal protective equipment, such as ear plugs, ear defenders and acoustic wool, may go some way towards preventing people from going deaf at work, but such a strategy must be regarded as secondary since it relies too heavily upon exposed persons wearing potentially uncomfortable and inconvenient protection for all the time they are exposed to noise. The majority of people simply will or do not do this! The first consideration must be that of tackling a potential noise problem at the design stage of new projects, rather than endeavoring to control noise once the machinery or noise-emitting item of plant is installed. Manufacturers and suppliers of machinery and plant must be required to give an indication of anticipated sound pressure levels emitted by their equipment and of the measures necessary, in certain cases, to reduce such noise emission, prior to the ordering of same.
Controlling the Noise Generated
Some of the methods of preventing machinery noise generation that should be considered are:
- Avoiding impacts, or providing arrangements to cushion them, for example buffers on stops, the use of rubber or plastic surface coating to avoid metal impacts on chutes
TABLE 1. Methods of Noise Control
Source and Pathways
Vibration produced through machinery operation
Reduction at source e.g. use substitution with nylon components for metal; use of tapered tools on power presses
Vibration isolation e.g. use of resilient mounts
and connection, anti-vibration mounts
Radiation of structural vibration
Vibration damping to prevent resonance
Turbulence created by air or gas flow
Reduction at source or the use of silencers
Airborne noise pathway
Noise insulation-reflection; use of heavy barriers
Noise absorption-no reflection; use of porous lightweight barriers
OHS Act 85 of 1993 (Section 8): General Duties of Employers to their Employees
Every employer shall provide and maintain, as far as is reasonably practicable, a working environment that is safe and without risk to the health of his employees.
- Without derogating from the generality of an employer’s duties under subsection (1), the matters to which those duties refer include in particular:
- the provision and maintenance of systems of work, plant and machinery that, as far as is reasonably practicable, are safe and without risks to health;
- taking such steps as may be reasonably practicable to eliminate or mitigate any hazard or potential hazard to the safety or health of employees, before resorting to personal protective equipment;
SANS 10083: 2013
The measurement and assessment of occupational noise for hearing conservation purposes.