Industries

Excessive exposure to noise causes irreparable damage to your hearing

Noise is a form of stress to humans and animals and has been linked to hearing loss, sleep disturbance, cardiovascular and mental health problems, performance reduction, annoyance responses, and adverse social behaviour.

High noise levels affect children more than adults. Preterm birth has been linked to noise, as well as learning disability, difficulty to concentrate, and lower test scores. Noise is unwanted sound that can cause impairments or damage to health. This article describes the problem of noise exposure at workplaces and the risk to health and safety of the workers.

Millions of employees in Europe are exposed to noise at work and all the risks this can entail. About 7% suffer from work- related hearing difficulties. Noise-induced hearing loss is one of the most prevalent recognised occupational diseases in the EU. While hearing loss is most obviously a problem in industries such as manufacturing, construction and agriculture, it can also be an issue in the entertainment sector, such as orchestras and discotheques.

Sources of Noise
Industry noise can come from various sources, factories, power plants, electrical generation, transformer stations, wind parks, open cast mining operations, refineries, gas compressor stations, ports and trucking companies to name a few. The noise is usually frequency dependent and can vary with time.




Occupational exposure limit to noise in a workplace
The permissible exposure limit (PEL) is a legal limit for exposure of an employee to be chemical substance or physical agent such as loud noise. Permissible exposure limits are established by the Occupational Health and Safety Act (OHSA).

What is a workplace exposure limit?
The workplace exposure limit value is expressed as a time weighted average (TWA) and there are two variations:

The Long-Term Exposure Limit (LTEL) which is the maximum exposure permitted over an 8-hour period and
The Short-Term Exposure Limit (STEL) which is the maximum exposure permitted over a 15-minute period.

Subject to regulations 9 and 10, no employer or self-employed person shall require or permit any person to enter any workplace under his or her control where such person will be exposed at or above the 85 dBA noise rating limit (Occupational Health and Safety Act, 1993; Noise-induced Hearing Loss Regulations, 2003).

The main problem in noisy plants is finding and documenting the 85 dB noise contour line. In areas where noise levels exceed 85 dB, workers must wear hearing protection.




Noise and hearing conservation according to the Regulations
Subject to the provisions of sub-regulations (3) and (4), no employer shall require or permit an employee to work in an environment in which he is exposed to an equivalent noise level equal to 85dB(A) or higher.

Where the equivalent noise level in any workplace cannot be reduced to below 85 dB(A), as contemplated in sub-regulation (3), the employer shall:

- Demarcate the boundaries of all noise zones in such a workplace by posting
up notices to that effect in conspicuous places along such boundaries and at
all entrances to and exits from any room where the whole of such room
constitutes a noise zone; and

- Prohibit any person from entering a noise zone unless such person wears
hearing protectors.

In case of building work where it is not reasonably practicable to comply with the provisions of sub-regulation (4)(a) owing to the nature or extent of the premises, the employer shall post up such notices at all exits from an entrance to such premises or where this is not reasonably practicable, display such notices in a conspicuous place as close as possible to the actual workplace or in such place as an inspector may direct.

Whenever an inspector is of the opinion that the employer has omitted or failed to reduce the equivalent noise level in a noise zone to as low as is reasonably practicable or to isolate the source of the noise acoustically, he may require such employer, by notice in writing, to take such further steps as such inspector considers reasonable and practicable for the purpose of conserving the hearing of employees entering or working in such noise zone (Occupational Health and Safety Act, 1993 Environmental Regulations for Workplaces, 1987).

Excessive exposure to noise causes irreparable damage to your hearing. Often the damage gets gradually worse with each repeat exposure, but some very high-level sounds, such as those from gunfire and explosions, can cause immediate damage.

Long term exposure can arise from regular working in a noisy occupation or workplace. Receptors that provide the signal from the ear to the brain are damaged by excessive noise, often without the sound seeming too loud or painful. The receptors do not recover. Over time more receptors are damaged, increasing the hearing loss. The risk to any individual is normally determined by their A-weighted daily or weekly personal noise exposure (the overall amount of noise in terms of level and duration in a working day or week).

Very high level-sounds, such as fireworks, gunfire or explosions can result in injury that causes immediate hearing loss or other hearing damage. The risk of instantaneous damage is normally determined by the maximum instantaneous C-weighted peak sound pressure of the sound.

Exposure to high levels of noise can cause permanent hearing loss. Neither surgery nor a hearing aid and help correct this type of hearing loss. Short term exposure to loud noise can also cause a temporary change in hearing (your ears may feel stuffed up) or a ringing in your ears (tinnitus). These short-term problems may go away within a few minutes or hours after leaving the noise. However, repeated exposure to loud noise can lead to permanent tinnitus and/or hearing loss.

Loud noise can create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals.

The effect of noise induced hearing loss can be profound, limiting your ability to hear high frequency sounds, understand speech, and seriously impairing your ability to communicate.

Because communication and hearing are affected by noise exposure the probability of accidents increases at relevant workplaces. Even relatively low noise levels can cause problems in the workplace because the noise is annoying and disturbing. Noise can give rise to stress reactions that have a detrimental effect on the ability to concentrate and, on productive efficiency. These problems are recognised for instance in call centres and sectors such as education and health care.




Chronic hearing loss
Noise exposure at the workplace over many years may lead to irreversible hearing loss if daily sound exposure levels reach or exceed 85 dB(A).

The incidence of noise-induced hearing loss can be described as follows:
Following exposure to noise, for instance during the working shift, the sensitivity of the ear is temporarily reduced. This can be demonstrated audiometrically as a temporary shift in the hearing threshold (temporary threshold shift). The affected individual has the sensation of his or her ears being blocked. The hearing may gradually recover if it is given a sufficiently long break. This may take hours or even days. If, however the recuperation period is not sufficient for the sense of hearing to recover completely and partial deafness from the previous day is still present at the beginning of the next shift, a metabolic deficit (metabolic fatigue) remains which over a longer period causes the hair cells of the inner ear to die. The consequence of this is a permanent hearing loss. Subsequent exposure to noise causes the symptoms to be worse over time.

Experience shows that the sense of hearing degrades with age, even in the absence of any particular adverse exposure to noise (age-related hearing loss - presbycusis). There is no cast-iron physiological rule that ageing must be accompanied by hearing loss. On average however, older people can generally be expected to have lower hearing sensitivity, particularly at higher frequencies. In this case, the damage can primarily be found in the inner ear. In addition, ageing may be accompanied by stiffening of the mechanism of the middle ear. This in turn also has an influence at low frequencies.

Noise-induced hearing loss is a particularly insidious condition, since it occurs virtually unnoticed by the affected individuals. They feel no pain and initially can communicate easily because hearing loss begins at higher frequencies around 4,000 Hz. Under continued exposure to noise, the hearing loss gradually spreads into lower frequency ranges including those of speech. As a result, the affected individuals have difficulty following a conversation, particularly in

Acoustically unfavourable environments and with strong background noise. The drop-in hearing sensitivity with increasing age intensifies this problem. Ultimately those who have suffered hearing loss are barely able to converse even in quiet environments, and easily become increasingly isolated from their fellow human beings. Hearing aids can compensate only partially for the hearing loss.

Acute hearing loss (acoustic shock)
In addition to the hearing loss from long-term noise exposure (metabolic fatigue), direct structural damage to the hair cells may occur if a certain exposure threshold is exceeded. In this case the hair cells break off as a result of excessive mechanical strain. This is described as traumatic or acute hearing loss.

A risk of acoustic shock exist under exposure to extremely high noise pulses with peak sound-pressure levels LC peak of 155 dB and higher for example gunshots, explosions or the burst of a truck tyre can cause such high noise impulses.

A single noise event of this kind may be sufficient to create permanent damage to an unprotected ear i.e. in the absence of hearing protection.

Noise is however not the only possible cause of hearing loss. Other reasons may be stiffening of the mechanism of the middle ear (otosclerosis), degenerative processes in the inner ear, exacerbated or premature ageing, infections, head injuries, certain forms of medication, and ototoxic substances (e.g. work-related industrial chemicals).

Employees may be distracted and irritated at work even by relatively low sound pressure levels, upwards of approximately 30 dB(A). The causes include air conditioning systems, PC cooling fans, and often conversations at adjacent workplaces. In the first instance, mental responses such as annoyance, tension and nervousness are observed. The reactions vary widely from person to person and are linked not only to the level of the noise exposure, but also to the complexity of the task performed, the individual’s attitude to the noise, and their instantaneous physical and mental constitution.

Exposure to noise above approximately 60 dB(A) is shown to lead to vegetative responses, for example increased respiratory and cardiac frequency, increased blood pressure and higher stress hormone values. These are clearly stress responses which in conjunction with exposure over many years to other occupational stresses, may harm the cardiovascular or gastrointestinal systems.

There is strong evidence that noise is associated with hypertension, evidence concerning cardiovascular diseases is weaker. Disruptive noise exposure and the associated stress responses have an impact upon work performance and this impact increases as a function of the complexity of the work to be performed. The influence of the noise can be compensated for in the short term by greater concentration and effort. Work stages are checked more frequently or simple solutions sought. Owing to the associated effort and fatigue however, lower productivity and a higher error rate must be anticipated. For this reason, investments in noise abatement measures may pay off economically even at relatively low sound pressure levels, since they lead to higher productivity and quality.

Ultimately, personal performance also has an influence upon occupational safety. More frequent accidents must therefore be anticipated under exposure to noise, owing to incorrect behaviour and startle responses. In addition, the disruption to speech communication in noisy environments and the poor perception of warning signals lead to an increased accident risk; employees may easily miss a colleague’s warning shout or an approaching forklift truck for instance.