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Occupational Noise and Health

Published: 01st Mar 2012

Many countries in the Middle East and Africa (MEA) have experienced rapid economic and industrial development over the past few decades following the discovery and exportation of natural resources such as oil, gas and minerals.

These countries have seen tremendous growth in mining and construction, transportation and oil exploration. As a result of these activities, there is increasing availability and use of machinery and equipment such as cranes, bulldozers, automated machines and pneumatic and electric power-tools. Advances in workplace technology and mechanisation have improved the efficiency and productivity of industrial processes, but have also increased exposure to occupational hazards, particularly noise and vibration.

Noise and decibels

Noise is one of the most common physical hazards encountered at workplaces in rapidly developing countries. It is estimated that approximately 600 million workers are exposed to occupational noise worldwide, but what is noise and how does it affect the workforce?

The World Health Organization states that there is no physical difference between sound and noise rather sound is a sensory perception and noise corresponds to ‘undesired sound’. The National Institute for Occupational Safety and Health (NIOSH) have extended that definition to describe noise as any unwarranted disturbance within a useful frequency band. When assessing the impact of noise on human health and wellbeing, noise is usually classified as occupational (e.g. noise in the workplace) or environmental noise (e.g. all other non-occupational settings at the community, residential and domestic level).

In brief, sound (or noise) involves pressure changes caused by a series of air vibrations which are picked up by the eardrum and transmitted to the brain. Technically, sound is measured in units of pressure (Pascals [Pa]). The human ear is capable of detecting a wide range of absolute pressure levels (from 0.00002 Pa to 200 Pa). In practice, sound is measured on a more practical simplified logarithmic scale using units of decibels (dB) which indicate the relative loudness of a sound.

Noise is a combination of sounds at various frequencies and intensities, and the human ear is not equally sensitive to sound pressure changes at different frequencies. Therefore, the different sound pressure levels are weighted to account for the perceived loudness of a sound at various frequencies. The most commonly used weighting of sound pressure levels is the ‘A’ weighting, which is expressed in units of ‘dBA’. Noise exposure durations can be continuous or impulsive.

The different features of impulse noise compared to continuous noise is that impulse noise is intermittent and characterised by a steep rise in the sound level to a high peak followed by a rapid drop. Occupational noise is usually a combination of both continuous and impulse-type sounds.

Noise-Induced Hearing Loss (NIHL)

Noise is one of the most important occupational factors affecting workers’ health and productivity. The size, shape and structure of the ear is specifically designed to maximise sensitivity to various sounds, but the trade-off is that the ear is not well equipped to protect itself from the harmful effects of noise.

Occupational hearing loss resulting from exposure to a high noise level is dependent on the duration of the exposure, in addition to the frequency, intensity and type of noise (continuous or impulse). Long term exposure to noise can temporarily or permanently damage the inner architecture of the ear which can lead to hearing impairment (e.g. reduced auditory sensitivity).

This is broadly categorised into either a conductive or sensorineural effect. Conductive hearing impairment occurs when there is a physical alteration in the structure of the conducting mechanism of the ear due to acute acoustic trauma (e.g. loud noise over a short time period) caused by impulse noises such as explosions, blasts and mass gun fire.

Hearing impairment from acute acoustic trauma may be permanent if surgery is not able to repair the inner ear structure (e.g. eardrum, ossicles, cochlea), but apart from military settings, hearing impairment due to acute acoustic trauma is rare in most occupational settings. Sensorineural hearing loss is the most common form of occupational-related hearing impairment and occurs as a result of damage to the inner ear hair cells following repeated exposure to excessive noise. It can also be caused by infection or blunt traumatic injury to the head. An obvious consequence of noise exposure is deafness.

Other effects are tinnitus, alterations in threshold shifts, and accelerated presbycusis. Tinnitus is a subjective condition characterised by the perception of a ringing sound in the ear in the absence of any corresponding external sound. It is usually transient with normal hearing acuity returning within 24-72 hours. Repeated attacks of tinnitus can occur following exposure to noise. Threshold shift occurs when a higher sound intensity is needed to elicit hearing and this condition can be temporary or permanent.

A temporary threshold shift usually results following exposure to a high noise level or impulse type noise (e.g. gunshot or explosion) and hearing acuity normally returns after a period away from noisy environments. In contrast, permanent threshold shift is non-reversible. One of the aims of periodic audiometry is to detect a temporary threshold shift, and to then institute measures to reduce further noise exposure before permanent threshold shift sets in. Presbycusis (also known as age-related hearing loss) is the term used to describe the progressive and symmetrical reduction in bilateral sensorineural hearing acuity at higher frequencies of the audio range due to the ageing process. Presbycusis is related to the degeneration of the cochlea hair cells as a result of ageing, but excessive noise can hasten the onset of natural hearing loss.

Consequences of NIHL and exposure to noise

Workers exposed to occupational noise (daily dose ≥ 85 dBA) are also at a higher risk of chronic disease and ill-health. NIHL causes a significant socio-economic burden on society as it can lead to the removal of skilled and experienced employees from the workplace, cessation of employment, and early retirement. Moreover, NIHL can reduce the quality of life in workers and cause additional problems such as social isolation, depression and increased risk of accidents.

Noise can increase the overall workload of operators during a specific task and negatively affect performance. Hearing loss can compromise the ability of the affected worker to identify important environmental cues in regard to effective communication, e.g. speech recognition and emergency warning signals. Other health effects attributed to noise are an increase in blood pressure, accelerated heart and breathing rate, and increased muscle tension. Hence, noise can be a physiological stressor with long-term exposure contributing to the development and aggravation of stress-related conditions such as high blood pressure, coronary heart disease and gastric ulcers. Related symptoms are subjective fatigue, nausea, and headaches. Noise can also affect psychosocial and psychiatric wellbeing. Noise can therefore act synergistically with stress, excessive workload, poor ambient air quality, poor diet and other risk factors for coronary heart disease.

Extent of exposure to noise

Governmental agencies have passed laws to protect workers against occupational noise exposure. For example, the UK Noise at Work Regulations (2005) requires personal hearing protection to be provided to all employees working in occupational settings where noise levels reach 85 dBA or above. Countries in the Middle East also have similar legislation to protect workers from exposure to noise at workplaces.

Many regulatory agencies and advisory bodies refer to 85 dBA as a warning level and 90 dBA as the danger limit for continuous work for eight hours. Occupations at the highest risk for NIHL include personnel working in the manufacturing, transportation, mining, construction, agriculture and military sectors. According to NIOSH, 14% of US workers are exposed to noise levels in excess of 90 dBA.

Accurate and reliable occupational noise exposure data for the MEA regions is scarce. The available evidence suggests that average noise levels exceed the occupational exposure standards in developed countries such as the UK and US. For example, there are reports of foundry workers in the UAE exposed to sound pressure levels >85 dBA in various sections of the foundry (e.g. furnace, rolling mill, mechanical and fabrication workshop), with the highest values recorded (100 dBA) in the casting area.

Airport personnel and agricultural tractor operators in Turkey, employees at an automobile/wagon factory and food production plant in Iran, and workers at a steel fabrication and air-conditioning manufacturing factories in Saudi Arabia were reported to have been exposed to a daily noise dose exceeding 85 dBA. This data suggests that a large proportion of the MEA workforce could be at risk of developing health complications due to excessive exposure to occupational noise.

Non-occupational exposure to noise

There are also non-occupational exposures to noise, e.g. construction activities can cause noise to affect communities living in the surrounding area. Non-occupational noise exposure also follows the pursuit of hobbies such as frequenting nightclubs and discotheques, membership of shooting clubs, and the continuous use of portable audio players through headphones (as is common among many adolescents and adults today). Traffic-related noise is a major source of occupational and environmental noise in both developed and developing countries. There is an association between noise exposure and driving performance with traffic noise capable of affecting safe driving.

Noise protection and hearing conservation

In many industrial sectors e.g. construction and casting industries, it is a challenge to minimise worker exposure to noise. Noise exposures can be reduced through efficient control measures at the worksite and/or the proper use of appropriate personal protective equipment. The average length of shift work in the MEA region for manual workers can be up to 10-12 hours and the majority of employees work a six day week with many taking annual leave only once a year. As such, industrial workers in the MEA region may be at a higher risk of NIHL compared to similar workers in other parts of the world.

A range of personal protective equipment (e.g. canal caps, ear plugs, ear muffs) is available to reduce occupational noise exposure to workers and choice of appropriate device will depend on the type and level of occupational noise, degree of noise reduction required and available resources.

Compliance with the use of personal protective devices is often poor, hence the main goal should always be to reduce exposure at source. Training of workers in the use and care of hearing defenders is an essential component of any hearing conservation programme in the workplace. Hearing conservation programmes should be introduced to monitor and control noise levels and ear defenders should be provided to all exposed workers.

Unfortunately, in some rapidly developing countries, personal protective equipment and exposure control measures are rarely used at many worksites, and are given minimal importance and preference by the majority of workers. In a study on two large factories in Saudi Arabia, hearing protection (ear plugs) was made available to all workers, but two-thirds of the noise-exposed workers reported non-usage of any form of hearing protection. Both education level of the workers and knowledge of the health hazards associated with noise were positively related to the use of hearing protection devices.

To prevent NIHL, hearing conservation programmes must educate the workforce about the detrimental health effects of exposure to noise and reinforce the use of hearing protection devices with close supervision and surveillance. The MEA labour force is composed of multinational workers with varying educational qualifications, work experience, religious beliefs, and cultural practices.

The development of occupational noise education programmes catering for all of these needs in different languages and dialects is challenging, but essential to the success of hearing conservation. The key components of a workplace hearing conservation programme should therefore include:

• Regular assessment of the noise levels at different parts of the workplace

• Clear designation of noisy areas (where residual noise occurs after all attempts at reducing noise at source) • Provision of noise-free rest areas

• Health education stressing issues such as the importance of hearing protection, and periodic reinforcement of the message to the workforce regarding precautions for protecting hearing

• Ensuring that standard safety procedures and precautions at the workplace are not circumvented

• Compliance with the use of personal protective hearing devices in work areas where they are required, and proper maintenance and care of these devices

• Periodic audiometry for workers at risk Regular hearing tests can be part of a comprehensive occupational health surveillance programme at the workplace. At best, this is a secondary prevention measure, with the primary preventive measure being reduction or containment of noise at source.

The aim of most health surveillance measures is the early detection of reversible health effects, to withdraw the worker from further exposure, and to institute further preventive measures before returning the worker to their regular work station. In the specific case of exposure to noise, the aim of audiometric screening is to detect a temporary threshold shift (TTS), and to remove any individual with TTS from further noise exposure before investigating whether additional measures are warranted at the workplace to reduce noise levels. Returning the worker with TTS to the same work area should only be considered if the likelihood of further temporary or permanent hearing loss has been reduced.

Conclusion

Do not let your workers suffer in silence! Addressing workplace noise will reduce cases of deafness and the negative psychological and physiological health conditions associated with long term exposure to occupational noise. It also has the potential to improve productivity through creating a safer and more work-conducive environment.

References

Aw TC, Gardiner K, Harrington JM. Pocket Consultant: Occupational Health. 5th Edition. Blackwell Publishing Limited, Oxford, UK. 2007. Baxter PJ, Aw TC, Cockcroft A, Durrington P, Harrington JM, eds. Hunter’s diseases of Occupations 10th edition. London: Hodder Arnold. 2010. Concha-Barrientos M, Campbell-Lendrum D, Steenland K. Occupational noise: Assessing the burden of disease from work-related hearing impairment at national and local levels. Geneva, World Health Organization, 2004. (WHO Environmental Burden of Disease Series, No. 9). National Institute for Occupational Safety and Health (NIOSH). Criteria for a recommended standard: Occupational noise exposure. Revised criteria 1998. Cincinnati, OH, NIOSH, 1998. Available at http://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf.

Authors

The United Arab Emirates University (UAEU) is the leading national university in the UAE and its Faculty of Medicine and Health Sciences (FMHS) is responsible for teaching medical undergraduates, organising and delivering continuing professional development activities for post-graduates, undertaking research and providing expert consultancy advice.

The FMHS houses the Department of Community Medicine, which has academic, scientific and support staff from various clinical and scientific disciplines in the fields of public health, accident prevention, epidemiology, biostatistics and occupational medicine. Faculty and staff are internationally recognised for their research, consultancy and training capabilities in occupational and environmental health; occupational safety and behavioural change; and public policy and regulation. The Department of Community Medicine is actively involved in the development and delivery of several occupational health training courses, including a Faculty of Occupational Medicine, Royal College of Physicians (Ireland) course on occupational medicine.

Further information can be found at http://www.fmhs.uaeu.ac.ae/cmd/ohs. A priority area for the FMHS is research into occupational and environmental medicine, public health and other disciplines of medicine with emphasis on areas of special interest to the UAE and Middle East. Please contact Dr Tom Loney (tom.loney@uaeu.ac.ae) for details on training, research or consultancy. Dr Tom Loney is an Assistant Professor in Occupational and Environmental Health in the Department of Community Medicine at UAEU.

Prior to joining UAEU, Dr Loney worked as an Occupational Physiologist for a private consultancy firm (Optimal Performance Limited) conducting research and providing consultancy services to optimise the performance and health of Military personnel in the UAE Armed Forces. Dr Loney has presented at a number of international conferences and his published research output includes more than 30 peer-reviewed papers, government technical reports, and book chapters. E: tom.loney@uaeu.ac.ae Professor Tar-Ching Aw is a specialist in Occupational Medicine and Chair of the Department of Community Medicine at UAEU. He has served as a consultant in occupational medicine for the UK Health and Safety Executive, World Health Organization in Kuwait, International Labour Organisation in Geneva, and the Malaysian Ministry of Health. Professor Aw was elected Board member of the International Commission on Occupational Health (ICOH) for two terms of office, and was formerly Chief Examiner and elected board member of the Faculty of Occupational Medicine, Royal College of Physicians (London). He is regularly invited as a keynote address at a number of international conferences and his published research output includes more than 100 peer-reviewed papers, government technical reports, and book chapters. E: tcaw@uaeu.ac.ae

Further reading

Professor Aw and colleagues have published several books that act as a useful reference guide for health and safety professionals. The first is the Pocket Consultant: Occupational Health 5th edition which offers a balance of theory and practice covering a wide range of topics for occupational health and hygiene practitioners such as physicians, nurses, occupational hygienists, safety officers, environmental health officers and personnel managers. The second book is the 10th edition of Hunter’s Diseases of Occupations, awarded best book in the medicine category by the British Medical Association Patient Information book awards in 2011. This book has been recognised as an authoritative source of information on occupational diseases in modern industrialised societies. Both books are available from online sources e.g. Amazon.com www.osedirectory.com/health-and-safety.php

Published: 01st Mar 2012 in Health and Safety Middle East

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Dr Tom Loney and Professor Tar-Ching Aw