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Noise Induced Hearing Loss

Published: 03rd Jun 2013 in OSA Magazine

Warren Fothergill explores the technical, legal, financial and administrative factors in the solution of noise control and its monitoring.


The overall aim of this paper is to introduce the concept of and need for the monitoring, assessment, prediction and control of noise, in both the environment and the industrial workplace. I want the reader to recognise the correlation between problems associated with industrial noise monitoring and human perception. It is hoped that readers will be able to understand, potentially select and use appropriate techniques to deal with a variety of occupational noise problems.

There are several important aspects to identify in the noise monitoring process:
• It includes many different activities, such as management, engineering, planning and both national and international legislation
• Knowledge of how humans respond to noise and how to predict noise levels is required, in addition to knowledge of the engineering principles necessary to reduce noise
• It requires a systematic approach to noise control and subsequent monitoring of problems
• The final choice of solution involves consideration of a wide range of factors in addition to noise, e.g. cost, use, location of monitoring, what is being monitored, and frequency range required

Basic principles

So where does sound originate? Speaking simply, sound comes from any vibrating surface, although sounds in gases or liquids may result from other modes of excitation, such as turbulence. The Oxford Dictionary states noise is a sound, especially one that is loud, unpleasant or that causes disturbance. Sound is a longitudinal wave motion in which molecules move back and forth along the line of sound propagation. The speed of sound depends solely on the physical property of the medium in which it is travelling and is thus independent of the intensity of the initiating disturbance.

Some of the basics of noise are outlined below:
• Sound is a form of energy
• Sound in air is associated with molecular disturbance. This begins at a vibrating surface and gives rise to pressure differentials around atmospheric pressure and temperature
• The speed of sound depends upon the medium through which it travels, the pressure and temperature
• Frequency is the number of vibrations or pressure differences per second
• Wavelength is the distance travelled by sound during the period of one complete vibration

Noise is an unwanted sound. It is measured in decibels (dB) - or at least its intensity is. The decibel scale is logarithmic, meaning a three decibel increase in the sound level represents a doubling of the noise intensity. A normal conversation, for example, may be about 65dB and someone shouting may be recorded at around 80dB. The difference between the measurements may only be 15dB but the shouting is 45 times as intense to the human ear. To take into account the fact that the human ear has differing sensitivities to different frequencies, the strength or intensity of noise is typically measured in A-weighted decibels, known as dB(A).

With the human ear being sensitive to noise, the duration of our exposure is also to be taken into account to determine theextent of the risk to our hearing.

Noise risks

Noise need not be excessively loud to cause problems in the workplace or a nuisance within the environment. Its frequency, wavelength and intensity are all aspects to consider. Noise can interact or be totally separate to other workplace hazards, though it may still increase risks to workers, both directly and indirectly.

Noise, when generated may:
• Mask warning signals, e.g. of a fork lift truck reversing
• Be a psychosocial hazard, as it may factor into work related stress

Exposure to noise may pose a variety of health and safety risks to workers, with an emphasis on human health. Excessive noise damages the hair cells in the cochlea, part of the inner ear, leading to a loss of hearing. In many countries, noise induced hearing loss (NIHL) is the most prevalent irreversible industrial disease. It is estimated that the number of people in Europe with hearing difficulties is more than the population of France; however, this pails to insignificance in comparison with the issues of workplace noise in Asia.

Asian NIHL

NIHL is the most prevalent and preventable occupational disease in the Asian continent. Sources of noise in these countries include manufacturing and agricultural industries, exploitation of natural resources and urban traffic, which is increasing with the growth of the Asian economy. NIHL is a serious health problem, not only because of the numbers of those affected, typically labourers, but also because Asia is developing its economies in areas where access to healthcare services and preventive programmes is limited.

Education and information on NIHL among employers, employees and healthcare professionals is one of the main barriers for the prevention of NIHL in Asia, and safety practises aren’t equal to the standards of Europe and North America. The World Health Organization (WHO) reports that “Countries in South East Asia generally have NIHL prevention programmes and legislation, but these are often poorly implemented and enforced and workers are ignorant of the problem. Studies in one country in the region demonstrated between one fifth and one third of workers in certain occupations have NIHL.”

Is this sustainable for the continent, given that some countries have legislative criteria and compensation systems? Owing in part to the lack of awareness among industrial workers, the first compensation in India in this regard was only paid in 1996, despite NIHL having been in the list of compensable diseases since 1948.

Other effects of noise exposure are:
1. Physiological effects - Noise exposure impacts on the cardiovascular system, which subsequently increases blood pressure and triggers the release of chemicals that are associated with stress.
2. Work related stress - Stress, work related or otherwise, rarely has a single trigger. It is normally a result of the interaction of numerous risk factors and so workplace noise can be a stressor at any level.
3. Increased number of accidents - Noise masks other sounds, depending on frequency and range. Higher noise levels make it difficult for employees to hear and communicate, which increases the probability of accidents, particularly in areas where noise risk assessments have indicated that hearing protection is required. Work related stress, in which noise may be a factor, can compound this problem.

Monitoring and control

Legislation within Asia varies from country to country; however, much of it is believed to be derived from the European Directive. The European legislation in relation to noise requires basic legislation to be set by countries to protect workers from health risks caused by noise. While the EU has moved on and reduced levels for noise exposure, the sub-continent, along with North America, seems to have stagnated.

Asia and North America appear to impose an action level of 85dB(A) at which to promulgate any positive actions; however, these appear to fail given the 1989 study by Professor Kacker, who found hearing impairment to range from 13.5% to 18.5% in Indian workers. 

The UK’s 2005 Noise Regulations introduced new requirements for action by employers. This action required employers to protect workers at levels of noise 5dB lower than the previous Noise Regulations of 1989.

So what can be done in Asia to prevent the increase of noise induced hearing loss? Well, employers can take ownership and become aware of the impact noise exposure has on its workforce. Firstly, they should assess the risks to the workforce, e.g. identify the noise hazard, estimate the likely exposure to noise, identify measures required to eliminate or reduce risks, control exposure and protect employees. In addition, all steps taken should be recorded in an action plan.

A basic method of noise assessment is suggested below; however, it is vitally important you have personnel who are totally competent in Workplace Noise Risk Assessment techniques. There is no special monitoring equipment needed and limited cost - other than a little time.

If levels are at the lowest levels indicated, look first to control the noise at source or along its path and finally as a last resort, at the worker. Utilising the hierarchy of control here is important. Is the elimination of the source of the noise an option? If not, consider substitution; however, if this is not an option then try engineering controls such as isolating the noise, or moving the noise or employee away. This is the easiest control due to noise levels being logarithmic in measurement. The last resort is the issue of hearing protection. Both its use and correct selection are also highly important to the employee - but this is another issue.

There are a number of electronic means by which you can monitor noise, determined by class or type, with standards defining two main specifications of sound level meter: Type/Class 1 or 2. These define the accuracy of the meter, are quite complex and are covered in detail in texts of the standards. In very basic terms, however, Type 1 and Class 1 are for laboratory and field use; Type 2 and Class 2 are for general field use.

The grade of sound level meter chosen should be defined by the regulations you need to meet. Most regulations for occupational noise measurement require the use of Type 2 sound level meters for basic noise level identification purposes.

In measuring environmental noise, regulations require the use of a Type 1 sound level meter. Type 1 instruments also tend to measure lower noise levels due to having a higher specification microphone.

After taking noise measurements, we need to be able to understand the readings. For individual assessments the daily personal noise exposure level (LEP,d) which corresponds to LEX,8h (level of exposure for eight hours) and is defined by the International Organization for Standardization (ISO) in ISO 1999: 1990 clause 3.6. This is expressed in decibels and is ascertained using the formula:
Te is the duration of the person’s working day in seconds; T0 is 28,800 seconds (8 hours); and LAeq,T is the equivalent continuous A-weighted sound pressure level, as defined in ISO 1999: 1990 clause 3.5, in decibels, which represents the sound the person is exposed to during the working day.

Where workers are regularly exposed to either steady noise throughout the working day, or to intermittent but regular periods of steady noise, estimating exposure is relatively straightforward. For situations where exposures are irregular, for example, where workers intermittently use a variety of different machines or spend time in different areas, determining a typical or likely exposure can be more complex. It is advisable to adopt a worst case approach in these situations, or alternatively to utilise a dosimeter, which will determine an accurate reflection of the Lep,d.

The author suggests that highly precise assessments of noise exposure are not required in the first instance; however, estimations of exposure should be reliable and precise enough for an assessment on whether any regulatory value has been exceeded. To demonstrate this, it is suggested that you record any data and reference this to any employee or role, while also identifying the exposure circumstance, their particular working practises and any uncertainties that were considered. As previously mentioned, the assessment needs to be conducted by someone who is trained, qualified and experienced in conducting noise risk assessments.

There are also simplified methods for assessing work exposure to noise when there is more than one machine in the area, giving rise to the noise problem in the first instance. Sometimes you will not even need to take readings, as information is often provided by manufacturers of new machinery and readings can be calculated initially from such information.

The table shows a simple method for estimating sound pressure levels and sound power levels without the need for calculators. If in a workshop, for example, we had a number of measurements from three machines, say 83dB, 88dB and 90dB, we would need to take the difference between the highest two readings, which is 2dB. In referring to the table, we are required to add 2dB to the higher reading, now giving us 92dB. We then identify the difference between the new figure and the lowest original, which is 9dB, requiring us to add 0.5dB to the highest figure. The cumulative noise level that a worker is therefore exposed to in the area (without looking at other noise sources) is 92.5dB, meaning there is a requirement to manage exposure.

The human factor

Industrial noise is a major hazard and people can suffer NIHL well below the levels identified in regulatory papers. The question is, how can monitoring identify this? The answer is to conduct periodic audiometric monitoring of the employee.

Taking UK legislation as an example, if levels are generally above 85dB it is a legal requirement to conduct health surveillance. This tool helps us identify issues with the individual employee, while also allowing us to monitor the workplace.

Audiometric testing, conducted by a competent individual, allows the tester to identify hearing loss before it becomes too significant to the individual. The test itself is quite simple: a tuning fork is tapped and held in the air on each side of the head to test the ability to hear by air conduction. It is tapped and placed against the mastoid bone behind each ear to test bone conduction.

Audiometry provides a more precise measurement of hearing. To test air conduction, the worker is required to wear earphones, which are attached to an audiometer. Pure tones of controlled intensity are delivered to one ear at a time and the test subject is asked to indicate when they hear a sound. The minimum intensity (volume) required to hear each tone is graphed. An attachment called a bone oscillator is placed against the mastoid bone to test bone conduction.


The Asian continent is at risk of a pandemic of NIHL claims, with a generation of personnel exposed to excessive noise sources. Employers should look at the prevention of noise, as it is better than a cure for NIHL, which does not and shall never exist. Conducting workplace noise risk assessment is relatively straightforward, cost effective and delivers vital information. Simple techniques of control, such as moving workers away from the source of noise, could be utilised to prevent noise induced hearing loss and make the workplace safer for all.

NIHL is a disability, but remembering it is the responsibility of the employer to prevent exposure. 


1. http://oxforddictionaries.com/definition/english/noise
2. Prevention of Noise-Induced Hearing Loss, Report of An Informal Consultation, WHO 28-30 October 1997
3. http://www.osamagazine.com/article.php?article_id=32
4. http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735
5. http://www.ilbs.in/index.php?option=com_content&view=article&id=221&Itemid=112
6. L108 The Control of Noise at Work Regulations, Table 1, pg 14

Published: 03rd Jun 2013 in OSA Magazine


Warren Fothergill

Warren Fothergill (CMIOSH) was born in the UK in 1968 and joined the Royal Air Force (RAF) in 1986 after completing a Business Studies Diploma. Having served around the world in the RAF, Warren studied for his NEBOSH (National Examination Board in Occupational Safety and Health) qualifications alongside a Management Diploma in 1995, passing both courses. On successful completion of the NEBOSH course, he undertook some consultancy work in warehousing, and continued for a further three years in the RAF, leaving in 1998.

Following further consultancy work, in 1999 Mr Fothergill joined J&A (International) Ltd, who operated in the UK’s screen printing sector. He quickly established the company as leading edge and forward thinking in terms of both Health and Safety and Environmental Management. The company was awarded the British Safety Council’s 5 Star Award in 2002 and attained ISO 14001 a year earlier.

In 2001, reed bed technology was introduced and the company was shortlisted for the Water Efficiency Awards 2001 (www.environment-agency.gov.uk/static/documents/Research/water_efficiency_a4_886777.pdf).

In 2003 Mr Fothergill moved into manufacturing of plasterboard at Knauf Drywall and in 2005 submitted the sector’s first Integrated Pollution Prevention and Control (IPPC) permit application under the combustion sector due to high energy consumption of the site. While at Knauf, he continued in his Health and Safety education and gained IOSH (Institute of Occupational Safety and Health) Graduate status.

In 2009 Mr Fothergill moved to Siemens Energy Services where he put his knowledge into the engineering construction sector and assisted the teams working on power stations in the UK and Ireland, promoting health and safety programmes, training and effectiveness of the mobile workforce.

In 2011, Mr Fothergill aided the Ferrybridge Power Station team from Siemens to achieve an Achilles Audit score of more than 98% and also to attain 60,000 man hours without an accident. It was during his time at Siemens that he became a Competent Workplace Noise Risk Assessor, and applied his skills in both the company factory and power stations.

Since attaining his Chartered Status of the Institute of Occupational Safety and Health (CMIOSH), Mr Fothergill worked as a consultant, before moving into training. It is by chance that Mr Fothergill, who was conducting some work in Oman, was offered a position as a lead trainer for Knowledge Grid LLC, which he accepted and was promoted on January 1, 2013, to the role of training assessment manager.

Warren Fothergill



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