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Occupational Noise Assessment (Dermot G. Moloney, MSc, BSc, MIEnvSc, MIOA): Excessive noise is ‘a global occupational health hazard with considerable social and physiological impacts’ (Nelson et al., 2005). According to the World Health Organization (WHO) ‘noise-induced hearing impairment is the most prevalent irreversible occupational hazard (Berglund, et al., 2000). In some cases, hearing impairment is so severe it is classed as a ‘hearing handicap’ and it can impose major disadvantages in communication and in the daily life of the sufferer. Despite an almost universal awareness of the risk of noise induced hearing loss (NIHL), there seems to be reluctance amongst some workers and their employers to actively engage in Hearing Conservation Programmes. Authorities worldwide have legislated for occupational noise and in many jurisdictions exacting obligations are imposed upon employers. However, there seems to be a reluctance to enforce the pertinent legislation within certain sectors and jurisdictions. The permanent effect of noise on human hearing has been subject to extensive research, primarily using field studies in industrial settings. In a 1972 study the National Institute of Occupational Safety and Health (NIOSH, 1972) identified the following factors as being significant in influencing the response of the ear to occupational noise: • • • • •

Overall sound pressure level of noise Total duration of exposure Frequency spectrum of the noise Sound transmission properties of the ear Individual susceptibility to noise induced hearing loss.

It has long been known that within groups of people, who are apparently subject to similar exposures, some will exhibit extensive hearing loss while others are minimally affected. While undoubtedly the individual differences (in permanent hearing impairment) can be partly attributed to differences in physiological susceptibility to the effects of noise, t is also attributed to actual differences in the encountered noise exposure. This is because all operators or workers in an industrial setting (or even in a particular job) do not necessarily experience the same noise exposure. It is interesting to note that NIHL first appears in the region of 4000 Hz, and it is relatively independent of the noise spectrum of the exposure. Studies of noise-exposed industrial populations, when contrasted to those not exposed, clearly indicate that time spent working in noisy environments may lead to hearing damage. However, it is a known fact that ‘less than normal hearing’ exists in large groups of people who have never been exposed to damaging noise. For this reason a number of methodologies have been developed to estimate the impact of industrial noise exposure. Perhaps the most authoritative methodology is that which is set out in the International Standard ISO 1999. This standard presents ‘in statistical terms, the relationship between noise exposures and the noise induced permanent threshold shift (NIPTS) in people of various ages’.

ISO 1999 provides procedures for estimating the hearing impairment due to noise exposure of populations free from auditory impairment other than that due to noise (with allowance for the effects of age). ISO 1999 states that ‘for a single individual, it is not possible to determine precisely which changes in hearing threshold level are caused by noise and which changes are caused by other factors… however, for a large population exposed to a specific noise, changes in the statistical distributions of hearing threshold levels can be determined ‘. While the standard does not stipulate any specific formula for assessment of the risk of handicap, it does specify uniform methods for the prediction of hearing impairment. All employers have a duty under health and safety law to reduce the risk of hearing damage to their employees by controlling exposure to noise. In many instances, noise exposure will be so low as to cause negligible risk and noise measurements are not warranted in certain situations. However, it may be essential that a competent risk assessment is undertaken. In practice, much of the noise assessment and survey work which is routinely undertaken falls far short of the required standard. In fact, many ‘assessments’ are clearly inadequate and have been undertaken using suspect equipment and/or sampling techniques. In addition, very often the person who undertakes the assessment may have little or no acoustical training or expertise. Employers must undertake a suitable and appropriate assessment of the risk arising from noise exposure. This is generally done by means of a detailed noise assessment which is undertaken by a suitably qualified and experienced assessor. The primary purpose of the risk assessment is to quantify the exposure levels and clarify what needs to be done to protect the health and safety of all employees who are exposed to noise. Noise measurements may not always be required, however, whenever any significant risk exists, it would be difficult to justify not using sitespecific measurement data for an assessment. This does not mean that every assessment will necessarily require a huge volume of measurement data. Moreover, it is generally a combination of reliable measurement and good interpretation that provides the real benefit. Some ‘assessments’ consist of a series of noise measurements and provide no interpretation and guidance. A good risk assessment will include a comprehensive set of data along with appropriate interpretation and conclusions. The findings of the risk assessment must be adequately reported and an action plan should be developed to identify and document the steps taken to meet the requirements of the law- e.g., what has been already done, what needs to be done, an indicative timetable and clear identification of the individual/s responsible for the work. It is critical that the assessment has been drawn up by someone who is competent to carry out the task. In essence he or she must be suitably qualified and/or experienced. Given that the assessor’s findings will be the foundation on which the company’s controls are built, it is important that they are RELIABLE. It is up to the employer to take reasonable steps to satisfy himself or herself that the assessment meets all necessary legal requirements, even if the assessment is carried out by someone outside the company (such as a consultant).

Unfortunately many companies learn that their risk assessments are inadequate or their consultants were not ‘really’ competent when it is too late, for example, when dealing with a claim for occupational hearing loss. In fact a useful test for a company to apply would be to question whether their assessments or assessor would stand up to scrutiny by an expert in the field (or to a cross examination in a court of law). If you undertake noise surveys yourself or if you are responsible for interpreting and managing risk it is important that you keep up to date with your own professional development. Like many aspects of safety management, in order to avoid long term problems and pitfalls, it is imperative that noise survey and assessment work is undertaken by competent persons. Noise assessors as well as individuals with responsibility for risk assessment and/or environmental noise management can benefit from a training course which enables them to interpret and evaluate environmental and workplace noise assessments. These courses should also enable participants to provide guidance and assistance in risk management as most companies will continue to have residual risk long after the assessment work has been completed. The Institute of Acoustics (IOA) Certificate of Competence in Workplace Noise Assessment and Environmental Noise Measurement have been specifically developed to provide participants with the necessary training to ensure that they can competently perform their duties. Details of the workplace and environmental noise assessment training options available through Moloney & Associates, Acoustic & Environmental Consultants, may be had from their website or email

References: Berglund B, Lindvall T., and Schwela D, (Eds) (2000). Guidelines for community noise, World Health Organisation, Geneva. International Organisation for Standardisation (ISO) (1990). Acoustics – determination of occupational noise exposure and estimation of noise induced hearing impairment. ISO 1999. ISO, Geneva. Nelson, D., Nelson R., Concha-Barrientos, M., Fingerhut, M. (2005). The global burden of occupational noise-induced hearing loss. American Journal of Industrial Medicine. Vol 48 (6) pp. 446 – 458. National Institute for Occupational Safety and Health NIOSH (1972). Criteria for a Recommended Standard - Occupational Exposure to Noise. Department of Health, Education, and Welfare, Health Services and Mental Health Administration, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. HSM 73-11001.

Occupational Noise Assessment