Noise risk assessments – exposure calculations and noise-induced hearing loss
31 January 2017
The survey outlined in part one of this two-part feature is only one part of the noise risk assessment process. The determination of daily personal exposure involves a series of calculations which take account of the sound level at specific positions (or during jobs/tasks) and the time spent at these positions/tasks during a ‘normal’ working day.
The daily noise exposure level of workers can be determined using the following formula: LEX, 8h = Leq + 10 Log (T/8), where Leq is the measured noise level and T is the exposure time in hours. This formula is used when only one form of activity or exposure arises over the working shift (or when the measured noise captures any variations).
In situations where a range of tasks, activities and/or noise levels arise, the following formula is used: LEX, 8h =10 Log [(1/8) (t1×100.l L1 + t2×100.l L2…+tn×100.l Ln)], where Ln is the SPL to which the employee is exposed (Leq for the nth measurement period) in dBA and tn is the duration of the exposure, i.e. the corresponding exposure time – nth measurement hours.
An estimate of exposure time is fundamental to the calculation of LEX, 8h and, in each case, consultations should be held with the individual workers and their supervisors in order to determine the appropriate time. As a form of quality control, it is recommended that a combination of calculation methods is used (e.g. scientific calculator, spreadsheet-based and/or exposure points system). The UK’s Health & Safety Executive’s (HSE’s) exposure calculators and ready-reckoners are available at: www.hse.gov.uk/noise/calculator.htm.
Reporting and uncertainty
Article 4 (5) of Directive 2003/10/EC expressly states: “The assessment of the measurement results shall take into account the measurement inaccuracies determined in accordance with metrological practice.” Therefore, a thorough risk assessment will include a comprehensive dataset and a calculation of the expanded uncertainty (JCGM, 2008 and ISO 2008 – Guides to the expression of uncertainty).
There have been a number of recent updates in the standards relating to instrumentation, with BS EN 61672-1:2003 being replaced by BS EN 61672-1:2013. However, the limitations of the instrument form only part of the uncertainty budget (Payne, 2004).
Some of the key elements to be addressed in the report include:
- Details of all measurement results, monitoring conditions and survey data;
- Calculations or estimates of employees’ exposures, assumptions used, and uncertainty;
- Comparison of the employee exposures with the statutory action values and exposure limit values;
- Consideration of variations in similar exposure groups (SEGs);
- Identification of all workstations/activities where there may be a risk from noise and who is likely to be affected;
- An assessment of exactly when and where hearing protection will be required;
- An assessment of the suitability and likely performance of hearing protection under site-specific conditions;
- Details of all areas and activities where noise-control measures are required;
- Preliminary recommendations on the types of control measures which are likely to succeed;
- Identification of all employees who need to be provided with health surveillance and training;
- Identification of workstations and or activities for which noise control measures should be prioritised.
The findings of the risk assessment must be carefully recorded 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 important to note that the survey and assessment are just one small part of the employer’s obligations and they should not be perceived otherwise. The survey/assessment should be used as a means to launch a site specific, hearing-conservation programme (HCP) which will include a periodic review of the noise assessment.
However, in the event of a case of noise-induced hearing loss, any changes in work practices/equipment, or if there is another reason to believe that an assessment is no longer valid, then a sooner review of the noise risk assessment should be undertaken.
Figure 1: Hearing Conservation Programme (HCP), adapted from OSHA, 2002.
Noise-induced hearing loss
In the USA, the National Institute for Occupational Safety and Health (NIOSH, 2016) has determined that noise-induced hearing loss (NIHL) is the most common occupational disease with approximately 22 million US workers exposed to hazardous noise levels and an annual expenditure of c. US$242 million on compensation for NIHL disability. However, occupational noise criteria and assessment methodologies in the European Union are significantly more protective of workers’ hearing than those in the USA and, as a consequence, the risk of NIHL in the USA is greater.
While the merits of HCPs have been well established, a comprehensive structured and coordinated approach is required to ‘engineer out’ the noise risk at some facilities. Providing hearing protection devices alone will not protect our workers’ hearing. Nor will any amount of safety signage or vague commitments to ‘purchase quiet equipment’.
Moreover, effective noise avoidance and engineered control measures, training and awareness programmes, properly managed hearing protection schemes and co-ordinated audiometric assessments must be provided. It is a fact that all of these elements are prerequisites, if we are to comply with the basic, minimum legal requirements whenever the upper exposure action value (85 dBA) is exceeded.
Directive 89/391/EEC (‘Framework Directive’) provides a well-defined hierarchy for implementing workplace preventative measures, with risk avoidance taking uppermost priority. Thus, the cornerstone of the EU’s legislation emphasises the need to eliminate risk. Furthermore, the 1989 Machinery Directive and subsequent amendments (89/392/EEC and 2006/42/EC) have ensured that since 1993 most machinery supplied in the EU has been well engineered to fulfil essential health and safety requirements.
The ‘Machinery Directive’ sets out procedures and standards that manufacturers must conform to and only conforming machinery is permitted to carry the CE mark. The provisions are designed to ensure that the accidents and injuries caused by the use of machinery can be reduced.
The EU emphasis, therefore, is on inherently safe design and construction of machinery and on proper engineering, installation and maintenance. This works in harmony with the ‘Physical Agents (Noise) Directive’ with the latter providing a commercial incentive for equipment designers and manufacturers to design and produce quieter or ‘silenced’ alternatives.
Controlling noise in the workplace has many advantages, such as reduced absenteeism, improved communication, less accidents, and enhanced efficiency. Many examples have shown that the incorporation of good design and engineering controls into a system will lead to process improvements, the benefits of which will be reaped by employer and employee.
Note: A reference list is available from the author.
Dermot Moloney MSc, BSc, MIOA, MIEnvSc, MInstSCE, CSci (Senior Consultant) is a Chartered Scientist. He holds an MSc in Occupational Hygiene (with distinction), a First Class Honours MSc (Env Protection) and an MSc in Applied Acoustics (with distinction). Moloney has held a number of consultancy positions and he is currently the Director of Moloney & Associates, an independent, Cork-based acoustic and environmental consultancy. In the field of noise and vibration and occupational hygiene, he has acted as an expert witness for a wide range of industries, local authorities, insurance companies and state agencies.
Moloney is the chief organiser of a conference on ‘Risk Assessment – the Health, Occupational Hygiene and Safety’ conference in Cork on Wednesday, 1 February 2017. The conference will allow a panel of distinguished speakers to consider how we should work together to assess risks. It will provide practical and current advice and consider some of the pitfalls of risk assessment. Speakers include leading industrial, academic specialists and consultants and experts from the Health and Safety Authority and the British Occupational Hygiene Society.
Further details are available at: www.env.ie.http://www.engineersjournal.ie/2017/01/31/noise-induced-hearing-loss/http://www.engineersjournal.ie/wp-content/uploads/2017/01/Noise-induced-hearing-loss-1024x683.jpghttp://www.engineersjournal.ie/wp-content/uploads/2017/01/Noise-induced-hearing-loss-300x300.jpgCivilnoise,occupational safety