Methodologies have been developed to utilise exposure data to develop noise exposure databases and to facilitate assessments (ASCC, 2008 and Hohmann, 2008). In addition, there are guidance notes, checklists and noise risk-assessment tools which help to determine when noise is likely to be problematical (EU-OSHA, 2014). While risk assessments can be undertaken without the need for noise measurements (HSE, 2005), this is clearly not acceptable in certain cases.
In any assessment, the key requirement is to assess risk using appropriate ‘criteria’. One of the legal obligations on employers is that they must make a ‘suitable and appropriate assessment of risk’, in consultation with the employees and/or their representatives.
The risk assessment must be undertaken by a competent assessor. The primary purpose of the assessment is to clarify what needs to be done to protect the health and safety of all employees who are exposed to noise. In theory, noise measurements may not always be required. However, whenever any significant risk exists, it would be difficult to justify not using site-specific measurement data.
When carrying out a risk assessment, particular attention should be given to the following:
‘(a) the level, type and duration of exposure, including any exposure to impulsive noise;
(b) the exposure limit values and the exposure action values specified in the 2007 Regulations;
(c) the effects of exposure to noise on employees whose safety or health is at particular risk from such exposure (e.g. particularly vulnerable employees);
(d) as far as technically possible, any effects on employees’ safety and health resulting from interactions between noise and work-related ototoxic substances, and between noise and vibrations;
(e) any indirect effects on employees’ safety or health resulting from interactions between noise and warning signals or other sounds that need to be observed in order to reduce the risk of accidents;
(f) any information on noise emission provided by the manufacturers of work equipment in accordance with Section 16 of the Safety, Health and Welfare at Work Act, 2005;
(g) the availability of alternative equipment designed to reduce noise emission;
(h) the extension of exposure to noise beyond normal working hours under the employer’s responsibility;
(i) appropriate information obtained from health surveillance including, where possible, published information; and
(j) the availability of hearing protectors with adequate attenuation characteristics.’
The above requirements constitute the minimum legal obligations (The Stationery Office, 2007, ‘General Application Regulations’) and they need to be interpreted relative to the likely magnitude of risk (refer to Appendix I).
Recommended survey/assessment strategies
A combination of well-planned, reliable, representative measurements with good interpretation is essential to establish the level of risk arising from exposure to noise. There are two principal types of instrumentation/survey methodologies to quantify noise exposure (dosimetry and static or SLM-based measurements).
In planning the assessment, it is recommended (ISO 9612:2009) that a logical strategy is followed, as follows:
- work analysis,
- selection of measurement strategy,
- conduct measurements,
- error handling and uncertainty evaluations,
- calculations, and presentation of results.
Although not mentioned by ISO, it is important that consultations are held with managers, supervisors, H&S committees and employee representatives in scoping out the survey/assessment. This will help to ensure its representativeness and its acceptability.
It is recommended that a Class 1 sound level meter (SLM) is used to determine LAeq values at the position(s) the employees occupy throughout their shift and at representative ‘static’ positons. The LEX, 8h can then be calculated based on the combination of LAeq values and the time spent in each area.
Alternatively, if a worker moves throughout a limited area, we can determine the LAeq for the entire area (spatial average SPL) by moving the microphone to all those areas that s/he occupies (i.e., measure at positions that their ears would occupy). This can be done by ‘shadowing’ an employee for a representative period. Alternatively, the maximum LAeq can be measured at the noisiest position and it can be assumed that the worker spends all of the time in that position (worst-case assumption).
The choice of instrument influences the uncertainty of the measurements and Class 1 instrumentation is recommended as it is more precise than Class 2. Clearly, we should not be using Class 2 instrumentation, it has many shortfalls and some of these are not well known. For example, the specified tolerance limits for Class 1 instruments are applied for the temperature range from - 10 °C to +50 °C. This is important if exposure arises in refrigerated environments (e.g., cold stores).
For Class 2 instrumentation, the influence of variations in air temperature on the measured SPL is only specified over the range from 0 °C to +40 °C (IEC 61672-1:2002 and IEC 61252).
The ‘SLM or static-based’ methodology is particularly useful when workers operate at fixed positions and where the measurement results describe the noise at the operator’s ear, attributable to a specific tool, workstation or task. It is recommended that this is supplemented with a ‘second method of quantifying exposure’ – by using dosimeters which are worn by the workers throughout the working day or for a representative period.
With dosimeters, the microphone is worn on the body (shoulder or lapel) and there is very likely to be an additional uncertainty to dosimeter measurements because of localised noise disturbance. Despite this, the International Standards Organisation previously (ISO, 1997) claimed them to be the preferred method for quantifying exposure. However, the ISO standard for workplace noise assessment was updated in 2009 and ISO, like many authorities, are now somewhat wary of dosimeters.
Using dosimeters
Many practitioners and researchers have first-hand experience of the dubious nature of dosimeter data. However, this has apparently been overlooked for their ease of use. Nonetheless, current HSE guidance includes a note of caution and states that a dosimeter ‘tends to increase the potential false contributions to measurements and thereby the measured sound pressure level’ (HSE, 2005, p. 96).
In 2004, a landmark publication described major difficulties with dosimeter data and highlighted some of the pitfalls associated with dosimeter-based surveys. Kardous and Wilson (2004) investigated various noise measuring instruments at firing ranges, and while emphasising the impulsive nature of the noise environment, they concluded that dosimeter readings were ‘nearly always in error’.
Their results highlighted ‘limitations exhibited by dosimeters, which include peak pressure clipping, unreliable dose-response relationship, and overall lack of capability to record signal parameters that may better describe and quantify the hearing damage risk from exposure to impulse noise’ (Kardous and Wislon, 2004).
This writer has had widespread experience of elevated dosimeter SPLs which defied explanation. Importantly a thorough risk assessment should seek to explain where, when and how elevated SPLs arose. In some cases static measurements will verify or disprove the dosimeter data. However, preference should always be given to precision SLM data and according to the ISO:
‘Any high peak sound levels recorded by the instrument which were not validated by observation shall be investigated and commented on in the report.’ (ISO: 9612, 2009):
Amongst the dosimeter’s drawbacks is that an instrument will provide a limited number of ‘useful’ measurements per day, despite the availability of data logging units. Generally the dosimeter will be attached to a worker who for practical reasons cannot be constantly observed. Thus, dosimeter data is not generally ‘attended’ by the assessor and the assessor cannot honestly testify to its validity, unlike a measurement which was personally supervised in its entirety.
For dosimeters, the size of the windscreen is usually limited. However, by using a hand-held or tripod-mounted SLM with a larger windscreen, the potential effect of airflow-induced noise (e.g., ventilation) can be minimised. ISO, 2009 states: ‘Contributions from wind and airflows depend on the wind speed and the size of the windscreen. A-weighted sound pressure levels around 80 dB are usually not significantly influenced by airflow speeds up to 10 m/s, provided the windscreen is of 60 mm diameter or more.’
Thus, dosimeter data which is sourced in impulsive, refrigerated and/or well-ventilated environments is likely to conceal potentially significant error. When we consider the use of SLM and dosimeter options along with various strategies for assessing noise, the measurement of noise from particular tasks with a SLM can be the most reliable method for various scenarios.
Coupled with information on the duration for each activity, a range of exposures can be easily estimated. However, dosimeters are useful where access issues arise (e.g. workers in machine cabs) and when employees are particularly mobile.
Activity, job or task basis
Thus, workplace noise measurements can be effectively made on an ‘activity, job or task basis’ by using a SLM to log a series of LAeq and peak (dBC) SPL readings over selected times. The selected monitoring periods must be representative of operational cycles when normal or elevated noise levels are likely to be recorded (thus, the need for scoping and consultation).
The instrumentation must be calibrated on-site directly before and after each series of measurements and should be subject to a traceable calibration by an accredited laboratory (preferably within one year). The SLM should be generally held at arm’s length or mounted on a tripod. The measurement locations should be generally located close to the worker’s ear position in an orientation which generates the maximum sound pressure readout. Photographs of survey positions and floor plans help clarify matters and add certainty to the data.
The duration of the sampling interval will be determined by the nature of the sound source and should always be long enough to obtain a representative measurement. If the noise is steady, a short term sample will be sufficient (e.g., 60 seconds), although ISO (2009) generally advocates a minimum sampling period of 5 minutes. If the noise level changes rapidly and varies, we must wait for the LAeq value to ‘flatten off’ and stabilise to within 1 dB. If the noise is from a cyclic operation we must sample over a number of cyclic activities/operations (a minimum of 3).
Thus, the measurement duration should be tailored to the variations in the workplace noise and this will be largely dependent upon the nature of the work and the characteristics of the noise. We should also ensure that any short-duration high level noise exposures are also included as these can have a significant effect on the Leq values.
Observations on activity levels and work patterns should be recorded and as well as logging noise levels, a range of data should be collected – e.g., variations in employee work patterns (durations and locations), use of portable hand tools, machine speeds or loads, rate of work, variations in production and/or raw materials which may affect the sound levels.
Filling lines (in food and drink manufacturing), for example, are often much noisier when they switch from plastic to glass containers. Very often localised factors will determine what sampling strategy should be adopted and a preliminary walkthrough and scoping visit is recommended to assist the planning and scoping of the assessment.
It is recommended that similar exposure groups (SEGs) are identified (e.g. operators, supervisors, maintenance and QA personnel etc.) and that representative samples and noise measurements are undertaken for all pertinent SEGs. At all times, notes should be taken of the operational conditions (machine speeds, products etc.). In addition consideration should be given to maintenance and cleaning activities, when different exposure scenarios may arise.
Note: A reference list is available from the author.
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). He has held a number of consultancy positions and he is currently the Director of Moloney & Associates, an independent, Cork-based Acoustic & Environmental Consultancy. In the field of noise and vibration and occupational hygiene, Dermot 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. The speakers include a combination of leading industrial and academic specialists as well as consultants and experts from the Health and Safety Authority (HSA) and the British Occupational Hygiene Society (BOHS).
Further details are available at: www.env.ie.