Ensuring accuracy and competency

Dermot Moloney investigates tolerances, monitoring programmes and worker competence in the face of noise exposure.

Recent data from the EU estimates that 20% of the population, circa 80 million people, suffers from unacceptable noise levels that cause sleep disturbance, annoyance and adverse health effects.

There are two main categories of noise: environmental and workplace noise. The former encompasses all types of noise that potentially affects people in their homes and in public areas.

Defining noise

Workplace noise is, by definition, the noise to which an individual is exposed while in the workplace. An employee using a machine can be exposed to a certain level of workplace noise and this may need to be assessed and managed in accordance with specific legislation. The noise from the machine, however, can become an environmental noise issue if it affects neighbours or pedestrians.

The need for noise monitoring can arise in many different circumstances and sometimes the monitoring requirements may form part of a contractual obligation and/or a legal imperative.

Situations in which noise monitoring is undertaken include:

• Assessing workplace exposure • The investigation of noise complaints • During an Environmental Impact Study (EIS) • Baseline monitoring as part of an environmental noise assessment, in support of planning applications which are exempt from EIS • During the planning or construction phase of a development • As part of the commissioning phase of a project • Compliance monitoring in fulfilment of specified planning or licensing obligations

The context and circumstances of the noise emission will largely dictate how the monitoring should proceed. This is because many different acoustic standards, guidelines and legislative codes have evolved in response to differing circumstances. In addition, there is a markedly varied human response to different sources and noise types.

The equivalent continuous sound pressure level (LAeq) is universally used to describe both workplace and environmental noise. It is defined as the equivalent steady sound level in dBA containing the same acoustic energy as the actual fluctuating sound level over a given period. Internationally, much progress has been made to harmonise environmental noise indicators and assessment methods and in the US and Europe the use of a 24-hour LAeq is now well established.

Noise tolerances

In a 2010 study, the European Environment Agency (EEA) reported that at an Lden of 55 dB, 4% of the population will be highly annoyed when the source is railway noise. When the source of the noise is wind turbines, however, the percentage of the population that will be highly annoyed (at 55 dB, Lden) increases to 26% (EEA, 2010).

People are markedly more sensitive to wind turbines than they are to industrial, railway and road traffic noise. This is borne out from international research that has verified and endorsed the findings of dose-response relationship studies. These are generally published as mathematical relationships between a measured noise level and a specific response, e.g. the percentage of the population highly annoyed at a certain level of noise exposure. In this context annoyance can be a precursor to serious health effects such as hypertension, changes to blood pressure and/or heart rate, changes in breathing, and sleep disruption with consequent physical and mental health effects.

Our tolerance of road traffic noise, as opposed to aircraft or railway noise, may be associated with its ubiquitous nature. In the US, “highway traffic noise seriously impacts more people than virtually any other source of environmental noise” (Bowlby, 1998).

Similarly, in the UK road traffic noise has been recognised as the form of noise that disturbs the greatest number of people, with estimates that 30% of the population is affected by noise from road traffic (Grimwood and Skinner, 2002). In a 2010 study, however, it is postulated by an expert group on noise and health that the UK population is now less tolerant of noise than it used to be.

It is important to note that dose-response relationships should always be interpreted and used with caution. Regardless of the source of either the dose-response curve or the noise, there is likely to be a wide range of responses and reactions to noise at a particular level, due to individual variability, susceptibility and a myriad of other personal factors. A case in point is a resident living beside an industrial location that commences night time production to keep up with demand for its products. In practice, the increase in night time noise could potentially cause disturbance and annoyance to any ‘reasonable’ resident. Other neighbours, however, who are exposed to the same level of noise might be encouraged by the apparent success of the industry and the prospect of their family or friends securing employment.

To help illustrate the different tolerances to noise from different sources, fourteen EU member states reported details of their relevant limit values to the European Commission.

Figure 1 shows a comparison of the limit values in the form of Lden for residential areas.

According to the EEA “the variation in values is not too surprising. The limit values for industry are significantly lower, and for railway noise higher. The average difference is 8 dB, and the maximum limit value is 57 dB for industrial noise, and 73 dB for railway noise.” It is noteworthy that this variation in EU limit values is indicative of the variable dose-response relationships alluded to above, but clearly they are also influenced by variable socio-political and economic factors.

In practice the reported limit values are extremely variable, bearing in mind that a 10 dBA difference would be perceived as a halving or doubling of the noise level. From this it is obvious that the public response to a particular noise will vary from case to case. Rather than focusing on the absolute noise levels from a source we need to consider a wide range of issues.

Noise is uniquely different from other pollutants in that its potential impact is dependent on a wide range of factors, such as: • The time and duration of the emission • The nature of the source, e.g. equal levels of aircraft and industrial noise are likely to give rise to significantly different degrees of annoyance • The location of noise sensitive receptors • The sensitivity of any individuals affected • The ambient and background noise level • The nature and character of the locality • The presence of special acoustic characteristics, such as tones and impulsive elements

Rather than simply comparing measured noise levels against a single limit or guideline, a noise specialist will need to carefully monitor and assess the noise in accordance with a particular standard or code of practice. When it comes to interpreting the data, the competent specialist will call on a wide range of criteria and guidance and form an opinion as to the likely effect of the noise.

Monitoring programmes

The starting point in any noise monitoring programme is an evaluation of the type of noise, the objective of the monitoring and the local circumstances. Very often a particular standard or code of practice will apply and in many instances there may be statutory requirements to fulfil and certain monitoring obligations which cannot be overlooked.

In the case of workplace noise the overriding objective should be to assess personal exposure to noise, so as to facilitate an assessment of the risks. The primary purpose of the risk 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 for a workplace assessment.

Normally a workplace survey will involve measuring noise levels in the form of a time average i.e. LAeq and the maximum value of the C-weighted instantaneous sound pressure level (SPL), which is the maximum peak SPL. Once the context and pertinent circumstances have been identified we then select an appropriate monitoring strategy.

In the case of workplace monitoring we generally will measure at a position close to the employee’s ears. Most surveys will require the assessor to make observations on activity levels and work patterns.

As well as logging noise levels, a range of data will need to be collected, e.g. variations in employee work patterns such as durations and locations, use of portable hand tools, machine speed or load, rate of work, variations in production and/or raw materials that may affect the sound levels. Very often these factors will determine what sampling strategy should be adopted and that may affect the choice of sampling equipment

Quantifying exposure

There are two principal ways to quantify the noise exposure of a worker. One requires a sound level meter (SLM) to determine LAeq values at the positions the operator occupies throughout the day. The daily personal exposure (LEX, 8h) is then calculated based on the combination of LAeq values and the time spent in each area.

LEX, 8h is a measure of the average noise energy a person is exposed to during a working day. It is defined as the steady or constant level which, over eight hours, contains the same amount of A-weighted sound energy as is received by the subject during the working day.

The term LEP,d is still used in the UK, although it is synonymous with LEX, 8h, with the latter prescribed by the International Organization for Standardization (and in EU legislation).

The SLM based methodology is particularly useful when workers operate machinery or tools, and where the measurement results describe the noise at the operator’s ear, attributable to a specific tool or task.

The second method of quantifying exposure is to use a dosimeter, which is worn by the worker throughout the working day or for a representative period.

The dosimeter generally displays the total dose over the sample period in pascal squared hours, or it will report the results as a percentage of LEX, 8h and often includes LAeq and other data. As the microphone is generally worn on the body, however, there is very likely to be an additional uncertainty to dosimeter measurements because of extra local noise disturbance. 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. Even so called ‘competent authorities’, notwithstanding their awareness of the problems, have advocated the use of dosimeters for many years.

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 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 2004 results highlighted “limitations exhibited by dosimeters, which include peak pressure clipping, an 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.”

Normally 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 that was personally supervised in its entirety.

Another disadvantage of dosimeters is the need for multiple units to facilitate a reasonable sample size. More importantly, however, dosimeter data that is sourced in impulse environments is likely to conceal significant error.

While dosimetry and hand held or tripod mounted SLM surveys are the principle approaches adopted in workplace noise monitoring, environmental noise surveys consist of either attended measurements or continuous noise monitoring programmes. The latter have become more commonplace, with some monitoring stations providing real-time access to the data.

Monitoring networks can also be designed to automatically notify certain parties when specified criteria are exceeded, allowing prompt intervention as and when required. In addition, monitoring stations can incorporate sound and video recording triggers, meaning audible and visible logs of the noise source can be assessed along with the measurement data. This helps to identify when extraneous or spurious noise causes an exceedance.

While advances in technology now provide possibilities in continuous noise monitoring that were entirely impractical even a few years ago, very often attended measurements will be needed to make a conclusive assessment. One of the principle benefits is that an attended measurement will allow an expert to give objective and definitive evidence in court, based on the collected data.

By field-calibrating the instrumentation before and after the survey and by being present for the duration of the survey, an expert can give testimony as to his or her subjective assessment of the noise. This can be reinforced with contemporaneous notes and referenced to the measurement data. Many of the uncertainties of continuous noise monitoring can thus be eliminated and by attending the survey a true assessment can emerge.

Past and present monitoring

Although we may take for granted some of the capabilities of modern instrumentation, it is not so long ago that noise monitoring was an esoteric pursuit involving bulky and unreliable equipment, which was particularly limited in comparison with modern SLMs. A 1957 Acoustical Society of America paper traces the history of the SLM and alludes to a 110 pound unit dating back to 1932, which was “housed in four wooden carrying cases.” The author also addresses the lack of standardisation and the fact that most SLMs were custom built in very small quantities, making the instruments extremely expensive. The author also refers to a sound level meter costing a thousand dollars or more at the beginning of the Great Depression in 1929, “when you could buy many automobiles for well under this figure.”

Modern instrumentation, however, despite all of its benefits, is but one of the prerequisites for effective noise monitoring. Unfortunately, some individuals and corporations are convinced that an ability to push the correct buttons on a SLM entitles them to undertake noise assessments. A competent noise assessor, however, will need to bring a lot more to the table.


In the workplace scenario, the concept and obligations of ‘a competent person’ are prescribed in law. In essence, the competent person is defined in terms of the suitability of their training, experience and knowledge, so as to provide informed and appropriate advice.

The complexity of the environment or workplace and/or the selection of appropriate noise controls may, in some instances, have a major bearing on the question of competency.

Given that the assessor’s noise monitoring results will be the foundation on which the company’s controls are built, it is of paramount importance that they are reliable. It is up to the employer to take reasonable steps to satisfy himself or herself that the monitoring and assessment meets all necessary legal requirements, even when the assessment is carried out by someone outside the company such as a consultant.

Unfortunately many companies learn only when it is too late that their risk assessments are inadequate or their consultants were never really competent, for example, when dealing with a claim for occupational hearing loss. 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.

In order to avoid long term problems and pitfalls it is imperative that noise monitoring and risk assessments are undertaken by competent persons. Therefore companies should closely examine an assessor’s credentials prior to commissioning their services.

When it comes to environmental noise the definition of competency is not often addressed in statute law. Nonetheless, it is vital that noise assessors, as well as individuals with responsibility for environmental noise management, are appropriately trained. Increasingly the competency requirements are addressed in codes of practice or in guidance documents and in some jurisdictions the enforcement authority will be particularly discerning.


Effective noise monitoring requires an understanding of acoustics, codes of practice, pertinent standards and practical skills.

The Institute of Acoustics’ (IOA) certificate of competence in the workplace and its courses on environmental noise measurement have been specifically developed to provide participants with the necessary training to ensure that they can competently perform their duties. Given the evolving nature of acoustics and its legislative framework, refresher courses are also seen as an important element of continuing professional development (CPD) and help to ensure that practitioners are kept up to date.

Published: 21st Aug 2014 in AWE International