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Noise Monitoring - Preventing the sad slip into silence

Published: 01st May 2010

Colin Chatten relates his early memories to the importance of monitoring noise in order to prevent hearing damage being caused at work.

As a youngster I can remember my Mum carting me round to Nan and Grandad’s every Saturday afternoon for tea with the grown ups and my army of cousins. They didn’t have a choice either, we were all press-ganged into the weekly ritual. Grandad was a lovely bloke and a great source of amusement. No, it wasn’t his ability to juggle with the fruit or make his cigarette smoke come out of his ears  - never did work out how he did that – it was the conversation at the tea table. No matter the topic or the question, he would always respond with something way off the mark and always very loudly.

As kids we would all snigger like mad, thinking it hilarious. He would wink and grin at us so we sniggered and laughed all the more, thinking he was doing it on purpose. It was only when the innocence of childhood and Grandad had passed on that the truth dawned on me. He had been almost deaf and had probably never actually heard any of us other than as a distant and muffled murmur. Earning a living in heavy industry had taken a heavy and sad toll. Fortunately things have moved on significantly since the 1900’s were in their infancy but that’s no reason to be complacent.

"Earning a living in heavy industry had taken a heavy and sad toll."

Today we have the Control of Noise at Work Regulations 2005 (the Noise Regulations) to help protect us. The Noise Regulations give priority to the control of noise by technical or organisational means, as opposed to providing personal hearing protection because:

• noise control is usually the most cost-effective solution for the longer term;

• control of the noise risk at source protects a greater number of people in the surrounding working environment;

• personal hearing protectors protect only the individual wearer and do not always give the protection expected, and

• a positive contribution to noise control can be made by making arrangements for effective controls. However, employers should be aware of their limitations and understand when they need to take further advice. Noise control is not necessarily difficult or expensive. There are effective, simple controls available that can be carried out 'in-house'.

Regulation 6

Employers need to be particularly aware of Regulation 6 because it addresses the elimination or control of exposure to noise at the workplace, requiring them:

• to take action to eliminate risks from noise exposure completely wherever it is reasonably practicable to do so;

• if it is not reasonably practicable to eliminate the risks completely, to reduce them to as low a level as is reasonably practicable;

• to introduce a formal programme of measures to reduce noise exposure whenever an employee's exposure to noise is likely to exceed the upper exposure action values (these measures cannot include hearing protection), and

• not to expose anyone above the exposure limit values.

Risk assessment

There is also a requirement to undertake a Risk Assessment (under Regulation 5). The purpose of the risk assessment being to enable employers to make a valid decision about whether their employees are at risk from exposure to noise and what action may be necessary to prevent or adequately control that exposure. The risk assessment must take into account all noise exposure at work, including, for example, piped music and personal stereos.

Health surveillance

Health surveillance isn’t something that should be overlooked either. A programme of systematic health checks will help to identify early signs and symptoms of work-related ill health and to allow action to be taken to prevent its progression. The requirement is covered under Regulation 9. It is also useful in monitoring the effectiveness of controls, though it is not in itself a control measure or a substitute for controlling risk at source. Suitable health surveillance usually means regular hearing checks (audiometric testing).

Measurement of the level of noise

The Regulations require employers to make measurements of noise 'if necessary'. Measurements will be necessary if they cannot make a reliable estimate of their employees' exposure in other ways. They may also wish to use measurements to demonstrate that the noise exposure is below a particular value and to assure themselves and others that they are complying with the regulations. Measurements also serve to confirm that control actions have reduced exposure. It follows that any measurements should be carried out by someone who is competent, i.e. someone who has the relevant skills, knowledge and experience to undertake measurements in the particular working environment

What should be measured?

When making measurements to estimate the noise exposure of a person at work, there is a need to ascertain the equivalent continuous A-weighted sound pressure level (LAeq) that represents the noise the person is exposed to during the working day. There is also a need to ascertain the maximum C-weighted peak sound pressure level or levels to which the person is exposed. The LAeq is combined with the duration of exposure during a working day to ascertain the daily personal noise exposure, LEP,d.

"When making measurements to estimate the noise exposure of a person at work, there is a need to ascertain the equivalent continuous A-weighted sound pressure level (LAeq) that represents the noise the person is exposed to during the working day"

In practice it is common to break the working day into a number of discrete jobs or tasks, and to make sample measurements to determine a representative LAeq for the job or task. The LAeq for each job or task is then combined with its duration during the working day to ascertain the LEP;d,

Other types of measurements that may be made include the equivalent continuous C-weighted sound pressure level (LCeq) or the Leq in octave frequency bands, for a job or task to perform calculations to predict the performance of personal hearing protection.

What should be used to measure noise?

The basic instrument for measuring noise is a sound level meter. A dosemeter (personal sound exposure meter) worn by the employee can also be used. Dual purpose instruments are also available which can operate as both a sound level meter and a dosemeter. A calibrator to check the meter and a windshield to protect the microphone against air movement and dirt are essential accessories. Other, more sophisticated, equipment such as data recorders, frequency analysers, and sound intensity analysers can be used for a more detailed assessment.

Personal sound exposure meters (Dosemeters)

Where a person is highly mobile or working in places where access for the measurement is difficult, a dosemeter is an alternative means of measuring a person's noise exposure. Dosemeters indicate the total noise dose received over the measurement period. Modern dosemeters commonly indicate the LAeq over the measurement period. Some meters indicate the dose in units of Pascal squared hours (Pa2.h)* or as a percentage of a given LEP,d (usually 85 or 90 dB). Meters are required to provide a means of converting the reading to Pa2.h if this is not directly indicated on the meter.

In the case where the meter indicates the dose as a percentage of an LEP,d there may be an assumption that the measurement period corresponds to the whole working day, or there may be the ability to key in a value for the length of day so that the instrument can make the calculation. You should make sure you understand how the LEP,d shown by the meter is calculated.

Many dosemeters have additional features. Those which record how the sound pressure level varies with time throughout the measurement (a logging dosemeter) can be useful to show when and where high noise exposures occur. All dosemeter measurements should be made with a 3 dB exchange rate (sometimes called the doubling rate).

"Many dosemeters have additional features. Those which record how the sound pressure level varies with time throughout the measurement (a logging dosemeter) can be useful to show when and where high noise exposures occur."

People wearing dosemeters should be instructed not to interfere with the instrument or microphone during the course of the measurements. They should also be instructed not to speak more than is necessary during the course of the measurement, since a person's own voice should not be included in an assessment of their daily personal noise exposure.

Calibrators

A sound calibrator should be used to check the meter each day before and after making any measurements. Calibrators give a tone at a specified sound pressure level and frequency for a specified microphone type using an appropriate adaptor. A word of warning though; make sure the  calibrator, adaptor and microphone are compatible.

Some meters have an internal electronic calibration. The internal calibration only checks the instrument's electronics and does not provide a check of the microphone. However, it can be a useful cross-check of the meter and calibrator.

Peak sound pressure level

Peak sound pressure should be measured with a C-weighting applied. When measuring peak sound pressure there is a need to ensure that the correct frequency weighting is applied. Some sound level meters include an 'I' (impulse) response. This should not be used for any measurements relating to the requirements of the regulations.

Periodic testing of instruments

Both the meter and calibrator need to have been tested in the previous two years to ensure they still meet the required standards. If the equipment is more than two years old, check for a test certificate confirming the performance of the meter and calibrator before starting the assessment.

Where should I measure and how should the measurements be made?

When measuring to estimate a person's noise exposure, make measurements at every location they work in or pass through during the working day, and note the time spent at each location. It is generally not necessary to record exposures to sound pressure levels below 75 dB, since such exposures are unlikely to be significant in relation to the daily noise exposure action levels.

Measurements should be made at the position occupied by the person's head, preferably with the person not present. Operators may need to be present while the measurements are made, e.g. to control a machine or process. If this is the case measurements should be made with the microphone positioned close enough to the operator's head to obtain a reliable measure of the noise to which they are exposed, but preferably not so close that reflections cause errors.

The results are unlikely to be significantly affected by reflected sound if the microphone is kept at least 15 cm away from an operator. The microphone should be placed on the side of the head where the noise levels are higher. To avoid making large numbers of measurements, e.g. where the sound pressure level is changing, or if the person is moving within a noisy area, it’s feasible to assume the worst case and measure at the noisiest location, or during the loudest periods. Alternatively, carrying out a spatial-average measurement by following the movement of the worker may provide a representative measure of the noise exposure.

When using a dosemeter to measure a person's noise exposure, position the microphone on the shoulder (ideally on the shoulder joint) and prevent it touching the neck, rubbing on or being covered by clothing or protective equipment. If the dosemeter body is connected to the microphone by a flexible cable, place the meter securely in a pocket or on a belt where it can be safe from damage during the measurement.

Measurements of noise very close to the ear

When a person is receiving significant noise exposure from sources close to the ear such as communication headsets or earpieces, or they are wearing helmets, which cover the ear such as shot-blasting helmets or motorcycle helmets, special measurement techniques are required. The methods used are very different from those where a measurement is made sufficiently far from the head of the exposed person to avoid the disturbed sound field. Measurements very close to the ear are complex and should only be carried out by those with the necessary expertise.

"Measurements very close to the ear are complex and should only be carried out by those with the necessary expertise."

How long to measure?

The noise level to which an individual employee is exposed will normally change throughout the day because, for example, different jobs might be done and different machines or materials might be used at different times. Enough noise measurements must be taken to account for all these changes, recording the sound level and the person's exposure duration at each noise level.

With a sound level meter, there is a need to measure at each position or during each job or task, long enough to obtain a representative measurement of the level the person is exposed to. There may also be a need to measure the LAeq for the entire period but a shorter measurement can be sufficient. In general if the noise is:

• steady, a short sample LAeq measurement may be enough;

• changing, wait for the LAeq reading to settle to within 1 dB;

• from a cyclic operation measure the LAeq over a whole number of cycles.

The time required depends on the nature of the work and the characteristics of the noise. Care should be taken to ensure that the measurement covers all significant noise during the job or task. In particular it is important to make sure that any short-duration, high-level noise exposures are included in the measurement, since these can have a significant impact on the true LAeq.

Noise dosemeters are designed to operate for long periods. They are ideal for measurements over an entire shift, or for a period of several hours during a shift. If measurements are taken over part of a shift all significant noise exposure should be captured to reflect a typical working day. Avoid very short measurements which can be inaccurate due to the limited resolution of the dosemeter's display. Also make sure that the dose reading relates to actual true noise exposure, not false input from unrepresentative noise sources when the meter is not supervised, e.g. artificial bangs, whistling, blowing and tampering with the microphone.

"Noise dosemeters are designed to operate for long periods. They are ideal for measurements over an entire shift, or for a period of several hours during a shift."

Sample measurements for a group

If several workers work in the same area, it may be possible to estimate the exposure for them all from measurements in selected locations. When making the measurements, choose the locations and times spent in each place so that the highest exposure that someone is likely to receive can be determined.

Mobile workers and highly variable daily exposures

For some jobs (such as maintenance) the work and the noise exposure will vary from day to day so there is no typical daily exposure. For people in these jobs, measurements need to be made of the range of activities undertaken, possibly over several days. From these measurements the likely daily exposure for a nominal day or days should be estimated.

Sources of error and other factors influencing the measurement result

Sources of error should as far as possible be avoided. To reduce errors, it is important to distinguish between sources of error and natural variables. The major factors influencing the result include:

• Impacts on microphone/cable

• Wind-induced noise

• Reflection from body to microphone

• Noise from PA systems, radio etc

• Speech (subject's and other people)

• Variations in local sound level

• Noise from hand-held tools

• Close-to-ear noise level

The relevant variables should be revealed during an analysis of the work under consideration and during measurements. If significant contribution from sources of error is detected, the measurements should be rejected or corrected.

The measured noise exposure and the uncertainty in the result depend on the measurement method used. A dosemeter tends to increase the potential false contributions to measurements and thereby the measured sound pressure level.

However, using a hand-held sound-level meter may lead to an underestimation of the worker's noise exposure. This is particularly connected to the difficulty in assessing the contribution from close-to-ear sound levels and noise from hand-held tools.

Accounting for the contribution of peak noises to daily exposure

Where events such as impacts or impulses occur during the normal working day as part of the typical noise emission from a machine or process, they will contribute to a measurement of LAcq, as long as they have not been specifically excluded and the instrumentation used has sufficient dynamic range.

"The measured noise exposure and the uncertainty in the result depend on the measurement method used."

Back to basics

As I mentioned at the start of the article, a positive contribution to noise control can be made by making arrangements that aren’t necessarily difficult or expensive. It starts with identifying those who are likely to be affected by the noise and how. While you may have some idea about who may be affected you need to ensure that all employees at risk have been identified. For example, not just the people operating the noisy tools and machine, but others working nearby who may also be affected. Consider also people who move between different jobs or types of work during the day, and make sure that their patterns of noise exposure are understood. In addition to employees there is a need to include others who may be affected by the work that’s being undertaken, e.g. visitors or subcontractors.

In considering the potential for people to be harmed in terms of hearing damage (deafness, tinnitus etc.) there is also a need to take into account the risks to safety which can arise from working in a noisy environment, such as noise interfering with communications, warning signals and the ability to pick up audible signs of danger. These risks to safety may be more closely related to the level of noise at a particular point in time rather than to daily personal noise exposure. And, finally, there is a need to consider employees with pre-existing hearing conditions, those with a family history of deafness (if known), pregnant women and young people.

We often look back at the glorious days of yesteryear through rose coloured spectacles, conveniently forgetting the human cost of industrialisation. That said, we wouldn’t be where we are today without it. The important thing is to learn lessons from those who’ve gone before and that’s where we all have a role to play.

For further information about tackling noise go to www.hse.gov.uk/noise/

For information of Noise Monitoring equipment please go to http://www.osedirectory.com/product.php?type=health&product_id=15

Published: 01st May 2010 in Health and Safety Middle East

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Colin Chatten