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Published: 01st Mar 2011

My first experience regarding the hazards of noise and noise measurement was in 1960 when starting my initial career as a shipbuilding apprentice.

At that time the Shipbuilding and Ship Repairing Regulations, 1960, were being introduced, which supplemented the requirements of the Factories Act and replaced the Shipbuilding and Ship Repair Regulations of 1931.

Unfortunately these regulations did not make provision for hearing protection.

However, some employers recognised the risks and in the early 60s ear muffs and plugs were being provided for workers, but there were no enforcement requirements and most workers did not wear them.

It was not until the introduction of the Health and Safety at Work etc Act 1974, and subsequently the 1998 noise regulations, that employers realised that they needed to do more to protect individuals’ hearing. Unfortunately by this time many workers in their late 30s and early 40s were suffering premature hearing loss (approximately 20%) leading to partial deafness.

Noise measurement in the automotive and shipbuilding industries

The intense bustle of the shop floor may be a welcome sign of productivity, but in many industries it often indicates an unwelcome side effect - excessive levels of noise.

While working as a health and safety officer in the automotive industry, where many types of vehicle components were being produced by robotic and manual operations, the noise levels throughout the factory, including access areas, were in excess of 90 decibels (dB) (A), and when working in close proximity to the robot operations the noise levels were approximately 98dB (A). Peak noises were also a problem, which meant that everyone working in or visiting the factory areas was required to wear hearing protection.

Noise in shipbuilding and repair work has always been very intense. For example, steel chipping hammers were used extensively to cut and remove metal, a technique specified by clients because it did not distort the ship’s metal structure or surrounding metals. This particular process generated noise levels as high as 143 db (A). However, there were many other sources of noise being generated from ship building construction techniques, including noises from extensive portable and fixed ventilation systems. There were also compressors producing noise levels in the high 80s, before workmen commenced their daily shift.

Case law innoisemeasurement

Early examples of noise measurement have been quoted in case law, e.g. Thompson versus Smiths Ship repairers (QBD) 1984, where Smiths’ representatives gave evidence about measurement of noise levels which had been carried out at intervals throughout a number of working days using a noise meter and a personal dosimeter.

They also stated that throughout the 70s in the Swan Hunter yards there were direct noise measurements being made using meters which gave readings of a continuous noise average (Leq).

Expert witnesses also advised that they had carried out inspections at Smiths and Swan Hunter between November 1982 and March 1983, producing readings of continuous Leq, but it was stated that these were not, as a rule, maintained for long enough to give a picture of the working day as a whole.

At the end of the case, one plaintiff was awarded £1,350 and the other £1,545 for hearing loss disability.

There can be no doubt that comparable measurements have been made on shop floors in the Middle East, where workers obviously have the same vulnerability to hearing loss.

As outlined above, hearing damaged by exposure to noise at work results in a permanent hearing disability which is incurable. The loss of hearing is usually gradual due to prolonged exposure to noise over the years, and when combined with normal hearing loss due to ageing, individuals will invariably suffer deafness. In addition, hearing damage can also cause tinnitus, which is a sensation of noises in the ears such as ringing or buzzing and can also occur in combination with hearing loss.

These disabling conditions can be avoided and are entirely preventable if employers ensure that noise measurements are carried out for all noise producing workplace tasks to identify the steps that will be required to reduce exposure to noise. They can also be avoided by providing personal hearing protection (or implementing other control measures) and health surveillance for employees.

Throughout my career in shipbuilding, ship repair, engineering, construction, the automotive industry and local government, I have regularly provided advice and successful solutions for noise problems encountered in these areas.

The UK Control of Noise at Work Regulations 1989 and 2005

As a result of the introduction of the Noise at Work Regulations 1989, additional control measures and noise measurement were introduced for daily time weighted average exposures from the risks caused by noise. These early regulations required employers to ensure that noise levels were assessed and appropriate workplace control measures implemented.

In addition to the measures to reduce exposure to noise, employers were also required to provide personal hearing protection. Following the introduction of these regulations in 1990, a peak action value was introduced and two additional action values to limit daily exposure; the first one was set at 85 decibels (dB) and the second at 90dB.

This in effect meant that assessments involving measurements had to be carried out for noisy workplace activities and when noise levels reached 85dB, employers were duty bound to provide hearing protection and at 90dB they had to ensure that employees used the hearing protection provided.

The 1989 regulations were superseded by the introduction of the Control of Noise at Work Regulations 1995. These regulations are based on a European

Union Directive requiring similar basic laws to be introduced throughout the Union to protect all workers from the risks caused by noise. The main differences from the 1998 Noise regulations are:

• The two original action values for daily noise exposure have been reduced by 5 dB to 85 dB and 80 dB

• There are now two action values for peak noise at 135 dB and 137 dB

• There are new exposure limit values of 87 dB (daily exposure) and 140 dB (peak noise) which take into account the effect of wearing hearing protection and which must not be exceeded

• There is a specific requirement to provide health surveillance where there is a risk to health

The 1995 regulations require employees to take action to protect workers’ hearing at levels of 85 dB (daily or weekly average exposure) and also stipulate that the levels at which employees must assess the risk to workers’ health and provide them with the necessary information and training regarding the new exposure values.

Measuring noise

Measuring noise intensity (loudness) of sound is measured in decibels dB (A). (A) denotes that the scale is adapted for the human hearing range. 20dB (A) is, for example, equivalent to a gentle breeze or a soft whisper. Sounds louder than 120dB (A) can provoke fear reactions and possible pain. The decibel scale is logarithmic, which means that a 3dB (A) increase equals a doubling of the volume of the sound.

Before commencing a noise assessment the Health and Safety Executive (HSE) recommend that the following factors are considered:

• What should be measured, are people exposed to noise?

• Are there machines, tools and processes that are obviously noisy?

• Are control measures in place?

• What instruments can be used?

• What are the general principles, techniques and strategies that should be adopted when taking measurements?

The initial measurements are noise surveys to determine if noise problems exist and if further measurements are needed.

Before taking measurements, it is important to determine the type of information you will require for a successful noise assessment. The person making the measurements must have received sufficient training to understand:

• What the purpose of measurement is for, e.g. compliance with the noise regulations, hearing loss due to excessive noise exposure and the preventative measures, noise control and community concerns or annoyances

• The source of noise, when the noise sources are operating and its duration

• The type and pattern of noise, e.g. continuous, intermittent, variable, or impulse

• Work activity locations of exposed persons

Measuring noise levels and workers’ exposure is the most important aspect of a workplace hearing conservation and noise control programme. The noise assessment helps to identify work locations where there are noise problems and the employees who may be affected.

For noise at work, the sound pressure level is measured to determine noise exposure. I have identified various instruments and techniques which can be used; however, the choice of instrument depends on the workplace noise and the information needed.

A good choice for general workplace noise from machines and noisy workplace activities is a Type 2 Integrated noise meter, which is fairly robust in use and the measurements taken using this instrument comply with the requirements of the Noise at Work Regulations. The integrated meter can measure sound pressure levels dB(A), Leq, peak noise, provide fast and slow responses and measure the various octave band frequencies in Hz from 32, 63,125, 250, 500,1K, 2K, 4K and 8K.

The octave band details are required to enable the assessor to select the correct hearing protection, e.g. when considering which hearing protection to recommend, the assessor will have to check the data sheet information (supplied with every type of hearing protection) which indicates the overall dB(A) and the level of protection for each frequency band within the hearing range.

All noise measurements carried out are automatically produced and can be downloaded onto an IT programme.

The initial noise survey

The first step is to determine whether or not noise is a potential problem in your workplace. A walk-through survey helps when making this decision. You will find that there are many indicators that will help to identify potentially hazardous noise levels, which include:

• Workers have to raise their voice to talk to someone at one metre distance away

• After working in excessive noise levels for a couple of years, employees find it difficult to communicate in a crowd or party situation where there are other sounds or many voices

• At the end of a work shift people have to increase the volume of their radio or television to a level too loud for others

Measuring noise using an integrated sound level meter

To commence the initial noise assessment, it is necessary to take measurements of the intensities experienced by workers who use particular types of tools which create noise and/or who are working at given distances from others who are also using their own particular work tools.

When carrying out measuring techniques to estimate a person’s noise exposure, it is better to take measurements at every location they work in or pass through during the working day, while also noting the time spent at each location.

With your sound level meter you 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. You may also need to measure the Leq for the entire period; however, a shorter measurement time can often be sufficient.

For example, if the noise is steady, a short sample measurement should suffice, whereas if the noise is changing, it is best to wait for the reading to settle to within 1 dB. For work tasks where the noise is generated from a cyclic operation, you will need to measure the Leq over a whole number of cycles.

Where events such as impacts or impulses occur during the normal working day as part of the typical noise emissions from a machine or process, they will contribute to a measurement of Leq as long as they have not been specifically excluded, and the instrument used has sufficient dynamic range to measure peak sound pressure (with a C-weighting applied).

You must also ensure when measuring peak sound pressure that the correct frequency weighting is applied. High-level peak sounds present a risk to hearing from immediate and permanent hearing loss and employers are required to take action to reduce the level of exposure if an employee is likely to be exposed to a C-weighted peak sound pressure level of 137dB or above, with an absolute limit of 140dB (which can take account of hearing protection).

It is not necessary to record exposures to sound pressure levels below 75 dB, as such exposures are unlikely to be significant in relation to the daily noise exposure action levels. To avoid making large numbers of measurements, especially where the sound pressure levels are changing, or if a person is moving within a noisy area, it is sometimes worthwhile assuming the worst case scenario by measuring the noisiest location, or during the loudest period.

Measuring and determining daily noise exposure

The Control of Noise at Work Regulations 2005 document provides details of the mathematical relationship between time-averaged noise level and daily exposure by using a formula for combining noise exposure from multiple tasks to calculate daily and weekly exposure. However, electronic spreadsheets are also available on the HSE website which do these calculations for you ( There are, however, simple methods for determining daily and weekly personal exposures by using their ‘ready-reckoners’.

An example of using the HSE’s Ready-Reckoner Table

The left side of the table is used for locating the matching Leq (dB) number that you have recorded from a sound source and the top section of the table is where the duration of exposure times are located. This table enables you to match the two corresponding numbers to identify a point number which provided an individual’s daily personal exposure time, e.g. when the time period number is moved down the table and the noise level of 85 Leq (dB) number is moved to the right, a matching corresponding number gives a point score of 25.

Using these details as an example, the following data is produced, e.g. where you have measured the noise from a workplace task which registered 85 Leq (dB) on your noise meter over a period of two hours of exposure, and you want to calculate an individual’s daily personal exposure, then you would check the numbers on the left side of the Ready-Reckoner (85-db) against the duration of exposure (two hours) on the top column which will give you noise exposure points of 25, which on the corresponding table equates to a daily personal exposure of 79 leq (dB).

At first it may seem difficult to understand the HSE’s simple chart, but it works in a similar way to a mileage chart found in a road atlas, e.g. miles located on the left side of the chart and the various destinations on the right side, by viewing the mileage across the page to any given destination provides the distance in miles to that destination.

Types of instruments used to measure noise

Personal sound exposure meters (dosimeters)

A noise dosimeter is a specialist sound level meter intended specifically to measure a person’s noise exposure over a period of time at every location they work in or pass through during the working day. The dosimeter is usually located close enough to the person’s head (just below the side of their neck and attached to their clothing) to obtain a reliable measure of the noise to which they are exposed.

In order to ascertain if employees are at risk, an assessment has to be carried out if the noise levels are likely to exceed 85 dB. This involves a survey taking noise measurements. One way of measuring noise is by using a sound level meter, but in certain situations this is not always practical. For example, forklift truck and overhead workshop crane drivers, or individuals who have a very complex work pattern are exposed to many different noise levels during the course of their working day. When this is the case, it is better to issue staff with a personal noise dosimeter, which is an instrument that can be attached to the person for their entire daily shift to measure and provide an average of how much noise they have been exposed to.

Sound level meters and noise meters used for simple noise measurement

For example, simple sound level meters with class 1 or class 2 performance can be used for basic noise assessments such as for checking alarm sound levels, machinery maintenance, pyrotechnic testing, community noise assessments and many other applications where sound pressure levels (SPL) are required, and dB(A) and dB(C) frequency weightings. Some of these instruments can be used for data logging and measure continuous noise average readings (Leq), taking into account all of the various noise levels in a particular area. This type of instrument is very useful for supervisors because they are easy to use and do not require a great deal of training or technical knowledge.

Sound level meters used for noise at work and occupational noise measurements

For noise at work assessments and occupational applications, the sound level meter needs to have integrated noise functions for continuous noise average readings (Leq), daily personal noise exposure (Lep,d) expressed in decibels and time weighted averages (TWA) which are often needed along with Peak (C) single impact noise measurements to complete the varied risk assessment requirements. Real time Octave Band Filters which measure individual noise frequencies can also be used to help select hearing protection, and to assess the effectiveness of noise control measures. With this type of instrument, users require more in-depth knowledge and often require intensive training for approximately one week or more.

Safety Officer’s noise kits for environmental and occupational noise

A Safety Officer’s noise measuring kit is a complete set of noise measuring tools that can be configured to meet their needs when carrying out noise assessments. Kits usually contain a sound level meter plus an integrated sound level meter with real-time octave band filters and audio recording facility, a dosimeter, calibrator and all of the necessary accessories for each instrument which is housed in a single robust carrying case.

Sound level meters for environmental and community noise

For environmental and community noise applications, repeated measurements over a period of time are often needed in combination with Leq and other statistical values for each measurement recorded. Audio recording and 1.3 octave band filters may also be useful to analyse and assess the impact of noise sources.

Sound level meters for special applications

Sound level meters that can measure loud impact noises such as gunfire, and also vehicle noise measurements which require a number of measurements to be made at a fixed distance from a vehicle’s exhaust, are classed in a special category because of their greater noise measuring ability.

Guidelines for instrument selection

A type 2 sound level meter is suitable for industrial field evaluations and is sufficiently accurate to comply with the requirement of the Noise at Work

Regulations 1995. It is more robust for industrial assessments, as opposed to a type 1, which is more accurate and much more expensive. Type 1 instruments are primarily used in research work or engineering laboratories. However, if you decided to purchase a type 1 instrument, you would have to be very careful how it is handled because it is a very sensitive piece of equipment.

Personal noise exposure

As identified above, the use of a dosimeter is the most accurate and best choice for measuring personal noise exposure, providing the dose or equivalent sound level.

Noise levels from a particular source

A standard type 2 sound level meter (SLM) will provide instantaneous dB (A) noise measurements, which are sufficient in workplace locations where continuous noise levels are being produced. The model I would choose would be a standard SLM with the additional Leq facility to enable a person’s average exposure to be measured over a work shift.

Integrating sound level meters

My first choice would be a type 2 integrating sound level meter (ISLM), which provides similar data to a dosimeter but is a hand held instrument that determines equivalent sound levels over a measured period at a particular location. The current crop of ISLMs (plus a dosimeter) can provide all of the necessary noise data required when carrying out a detailed noise assessment. The ISLM can also measure the noise level at each frequency or pitch. Frequency analysis is usually needed for the selection of appropriate engineering control methods.

Comprehensive noise measuring kits

Rather that buying individual instruments, I would recommend the purchase of the Safety Officer’s kit which will contain all the necessary instruments and software required for personal sampling and noise assessments - and be more cost effective. ?


• HSE Books; The Control of Noise at Work Regulations 2005, ISBN978 0 7176 6164 4 (Reprinted 2006)

• Case law - Thompson versus Smiths Ship repairers (North Shields) LTD. Reproduced by permission of the Incorporated Council of Law Reporting for England and Wales, Megarry House, 119 Chancery lane, London WC2A 1PP


Bill Knowles is the Director of Course Development for Vision Safety Associates LTD.

His health and safety experience spans in excess of 35 years and includes working as a Shipbuilding Group Health and Safety Manager, Sub Contractor

Health and Safety Controller and as a Chartered Safety Professional in a number of medium to high risk organisations which include shipbuilding, ship-repair, manufacturing, engineering, policing and the voluntary sector.

He is also a member of the following professional bodies: Chartered Member of IOSH, Member of the International Institute of Risk and Safety Management, Fellow of The Royal Society of Environmental Health.

T: +44 (0)7802 350673 E: W:

Published: 01st Mar 2011 in Health and Safety Middle East

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