Noise and vibration at work
This is an area of workplace law which changed radically during 2005, following new European directives on physical agents – which include noise and vibration. The new provisions came into force in April 2006, along with extensive transitional arrangements for industries where immediate
compliance would cause difficulty.
The noise provisions have most implications for the leisure and entertainment industry, especially for live musicians, and employee noise exposure in clubs and pubs. The vibration regulations affect any activity involving extensive use of power tools or heavy vehicles and equipment.
Why is noise and vibration at work important
Noise and vibration are both fluctuations in the pressure of air (or other media) which affect the human body. Vibrations which are detected by the human ear are classified as “sound”. We use the term “noise” to indicate when we are dealing with unwanted sound.
At the lower end of the range, vibrations can be felt in other parts of the body. Some of these vibrations are experienced both by hearing and feeling so there is an area of overlap in these definitions.
The normal range of hearing is from approximately 16 hertz (Hz) – a very low bass sound – to 20,000 hertz (20 kHz) – a very high pitched sound. Vibration can be detected by the human body from 1-80 Hz.
Noise and vibration are hazards to employees when they occur at high levels, or continue for a long time (examples of noise and vibration levels which can affect health are given below).
Employers who fail to minimise the risk from noise and vibration could face prosecution and substantial fines. Individual employees (including managers and health and safety specialists) can also face prosecution for failing to meet their individual obligations.
Employees who have suffered injury as a result of their employment can make compensation claims against their present or former employer. Any employee who is seeking compensation for an
industrial injury has four hurdles to overcome. They must prove –
1 they are suffering from a medical condition which affects them in a material way 2 their medical condition was caused by, or made worse by, their employment 3 their employer knew there was a risk to their health from the employment
4 their employer failed in their duty to look after their employee by preventing or reducing the risk to reasonable levels.
It is the last element of the case that indicates - it is in an employers own interest to ensure that they can demonstrate the steps they have taken to eliminate or minimise a hazard at work.
Noise at work
How big a problem is work-related noise?
A Medical Research Council survey in 1997-98 estimated that 509 000 people in Great Britain suffer from hearing difficulties as a result of exposure to noise at work.
Numbers of new cases of noise-induced deafness qualifying for Industrial Injuries Scheme disablement benefit fell steadily since the mid 1980s, reaching 226 in 2000. However since 1998 there has been little change and the number rose slightly to 263 in 2001 and 264 in 2002. The industry groups with the highest average annual incidence rates of new cases qualifying for benefit (based on 2000-02 figures) were extraction energy and water supply, manufacturing and construction.
Occupations with high incidence rates based on reports in 2000-02 included foundry labourers, NCOs and other ranks in the armed forces, other labourers in making and processing, and machine tool operatives.
Health effects of noise
Noise induced hearing loss (NIHL) can be caused be a single exposure to a very loud noise, or by exposure to raised levels of noise over a long period of time.
Short term hearing loss can be experienced as a temporary threshold shift (TTS). Most people have experienced this at some time in their lives – coming out of a noisy club and being partially deaf. Usually this disappears within a few hours, although it can take over 24 hours to disappear completely.
There is evidence that TTS can lead to permanent threshold shift (PTS). This is more likely top occur where there is insufficient recovery time between incidents of TTS, or where the circumstances causing TTS occur regularly.
Persistent high noise levels can contribute to stress levels at work.
Tinnitus is a continual ringing in the ear, causing disruption to sleep and affecting speech. It may be the result (among other things) of extended exposure to excessive noise levels and can be temporary or permanent.
Additional effects of noise
Noise levels which interfere with communication at work can contribute to accidents – verbal warnings, alarms may not be as effective if they are harder to hear. The effect on staff of having to raise your voice routinely to make yourself heard, and straining to make out what others are saying, may also contribute to stress levels at work.
There is strong evidence that excessive noise levels can interfere with task performance – affecting productivity.
Other factors leading to hearing loss
Exposure to noise is not the only factor which causes hearing to deteriorate. In compensation cases it is important to distinguish whether hearing loss was caused by these other factors (some of which may also be work-related).
Hearing damage by chemicals
Certain drugs and medications or chemical agents used in the workplace can damage the hair cells in the inner ear. These are called ototoxic chemicals - over 200 chemical agents are reported to have this property, which may be temporary or permanent. They include:
• antibiotics (eg, streptomycin)
• salicylates, such as aspirin, taken in large quantities
• loop diuretics (eg, lasix, ethacrynic acid)
• drugs used in chemotherapy treatment (eg, cisplatin, carboplatin)
•
quinine.Workplace ototoxic chemical agents include:
• solvents (eg, benzene, toluene, butanol and trichloroethylene)
• certain metals, including lead, cobalt, mercury, arsenic, and lithium.
Some of these agents are synergistic with noise exposure. In circumstances where neither the agent nor the noise exposure alone produce hearing loss, the combined occurrence will. Or, in some circumstances, the extent of hearing damage by noise is magnified by the effect of these ototoxic chemicals.
Presbyacusis
Loss of hearing as a result of growing old is called presbyacusis. The hearing loss is progressive, with the high frequencies affected first. While the process begins after the age of 20, it is often at ages 55 to 65 that the high frequencies in the speech range begin to be noticeably affected.
Trauma damage to the ear
Examples include fractures of the temporal bone, puncture of the eardrum by foreign objects, and sudden changes in air pressure.
How much noise does it take to affect employees’ health?
Because individuals are affected by noise differently, it is difficult to specify what level of noise is absolutely safe. What we can say is that damage to hearing has been recorded at noise levels above 75-80 dBA, with varying proportions of the population are potentially affected at different noise levels – there is no clear boundary between ‘safe’ and ‘unsafe’.
For example, after exposure to 85dBA for 8 hours a day for 15 years, 5% of workers will show hearing loss. 15 years of exposure to 90 dBA will damage the hearing of 14% of workers. And exposure to 95 dBA for 15 years will damage the hearing of 24% of workers.
How is noise measured
The unit of measurement used to assess noise at work is called the ‘daily personal noise exposure’ and its technical notation is LEP.d. However, in this Guide it will be written LEP.d, where:
• L = loudness
• E = exposure
• P = personal
• d = dose.
This is the continuous level of noise, over an eight hour period, which would produce the same amount of acoustic energy as the fluctuating noise levels actually experienced. It is a convenient way to think of noise, and to compare noise environments, because it gives a single number index. The human ear is incredibly sensitive to varying sound pressure levels. At the lower threshold of hearing, we can hear the faintest sounds – the slightest rustling, movement of air. At the upper range of hearing (the volume at which noise becomes physically painful and damages the ear irreparably), has 1,000,000,000,000 times (million x million) as much sound energy impacting on the ear.
Because of this enormous range, noise is measured in logarithmic units called ‘decibels’. The volume that can only just be heard at the threshold of hearing is referred to as zero decibels (written as 0 dB). An increase of 10 dB means that there is 10 times as much energy. So 10db has ten times as much energy as 0dB. And 20 dB has 10 times as much energy as 10 dB. So an increase of 20 dB means 10x10 times as much energy – 100 times as intense.
An implication of these logarithmic units is that an increase of 3 dB represents a doubling of loudness (acoustic energy).
But the response of the human ear is not directly proportional to the amount of energy. In fact a doubling of acoustic energy (ie, a 3dB increase) is barely noticeable to most people. A quadrupling of energy (Ie, a 6dB change) is clearly noticeable. And a tenfold increase in acoustic energy (ie, a 10dB difference) is perceived as a doubling of noise levels – providing a ‘rule of thumb’; each additional 10dB is a doubling of loudness.
Examples of noise levels and exposures
(in increasing levels)
• quiet office 40-60dba
• listening to radio or television at home 50-60dba
• a bulldozer with its engine idling 85dba
• noisy restaurant 80-90dba
• process plant 80-95dba
• lathes 90dba
• nightclub, as experienced by staff 95-115dba
• call centre up to 100dba in the headphones
• motorcycle courier up to 100dba
• pneumatic drill 100dba
• alarms (as experienced by engineers) 100dba
• sandblasting 110dba
• riveting 130 dba
• gunshot (near the ear) 140dba
• aircraft taking off 25 metres away 140dba.
The legal framework for work-related noise
The Noise at Work Regulations 1989 introduced the requirements of the first EEC noise directive. A second noise directive has been implemented via the Control of Noise at Work Regulations
2005/1643. This took effect on 6 April 2006 with a transitional period for certain categories of employer (eg, in the entertainment industry – see below).
In the intervening period the 1989 regulations remain in force, but employers who are reviewing their working arrangements, or buying new equipment, should act on the new requirements.
In general, the 2005 regulations provide for:
• risk assessment of the workplace for actual noise exposure, or where exposure is likely
• compared with the 1989 requirements: lower exposure action values, upper exposure action values, and exposure limit values for daily or weekly personal noise exposure and for peak sound pressure
• elimination or, where elimination is not reasonably practicable, reduction of exposure to noise to as low a level as is reasonably practicable
• a programme of measures, excluding the provision of personal hearing protectors, to be taken at the upper exposure action values to reduce exposure to noise to as low a level as is reasonably
practicable
• actions to be taken at the exposure limit values and prohibition on exceeding the exposure limit values
• the provision of personal hearing protectors upon request at the lower exposure action values and compulsorily at the upper exposure action values
• where necessary, designation of Hearing Protection Zones in the workplace
• employers' and employees' duties concerning the use of equipment, including personal hearing protectors, provided under the regulations
• health surveillance where assessment shows risk is indicated
• information, instruction and training. Risk assessment
Employers who undertake work liable to expose any employees to noise at or above a lower exposure action value (see below) must make a suitable and sufficient assessment of the risk that
noise poses to the health and safety of those employees. The risk assessment must also identify the measures needed in order to meet the requirements of the regulations (ie, eliminate or mitigate the exposure).
In conducting their risk assessment, employers shall assess the levels of noise by :
• observation of specific working practices
• reference to relevant information on the probable levels of noise corresponding to any equipment used in the particular working conditions
• if necessary, measurement of the level of noise to which his employees are likely to be exposed. The employer must also assess whether any employees are likely to be exposed to noise at or above a lower exposure action value, an upper exposure action value, or an exposure limit value.
Aspects to be considered by the risk assessment include:
• the level, type and duration of exposure, including any exposure to peak sound pressure
• the effects of exposure to noise on employees or groups of employees whose health is at particular risk from such exposure (eg, those who may already be suffering NIHL)
• so far as is practicable, any effects on employees resulting from the interaction between noise and use of ototoxic substances at work, or between noise and vibration
• any indirect effects on the health and safety of employees resulting from the interaction between noise and audible warning signals or other sounds that need to be audible in order to reduce risk at work
• any information provided by the manufacturers of work equipment
• the availability of alternative equipment designed to reduce the emission of noise
• any extension of exposure to noise at the workplace beyond normal working hours, including exposure in rest facilities supervised by the employer
• appropriate information obtained following health surveillance, including, where possible, published information
• the availability of personal hearing protectors with adequate attenuation characteristics. The risk assessment must be reviewed regularly. If there is reason to suspect that the risk assessment is no longer valid or there has been a significant change in the work to which the assessment relates, the risk assessment must be reviewed immediately.
Exposure limit and action values
The lower exposure action values are as follows:
• daily or weekly personal noise exposure of 80 dB (A-weighted)
• peak sound pressure of 135 dB (C-weighted). The upper exposure action values are:
• daily or weekly personal noise exposure of 85 dB (A-weighted)
• peak sound pressure of 137 dB (C-weighted). The exposure limit values are:
• daily or weekly personal noise exposure of 87 dB (A-weighted)
• peak sound pressure of 140 dB (C-weighted).
Where the exposure of an employee to noise varies considerably from day to day, employers may use weekly personal noise exposure (in place of daily personal noise exposure) in order to comply with the assessment requirements in the regulations.
When applying the exposure limit values (but not in applying the lower and upper exposure action values) the protection given by any personal hearing protectors provided by the employer must be taken into account.
Transitional periods
The regulations also detail transitional periods, namely:
• the music and entertainment sectors – the regulations do not come into force until 6 April 2008 and the regulations listed for amendment and revocation in regulation 15 and Schedule 3 remain in force unaltered until that date
• where, despite regulation 3(4), the regulations apply to the master and crew of a seagoing ship, regulation 6(4) – prohibition on exposure above a limit value - does not come into force until 6th April 2011.
Manufacturers’ duties
The ‘Supply of machinery (safety) regulations 1992’ (as amended in 1994) require manufacturers of equipment which is likely to give rise to noise exposure implications to provide acoustical information for the end-user.
Instrumentation for noise measurement
There are various instruments on the market for measuring noise, designed for different purposes. All should be used by competent technicians, who will take care to use the appropriate type.
Noise dosimeter
Dosimeters are electronic sound-level meters with in-built clocks and data-storage facilities. In effect, they measure the total sound energy impacting on the person under observation during the
surveillance period.
Personal noise dosimeters may be carried by the individual worker, where they will directly measure the daily noise-exposure level. The microphone should be placed within one metre of the employee's head, ideally clipped onto the lapel or brim of a safety helmet. This ensures that the dosimeter receives the same sound pressure as the employee's ear, ensuring representative measurements.
Sound-level meter
This instrument may be used in most work environments, and meters complying with the relevant British Standard for industrial sound level meters provide more reliable data than a dosimeter. A sound-level meter will generally measure in the range 10-130dB and may be connected to octave and one-third-octave band filters to analyse the frequency characteristics of the noise concerned. Sound-level meters are available with a variety of functions and levels of accuracy, it is important to be selective about this, as it has a bearing on the expense and usefulness of the data produced. They cannot be used to measure impulsive sounds, as their response time is too slow. However, specialist impulse meters are available for measuring noise from cartridge-activated tools, etc.
Sound-level meters must be regularly calibrated by a specialist laboratory against a known standard, and routinely checked with a local calibration device before and after every use, including after a battery change.
Octave-band analysers
These may be used to examine the frequency characteristics of noise, and the data may be printed via a computer or plotted manually. Third-octave band analysers provide detailed analysis, and electronic analysers can give very specific data on sound energy at particular frequencies.
Workplace noise control techniques
Once the risks have been assessed, a number of noise-control techniques are available. Both the source of noise and transmission pathway need to be considered.
Personal protective equipment should never be considered as the primary control measure, because it heavily relies on the wearer correctly using the protector, and wearing it at all relevant times.
Planning location of noise sources
Machines and processes may be set apart from workplaces where humans are constantly present. Where areas are divided into noisy and quiet sections, the separation should be as complete as possible, and this may involve extending the partitions to the walls, ceiling or roof. The walls and ceiling may also require the attachment of sound-absorbing material to prevent increases in sound levels due to reflections.
Other ideas include:
• specify quieter machines or processes when designing a new production process. When purchasing new machines, the contract specification should stipulate low noise generation. Suppliers and manufacturers must provide details of the potential noise to be produced but it must be noted that the levels quoted are those generated under test conditions and when installed, the noise levels may be greater. Reasons for the increases include reflections from walls, floor and ceilings, difference mounting and loading conditions, and the additive effect of noise from adjacent machines.
• re-arrange workflow so that part of the job may be carried out in a quiet area
• reduce the duration of individual exposure by rotating jobs between quiet and noisy areas
• run machines at slower running speeds
• use low-noise air nozzles, pneumatic ejector and cleaning guns designed on good aerodynamic principles.
• matching air-supply pressure to the needs of the equipment and operation, and avoid jet noise from leaks.
Change the process or activity
The best control strategy is to substitute a quieter process or machine. This may include changing the:
• process: squeeze riveting instead of percussion riveting, etc
• noisy machine: manual-turning lathes may be replaced with automatic computer controlled lathes
• activity: compressed-air tools may be replaced with quieter hydraulic alternatives.
• maintenance – poor maintenance may lead to more noise from gears, bearings, etc than is necessary.
Damping
Avoid impact noises by cushioning conveyor panels, cyclones etc with buffers, rubber/plastic surface coatings, etc. Modifying the motion of the contacting surfaces may reduce impact sound, or the surface shape may be altered or softer surfaces, such as resilient pads, provided.
Provide vibration damping. Energy is dissipated in a soft, resilient material, reducing the energy available for noise generation (panels, chutes, fan ducts, machinery guards, ducting, etc). Vibration isolation ensures movement is not transmitted to surfaces, which then radiate noise (fans, power presses, engines, pumps, guillotines, ventilation equipment etc).
Acoustic barriers/enclosures
Barriers and enclosures can be applied in three ways:
• Enclose the machine (ie, the noise source)
This introduces a barrier to noise transmission (machinery, generators, compressors, pumps, engines, transformers, quiet work stations, etc). The machinist should not enter the enclosure
• Enclose the operator (ie, the receiver of the noise)
ventilation and temperature control. If this is not practicable, it may be practicable to provide a noise refuge for use when the operator is not actually operating the machine, this may be of particular use where an operator moves around the plant
• Fit silencers (mufflers) to exhaust systems (ie, control a significant aspect of the noise source) These only work on noise sources where the rapid movement of air or gas is a factor (fans, blowers, compressed air, combustion noise, exhaust gases, etc). However, their effectiveness is limited to a fairly small frequency range, and the silencer must be selected following frequency analysis – tuned to the most annoying frequencies.
More about enclosures
If an enclosure is built, consideration should be given to the following:
• absorbent linings should never be made of flammable materials. If liquid fuels, cutting oils, solvents or other flammable liquids are present, it may be preferable not to use any sound-absorbent lining but to construct the enclosure from a material with increased sound-insulating properties. If water sprays are used, the internal lining should be water resistant, and in dusty environments, the lining surfaces should be regularly cleaned
• doors and removable panels must have efficient seals
• enclosures should be ventilated to discharge heat generated by machinery. If forced ventilation is used, consideration must be given to the noise generated by the fans, blowers, etc
• windows: large windows are generally not needed, although vision windows may be required to check processes. If small, windows may be constructed of single sections of shatterproof plate glass or plastic. Larger areas may need to be double-glazed
• other apertures, such as cable holes, leads, etc should be led through over-sized holes and then packed with sound-resistant and vibration-decoupling grommets or glands
Work-related vibration
According to a Medical Research Council survey in 1997-8, there were over 300,000 people suffering from vibration white finger in the UK, and there were over 2,400 new cases assessed for disablement benefit in 2001-2. In the same year nearly 800 cases of carpal tunnel syndrome were assessed for disablement benefit.
The Medical Research Council also estimated that 150 000 people suffered from back pain attributable to riding on industrial vehicles. However a large number of industrial vehicle users are also involved in prolonged sitting, and lifting operations, which may exacerbate the effect of whole body vibration.
Vibration affects the human body either through the hands and arms (HAV or hand-arm vibration) or through the legs or buttocks (WBV or whole body vibration). The health effects of hand-arm vibration are the more common, and contact with vibration in the frequency range 40-250Hz may cause contraction of blood vessels exposed to the vibration, as well as secondary tissue changes to bones, nerves and the musculature. This causes impaired sensation and eventually persistent pain.
Vibration is not usually a significant health problem unless it is a regular part of the work experience. However there are a number of medical conditions (such as Raynaud’s disease) which may render workers more susceptible to injury from vibration.
The effect of vibration may be exacerbated by working in a cold environment. Regular exposure to HAV can give rise to permanent injuries such as:
• damage to the blood circulation in the fingers (vibration white finger)
• pain in the wrists (carpal tunnel syndrome)
• pain or loss of sensation in the hands or fingers
• loss of grip strength
• tingling sensations (pins and needles)
• loss of manual dexterity
• loss of sense of temperature in the fingers. Vibration white finger
Vibration white finger (VWF) is a condition which begins with the tips of the fingers blanching
(whitening) and feeling numb. As the condition progresses the whole finger may be affected. Attacks are short-lived (usually up to 30 minutes) and often end with a painful throbbing as the blood returns to the finger. This is often characterised by a reddening of the finger at the end of the attack.
Approximately 40% of those reporting VWF in the Self-reported Work-related Illness Survey 1995 also reported work-related deafness or other ear problems, reflecting the fact that work which exposes people to hand-arm vibration is often noisy as well.
Carpal tunnel syndrome
Carpal tunnel syndrome (CTS) is a specific type of nerve/muscle damage caused (among other things) by vibration in which the nerves in the wrist are compressed, leading to pain and stiffness. Any part of the hand could potentially be affected by numbness, tingling, loss of strength and sensitivity.
Likely sources of vibration
HAV can be experienced when holding vibrating equipment, or when holding material which is in contact with vibrating or rotating equipment (for example, holding material against an abrasive wheel). The following list is not exhaustive, but gives a general idea of the types of equipment which can cause HAV problems:
• chainsaws
• concrete breakers
• drills, compactors
• grinders and polishers
• hammer drills
• hand-held grinders and sanders
• hedge trimmers
• nut runners
• pedestal grinders
• power hammers and chisels
• powered lawnmowers
• riveting hammers
• rotary burring tools
• scabblers
• strimmers, brush cutters
• swaging machines
• vibration levellers and compactors.
Legal requirements for work-related vibration
Until 2005, there was no specific legislation in the UK aimed at protecting workers from vibration. The Physical Agents Directive (2002/44/EC) requires EU member states to implement its requirements and this has been accomplished via the Control of Vibration at Work Regulations 2005/1093 Employers are required to:
• assess the vibration risk to employees
• decide if they are likely to be exposed above the daily exposure action value (EAV) and if they are: introduce a programme of controls to eliminate risk, or reduce exposure to as low a level as is reasonably practicable; provide health surveillance (regular health checks) to those employees who continue to be regularly exposed above the action value or otherwise continue to be at risk
• decide if they are likely to be exposed above the daily exposure limit value (ELV) and if they are: take immediate action to reduce their exposure below the limit value
• provide information and training to employees on health risks and the actions you are taking to control those risks
• consult trade union safety representatives or employee representatives on proposals to control risk and to provide health surveillance
• keep a record of the risk assessment and control actions
• keep health records for employees under health surveillance
• review and update the risk assessment regularly. Exposure action value
The exposure action value (EAV) is a daily amount of vibration exposure above which employers are required to take action to control exposure. The greater the exposure level, the higher the risk and the more action employers will need to take to reduce the risk. For hand-arm vibration the EAV is a daily exposure of 2.5 m/s2 A(8).
Exposure limit value
The exposure limit value (ELV) is the maximum amount of vibration an employee may be exposed to on any single day. For hand-arm vibration the ELV is a daily exposure of 5 m/s2 A(8). It represents a high risk above which employees should not be exposed.
The regulations allow a transitional period for the limit value until July 2010. This only applies to work equipment already in use before July 2007. The exposure limit value may be exceeded during the transitional period as long as all the other requirements of the regulations have been complied with and all reasonably practicable actions to reduce exposure as much possible have been taken.
The Supply of Machinery (Safety) Regulations 1992 (amended 1994) and the Provision and Use of Work Equipment Regulations 1998
This legislation imposes duties on the manufacturers of equipment, and also on the employer whose workers use the equipment.
The manufacturer must:
• design and construct equipment which will cause the minimum vibration injury
• provide purchasers with warnings of any residual risk
• provide information on vibration levels
• provide instructions in how to use the equipment to avoid risk of vibration injury. The vibration information given by manufacturers is given in m/s2.
Risk assessment of vibration at work
If any of the following conditions exist, there may have a significant vibration risk, indicating a survey and risk assessment. Alternatively, you can work on the presumption that vibration is excessive and introduce control measures without carrying out a detailed assessment:
• are workers using hammer action tools for more than a few minutes per day?
• are your employees using rotary action tools for more than half an hour per day?
• do the manufacturers of your equipment specify vibration risks?
• is vibration a known issue in your industry, or in the processes you carry out?
• have any of your employees complained of symptoms linked with HAV?
Data on vibration generated by equipment is available from manufacturers, but it cannot be assumed that laboratory experiments with equipment resemble real work processes. You may need to have the vibration levels measured by a competent person.
You will also need to know the ‘trigger time’, which is the time your workers are handling the
equipment and it is producing vibration exposure. A worker who uses a disc sander, hammer drill etc. is unlikely to use it continuously for the whole time they are holding the equipment.
When workers are exposed to vibration from different pieces of equipment in their working day, each piece of equipment must be assessed separately. With this data it is possible to calculate the daily exposure.
Processes known to have a significant vibration problem
• drilling and breaking rock, concrete etc
• compacting sand, aggregate or concrete
• riveting, caulking, hammering, clinching, flanging and hammer swaging
• preparing and dressing welds
• grinding, sanding or polishing
• cutting metal, wood, grass, stone, bone etc
• holding or supporting objects being worked upon
• component or product assembly.
How is vibration measured
Vibration is the rapid acceleration and deceleration of a body or body part, produced by rotating or oscillating machinery. When this movement is transmitted to the human body – usually through the hands, arms, feet or buttocks – it has the potential to cause injury.
Vibration is measured in 3 axes – the x axis is front to back, the y axis is left to right, and the z axis is up and down in the vertical plane. The acceleration in each of the planes is measured, and gives a reading in m/s2.
An accelerometer (equipment for measuring the rate of acceleration) is used to measure the vibration on each of the three axes, and calculate the value. This data has to be adjusted to give the equivalent value of exposure to vibration over a normalised 8 hour day. This is expressed as units of m/s2 (8hr).
Steps to reduce vibration exposure levels
Elimination of exposure through design of processes
• avoid or minimise the need to use tools which expose workers to vibration
• allow the use of vibration-minimised tools
• review the ergonomic design of workstations, equipment and working methods
• use adhesive or welded joints to avoid riveting
• specify architectural finishes which do not require use of needle guns and scabbling tools
• improve mechanise production of components to minimise need to cut and patch on site
• improve design and production of metal castings to reduce need for fettling
• using mobile trenchers or road cutting machines in place of hand-operated road breakers
• using abrasive blasting or pressure jetting to descale surfaces
• concrete breaking using “bursting” techniques. Personal protective equipment and vibration
Low body temperature increases the risk of VWF. Where practicable, workstations should be at 16oC
minimum. Warm clothing including gloves should be provided where processes cannot be carried out
at suitable temperatures.
Damp clothing, especially gloves, increases the effect of cold. Suitable water-protection should therefore be provided.
Vibration-protection gloves (manufactured to EN ISO 10819) are available, but there is no way of assessing the degree of mitigation they provide. They should be considered as a supplement to other, more effective, means of reducing vibration exposure.
Hand-arm vibration and whole-body vibration
The Directive makes specific reference to these two aspects of vibration exposure, which have there own regulatory limits.
Hand-arm vibration (HAV)
HAV is vibration transmitted from the work equipment or process into workers’ hands and arms. It can be caused by operating hand-held power tools or hand-guided equipment. Regular and frequent exposure to high levels of vibration can lead to permanent injury that eventually must be declared to the HSE and the Department of Social Security. The largest successful civil claim against an employer was in respect of hand/arm vibration experienced by British coal miners, and the condition is a leading cause of benefit claims under the Industrial Injury Scheme.
HAV symptoms
The typical conditions and symptoms are:
• vibration white finger (VWF) - painful finger blanching (triggered by cold or wet conditions)
• carpal tunnel syndrome - trapping of nerves in the wrist
• numbness and tingling in the hands - loss of sense of touch
• painful joints
• muscle weakening - loss of manual dexterity, loss of grip
• damage to bones in the hands and arms. HAV exposure control measures
Ideally, it is best to eliminate vibration exposure wherever possible, or deal with the source of vibration. However, the following steps should be taken if this is not possible:
• look for alternative methods of working - automation, jigs and fixtures to hold the work, etc
• use tool supports - anti-vibration mounts, tensioners, balancers, etc
• maintain tools and equipment: replace mounts regularly, ensure tools are correctly balanced, keep tools sharp
• design the task to avoid poor posture - avoiding strain on hands and arms
• introduce a purchasing policy specifying low vibration tools and equipment
• conduct regular health surveillance, including monitoring of vibration exposure. Act on the results
• use appropriate PPE - particularly if used in damp or cold conditions. Change gloves if they become damp or wet, as keeping the hands and arms warm is an important preventive measure
• implement a training programme to ensure that workers understand why the task is designed as it is, what PPE to use, and to report any symptoms of HAV immediately
• reduce exposure duration by implementing work breaks, job rotation, etc. What is the safe level of exposure to HAV?
The British Occupational Health Research Foundation (BOHRF) says there is some evidence showing the risk to be insignificant at exposure below 1m/s2. However exposure at the new limit and action levels may still result in some individuals developing HAV syndrome, or in the deterioration of HAV symptoms where they already exist.
Exposure should therefore be reduced as low as is reasonably practicable. Health surveillance has an important role to play in monitoring the effectiveness of exposure levels.
Health surveillance for hand/arm vibration
This will include pre-employment screening and regular health checks covering what symptoms are experienced, a physical examination, and advice to the employee. There are objective medical tests available to detect injury due to vibration, and the HSE has published a routine questionnaire.
How often should health surveillance be done?
The general occupational health view is that workers at risk of HAV syndrome should have an annual check with a questionnaire, and if necessary an examination.
Workers with frank symptoms should be seen more frequently following advice from an appropriately trained health professional. This advice will largely be based on the stage the worker has reached on the Stockholm Workshop Scale.
Stockholm Workshop Scale
The severity of symptoms is usually graded on the Stockholm Workshop Scale, and despite its limitations, this is the recommended means of grading the severity of HAV syndrome. It separates symptoms into two independent components:
• circulatory or vascular
• sensory or sensori-neural.
The vascular component is graded from Stage 0 (no symptoms) to Stage 4 (very severe symptoms), and the sensorineural component from Stage 0 (no symptoms) to Stage 3 (very severe symptoms).
Can affected workers recover?
After reducing or ceasing exposure, vascular symptoms reduce in some people over a period of years. BOHRF says there is evidence that smoking impedes recovery.
Whole-body vibration (WBV)
Whole-body vibration is experienced when vibration from a vehicle or machine a person is sitting or standing on is transmitted to the torso via the buttocks or feet.
WBV conditions and symptoms
The most common complaint from WBV is persistent back pain, but it may also cause:
• digestive disorders
• cardiovascular stress
• dizziness or motion sickness, due to balance organ or sensory system disorder.
Lower back problems arise from degeneration in the spinal vertebra or degeneration of the discs causing compression and pain. The lower back muscles can also become weakened, increasing the risk of injury through twisting or manual handling.
Sources of WBV Causes of WBV include:
• driving off-road too fast or over a rough route
• driving vehicles with poor suspension
• poor driving position - incorrect seat or control settings
• poor design of controls - making the difficult to operate
• poor driver visibility - making twisting and stretching necessary whilst driving
• other work activities - handling and lifting heavy objects
• personal factors - general fitness, age, weight, etc. Work activities of greatest risk for WBV include use of:
• agricultural and forestry vehicles and machinery - tractors, etc
• construction and quarrying vehicles and machinery - diggers, dumper trucks, etc
• haulage vehicles - road, rail, buses, etc
• industrial trucks - forklifts, straddle carriers, etc Control measures for WBV
Due to the nature of the source of WBV it may not be possible to eliminate exposure, but it is possible to reduce or control it by ensuring that:
• vehicles and machinery are well-maintained, particularly suspension
• drivers seats are in good order and give good support
• suspension seats are adjusted to suit height and weight of the driver
• where controls are adjustable, they are set correctly for the operator
• the vehicle is suitable for the work and the terrain
• vehicle tyres are inflated to the correct pressure for the terrain
• exposure duration is reduced by implementing work breaks, job rotation, etc
• a training programme is implemented to ensure that workers understand the causes and report any symptoms of WBV - sitting and posture, adjusting seats and controls for correct position, correct tyre pressures, keeping speed low on uneven terrain
• a purchasing policy is introduced specifying low vibration vehicles and machinery.
Particular care has to be taken if young persons are employed as their bones and muscles have not fully developed. It is worth noting that the limits quoted are for an assumed eight-hour day of
exposure; by reducing the period of exposure the risks of developing symptoms are proportionately reduced.
Selecting tools, equipment and vehicles to minimise WBV
It is important to study manufacturers’ data on vibration. Some equipment may not have a recognised standard of measurement or the data obtained may not be representative of a normal working
environment. As a result, values quoted may be measured from a single axis or may be the sum of all axes, so it is important to compare like with like.
Using the manufacturers’ vibration data it is possible to make choices for the most suitable equipment for the purpose intended. When choosing plant and equipment the following should be considered:
• is the equipment suitable for the task?
• do vibration reduction features need regular maintenance to retain efficiency?
• can the supplier offer technical support and advice on the equipment for specific tasks?
• is the equipment ergonomically correct or suitable for use (position and weight of equipment and driver/operator)?
• does it pose other hazards: noise, dust, fumes, etc?
• does the manufacturer recommend PPE?
• what are the training requirements?
• are the quoted vibration levels appropriate given the requirement to minimise operator exposure?
