Measurement matters
October 1st 2006 The Control of Vibration at Work Regulations 2005 cover Hand-Arm (HAV) and Whole-Body Vibration (WBV) and represent a formalised approach to human vibration risk assessment and control. Simon Bull of Castle Group outlines the requirements of the Regulations and explains some of the terminology
The Regulations lowered the acceptable levels of vibration exposure, above which both employers and employees are required to take action, and introduced Action and Limit values, compulsory health surveillance, weekly averaging and stricter monitoring protocols.
Limit Value: The Exposure Limit value is set at 5m/s2 for HAV and 1.15m/s2 for WBV. This is the maximum level of vibration that an employee may be exposed to on any single day. Equipment bought before 6 July 2007 is exempt from the Limit Value until 6 July 2010, and there is an exemption until 6 July 2014 for the agriculture and forestry industry for the WBV Exposure Limit Value. While this may provide breathing space, it will not protect against litigation.
Weekly Averaging Derogation: If workers are exposed to high levels of vibration for only a small part of a week then, under the regulations, it is possible to average the exposure they receive over the whole week, thus reducing the A(8). Care should be used when applying this derogation that the exposure is truly over a short enough duration and that it is not used simply as a means of circumnavigating vibration control measures.
When to measure: The focus should be on risk assessment; measuring actual vibration levels may not be necessary.
The theory here is that information on the levels of vibration emitted by most equipment should be readily available from manufacturers, on web sites, in shared information or in databases. The principle is that as long as employers are carrying out risk assessments and health surveillance, there will be a much reduced effect on the population from vibration-induced injuries. There is a problem, however, with not taking measurements and it is one that is recognised by many industry specialists. The problem occurs in producing evidence in defence of civil claims. To satisfy the HSE, a company may well not need to measure vibration levels, but not doing so could lead to indefensible claims and spiralling costs. Many insurance companies are taking this on board and may be able to offer advice.
Measurement technology is improving all the time and meters such as the Castle Pro-DX Excieo can give competent, reliable measurements with minimal training.
Health Surveillance: Any employee likely to be exposed to above the action value for either HAV or WBV must be placed under 'suitable' health surveillance. Screening usually involves an interview with an occupational health professional using a questionnaire to gather information about previous work, hobbies, indications of pre-disposition to injury and so on. This might be carried out preemployment and then at regular intervals, dependent on the level of risk and susceptibility factors.
Another form of health surveillance comes under the heading 'objective' testing (although this is currently only available for HAV). It generally involves sending an employee to a medical centre and is usually only used for high-priority cases.
Whole Body Vibration is a different matter and, as yet, there is no 'objective' test available to identify injury caused by vibration. The approach adopted by the HSE is that problems such as back injuries should be viewed holistically, taking into account ergonomics, manual handling and vibration as all potential causes.
What is Aeq: The term Aeq stands for Acceleration equivalent value.
Acceleration is the vibration parameter used in human vibration measurement and is measured in metres per second squared (m/s2). It is also possible to measure vibration in terms of Displacement (distance) and Velocity (speed), but these are not used in the context of the Control of Vibration at Work Regulations 2005. The equivalent part of the term simply means the average vibration level.
Daily Exposure - Aeq 'v' A(8): The main actions required by the law are based on assessing a daily vibration exposure figure – written as A(8). This is a fundamental point which, if not observed, will invalidate any risk assessment. Vibration exposure is like any other form of exposure – for example dust, gas, radiation and even sunlight. If the average strength of the sun, for example, is measured over the course of a day (call it 8h), this will give a figure showing how strong the sun is. It does not say anything about how burnt a person might get as this in turn depends on how long they stay in the sun. If they are in it for 4h, then they have had half of the available sunlight, so it would be logical to take half of the number measured and use that as the exposure figure. The same principle applies to vibration exposure, where Aeq is a measure of the level that exists at the surface of a tool or seat. This can be measured using a human vibration meter. The A(8) is then the proportion of that Aeq relative to the time of exposure.
There is a formula to calculate this as it is not simply a direct proportion, but the principle is the same.
Measurement Tips: Make sure that the measurement pickup (accelerometer) is rigidly fastened to the surface of the tool handle and watch out for overload or under-range messages. As some percussive tools have a huge difference between the peak and RMS, it is possible to encounter both states at the same time.
The Control of Vibration at Work Regulations 2005 are written from the point of view of the HSE, whose primary concern, and rightly so, is the protection of employees exposed to excessive vibration levels. It is not concerned with civil litigation. As long as an employer is taking enough action in the eyes of the HSE to prevent injury to people from excessive vibration levels while at work, they will be happy. The problem is that this may well not be enough to mitigate any future claims. More articles from Castle Group Limited: | 
