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September 22, 2008

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Tool vibration – health and safety legislation advice

In the first of a double-header on tool vibration, Andrew Sansom looks at the current legal landscape, and finds out what is being done to address a gap in understanding among employers.

In a Seventies’ comical song about a rather speedy milkman, the noise and vibration generated by the deceased Ernie’s “ghostly gold-tops a-rattling in their crate” was enough to stir a couple in bed on their wedding night.

Putting phantom pasteurised produce to one side, things are still rattling away in the birthplace of the song’s creator, Benny Hill.

Indeed, Southampton might well stake a claim to the title of unofficial capital of scientific study into noise and vibration — not only does the city boast the Institute of Sound and Vibration Research but also a purpose-built testing facility, recently set up by Specialist Construction Products (SCP) — part of Sheffield Insulations Group, a supplier to the construction and manufacturing sectors.

According to Dr Thomas Gunston, who heads up the testing laboratory, the biggest stumbling point for employers when managing vibration risk from tools is the risk assessment itself. In other words, how do they know if their employees are being exposed to too much vibration against the legally acceptable values?

With the introduction of the Physical Agents (Vibration) Directive, which was implemented in the UK via the Control of Vibration at Work Regulations 2005, the risk from vibration must be assessed and controlled in accordance with specific daily limits. The Directive introduced a daily Exposure Action Value (EAV) of 2.5m/s2 — above which employers are required to take action — as well as a daily Exposure Limit Value of 5m/s2, which must not be exceeded.

Although the new action level did not appear to represent a significantly tougher threshold from the previous value of 2.8m/s2, another change — the way the daily A(8) (the vibration an operator is exposed to averaged over an eight-hour working day) is calculated — had greater impact.

Prior to the Directive the vibration level was measured over the highest single axis of vibration, but now the level is calculated by taking the vector sum of the vibration intensity measured over three axes. In accordance with this approach, the original 2.8m/s2 corresponds to about 4m/s2 under the new method — which means that some employers may have needed to reduce the exposure to their employees by as much as 37 per cent.1

Dubious data

Prosecutions brought by the HSE for vibration-related issues have been few and far between, but offending employers are most likely to become embroiled in compensation claims and will settle out of court. Consequently, contractors need to be fully confident they are managing the risk.

Unfortunately, says Gunston, the information traditionally provided by manufacturers has been quite difficult for employers to make sense of in real work settings.

Part of the problem for employers is that there has been a lag in what manufacturers legally have to provide in respect of vibration-emissions information, and what employers expect in order to help them comply with the Physical Agents Directive.

To sell a power tool, a manufacturer has to comply with the Machinery Directive, the current version of which is now almost 20 years old. A revised version is due to be implemented in the UK in late 2009, and this will also require manufacturers to declare vibration values to be the total value along the three axes, bringing it into line with the ISO 5349 testing standard and the Physical Agents Directive.

Traditionally, manufacturers have provided customers with their own tool-vibration values, which have normally been obtained by using standards such as ISO 8662, which measure in only one direction.

These values have often been used to compare different tools of the same type — and, in most cases, they should reveal a reasonably accurate ranking of tools in relation to the vibration levels they generate in practice — but they are not suitable for risk assessment of vibration exposure.

The arrival of the tougher legal standards has now generated increased demand for the declared values to be more representative of the vibration levels that workers are likely to be exposed to in practice.

Gunston explains: “The legislation states that, where practicable, an employee should have an exposure less than the daily Exposure Action Value of 2.5m/s2 A(8). The manufacturer of a particular machine might report a vibration emission value of 9.5m/s2 for the machine, used with a particular insert, for a stated task.”

He continues: “The real challenge is presenting all of this in a useful way for someone on a building site. For instance, the easiest way to manage the exposure of a hammer-drill operator is to let them know how many holes — including size and depth — they can drill in a typical working day.”

Lights and points

The need to improve knowledge and understanding is hardly helped by the many different ways to present vibration data. Traffic-light systems, for example, have often been used to give employers quick, rule-of-thumb information about possible risks, but the Industrial Noise and Vibration Centre, for one, has cautioned against relying on such systems for risk assessment.

Loughborough University’s Off-Highway Plant and Equipment Research Centre (OPERC) has, however, made some progress in this area. Under its new traffic-light system, the red range represents anything over the Exposure Limit Value, indicating the tool should not be used; the amber range covers items that produce emissions between the Exposure Action Value and the Limit Value, where control measures should be applied; and tools falling within the green category are those that generate emissions below the Action Value, and should be safe to use.

Hire Association Europe is currently working on applying the system to a new traffic-light label, which could be attached to a device. The label may feature the green, amber and red bands, within which could be contained information according to the time the tool can be used with a given material, as well as productivity data on the number and size of holes that can be drilled.

Another system, which Gunston believes could be the most useful, is the still relatively new points system from the HSE. This approach assigns a points score to each machine and task, enabling employers to keep a tally of the points an operator has amassed during a working day. Points can be matched against the legal values for easy identification of vibration exposure.

Comments Gunston: “You are able to mix jobs and tasks and keep under the values. It is a simple way of managing multiple emissions, as it is very rare for someone to be using one machine all day.”

He also says it is important to try to learn as much as possible about a customer’s job and what they use their tools for.

The efficiency of the tool is important, as a tool which causes a worker to take longer than necessary to complete a job is not only likely to increase the frustration and effort of the operative but could also result in a higher vibration exposure than a more efficient tool with greater vibration emission. On the other side of the coin, tools may also be too powerful for the task, leading to potential exposure to unnecessarily high vibration levels.

Generic versus specific

Testing, of course, can throw up some discordance, as manufacturers have tended to seek measurements that can be replicated, and eliminate variance between other factors, in order that tools can be more easily compared — yet real-life testing tries to test such variables to give more accurate data.

The service provided by SCP is driven by the user, but Gunston is quick to stress that even this is not an exact science, as it is simply not possible to test every tool with every insert or appendage, on every material. He points out the test centre’s huge concrete block, which, although so scarred with drill holes it resembles some sort of industrial acne, he describes as probably more aggressive than anything its customers use.

It is vital, as well, that employers don’t underestimate the importance of a thorough maintenance regime to keep drill bits and tools sharp (see Blunt truthsfor more) — for example, using an angle-grinder that has lost bits from its disc can cause vibration exposure to leap up.

But, Gunston warns, it is better when employers and employees are well-informed and encouraged to solve power-tool problems themselves. Over-reliance on an external company to carry out maintenance checks, for example, could lead to complacency, with contractors and operatives assuming tools are fine to use in between inspection periods.

Different strokes, different folks

Nor is it safe to assume that employees are all the same, and affected in the same way. In recognition of this, health surveillance is now a legal requirement if an individual is likely to be regularly exposed at, or above, the Exposure Action Value, or is considered to be at risk for any other reason. Gunston recites a story of a worker who was subjecting himself to excessively high levels of vibration because, unbeknown to his employer, he was spending his lunchtimes drilling on another site.

With some parts of the construction industry, notably housing, likely to experience some tough times ahead, such cases could become more common, increasing the need for effective health-surveillance systems to pick them up.

However, the current climate also reinforces the need for employers to have access to accurate and easy-to-understand data, so they are clear about the risks that working with tools could pose to their workforce, and are not tempted to take dangerous shortcuts for productivity gains.


1 Blacksmith, M (2004): Shaking up the rules, SHP September 2004, pp26-28

Andrew Sansom is SHP’s deputy editor.


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