Can manufacturers’ declared vibration emission values be used for vibration exposure assessment?
In this article, Finch Consulting’s noise and vibration specialist, Sue Hewitt, and machinery safety expert and Head of Training, Martin White, provide advice to employers on the pros and cons of using vibration emission values as part of a vibration exposure assessment.
Experience of providing engineering expert reports for HAVS claims has shown that many Defendants have relied on manufacturers’ vibration data without question, and the consequence of this is often that they have failed to identify and control hazardous levels of vibration exposure. Of course, this may not be the only reason why a Defendant might fail to identify that there is a significant risk from vibration exposure in the workplace, but the fact that manufacturers’ data can be misleading certainly does not help.
So why would a power tool manufacturer declare vibration information, if not to provide a value suitable for use in a vibration exposure assessment? And how come the declared vibration emission value can be so far from the typical vibration under conditions of use of the tool? An analogy can be made here with how people use the fuel consumption figures stated in a vehicle manufacturer’s brochure; the figures quoted might be used when comparing fuel efficiency to choose a more economical vehicle, but who buys a car on the basis of the fuel consumption figures and actually expects to get that level of fuel economy? Most of us realise that how we drive, road conditions, tyre pressures, and so on, will have an effect (most likely negative) on the actual fuel economy of the vehicle. Similarly, the way a power tool is used by the operator, the work being done, or the type of inserted tool or consumable, can have an effect on the vibration to which they are exposed.
The requirement to declare the vibration emission of a power tool originates from the Machinery Directive (the first version was produced in 1989, the current version is 2006/42/EC and is implemented in the UK by the Supply of Machinery (Safety) Regulations 2008). The Machinery Directive requires manufacturers and suppliers of machinery to minimise risks, through the safe design and construction of their products, and to provide information to enable the management of any residual risks, so that their machinery can be used safely through all the phases of its life.
According to the Guide to the application of the Machinery Directive the two main purposes of the declared vibration emission values are; a) to help users choose machinery with lower vibration emissions; and b) to provide information useful for a risk assessment. The guidance goes on to say that if the values determined do not represent emissions during intended uses of the machine, further information or warnings are required to enable the risk to be managed. To facilitate this process, a raft of vibration emission test codes was adopted in Europe (originating from International Standards) and application of one of these harmonised vibration emission test codes conveys a presumption of conformity with the vibration emission declaration requirements of the Machinery Directive. A manufacturer is not obliged to apply a harmonised emission test code (in some cases, such as for less common machines, there may not be one) but if not, must provide a full description of whatever test method was used.
To create a vibration test code that is sufficiently consistent to be repeatable (i.e. if you repeat the test, you get the same result) and reproducible (if more than one test house does the same test, they get the same result) it is necessary to eliminate sources of variability and control operating conditions. This means that emission test conditions may need to be artificial, in some cases bearing very little relation to conditions when the power tool is used in a typical work situation. In our experience artificial test codes tend not to represent the full range of vibration from real use, and more often than not, produce values in the lower part of the typical range. This is particularly true for tools such as road breakers and chipping and demolition hammers, which are tested in an artificial test fixture and with operating forces carefully controlled. Repeatable and reproducible test codes, artificial or not, should be designed to represent the emissions during the intended uses of the machine to enable the potential risks to be assessed and managed.
Prior to about 2005, emission test data were mostly single axis (measured in only one direction), rather than triaxial (measured in three orthogonal directions), reflecting the standard vibration measurement technique at that time (ISO 5349:1986 and BS6842:1987). Also, in some tests, the vibration was only measured at one hand position when there was often a secondary hand position, such as on the chisel of a chipping hammer, which was a location of much higher vibration, but which was not measured.
Early versions of test codes for electrically powered tools specifically stated that the data produced should not be used for exposure assessment. This was probably not an issue for most of Europe until the Physical Agents (Vibration) Directive, 2002, was implemented in national Regulations in 2005. This Directive introduced Exposure Action and Limit Values and stated that the information supplied by manufacturers may be used for the assessment of vibration exposure. Also, a standard giving guidance on production of vibration test codes for pneumatically powered tools (BS EN ISO 20643, first published in 2005) introduced the requirement that the declared vibration emission value should be in the upper part of the likely range of in-use vibration. These changes meant that the original test codes were gradually redeveloped and improved. Consequently, emission data produced according to test codes dated from around 2006 onwards tended to be a better reflection of the typical vibration than had previously been the case, although data for tools such as road breakers and demolition hammers, are also still less likely to reflect the typical vibration magnitudes.
Due to improvements in vibration emission test standards, a clue to the validity of the vibration emission data can be found in the date of the standard test method referenced by the manufacturer in the information provided with the power tool. An emission declaration should be dated 2009, or later, to reference test codes that address the clarified requirements for vibration set out in Machinery Directive 2006/42/EC. Also, if the information does not include both a and K values (where a is the declared emission value and K is the uncertainty in the a value), the declaration is incomplete.
Current HSE advice from the second edition of L140, published in 2019, is that seeking at least two sources of vibration data for an initial risk assessment and comparing them will improve confidence in the value used. To help with this, in 2019 HSE produced a new version of its calculator spreadsheet, which now contains vibration magnitude information measured under conditions of real use and suitable for use in an initial risk assessment. An important factor to bear in mind in all of this is that any vibration exposure assessment only needs to be sufficient for the employer to know if an employee is likely to exceed the Exposure Action or Limit Values, so that the necessary action can be taken. If the Exposure Action Value is likely to be exceeded, then it is necessary for the employer to implement health surveillance and to develop a control action plan to reduce exposures to as low as reasonably practicable. Implementation of the control action plan, which should eliminate the vibration exposure by use of alternative methods where possible, should result in the exposure and risk being demonstrably as low as reasonably practicable.
So, whilst it is still not advisable to use manufacturers’ data in isolation for a vibration exposure assessment, in theory, manufacturers’ vibration data may be useful to help with purchasing decisions. Here too, however, there are a few considerations. Firstly, if you are at the point of attempting to select a low vibration power tool, this implies (perhaps wrongly!) that you have already searched for, and considered, all reasonably practicable work methods that do not involve the need for use of power tools.
Secondly, although the data are likely to be helpful to eliminate the tools with the highest vibration magnitudes from your list of possible options, they should not be relied on to choose between tools for which there is very little difference between declared vibration emission values. Consideration of the declared a value and the uncertainty in the a value, as represented by the K value, will in many cases mean that a choice solely on the basis of vibration magnitude is not possible because they are effectively the same. This is illustrated in the example below where three tools of the same type have the following declared vibration emission values (taken from real examples):
Comparing the three ranges of vibration on the chart shows that while Tool C could be considered as in a higher vibration range than A and B, the ranges for Tools A and B overlap, so that they are effectively the same. This can often be the case, because major power tool manufacturers have complied with the requirement of the Machinery Directive to produce power tools for which the risks associated with their use are minimised. Consequently, state-of-the-art power tool vibration declaration magnitudes may all be very similar, for equivalent products. The vibration to which an operator is exposed when used for any particular task, however, may not be the same, so the suitability and efficiency of the tool for the task should be considered alongside the vibration emission to ensure that the most appropriate choice is made after considering all the available information.
In summary, manufacturers’ vibration emission data can be helpful in selecting better tools, showing if the manufacturer has designed the tool to be safe, and allowing you to understand the risk, but you should be cautious about using the vibration information directly in a vibration exposure assessment. A clue to the validity can be in the information provided by the manufacturer about how the vibration emission tests were done – if this is missing or the standard used is undated, you cannot be sure the information is reliable. Finally, remember that managing the risks from vibration is more than simply choosing between tool A and tool B; make sure that you have considered all reasonably practicable options to avoid or reduce exposure to vibration.
Formerly a research scientist with HSE, Sue Hewitt is a specialist in Finch Consulting’s noise and vibration team, reporting on HAVS and NIHL claims as an expert witness and advising clients in reducing risk and good practice.
Martin has over 20 years of machine safety and consultancy experience. He is a Member of the Institution of Engineering and Technology (IET) and Martin is qualified to deliver training and development from City & Guilds and the Chartered Institute for Personnel and Development.