Awareness of hand-arm vibration syndrome (HAVS) has never been greater but more needs to be done to eliminate vibration-related health issues from the workplace. To this end, a practical understanding of how tools and consumables behave in practice and what effect this has on vibration exposure is helpful, says Dr Tom Gunston.
When the Control of Vibration at Work Regulations were published back in 2005 many industry sectors took some time to adapt to the changes they brought. The introduction of specific daily exposure limits and pressure from the noise and vibration team at the Health and Safety Executive led to much greater focus on an area of health and safety of which industry was aware but had not always taken seriously.
Fast-forward seven years and British industry has made remarkable progress. The risks of vibration exposure are now well documented; workers, managers and risk assessors are better informed; and improved tools and exposure data have been made available. While there remain problems in certain areas – for example, in the agricultural sector, where the HSE has little exposure data and the incidence of vibration-related disorders seems to be increasing, and the marine sector, where small boats operating at high speeds in rough seas can cause whole-body vibration exposures – generally, exposures seem to be dropping as a result of this collective understanding and awareness.
Health and safety professionals have been at the forefront of delivering these improvements. A lot of hard work has gone into translating the legislative limits and guidance provided by the Regulations into practical policies and procedures in the workplace. Manufacturers have also played an important role by investing in the development of low-vibration technology; new low-vibration power tools from quality suppliers now offer substantially lower vibration emissions without loss of performance.
Selecting low-vibration tools
Vibration emission is considered as part of the purchasing policy of most major companies that use a significant number of power tools. There are benefits to working with just a few suppliers (interchangeable batteries, maintenance contracts, etc.) – but manufacturers have rolling product development cycles, so it can be worth checking that a preferred supplier has a competitive low-vibration offering for the machines used most often.
It can also be worth checking how replacement tools are ordered. Tool users are likely to ask for the same old model they have always used, because they know it does the job, but there may be a better option out there.
There are various bases on which to make purchasing decisions – for example, declared emission values, carrying out structured ‘real use’ trials in partnership with manufacturers, and putting tools out on trial with sites and seeking feedback from the users.
With regard to the first of these, the manufacturer’s ‘declared emission value’ for a tool is based on a controlled type-test, and this information is a useful first step for estimating exposure. In theory, it should allow a purchasing manager to eliminate poor machines from a shortlist.
Recent research by the HSE1 suggests that the current standard laboratory tests for assessing the vibration emission from electric hammer drills, in particular, can provide realistic emission values.
Unfortunately, it also points out that the values published by power-tool manufacturers are sometimes noticeably lower than those measured by the HSE for the same machine and the same test. While some power-tool manufacturers are realistic with their declared emission values, it would seem that others are less consistent, and a few even post somewhat dubious results.
Also, in some cases, the standard test may not sensibly describe the intended use – for instance, 9-inch angle grinders can produce more vibration when used for chasing rather than grinding, but the declared emission value is based on a simulated grinding test.
Essentially, if vibration emission is a key factor in the purchasing decision, especially if it is an expensive purchasing decision, it may be worth substantiating the manufacturer’s claims. Furthermore, if a machine is likely to be used intensively, then it may be appropriate to take a closer look at actual usage conditions to take into account factors specific to the task.
A ‘real use’ test can, in theory, provide a ‘true’ measurement of how the machine will perform carrying out a particular task with a particular consumable. In practice, however, a ‘real use’ measurement should be treated as an exposure example, not the cast-iron truth, as various factors can affect vibration exposure during ‘real’ use.
For example, what about the person using the tool – how tall/strong are they, what is their posture like, how tired are they, and what about the mechanical impedance of their hands and arms? Most of the standard laboratory exposure tests typically use three operators for each task to try to obtain a reasonable ‘typical’ exposure, but the vibration experienced by any given individual at work on site on any given day may be greater, or less than this.
The substrate or material being worked on can also be important. A fixing hole in concrete, for instance, may be faster or slower to drill, depending on whether the drill bit hits a big chunk of aggregate, or not. Consequently, each task should be repeated several times to try to average this out, but this obviously takes more time.
Concrete is often specified in terms of compressive strength, but the choice of aggregate may be at least as important. Beware, particularly, of aggregates that use hard stone, such as flint or granite – sections of age-hardened concrete runway can be extremely difficult to drill into, for example.
As a general rule, ‘real use’ testing needs to involve enough repeat measurements, operators and other controls to give confidence that the value obtained can be reasonably assumed to be ‘typical’. It is wise to be cautious of a measurement based on one test with one operator, but it is also not worth expending too much effort trialling every machine in the fleet. Time is best spent on tasks that are frequent and therefore likely to involve severe exposures, and where measurements will help a mitigating decision to be made – for instance, to determine the number of operators to rotate on to the machine during a day.
Should real-use measurements be considered appropriate, they can be carried out by a competent consultant, a supplier, or using in-house expertise and experience. In all cases, it is important to have present during the measurements somebody who understands why the tests are being run and what the variables are likely to be.
Regarding the option of relying on user feedback, simply providing tool users with sample tools and asking for opinion will not provide a quantified, absolute vibration level. That being said, assuming comparable new and old tools are available to try side by side on the same task, a subjective comparison can be useful.
This method is obviously not very precise but can help rule out poor designs, or identify a tool with outstanding performance. Anecdotally, a 20-per-cent difference in vibration level is hard to judge but a difference of more than 40 per cent is usually apparent. Different users, however, may be sensitive to a greater or lesser degree. Tools should ideally be tried alternately a few times at least, rather than trying one then the other.
Also, beware of unconscious bias, especially if comparing several tools in this way. A task that becomes easier with practice may mean the last machine tested is favoured, while a task that is physically tiring may mean earlier machines are preferred. Ergonomics and appearance can also affect perception – good ergonomics should be encouraged but appearance is not usually safety-critical.
Effects of power-tool age
The effect of the age and usage of a power tool on the operator’s vibration exposure remains largely unknown. What is known, however, is that a ‘broken’ tool may cause substantially higher exposures, as in the case of a grinder with a damaged bearing, or may cause lower exposures, like a hammer drill with a worn-out hammer. In both such cases, the machine is faulty and should be repaired.
It is less clear what happens to vibration emissions as a ‘good-condition’ tool gets older. Major power-tool manufacturers will have information on how tools will perform as they wear but this information is very commercially sensitive and tends to focus on the life of the components and the speed of the machine, rather than the vibration emission. Consequently, there is virtually nothing in the public domain on the effect of power-tool wear on vibration exposure.
To try to address this, a study was carried out to compare the performance of electric power tools that had been well maintained but regularly used for at least one year with that of brand-new tools.2 Make, model, consumable, task and material were matched for both the new tools and the used ones, and repeat tests of the same task with different operators were carried out with each machine.
Six different tools were tested: a 230mm angle grinder; a drywall screwdriver; a sabre saw; a concrete planer; a battery hammer; and a combi-hammer. The study found that, with the exception of the angle grinder, none of the used machines showed an increased vibration exposure when compared to the new machines. In fact, some machines showed slightly lower vibration magnitudes, possibly due to gearboxes ‘wearing in’, smoothing the meshing between the components.
The used angle grinder showed somewhat higher vibration compared to the new machine, possibly as a result of bearing wear, but angle grinders are very sensitive to wheel balance and other factors. The vibration exposures measured on the concrete planers, which are essentially an angle grinder with a diamond cup wheel and a dust hood, were lower for the used machine.
Overall, no clear evidence was found to suggest that the vibration emission from a used but good-condition electric power tool will be substantially different to that declared for a brand-new example of the same make and model.
Staying sharp
Some types of consumable can significantly increase vibration exposure as they wear; others need not. Drill bits, jigsaw blades and other consumables that rely on a sharp point or edge will tend to cause increased vibration exposure as they wear – usually due to the task slowing down, which increases the trigger time per task, rather than the actual level of vibration going up (see figure 1).
Breaker tips, while nominally a ‘sharp’ consumable, rely more on impact energy to shatter the material rather than on the tip’s sharp point. In the test of the combi-hammer, standard and self-sharpening breaker points were used and it was found that the latter did not offer an obvious benefit in terms of reducing vibration exposure. As long as the conventional point was angled or rotated to maintain a reasonably pointed shape, the vibration did not substantially increase and the machine still seemed capable of breaking hard concrete effectively.
Self-sharpening points may be of more benefit in dedicated concrete breakers, as these are more likely to wear a tip flat. If a substantial quantity of concrete needs breaking, other methods, such as a vehicle-mounted pick, may be better.
Abrasive discs, diamond blades and other ablative consumables may cause vibration to increase or decrease, depending on their wear pattern, but they should not cause an overall increase in vibration exposure as they wear. Diamond blades used on non-abrasive materials, such as marble, are likely to need periodic sharpening by cutting into an abrasive material such as concrete block.
Also, the fastest blade is not always the optimal choice. A trial of 9-inch diamond blades found that the second fastest blade was the better option for a particular grade of hard concrete. There wasn’t a great deal of difference in cut speed, but the cutting process was markedly smoother.
Fit for the future
Several processes that require the use of power tools can be carried out in a different way with less risk. As vibration is essentially lost energy, a lower vibration process can be more efficient and may offer other safety benefits, such as lower noise, or a reduced spark chain.
The HSE wants to eliminate new cases of disability due to HAVS by 2015. Good practice is continually evolving as processes change and new equipment is developed, or adapted for other uses. Engaging with supply partners, tool users, regulators, collaborators and even direct competitors can help push vibration exposures down. Good suppliers will be able to offer advice and support on best practice, and even provide test results for various pieces of equipment tested for vibration exposure.
References
1 HSE (2011): Evaluation of EN 60745 test codes (Research Report 868) – www.hse.gov.uk/research/rrhtm/rr868.htm
2 The study was carried out at the VJT Test Laboratory and the results were presented at the UK Conference on Human Response to Vibration, hosted by the Health and Safety Laboratory in Buxton in September 2011
Tom Gunston manages the product-test laboratory at VJ Technology.
The Safety Conversation with SHP (previously the Safety and Health Podcast) aims to bring you the latest news, insights and legislation updates in the form of interviews, discussions and panel debates from leading figures within the profession.
Find us on Apple Podcasts, Spotify and Google Podcasts, subscribe and join the conversation today!
