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Bad vibrations

By Linda Johnson
| www.cos-mag.com

Using tools that vibrate less can reduce MSDs

Manufacturers of vibrating tools can reduce the incidence of musculoskeletal disorders (MSDs) among workers by redesigning the tools and making them lighter, according to a new study.

The purpose of the study, conducted by the Montreal-based Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), was to measure the transmission of vibration and muscle load based on different biomechanical variables. Researchers measured the effects of factors, including the wrist tilting and grip strength exerted on tool handles, on vibration transmission and muscle load.

By moving the centre of gravity of a tool closer to the wrist, as well as reducing the tool’s weight, manufacturers can help alleviate some of the effects of vibration to the upper body, the study found. Some commonly used vibrating tools include jackhammers, chainsaws, circular saws, hand-held grinders and buffing machines.

Vibrating tools can cause a range of health problems. Hand-arm vibration is recognized as the cause of white finger, a painful vascular disorder, says IRSST researcher Pierre Marcotte. But, while the association between vibration and white finger is well recognized, the connection between vibration and MSDs has been more difficult to establish.

“You can get musculoskeletal disorders without vibration, so we don’t know how much vibration contributes to the disorder. That’s what we wanted to assess,” Marcotte says. “We know that vibration has an effect on muscle load, but it’s always hard to quantify.”

This study is very useful because the studies that will follow on from it will serve as benchmarks for manufacturers of impact tools and hammer tools, says the study’s lead author, Denis Marchand, professor in the department of anthropokinetics at the Université du Québec à Montréal.

“For example, one would need only to design lighter tools whose centre of mass was closer to the hand to reduce the grip force required to use them and thus reduce the vibration transmitted to the muscles of the upper limbs,” he says.

The study, Vibrating Tools: Biomechanical and Sensorimotor Parameters Affecting the Biodynamic Response of the Hand-Arm System, is the first systematic analysis of the effects of vibration on a range of muscles, Marcotte says.

Tammy Eger, associate professor in the School of Human Kinetics at Laurentian University in Sudbury, Ont., and who recently co-chaired a conference on vibration at the University of Guelph, is at the centre of a lot of current research into the effects of vibration on workers.

Some researchers, she says, are examining how risk of injury is increased when vibration exposure is combined with other ergonomic risk factors, such as awkward working postures (non-neutral wrist postures, high repetition, heavy force and cold exposure).

“There’s evidence to suggest that where workers are exposed to vibration while in extremely poor, bent postures, lateral bends or twisted postures, there’s increased rate of back injury among those workers,” she says.

Another area of research is possible differences in gender response to vibration. While further study is needed, Eger says, current evidence points to some gender difference. For example, one conference speaker

discussed how, when seated, men and women have different postures.

“There is potential that vibration is going to travel through into the trunk of the woman differently than the man. That may indicate why some seats are designed in a way that women find them more comfortable and they may work better from the woman’s perspective to attenuate vibration than from a man’s perspective,” she says, noting the difference is in part caused by a difference in mass between men and women.

Eger says vibration can enter the body at any point that is in contact with a vibrating surface: at the hands (hand-arm vibration), buttock and back (whole-body vibration) or feet (foot-transmitted vibration).

Workers subject to whole-body vibration — transport truck drivers and operators of mobile equipment used in construction, mining and agriculture — often suffer lower back pain, spinal degeneration and neck problems. They may also suffer gastrointestinal tract discomfort, headaches and nausea.

Hand-arm vibration exposure causes hand-arm vibration syndrome (HAVS), Eger explains. In addition to vascular disorders such as white finger, it is associated with neurological and musculoskeletal problems of the hand-arm system. Exposure to foot-transmitted vibration may cause an analogous syndrome in the lower extremities, referred to as vibration-induced white-feet.

Researchers are also looking at

the design and materials used to make gloves and boots to discover ways

to attenuate vibration. However, before turning to personal protective equipment (PPE), Eger says, it’s

better to reduce risks posed by

vibration exposure by following the hierarchy of controls (elimination, substitution, engineering, administration and PPE).

Linda Miller, president of EWI Works, an ergonomics consulting firm in Edmonton, agrees alleviating the effects of vibration requires a wide variety of controls.

For employers, one of the most effective ways to reduce the risk of HAVS is to provide workers with the right tool for the particular job. Tools should not feel awkward or uncomfortable and should be the proper size for both the hand and the work area.

However, she notes, factors other than the tool itself can play a role in how vibration affects the body. These risk factors include: the duration of the exposure to the vibration; how the person uses the hand tool or operates the vehicle; and how well the tool or vehicle is maintained.

The approach to reducing whole-body vibration is three-pronged, Miller says. First, the risk can be modified at the source. Employers should monitor road quality, regularly repairing and smoothing out uneven surfaces. Tires should be appropriate for the vehicle, and correct tire pressure should be maintained. Large equipment, too, must be properly maintained.

The next goal is to reduce the transmission of vibration from the source to the person by improving vehicle or machine suspension; selecting the right seating for the vehicle and exposure; and by ensuring the seat is adjusted to the worker’s height and weight.

Finally, Miller says, it’s critical to educate workers on proper operating posture and on the importance of taking breaks to limit the duration of vibration exposure.

“It’s amazing how many people on their breaks end up sitting the whole time in the vehicle,” she says. “During your breaks, try to get out of your vehicle; try to walk around. Move around because (sitting) is still a very static posture,” she says.

Going forward, researchers will continue to examine the link between vibration and specific disorders.

“And there’s a lot of research occurring into what controls are truly effective. How do we control the vibration? How can we improve the worker environment so we have less risk for injury?” says Miller. “So there’s some really exciting things being done.”

Linda Johnson is a freelance writer based in Toronto. She can be reached at lindajohnson@sympatico.ca.

 

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