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Whole-body vibration

October 1, 2009

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It may be a major occupational hazard. Why do so few safety professionals know anything about it?

KEY POINTS
  • Whole-body vibration has been linked to adverse health effects, including lower back pain, musculoskeletal problems and digestive problems.
  • More than two-thirds of U.S. safety professionals in a survey had a less-than-basic understanding of whole-body vibration.
  • Vibration hazards can be mitigated through the proper use of well-maintained equipment.
By Kyle W. Morrison, associate editor

Imagine an occupational hazard that affects millions of workers and potentially contributes to one of the main reasons people see a doctor for pain. One might expect a specific standard that addresses this hazard, employees to realize what injuries the hazard may cause, and safety and health professionals to be knowledgeable about the subject.

However, no such standard exists. Employees who are being hurt may not even realize their injuries could be the result of this hazard. And perhaps worst of all, more than two-thirds of American safety professionals have a less-than-basic understanding of the problem.

This is the reality of whole-body vibration. Whole-body vibration occurs when the entire body is supported on something that shakes, typically sitting on a machine or vehicle, said Michael Griffin, professor of human factors at England’s University of Southampton. The mechanical vibrations from the machine are then transmitted into the entire body at various frequencies.

“We know whole-body vibration can cause injury, but the research and available information is not as much as it needs to be,” Griffin said.

Lack of knowledge

At first glance, whole-body vibration may not appear to be so serious. According to the Bureau of Labor Statistics, the number of occupational injuries or illnesses involving days away from work caused by “rubbed, abraded, or jarred by vibration” was 1,750 in 2007. However, these numbers may not accurately reflect the damage vibrations can do for various reasons.

In the United States, an estimated 6 million American workers are “regularly exposed” to whole-body vibration – meaning for more than two hours a day, according to Kristine Krajnak, a research biologist with NIOSH. This can lead to an array of health problems – most notably lower back pain, which is second only to colds and flu for reasons why Americans see a doctor, according to the National Institutes of Health.

Lower back pain has a “huge” economic impact, Krajnak said, adding the pain often becomes chronic, possibly affecting job performance and leading to hours away from work for doctor visits. Evidence also exists linking whole-body vibration to musculoskeletal problems, digestive problems and prostate problems, as well as miscarriages in women. Although research shows vibration is a major risk factor for various injuries, Krajnak said, the extent to which it contributes to those injuries is a bit of an unknown.

Vibration types
Vibration types Several different types of occupational vibration can be hazardous to the human body. Hand-arm vibration: Results when a piece of equipment, such as a chain saw or drill, transmits vibrations to the limb holding the equipment. Can cause circulatory damage, commonly known as “white finger.”
Whole-body vibration: Results when the entire body is supported – through standing, sitting or reclining – on a piece of equipment and absorbs the mechanical vibration from that equipment.
Low frequency: Vibrations occurring at a low level that can cause motion sickness or postural insatiability.
Noise: Noise travels through the air via vibrations; too much can lead to hearing loss.

“It’s really difficult to actually quantify,” said Ren Dong, senior research engineer at NIOSH. Dong noted that other risk factors such as posture or heavy lifting could contribute to injuries either alone or in tandem with vibrations. As a result, injuries caused by vibrations are likely to be underreported, he said.

In fact, so little data exists on whole-body vibration that outside of estimates, it is hard to know exactly how many Americans are exposed to the hazard and how many may be at risk of injury or illness due to their exposure.

“I don’t think any country has [good] statistics,” Griffin said. “That’s a problem.”

Given the lack of hard numbers on injuries from whole-body vibration – or even exposures to whole-body vibration hazards that could cause injuries – it may be no surprise that so few safety professionals have a great understanding of the issue.

A recent study published in the National Safety Council’s Journal of Safety Research (Vol. 40, No. 3) found that 69.5 percent of 2,764 U.S. occupational safety and health professionals who responded to a survey had little to no knowledge of whole-body vibration.

Using British estimates of workplace whole-body vibration exposures and applying them to U.S. demographics, the study estimated that as many as 29 million U.S. workers have occupational whole-body vibration exposure – 1.2 million of whom may experience exposures at “potentially significant levels.” Based on the results of the study, these 1.2 million workers “may not be adequately supported by occupational S&H professionals with sufficient WBV knowledge.”

With lower back pain being the largest risk of whole-body vibration hazards, and occupational back injuries accounting for nearly 20 percent of all workplace injuries and illnesses, the door could be opened for worker injuries if safety professionals are not up to date on vibration hazards.

Helmut Paschold, study co-author and assistant professor at Ohio University in Athens, said he was not surprised by the results of the research, but was concerned. “What it tells us is that we just need to start talking about it,” he said.

Accumulation

When it comes to whole-body vibrations, it is important to realize that not all cause injuries, and not all injuries that do surface – such as lower back pain – are caused by vibrations. Just about everyone is exposed to whole-body vibration to some degree, be it from driving a car or riding in an airplane or boat, Dong said. For most people, he said, these types of exposures will not cause injury.

People who are at risk are those in occupations such as agriculture, construction, mining and truck driving who operate heavy equipment, particularly the type of machinery that engages with the earth. Even then, those workers are not necessarily at immediate risk of injury due to the vibrations.

“Whole-body vibration is something that’s definitely a cumulative-type factor,” Paschold said. “Five minutes of it won’t cause you a problem. But it’s a matter of intensity and duration. That’s a hard thing to tie down.” Paschold gave the example of a worker who has been operating construction equipment. For six hours a day, the worker sits while operating the machine. One day, the worker climbs out of the cab, jumps to the ground and suffers a back injury. This type of injury used to be a mystery, Paschold said. Now, he believes such injuries may be the result of a stressed back caused by whole-body vibration.

Linking vibration to a particular injury can be difficult. Injuries such as these may take years and can first appear to be caused by something similar to a drop to the ground or lifting of a box rather than vibrations. Knowing how the length of exposure to whole-body vibration is associated with the risk of developing an injury is one of the big questions researchers are trying to tackle, Krajnak said.

“If you have an accident and cut your arm off, you know the cause of [the injury],” Griffin said. “If it takes you 10-20 years, it’s very difficult to know what caused it.”

Despite this, or perhaps because of it, attempts have been made to curb the hazard.

Risk reduction, user control

Ideally, a worker would never be exposed to vibrations, said Patrick Dempsey, acting team leader of NIOSH’s musculoskeletal disorder prevention branch in Pittsburgh. Because so many types of equipment cause vibrations, that ideal scenario is unlikely to play out, as is the complete elimination of the hazard. “You’re not going to eliminate the vibration, but in some cases you can certainly limit the magnitude of exposure,” Dempsey said.

At Peoria, IL-based Caterpillar, the manufacturer has been installing equipment on machinery to limit vibrations since the 1940s in an effort to decrease the impact of vibrations and ease the comfort of the user. Michael Contratto, senior engineering specialist at Caterpillar, stressed that Caterpillar is concerned about not only reducing vibration risks, but also improving the ergonomics of the operation by taking into account where a machine’s controls are and what position or posture the user must take to operate the device. Doing this, Contratto said, can help mitigate other factors that can cause injuries.

Simple administrative controls also can reduce risks associated with vibrations, Dempsey said. Workers can be rotated out of certain devices to limit exposure, or provided equipment with better seats designed to reduce vibration transmission. Ensuring the equipment is running well can reduce vibrations, as can maintaining roadways and reducing unevenness in road surfaces, he said.

Employees should be well-trained on safe operation of machinery and proper posture, Paschold recommended. Many workers may not like a “floating” seat, but they need to be made aware that making the seat more rigid increases the level of vibrations. Workers should be encouraged to reduce vehicle speeds, especially on rough terrain, he said.

“One of the key points of a machine vibration is that the operator and owner of the machine has more control over the vibration level than the machine manufacturer does,” Contratto said.

He compared the operation of work equipment and vibrations to that of a car. When driving a car, one can control how fast the vehicle goes. “How rough of a ride you get depends on what kind of road you’re driving on and how fast you’re driving,” he said. Driving at a high speed on an unpaved road is likely to produce more vibrations than a slow speed on a paved road.

In the past, buyers have wanted some vehicles, such as bulldozers, to be able to travel at a faster speed while using the blade to move earth, Contratto said. But when the dozer moves faster, the machine creates more vibrations and is unable to carry a larger load. Running the dozer slower may mean it cannot go from Point A to Point B as quickly, but as Contratto pointed out, it also means fewer vibrations and the ability to carry a heavier load. In the end, an employee could get more work done in the same amount of time with fewer vibrations.

“Just because they weren’t moving as fast doesn’t mean they weren’t as productive,” Contratto said. Echoing Contratto, Griffin said some employees may associate vibrations with working hard or working “better.” He stressed that even if roads and equipment are well-maintained and employees have been provided state-of-the-art seating, vibration mitigation may be negated when workers operate the machinery in such a way that pushes them back into potentially hazardous vibration levels. As such, employers need to educate their workers on the effect a user can have on the vibrations a piece of equipment emits, Griffin said.

Developing standards

The United States currently has no standard addressing whole-body vibration. Closely linked to the field of ergonomics, talk of a whole-body vibration standard may lead some to recall the contentious debate on OSHA’s ergonomics standard a decade ago – a standard that was overturned in 2001 before it could take effect. Paschold said a potential vibration standard would be easier to implement, meaning vibrations are a quantifiable force and could be structured parallel with a hearing conservation program.

“You can measure it … as you do with noise,” he said. All that would have to be determined is the permissible exposure limit and action levels, which may be difficult, as estimates to the number of workers exposed at a dangerous or unhealthy level is sparse at best.

Attempts to find such levels have been made. Several countries, including the Uni­ted Kingdom, have standards addressing vibrations; the International Organization for Standardization has several standards relating to whole-body vibration. The American National Standards Institute has voluntary standards similar to those of ISO, as does the American Conf­erence of Govern­mental Industrial Hygienists.

Paschold does not have any high expectations that whole-body vibration standards will appear in the United States overnight. As data improves and more research is done, however, he is hopeful that the safety community will come together to address the issue and OSHA will formulate a standard.

“It’s significant enough to be addressed,” Paschold said.

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