Husqvarna is moving in the direction of selling robots to demolish concrete, separating workers from exposure to vibration issues. Workers stand away from the machine and use joysticks to control the robot's movement.
Photo credit: Husqvarna
Manufacturers of hand-held tools reduce vibration acceleration by selling handles that "de-couple" from the tool, limiting most vibration from reaching the operators hands.
Photo credit: Joe Nasvik
Manufacturers are designing their tools to minimize vibration. For example, Bosch's DH1020VC SDS-max demolition hammer features an extended air cushion in the hammer mechanism and a de-coupled main handle to reduce vibrations in two locations inside the tool.
There’s much to be concerned about when it comes to the impact and vibration from tools and equipment. Almost all equipment on a jobsite vibrates to some extent — some much more than others. Over time, this exposure can have negative repercussions on the operators.
Thomas McDowell, a research engineer for the National Institute for Occupational Safety and Health (NIOSH), says the damage to a person’s body is primarily dependent on the magnitude of the acceleration; the frequency spectra of the vibration generated by the tool; and the length of worker exposure time. Other important factors include the environment a person is working in, their posture, their physical condition and potentially their genetic background.
If you use tools with higher levels of vibration or impact, over time permanent damage to your hands, arms, back, legs and joints can result. Here’s what you should be aware of, as well as how equipment manufacturers are trying to make their products safer to use.
How our bodies react to vibration
Long-term exposure to hand-transmitted vibration from using powered hand tools can lead to a disorder known as hand-arm vibration syndrome. David Rempel, a professor of occupational medicine at the University of California, San Francisco, and professor of engineering at UC Berkeley, is doing research on the effects of impact and vibration to hands and arms. He says these effects cause damage to capillary blood vessels and nerves, which can be serious and irreversible.
Prolonged vibration causes the inner lining endothelial cells to multiply and not function correctly, causing blood to leak through vessel walls. In addition, Kristine Krajnak, leader of the Biological Assessment of Mechanical Exposures team for NIOSH, says their studies show exposure to vibration can result in edema, inflammation and vascular dysfunction. These changes eventually lead to a thickening of blood vessel walls, vascular constriction and a reduction in blood flow.
Nerve damage also results from prolonged exposure to vibration. Rempel says the myelin sheath surrounding nerves gets destroyed, exposing the nerve. (Think of a nerve as an electrical wire and the myelin sheath as the plastic insulation surrounding it.) Nerve fibers also retract, disconnecting from the muscle fiber they activate, resulting in permanent damage.
Although the focus is on hands and arms, your whole body is affected by exposure to vibration and impact. It travels through the limbs to the rest of your body. Joint, neck and back problems can develop when tendons, ligaments, bone and cartilage are damaged.
Mitch Burdick, product manager for concrete tools at Bosch Tools, says regulations and guidelines for establishing vibration limits for power tools come from Europe. “There are no current regulations for tool manufacturing or use limitations in the U.S.,” he points out. Tool companies serving both markets manufacture their products to meet European standards, so U.S. contractors benefit from European requirements.
The European Committee for Standardization (Comité Européen de Normalisation or CEN) is the organization that establishes frequency and time-weighted action and exposure limit values for hand-arm vibrations and whole-body vibrations on the basis of a standardized eight-hour work day. The International Organization for Standardization (ISO) sets the guidelines for the tool manufacturers that test their tools according to established protocols and publish the vibration acceleration values of their tools (expressed in meters per second squared).
In the U.S., there are two voluntary consensus standards: the American National Standards Institute (ANSI) voluntary consensus standard (ANSI S2.70-2006), and the American Conference of Governmental Hygienists standard. These standards established Hand Arm Vibration and Whole Body Vibration Threshold Limit Values. These guidelines recommend methods for the measurement, data analysis, vibration and health risk assessments, and the reporting of human exposures to hand-transmitted vibration.
The U.S. guidelines echo the action and exposure limit values prescribed in the European Union directive established by the CEN. But with no enforceable standard in the U.S. to regulate tool makers, every manufacturer is free to define their tools’ vibration levels as they wish. Burdick thinks the industry would benefit if all manufacturers could agree on the same measurement protocols, such as those established by the ISO.
When you shop for a power tool, it’s difficult to know which manufacturer makes the tool with the least amount of vibration acceleration. You won’t find these numbers printed on the box as they are in Europe. Burdick says buyers must instead look at marketing claims about how they reduce vibration and impact.
How manufacturers reduce vibration
Workers shouldn’t use jackhammers to break concrete or rock for extended periods of time without taking breaks. But Richard Elliott, product development specialist for Atlas Copco, says the company is doing its best to minimize the risk.
Atlas Copco has developed air cushions for the top and bottom of hammer piston strokes to reduce vibration. It also sells optional handles that are linked to the tool by means of springs that are adjusted to decrease the vibration impact to the operator’s hands and arms by as much as 75% when used properly. The company sells its products in Europe, so it follows ISO standards and EU directives in the U.S., as well.
Mark Michaels, director of product management, notes that Husqvarna Construction Products makes remote-controlled concrete saws and demolition robots. “We are moving toward remote controls as a way to completely separate workers from vibration and impact,” he says.
Husqvarna sells breakers and crushers mounted on small track vehicles, allowing workers to stand away from the machine while operating a joystick controller. Wall saws also have remote controls. Walk-behind concrete saws and hand-held power cutter saws generate less vibration because handles are isolated from the crankcases.
The manufacturers of small hand tools such as angle grinders, reciprocating saws, hammer drills and chipping hammers also work to reduce vibration. Burdick says they do this by machining moving parts more precisely, introducing counterweights to minimize impact on hands, improving overall performance and efficiency and developing handles that are “de-coupled” from the tool. Reducing tool size and weight also helps. Rempel’s laboratory is developing a benchtop method for measuring handle vibration for hammer drills.
Nobody wants to experience the physical disability that exposure to vibration acceleration and constant impact can cause. Manufacturers don’t want to cause harm either. But in a very competitive industry, there’s a strong motivation to sell products at the right price. Consequently, the current voluntary guidelines aren’t likely to be adopted by U.S. regulatory agencies anytime soon. Unfortunately, for now, this means workers are put in the position of “let the user beware.”
In the meantime, research continues to strive to understand how vibration and impact affect our physiology and what we can do to minimize the risk. ET
Joe Nasvik is a writer and editor serving the concrete industry. He has 18 years experience as a concrete contractor. Contact him at firstname.lastname@example.org.