Working with construction powered hand tools such as drills, saws, etc. can pose several risk factors to the operators, including excessive vibration.  Gemne (1997) has listed some of the disorders that vibration could cause including: Hand-Arm Vibration Syndrome (HAVS), disturbance of finger skin circulation, diffusely distributed finger neuropathy, carpel tunnel syndrome etc. Excessive amount of vibration could affect different parts of body: 

• Vibration could affect the nerves of the fingers and result in initial numbness and tingling. While these injuries are recoverable if cured in time, neglecting early symptoms could lead to irreversible damage, such as impaired sensibility and limited control even on simple tasks. Carpal tunnel syndrome (caused by pressure on the median nerve in the wrist) also could coexist with HAVS.
• Blood vessels also can be damaged by vibration. “Vibration induced White Fingers” (VWF) or “secondary Raynaud’s disease” happens when the blood vessels become narrower due to vibration and cannot receive oxygen from the blood, causing white spots on operators’ hands and fingers. This results in major discomfort and pain when the blood flow returns to normal. Symptoms include numbness, tingling, ashen skin, loss of feeling and control. In more serious cases, in which the whole body is affected by vibration, workers experience low back pain and numbness in the upper legs.
• Muscles also are affected by vibration. While it is usually difficult to show the damage of high-vibration tools to the muscles, “microscope studies have shown that there may be significant changes in the fibers” (https://www.vibrosense.eu/knowledge-bank/medical-background/hand-arm-vibration-injuries). 

OSHA classifies all of these injuries under “Musculoskeletal disorders" (MSDs), and warns that “excessive vibration, usually from vibrating tools, can decrease blood flow, damage nerves, and contribute to muscle fatigue”. (https://www.osha.gov/Publications/osha3125.pdf). Obtaining low-vibration tools is a practical way to minimize the impacts of vibration on workers and to avoid subsequent injuries.

As mentioned above, the UVP system acts mainly through two separate mechanisms: 1) a spring-type dynamic vibration absorber and 2) a vibration-absorbing handle. The main mechanism consists of a counterweighting dynamic vibration absorber as demonstrated in Figure 2. In vibration cycles, every time the force is directed toward the worker’s body, the vibration absorber causes the weight to move in the opposite direction and absorb the force and reduce the movement. In the opposite situation, when the force tries to move the tool away from worker’s body, the springs move the weight toward the body, which cancels the effect of tool’s force (Figure 2a). In some cases, coil springs assist with weight movement (Figure 2a), while in others leaf springs have been used to create the same effect (Figure 2b).

Figure 2. UVP system in Rotary hammer drills. a) with coil spring, b) with leaf spring

The second simpler mechanism places several dampers (usually rubber) around the handle’s shaft to absorb the vibration and reduce its transfer to the operator’s body. Figure 3 depicts this mechanism in a demolition hammer.

Figure 3. Vibration absorbing handle for demolition hammer

Metabo HPT
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