Localized vibration, such as vibration of the hand and arm, occurs when a specific part of the body comes into contact with vibrating objects such as powered hand tools (chain saw, electric drill, chipping hammer) or equipment (wood planer, punch press, packaging machine).
Whole-body vibration occurs when standing or sitting in vibrating environments (driving a truck over bumpy roads) or when using heavy vibrating equipment that requires whole-body involvement (jackhammers).
Although using powered hand tools (electric, hydraulic, pneumatic) may help to reduce risk factors such as force and repetition, they can expose employees to vibration.
Vibrating hand tools transmit vibrations to the operator and, depending on the level of the vibration and duration, may contribute to the occurrence of Raynaud's phenomenon (i.e. vibration-induced white-finger MSDs) (Ex. 26-2). Vibration inhibits the blood supply to the hand and fingers, which leads to numbness and tingling in the fingers.
These vibration-induced MSDs show a progression of symptoms beginning with occasional or intermittent numbness or loss of color (blanching) in the tips of a few fingers. Continued exposure leads to more persistent attacks, affecting greater parts of most fingers and reducing feeling (tactile discrimination) and manual dexterity (see the Health Effects section for a more-detailed discussion of specific MSDs).
The level of vibration can be the result of bad design, poor maintenance, and age of the powered hand tool. For example, even new powered hand tools can expose employees to excessive vibration if it they do not include any devices to dampen the vibration or in other ways shield the operator from it. Using vibrating hand tools can also contribute to muscle-tendon stress and fatigue. Operators may have to use increased grip force to steady such hand tools.
Most jobs that involve contact with vibrating surfaces, machines and vehicles are easy to see, hear or feel. Since many products and processes are disturbed by vibration, employers often isolate and dampen vibration to levels below the threshold of effect on workers. However, there are some processes for which vibrating surfaces are unavoidable. An employee who comes into contact with such a surface may absorb enough vibration energy to create a health concern. Exposure to vibration energy usually results in one of two types of exposure - whole body vibration and hand/arm vibration. The exposures can result in an increase in forceful exertions, fatigue, numbness, tingling, and a loss of dexterity. These results are exacerbated by the presence of a cold environment.
Work conditions that involve sitting, standing or lying on a vibrating surface produce whole-body vibration. Excessive levels of whole-body vibration or exposure to it for prolonged periods can make it difficult to perform job tasks due to numbness and tingling and a loss of dexterity. Vibration energy can disrupt blood flow and affect the nervous system. Body parts that absorb the vibration (like the back and knees) are particularly vulnerable. Workers who stand on vibrating surfaces absorb most of the vibration energy in their legs, particularly the knees. Whole body vibration forces on the spinal discs can cause micro fractures in the disc structure, which may lead to herniated or ruptured discs. Vibration can also disrupt the blood supply to the tissue around the spine, resulting in fatigue and inflammation. When the feet or buttocks are in contact with a vibrating surface, injury is usually to the spine.
When the hands are in contact with a vibrating surface, the energy is primarily absorbed in the hands and arms and may lead to hand-arm vibration illnesses. The most common sources of hand-arm vibration syndrome are vibrating hand tools (chainsaws, rivet guns, back pack leaf blowers).
Some more subtle sources are holding pressurized hoses with nozzles, using a striking device such as a hammer, resting the hand on a vibrating machine, and holding a handle such as a steering wheel attached to a larger piece of equipment. In addition to the damage that is caused by the vibration energy, the muscles can become fatigued and strained due to the additional forces needed to compensate for the lack of tactile feedback and dexterity caused by the vibration. These losses are a result of the disruption of the peripheral sensory nerves caused by vibration. When the hands are in contact with a vibrating surface, injury is usually to the hands and arms.