Vibrations and motions are also factors which have an influence on our work performance. Although we hardly face situations in which a maintenance engineer has to use vibrating tools it still occurs. Vibrations in maintenance stem mainly from the use of tools, such as grinding and polishing machines or rivet guns. Engines, for example, are other dangerous sources. Their INFRA-SONIC WAVES can damage internal organs. ULTRA-SONIC WAVES which are above our hearing range can damage nerve canals. The use of vibrating tools results in a reduction of performance and leads to distraction and fatigue. Fingers and hands become numb and it can take a long time for feeling to return to the hands.