Human vibration is defined as the effect of mechanical vibration in the environment on the human body. During our normal daily lives we are exposed to various sources of vibration, for example, in buses, trains and cars. Many people are also exposed to other vibrations during their working day, for example, vibrations produced by hand-tools, machinery or heavy vehicles.
Just as sound can be either music to the ear, irritating or harmful noise, human vibration can be pleasant, unpleasant or harmful. Gentle vibrations, such as that experienced when sitting in a rocking chair, dancing or running are pleasant. More violent vibrations, for example, those experienced when travelling in a car down a bumpy road or when operating a power tool, are unpleasant or harmful. The harmfulness of vibration depends on its intensity and frequency content, and the time of exposure.
There are two main types of human vibration – whole-body vibration and hand-arm vibration.
- Whole-body vibration is transmitted to the body as a whole, mainly through the supporting surface (that is, feet, buttocks, back, etc.). Prolonged exposure to whole-body vibration can either cause permanent physical damage or disturb the nervous system.
- Hand-arm vibration is experienced through the hand and arm. Daily exposure to hand-arm vibration over a number of years can cause permanent physical damage, usually resulting in what is commonly known as “white-finger syndrome”, or it can damage the joints and muscles of the wrist and/or elbow.
As in the case for noise-induced hearing loss, this “white-finger syndrome” is often diagnosed when it is too late to do anything. Early symptoms are ‘white fingers’ in cold weather, followed by permanent loss of feeling and dexterity.
A lot of research and studies have been made to evaluate the effect of overexposure to human vibration, especially in the working environment. The results have been used to establish international standards that allow human exposure to vibration to be evaluated. The standards involve measurements of whole-body vibration and hand-arm vibration using instruments that fulfil the requirements of the standards. Human Vibration Analyzer Type 4447 is such an instrument. It is a portable system for measurement and evaluation of human vibration and designed for those who wish to monitor and reduce the exposure of human operators to the harmful influences of vibration. It is delivered together with PC software for calculation of vibration exposure to check the action values and limit values as stated in European Directive 2002/44/EC.