BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 3

14 - VIBRATION

VIBRATION Vibration is the mechanical oscillations of an object about an equilibrium point. The oscillations may be regular such as the motion of a pendulum or random such as the movement of a tire on a gravel road. If we could watch a vibrating object in slow motion, you could see movements in different directions.

VIBRATION

Any vibration has two measurable quantities. How far (amplitude or intensity), and how fast (frequency) the object moves helps determine its vibrational characteristics. Frequency The number of cycles that a vibrating object completes in one second is called frequency. The unit of frequency is hertz (Hz). One hertz equals one cycle per second. Amplitude - Amplitude is the distance from the stationary position to the extreme position on either side and is measured in metres (m). The intensity of vibration depends on amplitude.

Acceleration (measure of vibration intensity) Acceleration is a measure of how quickly speed changes with time. The measure of acceleration is expressed in units of (metres per second) per second or metres per second squared (m/s 2 ). The magnitude of acceleration changes from zero to a maximum during each cycle of vibration. It increases as vibrating object moves further from its normal stationary position.

Exposure to Vibration Exposure to vibration normally occurs during the operation of powered machinery such as hand tools or whilst travelling on vehicles. –Hand-arm vibration –Whole-body vibration Vibration induced health conditions progress slowly. Vibration-induced white finger (VWF) –Attacks of whitening (blanching) of one or more fingers when exposed to cold. –Tingling and loss of sensation in the fingers. –Loss of light touch. –Pain and cold sensations between periodic white finger attacks. –Loss of grip strength. Bone cysts in fingers and wrists.

Measurement of Vibration Vibration is usually measured by the use of accelerometers. Attached to the hand of a worker or tool. Unlike noise measurements, vibration ones have a subjective element.