Chapter 12 Guidelines for Whole-Body and Segmental Vibration

Definition Vibration is the oscillatory motion of a body rapid changes in direction of a body high acceleration

Definition Vibration is the oscillatory motion of a body rapid changes in direction of a body high acceleration

Definition Vibration is the oscillatory motion of a body rapid changes in direction of a body high acceleration Any body with mass and elasticity may vibrate machines structures human body

Two Classifications of Vibration: Free vibration when a system oscillates under the action of internal forces only Ie water-balloon in the air Forced vibration caused by external forces Opera singer and glass external force: sound waves glass vibrates

Quantifying Vibration Rate of oscillation Regular ==> periodic motion sine wave rep time = frequency Hertz ==> Hz Magnitude of oscillation size of the force Peak value maximum stress Average value absolute value Frequency Analysis

Effects: body & segments Primary determinants frequency Magic fingers (1-2Hz) vs “tooth rattling” induce sleep amplitude duration Secondary determinants Point of application: buttocks, feet, hands direction of input --fatigue orientation of segments -- segment mass presence of external supports?

Mechanical & Psychological Responses Mechanical effects strain on different tissues energy is absorbed by tissues and organs (muscles) voluntary & involuntary contractions of muscles (spindles) cause local muscle fatigue Psychological effects stress reactions

Effects on the spine Research suggests that more low back pain occurs at an earlier age in subjects exposed to prolonged vibration ie truck drivers, farmers, bus drivers, pilots

Effects on segments Vibration on segments typically High Hz Low Amplitude Vibration Syndrome (some all, some one) Injured blood vessels Nerves Bones Joints Muscles

Reynaud’s Syndrome (vibration white finger) Cause Vibration=> blocks finger circulation Symptoms Fingers ==> white, pale, cold, & painful. Impact on precision work. Symptoms are intermittent. 90% of the cases appear in women Etiology Changes in blood vessel walls Reflex contraction of blood vessel smooth muscle

Transmission of vibration in UE Tools = random vibration over wide Hz Hz Transmission is linear. Increase in tool vibration = increase in hand vibration Greater grip force attenuates transmission

Vibration Factors

Summary Vibration represents high frequency of application of a relatively low force FIT Best avoided Environment or task modifications Administrative intervention (ie rotation)