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12 INDUSTRIAL VIBRATION

In many fields of occupational activity employees are subject to vibration
which is caused by hand-held tools (mechanical vibration) and transmitted to the
body from the driver’s seat or the ground.
Exposure to vibration can severely affect workers’ health.
Thus, general efforts are required to prevent health hazards by taking technical,
organizational or personal precautions.
If exposure levels exceed a specific value (action value), the employees have to
be informed and instructed about the hazards involved and appropriate protection
measures.
Vibrations are mechanical oscillations transmitted to the human body via direct
contact. At low frequencies (3–100 Hz) with a large amplitude (0.5–0.003 mm), a
human perceives oscillation as a vibration.
Vibration is caused by work equipment performing continuous or repetitive
movements, such as power-driven tools, mobile appliances or rotating machines.
Thus, the strain caused by vibration results from vibration intensity and the
duration of exposure.
Hand-arm vibration (HAV) (local vibration) is passing into the human body
through the hand-arm system.
Whole-body vibration (WBV) (general vibration) is transferred to the body
through the legs when standing or through the buttocks when sitting.
By the direction of action, the general and local vibrations are characterized by
the axes of the orthogonal coordinate system (Figure 12.1).

Table 12.1 – Definition of the vibration parameters
Parameters of the vibration Definition
Vibration movement The instantaneous value of each of the coordinates
(s) describing the position of the body or material point during
vibration
Vibration amplitude The greatest deviation of a point that varies with a certain
(A), m frequency from the equilibrium position.
Vibrational speed A kinematic parameter that is equal to the speed of
(υ), m/s, movement (the first derivative of the vibration movement) of
υ =2πfA a point that varies with a certain frequency.
Vibration acceleration A kinematic parameter equal to the acceleration of the
2
(a), m/s , displacement (the second derivative of the vibration
a =2π A/T 2 displacement) of a point that varies with a certain frequency.
2
Vibration period The smallest time interval during which, while the periodic
(T), s vibration, each value of the magnitude that characterizes the
vibration is repeated.
Frequency of vibration The value is inversely proportional to the vibration period,
(f), Hz, which shows the number of oscillations per unit time of the
f=1/T point during vibration.
Vibration speed level Main relative parameter of the vibration.
(Lυ), dB, Where υ- the mean-square value of the vibration speed, m/s;
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Lυ =20lg(υ/υ 0) υ 0- the threshold quantity of the vibration speed – 5*10 m/s.

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