It has long been recognized that the effects of direct vibration on the human body can be serious. Workers can be affected by blurred vision, loss of balance, loss of concentration, etc. In some cases, certain frequencies and levels of vibration can permanently damage internal body organs.
Researchers have been compiling data over the last 50 years on the physiological effects of vibrating, hand-held power tools. The "white finger" syndrome is well known among forest workers handling chain saws. Gradual degeneration of the vascular and nervous tissue takes place so that the worker loses manipulative ability and feeling in the hands.
Standards recommend maximum allowable vibration spectra at the handles of hand-held power tools.
The first published international recommendation concerned with vibration and the human body is ISO 2631 — 1978 which sets out limitation curves for exposure times from 1 minute to 12 hours over the frequency range in which the human body is most sensitive, namely 1 Hz to 80 Hz. Later versions of the standard include more details.
The recommendations cover cases where the human body as a whole is subjected to vibration in three supporting surfaces, namely the feet of a standing person, the buttocks of a seated person, and the supporting area of a person lying down.LEARN MORE
HAND-ARM VIBRATION TRANSDUCER SET
Three severity criteria are quoted:
- A boundary of reduced comfort, applicable to fields such as passenger transportation, etc.
- A boundary for fatigue-decreased efficiency, that will be relevant to vehicle drivers and machine operators, and
- The exposure limit boundary, which indicates danger to health.
BY BRÜEL & KJÆR
It is interesting to note that in the longitudinal direction, that is feet to head, the human body is most sensitive to vibration in the frequency range 4 to 8 Hz. While in the transverse direction, the body is most sensitive to vibration in the frequency range 1 to 2 Hz.
A battery-operated vibration meter dedicated to the measurement of vibratory motion concerning its ability to cause discomfort or damage to the human body is available.
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