Absorption of vibration energy in the human hand and arm

Abstract: The risk assessment of hand-arm transmitted vibration is today based on measurements of the magnitude, frequency spectra and duration of the vibration stimuli. It is, however, reasonable to assume that the detrimental effects might depend on the vibration energy absorbed by the hand and arm. Therefore, the aims of this thesis have been to; (i) examine the mechanical and energy absorbing properties of the hand and arm during vibration exposure, (ii) perform theoretical calculations of the amount of absorbed energy, (iii) compare the calculated results with direct measurements. The results show that the mechanical and energy absorbing properties depend on the frequency and direction of the vibration stimuli. Higher vibration levels, as well as more firm handgrips, resulted in higher impedance and absorption of energy. The constitution of the hand and arm also affected, the results to a large extent whereas the varying hand-arm postures had only a small influence. Using the vibration characteristics for a certain tool and the mechanical properties of the hand and arm, a good agreement between theoretical calculations and direct measurements of the amount of absorbed energy could be established. Furthermore, the shape of the frequency spectra for the energy absorption was found to be unequal for different vibration directions and not in accordance with the currently used frequency weighting routine. Finally, the findings support the idea that future standards for risk assessment of vibrations should rather be based on the energy absorption concept.