Comparison of subjective responses to vibration and shock with standard analysis methods and absorbed power

Evaluation of human exposure whole-body vibration (WBV) and shock can be carried out in a variety of ways. The most commonly used standards for predicting discomfort from WBV are BS6841 (1987) and ISO2631-1 (1997) which offer different frequency weightings (W-b and W-k) and three methods of assessment: vibration dose value (VDV), estimated VDV (eVDV) and maximum transient vibration value (MTVV). Previous studies have also used DRI and absorbed power for assessments of shock and WBV. This paper reports a laboratory study in which 24 human subjects were exposed to 15 vertical vibration stimuli comprising of random vibration, repeated shocks and combinations of random vibration and shocks at 0.5, 1.0 and 1.5 m/s(2) r.m.s. Subjects rated the discomfort from the vibration on a numerical scale after each exposure. Acquired acceleration signals were analyzed using VDV, r.m.s. and MTVV for unweighted, W-b, W-k and DRI weighted signals. Acceleration and force were combined to give a measure of absorbed power. Subjective responses were correlated to vibration magnitude for the 13 analysis types. VDV was the best standard method of assessment: MTVV was the worst. W-b and rta frequency weightings showed slightly greater correlations between vibration magnitude and discomfort than DRI weighted or unweighted signals. For VDV, there were no significant differences between the correlations obtained using any frequency weighting. For assessment of all stimuli types together, absorbed power gave higher correlations with subjective discomfort than acceleration-based methods. It is concluded that the methods described in ISO2631-1 should be clarified and simplified. Due to the difficulty in measuring absorbed power in the field, methods proposed in BS6841 are recommended as the most appropriate for assessment of discomfort from continuous vibration or repeated shocks. (C) 2000 Academic Press.