Relation between vibration levels and perceptive and appreciative judgements of overhead crane operators

The objective of the study was to determine what conditions of exposure to vibrations were responsible for the complaints by workers and what the maximum acceptable vibration levels should be. Vibration was characterized by the unweighted intensity exceeded during 10% of the time (L10) and by the global weighted equivalent intensity (Leqw) during displacement phases and phases involving successive starts and stops or successive hookings and unhookings of the load. The opinions of the workers concerning the intensities of vibration and of shock, and their appraisal of the vibration, were collected. Results show that workers hardly discriminate between vibrations and shocks, and appear more sensitive to horizontal (X and Y axes) than to vertical (Z axis) vibration. Perception as well as appraisal votes are slightly better correlated with intensities of vibration not weighted according to frequency than with weighted intensities, and more with peak intensities (L10) than with r.m.s. values. The vibration intensity weighted globally, which was normally encountered and unpleasant, appears to be about 115 dB(w), which corresponds to the limit value for the intermediate criterion (efficiency reduced by fatigue) proposed by ISO 2631 (1978).