THE EFFECT OF SEAT SUSPENSION ON EXPOSURE TO WHOLE-BODY VIBRATION OF PROFESSIONAL DRIVERS

In this study the effectiveness of the seat suspension on the transmission of whole-body vibration through the driver's seat has been determined. Eleven types of seat frequently used in lorries, agricultural tractors and fork-lift trucks were selected. The transmissibility coefficient of each seat was measured by the ratio of the acceleration (weighted root-mean-square in the vertical axis) at the interface between the seat surface and the human body to the vibration at the attachment points of the seat on the vehicle floor. Measurements in the laboratory, using standardized representative vehicle vibration spectra and two volunteers of different weights, showed transmissibility coefficients of 0.34-1.28. Attenuation of the vibration input spectrum was obtained in 20 out of 24 (83%) measurements. Measurements in the field, conducted in vehicles under representative working conditions, showed transmissibility coefficients of 0.60-1.45. Attenuation of the vibration spectrum was obtained in 17 out of 24 (71%) vehicle-seat combinations. No significant differences were observed between seats with conventional suspension and those with air suspension. Laboratory measurements of the dynamic response of the seat suspension did no provide an adequate basis for predicting its performance in the field. In most work situations the magnitude and duration of vibration exceeded the 8 h fatigue-decreased proficiency boundary of 0.32 m s-2 in the vertical axis, which indicates that in many working situations with a daily exposure of 8 h or more suspended seats will not protect professional drivers from harmful exposure to whole-body vibration.