عباسعلی رجبی

Vibration of body especially that of hand-arm is a key factor in developing inconvenience in drivers, which decreases efficiency, triggers fatigue and disturbance in physiological activities, and finally predisposes drivers to occupational diseases and traffic accidents. This study examines the effect of hydraulic steering wheel system on controlling and attenuation of the vibrations transmitted to driver’s hand-arm. This cross-sectional study was carried out according to convenience sampling on two perfectly homogeneous automobile groups (15 with hydraulic steering wheel and 15 without hydraulic steering wheel). Steering wheel vibration measurement was carried out in three vibration axes and three specified positions of automobile movement (in the same atmospheric and physical conditions) using Bruel & Kjaer-2231 Vibrometer. The data were analyzed by SPSS 11.5 using t-test and two-way ANOVA. The results indicated that the superior effective acceleration axis in the two groups. of automobiles and in three measurement positions is axis Y. Comparing the results with the 4-hour standard showed that in all positions the effective acceleration (in rms) is less than the permitted exposure limits and care limits (p<0.05). Also, compared to the standard 8- and 16-hour values, some of the positions were higher than the permitted and care limits (p<0.05) and some had no significance difference from the standards (p≥0.05). Two-way ANOVA showed that the type of steering wheel system, speed, and gear (measurement positions), independently, simultaneously, and jointly, are effective on the vibration transmitted to the drivers’ arm (p<0.05). In contrast to the whole body vibration where axis Z has been reported as axis with superior effective acceleration, in the vibrations derived from steering wheel the axis with superior effective acceleration is axis Y and the hydraulic steering wheel can significantly decrease the vibration transmission to the drivers’ hand and arm. On the other hand, the decrease in hours spent for working with the automobiles without hydraulic steering wheel can be considered as a very useful managerial tool.