Work-Rest Schedules for Hand Tractor Field Operation with Hand-Transmitted Vibration Exposure Limitation

Purpose: The hand tractors produce hand-transmitted vibration, a significant occupational hazard for hand tractor operators. The present study aims to characterize the hand-transmitted vibration of hand tractors under various engine rotational speeds (1400 rpm, 1700 rpm, and 2000 rpm) and soil implements (moldboard plow, rotary harrow, and leveler) and develop work-rest schedules for hand tractor operations. Methods: The study involved field experiments in soil wet preparation and soil dry preparation operations to measure the vibration acceleration at the handle grip and the operator’s physiological cost of work. The data was then analyzed to obtain the maximum allowable time based on the American Conference of Governmental Industrial Hygienists (ACGIH) limits and the National Institute for Occupational Safety and Health (NIOSH) calculations. Results: The results showed that vibration acceleration was significantly affected by engine rotational speed and the soil implement used. The vibration acceleration was highest on the x-axis, followed by the z- and y-axis. The maximum allowable time was 3 h/day/operator and 2.5 h/day/operator and divided into four and five work bouts with 45 min and 30 min each for wet and dry soil preparation, respectively. The heart rate data indicated that at least 15 min of rest should be given in between work bouts, with an additional 30 min and 15 min of free time for each wet and dry soil operation, respectively. Conclusions: Based on this research, a work-rest schedule was designed for two hand tractor operators who work alternately to minimize hand-arm vibration syndrome.