Health Hazard Evaluation Report, HETA-99-0283-2855, Yellowstone National Park, Yellowstone National Park, Wyoming.
On July 6, 1999, the National Institute for Occupational Safety and Health (NIOSH) received a request from the Occupational Safety and Health Administration (OSHA) for assistance in conducting an ergonomic evaluation of National Park Service (NPS) personnel who ride snowmobiles at Yellowstone National Park (YNP). The NPS personnel, mainly rangers and maintenance workers, were experiencing musculoskeletal disorders of the hands, arms, shoulders, and back from riding the snowmobiles during the winter months at the park. On February 17, 2000, a NIOSH ergonomics specialist and a medical officer began an evaluation of the ergonomics aspects of snowmobiles and reported symptoms among personnel who routinely use them. A neurobehavioral psychologist administered hand coordination, tremor, and fingertip vibrotactile sensitivity tests to study participants. The study lasted until February 25, 2000, during which time 26 NPS personnel at the Park’s West Entrance, Madison, Old Faithful, Grant, and Mammoth Hot Springs locations were evaluated. During February 23-26, 2000, two additional NIOSH investigators evaluated the vibration and shock accelerations among NPS personnel who used snowmobiles dispatched from the Mammoth Hot Springs, Madison, and Old Faithful locations of the park. The ergonomics evaluation indicated that the snowmobiles used by the NPS personnel had adjustment features to allow for a comfortable seating position for the operator, but that in some cases the rangers and maintenance personnel chose seat positions that resulted in stressful postures for the shoulders, elbows, and wrists. Other adjustments of the snowmobile components such as the height and spacial location of the steering bar could be made with tools in the maintenance department to further improve comfort, but these could not be readily modified in the field, resulting in rangers and maintenance personnel often using snowmobiles not ideally configured for them. The throttle control design was not suitable for worker comfort and the pinch forces needed to depress and hold the throttle in place were fatiguing to the worker. Whole-body vibration measures indicated that the jolts sustained by NPS personnel riding snowmobiles under poor road conditions were high in magnitude and in frequency of occurrence, making the ride very uncomfortable and stressful. The median peak acceleration levels measured on the frame of the snowmobiles ranged from 3.13 to 4.71 g’s (1 g = 9.81 meters per second per second [m/s2 ]). These peak accelerations occurred at a rate of 276.5 peaks per hour when the NPS rangers were patrolling. The suspension of the snowmobiles was not designed to protect the workers from the jolts that occurred while driving on the rough roads. The jolts may also exacerbate the effects of some of the design shortcomings of the snowmobile components and controls. Health effects tests indicated that some workers had abnormal tremor and fingertip vibration threshold scores, and the right hand scores were worse than those of the left hand. However, there was no evidence that these results were due to chronic, irreversible conditions of the study participants. Confidential medical interviews indicated that NPS workers experienced back, shoulder, and hand pain that was consistent with the design features of the snowmobiles, the exposure to whole-body jolts from the poor roads, and the results of the diagnostic fingertip sensitivity and hand coordination tests. NIOSH investigators conclude that routinely riding snowmobiles on the roads at Yellowstone National Park is associated with the development of musculoskeletal symptoms of the back, shoulder, and hands. Poor road conditions and poor design of handle bars and throttle controls on the snowmobiles can cause and aggravate these disorders. Administrative controls and snowmobile component redesign intended to reduce the adverse health effects of riding snowmobiles at the park are contained in this report.