An apprentice mechanic lacerated his right forearm while quickly sliding out from under a hydrogen prototype bus when the bus slipped off a hydraulic jack. The apprentice and another mechanic had raised the bus about 1 foot from the ground to position it on jack stands when the hydraulic jack tipped over. The apprentice went to the site medical facility, where he needed five stitches to close the wound in his forearm.
The mechanics were raising the rear of a hydrogen prototype bus, like the one in the figure below, and placing it on jack stands. After chocking the wheels, they used bottle jacks on each side of the rear axle to raise the bus high enough to place a 20-ton hydraulic jack under the differential. With the bus resting on a pair of small jack stands, they raised the bus by the differential so that the weight of the bus was balanced on the hydraulic jack.
The mechanics then began to place a large jack stand under the driver's side of the bus. The mechanics were under the bus positioning the jack stand when the mechanic noticed that the hydraulic jack was beginning to tip, and he called out to the apprentice that the bus was coming down. The jack tipped to one side, causing the weight of the bus to drop suddenly onto the small jack stand on the passenger side of the bus. As the apprentice slid from under the bus, the weight of the bus landed on the small jack stand under the passenger side, causing it to break and drop the rear tire to the ground. The apprentice cut his right forearm on a jagged metal edge on the storage compartment as he moved out from under the bus.
The construction manager ordered a root cause analysis, which revealed a number of causal factors. The most obvious of these was the small jack stand breaking and dropping the bus to the ground on one side. Even more significantly, the work package failed to provide adequate information on the type of bus and environment in which the mechanics would be working, and no procedure existed for jacking up vehicles. Investigators were unable to conclusively determine the reason the hydraulic jack tipped.
The work package did not describe the bus that would be involved: a hydrogen prototype bus that is heavier than conventional fuel bus models and has an uneven lateral weight distribution. The bus’ total weight was 30,000 pounds, two-thirds of which was in the rear. The mechanics had never worked with this type of bus before, and were unprepared for the task. They proceeded to perform the task as they had done in the past with conventional buses.
The work package did not specify a safe location for working on this type of bus. The bus was sitting on an asphalt surface, with a slight slope toward the front, and was locked. The mechanics had no way to move it onto a concrete pad, which would have provided greater stability.
The mechanics were relying on skill-of-the-craft to perform this work because there was no procedure on safely jacking heavy vehicles. They did not use cribbing to more evenly distribute the bus’ weight, and the hydraulic jack was not equipped with a saddle or cup to prevent slipping. A procedure on jacking up vehicles would have significantly reduced the likelihood of this accident.
Following the critique, the construction manager began developing a procedure on jacking and cribbing mobile equipment. Training will be provided to mechanical personnel when the procedure is complete. In addition, the construction group will develop a system for identifying work requests involving different mobile equipment.
- Motive Power Systems
- Hydraulic Jacks
This event illustrates the importance of adequately planning and communicating work. Procedures should cover all types of equipment that will be utilized. Work packages should clearly describe the equipment that will be used and the surrounding environment. Workers should be aware of potential hazards and unknown configurations before they begin work. Job hazard analyses should identify all situations that could pose a hazard to workers.