Mechanical Engineering

Man v. Machine

Case Synopsis: On the morning of the incident, a machine operator reported that the clamps used to hold a workpiece were not gripping as tight as they normally do. The maintenance worker was alerted to this problem, and he and his helper went to repair equipment. The maintenance worker reported he adjusted the clamping mechanism and asked his helper to press the button to actuate the clamps. The helper moved to the control panel and depressed a button. At that time the two portions of the machine moved together, entrapping and crushing the lower portion of the maintenance worker’s body. The maintenance worker alleged the machine malfunctioned during the repair, resulting in him sustaining serious crush injuries to his lower body. It was further alleged that the equipment lacked the safety system to prevent motion of the machine during maintenance.

Expert Analysis: Investigation revealed that the incident occurred after the maintenance worker completed his repairs on the machine and was testing to verify the adjustments had corrected the problem. Based on the literature for the machine, it incorporated a key operated interlock system. When the key is removed, operation is limited to the workpiece clamping system, thereby preventing the two portions of the machine from moving as they did in the incident. Inspection of the machine verified that the interlock system was functional and with the key removed, only the workpiece clamps were functional. Deposition of plant personnel present at the time of the incident indicated the key had not been removed from the machine by the maintenance worker or his helper as required by the facility’s written lock-out, tag-out procedures. The instructions for the machine also stated that prior to personnel entering the space between the two portions of the machine, the key shall be removed from the control panel. The instructions further stated the key should not be placed back into the control panel until all personnel have exited the area between the two portions of the machine.

Analysis showed that the incident occurred due to the failure of the plant personnel to properly secure the machine as required by both the facility operations’ requirements and the manufacturer’s instructions. Had the maintenance worker or his helper removed the key from the control panel, the two portions of the machine could not have moved, and the maintenance worker would not have been entrapped or crushed. Additionally, it was determined that the helper who was at the control panel was unfamiliar with the equipment and depressed the incorrect button, and rather than activating the workpiece clamps as the maintenance worker intended, he mistakenly restarted the machine. Again, had the key been removed from the control panel, this mistake would have had no effect, as the machine startup would have been disabled.

Result: Based on the ability of the machine manufacturer’s expert to identify the cause of the incident, the maintenance worker’s improper use of the equipment, and the error of the helper in depressing the incorrect button, the claims against the machine manufacturer were withdrawn.

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