Die-cast operator fatally pinned by Unimate robot at Michigan plant

What happened

The incident took place at a Michigan die-casting company that ran 24 die-cast machines, two of them served by robots. The robot involved performed a 27-step cycle lasting about one minute: it removed a casting from the die-cast machine, dipped it in a quench tank and placed it in a trim press.

At about 1:15 p.m. on July 21, 1984, a coworker found the 34-year-old operator pinned between the back of the robot and a four-inch steel safety pole. NIOSH reported that the robot had stalled while continuing to press on his chest. Company staff, the city fire department and emergency medical services worked to free him. He was admitted to hospital in a coma and died five days later. The medical examiner attributed the death to brain damage following cardiopulmonary arrest and found no signs of crushing injury.

A safety rail with an electrically interlocked gate enclosed two sides of the robot’s work area. NIOSH concluded the operator most likely went over, under or around the rail. His reason for entering is not known, although an air gun was found next to him, and coworkers told investigators they had seen him enter the robot’s work area before.

The system involved

The machine was a Unimate hydraulic industrial robot integrated into an automated die-casting cell. It ran a fixed program without an operator inside the cell. Safeguarding consisted of a rail with an interlocked gate on two sides of the work envelope. A fixed steel safety pole behind the robot formed the pinch point with the rear of the machine.

Investigation and response

NIOSH investigated at the request of the medical examiner, interviewing managers, union representatives, coworkers and rescuers. It identified three contributing factors: the operator may have been overconfident about working safely near the robot, the rail was more effective against accidental than deliberate entry, and nobody had recognized the pinch point between the rear of the robot and the fixed pole. The employer replaced the rail with a chain-link fence.

NIOSH used the case to recommend better cell design and safety systems, safety training specific to robots and proper supervision.

What is not established

NIOSH did not name the company or the city. Why the operator entered the robot’s work area is not established. NIOSH’s description of this as the first documented U.S. robot-related fatality differs from sources that give that distinction to a 1979 death at a Ford plant in Flat Rock, Michigan, which involved an automated storage system.