Edited by Leland Teschler
Hazard analysis (here is that term again) and product testing under abnormal but reasonably foreseeable conditions can forewarn manufacturers about hazards that occur under abnormal conditions.
As an example, consider a power door for a warehouse. Suppose the controls are right next to the door so they can be reached from outside the doorway. That is, someone can stand outside the door when it is open and close it. Also consider the possibility that a person could place a pallet on edge in the doorway, such that the door in a fully lowered position would be blocked about 42 in off the ground.
The amount of cable deployed from a spool controls the uppermost and the fully lowered position of the door. So when the pallet blocks the door 42 in. from the floor, the door system still unrolls that 42 in. of cable.
The question becomes: What happens in this case to the 42 in. of cable that has been wound and stored around a take-up? The answer is possibly that it takes the shape of a coil 40 to 60 in. above the floor. When the subject accident occurred, I tested the system and that is exactly what happened.
On a cold and rainy night, one of the last people to leave the warehouse noticed the door was not completely down. He saw the pallet blocking it. He did not see the coiled cable, and reached for the control just inside the door so he could remove the pallet. In doing so, his arm went through the opening of the coil of cable. When the door-opener system wound up the cable to raise the door, his arm was caught in the tightened loop, seriously injuring him. He doesn't yet know if he'll lose his arm.
Was this series of events reasonably foreseeable? In my opinion it was. What could the manufacturer have done to avoid it back when the system was first designed?
- Give instructions to install pushbutton controls well out of reach of someone standing outside the door jam.
- Install a system that would keep the loose cable from forming a coil. There are numerous ways to do this cheaply and easily.
- Have an electric-eye system similar to that on residential garage-door openers to keep the door from closing when something is in the way. When I first started doing expert-witness work, I would be called in on a dozen or so investigations annually where a home garage door had descended and struck a child. That stopped when the electric eye became required on home garage doors.
All in all, it's critical to conduct a hazard analysis and product testing under reasonably foreseeable but unusual circumstances.
Lanny Berke is a registered professional engineer and a Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at email@example.com