Hot Strip Rolling Mill

Don also worked full time at the computer factory. One time he told me about a new computer they had built and installed for a hot-strip rolling mill. That is, a steel factory, where the computer would control huge buckets of molten steel, pour them out, and roll them into long, uniform strips.

The operator for this mill sat in a special cage hanging far above the factory floor. An operating rule was that any time the operator came down to the floor, as in time for breaks or change of shift, the mill had to be shut down, a procedure that was long and complex. The procedure to start it up again was also long and complex. To enforce this rule, the engineers had designed, and the technicians had built, a "dead-man's switch" for the cab. It was set so that the mill could not operate unless a weight equal to a human body were on the floor of the cab.

As it turned out, one operator figured out how to fool that switch. The next time the strip of steel started to buckle, and needed to be straightened out manually, this operator placed a heavy weight on the floor of the cab, so that he could climb down the ladder to the factory floor, where he fell into the strip of molten steel.

Don said, "We can make them fool proof, but we can't make them damned fool proof."