The man who cut the rope

Tall buildings are possible because of two things: strong structures and lifts that people are willing to step into. For a long time, the second was the problem. Hoists existed, but if the rope snapped, the platform fell. Nobody wanted to ride one.

The safety brake#

An American inventor named Elisha Otis worked on a fix. His design added a spring-loaded mechanism and a toothed rail on each side of the lift shaft. While the rope was under tension, the mechanism was held open. If the rope broke, the tension disappeared, the spring snapped the catches outwards and they gripped the rail, stopping the platform.

The idea was elegant, because it worked automatically, and because it failed safe: the thing that made it activate was the very failure it was meant to prevent.

The demonstration#

In 1854, at the Crystal Palace exhibition in New York, Otis stood on a platform raised high above the crowd. Then, as the story goes, an assistant cut the rope with an axe.

The platform dropped a few inches and stopped. Otis is said to have told the audience, "All safe, gentlemen, all safe."

It was a brilliant piece of showmanship. A technical safety feature became something people could see and believe.

What came next#

Otis began selling safety lifts, and the company he founded is still a major maker of lifts and escalators. Over the following decades, lifts were installed in hotels, shops and offices. By the end of the nineteenth century, buildings were rising higher than ever before, because it was now practical to get to the top.

Why it matters#

• Trust is part of a product. A device can be safe and still fail to sell if people do not believe it.
• Design for failure. The best safety systems work when something goes wrong, without anyone having to act.
• Show, do not just tell. A demonstration can persuade more than any explanation.

Next time you step into a lift, you are relying on a spring and a pair of teeth that were proved in public more than a century and a half ago.