Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff.
Speaker 1: Lauren vogel Bomb here with another classic episode of the podcast.
Speaker 1: In this one, we discussed the dramatic science of how
Speaker 1: modern elevators keep you safe even if it's cables break, which,
Speaker 1: by the way, is much less likely than the movies
Speaker 1: make it look. Hey brain Stuff, I'm Lauren Vogelbaum, and
Speaker 1: you may have heard about it in the news. In
Speaker 1: November of twenty eighteen, six people boarded an elevator at
Speaker 1: the former John Hancock Center in Chicago for the ride
Speaker 1: down from the Signature Room bar on the ninety fifth
Speaker 1: floor to the lobby, but one of the cables snapped
Speaker 1: and the elevator plunged eighty four floors to the eleventh floor. Amazingly,
Speaker 1: none of the passengers had to be hospitalized and there
Speaker 1: were no serious injuries. The passengers thought they had only
Speaker 1: fallen a few floors. However, they did have to wait
Speaker 1: three hours to be rescued by firefighters because there were
Speaker 1: no openings between the floors. So how is it possible
Speaker 1: that one of the worst things that can happen to
Speaker 1: people in an elevator occurred and everyone survived elevators in
Speaker 1: the real world have so many safety features that the
Speaker 1: kind of thing you see in movies where a villain
Speaker 1: cuts a single cable and disaster ensues usually never happens.
Speaker 1: Here's the breakdown.
Speaker 2: First, let's look at those cables in a cable elevator system.
Speaker 2: Steel cables bolted to the car loop over a sheave.
Speaker 2: A sheave is a pulley with a grooved rim surface
Speaker 2: at the top of the elevator shaft. The sheaves grooves
Speaker 2: grip the steel cables, so when an electric motor rotates
Speaker 2: the sheave, the cables move too. The cables that lift
Speaker 2: the car are also connected to a counterweight, which hangs
Speaker 2: down on the other side of the sheave. The car
Speaker 2: and the counterweight both ride along on steel rails. Each
Speaker 2: elevator cable is made from several lengths of steel material
Speaker 2: wound around one another. These cables very rarely snap, and
Speaker 2: inspectors look at them for wear and tear. But even
Speaker 2: a steel cable can break. So what happens then? Almost
Speaker 2: all pulley elevators have multiple cables, between four and eight
Speaker 2: in total. Even if one cable's snapped, the remaining cables
Speaker 2: would hold the elevator car up. In fact, just one
Speaker 2: cable is usually enough. But let's say all the cables
Speaker 2: did snap, then the elevator's safeties would kick in. Safeties
Speaker 2: are braking systems on the elevator car that grab onto
Speaker 2: the rails running up and down the elevator shaft. Some
Speaker 2: safeties clamp the rails, while others drive a wedge into
Speaker 2: notches in the rails. Typically, safeties are activated by a
Speaker 2: mechanical speed governor. The governor is a pulley that rotates
Speaker 2: when the elevator moves. When the governor spins too fast,
Speaker 2: the centervigal force activates the braking system. Even if the
Speaker 2: cables and the safeties all failed, sure, you would be
Speaker 2: plummeting rapidly, but you wouldn't quite be in freefall. A
Speaker 2: friction from the rails along the shaft and pressure from
Speaker 2: air underneath the car would slow the car down considerably,
Speaker 2: though you would feel a bit lighter than normal. On impact,
Speaker 2: the car would stop and you would keep going, slamming
Speaker 2: you into the floor. But two things would cushion that blow. First,
Speaker 2: the elevator car would compress air at the bottom of
Speaker 2: the shaft as it just as a piston compresses air
Speaker 2: in a bicycle pump, The air pressure would slow the
Speaker 2: elevator car down. Second, most cable elevators have a built
Speaker 2: in shock absorber at the bottom of the shaft, typically
Speaker 2: a piston in an oil filled cylinder that would push
Speaker 2: in the impact too. With all of these features in place,
Speaker 2: you would have an excellent chance of surviving any elevator mishap.
Speaker 2: In the case of the Chicago elevator incident, once the
Speaker 2: firefighters figured out where the passengers were, the crew put
Speaker 2: up struts to make sure the elevator did not drop
Speaker 2: any further. Then they broke through a wall, forced to
Speaker 2: the elevator door open, and put a ladder into the
Speaker 2: elevator to help people up and out. Chicago Fire Department's
Speaker 2: spooksman Larry Langford told the Chicago Tribune, we don't like
Speaker 2: to have to go through walls unless it's absolutely necessary.
Speaker 2: The only other way to get to the elevator would
Speaker 2: have been ropes from the ninety seventh floor, and that
Speaker 2: would not be safe. We don't come down like Batman,
Speaker 2: so we must go through the wall. You sometimes hear
Speaker 2: that you should jump immediately before an elevator crashes, so
Speaker 2: that you would be floating at the second of impact.
Speaker 1: Would that work?
Speaker 2: Now, even if you could perfectly time such a leap,
Speaker 2: it wouldn't help. Let's say you and the elevator are
Speaker 2: falling at one hundred miles per hour. That's around one
Speaker 2: hundred and sixty one kilometers per hour. Unless you have
Speaker 2: some superhero powered legs. When you jump up in the elevator,
Speaker 2: you'd still be going about one hundred miles per hour,
Speaker 2: and then you would hit the ground at one hundred
Speaker 2: miles per hour, just like the elevator. Your best bet
Speaker 2: would be toly flat on the floor. This would stabilize
Speaker 2: you and spread out the force of the impact so
Speaker 2: that no single part of your body would take the
Speaker 2: brunt of the blow. Today's episode is based on the
Speaker 2: article what if you are on an elevator and the
Speaker 2: cable broke on HowStuffWorks dot com, written by Catherine Whitbourne.
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