WEBVTT - BrainStuff Classics: What Happens When Elevator Cables Break?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff.

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<v Speaker 1>Lauren vogel Bomb here with another classic episode of the podcast.

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<v Speaker 1>In this one, we discussed the dramatic science of how

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<v Speaker 1>modern elevators keep you safe even if it's cables break, which,

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<v Speaker 1>by the way, is much less likely than the movies

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<v Speaker 1>make it look. Hey brain Stuff, I'm Lauren Vogelbaum, and

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<v Speaker 1>you may have heard about it in the news. In

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<v Speaker 1>November of twenty eighteen, six people boarded an elevator at

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<v Speaker 1>the former John Hancock Center in Chicago for the ride

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<v Speaker 1>down from the Signature Room bar on the ninety fifth

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<v Speaker 1>floor to the lobby, but one of the cables snapped

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<v Speaker 1>and the elevator plunged eighty four floors to the eleventh floor. Amazingly,

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<v Speaker 1>none of the passengers had to be hospitalized and there

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<v Speaker 1>were no serious injuries. The passengers thought they had only

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<v Speaker 1>fallen a few floors. However, they did have to wait

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<v Speaker 1>three hours to be rescued by firefighters because there were

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<v Speaker 1>no openings between the floors. So how is it possible

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<v Speaker 1>that one of the worst things that can happen to

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<v Speaker 1>people in an elevator occurred and everyone survived elevators in

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<v Speaker 1>the real world have so many safety features that the

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<v Speaker 1>kind of thing you see in movies where a villain

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<v Speaker 1>cuts a single cable and disaster ensues usually never happens.

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<v Speaker 1>Here's the breakdown.

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<v Speaker 2>First, let's look at those cables in a cable elevator system.

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<v Speaker 2>Steel cables bolted to the car loop over a sheave.

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<v Speaker 2>A sheave is a pulley with a grooved rim surface

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<v Speaker 2>at the top of the elevator shaft. The sheaves grooves

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<v Speaker 2>grip the steel cables, so when an electric motor rotates

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<v Speaker 2>the sheave, the cables move too. The cables that lift

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<v Speaker 2>the car are also connected to a counterweight, which hangs

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<v Speaker 2>down on the other side of the sheave. The car

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<v Speaker 2>and the counterweight both ride along on steel rails. Each

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<v Speaker 2>elevator cable is made from several lengths of steel material

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<v Speaker 2>wound around one another. These cables very rarely snap, and

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<v Speaker 2>inspectors look at them for wear and tear. But even

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<v Speaker 2>a steel cable can break. So what happens then? Almost

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<v Speaker 2>all pulley elevators have multiple cables, between four and eight

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<v Speaker 2>in total. Even if one cable's snapped, the remaining cables

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<v Speaker 2>would hold the elevator car up. In fact, just one

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<v Speaker 2>cable is usually enough. But let's say all the cables

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<v Speaker 2>did snap, then the elevator's safeties would kick in. Safeties

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<v Speaker 2>are braking systems on the elevator car that grab onto

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<v Speaker 2>the rails running up and down the elevator shaft. Some

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<v Speaker 2>safeties clamp the rails, while others drive a wedge into

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<v Speaker 2>notches in the rails. Typically, safeties are activated by a

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<v Speaker 2>mechanical speed governor. The governor is a pulley that rotates

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<v Speaker 2>when the elevator moves. When the governor spins too fast,

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<v Speaker 2>the centervigal force activates the braking system. Even if the

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<v Speaker 2>cables and the safeties all failed, sure, you would be

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<v Speaker 2>plummeting rapidly, but you wouldn't quite be in freefall. A

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<v Speaker 2>friction from the rails along the shaft and pressure from

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<v Speaker 2>air underneath the car would slow the car down considerably,

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<v Speaker 2>though you would feel a bit lighter than normal. On impact,

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<v Speaker 2>the car would stop and you would keep going, slamming

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<v Speaker 2>you into the floor. But two things would cushion that blow. First,

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<v Speaker 2>the elevator car would compress air at the bottom of

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<v Speaker 2>the shaft as it just as a piston compresses air

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<v Speaker 2>in a bicycle pump, The air pressure would slow the

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<v Speaker 2>elevator car down. Second, most cable elevators have a built

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<v Speaker 2>in shock absorber at the bottom of the shaft, typically

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<v Speaker 2>a piston in an oil filled cylinder that would push

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<v Speaker 2>in the impact too. With all of these features in place,

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<v Speaker 2>you would have an excellent chance of surviving any elevator mishap.

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<v Speaker 2>In the case of the Chicago elevator incident, once the

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<v Speaker 2>firefighters figured out where the passengers were, the crew put

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<v Speaker 2>up struts to make sure the elevator did not drop

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<v Speaker 2>any further. Then they broke through a wall, forced to

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<v Speaker 2>the elevator door open, and put a ladder into the

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<v Speaker 2>elevator to help people up and out. Chicago Fire Department's

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<v Speaker 2>spooksman Larry Langford told the Chicago Tribune, we don't like

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<v Speaker 2>to have to go through walls unless it's absolutely necessary.

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<v Speaker 2>The only other way to get to the elevator would

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<v Speaker 2>have been ropes from the ninety seventh floor, and that

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<v Speaker 2>would not be safe. We don't come down like Batman,

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<v Speaker 2>so we must go through the wall. You sometimes hear

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<v Speaker 2>that you should jump immediately before an elevator crashes, so

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<v Speaker 2>that you would be floating at the second of impact.

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<v Speaker 1>Would that work?

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<v Speaker 2>Now, even if you could perfectly time such a leap,

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<v Speaker 2>it wouldn't help. Let's say you and the elevator are

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<v Speaker 2>falling at one hundred miles per hour. That's around one

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<v Speaker 2>hundred and sixty one kilometers per hour. Unless you have

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<v Speaker 2>some superhero powered legs. When you jump up in the elevator,

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<v Speaker 2>you'd still be going about one hundred miles per hour,

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<v Speaker 2>and then you would hit the ground at one hundred

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<v Speaker 2>miles per hour, just like the elevator. Your best bet

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<v Speaker 2>would be toly flat on the floor. This would stabilize

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<v Speaker 2>you and spread out the force of the impact so

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<v Speaker 2>that no single part of your body would take the

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<v Speaker 2>brunt of the blow. Today's episode is based on the

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<v Speaker 2>article what if you are on an elevator and the

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<v Speaker 2>cable broke on HowStuffWorks dot com, written by Catherine Whitbourne.

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<v Speaker 2>A brain Stuff is production by Heart Radio in.

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<v Speaker 1>Partnership with how Stuffworks dot Com, and it's produced by

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<v Speaker 1>Tyler Klang. Four more podcasts my Heart Radio, visit the

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