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March 4, 2024 5 mins

Elevators cables are inspected on the regular, but what happens when one breaks? Learn about the ingenious systems that keep elevators safe when even the worst happens in this classic episode of BrainStuff, based on this article: https://science.howstuffworks.com/science-vs-myth/everyday-myths/question730.htm

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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff.
Lauren vogel Bomb here with another classic episode of the podcast.
In this one, we discussed the dramatic science of how
modern elevators keep you safe even if it's cables break, which,
by the way, is much less likely than the movies
make it look. Hey brain Stuff, I'm Lauren Vogelbaum, and

(00:26):
you may have heard about it in the news. In
November of twenty eighteen, six people boarded an elevator at
the former John Hancock Center in Chicago for the ride
down from the Signature Room bar on the ninety fifth
floor to the lobby, but one of the cables snapped
and the elevator plunged eighty four floors to the eleventh floor. Amazingly,
none of the passengers had to be hospitalized and there
were no serious injuries. The passengers thought they had only

(00:48):
fallen a few floors. However, they did have to wait
three hours to be rescued by firefighters because there were
no openings between the floors. So how is it possible
that one of the worst things that can happen to
people in an elevator occurred and everyone survived elevators in
the real world have so many safety features that the
kind of thing you see in movies where a villain
cuts a single cable and disaster ensues usually never happens.

(01:12):
Here's the breakdown.

Speaker 2 (01:13):
First, let's look at those cables in a cable elevator system.
Steel cables bolted to the car loop over a sheave.
A sheave is a pulley with a grooved rim surface
at the top of the elevator shaft. The sheaves grooves
grip the steel cables, so when an electric motor rotates
the sheave, the cables move too. The cables that lift
the car are also connected to a counterweight, which hangs

(01:35):
down on the other side of the sheave. The car
and the counterweight both ride along on steel rails. Each
elevator cable is made from several lengths of steel material
wound around one another. These cables very rarely snap, and
inspectors look at them for wear and tear. But even
a steel cable can break. So what happens then? Almost
all pulley elevators have multiple cables, between four and eight

(01:58):
in total. Even if one cable's snapped, the remaining cables
would hold the elevator car up. In fact, just one
cable is usually enough. But let's say all the cables
did snap, then the elevator's safeties would kick in. Safeties
are braking systems on the elevator car that grab onto
the rails running up and down the elevator shaft. Some
safeties clamp the rails, while others drive a wedge into

(02:19):
notches in the rails. Typically, safeties are activated by a
mechanical speed governor. The governor is a pulley that rotates
when the elevator moves. When the governor spins too fast,
the centervigal force activates the braking system. Even if the
cables and the safeties all failed, sure, you would be
plummeting rapidly, but you wouldn't quite be in freefall. A

(02:41):
friction from the rails along the shaft and pressure from
air underneath the car would slow the car down considerably,
though you would feel a bit lighter than normal. On impact,
the car would stop and you would keep going, slamming
you into the floor. But two things would cushion that blow. First,
the elevator car would compress air at the bottom of
the shaft as it just as a piston compresses air

(03:02):
in a bicycle pump, The air pressure would slow the
elevator car down. Second, most cable elevators have a built
in shock absorber at the bottom of the shaft, typically
a piston in an oil filled cylinder that would push
in the impact too. With all of these features in place,
you would have an excellent chance of surviving any elevator mishap.
In the case of the Chicago elevator incident, once the

(03:24):
firefighters figured out where the passengers were, the crew put
up struts to make sure the elevator did not drop
any further. Then they broke through a wall, forced to
the elevator door open, and put a ladder into the
elevator to help people up and out. Chicago Fire Department's
spooksman Larry Langford told the Chicago Tribune, we don't like
to have to go through walls unless it's absolutely necessary.

(03:45):
The only other way to get to the elevator would
have been ropes from the ninety seventh floor, and that
would not be safe. We don't come down like Batman,
so we must go through the wall. You sometimes hear
that you should jump immediately before an elevator crashes, so
that you would be floating at the second of impact.

Speaker 1 (04:00):
Would that work?

Speaker 2 (04:02):
Now, even if you could perfectly time such a leap,
it wouldn't help. Let's say you and the elevator are
falling at one hundred miles per hour. That's around one
hundred and sixty one kilometers per hour. Unless you have
some superhero powered legs. When you jump up in the elevator,
you'd still be going about one hundred miles per hour,
and then you would hit the ground at one hundred
miles per hour, just like the elevator. Your best bet

(04:24):
would be toly flat on the floor. This would stabilize
you and spread out the force of the impact so
that no single part of your body would take the
brunt of the blow. Today's episode is based on the
article what if you are on an elevator and the
cable broke on HowStuffWorks dot com, written by Catherine Whitbourne.
A brain Stuff is production by Heart Radio in.

Speaker 1 (04:46):
Partnership with how Stuffworks dot Com, and it's produced by
Tyler Klang. Four more podcasts my Heart Radio, visit the
iHeartRadio app, Apple Podcasts, or wherever you listen to your
favorite shows.

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Lauren Vogelbaum

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