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