Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, I'm Lauren vog O Bomb and you may have heard about it in the news. In November, six people board at an elevator at the former John Hancock Center in Chicago for the ride down from the signature Room bar on the ninety 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 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 was 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. Here's the breakdown. First, let's look at those cables and 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 to. The cables that lift the car are also connected to a counterweight, which hangs down on the other side of the sheave. The car and the
counterweight both right 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 in total. Even if one cable 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 clamped the rails, while others drive a wedge into 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 centivigal force activates
the braking system. Even if the cables and the safeties all failed, sure, you would be plumbering rapidly, but you wouldn't quite be in free fall. 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 fell, just as a piston compresses air 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 cushion the impact too. With all of these features in place, you would have an slint chance of surviving any elevator mishap.
In the case of the Chicago elevator incident, once the 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 spokes been Larry Langford told the Chicago Tribune, we don't like to have to go through walls unless it's absolutely necessary.
The only other way to get to the elevator would have been ropes from the 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. Would that work. Nah, Even if you could perfectly time such a leap, it wouldn't help. Let's say you and the elevator are falling
at a hundred miles per hour. That's around a 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 a hundred miles per hour, and then you would hit the ground at a hundred miles per hour, just like the elevator. Your best bet would be to lie 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 was written by Katherine Whitbourne and produced by Tyler Clang. For more on this and lots of other well backed up topics, visit our home planet, how Stuff Works dot com.