WEBVTT - What Happens When Elevator Cables Break? 0:00:02.040 --> 0:00:07.080 Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, 0:00:07.080 --> 0:00:09.080 I'm Lauren vog O Bomb and you may have heard 0:00:09.119 --> 0:00:12.760 about it in the news. In November, six people board 0:00:12.800 --> 0:00:15.079 at an elevator at the former John Hancock Center in 0:00:15.160 --> 0:00:17.480 Chicago for the ride down from the signature Room bar 0:00:17.560 --> 0:00:20.279 on the ninety floor to the lobby, but one of 0:00:20.280 --> 0:00:23.160 the cables snapped and the elevator plunged eighty four floors 0:00:23.200 --> 0:00:26.600 to the eleventh floor. Amazingly, none of the passengers had 0:00:26.600 --> 0:00:29.240 to be hospitalized and there were no serious injuries. The 0:00:29.280 --> 0:00:32.400 passengers thought they had only fallen a few floors. However, 0:00:32.479 --> 0:00:34.440 they did have to wait three hours to be rescued 0:00:34.440 --> 0:00:37.040 by firefighters because there were no openings between the floors. 0:00:38.159 --> 0:00:40.520 So how was it possible that one of the worst 0:00:40.600 --> 0:00:43.080 things that can happen to people in an elevator occurred 0:00:43.159 --> 0:00:46.599 and everyone survived. Elevators in the real world have so 0:00:46.640 --> 0:00:48.680 many safety features that the kind of thing you see 0:00:48.680 --> 0:00:51.080 in movies where a villain cuts a single cable and 0:00:51.120 --> 0:00:56.040 disaster ensues usually never happens. Here's the breakdown. First, let's 0:00:56.040 --> 0:00:59.000 look at those cables and a cable elevator system. Steel 0:00:59.080 --> 0:01:02.200 cables bolted to the car loop over a sheave. A 0:01:02.280 --> 0:01:05.119 sheave is a pulley with a grooved rim surface at 0:01:05.120 --> 0:01:08.120 the top of the elevator shaft. The sheaves grooves grip 0:01:08.200 --> 0:01:11.840 the steel cables, so when an electric motor rotates the sheave, 0:01:12.120 --> 0:01:14.840 the cables move to. The cables that lift the car 0:01:14.880 --> 0:01:17.560 are also connected to a counterweight, which hangs down on 0:01:17.600 --> 0:01:19.640 the other side of the sheave. The car and the 0:01:19.680 --> 0:01:24.080 counterweight both right along on steel rails. Each elevator cable 0:01:24.160 --> 0:01:26.919 is made from several lengths of steel material wound around 0:01:26.920 --> 0:01:30.600 one another. These cables very rarely snap, and inspectors look 0:01:30.640 --> 0:01:33.080 at them for wear and tear. But even a steel 0:01:33.120 --> 0:01:37.479 cable can break. So what happens then? Almost all pulley 0:01:37.480 --> 0:01:40.560 elevators have multiple cables, between four and eight in total. 0:01:41.000 --> 0:01:43.440 Even if one cable snapped, the remaining cables would hold 0:01:43.440 --> 0:01:46.320 the elevator car up. In fact, just one cable is 0:01:46.360 --> 0:01:50.040 usually enough. But let's say all the cables did snap, 0:01:50.520 --> 0:01:53.960 then the elevator's safeties would kick in. Safeties are braking 0:01:54.000 --> 0:01:56.440 systems on the elevator car that grab onto the rails 0:01:56.480 --> 0:01:59.680 running up and down the elevator shaft. Some safeties clamped 0:01:59.680 --> 0:02:02.080 the rails, while others drive a wedge into notches in 0:02:02.120 --> 0:02:06.480 the rails. Typically, safeties are activated by a mechanical speed governor. 0:02:07.240 --> 0:02:10.079 The governor is a pulley that rotates when the elevator moves. 0:02:10.360 --> 0:02:13.880 When the governor spins too fast, the centivigal force activates 0:02:13.919 --> 0:02:17.560 the braking system. Even if the cables and the safeties 0:02:17.639 --> 0:02:20.760 all failed, sure, you would be plumbering rapidly, but you 0:02:20.760 --> 0:02:24.040 wouldn't quite be in free fall. Friction from the rails 0:02:24.040 --> 0:02:26.680 along the shaft and pressure from air underneath the car 0:02:26.880 --> 0:02:29.680 would slow the car down considerably, though you would feel 0:02:29.680 --> 0:02:32.600 a bit lighter than normal. On impact, the car would 0:02:32.639 --> 0:02:35.320 stop and you would keep going, slamming you into the floor. 0:02:36.040 --> 0:02:39.520 But two things would cushion that blow. First, the elevator 0:02:39.560 --> 0:02:41.640 car would compress air at the bottom of the shaft 0:02:41.680 --> 0:02:44.359 as it fell, just as a piston compresses air in 0:02:44.400 --> 0:02:47.519 a bicycle pump. The air pressure would slow the elevator 0:02:47.520 --> 0:02:51.160 car down. Second, most cable elevators have a built in 0:02:51.200 --> 0:02:53.560 shock absorber at the bottom of the shaft, typically a 0:02:53.560 --> 0:02:56.680 piston in an oil filled cylinder, that would cushion the 0:02:56.680 --> 0:02:59.400 impact too. With all of these features in place, you 0:02:59.440 --> 0:03:02.280 would have an slint chance of surviving any elevator mishap. 0:03:03.520 --> 0:03:06.000 In the case of the Chicago elevator incident, once the 0:03:06.000 --> 0:03:08.960 firefighters figured out where the passengers were, the crew put 0:03:09.000 --> 0:03:10.920 up struts to make sure the elevator did not drop 0:03:10.919 --> 0:03:13.840 any further. Then they broke through a wall, forced to 0:03:13.840 --> 0:03:15.880 the elevator door open, and put a ladder into the 0:03:15.880 --> 0:03:20.440 elevator to help people up and out. Chicago Fire Department 0:03:20.480 --> 0:03:24.040 spokes been Larry Langford told the Chicago Tribune, we don't 0:03:24.080 --> 0:03:26.959 like to have to go through walls unless it's absolutely necessary. 0:03:27.360 --> 0:03:29.240 The only other way to get to the elevator would 0:03:29.240 --> 0:03:31.640 have been ropes from the floor, and that would not 0:03:31.720 --> 0:03:34.440 be safe. We don't come down like Batman, so we 0:03:34.560 --> 0:03:37.600 must go through the wall. You sometimes hear that you 0:03:37.600 --> 0:03:40.520 should jump immediately before an elevator crashes, so that you 0:03:40.560 --> 0:03:44.280 would be floating at the second of impact. Would that work. Nah, 0:03:44.880 --> 0:03:47.160 Even if you could perfectly time such a leap, it 0:03:47.160 --> 0:03:50.600 wouldn't help. Let's say you and the elevator are falling 0:03:50.600 --> 0:03:52.920 at a hundred miles per hour. That's around a hundred 0:03:52.920 --> 0:03:55.800 and sixty one kilometers per hour unless you have some 0:03:55.960 --> 0:03:58.720 superhero powered legs. When you jump up in the elevator, 0:03:58.800 --> 0:04:01.600 you'd still be going about a hundred miles per hour, 0:04:02.000 --> 0:04:03.800 and then you would hit the ground at a hundred 0:04:03.800 --> 0:04:06.800 miles per hour, just like the elevator. Your best bet 0:04:06.800 --> 0:04:09.119 would be to lie flat on the floor. This would 0:04:09.160 --> 0:04:11.360 stabilize you and spread out the force of the impact 0:04:11.400 --> 0:04:13.120 so that no single part of your body would take 0:04:13.160 --> 0:04:20.279 the brunt of the blow. Today's episode was written by 0:04:20.320 --> 0:04:23.080 Katherine Whitbourne and produced by Tyler Clang. For more on 0:04:23.080 --> 0:04:25.240 this and lots of other well backed up topics, visit 0:04:25.279 --> 0:04:38.600 our home planet, how Stuff Works dot com.