1 00:00:02,040 --> 00:00:07,080 Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, 2 00:00:07,080 --> 00:00:09,080 Speaker 1: I'm Lauren vog O Bomb and you may have heard 3 00:00:09,119 --> 00:00:12,760 Speaker 1: about it in the news. In November, six people board 4 00:00:12,800 --> 00:00:15,079 Speaker 1: at an elevator at the former John Hancock Center in 5 00:00:15,160 --> 00:00:17,480 Speaker 1: Chicago for the ride down from the signature Room bar 6 00:00:17,560 --> 00:00:20,279 Speaker 1: on the ninety floor to the lobby, but one of 7 00:00:20,280 --> 00:00:23,160 Speaker 1: the cables snapped and the elevator plunged eighty four floors 8 00:00:23,200 --> 00:00:26,600 Speaker 1: to the eleventh floor. Amazingly, none of the passengers had 9 00:00:26,600 --> 00:00:29,240 Speaker 1: to be hospitalized and there were no serious injuries. The 10 00:00:29,280 --> 00:00:32,400 Speaker 1: passengers thought they had only fallen a few floors. However, 11 00:00:32,479 --> 00:00:34,440 Speaker 1: they did have to wait three hours to be rescued 12 00:00:34,440 --> 00:00:37,040 Speaker 1: by firefighters because there were no openings between the floors. 13 00:00:38,159 --> 00:00:40,520 Speaker 1: So how was it possible that one of the worst 14 00:00:40,600 --> 00:00:43,080 Speaker 1: things that can happen to people in an elevator occurred 15 00:00:43,159 --> 00:00:46,599 Speaker 1: and everyone survived. Elevators in the real world have so 16 00:00:46,640 --> 00:00:48,680 Speaker 1: many safety features that the kind of thing you see 17 00:00:48,680 --> 00:00:51,080 Speaker 1: in movies where a villain cuts a single cable and 18 00:00:51,120 --> 00:00:56,040 Speaker 1: disaster ensues usually never happens. Here's the breakdown. First, let's 19 00:00:56,040 --> 00:00:59,000 Speaker 1: look at those cables and a cable elevator system. Steel 20 00:00:59,080 --> 00:01:02,200 Speaker 1: cables bolted to the car loop over a sheave. A 21 00:01:02,280 --> 00:01:05,119 Speaker 1: sheave is a pulley with a grooved rim surface at 22 00:01:05,120 --> 00:01:08,120 Speaker 1: the top of the elevator shaft. The sheaves grooves grip 23 00:01:08,200 --> 00:01:11,840 Speaker 1: the steel cables, so when an electric motor rotates the sheave, 24 00:01:12,120 --> 00:01:14,840 Speaker 1: the cables move to. The cables that lift the car 25 00:01:14,880 --> 00:01:17,560 Speaker 1: are also connected to a counterweight, which hangs down on 26 00:01:17,600 --> 00:01:19,640 Speaker 1: the other side of the sheave. The car and the 27 00:01:19,680 --> 00:01:24,080 Speaker 1: counterweight both right along on steel rails. Each elevator cable 28 00:01:24,160 --> 00:01:26,919 Speaker 1: is made from several lengths of steel material wound around 29 00:01:26,920 --> 00:01:30,600 Speaker 1: one another. These cables very rarely snap, and inspectors look 30 00:01:30,640 --> 00:01:33,080 Speaker 1: at them for wear and tear. But even a steel 31 00:01:33,120 --> 00:01:37,479 Speaker 1: cable can break. So what happens then? Almost all pulley 32 00:01:37,480 --> 00:01:40,560 Speaker 1: elevators have multiple cables, between four and eight in total. 33 00:01:41,000 --> 00:01:43,440 Speaker 1: Even if one cable snapped, the remaining cables would hold 34 00:01:43,440 --> 00:01:46,320 Speaker 1: the elevator car up. In fact, just one cable is 35 00:01:46,360 --> 00:01:50,040 Speaker 1: usually enough. But let's say all the cables did snap, 36 00:01:50,520 --> 00:01:53,960 Speaker 1: then the elevator's safeties would kick in. Safeties are braking 37 00:01:54,000 --> 00:01:56,440 Speaker 1: systems on the elevator car that grab onto the rails 38 00:01:56,480 --> 00:01:59,680 Speaker 1: running up and down the elevator shaft. Some safeties clamped 39 00:01:59,680 --> 00:02:02,080 Speaker 1: the rails, while others drive a wedge into notches in 40 00:02:02,120 --> 00:02:06,480 Speaker 1: the rails. Typically, safeties are activated by a mechanical speed governor. 41 00:02:07,240 --> 00:02:10,079 Speaker 1: The governor is a pulley that rotates when the elevator moves. 42 00:02:10,360 --> 00:02:13,880 Speaker 1: When the governor spins too fast, the centivigal force activates 43 00:02:13,919 --> 00:02:17,560 Speaker 1: the braking system. Even if the cables and the safeties 44 00:02:17,639 --> 00:02:20,760 Speaker 1: all failed, sure, you would be plumbering rapidly, but you 45 00:02:20,760 --> 00:02:24,040 Speaker 1: wouldn't quite be in free fall. Friction from the rails 46 00:02:24,040 --> 00:02:26,680 Speaker 1: along the shaft and pressure from air underneath the car 47 00:02:26,880 --> 00:02:29,680 Speaker 1: would slow the car down considerably, though you would feel 48 00:02:29,680 --> 00:02:32,600 Speaker 1: a bit lighter than normal. On impact, the car would 49 00:02:32,639 --> 00:02:35,320 Speaker 1: stop and you would keep going, slamming you into the floor. 50 00:02:36,040 --> 00:02:39,520 Speaker 1: But two things would cushion that blow. First, the elevator 51 00:02:39,560 --> 00:02:41,640 Speaker 1: car would compress air at the bottom of the shaft 52 00:02:41,680 --> 00:02:44,359 Speaker 1: as it fell, just as a piston compresses air in 53 00:02:44,400 --> 00:02:47,519 Speaker 1: a bicycle pump. The air pressure would slow the elevator 54 00:02:47,520 --> 00:02:51,160 Speaker 1: car down. Second, most cable elevators have a built in 55 00:02:51,200 --> 00:02:53,560 Speaker 1: shock absorber at the bottom of the shaft, typically a 56 00:02:53,560 --> 00:02:56,680 Speaker 1: piston in an oil filled cylinder, that would cushion the 57 00:02:56,680 --> 00:02:59,400 Speaker 1: impact too. With all of these features in place, you 58 00:02:59,440 --> 00:03:02,280 Speaker 1: would have an slint chance of surviving any elevator mishap. 59 00:03:03,520 --> 00:03:06,000 Speaker 1: In the case of the Chicago elevator incident, once the 60 00:03:06,000 --> 00:03:08,960 Speaker 1: firefighters figured out where the passengers were, the crew put 61 00:03:09,000 --> 00:03:10,920 Speaker 1: up struts to make sure the elevator did not drop 62 00:03:10,919 --> 00:03:13,840 Speaker 1: any further. Then they broke through a wall, forced to 63 00:03:13,840 --> 00:03:15,880 Speaker 1: the elevator door open, and put a ladder into the 64 00:03:15,880 --> 00:03:20,440 Speaker 1: elevator to help people up and out. Chicago Fire Department 65 00:03:20,480 --> 00:03:24,040 Speaker 1: spokes been Larry Langford told the Chicago Tribune, we don't 66 00:03:24,080 --> 00:03:26,959 Speaker 1: like to have to go through walls unless it's absolutely necessary. 67 00:03:27,360 --> 00:03:29,240 Speaker 1: The only other way to get to the elevator would 68 00:03:29,240 --> 00:03:31,640 Speaker 1: have been ropes from the floor, and that would not 69 00:03:31,720 --> 00:03:34,440 Speaker 1: be safe. We don't come down like Batman, so we 70 00:03:34,560 --> 00:03:37,600 Speaker 1: must go through the wall. You sometimes hear that you 71 00:03:37,600 --> 00:03:40,520 Speaker 1: should jump immediately before an elevator crashes, so that you 72 00:03:40,560 --> 00:03:44,280 Speaker 1: would be floating at the second of impact. Would that work. Nah, 73 00:03:44,880 --> 00:03:47,160 Speaker 1: Even if you could perfectly time such a leap, it 74 00:03:47,160 --> 00:03:50,600 Speaker 1: wouldn't help. Let's say you and the elevator are falling 75 00:03:50,600 --> 00:03:52,920 Speaker 1: at a hundred miles per hour. That's around a hundred 76 00:03:52,920 --> 00:03:55,800 Speaker 1: and sixty one kilometers per hour unless you have some 77 00:03:55,960 --> 00:03:58,720 Speaker 1: superhero powered legs. When you jump up in the elevator, 78 00:03:58,800 --> 00:04:01,600 Speaker 1: you'd still be going about a hundred miles per hour, 79 00:04:02,000 --> 00:04:03,800 Speaker 1: and then you would hit the ground at a hundred 80 00:04:03,800 --> 00:04:06,800 Speaker 1: miles per hour, just like the elevator. Your best bet 81 00:04:06,800 --> 00:04:09,119 Speaker 1: would be to lie flat on the floor. This would 82 00:04:09,160 --> 00:04:11,360 Speaker 1: stabilize you and spread out the force of the impact 83 00:04:11,400 --> 00:04:13,120 Speaker 1: so that no single part of your body would take 84 00:04:13,160 --> 00:04:20,279 Speaker 1: the brunt of the blow. Today's episode was written by 85 00:04:20,320 --> 00:04:23,080 Speaker 1: Katherine Whitbourne and produced by Tyler Clang. For more on 86 00:04:23,080 --> 00:04:25,240 Speaker 1: this and lots of other well backed up topics, visit 87 00:04:25,279 --> 00:04:38,600 Speaker 1: our home planet, how Stuff Works dot com.