1 00:00:01,840 --> 00:00:07,520 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff. 2 00:00:07,560 --> 00:00:10,880 Speaker 1: Lauren vogel Bomb here with another classic episode of the podcast. 3 00:00:11,520 --> 00:00:14,480 Speaker 1: In this one, we discussed the dramatic science of how 4 00:00:14,600 --> 00:00:19,120 Speaker 1: modern elevators keep you safe even if it's cables break, which, 5 00:00:19,200 --> 00:00:21,680 Speaker 1: by the way, is much less likely than the movies 6 00:00:21,680 --> 00:00:26,279 Speaker 1: make it look. Hey brain Stuff, I'm Lauren Vogelbaum, and 7 00:00:26,400 --> 00:00:28,520 Speaker 1: you may have heard about it in the news. In 8 00:00:28,560 --> 00:00:31,680 Speaker 1: November of twenty eighteen, six people boarded an elevator at 9 00:00:31,680 --> 00:00:34,280 Speaker 1: the former John Hancock Center in Chicago for the ride 10 00:00:34,280 --> 00:00:36,360 Speaker 1: down from the Signature Room bar on the ninety fifth 11 00:00:36,360 --> 00:00:39,159 Speaker 1: floor to the lobby, but one of the cables snapped 12 00:00:39,200 --> 00:00:43,480 Speaker 1: and the elevator plunged eighty four floors to the eleventh floor. Amazingly, 13 00:00:43,640 --> 00:00:45,640 Speaker 1: none of the passengers had to be hospitalized and there 14 00:00:45,680 --> 00:00:48,480 Speaker 1: were no serious injuries. The passengers thought they had only 15 00:00:48,479 --> 00:00:51,400 Speaker 1: fallen a few floors. However, they did have to wait 16 00:00:51,440 --> 00:00:53,720 Speaker 1: three hours to be rescued by firefighters because there were 17 00:00:53,720 --> 00:00:57,720 Speaker 1: no openings between the floors. So how is it possible 18 00:00:57,760 --> 00:00:59,520 Speaker 1: that one of the worst things that can happen to 19 00:00:59,520 --> 00:01:03,640 Speaker 1: people in an elevator occurred and everyone survived elevators in 20 00:01:03,640 --> 00:01:05,920 Speaker 1: the real world have so many safety features that the 21 00:01:06,000 --> 00:01:08,120 Speaker 1: kind of thing you see in movies where a villain 22 00:01:08,120 --> 00:01:11,640 Speaker 1: cuts a single cable and disaster ensues usually never happens. 23 00:01:12,000 --> 00:01:12,800 Speaker 1: Here's the breakdown. 24 00:01:13,480 --> 00:01:16,639 Speaker 2: First, let's look at those cables in a cable elevator system. 25 00:01:16,760 --> 00:01:19,720 Speaker 2: Steel cables bolted to the car loop over a sheave. 26 00:01:20,240 --> 00:01:22,880 Speaker 2: A sheave is a pulley with a grooved rim surface 27 00:01:23,040 --> 00:01:25,840 Speaker 2: at the top of the elevator shaft. The sheaves grooves 28 00:01:25,880 --> 00:01:29,520 Speaker 2: grip the steel cables, so when an electric motor rotates 29 00:01:29,560 --> 00:01:32,600 Speaker 2: the sheave, the cables move too. The cables that lift 30 00:01:32,600 --> 00:01:35,240 Speaker 2: the car are also connected to a counterweight, which hangs 31 00:01:35,280 --> 00:01:37,440 Speaker 2: down on the other side of the sheave. The car 32 00:01:37,520 --> 00:01:41,360 Speaker 2: and the counterweight both ride along on steel rails. Each 33 00:01:41,400 --> 00:01:44,200 Speaker 2: elevator cable is made from several lengths of steel material 34 00:01:44,319 --> 00:01:47,880 Speaker 2: wound around one another. These cables very rarely snap, and 35 00:01:47,960 --> 00:01:50,720 Speaker 2: inspectors look at them for wear and tear. But even 36 00:01:50,760 --> 00:01:55,000 Speaker 2: a steel cable can break. So what happens then? Almost 37 00:01:55,000 --> 00:01:58,080 Speaker 2: all pulley elevators have multiple cables, between four and eight 38 00:01:58,120 --> 00:02:01,040 Speaker 2: in total. Even if one cable's snapped, the remaining cables 39 00:02:01,080 --> 00:02:03,920 Speaker 2: would hold the elevator car up. In fact, just one 40 00:02:03,960 --> 00:02:07,400 Speaker 2: cable is usually enough. But let's say all the cables 41 00:02:07,480 --> 00:02:11,520 Speaker 2: did snap, then the elevator's safeties would kick in. Safeties 42 00:02:11,520 --> 00:02:14,080 Speaker 2: are braking systems on the elevator car that grab onto 43 00:02:14,080 --> 00:02:16,800 Speaker 2: the rails running up and down the elevator shaft. Some 44 00:02:16,919 --> 00:02:19,679 Speaker 2: safeties clamp the rails, while others drive a wedge into 45 00:02:19,720 --> 00:02:23,120 Speaker 2: notches in the rails. Typically, safeties are activated by a 46 00:02:23,120 --> 00:02:27,040 Speaker 2: mechanical speed governor. The governor is a pulley that rotates 47 00:02:27,040 --> 00:02:29,960 Speaker 2: when the elevator moves. When the governor spins too fast, 48 00:02:30,160 --> 00:02:34,440 Speaker 2: the centervigal force activates the braking system. Even if the 49 00:02:34,480 --> 00:02:37,440 Speaker 2: cables and the safeties all failed, sure, you would be 50 00:02:37,480 --> 00:02:41,120 Speaker 2: plummeting rapidly, but you wouldn't quite be in freefall. A 51 00:02:41,200 --> 00:02:43,600 Speaker 2: friction from the rails along the shaft and pressure from 52 00:02:43,680 --> 00:02:46,720 Speaker 2: air underneath the car would slow the car down considerably, 53 00:02:46,880 --> 00:02:50,080 Speaker 2: though you would feel a bit lighter than normal. On impact, 54 00:02:50,200 --> 00:02:52,600 Speaker 2: the car would stop and you would keep going, slamming 55 00:02:52,680 --> 00:02:56,959 Speaker 2: you into the floor. But two things would cushion that blow. First, 56 00:02:57,040 --> 00:02:59,320 Speaker 2: the elevator car would compress air at the bottom of 57 00:02:59,360 --> 00:03:02,359 Speaker 2: the shaft as it just as a piston compresses air 58 00:03:02,400 --> 00:03:05,120 Speaker 2: in a bicycle pump, The air pressure would slow the 59 00:03:05,120 --> 00:03:09,120 Speaker 2: elevator car down. Second, most cable elevators have a built 60 00:03:09,120 --> 00:03:11,440 Speaker 2: in shock absorber at the bottom of the shaft, typically 61 00:03:11,520 --> 00:03:14,519 Speaker 2: a piston in an oil filled cylinder that would push 62 00:03:14,600 --> 00:03:17,400 Speaker 2: in the impact too. With all of these features in place, 63 00:03:17,440 --> 00:03:20,359 Speaker 2: you would have an excellent chance of surviving any elevator mishap. 64 00:03:21,560 --> 00:03:24,040 Speaker 2: In the case of the Chicago elevator incident, once the 65 00:03:24,080 --> 00:03:27,000 Speaker 2: firefighters figured out where the passengers were, the crew put 66 00:03:27,080 --> 00:03:28,959 Speaker 2: up struts to make sure the elevator did not drop 67 00:03:29,000 --> 00:03:31,920 Speaker 2: any further. Then they broke through a wall, forced to 68 00:03:31,919 --> 00:03:33,880 Speaker 2: the elevator door open, and put a ladder into the 69 00:03:33,960 --> 00:03:38,560 Speaker 2: elevator to help people up and out. Chicago Fire Department's 70 00:03:38,560 --> 00:03:42,280 Speaker 2: spooksman Larry Langford told the Chicago Tribune, we don't like 71 00:03:42,320 --> 00:03:44,960 Speaker 2: to have to go through walls unless it's absolutely necessary. 72 00:03:45,400 --> 00:03:47,320 Speaker 2: The only other way to get to the elevator would 73 00:03:47,320 --> 00:03:49,320 Speaker 2: have been ropes from the ninety seventh floor, and that 74 00:03:49,360 --> 00:03:52,000 Speaker 2: would not be safe. We don't come down like Batman, 75 00:03:52,120 --> 00:03:55,480 Speaker 2: so we must go through the wall. You sometimes hear 76 00:03:55,520 --> 00:03:58,400 Speaker 2: that you should jump immediately before an elevator crashes, so 77 00:03:58,440 --> 00:04:00,480 Speaker 2: that you would be floating at the second of impact. 78 00:04:00,840 --> 00:04:01,480 Speaker 1: Would that work? 79 00:04:02,120 --> 00:04:04,920 Speaker 2: Now, even if you could perfectly time such a leap, 80 00:04:05,160 --> 00:04:08,320 Speaker 2: it wouldn't help. Let's say you and the elevator are 81 00:04:08,360 --> 00:04:10,640 Speaker 2: falling at one hundred miles per hour. That's around one 82 00:04:10,720 --> 00:04:13,680 Speaker 2: hundred and sixty one kilometers per hour. Unless you have 83 00:04:13,760 --> 00:04:16,799 Speaker 2: some superhero powered legs. When you jump up in the elevator, 84 00:04:16,839 --> 00:04:19,520 Speaker 2: you'd still be going about one hundred miles per hour, 85 00:04:20,080 --> 00:04:21,839 Speaker 2: and then you would hit the ground at one hundred 86 00:04:21,880 --> 00:04:24,839 Speaker 2: miles per hour, just like the elevator. Your best bet 87 00:04:24,880 --> 00:04:27,760 Speaker 2: would be toly flat on the floor. This would stabilize 88 00:04:27,800 --> 00:04:29,520 Speaker 2: you and spread out the force of the impact so 89 00:04:29,560 --> 00:04:31,279 Speaker 2: that no single part of your body would take the 90 00:04:31,279 --> 00:04:38,920 Speaker 2: brunt of the blow. Today's episode is based on the 91 00:04:39,000 --> 00:04:41,039 Speaker 2: article what if you are on an elevator and the 92 00:04:41,080 --> 00:04:44,359 Speaker 2: cable broke on HowStuffWorks dot com, written by Catherine Whitbourne. 93 00:04:44,680 --> 00:04:46,600 Speaker 2: A brain Stuff is production by Heart Radio in. 94 00:04:46,560 --> 00:04:48,960 Speaker 1: Partnership with how Stuffworks dot Com, and it's produced by 95 00:04:48,960 --> 00:04:52,400 Speaker 1: Tyler Klang. Four more podcasts my Heart Radio, visit the 96 00:04:52,440 --> 00:04:55,560 Speaker 1: iHeartRadio app, Apple Podcasts, or wherever you listen to your 97 00:04:55,560 --> 00:05:02,000 Speaker 1: favorite shows.