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Ride at 0.00000003% Risk: The Safety of Elevators

On Monday, September 14, 2020, Carrie O’Connor was killed when the elevator in her apartment building dropped with her in the doorway. The elevator in question had passed its most recent inspection less than six months prior to the incident, and up until then had given tenants little reason for concern. Now those same tenants may have a fear of elevators for the rest of their lives. However, death by elevator should be the last of your fears. Thanks to a carefully designed array of safety devices, elevator deaths are so rare that elevators are safer than stairs, cars, and even bathtubs. 

The most common safety device on an elevator is the counterweight, a massive stack of metal blocks attached to the opposite end of the hoisting cable from the elevator car. The counterweight usually weighs as much as a partially-loaded elevator cab. Its purpose is to minimize the net force on the elevator system under any given load. If the elevator motor were to fail, the counterweight would exert an upward force on the elevator cab, preventing it from falling at the rate of gravity. If the elevator is lightly loaded, it will actually fall up, but will not accelerate at the rate of gravity, because of the weight of the elevator car.

Obviously, the counterweight won’t do any good if the hoisting cables on the elevator break. In order to safeguard against this scenario, modern elevators are installed with multiple cables that are each capable of supporting more than the weight of a fully-loaded cab. All but one of the cables could break, and the elevator would still not fall.

Photograph by Ethan Jo

What if that last cable does break? People fear that the elevator would then plunge to the basement with nothing to stop it. That’s not common and hasn’t been since 1853. In 1853, Elisha Graves Otis invented the world’s first elevator safety brake, which suspended the elevator from the cable using a giant spring. If the cables broke, the spring would change shape, jamming into the elevator’s guide rails and stopping it. Modern elevator safety brakes use an auxiliary cable that winds over a device called a governor and then attaches to the counterweight.

The governor is a second pulley that rotates along with the elevator’s motion. If the elevator is traveling faster, the governor rotates faster. This increases the centrifugal force on the devices inside the governor. At a certain amount of centrifugal force, a switch inside the governor physically jams, which introduces tension on the auxiliary cable and applies the brakes on the elevator car. Therefore, if all the elevator hoisting cables break, the governor will stop the elevator with a brake.

Photograph by G-Tech Elevator Associates, August, 2018

Sadly, these highly advanced systems that prevent elevators from falling are not completely foolproof. If all the hoisting cables and the governor cable fail at once, the elevator will go into free fall. This happened in 1945 when a confused pilot crashed a B25 bomber into the Empire State Building. An unfortunate elevator operator fell 80 floors – and survived partly because of another safety device: the buffer in the elevator pit.

Photograph by G-Tech Elevator Associates, August 2018

The buffer in the elevator pit is a fairly simple device with a hydraulic ram, a spring, or both, combined to spread out the elevator’s sudden stop over a greater vertical distance. That decreases the instantaneous acceleration, thereby decreasing the force of impact. In the case of the Empire State Building accident, the buffer actually smashed through the center of the elevator floor. Though it did contribute to a survivable deceleration, anyone standing in the center of the elevator would likely have been killed.

Elevator safety systems, advanced as they are, are not perfect. Nothing is. But despite the dangers, they are still safer than the familiar staircase.  Out of 18 billion elevator trips per year, elevator accidents in the US cause about 30 total deaths per year and only about 5 passenger deaths. Meanwhile, stairs kill over 1600 people per year, and car crashes kill about 100 people per day. Even the seemingly-absurd case of drowning in a bathtub kills more people than elevator accidents, averaging about 380 deaths per year. Therefore, of all the deaths to fear, death by elevator is one of the least likely. Next time you get in the elevator, don’t worry. Your odds of death are only 0.00000003%. 

 

BIBLIOGRAPHY

“Motor Vehicle Injury,” CDC. https://www.cdc.gov/publichealthgateway/didyouknow/topic/vehicle.html

“Drowning — United States, 2005–2009,” CDC. https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6119a4.htm?s_cid=mm6119a4_w

McCann, M. and N. Zaleski, “Deaths and injuries involving elevators or escalators (revised),” CDC. https://www.cdc.gov/niosh/nioshtic-2/20039852.html

Waxman, Olivia B., “This Is the Patent for the Device That Made Elevators a Lot Less Dangerous,” Time. https://time.com/4700084/elevator-patent-history-otis-safety/

Landsverk, Gabby, “A man died after an elevator pinned his body between floors. You’re still more likely to be killed by a bear or in a bathtub.,” Insider. https://www.insider.com/man-dies-elevator-accident-how-common-dangerous-2019-8

“Safety systems in a modern high-rise elevator,” Otis. https://www.otis.com/en/us/tools-resources/high-rise-safety-systems/

Palmer, Brian, “Elevator plunges are rare because brakes and cables provide fail-safe protections,” The Washington Post. https://www.washingtonpost.com/national/health-science/elevator-plunges-are-rare-because-brakes-and-cables-provide-fail-safe-protections/2013/06/07/e44227f6-cc5a-11e2-8845-d970ccb04497_story.html

“The Day the Elevator Fell,” The Washington Post. https://www.washingtonpost.com/archive/1995/03/08/the-day-the-elevator-fell/22e87c01-6567-4d19-8b0b-8690d1818e87/

Anderson, Travis and Emily Sweeny, “Woman killed in Allston elevator accident was trapped in doorway,”The Boston Globe. https://www.bostonglobe.com/2020/09/16/metro/woman-killed-allston-elevator-accident-was-trapped-doorway-police-report-says/

 

22 Comments

  1. Actually, this made me feel a lot safer. I still might not use them frequently, but I know now that when I have to, I will be safe. 🙂 Great job on the article!

  2. Elise Kersten

    Wow dee wow wow, those statistics against stairs are statistics the world needs to hear!!! 😂 😂 Brilliant!!

    • Yeah, but it’s not likely that people will start putting elevators in their houses, because they’re too expensive.

  3. This was a surprisingly interesting topic XD Great job!

  4. I agree with Laura! This was cool!

  5. OK! cool thanks!

  6. Why did I know you wrote this just from the title…

  7. Joshua Wideman

    Wow… who knew elevators could be so interesting? Great article Ethan!

  8. @jalons Because. You know why.

    This is hilarious! Bathtubs kill 380 people a year??!! And an elevator can sometimes fall up!!! The “chances of death” tag…*fp*
    (why did you use that picture? The outside of that one would have been more interesting.)

  9. Charles Kersten

    Can it be fatal if the elevator falls up?? And It probably would feel wierd if the elevator you were in fell up. XD

    • My guess is that an upward fall would be about as likely to result in death as a downward one. The reason for this is that many counterweights have buffers too, so as soon as the elevator reaches the top of the shaft, the counterweight is stopped, and there is no upward force on the elevator cab anymore. So if there is enough space, the elevator will just slow to a stop.

      The danger would be if the elevator were to fail at high speed with a very lightly loaded cab, and little to no clearance at the top of the shaft.
      If the elevator doesn’t have enough time to slow down, it might hit the shaft roof, coming to a sudden stop.

      If that stop is sudden enough, you could conceivably get launched into the air and hit your head on the elevator ceiling. As head injuries tend to be quite serious, that is definitely not good.

      This particular scenario is probably extremely rare, as the counterweight is usually the cab weight+40% of the rated load (not 50%) That would mean that even with a lightly loaded cab, the elevator wouldn’t be very likely to fall up.

      So, to sum up, upward falls are probably rarer, but have the potential to be more fatal. So I think it more-or-less balances out.

  10. Wow that is really interesting! I didn’t know a lot about the way elevators work until now. Good job 🙂

  11. Sofia Barbieri

    Good job!! 😄 I still think I prefer stairs because elevators make me a little dizzy, I guess you could say… XD (Ever stepped out of one and the solid floor still felt like it was tilting and moving under your feet for the longest time afterward??) But it’s nice to know that when I do need to employ them, they’re safer than what I typically would use. 😁

    • Yes lel it feels so wierd when you step out of an elevator. So i think ill stay with stairs.
      However, GJ! This article was very well researched and I enjoyed reading it!

    • Huh I’ve never really noticed that except on really fast machines; I ride a lot of elevators though, (well I did before Covid) so I guess maybe I just built up a toleracne?

  12. Oliver+Munzer

    what will clay come up with next?? XD

  13. Elevators are scary, man!

  14. This made me even more scared for some reason… D:

  15. Eleanor McClain

    Eleanor was not surprised when she read that this was written by Ethan Jo, and she simply smiled to herself and said “wow, this makes me feel safe” Very good job on writing it! Twas intruiging

  16. Claire McDaniel

    This was so informative, awesome work Ethan! I was a little perplexed by the topic though…you and elevators?? Whaaaat?! 😉

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