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.
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.
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.
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%.
“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
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/