What Would Happen if you were in an Elevator and the Cables Broke?
What Would Happen if you were in an Elevator and the Cables Broke?
At the former John Hancock Center in Chicago, six passengers boarded an elevator at the Signature Room Bar on the 95thfloor. Not long after the passengers boarded, a cable broke and the car plummeted 84 floors; finally stopping at the 11th floor.
One of the passengers told CBS Chicago that he believed everyone was going to die while other passengers reported hearing a noise as they were closing in on the 11thfloor.
Miraculously none of the passengers had to be hospitalized and there were no serious injuries! The passengers assumed that they had only fallen a couple of floors but didn’t know the reality until hours later when they were rescued. It took 3 hours due to the fact that there were no openings between the floors for firefighters to get into.
So, how is it possible that these passengers survived an elevator fall?
Luckily, elevators have many safety features and mechanisms to prevent something like this from happening more often.
Snapping Cables
Inside a cable elevator system, steel cables that are bolted to the car also loop over a sheave. A sheave is a pulley with a grooved rim surface at the top of the elevator shaft. The responsibility of the sheave’s grooves is to grip the steel cables. That way, the electric motor rotates the sheave, making the cables move too. The cables that lift the elevator are also connected to a counterweight, which hangs down on the opposite side of the sheave. The counterweight and car both ride along on steel rails.
Each and every elevator cable is made of different lengths of steel material that is wound around one another. Elevator cables rarely snap and are inspected frequently for wear and tear; however, there is still a chance of a steel cable can break. What happens then?
Pulley elevators have between four and eight cables total. Meaning that even if one cable snapped, the remaining cables would hold the car up. Surprisingly, just one cable can hold the weight of an elevator.
Safeties and Governor
Let’s say that in a rare incident all of the steel cables broke, what would happen next? The elevators safety mechanisms would kick in. Safeties are the braking systems on the car that grab onto the rails that are running up and down the shaft. Some safeties drive a wedge into notches in the rails while others clamp the rails. Usually, safeties are activated by a mechanical speed governor. The governor is a pulley that rotates when the elevator moves. When the governor spins too fast, the centrifuge force activates the braking system.
At the Bottom
If all the safeties fail, you would be plummeting rapidly, but wouldn’t be in a total free fall. Friction from the rails along the shaft, including pressure from the air underneath the car, would slow the car down considerably. On impact, the car would stop but you would keep going, making you slam into the floor. However, there are two things that would cushion the blow. First off, the elevator car would compress the air at the bottom of the shaft as it fell. This air pressure would slow the car down tremendously. Next, most cable elevators have a built-in shock absorber at the bottom of the shaft, usually a piston in an oil filled cylinder. All of these things would cushion and lessen the impact. Therefore, these safety features would provide you with a great chance of surviving an elevator mishap.
In the Chicago elevator incident, firefighters were on the scene immediately. The crew put struts to make sure the elevator stayed in place preventing the elevator from dropping even more. After this, the crew had to break down a wall in order to force the elevator doors open and help people out of the car.
Elevators are a lot safer than people imagine. As long as you don’t try to open the doors and simply wait for help, you’ll be okay. Having all of these safety mechanisms make it possible to prevent tragedies.