Imagine Being Trapped in an Elevator When the Cable Suddenly Snaps

In November 2018, six individuals entered an elevator at Chicago's former John Hancock Center, descending from the 95th-floor Signature Room bar. Their journey took a terrifying turn when a cable broke, causing the elevator to drop 84 floors before halting at the 11th floor.

"Initially, I was convinced we wouldn't survive," a passenger shared with CBS Chicago. "We were descending normally, then suddenly it felt like we were in freefall, accompanied by a loud, rapid clacking noise."

Remarkably, none of the passengers required hospitalization, and there were no severe injuries. The group believed they had only dropped a few floors. However, they endured a three-hour wait for firefighters to rescue them, as there were no accessible openings between the floors [sources: CBS Chicago, Leone and Sobol].

How could such a catastrophic elevator incident occur without any fatalities? In action films, we often see the hero stepping into an elevator just as the villain severs the cables, leading to chaos.

Thankfully, real-world elevators are equipped with numerous safety mechanisms that make such disasters extremely rare. Here's how it works:

Breaking Cables

In a cable-driven elevator system, steel cables attached to the car loop around a sheave—a pulley with a grooved edge located at the top of the shaft. The grooves secure the cables, allowing them to move when an electric motor turns the sheave. These lifting cables are also linked to a counterweight on the opposite side of the sheave, with both the car and counterweight gliding along steel rails.

Elevator cables are constructed from multiple strands of steel tightly wound together. These cables seldom break, and they undergo regular inspections for signs of wear. However, even steel cables can fail. What occurs in such a scenario?

Most pulley elevators are equipped with multiple cables—typically between four and eight. If one cable were to break, the remaining cables would still support the elevator car. In most cases, a single cable alone is sufficient to hold the weight.

Safety Mechanisms and Governor

In the unlikely event that all cables fail, the elevator's safety systems would activate. These systems include brakes on the car that grip the rails within the shaft. Some safeties clamp onto the rails, while others insert a wedge into rail notches. These mechanisms are usually triggered by a mechanical speed governor.

The governor, a pulley that rotates as the elevator moves, triggers the braking system when it spins excessively fast due to centrifugal force.

At the Base

Should the safety systems fail, the elevator would descend rapidly, though not in complete free fall. Friction from the shaft's rails and air pressure beneath the car would significantly reduce its speed (though you might feel unusually light). Upon hitting the bottom, the car would halt abruptly, causing you to collide with the floor.

Two factors would help soften the impact. First, as the elevator descends, it would compress the air at the shaft's base, similar to how a piston compresses air in a bicycle pump. This air pressure would decelerate the car. Second, most cable elevators feature a shock absorber at the shaft's bottom—often a piston within an oil-filled cylinder—which would further reduce the force of the impact. Thanks to these safety measures, your chances of surviving an elevator accident are significantly improved.

During the Chicago elevator incident, once firefighters located the passengers, they installed struts to prevent further descent. They then breached a wall, pried open the elevator door, and used a ladder to assist everyone in exiting safely.

"We avoid breaking through walls unless absolutely necessary," explained Chicago Fire Department spokesperson Larry Langford to the Chicago Tribune. "The alternative would have been using ropes from the 97th floor, which isn't safe. We can't descend like Batman, so going through the wall was our only option."