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Yes, elevators are remarkably safe. Each car is held by four to eight steel ropes (any one of which can support the car alone), an overspeed governor that grips the guide rails if the car falls too fast, a spring-loaded machine brake that clamps on when power is cut, and a counterweight that pulls a lightly-loaded car up rather than down. In the US, elevators cause about 30 deaths a year across ~18 billion trips.
Elevators are an integral part of life for many people, particularly those living in buildings higher than 5 stories or those working in tall office buildings. Many people will take the elevator even if their destination is only on the next floor up or down, simply due to how easy they are to use. However, there are some people who are afraid of elevators, either due to the possibility of the elevator car falling or due to their fear of the small space of the elevator car.
That begs the question: are elevators actually safe? As it turns out, elevators are very safe… even safer than stairs, in fact!
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Elevator Cables Do The Hard Work
The mechanism that makes elevator cars particularly sturdy is the set of steel hoist ropes holding them up. How many cables are on every car? Most modern traction elevators use four to eight steel hoist ropes (newer machine-room-less designs use flat coated-steel belts instead). That’s right, even if all but one fail, the elevator will still be held up safely, since each rope is designed to support several times the weight of a fully loaded car. This means that only a freak accident could cause the car to plummet, since every rope would need to be severed at once. Such accidents have actually happened twice in modern memory. The first was on July 28, 1945, when a U.S. Army B-25 Mitchell bomber, lost in fog, crashed into the Empire State Building between the 78th and 80th floors. Twenty-year-old elevator operator Betty Lou Oliver was first thrown from her car and then placed by rescuers into another elevator whose damaged ropes promptly gave way, dropping her 75 stories to the sub-basement. Miraculously, she survived (with a broken back, pelvis, and neck), thanks to a combination of factors: air compressed in the relatively airtight shaft cushioned the car like a giant piston, the severed ropes piled coil-like in the pit absorbed some of the impact, and a hydraulic buffer at the bottom of the shaft soaked up the rest. Her fall is still the Guinness world record for the longest elevator drop survived.
The second cluster of incidents happened on September 11, 2001, when the World Trade Center towers were hit by two planes. The 9/11 attacks remain the worst elevator disaster in history, with around 200 people killed in the towers’ elevators. Even there, the safety systems mostly worked: many elevators whose hoist ropes were severed were stopped by the rail-grip safeties (one famous case saved 25 occupants), and most of the elevator fatalities were caused by fire and burning jet fuel rushing down the shafts, not by free-fall impact.
These two incidents shouldn’t deter you from taking the elevator, though, because each elevator is designed with a generous “factor of safety.” Under the ASME A17.1 elevator code (the dominant safety standard in the US and Canada), passenger-elevator hoist ropes are designed with a factor of safety of roughly 11 to 12, meaning each rope can carry many times the maximum load it is ever expected to see. The number of ropes follows from this factor, ensuring that the car you step into is as safe as the engineers can reasonably make it.
Elevator Brakes Will Slow You Down
Another mechanism that keeps elevators safe is a layered braking system. An overspeed governor watches how fast the car is moving, and if the car ever exceeds its rated speed (because, say, a rope snapped), the governor trips the safety brakes on the sides of the car. These safeties wedge against the steel guide rails that run the length of the shaft, gripping them like a vise and bringing the car to a controlled stop without the sudden jolt that would injure passengers.
There is also a second brake at the motor itself, called the machine brake. It’s a spring-loaded brake that is held open by electric current during normal operation. The moment power is cut (whether by a building blackout or by a controller fault), the springs automatically clamp the brake onto the drive sheave, stopping the car. In other words, the elevator’s default state is “braked,” and electricity is what keeps it moving.
The cables and brakes are not the only safety mechanism though. An elevator has one more interesting innovation that will always keep you safe.
The Counterweight Factor
The great thing about this final safety mechanism is that it will prevent the elevator from crashing to the ground, even if both of the above mechanisms fail.
Counterweights are basically a stack of weights attached to the other end of the ropes that hold the elevator car. By industry convention, they’re sized to balance the empty car plus roughly 40 to 50 percent of the elevator’s rated load. That makes the counterweight heavier than the empty car, but lighter than a fully loaded one. So if everything about the elevator fails and you are the only person in the car, the counterweight is still heavier than the car (plus you), and the car will actually drift up, not down. When it reaches the top, you don’t have to worry about crashing into the ceiling, since there is a buffer at the top of the shaft to cushion the upward impact.
So now you know: an elevator comes equipped with a layered set of innovative safety mechanisms (multiple hoist ropes, an overspeed governor and rail safeties, a spring-applied machine brake, and a heavy counterweight), and it would take a truly rare, freak accident for all of them to fail at once. Even with that distant possibility, statistically elevators are dramatically safer than the stairs. In the US, elevators kill roughly 30 people a year across about 18 billion passenger trips, while stair-related falls kill thousands of Americans annually. So next time you’re wondering whether to take the lift or the staircase, the numbers are firmly on the lift’s side.
