We, as humans, have lots of fears. Some are afraid of heights; others are afraid of falling. Then there is claustrophobia. Given this, is it a wonder that lots of people are afraid to ride elevators? If you think about it, riding an elevator combines all three of these basic human fears. Let’s take a moment to take a closer look into what all is in place to keep elevators from “falling” and to keep you safe from these first two fears.
What Are Traction Elevators?
All elevators have safety devices of one type or another. For example, traction elevators are those that are suspended by steel cables that have speed-limiting governors. These devices are set to trip at a predetermined speed according to the speed of the elevator. When tripped, these devices cause a clamping action on the governor’s cable, commonly called a governor rope. However, this rope is not a rope at all, but rather high-strength steel or iron.
As the elevator car moves downward at an accelerated pace, the governor rope is clamped, and its downward motion is stopped. As the elevator continues down, the stopped rope lifts the car’s wedge safeties causing them to wedge against the elevator’s main rails. This stops the car in a controlled manner at a predetermined distance according to the car’s speed.
How Can an Elevator “Fall” Up?
Let’s look at another scenario. There are tales of elevators “falling” or “plummeting” out of control, but what about going up? However, I have never seen this happen in almost 40 years in the trade or my father’s 30 years, for that matter. This is because it, for all intents and purposes, cannot happen.
Most traction elevators work on an “overbalanced” principle. Let me explain. The car is at one end of the cables, it weighs X number of lbs., and can carry X amount of weight, be it in the form of passenger or freight. But what’s at the other end of the cables?
Well, it’s called a counterweight or CW for short, and it’s just what its name implies. It’s a stack of weights that balances the weight of the car. This balance is usually 40% (there are other percentages used, but for our purposes, we use 40%). Let’s say with one person on the elevator, the CW (counterweight) is about 60% heavier than the car. So, what happens if the electrical braking mechanism fails or some other catastrophic failure occurs? The CW is heavier than the car, so the car is going to the top in an uncontrolled manner. In other words, it’s ascending (or “falling up”).
Elevators “Falling” Up
Relatively recent, there was a change made in the elevator code (ASME A17.1) that made a device called a “rope gripper” to be a required addition on new installations and any modernization where the controls were changed. What occurs now is when the elevator controller is signaled that the car is not supposed to be moving in the up direction, it sends a signal to the rope gripper, and a powerful set of jaws clamps down on the cables stopping the car’s upward movement.
So next time someone asks, “what if this elevator were to fall”? You can reply that it depends on whether it will fall up or down?
Authored by Keith Gaut – Field Supervisor and Safety Manager for Bagby Elevator Company