How much are you going to enter a lift in a day? Many are living and working over the ground 10, 20 or even more stories. But little do you think of the complex electronic devices that lift you up and down so you don’t think about a terrorist tower in the cellar.
The steel cables holding them up are the most robust instrument for the elevator cabin. What are the numbers of cables on each cabin? Six or eight are there. Thus, even though all except one fails, the lift is still secure, as each steel cable has greater weight than the lift cabin.
For a specific structure, building codes set the protection factor to 12, meaning the total weight of the lines must be sufficient to carry the mass of a fully loaded cabin 12 times as high. Each fabric can potentially carry more than the cabin weight.
In 1945, a B-25 bomber struck the Empire State Building and crossed all cables on the lift. The lonely passenger survived the 79th floor crash, when the cables under the cab slowed down and cushioned the landing. On 11 September 2001 the aircraft that struck the World Trade Center cut off the lift cables, which, tragically, contributed to injuries.
There are two or three kinds of frequencies in elevators. In the case of a mistake in the security chain, the pulley above the cab will be closed and the elevator will not move. The elevator brake is clamped down until there is a source of power to release the brake, unlike a car brake to be depressed to activate. This ensures that the engine break would be shut down due to some power loss, either due to equipment fault or an electric network malfunction.
In a lift attached to the underside of the building, a safety break is also mounted. This is the refurbishment that made it possible to use the Passenger Lift at the World Fair in New York 1853-1854.
How does a break in security work? When the sensors sense that the cabin is downwards, the metal rods that the elevator rides along are stuck from under the cab into a pipe. Friction builds between the wedge and the rail that puts the car to a convenient stop.
In this case they would meet a cockpit that would make the cabin an abrupt, but ideally survivable, stop if the counterweights had hit the top or bottom. A curious closing note, even with this remote chance, is that (statistically) lifts are always better than taking the stairs!