Elevator systems of today have a wide range of features intended to assist lower the likelihood of accidents and provide users with a rapid, dependable journey.
Elevator systems can be classified as either “Traction” or “Hydraulic.” Some of their safety mechanisms also vary amongst them because of how they each operate differently.
The majority of elevators that travel six floors or more have a “traction” feature. Strong steel cables that are pushed by a hoisting equipment suspend traction elevators. Counterweights balance the load and facilitate the elevator’s movement on the machine. The elevator’s full load of passengers as well as the strength of the steel cables, which are several times as strong, can be securely supported.
A speed-sensing governor and the safety brake work to halt an elevator if it should overspeed in the downward direction. When an elevator exceeds its speed limit, the governor triggers the safety to grab the rails that the car is moving along, safely stopping the elevator.
Several safety features are also built into the door mechanism of a contemporary elevator. Sensors stop the doors from closing further when they detect people or items in the door opening. Older systems include mechanical “safety edges” that cause the doors to retract or stop when they come into contact with someone or anything. Modern systems can detect people or things in the entryway and reverse or stop the doors without coming into touch with them by using a huge number of invisible light rays.
Door operators contain devices which limit the amount of closing force. Newer systems are better able to keep the closing force consistent even under unusual conditions such as the “stack effect” which can cause heavy air movement in elevator shafts.
The hoistway doors have interlocks that help ensure the elevator cannot depart a landing until the doors are completely closed and secured. If the doors are pushed open, the interlock circuit will be disrupted, resulting in an abrupt stop for the elevator.
At various points during its voyage, the car is detected by a variety of switches in the elevator shaft. They start slowdowns and stops when necessary, preventing overtravel in either an upward or downward motion.
Door restraints can allow regular operation of the door when the automobile is close to the floor level, but they will prevent forcible movement of the door when the car is away from the floor level, which is a particularly dangerous activity to discourage.
In most elevators, the emergency exit hatch can only be opened from the outside by qualified emergency personnel. This is also done to help stop any passenger from entering the risky elevator shaftway.
Buffers in the “pit” beneath the automobile act as a safety net for any unforeseen descent below the lowest landing.
There are a number of safety-related items in the elevator cab. A passenger can raise an alarm by pressing the emergency alarm switch. Most elevators have an emergency phone or intercom that can be used to get help if the elevator car should stall. Additionally, emergency lighting keeps everything illuminated for hours in the event of a power outage. Emergency power may be available in some systems, allowing the elevator to move and the passengers to be evacuated.
In many elevator systems, a special fire emergency system has been installed. It may be manually activated, or may respond to smoke sensors in the building. Exact operation varies by local codes, but generally such systems return the elevator to the main floor, open the doors to allow passengers to exit, and make the elevators available to emergency personnel.
Hydraulic elevators are propelled by a jack mounted below the elevator. A pump moves hydraulic oil into the jack, causing it to raise the elevator. For the down trip, valves control the oil’s to return to the system’s storage tank, safely lowering the elevator car.
Because of their bottom-supported design, hydraulic elevators do not utilize the type of safety brake found on traction elevators. However, for installations with older jack designs, Schindler has developed the LifeJacket® safety brake that can be added to existing elevators, offering an increased factor of safety in the remote chance of corrosion causing the rupture of the underground jack casing or piping.
Other systems on hydraulic elevators are essentially identical to those on traction systems, and have similar safety features.