Passenger safety has always been a priority with relation to elevators. Hence it comes as no surprise to know that they have to follow numerous guidelines and conform to various government norms and regulations. This has ensured a safety record which bests that of every other type of vehicle system. Statistically speaking the accidents that have taken place with regards to elevators have either been maintenance related or due to minor snags like the door not opening etc.
There has been as yet only one instance recorded wherein a bomber plane hitting the Empire State building on a foggy morning caused the elevator cable to snap thereby injuring the lift operator.
While theoretically speaking it is possible for the cable operating the cable to snap, the measures taken practically make it a highly unlikely incident. This is because:
• All modern elevators are fitted with state-of-art safety mechanisms aimed at preventing the free-fall of an elevator,
• Typically an elevator is hoisted and brought down using six to eight steel ropes or cables. Each of these hoist cables is capable of individually supporting the full weight of the elevator plus 25% more. Also each rope is made up of several steel strands which are wounded or wrapped around one another,
• Of the presence of devices which are able to kick-starts a preventive mechanism if it feels that the elevator is descending with speed which exceeds its normal descending speed. This mechanism involves the clamping down of the bronze brake shoes, thereby bringing the Elevator Installer to a complete halt and
• Even if all fails and the elevator does suffer a cable snap, the hydraulic buffer present at the extreme bottom of the shaft somewhat cushions the impact.
To further understand as to why it is absolutely safe to install a cable-borne elevator, it is necessary to understand the workings of the cable system. Simply put this popular and common type of elevator design uses traction steel ropes to raise and lower the carriage or car of the elevator. One end of the rope is attached to the elevator car and the other end loops around a deep-grooved pulley, also called sheave in elevator parlance. The grip between the sheave and the rope ensures that the rope only moves when the sheave is rotated.
Working of the cable system
The sheave is, in turn rotated, by using an electrical motor. When gears are present between the two, the motor is used to turn the gear train which, in turn, causes the sheave to rotate. On the other hand in gear-less elevators, the sheave is directly rotated by the motor.
A counterweight having a weight equally to that of the elevator car filled to 40% capacity is attached to the other side of the sheave. Both the counterweight and the elevator lift move on guide rails present along the shaft sides and this prevents swaying of either the weight or the elevator car thereby reducing any risk there might be. Both the elevator and the counterweights work in tandem in case of emergence and help stop the car thereby accounting for the safety of the passengers riding inside the elevator car.
The author is well-versed with the practicalities of installing a cable-borne elevator and feels them to be much more versatile and safe than the hydraulics ones. He believes that with so many safety factors working together, it is virtually impossible for the elevator car to suffer a free-fall due ever. Hence he confidently recommends and advices people to install a cable-borne life when they feel like installing at elevator either in their homes or offices.