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In this incident https://www.bbc.com/news/world-us-canada-46274458 an elevator was described as falling 84 floors, but all survived apparently with little or no injury.

It would seem that the car did not actually fall; a "hoist rope" failed, causing it to descend out of control, after which something brought it to a gentle enough stop that none of the occupants came to any notable harm.

My question is about the way in which elevators are designed such that this event unfolded as it did. Mention of a "hoist rope" seems to suggest that there are separate ropes for lifting/lowering the car and for counterbalancing it, and the counterbalance ropes remained intact. But, if it was out-of-balance enough to "fall", what kept it from accelerating, what terminal velocity might it have reached, and what caused it to stop without a significant impact?

Edit:

What I'd like to see is either:

  • a technical account of what actually happened, or alternatively,
  • a speculative account of what most likely happened, based on a known facts (or reasonable assumptions) about the elevator in question, and the details of the event as presented in the media.

The point of my question is to cut through the media hype and inevitable distortion of fact to better understand the mishap from a technical perspective.

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  • $\begingroup$ Without detail of what forces were being applied, this is too broad to answer $\endgroup$
    – Solar Mike
    Nov 21, 2018 at 6:58
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    $\begingroup$ A "creative " news story. I worked on a nearby building built around the same time as the Hancock building. It had 10 steel cables on each elevator. each ONE capable of holding the elevator. It is very likely they were built to the same standards. So failure of one cable would be a nuisance not a disaster. $\endgroup$ Nov 21, 2018 at 15:19

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Hollywood movies like to show elevators plunging at high speeds to the bottom of elevator shafts for dramatic effect.

This used to sometimes happen in the early days of elevators. Modern elevators have safety systems to prevent this.

Firstly the ropes that are used to hoist & lower the elevator have a factor safety designed into them so that ropes that are used are stronger than needed. This helps reduce the effects of wear and potential corrosion. Also, all elevators must undergo periodic safety inspections, which includes all aspects of the elevator system: winders, ropes sheaves, the elevator cage, counter weights, brakes.

Also, all modern elevators have brakes to slow down and safely stop elevators from an uncontrolled fall.

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  • $\begingroup$ To extend this answer a little further.... Engineers (and code writers, etc) have thought of what can go wrong and how to make it safer. This applies most parts of everyday life. $\endgroup$
    – hazzey
    Nov 21, 2018 at 13:18

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