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I recommend googling for the WSJ article "Injuries Put Safety in Spotlight at Cirque du Soleil" because it has a slideshow illustrating the following paragraphs

by jasode 11y ago

I recommend googling for the WSJ article "Injuries Put Safety in Spotlight at Cirque du Soleil" because it has a slideshow illustrating the following paragraphs: According to OSHA, it seemed as if she “flew up at a higher rate of speed than normal toward the grid without tucking in her feet or legs.” The impact of this collision then caused a series of system shocks, ultimately severing the wire rope. Later that night, according to the OSHA files, Kà’s assistant head rigger found the rigger who had been on Guillot-Guyard’s line curled in a ball and crying. He was saying, “I felt the rope go through my hand.” There may have been nothing he could have done. Ascending with her legs extended, instead of in a tuck—as witnesses testified—Guillot-Guyard collided with the grid. According to the OSHA report, “This collision caused a shock load to the winch; the wire rope came out of the sheave/pulley and scraped against a shear point cutting numerous wires in the wire rope. The wire rope broke apart.” Or as Pearson explained, “The cable jumped out of the pulley wheel and was exposed to the sharp edges of the mounting frame. This happened in a split second, almost instantaneously with the moment of impact. [The] cable got slammed against the edge of the wheel and into the sharp edge of the plate that was behind it, and that cut the cable.”

jacquesm 11y ago
That part is literally quoted further down in the article and it makes me wonder why all the focus is on the choice of rope with respect to being used in a swivel joint set-up earlier in the article. They might as well have left that out, it's a whole pile of data but it does not actually seem to have been a factor in the accident at all.
- raverbashing 11y ago
  Exactly The cord was cut. It was not an issue of internal torques or swivels. Unless the helicopter rescue rope was made of a higher shearing strength material that would have gone through the harness without being cut it wouldn't have mattered
  - jzwinck 11y ago
    Simple material strength is not the only consideration. I'm not saying ULT4 rope would have been better in this case, but it is worth noting that ULT4 comprises strands which are not round and are arranged in a special pattern which among other things widens the contact patch with drums, sheaves, etc. I'd like to see the design of the block with sheave that the rope came out of. Some designs have the rope quite captive, while in others it's easy for the rope to come out (sometimes intentionally). The point is, there is a lot going on when you see one of these shows--it is truly "high performance."
    - jacquesm 11y ago
      Shear strength for rope is a totally different parameter than load-bearing capability. It looks from the account that the rope encountered something approaching a knife edge while traveling at high speed. It could have all the load bearing capacity in the world, if it isn't designed to deal with impact damage like that it will fail. What surprises me about the whole affair is that a single rope breaking could lead to a death. This may be a function of the degrees of freedom required for the artists, so don't take this as a 'why don't they' entry, more of a what parameter caused them to choose this particular setup?
      - jzwinck 11y ago
        My experience is on high-performance sailboats rather than acrobatics, but single-rope seems to be the standard. You could imagine having two ropes for redundancy, but then not only would swiveling become more complex (at the sheaves, not the swivel), you would have something like twice the rope weight damping the movements of the acrobat. Coming from a sailing background, another question would be: could they use synthetic/polymer ropes? Where cost is not much of a concern, things like Dyneema have taken over in a lot of roles.
        jacquesm 11y ago
        Funny, I was writing that with my stint for a sailmaker in the back of my mind and yes, single rope is the standard. But in sailing gravity is not always luring to catch you if something goes wrong (though you can absolutely die from an accident during sailing if a line (or a stay) breaks). Probably a better comparison would be mountaineering and there there are plenty of people that climb without ropes at all...
AlbertoGP 11y ago
Yes, without the illustrations it's difficult to understand the details on how this happened. The WSJ article is here: http://www.wsj.com/articles/injuries-put-safety-in-spotlight-at-cirque-du-soleil-1429723558 http://www.wsj.com/articles/injuries-put-safety-in-spotlight... Direct link to the slideshow: http://graphics.wsj.com/cirque-embed-only-042215/?embed=1 http://graphics.wsj.com/cirque-embed-only-042215/?embed=1

by jasode 11y ago

jacquesm 11y ago

That part is literally quoted further down in the article and it makes me wonder why all the focus is on the choice of rope with respect to being used in a swivel joint set-up earlier in the article. They might as well have left that out, it's a whole pile of data but it does not actually seem to have been a factor in the accident at all.

raverbashing 11y ago
Exactly The cord was cut. It was not an issue of internal torques or swivels. Unless the helicopter rescue rope was made of a higher shearing strength material that would have gone through the harness without being cut it wouldn't have mattered
- jzwinck 11y ago
  Simple material strength is not the only consideration. I'm not saying ULT4 rope would have been better in this case, but it is worth noting that ULT4 comprises strands which are not round and are arranged in a special pattern which among other things widens the contact patch with drums, sheaves, etc. I'd like to see the design of the block with sheave that the rope came out of. Some designs have the rope quite captive, while in others it's easy for the rope to come out (sometimes intentionally). The point is, there is a lot going on when you see one of these shows--it is truly "high performance."
  - jacquesm 11y ago
    Shear strength for rope is a totally different parameter than load-bearing capability. It looks from the account that the rope encountered something approaching a knife edge while traveling at high speed. It could have all the load bearing capacity in the world, if it isn't designed to deal with impact damage like that it will fail. What surprises me about the whole affair is that a single rope breaking could lead to a death. This may be a function of the degrees of freedom required for the artists, so don't take this as a 'why don't they' entry, more of a what parameter caused them to choose this particular setup?
    - jzwinck 11y ago
      My experience is on high-performance sailboats rather than acrobatics, but single-rope seems to be the standard. You could imagine having two ropes for redundancy, but then not only would swiveling become more complex (at the sheaves, not the swivel), you would have something like twice the rope weight damping the movements of the acrobat. Coming from a sailing background, another question would be: could they use synthetic/polymer ropes? Where cost is not much of a concern, things like Dyneema have taken over in a lot of roles.
      - jacquesm 11y ago
        Funny, I was writing that with my stint for a sailmaker in the back of my mind and yes, single rope is the standard. But in sailing gravity is not always luring to catch you if something goes wrong (though you can absolutely die from an accident during sailing if a line (or a stay) breaks). Probably a better comparison would be mountaineering and there there are plenty of people that climb without ropes at all...

AlbertoGP 11y ago

Yes, without the illustrations it's difficult to understand the details on how this happened. The WSJ article is here: http://www.wsj.com/articles/injuries-put-safety-in-spotlight-at-cirque-du-soleil-1429723558 http://www.wsj.com/articles/injuries-put-safety-in-spotlight... Direct link to the slideshow: http://graphics.wsj.com/cirque-embed-only-042215/?embed=1 http://graphics.wsj.com/cirque-embed-only-042215/?embed=1