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Mandalay Bay video wall fall

Discussion in 'News' started by jayvee, May 10, 2019.

  1. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    @TimMc, the most persistent rumor I hear is that whether through malfunction, disconnection, or something missed at the controller, the rig was lowered and one hoist in the group didn't follow. Supposedly that hoist absorbed the load until it couldn't anymore, and then when the load dropped and was caught by the other hoists, it shock-loaded the verlocks to the lower truss which then ate their cables.

    Disclaimer / That could all be wrong but from the photos at least looks plausible.
     
  2. DavidJones

    DavidJones Active Member

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    I had seen all of those photos and have heard a few similar accounts. It sounds plausible that at some point either only one hoist ran, or one failed to run, or someone ran the hoists down, but accidentally missed a switch, had one hoist set to up.

    Either way It was the verlocks on the truss below that failed not the motors themselves. Those look to be 1/4" or 5/16" verlocks. That is a strange way to rig a video wall, to say the least, and with the turnbuckles there, a redundant form of leveling. The way verlocks work can easily wear out the cable and if these cables and verlocks were used often at around the same length it would create one spot on the cable that was particularly worn. All it takes is a couple of broken strands, and the cable is no longer thick enough for the gripping mechanism to hold. I would not have used a verlock to hang this truss, there are much better solutions to hang under a carrier truss.

    Side point about stagemakers. It's not that they eat the chain so much as, that any twist in the chain eats the chain guide. The SM series had plastic chain guides and later cast aluminum guides. You MUST run these out of the box with a pickle, and keep tension on the chain the last foot ot two as it takes the weight. Any twist that gets to the guide will shatter or crack it. Typically the chain is fine since its a harder material, but that motor is of no use until the guide is replaced.

    The current SR Motor series I think is a lot better about this, and has a lot of much nicer features than most other hoists out there. They also run SIGNIFICANTLY quieter than CM.
     
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  3. DavidJones

    DavidJones Active Member

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    And this you don't fly also, ever, full stop?

    I don't think this is a fair analogy. The 737 MAX was a manufacturing error. The pilots did not make a mistake, the equipment failed.
    Plane crashes do happen, and yet is it still statistically safer than driving, and nobody's going end all commercial flights.

    In the case of this video wall, the motors did not cause this, even it was a motor that got "stuck running," The part that failed was the Verlocks holding the lower truss, which in my opinion was an inappropriate choice of hardware for the application. The fault is not on the gear; it's on a person.

    Personally, I have known two people who were involved in runaways in theaters. This is not a reason to never specify counterweight fly systems. People either did not have proper training, or they made a mistake. Just because you don't understand something, are afraid of it, or have limited experience with it, does not make that thing inherently bad, it just means we have the opportunity to learn something new.
     
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  4. TimMc

    TimMc Well-Known Member

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    So a couple of phone calls later... the rumour mill grinds out that this was a multi-part failure - operator, design, hoist not working. I have no way of knowing first hand and my Vegas contacts were not on that show so consider this to be at least 4 degrees from Kevin Bacon.

    That said, a year or so ago in out downtown arena we had a heavy (lbs/tons,KG) and automation-centric (moving trusses dancing, etc) show that had 1 hoist on the mother grid hang up/not get power/had non-functional control as they brought the grid in. Fortunately the hoist operator hit the Big Red Button when the truss broke, 60 feet in the air. It was loud and for those of us who Had a Frickin' Clue, scared us downstage of the possible/likely "It's Raining Truss" moment. The Weather Girls did not sing, but it took a long time for some of the local hands to move out of the Gravity Sucks Zone in spite of all we graybeards yelling at them to vacate the area. {/story repeat}

    I hope to never be a part of such a situation again.

    I've said this before - for the most part, there are no accidents, no random and completely unpredictable failure of adequately rated materials, when used and deployed in accordance with KNOWN engineering principles. These are ultimately *people* failures, whether they are from inadequate training, improper training, operator failure to fully and completely implement that training, design defects or improper material selection, or improper assembly/use/storage/transport, one or more persons made a deliberate decision to deviate from best practices. And "stuff" happened.
     
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  5. TimMc

    TimMc Well-Known Member

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    Kinda my understanding from the "I wasn't there, but I heard...." mill as well.
     
  6. venuetech

    venuetech Well-Known Member

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    GripLock is another brand, with the largest for 5/16” cable. Looks to be German made.
     
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  7. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    The system failed and the motors reportedly not functioning as they were intended was a part of the system failure. You sound like a politician parsing their words.
     
  8. DavidJones

    DavidJones Active Member

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    My point was that from all the information that was gathered, this looks like it was a poor system design and/or application. If I used underrated or worn verlocks to hang something from a batton, and the verlocks failed, would you blame the counterweights, or the arbor, or the head blocks.... or maybe flyman?

    Knowing that a motor could potentially go out of weight is part of the consideration when planning something like this. If proper hardware had been used and one motor failed to run, the brake should start to slip at 125% of its rated load, the load would then roughly rebalance. I'd be willing to be this is exactly what happened. It will result in a shock load, but its proper safety factor is observed, the wall probably would have stayed in the air; some of the rigging and motors might have sustained damage. At that point, it would be prudent to cautiously disassemble this system and take the rigging out of service until inspection and load testing are done.
     
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  9. egilson1

    egilson1 Well-Known Member Premium Member

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    Yeah, that’s wrong. The break on cm hoists are designed to hold a LOT more than 125% of rated capacity. Now the protector is designed to slip at 125% to 230% of load. But remember the protector is there to prevent motor from overheating and not necessarily to stop the user from lifting to much.

    Another thing that has been bugging me in social media posts about this failure is that everyone is blaming the VERlock/glider. As I mentioned before unless there is evidence that the device physically failed, such as the the ball bearings inside the shaft came out, or the ring cracked, etc, the the photos I’ve seen seem to show that the wire rope itself failed. In every destructive test I’ve done on them the wire rope has failed at over its ultimate strength. I’ve even retested gliders on follow tests and they still worked.

    Now we can certainly call into question if they should have been using 1/4” (if that was indeed what size they were working with) wire rope.

    But we also can’t tell just by the photos alone. Without examination of the actual hardware we can’t determine what happened.

    Ok, off soapbox.

    Ethan
     
    Last edited: May 18, 2019
  10. TimMc

    TimMc Well-Known Member

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    Yes and yes to the text in bold. Metal fails when loaded beyond its tensile strength and at the point where its elasticity is compromised - a pinch point, kink, etc. Wire rope ain't exactly new stuff and the failure modes are well understood. The design choices based on what we can make from the pictures raise some questions with me as well, but they are unlikely to have *caused* the primary failure, the question is whether or not the design was appropriate for the load and if the design intent was for the secondary rigging to survive, intact, a primary suspension failure.

    I hope there are definitive answers to come from the investigation, but because there were no deaths or personal injuries I don't think Nevada OSHA will investigate and any findings by insurance investigators are proprietary.

    Ethan, you're absolutely right: without forensic metallurgical analysis we're left to speculation.
     
    Last edited: May 19, 2019

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