Also remember that proper use of chain hoists requires “that malfunction or failure of one hoist’s load bearing components does not cause load loss and/or overloading of any other hoists in the system.”
Hoists don’t just give up the ghost and fail. The same way a counterweightarbor doesn't just move on its own if its weighted correctly and the operator uses the rope lock properly.
And finally if the hoists are moving a static safety is irrelevant. They only work once the load is in final position.
Specifically regarding Boardwalk Hall... I may twist a memory ankle on this walk down memory lane... Mountain Productions installed and maintained the supergrid in BH, and all proposed loading of the supergrid was subject to Mountain's engineering dept specifying the points of loading. The fuzzy memory says *speculation* was that there was more than 1 issue - including not following the Mountain's point schedule, using the supergrid to lift a set piece, and a failure to individually confirm each hoist's operational status prior to raising the supergrid. It's easy to find pictures but a definitive causality seems harder to track down. I'm sure NDAs were involved.
Yup. They were lifting set pieces onto the stage that were not part of the load calculations. The lighting/PA/Video was already hanging on the mother grid. The additional point load on sections of the grid caused localized buckling.
What I'm seeing is failure during motion. Safeties wouldn't prevent that at all. I've only ever had close relations with a single motor failure. The motor didn't fail the chain did. During motion and not at height.
