They obviously should have had backup harnesses connected to something else on the ceiling. Whenever they do things like this in the US at concerts or shows they always have these things. And the chains obviously are supposed to be inspected and made much stronger than they need to be to give a big margin of error. Seems like a totally unnecessary accident that should have been avoided. Really tragic.
Rigging is usually a multiple of the load it experiences normally, depends on the locality. For something holding humans, 10x load plus harnesses is common.
This was clearly under specced, and that's why we have spec for such things, to prevent this.
