UKC

Is there any research that has meaningfully identified how high/far/fast a hold may bounce when dropped 10m onto rubber crumb. 

What impact might there be to the exclusion zone if the dropped object falls into a hold fixed to the wall.

What sort of material does the cordon need to be, is paper ok?

Is there anything better than a finger in the wind suggestion on what to do?

Don't use plastic poles or allow people to climb near where you're setting is apparently a wise idea (not for the squeamish) .https://www.mountainproject.com/forum/topic/120894130/anal-impalement

Not sure about formal research, but I have seen heavy holds hit rubber crumb and bounce off a fair distance.

My preferred option is fine scaffold netting over Corden netting. But either work to stop the hold.

I would say a cone and ropes don't really cut it.

I would say a good few meters around the work area and from anchor point as a minimum fenced off.

Generally customers will come stand close at the edge as they are interested in the process.  So prefer to set when closed off or quiet.

From my experience of setting up exclusion zones for rope access, the area should be bigger than you think it needs to be. There seems to be something in human nature which means people will linger right next to the barrier as though it's some sort of force field

It amazes me how lax this still is in the climbing industry. Only a few years ago at awesome walls Sheffield they were operating a diesel cherry picker in the main area, setting the big roof with paying customers on the side walls. Got your risk assessment for that sorted, Dave? Utter madness given corporate manslaughter and negligence legal precedents, not to mention legal obligations towards staff and public. "The googles do nothing!" 

Usually we work on height of drop = length of exclusion zone, though this is not always practically possible e.g. working within a city center. Climbing walls do seem particularly bad with this sort of thing especially when you consider that plastic holds can't be put on a lanyard and are likely to be dropped onto a bouncy floor! A barrier should be stop members of the public from physically entering and also offer some protection from dropped objects. A drops calculator is normally used when writing risk assessments (see attached)