Douglas, a 15 foot raised floor IS pretty high, and you are right: it becomes a safety hazard...

"Where did that database guy go to?" "Oh, I think he fell through a perf panel... maybe he's down there somewhere!"

At Netfloor USA, any raised floor over six feet and we like to have a serious conversation with the owner, architect and engineer about safety.

We did a pretty large data center project that called for 10 foot raised floors and we did questio the reasoning. But, the depressed slab had already been poured, so there was nothing to do, besides put a few rows of caution tape near the edge of the access floor as the install progressed, and to keep other trades up to date on the risks involved if they worked in the same area as us.

We did use adhesive and 4 concrete anchors for every pedestal, but were still concerned with the sheer height of the floor if some panels were removed.

The air velocity under the floor WAS pretty low, and most areas of the data center were quiet. I guess that's a safety factor: if you fall through the raised floor and it's quiet, SOMEONE might hear you hit the bottom! jk :)