I know the tiles your on about, and I have worked and stood on many of these and never broke one, to break them you would have to be really clumsy or very heavey.
I would have thought that the problem is Underlying the tiles and not the tiles them selfs.
I can't grasp why you have to walk over a tiled roof as an escape route? if it was a H&S issue they would have made you instal a metal platform with metal stairs.
As a machine designer, I'm sure you could design a simple single gantry type escape route, so much more safer than running along a roof in the dark and rain with no way down off the roof, if a house is on fire.
If this was my family's safety, it would be a case of sod the cost and build a proper escape route.