As Kevin Pellatt mentions in his post on the FCA website, in the days when the R30 (the building occupied by the ADRM) was operational (I was there from 76 - 81, with a brief break in Saxa Vord in the middle), it was deemed an acceptable risk ... to have the fire escapes from the upper floor leading on to the roof of the extended floor below (which might have been in flames, but we were hardier then!!).
There is, of course, more to this than is evident from Kevin's brief announcement; there appear to be a number of 'political' machinations involved with the 'purchase' of the ADRM buildings from the Defence Estate and this may well be just another move on DE's part to put pressure on the ADRM Trustees to take over the full responsibility for the now segregated site, including any responsibility for fire safety.
Hopefully, the closure will only be temporary but, in today's economic climate with the pressure on MOD to cut costs wherever and however possible, the ADRM is going to need more than just a few prayers to help it!