Chris' bomb refuge areas are equally idealistic (which doesn't help the average building manager in the slightest). The criteria are very simple. Although I agree that such an area must be assessed by a qualified specialist in the field, you're looking for a space that's safer than staying where you are (such as an open-plan office) and which represents a safer option than immediately evacuating the building. Important though they may be, other factors are something of a bonus.
Having assessed over 200 buildings in the City and West End of London, I've found that most of them will have somewhere that meets the criteria – but very few of them have ideal areas.
Source
SMT
Postscript
Dr John Wyatt, Technical Director, SDS Group Ltd













