Thanks Paddington.....Did you design for internal over-pressure or external over-pressure situation. We have an external overpressure situation our building is within overpressure zone however, only one corner (An occupied room) is being suggested to be designed for over pressure situation and rest for normal, obviously for economic reasons. Is it something you can do for external pressure - just design envelop of occupied room for blast pressure and rest of building for normal loading....and envlope will include four walls and roof of this occupied room....Thanks - any other experiences similar to this. Does API 752 or CCPS guideline offer any help.....