Early 70s. Exercise.....? ATCOs dispersed to Rwy caravan and radar head. (CR787). I was sent to the radar head on one exercise with a very competent NCO and we continued to provide a service for some 36hrs. Endex, we retired for debriefing and as we left the building, a GRSF cpl pointed out a notice that said "do not remain in the vicinity of this building for more than 4 hrs."
AFAIK neither of us suffered any harm! Happy days.