Now that I recall, this seems rather funny... wasn't really at the time...
I can't recall the time but it was maybe fifteen or twenty minutes before we were directed to leave... the chief of staff, a Navy captain, walked in to the office where we were all gathered watching the news. We were all riveted... A mile away from the Pentagon and we knew nothing about the crash there until we saw it on television. Anyway... the Captain walks in and tells us that we can all go home if we like. Of course, nobody moved.
Well... behind the office building is a Hilton Hotel. We can see the back of the hotel, where the service workers enter and exit and where the garbage is collected in one of those big bins that they drop with a tractor truck.
BOOM!
Well... they dropped one of those empty boxes. Imagine a office full of wide eyes and gasps... we each looked at each other in almost perfect unison, we said... "Gotta go!"
By the time we were all packed up and getting out, somebody started to worry about large gatherings of government employees and we we're ordered to leave.