From the Report of the Virginia Tech Review Panel, analyzing the mass murder there last year:

A female student trying to get into Norris Hall shortly before the shooting started found the entrance chained.  She climbed through a window to get where she was going on the first floor.  She did not report the chains, assuming they had something to do with ongoing construction.

I can’t imagine that if I showed up to work to find all the doors chained I would even consider that a gunman could be responsible, nor that he was inside at that moment preparing to start shooting.

However, I also highly doubt that upon finding the doors chained shut I’d consider climbing through a window to get in anyway.