The front door to the building is the only one that is open; all the others are closed and locked.  From the open door the faint smell of chemicals wafts out.  No sound has come out of the building sense the explosion.  The building was about three stories tall and had a flat roof.  On top of the roof there were the ends of some ventilation shafts.  There were covered by some grates but they could be easily taken off.  It would be impossible for a normal person to squeeze through the bends and turns at the start but if someone could move as if they had no backbone then they could make it through with little trouble.