I've actually thought about this scenario. It would be very easy for a gunman to enter the bowling alley where I bowl at and do what this guy did. Of course it could happen in any business environment, even my own office. In my mind, I've thought about what to do if I ever found myself in this sort of a situation, what would I do, where would I go. At the bowling alley, it would depend what section of the building I'm at. Where I bowl, Lanes 15 through 20 are around the front door. Lanes 1 through 10 are by the side door. These doors are always open and anyone can enter. the higher end of the lanes has no exterior entrance or exit, outside of a fire door in the back. If an event happens at my office, the best I could do is either hide under my desk, or run to the back fire door. I've always thought to always be aware of your surroundings at all times.
On the news, one guy who was at the bowling alley ran down the lane, hit the deck, slid to where the pins were and climbed up on top of the machinery to hide.