I saw this in the list of survival articles today. I do not think any one can predict how people will react in situations until they are there but the advice seems simple enough http://www.news.com.au/news/how-to-survive-a-shooting-massacre-hint-carry-a-torch/story-fnejlrpu-1226438563404.
First off no matter what the situation there may be some time for first response providers to get to you. Anything you can do on your own may save your life.
The bottom line is to carry a flashlight. In a dark building or at night it might give you an advantage. If nothing else it can make you feel better. There are a lot of small flashlights on the market, some that attach to keep rings or are small enough to go into a backpack, etc. See http://shop.vtarmynavy.com/outdoor-lighting-c507.aspx
The other advice was to get moving. The used to say in the Army that 3 second rushes were the most effective way no to shot during a fire fight. Unfortunately cover and the ability to shoot back greatly improve your odds of survival.
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