I recently finished a book on disasters and people's response to them called "Unthinkable." The book had a lot of insight and two points stood out. One is how fast things can go wrong and the second is how slow people are to react.
Here's an astonishing fact from the Giffords shooting.
In a hail of gunfire that lasts no more than 15 seconds...
32 shots, 6 dead and 13 wounded...in 15 seconds. Unbelievable. That makes the reaction of the crowd all the more impressive. Most people freeze in a crisis. The fact that the crowd jumped Loughner that quickly is really amazing.
We tend to think of disasters unfolding like they do in movies. In reality, most disasters are over before we can even begin to respond to them...and if you have to respond on the fly it's way too late.