You are in a crowd with thousands of other people when an explosion goes off.

What do you do?

Kevin Reeve recently wrote a helpful post on this subject, its called How to be Safe in Crowds and its worth reading.  Other than avoiding large crowds, he gives some good advice on how to develop good situational awareness and have a bias towards action.  This will help maximize your chances of survival during a disaster.  The main concept he highlights is controlling panic, as he writes:

The KEY to surviving any event in a crowded venue will depend almost entirely on your ability to control personal panic, to assess the situation, and to take immediate action.  If you panic, you drastically increase your odds of injury or death.

This is related to the concept of OODA loops in the decision-making process.  All four parts of the OODA loop require active participation (Observe, Orient, Decide, Act) and the more you practice these in everybody life, the more finely-tuned they become.  So keep these concepts in mind and put them into practice.  Who knows, someday you may need to react quickly to a disaster so develop your bias towards action now.

HT to Kevin (again).