It goes without saying but worth noting that there are no limits to the different things that could happen in scenerios such as the mass shootings in public areas. I think that the chance of me being in one of these terrible ordeals is so slim that I would not really practice for it other then normal pistol range practice and reloading quickly (if I ever decide more than a mag in the weapon should be carried). The ability to use your brain is more important than armament. The standard practice of making sure of your own safety before attempting to save others that is practiced by firefighters seems like a good place to start. (Unless becoming a hero is first on your list
) So many things come into play on when you should or desire to intervene that discussing the merits of when you engage isn't much help IMHO. Being involved in limited military action did prove to me that when the chips are down, I performed better than I ever thought I would. Trust your instincts. Most people do a good job in handling crisis situations. Being confident in yourself will serve you well. Unless you have an incurable medical condition, getting yourself home alive to your family is your #1 goal. Just my thoughts on a very interesting topic.