If you work in an organic chemistry lab, odds are excellent that eventually you're going to have to handle some sort of emergency. There are so many energetic materials used, and so many flammable substances around to go up with them, that sooner or later every working chemist has (or is close to) a fire or explosion.
I don't want to sound too alarmist, because most of these are small affairs that go out quickly. Some of them, though, are small affairs that should go out quickly, but get transformed by bad decisions into large, exciting ones. And once in a while you get one that starts off large and just keeps building, and good luck to all concerned. Here's the question, though: how do you behave?
There's no way to know a priori, and there's no way to know about your labmates, either. You can place some bets: a person who's normally level-headed has a better chance of remaining true to type in a sudden emergency (as does a person who's usually jumpy, for that matter), but there are no guarantees. You have to wait until a situation develops to find out. Some folks are going to surprise you, in either a positive or negative way.
The biggest problem many people have is that they freeze up, unable to think of the best course of action. In my experience, doing nothing in a lab crisis is a much likelier problem than doing something immediate, forceful, and wrong. (Immediate action is usually a sign that the person involved has thought about their options in advance). It always pays, when setting up some chemistry that might turn lively, to picture yourself bolting for the nearest fire extinguisher. That'll at least fix its location in your mind, not to mention concentrating your attention a bit on what you're doing. If a fire extinguisher isn't the answer to your potential problem (which it is, in many cases), then by all means imagine doing whatever else you'll need to do if things go wild - heaving in buckets of sand or handfuls of ice, shutting off valves, what have you.
The problem with freezing up (or with its equivalent, running around in circles), is that not only are you not doing anything about the problem at hand, you're probably interfering with the efforts of anyone who is. You'd be surprised at how many times you have to push someone aside to get a clear shot with an extinguisher, for instance. Doing something is the first choice, but getting out of the way for someone else to do something is not to be disparaged.
In some twenty-five years in academic and industrial labs, I've probably been in the vicinity for about six incidents which were serious trouble, either real or potential, and several others that could have turned that way, but didn't. It's been a while since the last one, though, and that's how I like it. But once I get back into the lab, you can be sure that I'll be checking to see where the fire extinguisher is, because you never know.