How I react to a fire alarm depends on where I am.

When I was working in a hospital, heavily compartmentalized by firewalls, sprinklers and an exit only twenty seconds away, I generally waited for the second shoe to drop or some indication of the size and location of the problem to be revealed.

When I was working at a chemical plant, surrounded by a buttload of flammable, explosive and corrosive chemicals, you were risking getting run over if you got between me and the exit. We would stay aware of the wind direction and make sure we could leave quickly and stay upwind.

It always pays to know where the exits are and contemplate them in terms of what you do if your first, or second, choice is blocked. Keeping this in mind means you don't have to spend time thinking about it.