Since then, more studies have been done showing that a human being can survive up to 90 seconds in vacuum, assuming that they have outside help (you become unconscious a lot sooner), and haven't done anything stupid like try to hold their breath.

Kubrick and Clarke looked at these studies when deciding if their astronaut in "2001" could survive the helmet-free airlock entry in the movie. YouTube of that scene here. Note that Bowman seems to be holding his breath! Best tactic: a good scream when the port blows out. Then hope you can do something in the ten seconds of consciousness you might have left...

More here.