2001

Would anyone remember the scene in 2001: a space odyssey wherein David
Bowman has to basically bust his way back into the spaceship Discovery?

He's not wearing a helmet and he takes about 5 seconds before he starts
closing the powered door and flooding the room he's blown himself into
with oxygen.So basically he's in orbit above Jupiter,or thereabouts,for
at least 5 seconds without a helmet.

What I am wondering is this: wouldn't his head have been freeze dried
instantly? Or wouldn't the vacuum have done something horrible to it?

Thanks