In article ,
(Lins) wrote:

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?

Briefly, no. NASA and the US Air Force experimented with this in the
early 1960s. No exploding heads, etc. One has only 10 to 15 seconds of
consciousness because oxygen will be pouring out of your lungs into the
vacuum, which leads us to the big mistake shown in that sequence. The
astronaut should not have taken a big breath and holding it before
blowing the door. That would have killed him, because his chest would
have burst. If you ever find yourself about to be immersed in vacuum,
exhale completely and keep your airway wide open.