Mongoose Steele said:
Actually, Warrior-breed Gaim can survive a pretty long time in the void.
That, and breaching marines should have sealed armour - otherwise they could not board ships that have alternate atmospheres.
Anyway, back to work!
Bry
Regardless of whether they can survive or not, they _did_ just get their chittering selves sucked out into space... and in the case of this example, hyperspace... and it seems unlikely (I don't have RPG data on Gaim, so I can't say for sure) that they have some sort of EVA capability, so regardless of whether they can survive, the decompression of being sucked out into space essentially means they arn't your ship's problem anymore.
I find it curious in the two significant examples of EarthForce Marines we see (Severed Dreams and GROPOS) they have no "hostile environment" equipment... really, they're not much better equipped than the Marines they're obviously modeled on today. And even more curiously, why do the Marines in Severed Dreams have canteens for water, but no dedicated assault equipment, like flashbangs, concussion grenades, etc? You assume the air mix of the station is balanced to be like Earth's, because if it had a higher mix of oxygen to the point where exposives would be dangerous, the PPG fire would ignite it... so, why don't these supposedly dedicated assault troops have any dedicated assault equipment? They have water, but no breaching charges, grenades of either the lethal or non-lethal sort, or anything of the like.
Then of course, you have the question on why Sheridan or Garibaldi didn't just have those levels voided of all atmosphere in the first place, but the answer to this, I think, is readily apparent: They didn't know if the EA Marines coming were equipped for EVA, and it the Marines were and they voided the atmosphere, Bab5's defence forces wouldn't be able to respond (And worse, since _they_ didn't have any EVA gear, the EA Marines could void parts of the station to clear out pockets of resistance, making their defense untenable).