[quote=@BCTheEntity]
[@Sophrus] ...sized for humans, or Space Marines? Bearing in mind, of course, that a fully-functional suit of power armour negates the need for a pressure suit.
[/quote]

Also bear in mind that this is a pre-heresy ship, which would be much better outfitted. In addition, a pressure suit, while not strictly necessary for a properly equipped marine crew, would always be helpful for emergency situations and quick repairs to the outside of the ship. It is known that space marines do not, in fact, spend 24/7 in their armor. They take it off regularly for cleaning and maintenance.
As well, the lower-ranking members of a space marine chapter, while not full blown marines, would still not be stock-standard humans. Instead, especially before the heresy, they would be noviates, which are roughly marine-sized anyway. So, in all likelihood, there would be a spare pressure suit or two among the equipment of this pre-heresy space marine vessel.