Slug_A:— Fire in Medbay/O2 is not really a problem since you start with lv.2 door, you can either turn off O2 and just wait for it to die out or sent someone to go deal with it (you rarely have to do this, but if you need to, it's very safe since both room are next to each other) or just vent the ship using the topmost vent— it may seem like you have to vent "half of the ship" to reach medbay, but really it just 3 rooms, all of them are 2 square (quick to vent) and contain no man-able system (can be vent without losing any bonus while in battle)
Also, despite its asymmetric and weird looking layout, all of the ship's main system room are very close to each other and laid out in a way that allow your crew to quickly convene and help each other when something happen.
Slug_B: It has vent all over the place, many of which are right next to the most vulnerable room which allow you to quickly vent the air out. It also has tons of empty room that, because of its placement between each system room, acts as a trap to delay boarder. These 2 traits combined made the ship not only easy to defend from enemy boarders attacks or fires at (almost) any room, but can quickly kill them as well without requiring any help from your crew at all; it made going through a mantis sector surprisingly easy despite the absent of medbay— if enemy boarded you, just open a few airlock, move your crew a bit out of the way if needed and maybe fire the Artemis at the tele room if you feel like it, and then just sit back and watch them suffocate to death!
One of its biggest strong point for both type (but more pronounced in the A type) that may not immediately obvious by looking at the layout until you actually playing it, is that it resilient to
everything, not just fire— and more than that, if you play your card right, it can withstand all these threats happening
all at once! 
... Imagine 2 mantis teleport on your door room, a boarding drone smash hole & wreck havoc on the O2 room and firebomb at the medbay, all of these happen simultaneously! ... As extreme as that may sound, but with some experience, you can actually survive this only with the starting crew, i.e. 2-3 slugs, and without any upgrade— it may not be a painless battle, but you won't going to die a horrible death.
If they can't fix the air, they can't fix anything else (Maybe the teleporter, and MAYBE the piloting but I've never tried those. Everything else is assuredly too far away). I'm not going to say this is super common or anything, but it's about as common as a solar flare taking out your doors and lighting them on fire while the airlocks are all closed.