The ship has suddenly run out of power and the crew are forced to evacuate to only a small number of decks. When did this happen?
It seems rather sudden considering the extreme measures being taken, but I guess we'll get an interesting story about the crew rationing things now, eh?
They land on a planet and get replicated by pools mercury, you say?
It is hard to pin just why this episode fails, it's a perfect storm of suckiness. The humour is bad, there is a group of scenes between Tom and Harry at the beginning where they say lame jokes to one another until you just wish they would suffocate. Then their air runs out and they suffocate, and the episode earns itself a point.
While this is happening there is some "hilarious" scenes where Neelix moves into sickbay with three mutes and they annoy Dr Shmully, but sadly none of them suffocate.
Then there's a whole bunch of crap about silver blood trying to eat the ship, B'Elanna talked to Vorrik in engineering because he is now her deputy (poor Carey), and Tom and Harry manage to survive for around 8 hours without oxygen. To finish it off the whole crew replicate themselves and leave silver blood clones on the planet. I'm not even going to get into how stupid that is.