Attention span short, didnt read all the replies.
Is the server room equipt with ceiling sprinklers that activate from heat? And is the server room cooled by an air conditioner unit? (Why an A/C unit? You dont want a sprinkler or automatic fire extinguisher going off due to high heat caused by the servers themselves)
A sprinkler will damage a computer, as you can imagine, but, at least the entire building wont catch on fire.
Unless the server room is covered by an actual person 24/7, during the evening, no one will be there to actually put the fire out...
In your server room, there should be a switch that will shut down the servers completely and instantly in the even of an earthquake or in the even that a fire starts or anything like that. If the fire is caused by something inside the server, you can expect that if you put it out with a dry fire extinguisher, its going to eventually start again.