I've been surprised just how long "amateur" server rooms survive cooling failure. Mostly becuase the densities tend to be lower, but also becuse you just get lucky with the way they're built. At our current office we had a server room total cooling failure (due to copper piping stolen off the back of the building...) and although it got very hot (and very loud) in there, we didn't get any machine failures or thermal shutdowns. But you could feel the heat radiating out of the walls the rooms around and above the server room were noticably hotter. If we'd been an older building or the server room had been built for physical security, the thicker walls would have trapped the heat and it would be a different story.