I was installing some small and short flouresent fixtures, and 7 of the 8 fixtures heated up just fine. But one tube kept blowing out as soon as i turned on the switch to energize the circuit. I went through three lamps like this. What would cause a tube to immediately blow when energized?
I'd second that. I don't know about your fixtures, but some of our fluoros have the wiring from the end sockets brought back into the middle of the fitting, and it is possible for someone to have crossed the wires so that one filament of the tube is straight across the supply (via the ballast).
Otherwise, it could be something like a shorted ballast or starter.