Why is compressed air flammable? I have a can of compressed air. The type you use to clean the insides of computer. It's "100% ozone friendly" and "pure compressed gas". So I assume its everyday regular breathable air. I used it to try blow out a candle. It had precisely the opposite effect.

Why?
Most probably some hydrocarbon like butane = big flame. A quick way to check is if the can makes a sound when you shake it. If it does then it's most likely hydrocarbon. It would have been less confusing if it said "compressed gas".