KG2V: When I replaced my gas/hot water furnace a few years ago, for $150 extra, I had the plumber install a sprinkler head over the furnace. Cheap insurance in my estimation.
I've seen people do this above their 250 gallon propane tank... really what's sprinkler water gonna do when your propane tank is blowing a 50ft flame out the release valve? Never really understood that.