I'm guessing that in very general terms if its chest or head it could be life threatening whereas a broken leg isn't. I wonder what percentage of these high category calls end up really being nothing more than a headache or gut ache?! When I broke my leg falling off a horse I waited I think about an hour for the ambulance (They did have a long walk) then I think about 30 mins for the helicopter (they didn't fancy the long rough walk carrying me). I did have concussion as well which I think was reported by the caller (a passing nurse and police officer!) so I'm suprised it was so long. I didn't really mind waiting as it didn't hurt too much so long as I didn't move, although I was getting pretty cold sat on damp grass.