Capt Claret, when the oxygen level reduces to a level of about 13-15% from the normal value of 21% a fire will extinguish, as the oxygen/vapour mix is incombustable. I can't believe that it is not mandatory for cargo holds to have a halon or halon substitute (FM-200) as a very rapid fire extinguisher method. Get rid of the O2, get rid of the heat and things are a little less drastic than they were a couple of seconds earlier.