CV880 has it correct. No fire suppression in the lower holds except the smothering effect oof a sealed compartment. By the time the B707/Comet/DC-8 came out Halon or its equivalent were the fire agent in use. Halon replaced the CO2 systems on the L-1049G and H series Super Constellations. I have a blank spot in my memory for the DC6 and DC-7.