All MD11s (but 747, 777,767 etc. are the same) have class "C" lower compartments, that means there are heat and fire detectors and fire extinguisher bottles,
but the main deck is a class "E". There are heat and fire detectors (36 in the md11) but the only way to extinguish a fire is by closing the air supply leaving the compartment with no oxygen (helped by increasing the cabin altitude) there are also some portable fire extinguishers but they are of little help.
This equipment leaves all the pilots with many dubts about the probability to effectively win over a fire in the main deck, but the size of the compartment does not allow the installation of fire ext. bottles