The fire started on the main deck near the side cargo door. Which is where two pallets with DG were loaded in position ML &
PR. The pallets contained, among other DG; lithium batteries and photo-resist/IC, a highly flammable fluid.
I question the practice of loading lithium batteries on the maindeck, which is a class E compartment on the B747. Firefighting in a class E compartment is by depressurizing it to 25.000 feet. The FAA has reported that depressurization is ineffective in extinguishing lithium fires. The bellies of a B747 are class C compartments, with halon fire extinguishing. The halon may not put out the lithium fire itself, but it will certainly help to keep the fire down in the surrounding packaging material such as cardboard boxes, plastic sheeting and other flammable material.
And smoke from a lower belly fire would take longer to reach the cockpit.
An added advantage of stowing Lithium batteries in the lower belly would be the extra distance from the vulnerable flight control cables, which run above the ceiling of the main deck.
In the UPS B747 crash at Dubai pitch control was affected within mere minutes of the fire warning. The Asiana crew did not report loss of rudder control untill 12 minutes after reporting a cargo fire, possibly because the fire started much further aft. Allthough from the altitude graph it appears their altitude varied quite a bit.
All this could buy the flight crew extra time to divert, ditch or make an off-airport landing.
ASAP.