Some of the comments about loading of dangerous goods and accessibility have been way off base. The ICAO Dangerous Goods Panel reviewed and revised the accessibility requirements over two years ago. The new provisions came into effect January 2009. This recognised that it may be safer to load the CAO DG in the underfloor compartment where that compartment is Class C. That way the crew actually have some fire suppression, rather than just having to depressurise the aircraft and hope that the fire goes out, which is all that you have with the maindeck Class E compartment.
As for lithium batteries, so far all of the incidents in cargo have been as a result of non-compliant shipments. For lithium ion batteries, the halon will supress the fire.