Ronnie
I am assuming from your questions that you are an interested bystander and unable to reference a technical publication abou the subject. For your info, at first warning of Cargo Smoke/fire, Boeing's checklists ( and I assume Airbus) call for depressuriation of the aircraft and descent to 14000' or MEA/LSALT. This would be to "...reduce Cabin Differantial Pressure and resultant cargo compartment ventilation."
BTW unlikely to have VHF comms with anyone two hours out of Tokyo, even at normal cruise levels.
Cheers
Bendy