But I still haven't said how to fight a fire in the CO2 room, only why it is unlikely to have one! Most CO2 rooms have Electrical Lighting and an Electric Exhaust Fan which could catch fire. There is also a natural vent to let air in to replace the air removed by the Exhaust Fan.
Now lets hear something from Subhasis about what he thinks the answer to his question is.
It is always better to ask a stupid question than to do a stupid thing.