From the days of L1011 underfloor galley, we know the problems with storage of dry ice; CO2 in gas is heavier than dry air, most airliners are designed with air flow from top to bottom and outflow valves are positioned mostly in the rear lower fuselage, far from operating crew whom in any case usually get a more dedicated supply to the flight deck; of course we also know that with modern airliners there is a % of re-circulation, even the old trusted B747 had such but again the fans were in the upper fuselage area. Good to know the knowledge is out there with safe approach.