This whole thing relies on a single fire sprinkler head of an industry standard design that is capable of delivering 25 GPM and will cover the entire enclosed area, floor-to-ceiling thereby smothering the fire.
If the fire has a secondary source of fuel and air, all is lost.
I wasn't intending the CO2 as a primary fire suppression agent; I was suggesting its use as a propellent (though having large quantities of it dissolved in water may not be too good, limitting the time that water is exposed to CO2 under pressure would keep that down). The quantity of gas needed as a propellent is small enough that asphyxiation should not be a problem.