Temperature and injuries aside, a dewar of LN spilled in a room temperature enclosed space will boil and evaporate into an asphyxiating cloud very, very quickly

Temperature and injuries aside, a dewar of LN spilled in a room temperature enclosed space will boil and evaporate into an asphyxiating cloud very, very quickly. A box of dry ice dumped on the floor will take quite a bit longer to sublimate enough, partly because the phase change temperature is much higher, and also because thermal contact between a very low viscosity liquid and surfaces is very much higher than a solid pellet sitting on the surface. Nitrogen will also kill you silently, while you will definitely know when CO2 levels are getting high (because it really really hurts).