ABSTRACT
In addition, dry ice can keep things much colder than can ordinary ice. In order to form liquid CO2 the system must be pressurized to 5.07 bar or greater. The contents of a CO2 fire extinguisher at 25°C consist of liquid CO2 in equilibrium with gaseous CO2 under an equilibrium pressure of 67 bar. When the valve is opened and the contents allowed to escape, the rapid expansion causes the pressure inside the fire extinguisher to suddenly drop to about one atm with an accompanying rapid cooling effect which takes the temperature of the gas down to below –78°C. When this happens, the system is unable to absorb heat from the surroundings fast enough to restore the temperature to 25°C, and therefore the gas condenses to form the jet of solid “snow” characteristic of a CO2 fire extinguisher.
