It cost just under $30 to refill the tank to get about 2 lbs of dry-ice. Contrasting that with the cost of dry-ice at the local grocery store ($1.00/lb) doesn't make financial sense, but this method is much more fun! If pressurized liquid CO2 is quickly depressurized, the CO2 expands to a gas, and cools its surroundings. This is called adiabatic cooling. Because the CO2 sublimates directly into a gas, it's very clean and doesn't leave behind any residue. Some fire extinguishers utilize CO2 as the medium for suppressing fires. These types are mainly found in restaurant kitchens, mechanical rooms, and in areas that hold sensitive equipment like computers.
CO2 fire extinguishers are usually charged with food grade CO2 and are referred to in terms of pounds. For example, a 5lb CO2 extinguisher is charged with a 5 lb weight of liquid CO2. CO2 fire extinguishers are marked with stickers, or holes punched in the servicing labels. They also have unusually large discharge horns, and no pressure gauges.