"Dry ice" is the common name given to frozen carbon dioxide which is often used to transport specimens that must remain frozen. Dry ice sublimates at room temperature, meaning it transforms from a solid directly into a gas. Too much carbon dioxide gas in a small space will reduce the oxygen levels in the area potentially causing dizziness and asphyxiation. If this happens in a vehicle, the driver could become unconscious while driving!
Dry ice may be placed in a cooler in the courier vehicle, and samples are placed inside until delivery to the reference laboratory. Couriers should limit the amount of dry ice placed inside the cooler that will rest in the vehicle. It is recommended that no more than three pounds of dry ice be placed in that cooler. The cooler should never be completely sealed (remember the ice sublimates to gas, and the volume of the gas in the cooler will expand- a sealed container could explode!). Also, if dry ice is kept inside of a vehicle, the windows should be left opened, even if only a tiny bit. Always ensure proper ventilation in the vehicle when transporting dry ice.