Dry ice is the solid form of carbon dioxide (\(\text{CO}_2\)), widely used for its exceptional cooling capabilities in shipping, storage, and special effects. This compound does not melt into a liquid; instead, it transitions directly into a gas in a process called sublimation. Sublimation occurs at an extremely low temperature of \(-78.5^\circ \text{C}\) (\(-109.3^\circ \text{F}\)), making it a powerful refrigerant. Safe use requires strict adherence to precautions managing the hazards associated with its extreme cold and gaseous state.
Hazards of Extreme Cold and Ingestion
The principal physical danger of dry ice is its capacity to cause severe tissue damage upon direct contact due to its intense cold. This immediate chilling effect rapidly causes frostbite, a cold burn that freezes skin cells and damages underlying tissue. Prolonged contact for even a few seconds can lead to blistering, peeling, and permanent injury similar to a heat burn. Handling dry ice without a thermal barrier is strongly discouraged.
Ingestion poses an even more serious threat. Swallowing a piece can cause immediate, severe frostbite to the mouth, throat, and esophagus. The most significant internal risk comes from the rapid sublimation of the solid \(\text{CO}_2\) upon contact with the body’s moisture and warmth. This generates a large volume of \(\text{CO}_2\) gas inside the digestive tract, creating pressure buildup. This pressure can potentially cause severe internal injuries like stomach rupture, which can be fatal, or intense abdominal pain and vomiting. Dry ice should never be placed in beverages where pieces could be accidentally consumed.
Understanding Ventilation and Asphyxiation Risk
Sublimation converts dry ice into a very large volume of carbon dioxide gas; for example, one pound yields approximately 250 liters of \(\text{CO}_2\). This massive expansion creates an atmospheric hazard, particularly in enclosed or poorly ventilated areas.
Carbon dioxide gas is heavier than the air we breathe, meaning it tends to settle in low-lying spaces. This includes the bottom of coolers, basements, or the floor of a vehicle, where it displaces ambient oxygen. The primary risk from elevated \(\text{CO}_2\) concentration is asphyxiation, leading to unconsciousness or death. Exposure to high concentrations can cause initial symptoms like dizziness, headache, and shortness of breath. Concentrations above 8\% to 10\% can cause immediate unconsciousness and respiratory arrest. Proper air circulation is necessary to prevent dangerous accumulation.
Essential Safety Procedures for Use and Disposal
Handling dry ice requires the use of appropriate personal protective equipment (PPE). Insulated gloves, such as thick leather or cryogenic gloves, must always be worn to protect the skin. Safety goggles or a face shield should also be worn, especially when breaking up larger blocks, to protect the eyes from flying fragments or intense cold vapor.
Dry ice must never be stored or transported in a completely airtight container. As the solid sublimates, the trapped \(\text{CO}_2\) gas creates immense pressure, which can cause the container to rupture or explode. It should be kept in an insulated cooler that is not sealed, allowing the gas to vent safely.
Transport
During transport in a vehicle, the dry ice container should be placed in the trunk or a cargo area separate from the passenger compartment. If this is not possible, the vehicle’s windows must be kept open to maintain constant ventilation and prevent gas buildup.
Disposal
The safest method for disposal is to allow the dry ice to sublimate completely in a well-ventilated location, such as outdoors or in a room with open windows, away from people and pets. Dry ice should never be thrown in the trash or disposed of down sinks, toilets, or drains, as the extreme cold can damage plumbing fixtures.