Dry ice, the solid form of carbon dioxide, is a temporary refrigerant often used for shipping frozen goods or preserving food during power outages. Its extreme cold temperature, which is \(-109.3^\circ\text{F}\) (\(-78.5^\circ\text{C}\)), makes it a powerful cooling agent far colder than standard water ice. The longevity of dry ice is a common concern because, unlike regular ice, it does not melt into a liquid but instead transforms directly into a gas, a process called sublimation.
Understanding Dry Ice Sublimation
The reason dry ice does not last long is rooted in its process of sublimation, which is the direct phase change from a solid to a gas. This transformation occurs at any temperature above its sublimation point of \(-109.3^\circ\text{F}\) (\(-78.5^\circ\text{C}\)) at normal atmospheric pressure. A standard household freezer is typically set to \(0^\circ\text{F}\) (\(-18^\circ\text{C}\)), a temperature significantly warmer than the dry ice itself. Because the dry ice is constantly absorbing heat from its surroundings, the sublimation process is continuous inside a home freezer. The freezer’s cooling system is designed to maintain a temperature of \(0^\circ\text{F}\), meaning it can only slow down the sublimation rate; it cannot stop it entirely.
Expected Lifespan in Household Freezers
Storing dry ice in a standard household freezer is not an effective long-term solution because of the constant temperature difference. Under typical conditions, dry ice sublimates at a rate of approximately 5 to 10 pounds every 24 hours in any minimally insulated container. For a common 5-pound block of dry ice, the expected lifespan in a regular home freezer is relatively short, usually lasting between 18 and 24 hours.
Maximizing Storage Time and Longevity
To extend the lifespan of dry ice beyond the baseline expectation, insulation and minimizing heat exposure are the most effective strategies. The most significant factor is using a highly insulated container, such as a Styrofoam or thick-walled cooler, to store the dry ice inside the freezer. This secondary layer of insulation drastically slows the transfer of heat from the warmer freezer air to the extremely cold dry ice. Further improvements can be made by immediately wrapping the dry ice blocks in an insulating material like a towel or several layers of newspaper before placing them into the cooler. Reducing the empty air space within the storage container also helps, which can be accomplished by filling the gaps with crumpled paper or towels.
Using a large, solid block of dry ice is also beneficial, as solid blocks have a smaller surface-area-to-volume ratio than chips or pellets, which slows the sublimation process. The type of freezer used also plays a role in longevity, with chest freezers generally superior to upright models. Chest freezers retain their internal temperature more efficiently because their top-opening design prevents cold air from spilling out when the lid is opened.
Essential Safety and Handling Guidelines
Handling dry ice requires careful attention to safety due to its extreme temperature. Direct contact with bare skin can cause severe frostbite or “freezer burn” within seconds, so thick gloves or tongs must be used at all times. Dry ice should never be stored in a completely airtight container, such as a sealed glass jar or a tightly closed cooler. As the dry ice sublimates into carbon dioxide gas, the pressure inside a sealed container will build up rapidly, creating a risk of explosion, so the storage vessel must be loosely closed or vented.