Dry ice is the solid form of carbon dioxide (CO2), maintained at an extremely low temperature of \(-109.3^\circ\text{F}\) (\(-78.5^\circ\text{C}\)). It is widely used for extreme cooling and freezing applications, especially when transporting temperature-sensitive materials. Unlike regular ice, dry ice bypasses the liquid phase entirely, turning directly into CO2 gas through sublimation. Proper storage in a cooler is necessary to ensure personal safety and maximize its cooling power.
Essential Safety and Handling Requirements
Handling dry ice demands caution due to its dual hazards: extreme temperature and gas production. Direct contact with the solid CO2 can cause severe cryogenic burns similar to frostbite in a matter of seconds. Always use heavy, insulated gloves, such as leather work gloves or oven mitts, or a pair of tongs when moving the dry ice. Never attempt to handle it with bare skin or thin fabric gloves.
Sublimation releases carbon dioxide gas, which is approximately 1.5 times heavier than air. This gas can quickly displace breathable oxygen in an unventilated space, leading to a risk of asphyxiation. Dry ice must always be stored in an area with good airflow, such as an open garage, outdoors, or a room with open windows. Never place a dry ice cooler in a small car trunk, a closed closet, or a basement, as the accumulating gas settles in low areas.
Selecting and Preparing the Storage Cooler
An insulated cooler is the best option for slowing the sublimation rate. A foam or rotational-molded plastic cooler with thick walls provides the necessary insulation to keep the internal temperature low. The container must not be airtight or have a sealed plug.
If CO2 gas is trapped, the pressure buildup can cause the cooler to rupture or explode. Ensure the container has a slightly ajar lid, a drainage hole, or a vent to allow the gas to escape safely. For plastic coolers, line the interior with cardboard or Styrofoam pieces to prevent direct contact between the dry ice and the plastic, which can become brittle from the extreme cold.
Before placing the dry ice inside, wrap it in an insulating material like newspaper or a towel. This wrapping creates a buffer layer that further slows the rate of heat transfer. Since cold air sinks, the dry ice should be placed on top of the items you wish to keep frozen for maximum cooling efficiency.
Strategies for Maximizing Sublimation Time
Maximizing sublimation time requires minimizing the dry ice’s exposure to warm air. A large block or slab will last longer than the same weight of pellets because a block has less surface area relative to its total volume. This limits exposure to ambient air and slows the sublimation rate.
Empty air space inside the cooler should be kept to a minimum, as warm air accelerates sublimation. Fill any remaining gaps or voids with crumpled newspaper, towels, or insulating foam. This reduces the volume of warm air that needs to be cooled and provides additional insulation.
Once the cooler is packed, limit how often you open the lid to prevent the exchange of cold gas with warmer outside air. Each time the cooler is opened, a fresh influx of heat energy enters, speeding up the sublimation rate. Store the cooler in the coolest, shadiest location available, as minimizing the external temperature gradient reduces heat transfer through the walls.
Proper Disposal of Remaining Dry Ice
Leftover dry ice must be disposed of safely by allowing it to sublimate completely. Never attempt to dispose of dry ice by placing it in a sink, toilet, or drain, as the extreme cold can damage plumbing fixtures and pipes. Do not discard it in a trash receptacle or sealed garbage bag, as this risks pressure buildup and bursting.
The safest method is to leave the remaining dry ice in its cooler, ensuring the lid is unsealed or slightly ajar to allow the CO2 gas to vent. Place the cooler in a well-ventilated area, such as a porch or open garage, away from children and pets. Depending on the remaining amount, it generally takes about 24 hours for five to ten pounds of dry ice to fully turn into gas. Once the solid is completely gone, the empty container can be stored or discarded as usual.