Dry ice is the solid form of carbon dioxide (\(\text{CO}_2\)). Unlike regular frozen water, dry ice does not melt into a liquid; instead, it transitions directly from a solid into a gas in a process known as sublimation. This phase change occurs at an extremely cold temperature of \(-78.5^\circ\text{C}\) (\(-109.3^\circ\text{F}\)) under normal atmospheric pressure. Because it cools items without leaving liquid residue, dry ice is a preferred cooling agent in various applications.
Essential Safety and Handling Procedures
The extreme cold temperature of dry ice poses an immediate hazard. Direct contact with bare skin can cause immediate freezing of tissue, resulting in frostbite. Always use insulated gloves, such as thick winter gloves or oven mitts, or tongs when handling dry ice to create a barrier between the substance and your skin.
The gas released during sublimation is carbon dioxide. Since \(\text{CO}_2\) gas is denser than air, it settles in low-lying and enclosed spaces. If used in a small or poorly ventilated area, the concentrated \(\text{CO}_2\) can displace oxygen, presenting a risk of asphyxiation.
Always ensure excellent ventilation when using or storing dry ice, such as an open window or a well-circulated room, to allow the gas to disperse safely. This is particularly important when transporting dry ice in a car, where ventilation must be maintained to prevent gas buildup. Never store dry ice in completely airtight containers, such as glass jars or sealed plastic bottles, because continuous sublimation creates pressure that can cause the container to rupture or explode.
Storage should be in a well-insulated container, like a Styrofoam chest or a cooler, which is loosely covered to allow the gas to escape. Keep the dry ice away from children and pets, as accidental ingestion or prolonged contact can be extremely dangerous. Treat any contact burns like a heat burn, seeking medical attention if blistering or skin breakdown occurs.
Common Practical Applications
Dry ice is commonly used for shipping perishable goods, such as frozen foods, biological samples, and temperature-sensitive pharmaceuticals. When shipping, place the dry ice in an insulated container with the contents and ensure the container is clearly labeled and not fully sealed.
During a power outage or when a freezer fails, dry ice can temporarily preserve large amounts of frozen food. Placing a 10-pound slab on the top shelf of a full 10-cubic-foot freezer can maintain freezing temperatures for up to 24 hours. Keep the dry ice elevated and insulated from direct contact with the freezer walls or glass shelves to prevent damage.
The dramatic visual effect of dense, low-hanging fog is popular for parties or theatrical productions. This effect is created by placing dry ice into hot water, which accelerates sublimation. The cold \(\text{CO}_2\) gas quickly cools the surrounding water vapor, causing it to condense into visible fog.
Dry ice can also be used for specialized household tasks, such as removing minor dents from car bodies. Applying the extreme cold to a metal surface causes the metal to contract rapidly, sometimes popping out a small dent. Another application is pest control, where dry ice is placed in a rodent’s burrow, and the sublimating \(\text{CO}_2\) displaces the oxygen, eliminating the pest.
Proper Disposal Methods
Disposing of dry ice is straightforward, but it must be done with attention to safety and ventilation. The only correct method for getting rid of leftover dry ice is to allow it to fully sublimate into gas. Place the remaining dry ice in an open container, such as a cooler, and leave it in a secure, well-ventilated location.
The best disposal location is outdoors, away from areas where people or pets might gather, to ensure the harmless dispersion of the carbon dioxide gas. If outdoor disposal is not possible, a garage with an open door or a room with open windows provides sufficient airflow. The time required for complete sublimation depends on the amount of dry ice and the ambient temperature, but it is typically a matter of hours.
Never dispose of dry ice in a sink, toilet, or down any drain. The extreme cold can damage plumbing components, causing plastic pipes to crack or metal fixtures to shrink and break. Do not place dry ice in the regular trash or a sealed garbage receptacle. The buildup of \(\text{CO}_2\) in a confined trash area creates a pressure hazard for sanitation workers and can cause containers to burst.