Dry ice, the solid form of carbon dioxide (CO2), is distinct from regular water ice. Unlike water ice, dry ice does not melt into a liquid; instead, it transitions directly from a solid to a gas through a process called sublimation. This unique property, along with its extremely cold temperature of approximately -78.5 °C (-109.3 °F), makes it valuable for various applications. Dry ice is commonly used for temporary refrigeration, such as preserving food and medical samples, and also for creating dramatic fog effects in theatrical productions.
Essential Safety Measures
Working with dry ice requires careful attention to safety to prevent injuries. Adequate ventilation is important because as dry ice sublimes, it releases quantities of carbon dioxide gas. Since CO2 is heavier than air, it can accumulate in enclosed or poorly ventilated spaces, displacing oxygen and potentially leading to asphyxiation. Symptoms of elevated CO2 levels include shortness of breath and headache, and high concentrations can be fatal.
Direct contact with dry ice poses a severe risk of frostbite, often called a “cold burn.” The extreme cold rapidly freezes skin cells, causing tissue damage similar to a heat burn. Always wear appropriate personal protective equipment (PPE), including heavy-duty insulated gloves (not thin nitrile gloves) and eye protection like safety goggles or a face shield. Long-sleeved clothing and closed-toe shoes offer additional protection. Never ingest dry ice, as it can cause serious internal injury or death.
Methods for Creating Dry Ice
Creating dry ice at home involves rapidly depressurizing liquid carbon dioxide, a process known as adiabatic expansion, which causes the CO2 to cool and solidify into a snow-like consistency. Two common methods utilize readily available CO2 sources. One method involves a CO2 fire extinguisher, which must be a carbon dioxide type, identifiable by “CO2” markings and typically a large discharge horn, rather than ABC powder extinguishers.
To produce dry ice with an extinguisher, secure a cloth bag, such as a pillowcase, tightly around the nozzle. Ensure the bag covers the discharge horn to trap the solid CO2. With insulated gloves and eye protection in place, remove the extinguisher’s safety pin and discharge the contents into the bag for about 4 to 6 seconds. The rapid expansion of the liquid CO2 within the bag will create dry ice snow.
Another method uses a siphon CO2 tank, commonly found for welding or soda machines, which is designed to draw liquid carbon dioxide from the bottom of the tank. An adapter or a cloth bag can be attached to the tank’s nozzle. When the valve is opened, the liquid CO2 expands, cools, and transforms into dry ice snow within the collection bag.
Safe Handling and Storage
Once dry ice has been created, careful handling remains necessary to prevent injury. Always use insulated gloves or tongs when touching dry ice.
Proper storage is important for both safety and preserving dry ice. Store it in an insulated container, such as a cooler or styrofoam chest, that is not airtight. As dry ice sublimates, it releases CO2 gas; a sealed container can build pressure and explode, so it must allow gas to escape. Store the container in a well-ventilated area, away from living spaces, children, and pets, to prevent CO2 buildup. Dry ice sublimates at a rate of 5 to 10 pounds every 24 hours, lasting 18 to 24 hours in a well-insulated cooler.
When disposing of dry ice, allow it to sublimate completely in a well-ventilated outdoor area or a room with open windows. Placing it on a non-metal, hard plastic surface is advisable to prevent damage to floors or countertops. Never dispose of dry ice in a trash can, sink, toilet, or any drain, as the extreme cold can damage plumbing and the gas release can be hazardous in confined sewer systems.