Dry ice is frozen carbon dioxide (CO2). In the dry ice manufacturing process, pure CO2 gas is first pressurized and cooled in order to turn it into a liquid. The liquefied CO2 is then fed into a dry ice production machine, where the pressure is released, a process which creates CO2 "snow" that is then compressed into pellets or blocks of dry ice.
What Is Sublimation?
The surface temperature of dry ice is –109.3° F (–57° C). Above this temperature, dry ice sublimes, or sublimates. Both words describe the same thing—when a substance turns directly into a gas without first becoming liquid. This means that dry ice will evaporate without leaving moisture or wetness.
Because dry ice is very cold but disappears without getting things wet or leaving liquid behind, it has many industrial applications. It's used to preserve foods, chemicals and medical samples and supplies, especially during transportation. It's also used for dry ice blasting, a cleaning process used on machinery and tools and for removing mold and graffiti.
Dry Ice Safety Tips
Following these three tips can help minimize hazards when you're handling dry ice.
- Protect your hands and eyes.The extremely cold surface temperature of dry ice means that it can cause skin damage and frostbite. Follow these steps to help prevent contact injuries:
- Don't touch dry ice with your bare hands. Nitrile exam gloves will not give you enough protection. Insulated gloves are recommended. Cryogenic gloves are specially designed for handling very cold objects.
- Wear appropriate eye protection, such as safety glasses or a face shield.
- Don't store dry ice in poorly ventilated enclosed areas, such as walk-in freezers or basements.
CO2 is about one and a half times heavier than air and can displace oxygen in small or enclosed spaces. Even a relatively small piece of dry ice can produce a large quantity of CO2 gas if it sublimes quickly. CO2 also has toxic effects at high concentrations and can quickly cause someone to stop breathing and lose consciousness. If dry ice is subliming in a small, poorly ventilated space, such as a walk-in freezer, the CO2 can cause suffocation, unconsciousness and respiratory arrest.
- Don't store dry ice in air-tight containers.
If dry ice sublimes inside a sealed container, the CO2 gas will pressurize the container and can eventually cause it to rupture or explode. Keep dry ice only in containers that allow gas to escape.
Storing Dry Ice
Dry ice can be stored in non-air-tight chests or buckets made from insulating foam to help slow the rate of sublimation. Dry ice will sublimate at any temperature above –109.3° F. The rate at which it sublimates can vary considerably depending on the quantity and form of the dry ice. A small amount of pellets will sublimate much more rapidly than a single large block, according to a report published by the Federal Aviation Administration (FAA).
Dry ice containers should be kept only in places with good ventilation.
Dry Ice Disposal
Allowing dry ice to sublimate at room temperature is an effective way to dispose of it, but it's important to take precautions to help prevent hazards.
- Make sure to allow dry ice to sublimate only in well-ventilated areas to avoid a harmful buildup of CO2.
- Do not leave dry ice unattended in public places.
- Never dispose of dry ice in a toilet, sink or garbage disposal. The extreme cold can damage plumbing.
- Never dispose of dry ice in a trash can.
- Avoid putting dry ice directly on tile or laminated countertops. The cold can weaken adhesives and cause cracking.
First Aid for Dry Ice Burns
Skin contact with dry ice can cause frostbite or ice burn. OSHA recommends these first aid steps for treating dry ice contact injuries:
- Get medical assistance as soon as possible
- Remove clothing that is not frozen to the skin
- Put the affected body part in a bath of warm water—not above 40° C, or 104° F.
- Do not use dry heat to warm the area.
- Do not rub the affected area.