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Dry ice is the solid form of carbon dioxide (chemical formula CO2),
comprising two oxygen atoms bonded to a single carbon atom. It is colorless, odorless, non-flammable, and slightly acidic.
At temperatures below −56.4 °C and pressures below 5.13 atm (the triple point), CO2 changes from a solid to a gas with no intervening liquid form, through a process called sublimation. The opposite process is called deposition, where CO2 changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at −78.5 °C.
Safely Using Dry Ice
Carbon dioxide gas is heavier than air, and therefore, it can pool in basements or other low areas.
When transporting dry ice, always keep vehicle windows open to bring in fresh air.
The quantity of dry ice used in a regular storage freezer or refrigerator is unlikely to produce carbon dioxide gas in sufficient quantity to cause a health problem. Dry ice can readily be used to keep foods cool in those types of containers.
Are there any special precautions I should take when using dry ice?
There are a number of important precautions to take when handling dry ice:
Keep dry ice out of the reach of children.
Never eat or swallow dry ice.
Avoid inhaling carbon dioxide gas.
What are some tips for using dry ice to keep foods cool?
- Order dry ice in the form and size in which it will be used. It can be difficult and dangerous to cut.
- Store dry ice in a container that allows some leakage. If unvented, carbon dioxide gas can build up pressure inside a jar or container as dry ice melts.
How much dry ice will I need?
The quantity of dry ice you will need to maintain temperature in a storage freezer or refrigerator will vary. Some basic tips for using dry ice to cool foods are:
IN A REFRIGERATOR:
- A home-style refrigerator may use about 5 kg of dry ice per day.
- Dry ice may freeze items, so place foods that may become damaged by freezing as far from dry ice as possible.
- Place ice on the bottom of a household type unit. Place newspaper or other materials as insulation on glass shelves to prevent the shelves from cracking.
- Keep liquids tightly covered so they do not become carbonated as the refrigerator fills with carbon dioxide.
IN A FREEZER:
- A chest freezer may use 18 to 22 kg of dry ice per day, placed on top of the food.
- A home-style refrigerator/freezer combination unit.
- A unit with the freezer on bottom may use 7 to 12 kg per day, placed on top of food.
- A unit with the freezer on top may use 9 to 14 kg per day, placed on top of and surrounding food.
- A unit with a side by side freezer may use 18 to 22 kg per day, placed on top of and surrounding food.
How do I dispose of dry ice?
- Because dry ice can cause carbon dioxide gas to accumulate and build up pressure, do not dispose of dry ice in a sewer, garbage disposal, garbage chute, etc.
- Allow leftover dry ice to melt and turn into gas in a well-ventilated area.
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