A Look at the Chemistry, Dangers Behind Dry Ice Dry ice is solidified carbon dioxide that is so cold (minus 109.3 degrees Fahrenheit) that touching it without gloves can cause severe frostbite. It changes from solid to gas form at room temperature through a process called sublimation that looks like a fog or smoke coming off it. Dry ice generally is used to keep food, medicine or biological materials, such as breast milk, frozen or chilled. It is colder than ice made from water and leaves no liquid behind as it changes into a gas. Passengers can pack perishables in up to 5 pounds of dry ice in their carry-on or checked baggage as long as it's properly packaged - meaning the container is vented, according to the Transportation Security Administration. Even so, the agency reserves the right to prohibit dry ice on a plane if officials believe it poses a security concern. Dry ice is considered a hazardous material and can be difficult to handle because it's so cold. When transporting dry ice, packages must allow for the release of carbon dioxide gas. If a package is put in a sealed container without venting, the buildup of carbon dioxide as it changes into a gas can lead to an explosion. Adding water accelerates the process. That's how people make "dry-ice bombs," which vary in size based on the size and type of container and the amount of dry ice used. The devices can cause injuries to people nearby if the built-up pressure is high enough and includes flying bottle shards. If you travel with dry ice, storing it in a foam cooler will allow the vapor to escape safely. It's also advised that dry ice containers be opened only in larger rooms or ones that are well-vented. The buildup of carbon dioxide in an enclosed space eats away at available oxygen and could lead to carbon dioxide poisoning. In a properly ventilated aircraft, small amounts of dry ice aren't a concern. But excessive amounts can incapacitate an aircrew, according to a Federal Aviation Administration advisory.