Mad about Science: Dry ice

By Brenden Bobby
Reader Staff

Have you ever watched a music video from the 1980s to see fog rolling across a stage and wonder to yourself, ”Wow, how did they do that?”

Dry ice is the curious substance responsible for rock ’n’ roll stage fog, in addition to transporting lifesaving medications, organs and foodstuffs around the world. It has been in commercial use for well over a century, though it was discovered nearly 200 years ago.

The first recorded observation of dry ice was by French inventor Adrien-Jean-Pierre Thilorier in 1835. He had been experimenting with pressurized carbon dioxide in a sealed container to bring the gas into a liquid state. Upon opening the container, he discovered that a thick gas emerged while also leaving behind a solid block of ice.

This was really a block of carbon dioxide that steadily outgassed due to its contact with water moisture in the atmosphere.

Water-based ice will go through phase transitions when heat is applied. Beginning as solid ice, heat that brings the ice to 32 degrees Fahrenheit will cause it to change into its liquid form of water. Water will naturally evaporate into the atmosphere over time, but will rapidly expand into a gaseous form at 212 degrees F to create steam. This will predictably occur at sea level within Earth’s atmosphere, but pressure will change the temperatures in which water will transition into its other forms. This is true of many things in the universe, including metals.

Iron will transition into a liquid form at 2,800 degrees F, and it will evaporate at 5,182 degrees F. (“Irongas” would be a sweet band name.)

Carbon dioxide is unique in that it will actually skip transitioning into a liquid state while subjected to Earth’s atmospheric pressure. It will go straight from a solid to a gas in a process called sublimation. 

We explored sublimation in the April 17 edition of the Reader. Sublimation occurs when something skips the transition step to a liquid. H2O can do this in a very low-pressure environment, which occurs inside of freeze dryers. Freeze dryers are favored for the same reason dry ice is: liquid water residue create a breeding ground for bacteria, which will spoil food rapidly.

The lack of residue is certainly one of dry ice’s biggest benefits. The other is that the gaseous carbon dioxide looks really cool as a rolling fog that can be used in haunted houses and rock concerts, though other forms of artificial vapor have overtaken the use of dry ice in recent years.

Dry ice can be dangerous to use for a number of reasons. Its extreme cold and reaction to water can cause frostbite when handled by human hands. Additionally, elevated CO2 can cause asphyxiation, which means it shouldn’t be used in large quantities in enclosed and unventilated spaces.

Industrial production of dry ice captures carbon dioxide from other manufacturing processes, such as during industrial sugar fermentation when creating alcohol at breweries. The breweries themselves don’t produce the dry ice, but can capture and sell the carbon dioxide to a dedicated manufacturer. This also occurs during the process of refining crude oil, but the mixture needs to be refined or it can be very dangerous to manufacture later.

Due to its evaporative nature, dry ice is fairly detrimental to the environment when used regularly. The production of dry ice requires energy and the evaporation releases CO2 into the atmosphere; so, from an environmental perspective, it could be considered a stay of execution at best. Its practicality lies in its ability to chill and preserve items when mechanical refrigeration is impossible or impractical. 

This is especially useful during organ transplants, when an organ must be quickly harvested from a donor and transported — often by air. 

Organs are small and each one may be headed to a different location, depending on how urgently they are needed. This means you can’t simply load them onto a refrigerated truck and ship them off to a distribution center to be housed for weeks at a time. Styrofoam containers act as an insulator to trap the cold air while the organ is wrapped in plastic or another container to prevent frostbite from contact with the dry ice. They are then transported, usually by helicopter or an emergency vehicle, to be transplanted into the waiting recipient.

Vaccines and blood are also often stored using dry ice, due to their small size and portability. An extra measure of safety is that dry ice evaporates predictably, whereas mechanical refrigeration is threatened by sudden power outages.

It is predicted that 13.6 million pints of blood are collected and used annually in the United States. If the entire electrical grid were to be disrupted due to terrorism or natural disasters, that has the potential to put hundreds of thousands of lives at risk overnight — something that could be prevented by storing dry ice as a contingency.

Stay curious, 7B.