Health Advice



Dry ice, the unsung hero of the COVID-19 vaccine rollout, explained

Tom Avril, The Philadelphia Inquirer on

Published in Health & Fitness

PHILADELPHIA — Robert Levis dumped chunks of a whitish substance into a beaker of water, and immediately the liquid began frothing and churning like a sorcerer's potion, spewing plumes of fog across the table of his office at Temple University.

"It looks like the water is boiling," said Levis, a chemistry professor.

Just the opposite. The fog was not steam, but water droplets that had frozen — thanks to a blast of subzero cold from the whitish substance: dry ice.

Formally known as solid carbon dioxide, dry ice gets its nickname from a chemical property that is fairly described as sublime. It does not melt, but sublimates — going straight from solid to gas, with no messy liquid involved. And because the solid form has a temperature of negative 109 degrees Fahrenheit, it cools everything nearby like a champ.

Such as vaccines. As we've been hearing for months, the COVID-19 shots made by Pfizer Inc. and BioNTech SE require particular attention to the "cold chain" — keeping the vials at ultra-low temperatures on the trip from factory to clinic so the RNA-based product does not degrade. Regular freezer temperatures are OK for two weeks before usage, but for long-term storage and transport, the required range is between -112 and -76 degrees: a perfect fit for dry ice.

Levis illustrated the material's cool properties recently with a series of demonstrations. There were popping balloons. Food coloring. A toy gun that shot soap bubbles!


His real job involves research on such cutting-edge topics as using lasers to measure the chemical "markers" of brain injury, but who says university types can't have a little fun? Levis, who also lectures on the chemistry of making wine, is a big proponent of using everyday phenomena as teaching tools.

And dry ice, used for such varied purposes as making ice cream, blasting graffiti off walls, and creating "fog" for special effects, is about as everyday as you can get.


Simply put, molecules of carbon dioxide do not cling to each other well.


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