Exploding Frozen Soda Can Leaves Boy with 38 Stitches
Frozen soda can explosions are not due directly to water expanding as it freezes, but to the resulting pressure put on an isolated pocket of C02.
Credit: Image via Shutterstock

A boy in China who tried to chill a soda in the freezer wound up with 38 stitches when the can exploded in his face, according to Rocket News 24.  

The incident was publicized by the boy's mother on Sina Webo, a Chinese microblogging site similar to Twitter, in a purported effort to warn other families about the dangers of freezing carbonated beverages.

According to the boy's mother, he took an intact can of cola out of the freezer on the night of Aug. 25. The moment he popped the tab, the top blew out, propelling shards of aluminum into his face and sending him to the hospital where he reportedly received 31 stitches on his face and 7 inside his mouth.

So what happened?

Attempts to speed-cool a soda often result in a busted hull of aluminum and a wall-to-wall coat of sticky slush on the inside of the freezer. A popular belief is that this is because water in the soda expands when it freezes, exceeds the can's carrying capacity, and blows it open.

But that's not the whole story.  The boy would not have been hurt if the can had been filled with water alone.

"What's dangerous is the carbon dioxide gas," said Louis Bloomfield, a physicist at the University of Virginia. "Once it has been forced out of the water as the water crystallizes, the carbon dioxide accumulates in the small remaining space in the can and the pressure of that gas skyrockets."

The expansion of water as it freezes is important to soda detonation not because it puts pressure on the can but because it puts pressure on an increasingly cramped reservoir of gaseous C02, which can change volume more radically and store far more energy than pressurized ice.

But if the water had already frozen and created a pocket of pent-up CO2 capable of rupturing the can, why hadn't the Chinese boy's soda already exploded on its own in the freezer?

"The can was stressed to its limit and when he introduced new stresses while trying to pop the top, he evidently found the weak point," Bloomfield told Life's Little Mysteries. "Whereas many cans with tiny defects would already have burst at that point, this particular can was holding on especially long. It might have held out forever, had the boy not handled it."

Though Bloomfield guesses that the boy was "seriously unlucky," the clear lesson of his misfortune for the cautious and occasionally absentminded is to give sodas time to cool in the fridge.

Either that, or switch to canned tomato juice, which won't blow up in your face even if you freeze it. 

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