Professor reveals explosive risks of leaving this item in hot car: 'These are like little bombs'

If you've ever returned to a hot car to find a bloated or, worse yet, exploded can of soda, you might have wondered just how such a thing could be possible.

If so, a college chemistry professor has the answers you seek.

Kate Biberdorf of the University of Texas at Austin broke down the science behind why and how beverage cans explode in hot cars for Texas Public Radio.

What's happening?

As average global temperatures soar and heat waves become more commonplace, many people have noticed that aluminum beverage cans left in hot cars can become deformed or even burst.

According to Biberdorf, this is a result of three things: the high temperature inside a car, the carbonation inside the canned beverage, and the nature of the can itself.

First, the hot car.

"It's really, really hot inside your car," Biberdorf said, per TPR.

While such an observation does not require an advanced degree in chemistry, many people are unaware of just how hot the interior of a car can become on a scorching day.

Within just one hour, the temperature inside a vehicle can reach 43 degrees Fahrenheit hotter than the outside temperature, Biberdorf told TPR.

This means that, on a 100-degree day, the mercury inside a vehicle can quickly reach a broiling 143.

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Inside a can of carbonated soda, this intense heat excites the carbon dioxide molecules that make up the carbonation. As these molecules move faster, they separate from the soda.

"As [CO2] slams into the side of your container, it is providing more force," Biberdorf explained, per TPR. "As the temperature increases, the pressure is going to increase because we're having more collisions with more force inside that can."

Pushing back against the carbon dioxide from outside the can is the weight of the air in the atmosphere. However, as the carbon dioxide molecules get hotter and more excited, the pressure inside the can can become greater than the pressure pushing back from the outside.

That is where the design of the can comes in.

To prevent bursting, aluminum cans can withstand pressure equal to about six Earth atmospheres. However, in a hot vehicle, the pressure from inside the can is capable of exceeding that limit, per TPR.

Should this happen, manufacturers of aluminum cans have sneakily designed one last line of defense. The area around the top of the can is made to expand under pressure.

"That top part [is] accordioned in when they manufacture it so it can push out once the carbon dioxide is popping," said Biberdorf, according to TPR. "It's a safety thing because these are like little bombs, essentially."

Sometimes, however, the pressure inside the can is too much, even with this leeway. At that point, the can will fail and burst. Even then, the clever designers of aluminum cans have one last trick up their sleeve: The tops of the cans are designed to come apart safely, preventing a dangerous explosion.

"They are designed so that hopefully it doesn't fly off," Biberdorf explained, per TPR. "It kind of opens up more like a [tin] can."

Of course, with 280 billion aluminum cans being manufactured every single year, there are bound to be some that malfunction.

"But, again, it's not perfect," Biberdorf said, according to TPR. "We make so many of them there are going to be flaws." 

Why are exploding cans important?

Having to worry about a can of soda bursting after being left in a hot car is just one of the many ways, large and small, that rising global temperatures are impacting everyday life around the world.

Though perhaps trivial in the scheme of things, the risk of exploding cans is representative of the ways in which things that used to be taken for granted, such as the ability to leave a canned beverage in an unattended parked vehicle, have changed.

It is also a stark reminder of just how quickly the interior of a car can become dangerously hot, even if the windows are left cracked open. 

What's being done about exploding cans?

The best way to prevent exploding cans is to avoid leaving them, and any other heat-sensitive items, in a vehicle on a hot day.

However, in order to solve the much larger issue of rising temperatures, the world must stop releasing so much heat-trapping pollution into the atmosphere.

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