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Why Hot Cars Are So Deadly

National Highway Transportation Safety Administration officials demonstrate how hot it can get inside a parked car with a demonstration outside of the Medical Center of Central Georgia in Macon, Georgia. (Adam Ragusea)

National Highway Transportation Safety Administration officials demonstrate how hot it can get inside a parked car with a demonstration outside of the Medical Center of Central Georgia in Macon, Georgia. (Adam Ragusea)

It’s an annual summer tragedy. So far this year, 17 children in the U.S. have died of heat stroke inside a parked car. Some of those cases have been getting extra attention this summer, but that number is not unusual. Georgia Public Broadcasting’s Adam Ragusea looked into the science that explains how a parked car can get so hot, so fast.

It’s a sunny, summer day in Macon, Georgia. I’m standing with Matt Marone outside his truck, and the A.C. is on full blast.

“Right now it’s 97 degrees outside, and the interior temperature is, what, 79 and a half,” Marone says. “So then we can shut it off, and then we’ll just keep track of the temperature and how it changes over time.”

Marone is a physics professor at Mercer University. I ask him about leaving kids in the car — even for bit. You think, “At worst, it’ll just get as hot inside the car as it is outside.” But Marone explains how it can get a lot hotter — fast.

“There’s a lot of energy penetrating the windshield, some of it’s reflecting off and bouncing back, some of it’s going inside the car, heating up the interior of the car,” Marone says.

After three minutes, it has already hit 90 degrees inside the car — and the temperature is still climbing.

With the windows closed, the inside of the car is just like a greenhouse. Light from the sun comes in through the glass and is absorbed as heat on the seats, the dash. Glass doesn’t transmit that heat nearly as well as it transmits light, so energy pours into the car, and gets trapped. It accumulates. Marone says the only quick way for all that energy to escape is through the air.

“But if the car is all sealed up, is there gonna be a way for convection currents to let cool air flow in and displace the warm air and blow it out? How’s that gonna happen?” Marone asks.

We try cracking the windows a few inches, the way you would before leaving a car. But it doesn’t allow enough air flow to make a real difference. Before long, it’s 116 degrees in Marone’s truck, almost 20 degrees hotter than it is outside. Now, you might be thinking, “That’s hot, but deadly?”

“Please, never leave your child alone in a car, not even for a second.”

– Jenny Stanley

“Young children have poorer tolerance to heat when compared with adults,” says pediatrician Mark Zonfrillo, who leads the Child Road Traffic Safety Research Group at Children’s Hospital of Philadelphia. “They sweat less, and they also have a larger body surface area to mass ratio than adults. But the main reason that children cannot tolerate heat in the vehicle is because they’re literally trapped in these instances, and developmentally, they can’t escape from the car.”

Jenny Stanley of Evans, Georgia, lost her 6-year-old daughter Sydney this way four years ago.

“Please, never leave your child alone in a car, not even for a second. Because I can tell you, a hundred percent, it is not worth it,” Stanley says.

Now she gives talks, sharing her story. Stanley didn’t even leave her daughter in the car. Little Sydney climbed in by herself, right there in the driveway. No one could find her until it was too late.

“I don’t want any other family to go through this pain. I want you to leave here knowing you should always lock your car. You have to check and make sure all the children are out, but make sure the car is locked so they cannot get back in.”

An average of 38 kids die in a hot car every year in the U.S. That number hasn’t budged, in spite of a big public awareness campaign the National Highway Transportation Safety Administration launched in 2012.

So now, safety advocates are getting creative. Brett Garrett, a firefighter and paramedic in Tuscaloosa, Alabama, pulled a stunt recently to illustrate the danger. He actually baked cookies inside a car warmed only by the sun.

“According to the oven thermometer, it’s 174 degrees on the dash. These have been in there just over 40 minutes, but these are done,” he says, taking a bite. “It’s hot.”

Here’s the lesson to remember: It’s not just the heat of a really hot day that heats up a parked car, it’s the sunshine. One study from San Francisco State University found that on a sunny day, a car can get deadly hot for a child even when temperatures outside are in the low 70s.


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Robin and Jeremy

Robin Young and Jeremy Hobson host Here & Now, a live two-hour production of NPR and WBUR Boston.

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