Study: Car Interiors Reach Dangerous Temps All Year

Medically Reviewed by Brunilda Nazario, MD on July 24, 2014
From the WebMD Archives

July 24, 2014 -- After a string of high-profile cases of kids being left in hot cars this year, a new study shows just how quickly heat can become a danger, even in cooler months of the year.

Researchers in Texas measured in the temperatures inside a car on a single day each month in 2012, checking temps every 5 minutes from 8 a.m. to 4 p.m. They hung the thermometer in the back seat, out of the sun, about where a child’s head would be if they were sitting in a car seat.

“We wanted to simulate what might happen on an average work day,” says Sarah Duzinski. She’s a research scientist at Dell Children’s Medical Center in Austin.

They took care to pick days that were sunny, with little cloud cover, but they also tried to stay away from extreme weather. They only sampled on days when the temperature was going to be within about 20 degrees of the historical average.

“What we found, in Austin, at any rate, is that children face the threat of hot car death in every month of the year,” Duzinski says.

In all 12 months, temperatures rose to at least 90 degrees in the car. Ninety degrees is the point where the National Weather Service says people should use "extreme caution," because the risk of heat illness is higher. In all but 2 months -- December and January -- temps inside the car shot up to National Weather Service “danger” levels of greater than 105 degrees.

In June, the hottest day they measured, temps inside the car topped 90 degrees by 8:35 a.m. and hit 105 by 9:25 a.m. In some cooler months, including February, April, October, and November, temps were over 90 degrees in the car before noon.

If a child was in the car, “it wouldn’t take long for that child to [die],” Duzinski says.

How soon temperatures become a danger to kids varies. How well children tolerate heat depends on how acclimated to the heat they are, how much water they’ve had to drink, and genetics, among other things, she says.

Hot cars also become more dangerous as children breathe and sweat, which raises the humidity level. More humidity makes it even tougher for little bodies to stay cool. Because of their smaller size, children can overheat three to five times faster than adults.

Beware of Cooler Outside Temps

Cooler fall and spring temperatures can be dangerous, too. A previous study in the journal Pediatrics found that even when the temperature outside is a mild 72 degrees, the temperature inside a car can rise as much as 40 degrees within an hour. This study showed that even when outside temperatures were as low as 68 degrees, the inside of a car can reach temps greater than 105.

“You wouldn’t think that, right? You wouldn’t think ‘I’m in Texas, it’s March, it feels great outside. I can leave in the kid in the car, right?’ Well, you can’t,” says Graham Snyder, MD, an emergency room physician at WakeMed Health & Hospitals in Raleigh, N.C.

Of the nearly 400 cases where kids have died as a result of heatstroke in a car since 2003, roughly one-third happened when the outside temperatures were between 80 and 89 degrees, according to the study.

“A car is a very nice, very expensive greenhouse. When the light comes in, the air gets hotter, and the air does not come back out,” Snyder says. “You roll those windows up and park in the sun, it’s going to get very, very hot.”

Heatstroke Deaths of Children in Cars

“Leaving a child in a car is just a disastrous idea, or even a pet, for that matter,” he says.

But it happens far too often.

Media reports suggest there have been 17 heatstroke deaths of children in cars in 2014.

Since 1998, there have been about 623 similar deaths, according to statistics compiled by Jan Null, a meteorologist at San Francisco State University. And he says the problem doesn’t seem to be getting any better. Over the past 16 years, the 5-year annual average has stayed flat at around 38 deaths each year.

“Parents aren’t getting the message, and we haven’t found good ways to communicate that,” Null says.

About half the deaths happened as a result of a caregiver forgetting a child in the back seat, according to Null’s statistics. About 30% happened when kids were playing in an unattended car, and 18% were as a result of parents intentionally leaving a child unattended in a car.

Tips for Parents

Experts say distracted parents can take steps to minimize the risk that they’ll forget a child, or that a child might accidentally trap themselves in a parked car.

Leave a purse, briefcase, or cell phone in the back seat, Duzinski recommends. That way, you get in the habit of checking in the back seat before leaving the vehicle.

She says it’s also a good idea to make an arrangement with your child’s daycare to have them call you if the child doesn’t show up as expected.

Always lock your car and car trunk, even if the car is parked in the driveway at home, and always keep keys and fobs out of the reach of little fingers, Null recommends.

Snyder thinks anyone who sees a child left alone in a car should call 911.

“As citizens, we all have to be alert for that. If you see it, you have to do something about it,” he says.

Show Sources


Sarah Duzinski, MPH, research scientist, Dell Children’s Medical Center, Austin, TX.

Graham Snyder, MD, emergency room physician, WakeMed Health & Hospitals, Raleigh, N.C.

Jan Null, meteorologist,  San Francisco State University, San Francisco.

Journal of Injury Prevention, August 2014.

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