This Is How Long It Takes a Hot Car to Reach Dangerous Temperatures

In the last decade, nearly 750 children have died after being left in a hot car, and a new study highlights just how quickly that can happen.

On a hot day, a car parked in direct sunlight may reach temperatures that are dangerous to a child in approximately one hour, according to a paper published in the journal Temperature. Even a vehicle in a shady area could warm up to risky levels after around two hours, the study says.

Children are particularly susceptible to heatstroke. Their core temperatures rise more quickly than those of adults, and their bodies are less adept at cooling. Kids may also be unable to control or leave their environment in the event of an emergency. For the purposes of the study, the researchers assumed that a toddler was at risk of extreme heat-related illness—which happens when the body cannot regulate its temperature, potentially resulting in organ failure, brain damage and death—at a body heat of 104 degrees and above.

To determine how long it would take a vehicle to reach dangerous temperatures, the researchers parked three pairs of identical cars—two silver sedans, two silver economy cars and two white minivans—in sunny and shady areas of a parking lot in Tempe, Ariz., multiple times in June and July of 2014. They measured the heating effects inside the cars and compared the results to calculations about how high temperatures would affect the body of a hypothetical 2-year-old boy.

They found that vans took the longest time to heat up, and economy cars the shortest. But on average, the temperature inside a vehicle after an hour in the sun was 116 degrees; the dashboard, seats and steering wheel were even hotter. After an hour in the shade, the car interior was an average of 100 degrees. That means, according to the researchers, that a child’s internal body temperature could reach unsafe levels after about an hour in a car parked in the sun, and after about two hours parked in the shade.

While the actual effects would vary depending on the individual child, make of car and temperature outside, the research underscores the importance of keeping a watchful eye on kids—and never leaving them unattended in a vehicle.