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Hot cars can hit deadly temperatures in as little as one hour

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The dashboard of a car parked in the sun on a hot summer day can reach 70°C in about an hour. One hour is also about how long it can take for a young child to suffer heat injury or even die from hyperthermia – when the body warms to above 40°C and cannot cool down.

A new study published in the Taylor & Francis journal Temperature compares how different types of cars warm up on hot days when exposed to different amounts of shade and sunlight for different periods of time. The research team took into account how these differences would affect the body temperature of a hypothetical 2-year-old child left in a vehicle on a hot day. The study highlights the need for greater awareness and prevention measures for pediatric vehicular heatstroke, even perhaps a technological solution for in-car alerting systems when a child is mistakenly left behind.

“Our study not only quantifies temperature differences inside vehicles parked in the shade and the sun, but it also makes clear that even parking a vehicle in the shade can be lethal to a small child,” said co-author Nancy Selover, an Arizona State climatologist.

The findings

Researchers used six vehicles for the study: Two identical silver mid-size saloon cars, two identical silver city cars, and two identical silver minivans. During three hot summer days with temperatures above 35°C in Tempe, Arizona, researchers moved the cars from sunlight to shade for different periods of time throughout the day. Researchers measured interior air temperature and surface temperatures throughout different parts of the day.

“These tests replicated what might happen during a shopping trip,” Selover said. “We wanted to know what the interior of each vehicle would be like after one hour, about the amount of time it would take to get groceries. I knew the temperatures would be hot, but I was surprised by the surface temperatures.”

For vehicles parked in the sun during the simulated shopping trip, the average cabin temperature hit 46°C in one hour. Dash boards averaged 69°C, steering wheels 53°C, and seats 51°C in one hour.

For vehicles parked in the shade, interior temperatures were closer to 38°C after one hour. Dash boards averaged 48°C, steering wheels 42°C and seats 41°C after one hour.

The different types of vehicles tested warmed up at different rates, with the city car warming faster than the mid-size saloon and minivan.
“We’ve all gone back to our cars on hot days and have been barely able to touch the steering wheel,” Selover said. “But, imagine what that would be like to a child trapped in a car seat. And once you introduce a person into these hot cars, they are exhaling humidity into the air. When there is more humidity in the air, a person can’t cool down by sweating because sweat won’t evaporate as quickly.”

Hyperthermia prevention

A person’s age, weight, existing health problems and other factors, including clothing, will affect how and when heat becomes deadly. Scientists can’t predict exactly when a child will suffer a heatstroke, but most cases involve a child’s core body temperature rising above 40°C for an extended period.

In the study, the researchers used data to model a hypothetical 2-year old boy’s body temperature. The team found that a child trapped in a car in the study’s conditions could reach that temperature in about an hour if a car is parked in the sun, and just under two hours if the car is parked in the shade.

“We hope these findings can be leveraged for the awareness and prevention of pediatric vehicular heatstroke and the creation and adoption of in-vehicle technology to alert parents of forgotten children,” said Jennifer Vanos, lead study author.

Further information

For an interview, please contact:
Dr Jennifer Vanos
Assistant Professor, University of California, San Diego
Phone: +1 858-534-9968

For a copy of the journal article, and other queries:
Jodie Bell, Press & Media Relations Manager
Phone: +44 (0)20 7017 6571