It is well known that a car parked outside on a hot summer day can become a scorching furnace. But how fast does the interior of a car take to heat to deadly temperatures?
The answer can be a matter of life or death. Each year in the United States, an average of 37 children die after being abandoned in hot cars, according to researchers from a new study, published online today (May 24) in the journal Temperature.
To investigate the matter, the researchers studied how long different types of cars take to warm up on hot days. The results were instructive: within 1 hour, the temperature inside a car parked in the sun on a day that reached 95 degrees Fahrenheit (35 degrees Celsius) or more, averaged 116 degrees F (47 degrees C). [Why Does Being in the Heat Make Us Feel Tired?]
Car dashboards got even hotter, reaching 157 degrees F (69 degrees C), on average; the leaflets went up to a temperature of 127 degrees F (53 degrees C), on average; and the temperature of the seats reached 123 degrees F (51 degrees C), on average.
Cars parked in the shade on a hot day had lower temperatures, but still scorching. After 1 hour, the interior temperature of these cars reached an average of 100 degrees F (38 degrees C). The boards of these cars averaged 118 degrees F (48 degrees C); the steering wheel averaged 107 degrees F (42 degrees C); and the seats found an average of 105 degrees F (41 degrees C), the researchers found.
"We have all returned to our cars on hot days and we have barely been able to touch the wheel," study co-investigator Nancy Selover, a climatologist at Arizona State University, said in a statement. "But imagine what that would be like for a child stuck in a car seat." (More on this later.)
Selover added that anyone sitting in such a car, of course, would breathe, and that each breath would introduce moisture into the vehicle.
"They are exhaling moisture in the air," said Selover. "When there is more moisture in the air, a person can not cool sweating because the sweat will not evaporate so quickly."
Researchers used six vehicles in the study: two identical silver-economy cars, two identical silver-medium sedans and two identical silver minivans. Then, on three different summer days in Tempe, Arizona, they monitored parked cars in both sunny and shady locations.
"These tests replicated what could happen during a shopping trip," said Selover. "We wanted to know what the interior of each vehicle would look like after an hour, about the amount of time it would take to buy groceries, I knew the temperatures would be high, but I was surprised by the surface temperatures."  As expected, the cars were heated at different speeds. The economy car heated up faster than the median sedan and minivan, the researchers found.
Children in cars
A person trapped in a car that is quickly heated is at risk of heat stroke, which can be fatal.
It is difficult to predict when heat stroke will hit, largely because the condition involves many factors, including a person's age, weight and existing health conditions, the researchers said. But most cases occur when a child's core body temperature rises above 104 degrees F (40 degrees C) for a prolonged period. [What is Heat Stroke?]
To learn more about the risks children face, researchers used the data to model a hypothetical 2-year-old child. When it was attached to a car seat in a car parked on a hot day, this child met the criteria of heatstroke in only 1 hour if the car was parked in the sun and 2 hours if the car was parked in the shade, found the researchers
"We hope these findings can be used to raise awareness and prevent pediatric heat stroke and the creation and adoption of technology in the vehicle to alert parents of forgotten children," the study's lead researcher, Jennifer Vanos, Assistant professor of climate and human health at the University of California, San Diego, said in the statement.
Vanos added that the effects of hyperthermia (having a higher body temperature than normal) and heatstroke occur along a continuum, from internal injuries to damage to the brain and organs.
Original article Live Science .