Experts say lesser-known dangers of hot cars include common items left in vehicles

The inside of a car is one of the most dangerous places for small children and pets during a heatwave. But everyday objects can be dangerous too.

Water bottles, for example, pose unique dangers when temperatures start to rise, experts say.

One of the unexpected risks is the ability of water bottles, especially clear bottles containing clear liquid, to start a fire, David Richardson, a student administrator with the Midwest City Fire Department in Oklahoma, told ABC News.

Depending on the presence of sunlight, the reflective qualities of the bottle and liquid can heat nearby objects to the point of catching fire if they are hot enough, Richardson said.

When Richardson first heard about the potential danger of water bottles, he didn’t believe it. So he tested them in a controlled environment and found that a water bottle could burn a hole in a piece of paper, just like a magnifying glass.

Richardson stressed that for this phenomenon to occur, a “perfect storm” of conditions is needed. Not only must the bottle and liquid be clear, but sunlight must enter the car at just the right time. Vehicles with tinted windows probably do not pose a similar risk, he said.

“The chances are quite small, but they are not impossible,” he explained.

Ingesting liquid that has been cooking inside a plastic water bottle in a hot car for a period of time could also affect human health.

A bottle’s manufacturing process, chemical composition, outside temperature and how long the bottle has been exposed to heat mean the liquids could become contaminated with toxins, Dr. Stephanie Widmer, a board-certified toxicologist and emergency physician, told ABC News.

While research and expert opinions differ, the risk is not zero, Widmer said. It’s best to avoid drinking from plastic bottles that have been exposed to high temperatures until there is more conclusive research, she added.

Electronic devices with lithium batteries, such as a vape pen, electric scooter or toy, could also become a hazard if left in a hot car, Richardson said.

If the plastic casing surrounding the battery melts and the lithium-ion battery is exposed to direct sunlight and high temperatures, there is a chance it could explode, Richardson said.

Other everyday items that experts recommend not leaving in hot cars due to their risk of explosion include aerosol cans, canned and bottled soft drinks, and cigarette lighters. Items commonly left in hot cars, such as sunscreen, medications, and alcohol, have the potential to spoil, while glasses and sunglasses can melt and warp.

Leaving humans in hot cars remains the number one danger, often with fatal consequences.

It’s critical to remember that leaving children or pets in a parked car, even for a short period of time, is very dangerous and can be fatal, Widmer said.

More than a dozen children have died so far this year after being left in hot cars. Nearly 1,100 children have died in hot cars since 1990, according to KidsAndCars.org.

Extreme heat is expected through the rest of the summer across much of the United States, forecasts show.