Why it’s important to take everything out of your car on a hot summer day
Summer heat means blasting the air conditioning, hunting for shady parking spots, and heading to the pool. But while we do everything we can to escape the soaring temperatures, the everyday items we leave behind in our vehicles are trapped in an absolute pressure cooker.
It does not take a triple-digit heatwave to turn your car cabin into a literal oven. The glass windows of your vehicle act exactly like a greenhouse. Shortwave solar radiation passes cleanly through the windshield, where it is absorbed by your dark dashboard, steering wheel, and cloth or leather seats. That energy is then re-radiated as longwave infrared heat, which cannot pass back out through the glass.
Because the heat is completely trapped, the temperature spike happens fast. On a nearly 90-degree day, the interior of a parked car can easily surge past 100 degrees in less than ten minutes. Within an hour, dashboard temperatures can clock in at a staggering 140 degrees or higher.
So, why is this a nightmare for a can of dry shampoo or aerosol sunscreen? It comes down to basic atmospheric physics: when temperature goes up, pressure goes up.
Inside a closed aerosol container, the liquid propellant and gas molecules are already packed incredibly tightly. When that can is exposed to extreme vehicle heat, those molecules absorb the energy, start moving frantically, and slam into the interior metal walls with massive, compounding force.
Most consumer aerosol cans are only manufactured to withstand temperatures up to 120 degrees. Once your car dashboard sails past that threshold, the structural integrity of the metal fails. The result? The can can rupture violently, turning a harmless bottle of sunscreen into a dangerous projectile that can shatter windshields and dent roofs.
Pressurized cans are the most dramatic danger, but they aren't the only items that suffer under the summer sun. Before you lock up your vehicle, make sure these common culprits are cleared out.
First, any aerosol cans, as the failure of the bottom or top seals can lead to the can being launched across the vehicle cabin. Second, any canned soda or sparkling water, as the carbon dioxide gas will expand until the aluminum seams rip, coating your interior in a sticky mess. Third, make sure to grab any prescription medications, as the extreme heat can alter the molecular structure of specific types of drugs, rendering them useless after enough time has passed. Finally, don't leave any electronics in the car, as the internal lithium-ion batteries can warp, leak, permanently lose capacity, or experience thermal runaway.
The easiest way to protect your car, your wallet, and your peace of mind is to always double-check that nothing is inside the car before leaving it outdoors for a long period of time. Taking an extra 30 seconds to grab your bag and clear off the passenger seat before heading away from the car ensures that you don't come back to any unpleasant surprises or costly repairs.
