As soon as it became clear that the coronavirus was much more threatening than the seasonal flu, people started hoarding everything they'd need to wait out the pandemic. Hand sanitizer was an early high-demand item that sold out almost instantly, and people went directly from that craze to sharing videos of flaming cars with warnings not to keep sanitizer in a hot vehicle. The images and stories were frightening but as these things often go, they weren't sharing the whole truth. Let's take a look at why.
The National Fire Prevention Agency’s Director of Technical Services, Guy Colonna, told The Drive that the spontaneous ignition temperature for hand sanitizer is more than 700 degrees Fahrenheit. In order to reach those temperatures, he says the sanitizer would need to self-heat, which is an unlikely occurrence. More importantly, at 700 degrees you’ll have many other issues to worry about than just hand sanitizer—like a melting car. Common plastics melt at temperatures far less intense than the 700-degree spontaneous flash point of sanitizer.
Hand sanitizer starts giving off ignitable vapors at room temperature, but still needs to be exposed to extreme temperatures to ignite. As the NFPA puts it, “A flame can do it. A hot car can’t.” There's even some disagreement in the fire prevention community about auto glass, plastic, and their ability to magnify the sun's rays as some have claimed. Colonna said, "Heat from the sun may be magnified by the car's windows or by the sanitizer bottle itself, but it's still not going to be enough to ignite. Tests have seen temperatures hitting 300 to 400 degrees, which are a long way off from the 700 we need to see fire."
So, myth debunked. Even in the hottest weather, there's no way a car is getting hot enough to cause a sanitizer fire. The animation below is from General Motors and shows that car temps can climb quickly, but don't reach anywhere near the level needed to send a bottle of Germ-X into flames.
Colonna says that a much more likely outcome is that the sanitizer just loses its effectiveness. "Anything above room temperature is just going to cause alcohol to evaporate and make the sanitizer weak,” he explained. Some hand sanitizers also contain hydrogen peroxide, which decomposes after exposure to UV light. That basically means heat and light—both of which are abundant in summer—attack the active ingredients in most hand sanitizers, making them less effective after extended exposure.
Experts recommend keeping hand sanitizer at temperatures between 45 and 75 degrees Fahrenheit, which is nearly impossible in the summer heat. If you absolutely have to store hand sanitizer in your vehicle, keep a small bottle in your center console or glove box. It’s better to refill a small bottle regularly than it is to keep a large bottle in your car for long periods of time.
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