Pandemic-specific concerns continue to arise as we tick off the weeks of quarantine (remember the collective chemistry lesson about mixing bleach, a few months ago?). With temperatures on the rise, the latest fear is that alcohol-based hand sanitizers will spontaneously explode in parked cars.
The recent flurry of concern was sparked (heh) by a few widely shared videos on Facebook and Twitter, showing cars catching fire, with captions warning of the unknown hazards of Purell. A warning post from a Wisconsin fire department (since deleted) further stoked general fear. Leaving a car safely parked and returning to it aflame is understandably terrifying, but a quick investigation of the source material and a consultation of existing science puts any such concerns to rest.
The quick and simple answer is: Alcohol-based hand sanitizer will almost certainly not burst aflame in a parked car. Agence France-Presse (AFP) Fact Check traced at least one of the shared car clips to a video first uploaded to YouTube in September 2015, which shows a car fire in Saudi Arabia that, as shown in the video, was clearly not started by abandoned hand sanitizer. Poynter also fact-checked the videos, and found most are years-old, and simply the latest coronavirus-related hoax.
Responding to fears of cars exploding, the National Fire Protection Association explained in a Facebook video that temperatures in a parked car would have to reach over 700 degrees to set hand sanitizer on fire without a direct ignition. A flame from a lighter or a blowtorch, or whatever you use to light your cigarettes, would hit 700 degrees, potentially igniting a fire. But a car sitting in direct sunlight is unlikely to ever reach such a temperature. So…. Don’t hold a flame to your Purell, is the key takeaway here.
For what it’s worth, parked cars do reach dangerously high temperatures, particularly if the things left inside of it are people, animals, flowers prone to wilting, prescription medications, and/or sunscreen. According to information compiled by heatkills.org, the internal temperature of a parked car on even a mild, 70-degree day, can reach upwards of 113 degrees after only an hour. A 2005 study by researchers at Stanford University found that cars heat up an average of 40 degrees per hour, with most of the temperature increase occurring within the first hour, even if the windows are partially opened. This video from General Motors gives a nice visual element to all of this:
Maybe you’re naturally inquisitive and are now thinking, Hmm, so with an average 40-degree temperature increase per hour, would my parked car not hit the 700-plus degrees necessary to ignite an alcohol-based sanitizer in… like 15 hours? Once again, the answer is: Almost certainly not. The hottest ever recorded internal car temp seems to be around 170 degrees, nowhere near the 700-degree mark. The key factor in cars heating up is sun, not outside temperature, the Stanford study notes. Just like the sun warms greenhouses in the winter—a phenomenon literally called the greenhouse effect—by heating up air trapped within a glass building, it heats up the air trapped within a parked car. But when the sun goes down, as it does each night without failure, the temperature in the car gradually decreases. It would still be uncomfortable and even deadly for a person or animal, but not near enough to spontaneously ignite your hand sanitizer. Stay washing your hands, and HAGS.
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