Will Hand Sanitizer Combust If Left in a Hot Car?
Hand sanitizer is definitely flammable … but enough to start a car fire?
- Published 22 May 2020
A bottle of hand sanitizer will spontaneously combust if left in a hot car.
Editor’s note: Fire experts warn that a plastic bottle containing any liquid — including, but not limited to, hand sanitizer — left in a car and exposed to direct sunlight can potentially focus sunlight into a beam hot enough to start a fire. The following article deals specifically with the specific claim that hand sanitizer will “spontaneously combust” if left in a hot car.
In April 2020, a series of photographs started to circulate on WhatsApp and Telegram that supposedly showed the aftermath of a car fire caused by an unattended bottle of hand sanitizer.
These posts, many of which were written in Portuguese, urged people to be cautious about leaving hand sanitizer in their cars because, they claimed, it can spontaneously combust.
A month or so after these posts went viral in Brazil, a similar rumor started to circulate on English-language pages. In addition to being spread by anonymous social media users, these warnings also made their way onto the pages of a real fire departments. The Western Lakes Fire District of Wisconsin (WLFD) in Wisconsin, for instance, shared the following post to its Facebook page on May 21:
Soon after, a number of news outlets picked up on this story and ran articles about how a fire department was warning people not to leave hand sanitizer in their cars. Although WLFD truly did post the above-displayed warning, the department later removed the post for stirring confusion.
Can Hand Sanitizer Spontaneously Combust?
One of the major fears that people had after encountering this rumor on social media was that their hand sanitizer was going to “spontaneously combust” if left too long in a hot car. We won’t say that this is impossible, but we will say that it is extremely unlikely.
According to the National Fire Protection Association (NFPA), hand sanitizer would have to be exposed to extreme heats (over 700 degrees Fahrenheit) in order to spontaneously combust.
Spontaneous ignition, on the other hand, involves a substance self-heating to a point where it ignites, without the need for any outside ignition source like a flame. Hand sanitizer is not subject to self-heating and would require temperatures to reach over 700 degrees Fahrenheit to spontaneously ignite, according to Guy Colonna, director of Technical Services at NFPA.
Those sort of temperatures just aren’t going to be seen inside of a parked car (so long as that car is parked on Earth). A 2018 study published in the journal Temperature found that the average temperature in a parked car on a 95-degree day was about 116 degrees. Specific parts of the car, such as the dashboard, climbed closer to 160 degrees, but that is still far from the 700 degrees needed for spontaneous combustion.
The NFPA continued:
“Spontaneous ignition would be an ignition source independent of a flame or a spark, [and] it requires a material that is reactive to do what’s called self-heat,” Colonna says in a new video interview on the topic (above). “Internally, it undergoes a reaction and changes its properties, and when changing its properties, it releases lots of heat energy. Hand sanitizer, the alcohol [in it], is a material not inclined to do that. … The ignition temperature of the alcohols are going to be something in excess of 700 degrees Fahrenheit.”
In other words, while hand sanitizer gives off ignitable vapors at roughly room temperature or above, that vapor-air mixture still needs to be exposed to very high temperatures to ignite. A flame can do it. A hot car can’t.
The claim that hand sanitizer was causing car fires first gained traction in Brazil in April 2020 via social media posts on WhatsApp. This spurred the country’s Corpo de Bombeiros de Campo Grande (Campo Grande Fire Department) to issue a warning about the potential dangers of leaving hand sanitizer in a hot car. However, the fire department admitted that it had yet to see any fires caused in such a manner. Likewise, we have yet to uncover any confirmed reports about hand sanitizer causing a fire while left in a parked car on a hot day.
However, many hand sanitizers are still flammable and do pose some risks. Alcohol-based hand sanitizers should not be used near open flames, and people storing large amounts of hand sanitizer should adhere to the National Fire Protection Association’s Flammable and Combustible Liquids code.
Although keeping a small bottle of hand sanitizer in your car won’t result in spontaneous combustion, cautious drivers may want to store their hand sanitizer (and any other liquids kept in plastic bottles) out of direct sunlight in their glove boxes or center consoles.