Can hydroalcoholic gel explode under the effect of heat?

• The photo of a car door that partially caught fire due to an alcohol-based solution questions Internet users.
• This cliché and these warnings have been circulating on the Internet for several weeks, in particular on the Brazilian side.
• In reality, for such a hydroalcoholic solution to catch fire, it would have to be exposed to temperatures above 400 °.

For several days, internet users have been wondering after the publication, on Facebook, of a photo showing the interior of a car door partially burned due to the inflammation of a vial of hydroalcoholic solution. According to the commentary accompanying this photograph, “the disinfectant gel in contact with heat and the sun explodes. Pay attention ! " This publication has been shared more than 2,100 times at the time of publication.

This Facebook post suggests that hydroalcoholic gel can catch fire if left in the sun. - Screen capture

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Before giving the floor to a chemist, we started by searching the origin of this photo on Google. Very quickly, you realize that the photo does not date from yesterday. A similar warning message accompanied by the same photograph had indeed already appeared on social networks in Brazil as early as April and was fact-checked by the media Estadao .

Simple research on the instructions for use of certain hydroalcoholic solutions tells us about the specifics of these products, especially with regard to the auto-ignition temperature. This corresponds to the temperature at which the product can ignite without having been in contact with a flame or spark. However, we realize that most of these gels can catch fire only when exposed to temperatures above 400 °.

In addition, the auto-ignition temperature of ethanol, which makes up the majority of these hydroalcoholic solutions, is also between “363 ° and 425 ° (according to sources), according to the toxicological sheet published by the Institute National Research and Security Center (INRS).

"No danger in leaving a hydroalcoholic solution in a passenger compartment"

But to be completely sure that a hydroalcoholic solution cannot catch fire if it is exposed to strong heat, as it can be the case in the passenger compartment of a vehicle left long in the sun, we contacted François-Xavier Coudert, director of research at the CNRS at the Institut de Recherche de Chimie ParisTech.

"Basically, like most fake news, it's not true, but there is a little something true all the same: it is the fact that when you use hydroalcoholic gel, you shouldn't not be in contact with a flame or be smoking, he explains. It easily catches fire. I did this this morning in my kitchen to check if it worked and, indeed, by putting a small background of solution in a glass and turning on, it makes a pretty blue flame. "

Taking a break, lighting some hand sanitiser on fire… (I swear it's work-related, somehow) pic.twitter.com/vXavw21kQ8

"For such a gel to catch fire, you need a flame or exposure to very, very high temperatures," continues the chemist. If we take the photo again, it would be necessary for example that a magnifying glass was left in the car, that the rays of the sun reach it and that the solution is on the way. In reality there is no danger in leaving a hydroalcoholic solution in a passenger compartment, even in very hot weather. I am a first aid worker at the Red Cross in my spare time and I know that in all ambulances there are small bottles of 300 ml gel. We sometimes park them in full sun but that does not cause any danger. We are reassured. 

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