Spontaneous combustion unlikely, but don’t store on the dash
The Pelham Fire Department offers guidelines on the safe storage of alcohol-based hand sanitizers in vehicles.
While recent claims on social media suggest that spray bottles of sanitizer can spontaneously combust—blow up—when left in a closed car parked in summer sunlight, the odds of this happening are slim to none.
“The auto-ignition point [for sanitizers] is well over 500 degrees Fahrenheit,” says Pelham Fire Prevention Officer Jason Longhurst. Even in extreme summer heat in Ontario, auto interiors will at most reach around 120 F—hot enough to kill a pet or child, but not hot enough to turn your Purell into a hand grenade.
However, there remains a risk that magnified sunlight could trigger combustion.
“Our recommendation is to store these products in an area of the vehicle that is out of direct sunlight. There is a chance that glass could create a magnification scenario and cause combustion, so storing the product on your dash is not recommended.”
There is also the flashpoint of alcohol to consider. Longhurst says that this is 71 F, meaning that an open flame or spark could ignite either liquid or vaporised sanitizer. As heat increases, alcohol evaporates more rapidly. A loosely closed bottle of high-percentage alcohol sanitizer, if left in a hot car for a long period of time, could theoretically emit enough vapour that an electric spark or the lighting of a cigarette might cause the accumulated vapour to ignite. Far more likely, however, is that the potency of the product will simply diminish over time.
The best advice: Screw caps on tight, and store sanitizers in shaded areas inside your car when parking it on hot summer days.