Handgel and hot cars

There’s some deceived wisdom doing the rounds about not leaving bottles of 60% alcohol hand sanitizer in your car when it’s hot because it could spontaneously burst into flames. There are pictures of the damage apparently caused by the hand gel burning through the dashboard.
This is not at all likely to happen at the temperatures you’re like to reach in the passenger compartment of a car. Moreover, if the interior of your car were to reach the necessary temperature for spontaneous combustion of hand sanitizer, that little bottle of gel is the least of your worries.
The flashpoint for 60% ethanol in water, may well be low (about 23 Celsius), but you need something to *ignite* the liquid, it won’t spontaneously burst into flames. Even petrol cannot spontaneously combust until it’s above 280 Celsius, hence the spark plugs to ignite it (an electric spark will peak at about 4500 Celsius).
However, the handgel may well get very hot and opening the lid might lead to it spurting out and scalding you. There is also the issue of putting handgel on your hands while smoking or holding a candle…that would be risky-ish.

Source: David Bradley Sciencebase - Songs, Snaps, Science - May 18, 2020 Category: Science Authors: David Bradley Tags: Sciencebase Source Type: blogs