There has been recent reports of the potential fire risk in vehicles, caused by alcohol-based hand sanitiser when left in vehicles in the hot weather.
Although alcoholic hand sanitisers are potentially flammable, however there would need to be a spark to start a fire.
To be safe, you should store them out of the heat, and away from open flames, sparks and hot surfaces.
Source: https:fullfact.org/online/hand-sanitiser