Flash Points
To simplify, Flash Point is the temperature at which a fuel produces sufficient vapor to ignite if exposed to a spark. The lower the flash point, the more volatile the fuel.
Here's a link to the flash points of many different fuels:
http://www.engineeringtoolbox.com/flash-point-fuels-d_937.html
Note that diesel fuel has flash points ranging from 100-130F; kerosene, from 100-162F; napthalene 174F (although naptha fumes can harm eyes and lungs, so exercise caution). The Navy bans JP-4 from ships; JP-5 was designed with a higher flash point (140F) for shipboard use, due to the greater hazard fire poses at sea.
In contrast, the flash point for gasoline is -45F. At any temperature where a human can survive without extreme winter survival gear, gasoline will ignite if a spark is introduced.
Compare that to JP-5: one can toss a lighted match into a bucket of JP-5, and not only will the fumes not ignite (assuming temperature is less than 140F), but the liquid JP-5 will extinguish the match.
People may use gasoline as a solvent, but that doesn't mean it's a good idea.
Gasoline can linger on the body longer than one might realize, too, and those fumes remain volatile even in low concentrations. Here's a case from last month:
http://news.yahoo.com/blogs/sideshow/man-dies-accidentally-drinking-gasoline-salsa-jar-then-224208413.html