Modern gasoline (especially winter blends in some areas) have butane gas dissolved in the liquid. Whenever you have a liquid that has a gas dissolved in it, that gas will tend to come out of solution as the temp rises. Look at soda pop for instance. CO2 (carbon dioxide) is dissolved in water. If you leave that can of soda open a while, all the fizz will go out, it will go "flat". You notice this happens much more readily when the soda is warm, in fact explosively if you shake the can and then pop the top. As the temp warms up, some of the butane comes out of solution and makes the gasoline container swell with the gas pressure. You open the top and butane gas rushes out with a hisssssss. It goes without saying you wouldn't want to be anywhere near a heat source or spark (battery cables, switches, lit cig, etc) when that happens because of course butane is highly flamable. The gasoline will still be perfectly fine... oh, it may be a tad "flat" in cold weather but should still be perfectly usable.
This is one reason why your gasoline storage should be in a very well ventillated area. Imagine a dozen gasoline cans out-gassing butane for a few months, then you walk into the storage shed and flip on the light switch or your flashlight.... OOPS!
In a crazy world, it's the crazy man who can get by - and it's about to get cray-cray up in here.