[save_old_iron]

The "boiling gas" is interesting. Different blends of gasoline will "boil" at temperatures from 100 F to near 500F.
If you did not burn your fingers on the metal cap of tank then I assume the temperature of the tank was less then 150 F.

Is it possible you are at a high altitude or have a winter blended gasoline pumped earlier this year in the winter / spring time frame ?
Winter blends would vaporize / boil at lower temperatures.