EE pulled beside tank in pit, EE attempted to fuel up a pump in the pit. EE noticed cap was tight, used both hands to remove the cap. Used cell phone for light to see if any fuel was in tank, laid phone on tank. Then the diesel fumes ignited, causing flash. Hair on head and face were singed. EE drove out of pit/talked w/an EE. Drove self to hospital, treated for 2nd deg burns.