TWO EE INSTALLING FUEL TANK, ACCUMULATED FUEL RESIDUE WAS DEPOSITED ON LOWER COVERALL LEGS. LATER WHILE INSTALLING STINGER COVER, EE WAS STANDING ON COVER HOLDING IT IN PLACE WHEN SPARKS FROM WELDER IGNITED COVERALL LEGS. EE RECEIVED 1 ST. DEGREE BURNS ON HANDS AND LEFT LEG AND SMALL 2ND DEGREE BURN ON RIGHT CALF.