An employee removed a fuel gauge sending unit to access the fuel tank and remove old fuel. After removing the old fuel and adding new fuel to the tank, the employee replaced the fuel gauge sending unit. In this process, he found one of the electrical connectors was damaged and needed to be replaced. He replaced the connector and used a butane torch to shrink the heat-shrink tubing used to protect the connector. The flame from the butane torch ignited the vapors from the fuel and a flash fire occurred, burning the employee's face, arms, chest, leg, and stomach.