Unit 1 was starting the engine at the boat ramp to unload from trailer. When the operator turned the key the boat exploded knocking the console off. Victim was burned on the left elbow and singed about the head and legs. Subject went for treatment at Doctor's Care. According to the officer's conversation with the arson investigator, he stated that "the arson investigator noted that the additional of fuel vapors from recent fueling was ignited by an arch that occurred from two loose battery terminals. The operator tightened the wing nuts on the battery which caused spark and boom.