The pilot's failure to maintain clearance from the runway during a low-level aerobatic maneuver due to his impairment by an over-the-counter antihistamine. Contributing to the severity of the pilot's injuries were the pilot's lack of fire protective clothing, his inability to egress the cockpit, the rapid spread of the fire, and the decision of the air show's organizers not to have the airport rescue and firefighting services at their highest level of readiness, which delayed arrival of fire suppression equipment.