An employee was hot air welding PVC roof seams and transitioning to a new location on a roof when his extension cord bumped a gallon container of acetone. The container began to tip and he tried to catch it with his right hand. Some contents spilled and were subsequently ignited by a flameless hot air welder that was approximately 2 feet away. His pants and shirt caught fire, and he received second degree burns to his right hand, arm, and bicep. He was hospitalized.