Vernon Brubaker, age 19, was using a torch to weld something onto a small propane tank that caused the tank to explode, police said. He was killed instantly at the scene.
Brubaker was working on the farm equipment at 1069 Cook Road in a rural part of the county.
Investigators said the power of the explosion was surprising.
A 12-year-old boy, who was working with him, was sent flying through the air several feet, but suffered no serious injuries.