The accident happened on a baseball field in Comanche, about 100 miles southwest of Fort Worth.
A spokesperson for the Comanche County Medical Center says three people were treated for burns and then released and one person has been transferred to a burn unit.
The Kiwanis Club puts on a Fourth of July show at the high school every year. Officials says it's unclear what caused the explosion in the trailer, which was hooked to pickup truck. State and federal authorities are investigating.
Because of the accident, all activities there for Friday have been canceled.
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