The incident happened shortly before 3:00 p.m. at #1 Hausel Road in the Port of Wilmington.
The worker, a 48-year-old man, was working on the gas tank of a vehicle when gasoline leaked, causing the flash explosion.
The injured man was taken to Crozer-Chester Burn Center.
His name has not yet been released.
Authorities on the scene say this has been ruled an accident.