Media reports say a man in his 50s was taken to a hospital Monday with second-and third-degree burns over 80 percent of his body following the explosion.
The man's name has not been released and it wasn't immediately clear if he works at the refinery. HollyFrontier's corporate office was closed for the Labor Day holiday, and email messages from The Associated Press were not immediately returned.
A Butler County dispatcher says no one else was hurt and the plant was not evacuated.
HollyFrontier's website says the El Dorado refinery has a crude oil capacity of 135,000 barrels per day.