It was seen from miles away and at one point seemed to dwarf the refinery's tallest smokestacks, residents reported.
The Tulsa Fire Department was notified of the blaze shortly before 2:30 a.m. and stood by as the refinery's private fire department handled the fire, firefighters said.
The cause of the explosion was not immediately clear, but the company said in a statement that it came from a diesel hydrotreater, which is used to remove sulfur from the fuel. No one was injured, according to a company statement.
Matt Shaffer, who lives on the 27th floor of the University Club tower at 1722 S. Carson Ave., said the blast awoke him and several of his neighbors about 2:15 a.m.
"As I was laying there, I thought, woah, maybe there was a fire in my building," he said. "That's how clear the sound was."
The initial blast was followed by what sounded like a jet engine, he said. He watched as the largest flames lasted about 15 minutes.
"I looked out my window and I saw this big old ball of flame," he said. "It was huge."
Refineries use hydrotreaters to help meet government standards for sulfur levels in their fuel, according to an Oklahoma Department of Environmental Quality spokeswoman.
The spokeswoman said an air quality monitor northwest of the refinery Thursday morning detected a slight increase in sulfur dioxide, a possible result of the explosion.
The increase was not dangerous and did not exceed air quality standards, the spokeswoman said.
The explosion occurred at the former Sinclair refinery, which HollyFrontier Corp. calls its Tulsa East refinery.
Dallas-based Holly Corp. bought Tulsa's Sunoco Inc. refinery in June 2009 and the nearby Sinclair refinery six months later in deals worth more than $300 million combined.
The facilities are connected by pipelines and are capable of processing up to 125,000 barrels per day in diesel, jet fuel and other petroleum products.
The HollyFrontier Corp. complex made national headlines in April 2011 after fire erupted from Tank 13 at the former Sunuco refinery, now called the Tulsa West refinery. The tank held slop oil, or a mixture of refinery product and water, the Tulsa World previously reported.
The company initially said that lightning apparently caused that fire, but later refused to release the findings of its fire investigators.
The DEQ reported in April 2012 that the company's investigators had determined that a bad valve had allowed hydrocarbons to slip into the wrong tank.
The company became HollyFrontier Corp. when it entered into a $7 billion merger with Frontier Oil Corp. of Houston in 2011. The new company has refineries in Tulsa, New Mexico, Utah, Wyoming and Kansas.
Written by Tulsa World