Rhodes said as many as 2,000 employees and contractors were on-site at the time of the accident as one shift was preparing to leave and another was scheduled to start. That's an unusual number of employees at the refinery but is common during turnaround periods, which occur every four years, he said.
He said the blast did not cause a fire, but highways were closed for several hours to accommodate emergency responders.
The Wynnewood facility, which refines up to 70,000 barrels of crude oil a day into petroleum products, was acquired by CVR Energy in December. Company officials issued a statement late Friday expressing their sympathies to the employees and families affected by the explosion.
Occupational Safety and Health Administration officials arrived early Saturday to investigate, Rhodes said.