Todd said she could not discuss what investigators have found while the investigation is under way.
CVR Chief Executive Officer Jack Lipinski released a statement Sunday that said the company was “cooperating fully” with the investigation.
“Our focus is to determine how this accident occurred and what steps must be taken to avoid a repeat of this incident,” Lipinski said.
CVR purchased the refinery, which has a daily capacity of 70,000 barrels of crude and produces gasoline, diesel fuel, military jet fuel, solvents and asphalt.
Previous incidents at the refinery include a boiler explosion in 2010, a propane leak in 2008 and fire that was sparked by lightning in 2007.
There were no injuries in those incidents.