The fire marshal said Tuesday afternoon that investigators have not yet been able to enter the fire zone where the blast occured.
The fire was finally extinguished late Monday.
Authorities and company officials said no injuries were reported and no evacuations of surrounding neighborhoods were ordered.
The 781-acre complex ranks 39th by total production out of the nation's 150 operating refineries, according to the U.S. Department of Energy.
A spokesman said the blast hit an area that makes a chemical used in plastics.
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