An inspection contractor found a chemical tank at a Washington state paper mill "not fit for continued service" 10 months before it failed in May.
The plume from the chemical reaction that followed the outbreak of the fire could be seen for miles
The company said the fire is contained to the refinery's property, about 40 miles west of New Orleans, and there have been no injuries.
At least one employee was injured and treated at the scene early Monday, authorities said.
Residents near the plant had to shelter in place for hours and were ordered to turn off air conditioners after tall flames and heavy smoke could be seen rising from the site.
The moment of the explosion was caught on video.