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.
The Carus company said Thursday that cleanup is expected to wrap up by the end of next week. However, several parts of the plant will have to be torn down.