An explosion at a St. Louis-area chemical plant left one worker burned and the plant badly damaged.

The Sunday morning explosion at the SantoLubes LLC plant in St. Charles, Mo., occurred in a building that housed several chemicals used to produce insecticides.

St. Charles Battalion Chief Michael Grzyb said the blast happened almost immediately after workers began a mixing process.

He said at least half the structure was in flames when firefighters arrived.

The injured worker was able to escape the fire on his own. Fire officials said he was hospitalized with burns over at least 30 percent of his body.

A woman answering the phone at SantoLubes on Monday said no one was available to comment.