Thirty people were taken to hospitals, three of whom were evacuated by helicopter, Louisiana Department of Environmental Quality spokeswoman Jean Kelly said.
The William Olefins plant makes 1.3 billion pounds of ethylene, a widely used flammable gas, and 90 million pounds of polymer grade propylene, common plastics, each year.
Environmental officials were monitoring air quality since they did not yet know what kind of chemicals -- if any -- might leak into the air, Kelly said.
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