Fire crews from several communities fought the blaze at the Ag Processing Inc. plant, about 20 miles south of Sioux City, said Woodbury County Emergency Management Coordinator Gary Brown.
Three of the eight people injured were in critical condition at Mercy Medical Center in Sioux City, said Dr. Larry Sellers, chief medical officer. Most of the injuries involve burns and internal injuries from inhaling the hot gas, he said.
The plant, which employs 50 people and makes soybean oil and soybean meal, was shut down for routine cleaning and maintenance when the explosion occurred just before 9 a.m.
Brown said the explosion involved hexane gas, a highly flammable chemical used to extract vegetable oils from crops such as soybeans.
Jim Rodenburg, a spokesman at Ag Processing headquarters in Omaha, Neb., said there had been an incident at the company's plant, but he said he could not elaborate. The company was investigating, he said.
Nine years ago, an explosion at a fertilizer plant in the same industrial complex killed four people, injured 18 and released a toxic cloud of ammonia.
