Omaha fire and rescue authorities have not been able to determine the cause of the blast. Omaha Interim Fire Chief Bernie Kanger said at a news conference Monday night that he couldn't say for sure there was an explosion, though workers and other witnesses described hearing one.
The Occupational Safety and Health Administration will investigate the cause of the accident, which could take weeks. There are no hazardous chemicals at the Omaha plant, which produces nutritional additives for livestock and poultry feed.
Search-and-rescue workers worked Monday evening to stabilize the building and remove the body of one victim, 53-year-old Keith Everett of Omaha. The name of the second victim has not been released, according to Associated Press.
Omaha Police Lt. Darci Tierney said all 38 of the workers who were in the building at the time had been accounted for, so the death toll wasn't expected to grow.
Search effort will resume this morning. "We've got tens of thousands of pounds of concrete, reinforced concrete and steel," Kanger said. "This is a very significant rescue operation."