The explosion at Totall Metal Recycling in Granite City occurred about 6:25 a.m., police said. Bomb technicians were still trying to secure the scene Monday afternoon, sweeping the site for other possible explosives.
The victims, whom responders could not initially get to because of the fear of further explosions, were not immediately identified. A third person was injured and taken to a St. Louis hospital, police said, but a condition was not available.
Totall Metal Recycling, which employs about 160 people, according to its website, does business with the military and it's not unusual for it to have items such as "military engines and ammunition casings," police chief Rich Miller said.
"This corporation recycles everything you can think of, from plastics to cardboard to metals, and some of their contracts involve getting materials from the military," Miller said at a briefing for reporters near the plant Monday afternoon.
He said authorities do not suspect any malicious intent and were investigating the explosion as an "industrial accident." Miller did not comment on whether the facility has ever received a live mortar before or whether proper procedures were followed in handling it, saying that would be part of the investigation. He also said investigators are looking at what was happening when it exploded.
The Illinois secretary of state's bomb squad was dispatched to the scene to support an explosive ordnance disposal unit from Scott Air Force Base, secretary of state's spokesman Henry Haupt said. Their job was to ensure "there are no other explosive or dangerous devices and, if there are, to render them safe," he said.
Also on the scene were agents from the federal bureau of Alcohol, Tobacco, Firearms and Explosives, and St. Louis city and county police agencies, Miller said.
Robert Nosbisch, resident agent in charge of the ATF in Fairview Heights, said it's not unusual in a situation like this one to get help and other resources from area agencies with expertise in explosives. The heat played a role, too, requiring the rotation of investigators wearing special gear on the plant grounds, Miller said.
Police kept the site secure Monday afternoon as bomb experts combed the area for other possible explosives.
A statement released by the company did not give any details about what might have occurred. It said the firm was cooperating with local, state, and federal authorities during the investigation.
"Our thoughts and prayers are with the families as we collectively cope with this tragedy," the statement said. "We are committed to providing each employee and his or her family with counseling resources during this difficult time."
No information was released Monday on the victims pending positive identification, Madison County chief deputy coroner Roger Smith said. Autopsies were underway, and he said more information might be available Tuesday.
Prather Elementary School, with about 500 students in kindergarten through fourth grade, is about half a mile west of the plant. Granite City School Superintendent Jim Greenwald said the students reported to school shortly after the accident occurred and school proceeded normally.
Greenwald said the principal decided to keep the students inside for recess Monday, but authorities had assured the district there were no chemicals in the air or other hazards.