INDEPENDENCE, Mo. — Tuesday’s fatal explosion at Lake City Army Ammunition Plant wasn’t the first time someone had been killed mixing primer at the Independence facility.

A spokesperson for the plant said in a statement that an explosion occurred at approximately 1 p.m. on Tuesday in a primer mixing building that resulted in one fatality and four employees being evaluated on scene, who each refused further medical treatment. The deceased victim’s identity has not yet been released.

“We’re a family here at Lake City and today we lost a family member. Our hearts truly go out to the family,” Jim Nichols, Orbital ATK Small Caliber Systems Vice President Jim Nichols said.

A 1990 OSHA report shows a worker at Lake City was killed when a primer mixture exploded as the employee tried to push it down a bowl with a sponge.

In 2011, the same year six people were injured in an explosion OSHA initially fined ATK $28,000 for four serious violations. The company ultimately paid $5,600. OSHA cited another serious violation in 2008.

The Bureau of Alcohol, Tobacco, and Firearms has called in chemists and other explosive experts from around the country to try to figure out what went wrong. An ATF bus that will serve as a command post for the investigation arrived shortly after 9 p.m. Tuesday.

“It’s going to be a several day event, it’s nothing that we can do quickly. Out of safety and being careful that we don’t miss anything in our investigation it will be a slow and methodical process, but after several days I’m confident we will have an answer,” ATF Agent John Ham said.

Lt. Col. Eric Dennis, Lake City Commander, said the plant has approximately 1,800 government and contractor employees. All workers involved in the accident were employed by contractor Orbital ATK.

“The person who gave his life today is a hero, our men and women wouldn’t be able to do what they do without this facility and for us to come in at a time like this is very important to us and certainly important to law enforcement community as a whole,” Agent Ham said.

Dennis took over command of the facility on July 13, 2016, and oversaw a $434 million modernization program that ” improved security, safety, manufacturing and infrastructure” at the plant, according to a U.S. Army news release.

Lt. Col. Dennis said the building where this happened today did not see any upgrades, or have any changes from that modernization program.

NASDAQ reported Tuesday morning that Orbital ATK had secured a $92 million order from the U.S. Army to be manufactured at the Lake City plant. The report also says that last week the company secured a $21 million contract with the U.S. Navy, and in January received a $50 million order from the U.S. government to supply ammunition to the Department of Defense “in support of international allies.”

By Wednesday morning, Agent Ham said the ATF had conducted some preliminary interviews with employees and first responders.

“Our explosives specialists also spent considerable time with ATK personnel to make sure that we understand their production processes.  This will help us in determining what could could have caused the explosion,” Agent Ham said in his Wednesday morning update. “ATF Explosion Investigation National Response Team members began arriving last night and will continue to arrive this morning, which will put us in a position to begin the more detailed portion of our investigation later this afternoon.”