Workers were mixing primer at the time of an explosion Tuesday at the U.S. military's largest ammunition plant that killed one employee and injured four others, officials said.
"Primer mixing was going on," said Jim Nickels, vice president and general manager for Orbital ATK, which runs the Lake City Army Ammunition Plant in Independence, Missouri. "There's a chemical mix process that occurs to form the compound that goes into a primer."
The Orbital ATK employee who died was identified Wednesday as Lawrence Bass, a 55-year-old resident of Blue Springs, Missouri.
"The entire Lake City Army Ammunition Plant community continues to hold the family of Mr. Bass in our thoughts and prayers during this difficult time," Justine Barati, director of public and congressional affairs at Joint Munitions Command, said in an email to Military.com.
The four injured workers, all employees of Orbital ATK, were treated by medical personnel at the scene and refused additional treatment, she said.
The sprawling plant located on nearly 4,000 acres in Independence, Missouri, dates to World War II and produces more than 1 billion rounds of small-caliber ammunition each year.
The facility, which employs some 1,800 workers -- including 30 U.S. government employees -- was shuttered for the rest of the day on Tuesday. Only certain workers were permitted to return to work on Wednesday.
"Orbital ATK salaried staff, maintenance personnel and some bargaining unit employees are on the plant," Barati said during a telephone interview on Wednesday. "All other employees will not report to work at least until Monday."
During a press conference at the site on Tuesday afternoon, officials ruled out any connection between a recent renovation to upgrade the plant and the explosion.
Nickels said officials with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF, continue to investigate the cause of the accident. He said workers at the time of the explosion "were working on a specific primer mix."
"A primer is basically an initiator for a small caliber round," he said. "We mix those energetics at this facility to put in the primer that are installed in the round."
The last time an explosion rocked the location was in 2011, but no fatalities occurred in that incident, Nickels said.
Orbital-ATK on Monday received a nearly $100 million contract from the Army to produce 5.56mm and 7.62mm ammo for the service.
Both Nickels and Army Lt. Col. Eric Dennis, commander of Lake City Army Ammunition Plant, offered their condolences to Bass' family.
"Making ammunition is dangerous work and our employees risk their lives to protect our men and women in uniform," Dennis said. "This is a sacrifice they make to support our county and I'm humbled by the ultimate sacrifice this employee made today."