Investigators are now trying to pinpoint why chemicals they were cleaning up exploded around 5:40 Thursday evening.
Retiree and army veteran Dennis Hughes spent 39 years working for Crane.
When he heard scanner traffic at his home Thursday about extra crews called to a fire at Crane, he knew something on the military base had gone very wrong.
"The fact that they called for assistance surprised me. I have never known of the facility requesting outside assistance unless it was something that would be serious," Hughes said.
Turns out, it was serious: an explosion in the pyrotechnic facility in the army section of the base injured five workers.
"That immediately alerted me that it was in a very dangerous area," Hughes said.
Three men and two women, all civilian employees with Crane Army Ammunition Activity, were treated for minor injuries at Bloomington Hospital and released that same night.
Crane says the explosion happened during routine clean-up in a building where they manufacture illumination candles - chemically-created flares used to light the sky for soldiers.
"Obviously these are volatile chemicals and have to be handled very carefully and we have strict procedures in place, so that is why it's so important in this investigation, we determine exactly what caused the accident. But we take a great amount of effort to protect our people," said Tom Peske, public affairs officer for Crane Army Ammunition Activity.
Peske says safety procedures to douse chemical fires worked properly after the explosion.
But what caused it is still a mystery.
The pyrotechnic facility on the base is now closed and Army investigators are on scene looking for answers.
"What caused the accident and what damage may be done to the facility, what needs to be done to prevent it in the future," Peske explained.
They're questions Dennis Hughes wants answered as well, especially since he still has friends and family who work at Crane.
"Very concerned," Hughes said. "If you have connections to the facility, yes you're concerned."
Crane staff say this is the first accident they've ever had at the pyrotechnic facility.
They also say this was nothing like the deadly explosion that happened recently at an Army depot in Nevada.
That incident involved ammunition while this one only involved chemicals.