Officials say a piece of machinery exploded inside Arens Control at 8:30 a.m. Tuesday. The plant manufactures technology used in vehicles.
"Our primary concern right now is the family of the deceased and the other employees," said Ken Kunin, president Arens Control. "That's our focus."
The victim, who has not been identified, was a man in his 50s. The other injured workers were treated and released from the hospital.
About 150 people work inside the Arens Controls. The area surrounding the plant is mostly residential.
After reviewing the damage caused by Tuesday morning's explosion, emergency responders declared that it could have been much worse.
"The explosion went up vertically and damaged the roof," said Chief Glenn Ericksen of the Arlington Heights Fire Department. "But it was contained in that testing area, which was inside of a caged area, which helped contain the explosion and protected the other workers within the plant."
According to the fire department, the machine that exploded was using a chemical called potassium chloride, but it was contained within the building.
"There was no danger to the residents or the community at all," said Ericksen.
Three of the injured were police officers who suffered from smoke inhalation when they rushed to help those inside.
Nearby resident Bob Lee says the explosion sounded like a car backfiring and described the initial triage of the injured.
"They were just checking them out one by one," he said. "They just looked really shook up. They were holding on to each other."
The plant does not appear to have a record of previous accidents.
Representatives from the Bureau of Alcohol Tobacco and Firearms declared the explosion to be just a tragic accident. Officials from Occupational Safety and Health Administration are also on the scene.
"OSHA does all the inspections to make sure they were following procedures and handling the chemicals they were handling inside," said Captain Ken Galinski, Arlington Heights Police Department.
OSHA is interviewing employees as well as company officials to determine whether the accident was due to mechanical failure or operator error.
The plant may remain closed for a few days due to the investigation and extensive damage.