The fire broke out about 7 p.m. at a gun range located in the basement of the building while dozens of people were playing bingo upstairs.
According to investigators, the injured were workers doing repairs to the gun range. Two are in critical condition.
At least 50 people were already in the hall before 6:15 p.m., nearly an hour before the game was supposed to start.
"Over the years, all the gun powder probably built up," said Ronald J. Rakosnik, Lombard battalion chief. "They ignited the gun power, it appears, we are going to do an investigation right now. A fire occurred and when it got to the stairs ... an explosion occured."
Some of the workers ran up the stairs to warn the bingo players to evacuate as smoke filled the building.
"I have never seen smoke move like that," said Vivian Kanelos, bingo player. "When you see smoke blow in over your head, all of a sudden you realize you cannot see any more, it's scary."
The hall will be closed while firefighters complete their investigation.