An explosion at an Illinois chemical plant on Tuesday morning left two employees injured, sparking a significant hazardous materials response and leading to a temporary shelter-in-place order for workers in the vicinity.

The blast took place at the Coogee Chemical facility in Ottawa, a small city located southwest of Chicago, just before 8 a.m., according to local authorities.

The explosion was reportedly caused by a magnesium fire, a highly intense and dangerous blaze that cannot be put out with water. The fire was believed to have started due to a malfunction in oxygen sensor equipment, which allowed the oxygen levels to increase.

“Preliminary investigations indicate that the explosion might have resulted from equipment failure during the process of transferring magnesium into a storage container,” stated the Ottawa Fire Department (OFD).

Responding crews had to deploy specialized industrial dry chemical agents to safely extinguish the magnesium fire, as using water could exacerbate the reaction.

Crews also had to use specialized on-site industrial dry chemical agents to safely suppress the magnesium fire, as water can further intensify the reaction.

The fire department said the blaze was brought under control at approximately 8:14 a.m., roughly 15 minutes after it broke out.

As a safety precaution, the Ottawa Police Department and the Illinois Department of Transportation temporarily closed a nearby road, and individuals in the area were advised to shelter in place.

Firefighters inspect the interior of a chemical facility after a blast rocked the manufacturing plant in Ottawa, Illinois, on April 21, 2026. (Fox 32 Chicago)

All responding personnel underwent standard decontamination procedures on scene, while hazmat teams assisted with patient decontamination at the hospital.

The fire reportedly caused minimal damage to the facility, and plant operations have been suspended pending an investigation.

The Illinois Occupational Safety and Health Administration (Illinois OSHA) is assisting with the investigation.