When Casey dons his alderman's cap to go inspect a warehouse, it seems to be just another routine day on the job - until one worker appears to have some sort of medical emergency and crashes his vehicle into a piece of decontamination equipment, causing a dangerous chemical spill that could be deadly. And one of his unlucky colleagues finds himself in the wrong place at the wrong time, with horrific results.
Complicating matters? The driver of the vehicle's teenage daughters is at the plant - which, as Casey notes even before the accident, is definitely not a safe place for children.
Watch the exclusive clip to see what happens.
Chicago Fire airs Tuesdays at 10/9c on NBC.