Excerpts from ABC7Chicago.com:

A tractor was towing two, two-ton containers of anhydrous ammonia near 29th Street and Green Bay Road in Beach Park when one of the containers leaked and created a chemical cloud.

Police and fire units responded to a report of a possible vehicle fire in the area at about 4:30 a.m., and as a Lake County Sheriff’s sergeant and deputy got out out of their squad cars, they were overcome with the airborne chemical and forced to retreat.

Several victims at the scene were rescued as a total of 140 first responders firefighters, paramedics, and police officers came to the scene. Authorities said 37 people, including the Lake County deputy and sergeant and a Zion police officer, were transported to hospitals. Eight of the injured were hospitalized in critical condition.

People within a one-mile radius were ordered to stay inside with their windows closed and to turn off HVAC units. The shelter-in-place order was lifted shortly after 10 a.m.

Investigators are looking into what the tractor was doing on the road and if proper agricultural laws were followed. Anhydrous ammonia is a chemical used as an agricultural fertilizer. The substance can expand rapidly forming a large cloud that can cause difficulty breathing even death.