A massive fire broke out at a chemical plant in Northern Illinois on Monday, forcing the residents to evacuate their homes. The city department ordered a mandatory evacuation for all residents and businesses within a mile of the Chemtool Inc. plant in Rockton after flames were reported at about 7 a.m.

James Berger, a resident of Rockton, said that explosions could be heard around the neighborhood and every time an explosion went off, the flames would go sky-high.

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Rockton Fire Chief Wilson said the city hopes to avoid “an environmental nightmare” that might occur if any of the Chemtool’s oil-based lubricants ran off into the Rock River.

Here’s what we know so far: 

1. The fire department’s water-based firefighting suppression has stopped inside the building and they plan to let the flames continue to burn off.

2. The building is pretty much consumed, the fire is going to be a several-day event to have all of the product burned off.

3. The cause of the fire was not immediately known. It wasn’t clear what started the fire, nor is it clear when it will be extinguished.

4. Another concern is the large plume of smoke moving south and southeast from the explosion site.

5. Officials are worried about chemicals like sulfuric acid, nitrogen and lead could spread through smoke, though ground-level monitors so far showed no impact on air quality.

6. The department has asked people to wear a mask if they need to be outside.