The cause of the massive chemical plant explosion and fire at Chemtool in Rockton, Illinois, on June 14 was determined to be accidental, Rockton fire officials said Friday, nearly two weeks after the blaze.
Officials said a scissor lift involved in the replacement of insulation on an elevated heat transfer piping network at the Chemtool lubricant production plant, located at 1165 Prairie Hill Road, likely struck a valve or piece of piping "with sufficient mechanical force to cause the release of mineral oil."
"That morning, an employee of an outside contractor performing the insulation replacement project was working in the area of origin," Rockton Fire Chief Kirk Wilson said in a statement. "They were utilizing a scissor lift to access the elevated heat transfer piping network."
Just before 7 a.m. on June 14, "a release occurred from the elevated piping" and "an unknown amount of mineral oil immediately began falling and pooling on the floor in the area of origin."
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Wilson said Chemtool operators "promptly detected the release and shut down the boiler. They were in the process of placing containment booms, as well as de-pressuring the heat transfer piping network, when the fire ignited."
The exact source of ignition has yet to be determined. Rockton, Illinois, is a village located about 95 miles northwest of Chicago.
The fire forced an evacuation of the area, with a one-mile radius evacuation zone from the plant. Anyone within a three-mile radius of the plant was also asked to wear a mask.
Fire officials put into place a plan to suppress the flames while protecting the nearby Rock River - a vital groundwater source for the community.
Crews stopped using water to battle the blaze early Monday in order to prevent an "environmental nightmare" of product runoff into the Rock River, with authorities saying at the time that the fire could continue to burn over the course of a "several-day event."
The plant, which produces more industrial grease than any other plant in the country, houses dozens of chemicals, with some like lead and sulfuric acid, potentially posing hazards to nearby areas.
But on Tuesday, Wilson said U.S. Fire Pumps, a private industrial firefighting crew from Louisiana, was called to the scene to help with the effort, drawing on their experience in battling numerous refinery fires across the country.
Part of the action plan also includes strike teams to handle any spot fires, to cover other unrelated emergencies within Rockton like medical calls, and also to rotate personnel and fire equipment at Chemtool out every eight hours to prevent exhaustion, he added. The effort as of Tuesday has involved a total of 84 separate fire departments.
About 70 Chemtool employees on site evacuated the building before firefighters arrived, with no injuries reported. Two firefighters were taken to area hospitals - one for a minor injury to his leg and the other to be pre-evaluated for smoke inhalation - but have since been released.
The Red Cross, along with the Salvation Army, the Illinois National Guard, and a slew of state and federal agencies and departments, immediately mobilized after the fire broke out.