By CBS 2 Chicago Staff

(CBS) — The cause of the massive fire at the Chemtool plant in Rockton earlier this month was accidental, likely caused when a scissor lift struck a valve.

On June 14, a worker for an outside contractor was replacing insulation on an elevated heat transfer piping network that was part of the site’s system for heating certain vessels used in the manufacturing of lubricating greases. This network of piping carried heated mineral oil.

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Rockton Chief Kirk Wilson said that the scissor lift used to reach the area struck a valve or pipe, causing mineral oil to leak.

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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.

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The investigation has not yet determined the source of ignition.

CBS 2 Chicago Staff