This story is courtesy of our partners at KHOU 11. Click here to read the fire marshal's full report and see KHOU's related video. HARRIS COUNTY, Texas — The Harris County Fire Marshal’s Office has completed its investigation of the devastating fire at the ITC plant in Deer Park in March. Investigators have ruled the fire accidental. The final report says the fire was caused by a mechanical failure within the "manifold power frame" at one of the storage tanks at the site.