CHARLOTTE, N.C. – A fire at a northwest Charlotte warehouse has been ruled accidental. The fire happened just before 7:30 Tuesday morning on Tar Heel road. In video posted from the Charlotte Fire Department, you can see smoke coming from the building as crews spray the warehouse with water. A portion of the roof is heavily damaged. Investigators say the fire was caused by the improper thawing of a chemical. It resulted in about $425,000 worth of damage.