At a mill, workers employed by a subcontractor were welding a hairline crack in the wall of a large steel tank, which normally contained hazardous substances. An explosion caused the tank’s top section to be driven upward into the steel beams supporting the roof, creating a large hole in the roof and a debris field with a radius of about 300 feet. A mill worker was killed and the subcontractor’s workers required medical attention. The MOL’s investigation found that the explosion started within the tank when existing hazardous substances were ignited. The welding repairs to the tank had been allowed to proceed before the tank was free of any hazardous substances. The mill pleaded guilty to failing to ensure a tank was rendered free from any explosive, flammable or harmful substance before repairs or alterations were made and was fined $275,000 [Terrace Bay Pulp Inc., Govt. News Release, April 4, 2014].