Experts trying to prevent a tank of hazardous chemicals from exploding in southern California found a “potential crack” in the container that might be reducing the pressure, a fire official said on Sunday.Since Friday, officials have warned that the tank, which contains methyl methacrylate, a flammable chemical used in plastics and manufacturing, could rupture and spill up to 26,500 litres (7,000 gallons) of toxic material or explode and endanger other tanks on the GKN Aerospace...