Tanks which contained flammable oil, gasoline, vapors or gas must be handled with caution when making repairs by welding. These tanks may contain sufficient air and residual fumes to cause an explosion when mixed with the gas used with a cutting or welding torch. The document, AWS F4.1, Recommended Safe Practices for the Preparation for Welding and Cutting Containers and Piping That Have Held Hazardous Substances, should be consulted.
Before welding or cutting a tank with an arc or torch it is essential to clean the tank thoroughly and remove all possibility of a flammable mixture remaining in the tank.