Abstract: On March 31, 2011, employees were removing the old external fill line pipe and creating a new external fill line for a storage tank, Tank 223. Tank 223, which previously held a coal tar naphtha product, was drained two days prior to the work operation. The top pipe portion was bolted to an unvalved flanged pipe section that was secured to the dome portion of the original tank. A "slip blind" was observed to have been installed between the unvalved tank pipe flange and the newly installed pipe and associated flange. The new pipe was to extend downward along a vertical side of said storage tank and be connected to an additional horizontal pipe section. The line was to allow the filling of said tank with future product. Employee # 1 was working on the ground along the base of a storage tank, Tank 223, assisting in the alignment of a horizontal section to a new 2.5 inch O.D. black iron pipe. The attachment of the vertical and horizontal sections of these pipes was to be performed by the electric arc welding of these two sections via a 90 degree elbow. Employees #2 and #3 were doing the black iron pipe connection welding work from within a basket of a mobile elevated aerial work platform. When a welding arc was struck to begin the joining of the vertical and horizontal sections of the new black iron pipe, Tank 223 exploded causing crushing injuries to Employee #1 and unspecified serious injuries to Employees #2 and #3.