Allied Terminals Fertilizer Tank Collapse

On 12 November 2008, Tank 201 at the Allied Terminals facility in Chesapeake, Virginia, failed catastrophically. The tank was being filled with approximately 2.1 million gallons of liquid Urea Ammonium Nitrate (UAN) fertilizer—a clear, corrosive liquid denser than water. As the liquid reached a level just inches below its maximum height, a vertical weld seam split open nearly instantaneously. The resulting tidal wave of fertilizer overtopped the secondary containment berm, flooding an adjacent business and a residential neighbourhood of 43 homes (South Hill).

The CSB investigation determined that the tank was originally a riveted structure built in 1929 for oil storage. To convert it for fertilizer use, Allied Terminals had commissioned a contractor to remove the vertical riveted seams and replace them with welded plates. The CSB found these welds to be of "unacceptable quality," citing significant defects such as lack of fusion, porosity, and undercut. Furthermore, Allied Terminals failed to perform the required "spot radiography" (X-ray) inspections that would have identified these internal flaws before the tank was put into service.

A critical human factor was identified: Allied had no safety procedure for the "initial fill" of a modified tank. Instead of excluding personnel from the area, the company directed a welder and a helper to work directly on the tank shell to plug minor rivet leaks as the tank was being filled. When the weld failed, the collapsing wall and the force of the liquid seriously injured both workers. The environmental impact was also significant; roughly 200,000 gallons of fertilizer reached the Elizabeth River, causing elevated nitrate and ammonia levels in the local watershed.