Tank failure spurs review

The US Chemical Safety Board (CSB) has issued urgent safety recommendations following the November 12, 2008 collapse of a 2m-gal (7,600 m3) liquid fertiliser storage tank at the Allied Terminals distribution facility in Chesapeake, Virginia.

The operator was asked in no uncertain terms to verify the integrity of three similar tanks at the site as quickly as possible. Industry-wide recommendations are likely to follow once the CSB investigation is complete.

The collapse of the tank seriously injured two contract workers and two members of the public who tried to aid the injured men required treatment after breathing ammonia fumes. The spilt fertiliser overtopped a containment dike and flooded sections of a nearby residential area, requiring ongoing remediation of the soil. At least 200,000 gallons (760 m3) of spilled fertiliser could not be accounted for; some reached the nearby Elizabeth River, which flows into Chesapeake Bay.

CSB investigators concluded that the collapse of Tank 201, which contained an aqueous solution of urea and ammonium nitrate fertiliser, likely resulted from defective welds on the tank wall. The welding was performed in 2006 as part of a project to strengthen four tanks that were constructed around 1929 by replacing vertical riveted seams. The other three tanks on the site were welded at around the same time and it is thought they could suffer a similar catastrophic failure.

Following the welding of the four tanks, Allied Terminals hired HMT Inspection to examine each tank in accordance with existing industry safety guidelines for petroleum tanks. HMT's report did not identify the welding defects that led to this failure; it recommended a safe fill height for each tank. However, the November 12 collapse occurred while the tank was being filled to a level about three inches (7.6 cm) below the safe fill height recommended by HMT.

"We are calling on Allied Terminals to immediately reduce the hazard from the remaining tanks by lowering the maximum safe fill height and to retain a qualified tank engineering firm to assess the tanks' safety," said CSB chairman John Bresland.

"At this stage in the investigation, we are concerned there is an apparent lack of clear regulations covering the safety of non-petroleum aboveground storage tanks," Bresland said. "Because of the hazard such tanks can pose, CSB will examine whether additional safeguards are necessary at national and state levels."

CSB has identified similar oversight issues in other aboveground storage tank accidents. For example, it investigated a sulphuric acid tank collapse in 2001 at the then-Motiva oil refinery in Delaware City, Delaware. Following that accident, which killed a contractor, injured eight others and polluted the Delaware River, the Delaware state legislature enacted an extensive regulatory system for aboveground storage tanks, under the Jeffrey Davis Aboveground Storage Tank Act.