(96f) Tank 15 - the Perfect Storm

On July 11, 2007, a cone roof, 56,000 barrel xylene tank at Sunoco's Eagle Point Refinery was struck by lightning, causing an explosion which ripped the roof of the tank almost completely off. The subsequent full surface fire was extinguished in approximately 3-1/2 hours using an ?over-the-top? foam attack. Twelve Sunoco response units with 65 Sunoco emergency personnel, along with numerous local fire departments and state agencies were on site within two hours. Managing all of these parties became almost as challenging as extinguishing the fire.

While it would be easy to say that lightning strikes cannot be avoided and close the investigation, there were several additional factors which contributed to causing the event, as well as factors which amplified its magnitude. There were key lessons learned from the incident, ranging from hazard analysis and recognition before the event to emergency response activities during and after the event.

The tank met the requirements of all local, state, and federal regulations for the tank's size, location, construction, and material being stored. Tank 15 was properly grounded, and it was well maintained and inspected on a regular basis. So why did it explode? Xylene will form an explosive mixture with air at daytime summer temperatures, so the vapor space in the tank during this July day was in the explosive range. Even though the tank was properly grounded, the direct lightening strike provided enough energy to ignite the xylene vapors in the tank, causing the explosion which ripped it open. The only way to eliminate the hazard is to store these types of materials in floating roof tanks. Sunoco completed a review of all of their tankage after this event to ensure that this condition did not exist anywhere else.

The other lessons learned came after the fire started. This fire was dubbed the perfect storm because several factors ended up coming together to allow successful extinguishment of a large tank fire in a short amount of time. First, while Tank 15 is a large tank, it is not nearly as large as other tanks on site. The largest tank at Eagle Point is a 280 foot diameter floating roof tank. Second, xylene does not provide the same firefighting challenges as other materials, crude oil for example, since it doesn't have the propensity for boilover. Third, Tank 15 had a weak seam joint just under the roof which allowed the roof to lift off and be thrown out of way during the initial explosion. This allowed complete access to the burning surface of the liquid. Fourth, the tank is located at the edge of the tank farm, allowing for short hose lays and good road access to the tank. Lastly, the wind was blowing away from the best access road, which allowed excellent unobstructed laydown areas. So while it was unlucky that lightening struck the tank, these factors worked together to make the challenge of fighting the fire much more manageable.

There were many other lessons learned from this incident and this report will cover the physical, human, and latent causes which our incident investigation uncovered which helped contribute to the fire, as well as the lessons learned from the emergency response activities after the fire started.