A Learning Experience For the Industry or Endless Jobs for the Academics
Volume 22 Number 5
Around 6 a.m. on Sunday, Dec. 11, 2005, a number of explosions occurred at the Buncefield Oil Storage Depot, about 20 miles north of London in the U.K. About half the terminal was destroyed and many of the neighboring buildings were devastated by the overpressures created when a massive gasoline vapor cloud ignited. The resulting fires continued to burn for almost four days.
When the smoke cleared it was plainly evident that all of the neighboring buildings for hundreds of feet were exposed to a 1 to 3 psi overpressure, blowing out the windows of the brick fa?ade buildings and blowing in the walls of the more easily damaged metal buildings. Along with the area building damage some very severe damage occurred to automobiles in parking lots that were inside the large vapor cloud before ignition. The damage to the automobiles indicated much, much higher pressure than outside the vapor clouds.
The Buncefield Major Incident Investigation Board has been overseeing a comprehensive investigation of the incident, publishing a number of reports. The Board invited explosion experts from academia and industry to form a working group to advise on what would be required to explain the severity of the Buncefield explosion.
In August, the board's Explosion Mechanism Advisory Group issued a report, available at www. buncefieldinvestigation.gov.uk. In it they basically outlined the two or three ways that overpressure can be generated from vapor fuel air mixtures. Then they state over and over again that the exact overpressure mechanism is "unlikely to be found without the conduct of further experimental and theoretical research."
The report suggests setting up a committee to postulate on how to do testing and further study. The amount needed to actually conduct the tests is still unknown.
Studying this particular problem to death gains very little that is not already known. We already know how to prevent these kinds of loses. We've had lots of gasoline type overfills and fires in the last 40 years, three of which produced exactly the same kind of massive damage to cars inside the vapor cloud and low pressure damage outside the cloud. How do we prevent these events.
- Keep the gasoline in the tanks or the pipes.
- Have a gauging system on each tank that constantly monitors the level of the tank with respect to incoming and outgoing product.
- Use independent high level alarms.
- Use independent high-high level alarms that automatically shutdown the product.
- Put all the alarms and shutdown bypass switches on a big panel in the control room with a light beside each one. Each alarm can only be bypassed with a key operated by management personnel. When these devices are bypassed, a big red light stays on until the bypass is cleared. The bypassed devices should be also highlighted in red on the control room computer system.
- Dikes built around storage tanks should not have penetrations or expansion joints that can fail when exposed to fuel or fire.
- If the tanks are located "close to the public," add more levels of protection such as flammable gas detectors in the dike and along the perimeter.
Why are we wasting valuable time and money overthinking a very simple problem? Do we really need to relearn the mechanisms of overpressure?
One, do not let flammable vapors enter into buildings or enclosures. They explode when the cloud ignites. We have known this for years. Standards exist on pressurizing enclosures with fresh air from safe locations to keep these vapors from getting inside.
Two, the destruction of the automobiles and other things inside the vapor cloud resulted from the flame front being accelerated at high speed, then running into an obstruction, i.e., car, causing large overpressures over very short distances. This caused the vehicles to be mangled without moving them from where they were parked.
The purpose here is to find out what happened at Buncefield and keep it from happening again. Stop the overfills and you stop the vapor clouds. If you dump tons of gasoline into the atmosphere, when it ignites it's going to mess up your day and everyone else that lives in your neighborhood.