1. Case Study: Buncefield Fire What We Have Learned
Amro Kasht, Ariful Azam, Moataz Nour & Solayman Kawsher
Mary Kay O’Connor Process Safety Center Extension in Qatar
Texas A&M University at Qatar, PO Box 23874, Education City, Doha, Qatar
Introduction
Incident Analysis b
The Buncefield fire was a major conflagration caused by a series of explosions on 11 December 2005 at the Hertfordshire Oil Storage depot near the M1 motorway in Hertfordshire, England.
Buncefield Oil Storage depot was used to receive petrol, aviation fuel, diesel and other fuels by pipelines, where they were stored and later distributed via pipelines or road tankers to other facilities like petrol stations and airports.
The general mechanism of ‘confined explosion’ does not explain the type of explosion that occurred at Buncefield as the majority of the cloud was not confined.
There are two known mechanisms for generating an explosion in a relatively unconfined vapor cloud. One is a deflagration and the other is detonation.
Buncefield accident that cannot be simply explained by deflagration and some of the fact that suggest deflagration to detonation (DDT) mechanism include: a) High overpressures b) Directional Indicators c) Pressure decay outside the cloud
Consequences
Fig: Vehicles , drums and other enclosures which exhibited damage consistent with overpressure in excess of 200 KPa
Fig: Extent of flammable cloud
Fig: Direction of net drug impulse across the Buncefield site
Sector
Cost (£ million)
Site operators (compensation claims)
625
Aviation
245
Competent Authority and Government response 15
Emergency response 7
Environmental impact (drinking water) 2
Total
894
Taking the combination of all analysis, following explosion scenario can be suggested:
Ignition in the Pump House resulting in a confined explosion venting into the external cloud.
The flame propagated into the tree line to the north of the Pump House.
The flame accelerated (deflagration) in the tree line
Instead of continuing as a deflagration, transition to detonation occurred somewhere near the junction of Buncefield Lane and Three Cherry Trees Lane.
Design and Operation Improvements
The MIIB Design and Operation recommendations
Systematic assessment of safety integrity level requirements
Protecting against the loss of primary containment using high-integrity systems
Engineering against escalation of loss of primary containment
Engineering against escalation of loss of secondary and tertiary containment
Operating with high-reliability organizations
Delivering high performance through culture and leadership
Overfill protection strategies
Incident Timeline
10/Dec/05 06:50 pm
Tank 912 in bund A started receiving motor fuel from the T/K South pipeline, pumping at about 550 m3/hour.
11/Dec/05 03:05 am
ATG system failed to show an increase in levels, despite the tank continuous filling.
11/Dec/05 05:37 am
Tank started to overflow (~ 300 tons) and vapor cloud started to form.
11/Dec/05 06:01 am
Vapor cloud exploded, registering 2.4 on Richter scale.
11-16/Dec/05
Emergency services took control of the scene. The fire took 5 days to control.
Perspective Approach (API RP)  precise solution for an application
Functional Approach (IEC) methodology and performance standards
Standard Safety Approach in Industry
Design Recommendations
Remotely operated shut off valve
Fuel transfer Management
Safety management procedure for fuel transfer is required.
Written procedure should be in place and consistent with current practice.
During equipment failure, ROSOV can be used to avoid major disaster.
The ROSOVs should fit the outlet pipe of the tanks and should be in fail safe mode. .
Tank Roofs
Vent
Rim seal
Valve
Piping
In earthquake prone areas, piping should have step geometry .
Pipe supports should have fire protection
Double deck floating roof.
Anti-rotation device on floating roofs
Hydrocarbon detection in drained water with automatic isolation.
Storing materials with a flash point below 21°, flame arresters should be provided.
Fixed roof tank to be fitted with a gas blanket (N2)
Dual rim seal
Foam dam should be provided.
Valves on atmospheric tanks should be labeled.
The isolation valves and actuators should be secured directly to The Tank wall
References
The Buncefield Incident 11 December 2005, in: The final report of the Major Incident Investigation Board, Buncefield Major Incident Investigation Board, London, 2008, Volume 1 & 2.
Special thanks to Dr Luc Véchot.