Slight breeze

- Foam compound supplies were planned to fight only the floating roof joint fire, which was the main accident scenario retained for such tanks at that time.

The fire department of the refinery sprayed the tank roof with foam liquid using a canon fixed onto an aerial platform. The firemen required up to 26 water canons to cool down the tank shell and protect the two adjacent distillate tanks with a water curtain.

Couple of hours after the onset of the accident, the tank TO11 started to empty at a rate of 1,700 tonnes per hour while the crude oil burnt at 300 tonnes/hour, however it was deemed easier to empty the two adjacent tanks. Draining the tank TO11 completely while its shell was swelling seemed unpractical (i.e., the draining the tanks at the beginning of the accident would have been risky as small quantities tend to heat up sooner and are likely to cause an explosion due to overpressure in the fixed roof distillate tanks and hasten the boil-over of the tank O11).

As the fire was raging and aggravating, the internal response team was no longer in a position to control the fire and the regional fire-fighters took on the management of the operations. The security guards limited the number of response workers in the high risk zone to a strict minimum.

The intense heat destroyed the fire fighting equipment on several occasions, disintegrated the foam in the tank TO11 during the attack on the second night, and contributed to difficult conditions of operation for firemen who could only maintain the front line for a few minutes.

The fire was brought under control on the 1st of September at 10.00 am, and declared extinguished at around 3.00 pm. More than two days and 765 m³ of foam compound diluted at 3% and 6% were required to extinguish the fire.

The operation called for 150 firemen, 50 fire engines, 44 fire-fighting pumps, 6 aerial platforms and 70 foam tanker trucks.
A backup of firemen from the neighbouring counties helped relay the teams exhausted due to the heat and length of the operation.

6

Six firemen sustained mild injuries during the first boil-over. One of them was hospitalised.

17800 tonnes of light crude oil from the North Sea (classified as flammable by the Seveso directive, flash point 38 °C) were released.
There is no indication available for any possible environmental consequences.

6.7 M USD

The tank TO11 was destroyed, the adjacent tanks were seriously damaged and 17800 tonnes of crude oil were released.
The cost of this accident was assessed at about 10 M GBP in 1983, equivalent to 6.7M USD (or 17.8 M EUR) based on the exchange rate on 30/08/1983 (i.e., about 26 M EUR in 2007).
There were no production losses.

An evacuation plan was organised but not implemented since very few residents lived in the vicinity or were exposed.

The thick column of black smoke that rose several hundred metres above the refinery resulted in “soot rains” in the villages and the surroundings.

- The containment dike of tank TO11 was conservatively designed with redundancy, as the rules in force would allow three tanks identical to the TO11 to be implanted in the same containment dike.

- The absence of a fixed fire protection system on the tank (fixed water spray systems, foam box, etc.) enabled the fire spread. This leads to the lesson learned that the presence of fixed fire protection devices on the tanks would have facilitated the response operations. A foam box would have probably put out the joint fire and the fixed water spray system would have prevented the empty portion of the tank from deformation and folding. The fixed and mobile fire protection devices must be adapted to the site’s configuration. After the accident, the operator equipped the tanks with fixed fire extinguishing devices (foam boxes, fixed water spray systems, etc.).

- The planned foam compound supplies to fight only the floating roof joint fire (the main accident scenario considered for tanks like TO11 at that time) contributed to less efficient fire fighting operation during the 12 hours preceding the first boil-over. As a lesson learned, the presence of sufficient foam compound stocks is necessary for major accidents together with appropriate fire extinguishing devices suited to the surface area and the quantities of product likely to catch fire.

- The huge size of the tank TO11, 4 778 m² of surface area and 20m high, rendered the access with foam nozzles difficult.

- Accident feedback generally show that hydrocarbon fires involving large surface areas and a product volume of several thousand meter cubes are specially hard to control and require significant extinguishing and cooling resources. Failing which, these fires can last for long durations and spread to adjacent facilities.

- The presence of fire pockets made it hard to access behind the metal folds of the tank, forcing the firemen to mount a wagon pipe and a foam canon on a refinery crane to spray foam.

- Due to connection problems between the fire-fighting pumps and the foam tanker trucks sent on site, the firemen were forced to design a new joint on site.

- Exhaustive risk analysis by taking the cascade effects into account and not ruling out certain phenomena such as floating roof tank on fire.

-Studying the advantages and shortcomings inherent to large capacity storage sites and to surface areas of the corresponding containment dikes.

- Adapt the distance between the flare and other facilities especially according to weather conditions.

- Adapt the flare clean up frequency to its use to avoid incandescent particles from being projected onto the other facilities of the refinery.

- When a malfunctioning is known or detected, take into account the risk associated with any degradation of the situation and plan out measures to face or overcome the crisis while giving priority to repair operations rather than waiting for scheduled maintenance operations.

- Share feedback: positive and negative aspects, problems in rescue operations, etc.

- Perform fire drills for such extreme scenarios and clearly define the responsibilities of the operator and the public authorities during emergency response operations.

- Weigh the advantages and shortcomings of quick emergency response operations with limited resources against waiting for additional resources to launch a massive attack.