StatoilHydro Investigates Major Accident Potential at Mongstad

An incident at the Mongstad refinery in August this year had a considerable higher accident potential than originally expected. The incident is under investigation by StatoilHydro.

On Saturday, August 23, there was a failure in the power supply to important control units for the sliding valves in the cracker plant at Mongstad. This led to extensive smoke development from the emergency stack in the cracker plant and somewhat later a fire in the top of the stack.

The findings of the ongoing investigation show that the incident quickly could have escalated further as air could have forced its way into the reactor and led to an explosive development. This was prevented by an emergency stop. An explosion in the cracker reactor could have had major and highly serious impacts on people, the environment and the plant. During the incident 17 people were present in the cracker complex to prepare a scheduled shutdown of the plant.

"This is a serious incident which both the unit at Mongstad and StatoilHydro must learn from," said Einar Stromsvag, senior vice president for the manufacturing cluster. "In the ongoing investigation effort we must turn all stones to ensure that we understand what happened and why. This applies not only to the technical, but also to the organizational and human aspects. It is important that we have an overall understanding of the incident and develop concrete measures to avoid this type of incidents in the future."

A study has also been initiated to determine the scope of the emission that occurred during the incident and any health and environmental impacts.

The cracker has been shut down for extensive maintenance and modification work during an ongoing scheduled shutdown. Further improvement measures have also been implemented as a result of the incident.

"Much higher robustness and independence have been built into the important control systems that failed during the incident. The technical integrity of the plant has thus been strengthened," said Stromsvag.

Based on experience from the incident organizational and skills upgrading measures have also been introduced to strengthen the human barriers.

The incident is currently being investigated and the final overview of long-term actions will be finalised on the basis of the investigation report. The final conclusions of the investigation effort are expected to be ready at the turn of the year and will then be submitted to the Petroleum Safety Authority Norway.