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A maintenance team opened the manhole cover to the inlet separator to begin ventilation before cleaning. Oxygen entered the separator, causing iron sulphide deposits on the pall ring cage to spontaneously ignite.
When the tank operator was about to start cleaning, he discovered an open flame in the separator. The operator safely exited the tank, and the emergency response team brought the fire under control. No one was injured in the incident.
Iron sulphide often occurs in tanks and systems where hydrocarbon residues, which are also flammable, are already present. If ignited, it produces a dense, grey smoke that can be mistaken for water vapour. The smoke contains sulphur dioxide, which is harmful to health and should not be inhaled.
Ageing continental shelf
Spontaneous ignition of iron sulphide is an important topic as we have an increasing number of mature fields on the Norwegian continental shelf. The risk associated with iron sulphide will likely increase in the years to come, therefore it is important to map the risk in connection with maintenance shutdowns and opening of hydrocarbon-carrying systems.
Investigation
The incident at Statfjord A was investigated by the Offshore Industry Authority (Havtil). See link below.