The incident occurred on Statfjord A on 17 April 2024 during a scheduled turnaround. The processing facility was shut down and emptied of hydrocarbons. One of the tasks to be performed during the turnaround involved cleaning and inspecting the inlet separator, a three-phase separator which is situated on the cellar deck of Statfjord A, which receives the production flow from the wells and separates oil, gas and water for further processing in the processing facility. The separator was last opened for inspection in 2019.
The fire was discovered by someone who was cleaning the inside of the separator. The person concerned had fresh air breathing equipment and exited the tank rapidly.
Actual consequences
The actual consequence was a fire with associated fumes inside the inlet separator. Two members of the work team were exposed to fumes.
The turnaround period was extended as a result of the fire.
Potential consequences
It is our assessment that there was limited potential for the fire to spread.
Without fresh air breathing equipment and protective clothing, an iron sulphide fire generating fumes containing sulphur dioxide (SO2) and potentially other harmful components could rapidly have had life-threatening consequences.
The rescue plan that had been prepared did not mention the risk of fire linked to iron sulphide, nor did it cover rescue from a tank filled with harmful SO2 fumes.
Equinor estimates that there had originally been between 2,000 and 4,000 kg of iron sulphide present in the tank, and only limited quantities of sediments had been removed from the tank when the fire started. Thus, there were large quantities of iron sulphide still present in the sediments in the tank, and ignition of the iron sulphide, along with residues of hydrocarbons, could have led to substantial heat generation. This could have damaged the tank operator’s fresh air hose and thus put the person concerned in significant danger.
During the investigation, we were informed that there were several tanks in area CD9 that were open at the same time as separator CD2101 in CD12. This could potentially have led to a fire in two modules on SFA, in both CD12 and CD9.
Triggering causes
The direct cause of the incident was iron sulphide in the inlet separator being exposed to atmospheric oxygen. This led to auto ignition.
Iron sulphide as an ignition source
Iron sulphide is formed when sulphur reacts with iron in an oxygen-free environment. In connection with the extraction of oil and gas, iron will primarily occur in the reservoir, but it may also originate from the corrosion of ferrous tanks and pipes. The iron reacts with hydrogen sulphide, which is mainly produced by sulphate-reducing bacteria (SRB). Varying concentrations of hydrogen sulphide and iron lead to the formation of different types of iron sulphides
Experience has shown that ignition can occur if oxygen comes into contact with iron sulphide in deposits, for example in connection with:
- Splitting/opening of tanks and pipe systems.
- After an extended period of tank venting.
- Handling of waste.
The reaction between iron sulphide and oxygen is rapid, being of the order of minutes. It causes the particles to glow and leads to substantial heat generation (exothermic reaction). The fumes that are formed are white and can be misinterpreted as water vapour. They contain a high proportion of sulphur dioxide (SO2). Furthermore, the iron sulphide that spontaneously combusts in a tank can ignite nearby combustible materials, such as hydrocarbon residues.
Underlying causes
The investigation has shown that a number of factors contributed to the situation of hazard and accident involving the fire on Statfjord A, and had an impact on the scope for managing the incident.
The underlying causes are primarily linked to:
- Deficiencies in Equinor/Equinor FLX governing documents and their use.
- Roles and responsibilities linked to the performance of the iron sulphide analysis and use and dissemination of the results.
- Planning and execution of the tank cleaning.
- Information about iron sulphide was known
Information on iron sulphide deposits on Statfjord A was known within Statfjord’s operating unit. Iron sulphide samples have been taken regularly in recent years. There have been no incidents of auto ignition of iron sulphide on Statfjord A. However, Statfjord B and Statfjord C have both experienced several iron sulphide fires, the most recent one occurring on Statfjord C in 2023.
In 2019, a similar incident occurred involving an iron sulphide fire on the Equinor-operated facility Snorre B. This incident led to a number of governing documents being updated to better address the risks that iron sulphide may entail.
The planning of Statfjord A's turnaround did not take account of either the updated governing documents or the fact that iron sulphide was known to be present on Statfjord A. No measures to reduce the risk of iron sulphide fires were therefore implemented.
Operator and supplier
The investigation of the incident on 17 April 2024 was first notified to Equinor. On 2 May 2024, supplier IKM Testing was notified that it would be required to participate in the investigation with a start-up meeting held on the same day. IKM was responsible for cleaning the inlet separator and it was their personnel who discovered the fire in the separator. The investigation has not identified any breaches of the regulations committed by IKM Testing.
Turnaround
The incident occurred during a scheduled turnaround during which the wells on the platform were closed and the processing facility shut down and emptied of hydrocarbons. Turnarounds are often used on a platform when many maintenance hours have to be carried out and the work requires the processing facility to have been cleaned. Planning of the turnaround on Statfjord this year, and more generally on other platforms, normally takes place around a year before the job is actually carried out. In the case of Statfjord A, several companies, including IKM Testing, were involved in the planning process and carried out jobs during the turnaround. Many people are involved and many activities take place during turnarounds. As a result, it is important that equipment, personnel, turnaround activities and HSE risks are planned and assessed well in advance of the start of the turnaround activities.
Observations
The investigation has identified six non-conformities relating to the incident:
- Inadequate information in connection with the planning of tank cleaning during the turnaround
- Inadequate risk assessment in connection with opening of the manhole cover on the inlet separator (splitting of hydrocarbon systems)
- Inadequate awareness of requirements in governing documentation
- Handling of iron sulphide
- Inadequate personnel controls
- Inadequate planning of fire-fighting measures
We also observed four factors that we have categorised as improvement points.
Deficiencies in the company’s follow-up to ensure that new requirements are implemented
Inadequate staffing of the Search and Rescue team (S&R team)
Inadequate radio communication
Inadequate emergency preparedness training and drills concerning work in tanks
Order
Through the investigation, we have identified serious breaches of the regulations linked to the dissemination of essential information concerning the risk of iron sulphide, with the consequence that the incident could have been avoided, and the management of this risk through governing documents and planning/safety clearance of activity; cf. non-conformities 8.1.1, 8.1.2, 8.1.3 and 8.1.4 in the report.
On this basis, we have issued Equinor with the following order:
Pursuant to the Framework Regulations, Section 69 concerning administrative decisions, Equinor is ordered to:
- Map the aspects of Equinor’s management system that are relevant to the identification and management of iron sulphide risk, and prepare a self-assessment as to whether the relevant aspects of the management system function as intended; cf. the Management Regulations, Section 21 on follow-up, first paragraph; cf the Activities Regulations, Section 24 on procedures, second paragraph.
- Map the systems that have been established on Statfjord A to ensure the timely dissemination of essential information concerning the risk of iron sulphide to relevant users in connection with the planning of activities; cf. the Management Regulations, Section 15 on information, third paragraph, cf. second paragraph, cf. the Activities Regulations, Section 29 on planning, first paragraph.
- Identify, assess and implement measures to ensure that essential information concerning the risk of iron sulphide is communicated to relevant users in a timely manner in connection with the planning of activities, and that relevant governing documents for managing the risk of iron sulphide are known within Equinor; cf. the Management Regulations, Section 15 on information, second paragraph; cf. the Activities Regulations, Section 29 on planning, first paragraph; cf. the Activities Regulations, Section 20 on start-up and operation of facilities, second paragraph letter b, cf. the Management Regulations, Section 22 on the handling of non-conformities, second paragraph.
The deadline for complying with parts 1 and 2 of the order is 21 February 2025.
The deadline for complying with part 3 of the order is 20 June 2025.
We are to be notified when the respective parts of the order have been carried out.