Norwegian offshore safety agency, the Petroleum Safety Authority Norway (PSA), has completed its investigation of an incident on the Snorre B platform in the North Sea on May 1, 2019, where a fire broke out in the inlet separator. The agency has identified several breaches of the regulations.
Since the fire broke out the day before the start of a planned turnaround, the process plant was depressurized, drained and purged with inert gas, the PSA revealed on Monday.
One of the turnaround activities involved replacing the inlet separator’s internals. The fire started in connection with preparatory activities ahead of entering the separator.
Rough cleaning of the separator had been completed and it was being vented when the incident occurred. Analyses of the separator contents after the fire revealed the presence of iron sulfide.
Spontaneous combustion as cause
The PSA team’s view is that the fire was caused by spontaneous combustion of iron sulfide in contact with the air, which then ignited oil deposits remaining in the separator.
It emerged from the investigation that iron sulfide was not known to be present in the separator nor did anyone know about the problem posed by pyrophoric iron sulfide. No measures for handling this as a potential ignition source had therefore been assessed or implemented.
Consequences
The actual consequence of the incident was a fire lasting for about three hours in the inlet separator on Snorre B. Subsequent analyses show that the integrity of the actual separator had not been weakened by the fire. No personal injuries were suffered in connection with the incident. The wind direction was favorable for avoiding smoke exposure.
Where potential consequences are concerned, the fire was unlikely to spread beyond the separator. The process plant had been depressurized and drained in connection with the turnaround, and no other flammable materials were in the vicinity. However, the incident could have had more serious consequences had the fire broken out when personnel were inside the separator or the wind direction was more unfavorable, so that exposure to smoke could have been greater.
No assessment had been made of the waste as a potential ignition source, with no special measures therefore implemented to prevent spontaneous combustion when handling or transporting it. However, it emerged from interviews that this material was treated as low radioactive (LRA) waste, which means it is kept moist, and thereby also indirectly prevented the iron sulfide in the waste from igniting. The team therefore considers it unlikely that handling of the waste could have resulted in a fire elsewhere on the platform.
Non-conformities
The investigation has identified three non-conformities related to risk assessment before starting the activity; experience transfer; and procedures.
Namely, the PSA says that it was not sufficiently ensured that important risk contributors were kept under control while planning and implementing activities for rough cleaning.
Furthermore, no assessments were made as to whether iron sulfide could be present and thus no measures were undertaken to prevent self-ignition in connection with venting.
In addition, there was a lack of knowledge that iron sulfide could be a pyrophoric compound. Analysis results from hydro-cyclone downstream inlet separator deposits showed the presence of iron sulfide, but this was not addressed further in planning this job.
The waste from the cleaning process was not handled according to requirements for waste that may contain iron sulfide.
Equinor has been asked to explain how these non-conformities will be handled. The deadline for its response is set for September 20, 2019.
Equinor is the operator of the Snorre field, which consists of the Snorre A and Snorre B platforms. The Snorre B platform came on stream in June 2001. This semi-submersible PDQ floater lies about seven kilometers north of the A platform.
Oil from Snorre B is piped for 45 kilometers to Statfjord B for storage and export. Part of the gas is injected back into the reservoir, while the rest is transported by pipeline via Snorre A on to continental Europe through the Statpipe system and to St Fergus, Scotland through the Tampen link pipeline.
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