Tambar field is located in the southern part of the Norway’s North Sea sector. The field is operated by Aker BP and started production in 2001.

Production from Tambar utilises a normally unmanned wellhead facility controlled from Ula. In normal operation, this facility is manned once a week for maintenance with personnel transferred to/from Ula by helicopter.

In connection with modification work on Tambar, Aker BP decided to use a ship with a motion-compensated walkway – known as a walk-to-work (W2W) vessel – to transfer personnel to the facility. This was intended to reduce the number of helicopter flights and speed up completion of the modification.

Aker BP chartered W2W vessel 'Island Diligence' in June 2018 from Norwegian shipping company Island Offshore. Landing platforms to receive the walkway were installed on three sides of the Tambar facility.

The incident

The incident occurred in connection with a test landing of the walkway on 28 July 2018.

During this process, the walkway missed the landing platform and hit the edge of the latter before sliding off. It then attempted automatically, in line with its design, to find a fixed point to engage with on the receiving side.

The consequence of the incident was damage to railings and cable trays on the facility. There were no injuries.

Findings

PSA's investigation has established that this incident, under slightly different circumstances, could have resulted in a major accident with the release of large quantities of hydrocarbons, substantial material damage and possible loss of life.

This is because the incident could equally well have happened when using the landing platform at the southern end of the facility, where hydrocarbon pipelines and equipment could have been hit.

On 26 May 2018, the PSA ordered Aker BP to secure consent before using the W2W vessel to accommodate personnel on Tambar. Following the incident, Aker BP decided to cancel its planned use of a ship with a motion-compensated walkway on Tambar, and the consent application was withdrawn. The PSA therefore did not complete its consideration of the application.

Safety violations

The PSA’s investigation has identified several breaches of the regulations, all with their background in Aker BP’s planning process for utilising the walkway solution. The principal observations apply to the following areas:

  • dimensioning accidental loads
  • documentation of structural integrity
  • decision base and planning
  • organisation and coordination of roles, responsibilities and information exchange.

The PSA has asked Aker BP to provide it by 13 February with an explanation of how it intends to deal with the non-conformities, and will verify that these are corrected.