Offshore safety watchdog Petroleum Safety Authority Norway (PSA) has started an investigation of the dropped object incident on the West Bollsta semi-submersible rig, operated by Seadrill Europe Management.

The incident took place on 17 October when a length of riser fell during its lifting from a horizontal position to the vertical with the support of hydraulic handling equipment.

The PSA granted an acknowledgement of compliance (AoC) to the mobile drilling facility this month.

The rig was under contract to operator company Lundin when the incident took place on West Bollsta’s drill floor.

The 26.5t pipe is said to measure 22.9m-long. It detached from the handling equipment, skidded and fell to the drill floor after reaching almost vertical.

The incident did not result in personal injury and the area was reportedly cordoned off.

The PSA said it regards the incident as serious, and an investigation team drawn from its specialist staff is now starting work.

As part of the investigation, the team will identify the incident causes and possible lessons to be learnt, as well as share the outcomes with the industry.

The watchdog will clarify the course of events and the scope of the incident, assess the actual and its possible consequences apart from identifying direct and underlying causes.

It will identify non-conformities and improvement points associated with the regulations, apply required enforcement powers to correct potential regulatory breaches.

Lundin is using the West Bollsta rig to drill the Polmak well in the Barents Sea offshore Norway.