COSL Drilling - COSLInnovator - Investigation of incident with fatal consequences

At about 16.38 local time on 30 December 2015, part of the topside on COSLInnovator was struck by a wave. The unit was disconnected from the well at the time and raised to its survival condition.

The wave struck the unit on the port side of the front bulkhead of the forward box girder and smashed 17 windows: six on the lower deck and 11 on the mezzanine deck. Water intrusion caused extensive damage to cabins on these two decks. One person was killed and four others suffered light injuries from the damage which followed the wave’s impact with the unit. The wave also caused deformation to the forward bulkhead on the box girder.

Had the incident occurred at a time when more of the people on board were in their cabins, more lives could have been lost.

On 23 May 2016,  COSL received an order following the fatal accident on COSLInnovator of 30 December 2015.

The dialogue with COSL in the wake of the order has contributed to new information in the case. The PSA and the Norwegian Maritime Authority (NMA), as the PSA’s technical assistance authority, have assessed the new information and have decided that grounds are present for withdrawing the decision to make the order.

This new information relates to the application of the regulations, and makes it clear that the regulations have been too vague with regard to the applicable calculation methodology for horizontal wave forces on mobile units.

The PSA has amended its investigation report to reflect the fact that conditions related to the air gap and horizontal wave slamming did not represent breaches of the regulations at the time of the incident.

The NMA’s requirements for maritime operations normally govern mobile units on the Norwegian continental shelf (NCS). These refer in turn to the requirements set by a classification society, such as DNV GL.

In collaboration with the PSA, the NMA and DNV GL are now in the process of clarifying their requirements in order to ensure that new lessons which have been learnt in connection with the accident are taken into account. That includes better guidelines for calculating the air gap and horizontal wave slamming on semi-submersible facilities.

The main goal for the PSA’s follow-up of the fatal accident on COSLInnovator has been to establish what happened and why so that the industry and the authorities can learn from the incident and prevent such an accident from recurring.

Its investigation has identified weaknesses in the way calculations of wave forces are utilised when designing mobile units. These could also apply to other facilities on the NCS. COSL and other companies are working to utilise the new lessons learnt.