Australia’s offshore regulator, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), has issued a safety alert following a recent incident where a vessel lost position while diving activities were being conducted approximately 130 meters from a hydrocarbon facility offshore Australia.
NOPSEMA’s safety alert, which represents brief reports on safety improvement issues arising from its investigative and assessment activities, did not reveal the name of the vessel operator nor the name of the hydrocarbon platform. However, the agency did say that the incident could have resulted in a diver fatality.
The report said that recently a vessel undertaking construction activities had an unplanned movement while diving activities were being conducted approximately 130 metres from a hydrocarbon facility. According to the agency, the loss of position was caused by a deactivation of the forward/aft automatic positioning function by unintentionally deselecting the ‘surge’ button on the DP (Dynamic Position) console located on the bridge which then deactivated the ‘Auto Position’ mode.
NOPSEMA said that the deselection was thought to have occurred by the placement of a notepad on the side of the console. The vessel drifted off location by over 40 metres and this drift was initially noticed by a diver when his umbilical started to become taut. Once the DPO (Dynamic Position Operator) became aware of the excursion, the ‘Auto Position’ mode was reactivated causing the vessel to stop moving and remain in position. During this time, the diver had followed his umbilical, moved clear of any obstacles, and walked with the vessel, NOPSEMA said.
What could go wrong?
A loss of position during diving could cause diver fatalities if their umbilicals or other equipment becomes entangled or snagged on subsea infrastructure during the excursion. A loss of position whilst working in close proximity to a hydrocarbon facility could also potentially cause a collision, leading to a loss of hydrocarbon containment and subsequent fire or explosion. In both cases the consequences could involve multiple fatalities, the agency noted.
Due to the potential severity of the consequences of this incident NOPSEMA directed its inspectors to investigate the incident by conducting an OHS inspection on board the facility which is independent of the facility operator’s own investigation. NOPSEMA’s investigation identified that the auto DP mode buttons (Surge, Sway and Yaw) were located in the left hand corner of the console next to desk space commonly used for completing DP related checklists and logs. Consequently, these buttons were susceptible to accidental activation by personnel, the agency noted.
The inspectors found that although the incident arose by an accidental and unknowing double press of a button by the DPO, the design of the DP system allowed a human error to escalate this act into a dangerous occurrence by neither requiring any positive confirmation of deactivation of ‘Auto Position’ mode nor providing any alarm that required acknowledgment that ‘Auto Position’ mode had been de‐activated. The agency stated that the situation was exacerbated and recovery impeded as deselecting the ‘surge’ button automatically deactivates the excursion alarms in that axis and the DP display was no longer providing useful feedback in terms of the loss of position event as the excursion rings started to track with the vessels movement.
If either of the controls identified above were in place, it is unlikely the incident would have escalated to a loss of position event. In order to rectify the issue the operator, with assistance from the manufacturer, are currently upgrading the control systems software to provide a separate dialogue box confirmation requirement when deactivating the ‘Auto Position’ mode.