DP manufacturers are recommended to ensure that operators cannot inadvertently deactivate their systems’ auto-position modes
Dynamic positioning (DP) systems are susceptible to faults that can lead to serious, and potentially fatal, consequences to subsea operations. Some of these faults have been highlighted in a report published by Australia’s National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA).
An article in the Q4 2017 issue of its magazine the Regulator reported that NOPSEMA is aware of 16 such incidents around the world. It described three of them in which a DP auto-position fault led to a loss-of-position incident that could have led to a major accident, such as the loss of a remotely operated vehicle or of a diver working subsea or a well blowout.
These faults might be described as human error but NOPSEMA believes that DP operating systems should be more robust. One of the incidents the article highlighted occurred in Australia in 2016. On a diving support vessel, a DP operator accidently placed a notepad on the console which pressed down on the ‘surge’ button twice, unintentionally deactivating the auto-position mode. This led to the vessel drifting off-location while a diver was working on the seabed.
Vessel personnel had to be alerted by the diver who followed his umbilical and walked with the drifting vessel. If this umbilical had snagged on subsea infrastructure he could have died, but fortunately he survived unharmed and was able to help NOPSEMA in its investigation. The authority concluded that this incident was the result of human error made possible by a weakness in the design of the DP system.
If an accidental loss of positioning occurs on an offshore drilling rig or drill ship it could lead to a well blowout and a potentially explosive hydrocarbons emission, and NOPSEMA highlighted two incidents of a loss of positioning on drilling units in the North Sea and Gulf of Mexico.
In the North Sea example, a semi-submersible drilling rig lost control of its position for several minutes due to an accidental disengagement of the DP system while drilling. It took rig personnel six minutes to realise that the auto-positioning system had been disengaged. As a consequence, the drill pipe was sheared and the lower marine riser package was disconnected. The UK Health and Safety Executive attributed both the loss of position and inadequate crew response to the “poor ergonomic design of the control system”.
In the US Gulf of Mexico, a drill ship unintentionally drifted off position while dealing with a well kick. The US Coast Guard said the DP operator inadvertently deactivated the auto-position mode by accidentally double-pressing the manual button while reaching across the console. On realising the mistake, the operator re-engaged the auto-positioning to bring this vessel back into position. The US Coast Guard stated the incident was the result of “human error with a mix of ergonomics”.
NOPSEMA recommended that DP system manufactures should consider designing centralised controls that are more resilient against human error, so that a single, inadvertent act by an operator will not lead to an emergency with a high probability of fatalities.
“Control systems should also provide adequate feedback to operators to allow them to promptly identify the issue and take appropriate action,” said NOPSEMA. It also recommended that offshore vessel and rig operators check their systems to ensure they are not susceptible to this type of design-induced human error. “They should also ensure that suitable controls are in place to prevent, identify and adequately recover from the error.”
Robust controls could have tactile differentiation for error prevention and action confirmation dialogue boxes. DP systems should have high-visibility displays for error identification and recovery and audible alarms or warnings.
DP manufacturers should include built-in safeguards of their systems to ensure they provide sufficient protection, feedback and recovery against this type of design-induced operator error, said NOPSEMA. It is apparent from past incidents that systems – even with a double-press requirement for deactivating the auto-position mode – are still susceptible to human error.
These issues will be discussed at Riviera Maritime Media’s European Dynamic Positioning Conference, to be held in London on 6 February 2018. For more details click here.
Read the NOPSEMA article on pages 12-13 of the Regulator via http://bit.ly/MEC-DPfaults.