|Health and Safety Executive - Safety Alert|
|Department Name:||Maritime Integrity Team|
|Bulletin No:||ED3 2016|
|Issue Date:||19 December 2016|
Dynamically positioned vessels and offshore installations, drilling rigs, flotels etc.
Human factors - Ergonomics - protection against accidental change of mode of control - Adequate display of active control mode (DP or manual).
A semisubmersible DP drilling rig lost control of position for several minutes. During this time it was obliged to shear the drill pipe and disengage the lower marine riser package, LMRP. The initial loss of control was due to accidental disengagement of the DP system. The crew immediately noticed loss of position but did not appreciate that DP was disengaged. They initially believed there was a technical fault with the DP and it took 6 minutes before they realised the DP was disengaged.
Both the loss of position control and the inadequate initial crew response were due to poor ergonomic design of the control system. Firstly, the button for transfer from DP to manual control was not protected against accidental operation. Secondly, there was no clear indication at the DP desk that DP was no longer engaged, and that the vessel was then under manual control.
The Company’s investigation found that the initiation of the incident was accidental, unknowing, operation of the button used to transfer control from DP to manual. (A dual push was required but this gave inadequate protection in this instance.)
The DP Operators thought that DP was still engaged and continued to operate at the DP control desk and tried to find a technical fault. There was no clear indication at the DP desk that control had passed from DP to manual lever mode. (The utility panel for selection of DP or manual mode was some distance away from the DP desk, and there was no clear indication on the DP screen.)
Two ergonomic factors contributed to this incident:
Industry guidance is provided in Ref 1; Section 2 Controls 2.7 Prevention of Accidental Activation which states:
Controls should be designed and located so they are not susceptible to accidental activation. Methods to reduce the likelihood of accidental activation include:i) Locating and orienting the control so that bumping is unlikely to cause activation
Since the incident, a cover guard has been fitted to the button.
There was no clear indication at the DP control desk that DP was disengaged and the vessel was now under manual control.
Industry guidance in Ref 1, Section 3 2.4 Status Information states:
Similarly ref 2, Section 18.104.22.168 states:
Since the incident, tests were conducted on the onboard simulator of another DP drilling rig. Control was switched from DP to manual and it was found that no clear indication of the transfer was displayed on the DP desk screen.
Also, recently the Australian authorities have issued a Safety Alert, Ref 4, following a similar incident where DP was inadvertently disengaged.
Operators of dynamically positioned vessels and offshore installations should review the ergonomic aspects of their control system. In particular they should check
Where weaknesses are found;
1. crews should be alerted to the situation, and
2 appropriate improvements should be made to the DP control system in line with references 1 & 2.
Contact the HSE’s ED 4.3 Maritime Integrity team for further information
This Safety Notice should be circulated to all relevant duty holders/employees that are involved in the design, selection and operation of dynamically positioned vessels in the offshore industry.