Description On the 10th October 2010 at 22:30hrs, an axle retaining block weighing 2lbs fell 51ft to the rig floor from the Pipe Racking System (PRS3i) in the derrick. It came to rest in the mouse hole area within the “Red Zone”. There was no harm to personnel although three floormen were standing 3 to 4m away, outside of the ”Red Zone”.
The axle retainer fell from this assembly. (Note in the photo, it is shown at the upper end of its travel – it can move up/down the track and was 15m up when the retainer fell.. Photo taken from the stbd side of the rig floor, looking port. It shows the Pipe Racking System (PRS) with its upper & lower grabs retracted, facing aft
PRS3i Upper Carriage Grip Jaws Stop Axle Retainer Roller Arms Photo of upper carriage on PRS3i with jaws and rollers open. Axle retainers on top of roller arms which also prevent the roller arms extending beyond the grip jaws Close up of closed roller arms with the retainer block missing. The job was stopped and a Time Out for Safety held with a dropped object inspection of the PRS taking place. Of the two securing bolts for the dropped retainer block, one appears to have backed out while the other was sheared, possibly due to a clash between the partially secured block and the roller arm itself (not the stop) overloading the fastener thus allowing the block to fall. Retainer Block
Red Zone & Personnel Positions Position of PRS Position of Roughneck #2 Impact Position of Roughneck #3 Position of Roughneck #1 Resting Place
Incident Classification From the outset the incident was investigated and reported as a high potential, but on completion of the incident investigation that classification was down graded. • The reasons for this are: • The dropped axle retainer fell from the PRS3i which is within the “Red Zone”. NOTE: The introduction and use of the “Red Zone” was a requirement of the Norwegian PSA (Based on OLF/NR-081) which was introduced in 2009, prior to the rig going to work in Norway. The Safety benefits of ensuring people are not working below moving equipment that has the potential to drop objects was seen as very positive and a conscious decision was made to continue the practice when the rig returned to work in the UK. • As per established rig practice, nobody was in the “Red Zone” while the remotely operated equipment was being used therefore it was not possible for a person to be directly hit by the dropped object falling vertically from its source. There is the potential for the retainer to have deflected off other equipment or bounced back off the rig floor & struck an individual but it is likely that the majority of the energy would have been dissipated & injury potential decreased accordingly. This reduces the potential from “Single Fatality” (P2) to “Lost Time Injury” (P3).
Findings / Actions • The risk of an issue with the roller arm and retaining block had been identified by Varco in 1999 & Product Bulletin PRS-98-01 was issued with the recommendation to fit a revised design that eliminates the overloading of the fasteners. • The Varco Product Bulletin had not been identified by the rig owner, therefore had the revised design had not been installed. A “One Page Flyer” was prepared & distributed to other rigs with similar equipment. • All of the Technical Bulletins for all of the equipment on the rig which have the potential for dropped objects causing harm to people are currently being reviewed & a detailed review of the structure & execution of the rig maintenance system (vsOEM recommendations) will also be undertaken.