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					Lessons from Offshore
Accidents
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Tekna Prosessikkerhet, Bergen 2007-11-27

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Jon Erik Pettersvold/DNV Energy
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With extracts from Petrobras Presentation June 2001
Source: www.petrobras.com.br
 Lessons from Offshore Accidents


 Each Accident is Unique!


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          It could never happen to us !
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Version                 27 November 2007            Slide 2
 Accidents to Offshore Installations
          March 1980: Alexander Kielland                          July 1988: In the world's worst oil rig
          accommodation semi on the Ekofisk                       disaster, 167 people were killed when
          field of North Sea broke up with                        Occidental Petroleum's Piper Alpha
          fatigue fracture and capsized, killing                  oil rig in the North Sea exploded after
          123 people.                                             a gas leak.
          October 1981: U.S. oil rig Ocean                        September 1988: One person was
          Ranger keeled over in the North
          Atlantic, killing 84 people.                                  com
                                                                  killed and 66 people rescued
                                                                     u.
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                                                                  uninjured after Ocean Odyssey
          January 1985: Two men were killed
                                      .9
          and two injured in a pump room      5g                  drilling rig burst into flames in the
                                                                  North Sea.
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          explosion on drilling unit Glomar
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          Arctic II rig in the North Sea.                         March 2001: Eleven people were
                                                                  killed after explosions/capsizing of
                                                                  the P-36 offshore floating platform
                                                                  belonging to Petrobras.




Version                                        27 November 2007                                          Slide 3
   P-36 Roncador Field, Brazil March 2001




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                 w                            11 dead
                                              $500M Asset
                                              Lost
                                              Lost Production

Version                    27 November 2007                     Slide 4
          10 bar                            Starboard Tank
                                            Leak Scenario
                                            Initial Condition
                                            • Port & Stbd 50%
                                            water content

                       Blinded u. com       • Stbd Tk isolated
                                            26th February

                      5g ow                 •Vent blinded March

            ww     .9    Valve
                                            9th
          w              for
                         isolation
                                            •At 50% filling, tank
                                            to be emptied

               Blinded




Version                  27 November 2007                           Slide 5
          The P-36 Accident development
 First event occurred at 00:22 on March 15 as a “thud” in Starboard Aft Column - no
 advance warning, no prior upsets
 Alarms sound almost immediately: low firewater pressure, flammable gas, ESD-3
 (Fire-Mode)
 P-36 lists 2o within 5 minutes

                                                      comColumn
 Emergency Brigade, EB, responds to location, expecting to find a fire
                                                  u. into
                                             ow
 No apparent damage, slight smoke or mist, EB descends
                                        5gsituation - complex pattern of alarms
                                     .9
 Operators and Ballast staff try to diagnose
                            ww immediately, 1 dies later of burns, ESD-4
                        w
 Violent explosion at 00:39 kills 10
 Rescue operations commenced for some time - access difficult, no firewater
 Evacuation commenced at 01:45 and completed at 03:30 (by crane)
 Loss of all power and control at 04:30, final abandonment 06:00 (by helicopter)
 Progressive sinking, recovery attempts fail, sinks March 20
Version                                27 November 2007                            Slide 6
 Details of the aft starboard column


                         Ventilation
             3rd level   duct existing

                                               Waste oil

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                                               tank
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                    ww .9        Seawater                  Drain
                                                           storage
                w                supply line
                                                           tank

                         Drain storage
                         pump

             4th level   Waste oil pump


Version                     27 November 2007                         Slide 7
          10 bar                            Starboard Tank
                                            Leak Scenario
                                            Initial Condition
                                            • Port & Stbd 50%
                                            water content

                       Blinded u. com       • Stbd Tk isolated
                                            26th February

                      5g ow                 •Vent blinded March

            ww     .9    Valve
                                            9th
          w              for
                         isolation
                                            •At 50% filling, tank
                                            to be emptied

               Blinded




Version                  27 November 2007                           Slide 8
          10 bar                                           Starboard Tank
                                                           burst scenario
                                                           •Decision made to pump
                                                           out water from port EDT

                                                    m with port/stbd. EDT
                                                     •Production header lined
                                                 .co up
                                      wu
                                                 Blinded


                        5g          o       Pressure       •Pump start delayed 1

            ww       .9      Valve
                                             builds        hour

          w                  leaks                         •Inlet valve to stbd. EDT
                                                           leaking app. 70 t of crude
                                                           •Pressure build up in
                   Blinded                                 stbd. EDT
                                    Starboard
                               Emergency Drain Tank




Version                  27 November 2007                                          Slide 9
                                                                    Starboard Tank
                                                                    burst scenario

                                                                   •Pumping from port EDT

                                                     com pressurisation of
                                                   u. •Cont.
                                                         Blinded
                                                                   starts at 23:15

                                  ow Press
                                5g Hi                              port EDT

                   ww .9 Valve                     Oil             •Port EDT burst at 00:22
            w                   leaks
                                                   Water
                                                                   at P≈10 bar
                                                                   •450 mm seawater line
          19 bar
                      Blinded                                      breaks
                                              Starboard
                                         Emergency Drain Tank



Version                         27 November 2007                                           Slide 10
 Basis for conclusion on immediate cause
          Interviews of witnesses
          Documentation/material retrieved from P-36
          ESD and Fire & Gas alarm records (approx. 1700 alarms in 17 min.)
          Platform project documentation
          Photographic evidence
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          Timeline analysis
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          HAZOP reviews
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          Stability analysis   w
          Dispersion and explosion analysis
          Visit to sister unit Jack Bates




Version                                       27 November 2007                Slide 11
     Most Likely Accident Scenario

          Burst tank ruptures 450mm seawater line
          Also ruptures nearby buoyancy tank vent lines
          Firewater system alarms Low Pressure


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          Crude oil outgasses flammable vapors

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          Gas alarms on Main Deck + elsewhereu.
                                 .9     g
                                     5alarms
          P-36 enters ESD-3, flaring &
                       w   ww to 2m height
          Water level builds up quickly
          Water flows down ventilation pipes
          Pontoon spaces start to flood
          P-36 lists 2 degrees

Version                              27 November 2007     Slide 12
 Most Likely Accident Scenario, contd.
          Emergency brigade enters Starboard Aft Column
          Flammable gas ignites, major explosion inside P-36
          Local Emergency Brigade caught in explosion
          Flooding continues until downflooding points are reached
          Unit capsizes and sinks                           u. com
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Version                                  27 November 2007            Slide 13
 Sinking of P-36




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Version                    27 November 2007            Slide 14
 Combination of Errors
Fault Description of fault                        Outcome if Fault did not occur
                                                  (No explosion means also no fatalities)
    1     Leak condition of inlet valve of        No accident
          Starboard EDT

    2     Starboard EDT vent isolated with blind No accident, but overflow into vent header,
                                                 not serious

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    3     No blind for inlet valve of Starboard  No accident
          EDT

                                                     ow              u.
    4     Select Production Header for outlet
          rather than Caisson
                                        .9        5g
                                                 Elastic deformation only of EDT, no
                                                 explosion, no sinking
    5
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          Delay in start of pump for Port EDT
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                                                 Plastic deformation and maybe rupture, but
                                                 no explosion and no sinking
    6     Failure of compartment watertight      Seawater pipe rupture and explosion, but no
          dampers                                sinking
    7     Opening of Tanks 26S and 61S for       Seawater pipe rupture and explosion,
          natural ventilation                    borderline sinking - but more time available
                                                 to diagnose problem
    8     Two seawater pumps out-of-service      Seawater pipe rupture and explosion, but no
                                                 sinking as immediately switch away from
                                                 pump D

Version                                           27 November 2007                              Slide 15
                                                                   Incorrect conditions:
                                                                   •Leak condition of inlet
                                                                   valve of Starboard EDT:
                                                                   NO ACCIDENT
                                                                   •Starboard EDT vent
                                                                   isolated with blind: NO
                                                                   ACCIDENT
                                                     comStarboard inlet valve
                                                   u. •No blind for EDT: NO
                                                         Blinded

                                  ow Press
                                5g Hi
                                                       of
                                                                   ACCIDENT

                   ww .9 Valve                     Oil             •Select Production
            w                   leaks
                                                   Water
                                                                   Header for outlet rather
                                                                   than Caisson: ELASTIC
                                                                   DEFORMATION
                      Blinded
          19 bar                                                   •Delay in start of pump
                                                                   for Port EDT: PLASTIC
                                                                   DEFORMATION


Version                         27 November 2007                                           Slide 16
 Lessons learned from the P-36 accident
          Operators of similar units have performed reviews together with DNV
          (typically SWIFT) in order to identify potential for similar faults
           -   WP system to address all critical situations
           -   Focus on combined operations
           -   MoC to be given focus
           -   No HC tanks un lower hull
           -   Training of operators
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           -
           -
               Limit use of WT dampers
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               Separate alarm VDU for critical marine alarms
           -   Etc.
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          Applicable DNV rules address some relevant issues
           - Safety assessment to be carried out if HC tanks are located in lower hull of a
             unit
           - The number of alarms during abnormal situations shall be assessed and
             reduced as far as practicable
           - Location of safety systems to give maximum availability during DALs

Version                                       27 November 2007                           Slide 17
          This could never have happened to
                   you……...??????
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Version                   27 November 2007            Slide 18
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Version            27 November 2007            Slide 19

				
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