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Bowtie risk templates

Bowtie — Dropped Object from a Drilling Derrick

Offshore DROPS bowtie for tools and tubulars handled 30 m above the drill floor, turning 3.65 release opportunities a year into 0.353/yr of falling objects and ranking the tool-tethering policy above every inspection regime on the rig.

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Dropped object from the drilling derrickHAZARDTools and tubulars handled 30 m above the drill fl…THREATSPREVENTIVE BARRIERSRECOVERY BARRIERSCONSEQUENCESRegister not updated after a rigmoveRig-move checklist signed bythe OIMColour-coded six-monthlyLOLER inspection75% · detectionCertified lifting registerand pre-use check60%Survey scope excludes the crownblockTool tethering policyabove 2 m70%Dropped object surveybefore every drillingphase65% · detectionStructured derrick DROPSinspection each quarter80% · detectionSecondary retention wireon every fitting85%Red zone exclusion withautomated pipe handling80%Impact-rated helmet anddrill floor canopy40% · mitigationProtective grating overthe moonpool area55% · mitigationCritical spares held onthe rig60% · recoveryContingency to suspend thewell safely50% · recoveryLifting sling orshackle fails underload0.8/yr → 0.08/yrUnsecured hand toolleft on themonkeyboard2.5/yr → 0.2625/yrCorroded fixing on aderrick-mounted light0.35/yr → 0.0105/yrFatality on the drillfloorsev 5 · risk 0.2118Damage to the BOPcontrol podsev 4 · risk 0.6354Well controlequipment downtimesev 2 · risk 0.1412Object fallsfrom heightinto the red…0.353/yrtop-event frequencyTop event0.353/yrinherent 3.65/yrResidual risk0.9884inherent 40.15Risk reduction97.5%threat side 90.3%Barriers113 threats · 3 consequencesDominant threatUnsecured hand tool left on the monkeyb…74.4% of the top eventResidual risk 0.9884 against an inherent 40.15 — the barriers remove 97.5% of it. 2 things are probably not what was meant — every path and every escalation factor was checked.Barrier criticality — residual risk if that one barrier were removed1. Tool tethering policy above 2 m+1.71 ×2.72. Dropped object survey before every drilling phase+1.36 ×2.43. Red zone exclusion with automated pipe handling+0.8472 ×1.94. Protective grating over the moonpool area+0.7766 ×1.85. Colour-coded six-monthly LOLER inspection+0.672 ×1.76. Certified lifting register and pre-use check+0.336 ×1.3FindingsConsequence "Damage to the BOP control pod" rests on ONE barrier. Defence in depth is the claim a bowtie is drawn to make, and a single barrier is a single point of failure: the day it fails is the day the consequence lands in …Escalation factor "Survey scope excludes the crown block" degrades barrier "Dropped object survey before every drilling phase" and nothing is holding it off. The 65% credited to that barrier — and every figure computed from it …Each of the 3 consequences is credited the full top-event frequency of 0.353/yr — the model here is that one top event produces all of them, so the residual score of 0.9884 adds 3 outcomes to one event. That is right when they …

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title "Dropped object from the drilling derrick"
hazard "Tools and tubulars handled 30 m above the drill floor"
top "Object falls from height into the red zone"
unit "/yr"

threat "Lifting sling or shackle fails under load" likelihood: 0.8
  barrier "Colour-coded six-monthly LOLER inspection" effectiveness: 0.75 type: detection
  barrier "Certified lifting register and pre-use check" effectiveness: 0.6
    escalation "Register not updated after a rig move"
      control "Rig-move checklist signed by the OIM"

threat "Unsecured hand tool left on the monkeyboard" likelihood: 2.5
  barrier "Tool tethering policy above 2 m" effectiveness: 0.7
  barrier "Dropped object survey before every drilling phase" effectiveness: 0.65 type: detection
    escalation "Survey scope excludes the crown block"

threat "Corroded fixing on a derrick-mounted light" likelihood: 0.35
  barrier "Structured derrick DROPS inspection each quarter" effectiveness: 0.8 type: detection
  barrier "Secondary retention wire on every fitting" effectiveness: 0.85

consequence "Fatality on the drill floor" severity: 5
  barrier "Red zone exclusion with automated pipe handling" effectiveness: 0.8
  barrier "Impact-rated helmet and drill floor canopy" effectiveness: 0.4 type: mitigation

consequence "Damage to the BOP control pod" severity: 4
  barrier "Protective grating over the moonpool area" effectiveness: 0.55 type: mitigation

consequence "Well control equipment downtime" severity: 2
  barrier "Critical spares held on the rig" effectiveness: 0.6 type: recovery
  barrier "Contingency to suspend the well safely" effectiveness: 0.5 type: recovery