Bow Tie Risk Analysis
A barrier based major accident model that has become the common language of the modern safety case
Bow Tie
Risk Analysis
Bow Tie has grown from a Shell visualisation aid in the 1990s into the dominant barrier based risk model across upstream oil and gas, COMAH safety cases and increasingly hydrogen, ammonia and battery storage operations. The CCPS Bow Tie Guidelines and the Energy Institute Bow Tie Standard set out the discipline, running from threat to preventive barrier to top event to mitigative barrier to consequence, with explicit treatment of escalation factors, degradation controls and barrier effectiveness scoring. The strength of the technique is that it communicates major accident logic to people who are not specialists, so that your directors, operators and regulators all see the same picture. The execution risk is barrier inflation where teams claim controls that are neither independent nor effective, along with missing degradation factors and a disconnection from LOPA. We build a defensible programme that draws on your HAZOP findings upstream, sits alongside LOPA and SIL allocation in parallel and feeds barrier health indicators and safety critical element performance standards downstream.
How the study is executed
A structured, facilitated process that runs from scope definition through close out and produces defensible, actionable outputs.
Define Major Accident Hazard (MAH) set from HAZID / QRA, specify Top Events per loss of containment category (gas cloud, liquid spill, BLEVE, toxic release, fire), confirm Top Event definitions with physical state taxonomy per Energy Institute Bow Tie Standard (2019).
Decompose each Top Event to its threat (cause) set with HAZOP deviation traceability, assign threat categories (hardware failure, human error, external event, corrosion / degradation), build Threat Top Event Consequence chain for each MAH.
Map preventive and mitigative barriers per EI / CCPS taxonomy (passive, active hardware, active human, instrumented), score each barrier against CCPS effectiveness criteria, independence, reliability, audit frequency, validation record, flag weak or uncredited barriers.
Identify escalation factors (maintenance backlog, weather, MOC state, bypass) for each barrier, specify degradation controls (inspection intervals, proof test regimes, impairment permits), link escalation factors to Bow Tie barrier to create risk pathway visibility.
Designate Safety Critical Elements (SCEs) per UK KP4 / PFEER / NORSOK S 001 criteria, specify performance standards (functionality, availability, reliability, survivability) per SCE, align LOPA SIF designations and SIL targets to SCE performance standard requirements.
Specify barrier health KPI dashboard per API RP 754 Tier 3/4 leading indicators, build MOC impact assessment procedure for barrier affecting modifications, export BowTieXP / RiskView files with version control, produce COMAH / CCPS RBPS aligned safety case deliverable.
What the study covers in full
Outcomes of Bow Tie Risk Analysis
- We surface the silent single point barrier dependencies that incident reviews cite again and again
- You gain a clear line of sight from an operator action through to corporate major accident risk
- Barrier health indicators complement your Tier 1 and 2 lagging indicators
- We address the escalation control gaps that Texas City, Buncefield and Macondo exposed
- Your analysis withstands COMAH, Seveso III and NORSOK S 001 safety case examination
- It aligns with HSE KP4 safety critical element designation and the PFEER duty to demonstrate ALARP
- It supports OSHA PSM PHA recommendation tracking with structured barrier evidence
- It gives regulators a defensible barrier effectiveness argument for novel hazards such as hydrogen, ammonia and battery storage
- We translate engineering risk into language your operators, supervisors and directors all understand
- We align inspection, maintenance and proof test priorities to safety critical element criticality
- Your management of change reviewers gain a clear view of barrier impact
- We build a barrier degradation reporting culture from the shop floor up
- We target capital at genuinely weak barriers rather than an across the board uplift
- We can defer safety instrumented system rebuild capital by showing layered preventive barriers
- Visible barrier management rigour reduces your underwriter loadings
- We cut incident driven retrofit cost, which typically runs five to ten times the proactive Bow Tie investment
Codes & standards we work to
Triggers that signal the need
Where Bow Tie Risk Analysis applies
Wellheads, separators, gas compression, FPSO topsides, produced water systems.
Distillation columns, reactors, heat exchangers, storage spheres, LPG handling.
Cryogenic exchangers, liquefaction trains, BOG compressors, storage and sendout.
Reactive systems, batch reactors, solvent handling, runaway reaction scenarios.
Boilers, HRSGs, steam headers, hydrogen systems, ammonia SCR units.
Sterile vessels, CIP/SIP, pressure fermenters, solvent recovery, spray dryers.
Tangible deliverables
- Bow Tie diagrams for each major accident hazard exported from BowTieXP or RiskView
- A threat, top event and consequence register
- A barrier inventory with effectiveness scoring against the CCPS criteria
- An escalation factor and degradation control register
- A safety critical element register with performance standards in UK KP4 format where it applies
- A barrier health indicator dashboard specification
- Cross mapping to your HAZOP findings and LOPA safety instrumented functions
- A management of change procedure for barrier impact assessment
- A cybersecurity barrier overlay aligned to IEC 62443
Ready to start your project?
Speak with our team to scope an engagement tailored to your facility, regulatory context, and lifecycle stage.