In complex industrial operations, a single initiating event can trigger multiple outcomes — some harmless, others catastrophic. Event Tree Analysis (ETA) provides a systematic, forward-looking approach to understand these event sequences and quantify how safety systems perform under stress.
At iFluids Engineering, our Event Tree Risk Assessment studies help clients in the oil & gas, refining and petrochemical industries identify weak links, strengthen barriers, and enhance their overall process safety and risk evaluation framework.
Event Tree Risk Assessment – Understanding the Basics
Event Tree Analysis is a logical, graphical technique that starts with an initiating event (for example, an equipment malfunction or human error) and tracks every possible outcome as the system responds. Each branch in the Event Tree Diagram represents success or failure of safety barriers — such as alarms, interlocks, or operator actions.
Unlike backward-looking methods like Fault Tree Analysis, ETA looks ahead: “If this happens, what could occur next?” This forward-thinking approach makes it invaluable in proactive risk assessment and process safety studies.
Event Tree Methodology – How the Analysis Works
Our Event Tree Methodology follows a structured six-step approach that aligns with international standards such as IEC 61511, API 581 and ISO 31000.
- Define the Initiating Event
Identify the starting point — for instance, a loss of containment, pump seal failure or instrument malfunction. - Map the Event Tree Diagram
Construct the diagram showing all possible paths after the initiating event. Each node represents whether a safety layer acts successfully or fails. - Assign Probabilities to Branches
Use reliability data, maintenance records and expert judgement to assign probabilities to each outcome path. - Quantify End-States
Determine the likelihood of each consequence — e.g., safe shutdown, process upset, fire, or explosion. - Interpret Results and Rank Scenarios
Identify critical sequences that contribute most to overall risk. This forms the basis for quantitative risk assessment (QRA) and decision-making. - Recommend and Implement Controls
Suggest targeted risk-reduction actions — additional safeguards, redundancy, automation improvements, or operator training — and monitor performance over time.
Consequence Analysis and Quantitative Insights
The strength of Event Tree Analysis lies in its ability to link technical reliability with consequence modelling. By combining ETA outputs with Quantitative Risk Assessment tools, we can estimate frequencies and consequences of hazardous events more accurately.
This approach helps determine whether risks are within ALARP (As Low As Reasonably Practicable) limits and supports alignment with HAZOP, SIL and RBI studies. It also highlights where barrier effectiveness or human-response times dominate event progression.
Applications of Event Tree Analysis in Oil & Gas
Event Tree Analysis is used across multiple stages of the asset lifecycle, including:
- Design stage: Assessing emergency shutdown (ESD) and instrumented protection systems.
- Operation phase: Evaluating failure responses of pumps, compressors, or pressure systems.
- Maintenance planning: Prioritising inspection or testing for high-criticality barriers.
- Incident investigation: Understanding post-event sequences to refine process safety barriers.
Whether for an LNG terminal, refinery, offshore platform or petrochemical complex, Event Tree Modelling for Process Safety ensures that decision-makers have a clear, quantitative picture of their defence layers.
Event Tree vs Fault Tree Analysis – Complementary Tools
Both methods are pillars of Safety System Analysis. While Fault Tree Analysis (FTA) works deductively to identify root causes of an undesired event, Event Tree Analysis works inductively — projecting how an initiating event can escalate into various outcomes.
Together, they form a robust reliability framework: ETA for “what happens next” and FTA for “why it happened.” Integrating both delivers a comprehensive risk perspective for consequence analysis and barrier management.
Limitations and Good Practices
Although powerful, Event Tree Analysis depends on the quality of input data and engineering judgement. It is best used when:
- Safety systems are clearly defined and performance data are available.
- Complex, multi-barrier processes need visualisation of branching outcomes.
- Results are integrated with other quantitative risk assessment or probabilistic safety studies.
For very dynamic or real-time operator-dependent scenarios, ETA can be supplemented with dynamic simulation or human-reliability analysis.
Why Choose iFluids Engineering for Event Tree Analysis
With over a decade of experience in process safety consulting, iFluids Engineering brings proven expertise in conducting Event Tree Risk Assessments across refineries, terminals, offshore facilities and chemical complexes.
Our multidisciplinary engineers deliver:
- ETA studies aligned with API, IEC, and ISO standards.
- Integration with HAZOP, SIL Verification, RBI and LOPA frameworks.
- Practical insights linking engineering logic with operational performance.
- Custom deliverables — detailed event tree diagrams, probability tables, and consequence maps.
We also employ specialised Event Tree Analysis software and reliability databases to ensure accuracy and repeatability.
Get Started with Your Event Tree Risk Assessment
Every process system tells a story — from the moment a deviation starts to the barriers that prevent escalation. Event Tree Analysis captures that story in a structured, data-driven way, helping organisations protect people, assets and the environment.
Contact iFluids Engineering today to discuss how a tailored Event Tree Analysis can enhance your process safety and risk-management program.