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Risk assessment methodologies form the backbone of how organizations identify, analyze, and prioritize threats before they become costly failures or safety incidents. You're being tested on your ability to distinguish between these approaches—understanding not just what each method does, but when to apply it and why it works. The methodologies you'll encounter fall into distinct categories: some work backward from failures to find root causes, others work forward from initiating events to predict outcomes, and still others provide frameworks for prioritizing and communicating risk levels.
Don't just memorize acronyms and definitions. Know which methodology fits which situation—a design-phase project calls for different tools than an operating chemical plant. Understand the logic behind each approach: deductive vs. inductive reasoning, qualitative vs. quantitative analysis, proactive vs. reactive assessment. When exam questions present scenarios, you'll need to recommend the right methodology and justify your choice. Master the underlying principles, and the specific techniques will make intuitive sense.
These methodologies start with an undesired outcome (system failure, accident, hazard) and work backward to identify all possible causes. They use top-down logic to decompose complex failures into their contributing factors.
Compare: FTA vs. HAZOP—both identify causes of failures, but FTA uses formal logic diagrams for quantification while HAZOP uses structured brainstorming for process deviations. Choose FTA when you need probability numbers; choose HAZOP when examining how operating conditions might drift from design specifications.
These approaches start with an initiating event or failure mode and trace forward to determine possible consequences. They use bottom-up logic to understand how problems propagate through systems.
Compare: ETA vs. FMEA—both work forward from failures, but ETA traces a single initiating event through multiple barriers while FMEA catalogs all possible failure modes across components. Use ETA for accident sequence modeling; use FMEA for systematic design review.
Some methodologies combine deductive and inductive approaches, providing a more complete picture of risk by examining both causes and consequences in a unified framework.
Compare: Bow-Tie vs. PHA—Bow-Tie provides comprehensive cause-consequence visualization for known hazards, while PHA is a preliminary screening tool for early project phases. If an FRQ asks about lifecycle timing, PHA comes first; Bow-Tie comes later when hazards are well-defined.
These approaches rely on expert judgment and systematic questioning rather than quantitative data. They're valuable when statistical failure data is unavailable or when creative exploration of risks is needed.
Compare: What-If Analysis vs. Risk Matrix—What-If identifies risks through creative questioning, while Risk Matrix categorizes and prioritizes already-identified risks. They're often used together: What-If generates the risk list, Risk Matrix ranks it.
When organizations need numerical precision for regulatory compliance, insurance, or high-stakes decisions, these approaches provide rigorous statistical analysis.
Compare: QRA vs. ALARP—QRA quantifies risk levels numerically, while ALARP provides the decision framework for what to do with those numbers. QRA tells you the risk is per year; ALARP tells you whether that's acceptable or needs reduction.
| Concept | Best Examples |
|---|---|
| Deductive (top-down) reasoning | FTA, HAZOP |
| Inductive (bottom-up) reasoning | FMEA, ETA |
| Integrated cause-consequence analysis | Bow-Tie Analysis |
| Early-phase screening | PHA, What-If Analysis |
| Risk prioritization and communication | Risk Matrix, Bow-Tie |
| Quantitative probability analysis | QRA, FTA (with data), ETA (with data) |
| Risk acceptability decisions | ALARP Principle |
| Process industry applications | HAZOP, Bow-Tie |
| Product/system design review | FMEA, PHA |
A chemical plant manager needs to examine how deviations in temperature, pressure, and flow rate could create hazards. Which methodology is most appropriate, and why does its use of guide words make it effective for this application?
Compare and contrast FTA and ETA: both use tree diagrams, but how do their logical directions differ, and when would you choose one over the other?
An engineering team has calculated that a system failure has a probability of per year. Which methodology produced this number, and which principle would they apply to determine if this risk level is acceptable?
You're beginning a new project with limited design details. Which two methodologies are best suited for this early phase, and what distinguishes their approaches?
A safety manager needs to present risk information to executives who lack technical backgrounds. Which two methodologies excel at visual communication, and what makes each effective for different audiences?