CRE Risk Assessment and Mitigation 3 — Questions and Answers
Question 1: In Bow-Tie analysis, the 'top event' represents:
- The root cause of a failure
- The hazardous event at the center connecting threats and consequences (Correct answer)
- The final outcome of a consequence chain
- The most likely failure mode
Correct answer: The hazardous event at the center connecting threats and consequences
The top event in a Bow-Tie diagram is the central hazardous event that separates threat-side barriers from consequence-side barriers.
Question 2: Which technique is most appropriate for identifying common-cause failures that can defeat redundant systems?
- FMEA
- Cause-and-Effect Diagram
- Common Cause Failure (CCF) analysis (Correct answer)
- Pareto Analysis
Correct answer: Common Cause Failure (CCF) analysis
CCF analysis specifically examines shared dependencies and environmental factors that can simultaneously affect multiple redundant components.
Question 3: The beta factor model in common-cause failure analysis represents:
- The fraction of total failure rate attributed to common-cause events (Correct answer)
- The ratio of detected to undetected failures
- The probability of human error
- The system's average failure rate
Correct answer: The fraction of total failure rate attributed to common-cause events
The beta factor (β) is the proportion of component failures that are common-cause failures relative to the total failure rate.
Question 4: Which risk assessment output is most useful for prioritizing corrective actions in a resource-constrained environment?
- Fault tree cutsets
- Risk Priority Number (RPN) ranking (Correct answer)
- Mean Time Between Failures
- Reliability block diagram
Correct answer: Risk Priority Number (RPN) ranking
RPN = Severity × Occurrence × Detection provides a ranked list that helps teams prioritize corrective actions when resources are limited.
Question 5: Residual risk is best defined as:
- Risk before any mitigation is applied
- Risk that remains after all planned mitigation measures are implemented (Correct answer)
- The highest-rated risk in a risk register
- Risk transferred to a third party
Correct answer: Risk that remains after all planned mitigation measures are implemented
Residual risk is the level of risk that persists after controls and mitigations have been applied, which must then be evaluated for acceptability.
Question 6: In risk assessment, a 'barrier' or 'safeguard' is most accurately described as:
- A redundant component
- Any measure that prevents a hazard from causing harm or reduces consequence severity (Correct answer)
- The probability of failure on demand
- A risk acceptance criterion
Correct answer: Any measure that prevents a hazard from causing harm or reduces consequence severity
A barrier is any physical, procedural, or administrative control that interrupts the accident sequence between a hazard and its consequences.
Question 7: When applying risk-based maintenance, the primary criterion for setting maintenance intervals is:
- Equipment manufacturer recommendations only
- The consequence and likelihood of failure without maintenance (Correct answer)
- Total component age
- Regulatory inspection schedules exclusively
Correct answer: The consequence and likelihood of failure without maintenance
Risk-based maintenance uses the probability and consequences of failure to determine the optimal inspection and maintenance frequency for each asset.
CRE Risk Assessment and Mitigation 3
In Bow-Tie analysis, the 'top event' represents: