CRE Risk Management & Maintenance 3 — Questions and Answers
Question 1: Which quantitative risk metric represents the probability of an individual being harmed per year due to a specific hazard?
- Collective risk
- Individual risk (Correct answer)
- Societal risk
- Residual risk
Correct answer: Individual risk
Individual risk is expressed as the annual probability that a specific person will be harmed by the hazard.
Question 2: In FMECA, the Criticality Number (Cm) is calculated by multiplying failure mode ratio, failure rate, and:
- Detection probability
- Mission time (Correct answer)
- Severity class
- Redundancy factor
Correct answer: Mission time
Cm = failure mode ratio × item failure rate × mission time, giving the expected number of critical failures per mission.
Question 3: The concept of 'safe-life' in maintenance refers to a component that:
- Is replaced after a condition threshold is exceeded
- Is replaced at a fixed interval before expected failure (Correct answer)
- Has redundant backup during its operating life
- Triggers an alarm upon exceeding a safety limit
Correct answer: Is replaced at a fixed interval before expected failure
Safe-life components are retired at a predetermined usage limit to prevent in-service failure regardless of apparent condition.
Question 4: An FTA uses which logic gate to represent a condition where ALL inputs must occur for the output event to occur?
- OR gate
- AND gate (Correct answer)
- NOT gate
- Inhibit gate
Correct answer: AND gate
An AND gate in a Fault Tree requires all input events to be TRUE simultaneously for the output event to occur.
Question 5: Which maintenance performance metric measures the proportion of total time that a system is available for use?
- OEE
- MTTR
- Availability (Correct answer)
- Reliability
Correct answer: Availability
Availability = Uptime / (Uptime + Downtime), representing the fraction of time the system is in a functioning state.
Question 6: In risk management, the hierarchy of controls places which option as the most effective risk reduction method?
- Administrative controls
- PPE
- Engineering controls
- Elimination of the hazard (Correct answer)
Correct answer: Elimination of the hazard
Elimination removes the hazard entirely and is the most effective control because it makes risk zero at the source.
Question 7: A system has MTTF = 1000 hours and MTTR = 50 hours. What is the steady-state availability?
- 0.95
- 0.952 (Correct answer)
- 0.980
- 0.967
Correct answer: 0.952
Availability = MTTF / (MTTF + MTTR) = 1000 / (1000 + 50) = 1000/1050 ≈ 0.952.
CRE Risk Management & Maintenance 3
Which quantitative risk metric represents the probability of an individual being harmed per year due to a specific hazard?