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SIL and Functional Safety Quiz

Test yourself with 20 multiple choice questions. Check your answers to get a score and an explanation for every question.

20 questionsInstant scoreExplanationsInterview practice

SIL and Functional Safety Quiz: 20 Questions

Choose one answer for each question, then press Check answers. Explanations appear after checking.

1. SIL 2 PFDavg range is:

Answer: 10⁻³ to 10⁻². RRF 100 to 1000. Learn more: Safety Integrity Level

2. RRF equals:

Answer: 1 ÷ PFDavg. Risk reduction factor is the inverse of PFDavg. Learn more: Risk Reduction Factor

3. For 1oo1, PFDavg ≈:

Answer: λDU × TI ÷ 2. Hidden failures build up linearly between tests. Learn more: PFDavg

4. λDU = 2 × 10⁻⁶ /h, TI = 8760 h gives PFDavg about:

Answer: 8.8 × 10⁻³. 2e−6 × 8760 ÷ 2 = 8.76e−3, SIL 2 range. Learn more: PFDavg

5. Which failures dominate PFDavg?

Answer: Dangerous undetected. Only proof tests find them. Learn more: Failure Rate
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6. Safe failure fraction is:

Answer: (λS + λDD) ÷ λtotal. Share of failures that are safe or detected. Learn more: Safe Failure Fraction

7. Under IEC 61511 Ed. 2, minimum HFT for SIL 3 is:

Answer: 1. SIL 1 and 2 (low demand) need HFT 0; SIL 3 needs 1. Learn more: Hardware Fault Tolerance

8. Which voting gives HFT 1 with low spurious trips?

Answer: 2oo3. 2oo3 tolerates one dangerous and one safe failure. Learn more: Voting Architecture

9. The beta factor models:

Answer: Common cause failures. A fraction β of failures hit all channels together. Learn more: Common Cause Failure

10. Proof test coverage below 100 % means:

Answer: Some failures stay hidden until replacement. Uncovered failures accumulate over mission time. Learn more: Proof Test Coverage
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11. In LOPA, a BPCS loop can be credited with a PFD no better than:

Answer: 0.1. IEC 61511 limits BPCS risk reduction claims. Learn more: Independent Protection Layer

12. Initiating 0.2 /yr with two IPLs of 0.1 gives a frequency of:

Answer: 2 × 10⁻³ /yr. 0.2 × 0.1 × 0.1. Learn more: Layers of Protection Analysis

13. High demand mode uses which measure?

Answer: PFH. PFH is dangerous failures per hour. Learn more: PFH

14. Process safety time is:

Answer: Time from fault to hazardous event without action. The SIF must act well within it. Learn more: Process Safety Time

15. De energise to trip design means:

Answer: Loss of power causes the trip. Wiring and power failures fail safe. Learn more: Safe State
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16. The document defining each SIF requirement is the:

Answer: Safety requirements specification. SRS per IEC 61511. Learn more: Safety Requirements Specification

17. A long term SIS bypass should be handled through:

Answer: Management of change. Bypass procedures and MOC control risk. Learn more: Safety Bypass

18. MTBF of 500,000 h corresponds to λ of:

Answer: 2 × 10⁻⁶ /h. λ = 1 ÷ MTBF. Learn more: Mean Time Between Failures

19. Diagnostic coverage is:

Answer: λDD ÷ (λDD + λDU). Fraction of dangerous failures detected online. Learn more: Diagnostic Coverage

20. HAZOP uses:

Answer: Guide words applied to process parameters. No, more, less, reverse and so on. Learn more: HAZOP
0 of 20 answered
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About this Quiz

20 multiple choice questions on sil and functional safety, the kind asked in instrumentation interviews, technician exams and plant training. Each answer comes with a short explanation, so the quiz works as a revision sheet too.

Show answer key
  1. 10⁻³ to 10⁻²: RRF 100 to 1000. Learn more: Safety Integrity Level
  2. 1 ÷ PFDavg: Risk reduction factor is the inverse of PFDavg. Learn more: Risk Reduction Factor
  3. λDU × TI ÷ 2: Hidden failures build up linearly between tests. Learn more: PFDavg
  4. 8.8 × 10⁻³: 2e−6 × 8760 ÷ 2 = 8.76e−3, SIL 2 range. Learn more: PFDavg
  5. Dangerous undetected: Only proof tests find them. Learn more: Failure Rate
  6. (λS + λDD) ÷ λtotal: Share of failures that are safe or detected. Learn more: Safe Failure Fraction
  7. 1: SIL 1 and 2 (low demand) need HFT 0; SIL 3 needs 1. Learn more: Hardware Fault Tolerance
  8. 2oo3: 2oo3 tolerates one dangerous and one safe failure. Learn more: Voting Architecture
  9. Common cause failures: A fraction β of failures hit all channels together. Learn more: Common Cause Failure
  10. Some failures stay hidden until replacement: Uncovered failures accumulate over mission time. Learn more: Proof Test Coverage
  11. 0.1: IEC 61511 limits BPCS risk reduction claims. Learn more: Independent Protection Layer
  12. 2 × 10⁻³ /yr: 0.2 × 0.1 × 0.1. Learn more: Layers of Protection Analysis
  13. PFH: PFH is dangerous failures per hour. Learn more: PFH
  14. Time from fault to hazardous event without action: The SIF must act well within it. Learn more: Process Safety Time
  15. Loss of power causes the trip: Wiring and power failures fail safe. Learn more: Safe State
  16. Safety requirements specification: SRS per IEC 61511. Learn more: Safety Requirements Specification
  17. Management of change: Bypass procedures and MOC control risk. Learn more: Safety Bypass
  18. 2 × 10⁻⁶ /h: λ = 1 ÷ MTBF. Learn more: Mean Time Between Failures
  19. λDD ÷ (λDD + λDU): Fraction of dangerous failures detected online. Learn more: Diagnostic Coverage
  20. Guide words applied to process parameters: No, more, less, reverse and so on. Learn more: HAZOP
Tip: take the quiz before an interview, note the questions you missed and read the linked article for those topics.
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Frequently Asked Questions

Is this quiz free?

Yes. No sign up is needed and you can retake it as often as you like.

Are the answers explained?

Yes. After you check your answers, each question shows the correct answer and a short explanation.

Where can I find more questions?

See the Interview Q&A section of instrumentationblog.in and the linked article below.

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