SIL Risk Assessment & Hazard Analysis 4

Question 1

In IEC 61511 SIL verification, the 'Average Probability of Failure on Demand (PFDavg)' for SIL 2 must be:

Accepted Answer

≥10⁻³ and <10⁻²

Answer

SIL 2 in low-demand mode requires a PFDavg between 10⁻³ (inclusive) and 10⁻² (exclusive), corresponding to a risk reduction factor of 100 to 1,000.

Question 2

The 'Demand Mode' classification of a Safety Instrumented Function is based on:

Accepted Answer

The frequency of demands relative to the proof test interval

Answer

A SIF operates in low-demand mode when demands occur less frequently than once per year or less than twice the proof test interval; otherwise it is high-demand or continuous mode.

Question 3

Which element is NOT typically included in a Process Hazard Analysis (PHA) report?

Accepted Answer

Detailed financial cost-benefit analysis of all recommendations

Answer

PHA reports document hazards, consequences, safeguards, and recommendations, but a detailed financial cost-benefit analysis is not a standard required PHA deliverable.

Question 4

In Event Tree Analysis (ETA), a 'success' branch on a safety system node means:

Accepted Answer

The safety system functions as designed, preventing escalation

Answer

A success branch in ETA indicates that the safety barrier or system functions correctly, typically leading to a less severe outcome.

Question 5

What is the purpose of a 'Risk Graph' in SIL determination per IEC 61508?

Accepted Answer

To qualitatively assign a required SIL based on consequence, frequency, probability, and demand rate parameters

Answer

A risk graph is a qualitative/semi-quantitative tool that uses parameters like consequence severity, occupancy, and demand rate to determine the required SIL for a safety function.

(SIL) Safety Integrity Level Certified Practice Test

(SIL) Safety Integrity Level Certified Practice Test

SIL Risk Assessment & Hazard Analysis 4