Risk Assessment & Hazard Analysis Flashcards
7 cards from real SIL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Risk Assessment & Hazard Analysis flashcards as text
In IEC 61511 SIL verification, the 'Average Probability of Failure on Demand (PFDavg)' for SIL 2 must be:
Answer: ≥10⁻³ and <10⁻²
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.
The 'Demand Mode' classification of a Safety Instrumented Function is based on:
Answer: The frequency of demands relative to the proof test interval
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.
Which element is NOT typically included in a Process Hazard Analysis (PHA) report?
Answer: Detailed financial cost-benefit analysis of all recommendations
PHA reports document hazards, consequences, safeguards, and recommendations, but a detailed financial cost-benefit analysis is not a standard required PHA deliverable.
In Event Tree Analysis (ETA), a 'success' branch on a safety system node means:
Answer: The safety system functions as designed, preventing escalation
A success branch in ETA indicates that the safety barrier or system functions correctly, typically leading to a less severe outcome.
What is the purpose of a 'Risk Graph' in SIL determination per IEC 61508?
Answer: To qualitatively assign a required SIL based on consequence, frequency, probability, and demand rate parameters
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.
The concept of 'ALARP' (As Low As Reasonably Practicable) requires that risk be reduced until:
Answer: The cost of further reduction is grossly disproportionate to the benefit gained
ALARP requires risk reduction until further reduction would cost more than the benefit it provides (gross disproportion test), balancing safety investment against residual risk.
Which scenario would most likely increase the required SIL of a safety function?
Answer: Increasing the demand rate from once every 10 years to once per year
A higher demand rate means the SIF must respond more frequently, increasing the required risk reduction and thus potentially requiring a higher SIL.