Safety Instrumented Systems Design & Validation 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 Safety Instrumented Systems Design & Validation flashcards as text
What does 'Common Cause Failure' (CCF) mean in the context of redundant SIS architectures?
Answer: A single event that defeats multiple redundant channels simultaneously
Common Cause Failure (CCF) is a single event (e.g., environmental condition, software bug, design error) that causes multiple redundant channels to fail at the same time, defeating redundancy.
The beta factor in SIL calculations is used to:
Answer: Quantify the susceptibility of redundant channels to common cause failures
The beta factor (β) estimates the proportion of independent failure rate that also contributes to common cause failures across redundant channels in IEC 61508 simplified equations.
Which element is NOT typically part of a Safety Requirements Specification (SRS)?
Answer: Detailed P&ID design and piping specifications
The SRS documents functional and integrity requirements for the SIS, but detailed P&ID piping design is a process engineering deliverable, not an SRS requirement.
A 'fail-safe' design for a final element (e.g., a valve) means:
Answer: The valve automatically closes on loss of power or signal, placing the process in a safe state
A fail-safe valve moves to its safe position (typically closed or open, depending on process) upon loss of power, air, or signal, ensuring a safe state without active control.
Under IEC 61511, 'Prior Use' justification for a device allows an end user to:
Answer: Use a device in an SIS without full IEC 61508 certification if adequate field history exists
IEC 61511 Clause 11.5 allows end users to justify using devices with a documented, adequate prior use history in lieu of full IEC 61508 certification.
What is the role of the 'Logic Solver' in a Safety Instrumented System?
Answer: To receive sensor inputs, evaluate the safety logic, and generate output signals to final elements
The logic solver (e.g., safety PLC or relay system) is the processing element that receives inputs from sensors, executes the safety logic, and commands final elements to take the safe state.
Which analysis method systematically examines how individual component failures affect SIS safety function integrity?
Answer: Failure Mode and Effect Analysis (FMEA)
FMEA systematically evaluates each component's potential failure modes and their effects on system performance, identifying contributions to dangerous or safe failures.