Safety Systems and Functional Safety Flashcards
7 cards from real SACA 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 Systems and Functional Safety flashcards as text
What is a 'common cause failure' (CCF) in the context of redundant safety systems?
Answer: A single event that causes multiple redundant channels to fail simultaneously
Common cause failure is a single root cause (e.g., a shared environment, design flaw, or maintenance error) that defeats multiple redundant channels at the same time.
In the context of the Safety Lifecycle, what activity immediately follows the Hazard and Risk Assessment?
Answer: Definition of overall safety requirements
After identifying hazards and assessing risks, the next step in the IEC 61508/61511 safety lifecycle is to define the overall safety requirements that the system must meet.
Which metric quantifies the average probability that a safety function will fail to respond when a demand occurs?
Answer: PFD (Probability of Failure on Demand)
PFDavg (average Probability of Failure on Demand) is the key metric used to quantify SIS reliability for low-demand mode safety functions.
Under IEC 62061, which term describes the portion of dangerous failures detected by the system's own diagnostics?
Answer: Diagnostic Coverage (DC)
Diagnostic Coverage (DC) is the fraction of dangerous failures that are detected by automatic diagnostic tests within the safety-related system.
What is the role of a 'final element' in a Safety Instrumented Function?
Answer: To perform the physical action that brings the process to a safe state
The final element (e.g., a shutdown valve or contactor) is the actuator component that physically implements the safety action commanded by the logic solver.
What does 'Hardware Fault Tolerance' (HFT) of 1 mean for a safety subsystem?
Answer: The subsystem can still perform its safety function with one fault present
HFT of 1 means the subsystem can experience one hardware fault and still correctly perform its intended safety function, requiring at least two channels in a redundant configuration.
In functional safety management, what is the primary purpose of a 'functional safety assessment' (FSA)?
Answer: To provide an independent judgement that safety requirements have been correctly implemented
A functional safety assessment is an independent, systematic review performed to verify that the safety lifecycle activities and their outputs satisfy the applicable functional safety requirements.