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 does the term 'safe state' mean in the context of functional safety?
Answer: A condition in which the system does not pose an unacceptable risk
A safe state is a defined operating condition in which a system no longer poses an unacceptable risk, even if it cannot continue normal operation.
In IEC 61511, what is the primary purpose of a Safety Instrumented Function (SIF)?
Answer: To bring a process to a safe state upon demand
A Safety Instrumented Function is designed to bring a process to a safe state when a predetermined condition is detected, preventing or mitigating a hazardous event.
Which failure mode is addressed by 'deenergize-to-trip' design philosophy in safety systems?
Answer: Power supply failures causing loss of safe actuation
Deenergize-to-trip ensures that loss of power causes the safety actuator to move to the safe position, preventing power failure from leaving the system in a dangerous state.
What is the purpose of proof testing in a Safety Instrumented System?
Answer: To detect dangerous undetected faults and restore the PFD to its initial value
Proof testing exercises the full safety function to reveal dangerous undetected faults and reset the probability of failure on demand (PFD) accumulation.
In a redundant 2oo3 voting architecture, how many channels must agree on a fault for a trip to occur?
Answer: 2 out of 3
In a 2oo3 (two-out-of-three) voting system, at least two channels must detect the hazardous condition before the system initiates a protective action.
Which IEC standard specifically addresses functional safety of electrical/electronic/programmable electronic safety-related systems in general industry?
Answer: IEC 61508
IEC 61508 is the foundational standard for functional safety of E/E/PE safety-related systems across general industries, from which sector-specific standards like IEC 61511 are derived.
What does 'spurious trip rate' measure in a Safety Instrumented System?
Answer: The rate at which the system initiates unintended safe shutdowns
Spurious trip rate (STR) quantifies how often a SIS activates unnecessarily, causing production losses without an actual hazardous demand.