CAS CAS Automation Specialist Safety & Standards 2

Question 1

What is the definition of Probability of Failure on Demand (PFD) in a safety system?

Accepted Answer

The average probability that a safety function fails to respond when a demand occurs

Answer

PFD is the average probability that a safety instrumented function will fail to perform its intended function when called upon.

Question 2

Which safety architecture uses redundancy where all channels must agree before a protective action is taken?

Accepted Answer

2oo2 (2-out-of-2)

Answer

2oo2 (2-out-of-2) requires both channels to vote for a shutdown, reducing spurious trips but lowering fault tolerance.

Question 3

In NFPA 70E, arc flash boundaries are established to protect workers from which specific hazard?

Accepted Answer

Thermal energy from an electrical arc

Answer

NFPA 70E arc flash boundaries define safe working distances based on incident energy (cal/cm²) from an electrical arc event.

Question 4

What does the term 'proof test interval' mean in the context of safety instrumented systems?

Accepted Answer

The periodic interval at which a safety function is tested to detect dangerous undetected failures

Answer

The proof test interval is the time period between full functional tests of a SIS to reveal and correct hidden dangerous failures.

Question 5

Which standard specifically addresses cybersecurity for industrial automation and control systems (IACS)?

Accepted Answer

ISA/IEC 62443

Answer

ISA/IEC 62443 provides a comprehensive framework for cybersecurity in industrial automation and control systems.

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