ISA CAP Safety & Regulatory Compliance 3 — Questions and Answers
Question 1: What is 'common cause failure' (CCF) in redundant safety systems?
- Failures caused by common software bugs only
- A single event that causes multiple redundant channels to fail simultaneously (Correct answer)
- Sequential failures in a 1oo2 voting architecture
- Failures detected during the same proof test
Correct answer: A single event that causes multiple redundant channels to fail simultaneously
CCF is a single root cause event (e.g., common environment, design flaw) that defeats the independence of redundant channels and causes them to fail together.
Question 2: In a 2oo3 voting architecture, how many channels must fail dangerously before a safety function is lost?
- 1
- 2 (Correct answer)
- 3
- All 3
Correct answer: 2
In a 2oo3 (two-out-of-three) architecture, two channels must fail dangerously before the safety function is lost, providing high fault tolerance.
Question 3: Which document within a Safety Lifecycle defines the target SIL for each Safety Instrumented Function?
- Process Flow Diagram (PFD)
- Safety Requirements Specification (SRS)
- Cause and Effect Matrix
- SIL determination study (Correct answer)
Correct answer: SIL determination study
The SIL determination study (using methods like Layer of Protection Analysis or Risk Graph) assigns the required SIL to each SIF based on risk reduction needed.
Question 4: The EPA Risk Management Program (RMP) Rule requires facilities to submit an RMP to the EPA when:
- Any hazardous chemical is stored on-site
- A regulated substance exceeds its threshold quantity in a covered process (Correct answer)
- Annual revenues exceed $10 million
- The facility employs more than 50 workers
Correct answer: A regulated substance exceeds its threshold quantity in a covered process
The EPA RMP rule (40 CFR Part 68) is triggered when a regulated substance is present in a process above its listed threshold quantity.
Question 5: What is the purpose of a 'bypass management' procedure in a Safety Instrumented System?
- To permanently disable nuisance alarms
- To control and document temporary defeats of safety functions during maintenance (Correct answer)
- To route process flow around faulty instrumentation
- To manage software version bypasses in the logic solver
Correct answer: To control and document temporary defeats of safety functions during maintenance
Bypass management procedures ensure that temporary SIS defeats for maintenance are authorized, documented, time-limited, and compensated with alternative safeguards.
Question 6: Which term describes the probability that a safety system fails to perform its required function on demand?
- Spurious Trip Rate (STR)
- Probability of Failure on Demand (PFD) (Correct answer)
- Mean Time Between Failures (MTBF)
- Dangerous Detected Rate (DDR)
Correct answer: Probability of Failure on Demand (PFD)
PFD (Probability of Failure on Demand) is the average probability that a safety system will fail to respond correctly when a demand occurs.
Question 7: Under NFPA 72, which class of initiating device circuit allows the system to identify the specific device that has activated?
- Class A
- Class B
- Class C
- Addressable/Class X (Correct answer)
Correct answer: Addressable/Class X
Addressable (Class X) initiating device circuits allow the fire alarm control panel to identify the exact device location that activated, improving response time.
ISA CAP Safety & Regulatory Compliance 3
What is 'common cause failure' (CCF) in redundant safety systems?