SACA Safety Systems and Functional Safety 5

Question 1

What is a 'common cause failure' (CCF) in the context of redundant safety systems?

Accepted Answer

A single event that causes multiple redundant channels to fail simultaneously

Answer

A failure that occurs only in a single channel

Answer

A failure mode exclusive to software components

Answer

A fault detected by the diagnostic self-test

Question 2

In the context of the Safety Lifecycle, what activity immediately follows the Hazard and Risk Assessment?

Accepted Answer

Definition of overall safety requirements

Answer

Installation and commissioning of the SIS

Answer

Selection of safety integrity level

Answer

Design and engineering of the safety function

Question 3

Which metric quantifies the average probability that a safety function will fail to respond when a demand occurs?

Accepted Answer

PFD (Probability of Failure on Demand)

Answer

SIL (Safety Integrity Level)

Answer

MTTFd (Mean Time to Dangerous Failure)

Answer

DDC (Dangerous Detected Coverage)

Question 4

Under IEC 62061, which term describes the portion of dangerous failures detected by the system's own diagnostics?

Accepted Answer

Diagnostic Coverage (DC)

Answer

Safe Failure Fraction (SFF)

Answer

Beta factor

Answer

Hardware Fault Tolerance (HFT)

Question 5

What is the role of a 'final element' in a Safety Instrumented Function?

Accepted Answer

To perform the physical action that brings the process to a safe state

Answer

To measure the process variable and transmit it to the logic solver

Answer

To execute the safety logic and make trip decisions

Answer

To provide operator interface and alarm management

Question 6

What does 'Hardware Fault Tolerance' (HFT) of 1 mean for a safety subsystem?

Accepted Answer

The subsystem can still perform its safety function with one fault present

Answer

The subsystem can tolerate zero faults before losing the safety function

Answer

The subsystem requires one channel to be active at all times

Answer

The subsystem has a 1% probability of hardware failure per year

Question 7

In functional safety management, what is the primary purpose of a 'functional safety assessment' (FSA)?

Accepted Answer

To provide an independent judgement that safety requirements have been correctly implemented

Answer

To calculate the SIL target for each safety function

Answer

To update the process hazard analysis after a near-miss event

Answer

To train operators on emergency shutdown procedures