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

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.

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

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.

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

PFDavg (average Probability of Failure on Demand) is the key metric used to quantify SIS reliability for low-demand mode safety functions.

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

Diagnostic Coverage (DC) is the fraction of dangerous failures that are detected by automatic diagnostic tests within the safety-related system.

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

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.

SACA - Smart Automation Certification Alliance Practice Test

SACA - Smart Automation Certification Alliance Practice Test

SACA Safety Systems and Functional Safety 5