SIL Functional Safety Principles & Standards 3

Question 1

In IEC 61508, what does 'systematic safety integrity' refer to?

Accepted Answer

The freedom from systematic faults caused by design errors, specification faults, or human error

Answer

Systematic safety integrity addresses freedom from faults caused by design, specification, or process errors as opposed to random hardware failures.

Question 2

According to IEC 61511, which party is primarily responsible for ensuring the SIL target is correctly allocated for each safety instrumented function?

Accepted Answer

The asset owner/operator

Answer

IEC 61511 places responsibility on the asset owner/operator to define the hazards and determine SIL targets through risk assessment.

Question 3

What does the Common Cause Failure (CCF) beta factor represent in a redundant SIS architecture?

Accepted Answer

The fraction of dangerous failures attributed to a single common cause affecting multiple channels simultaneously

Answer

The beta factor is the fraction of total random hardware failures assumed to be common cause failures that defeat redundancy simultaneously.

Question 4

Which of the following is an example of an independent protection layer (IPL) that would typically NOT be credited in a LOPA?

Accepted Answer

A basic process control system (BPCS) action that also initiates the initiating cause

Answer

A BPCS action cannot be credited as an IPL if the BPCS failure is also the initiating cause, violating the independence requirement.

Question 5

In IEC 61508, the Safe Failure Fraction (SFF) is calculated as the ratio of:

Accepted Answer

Safe failures plus dangerous detected failures to total failure rate

Answer

SFF = (λS + λDD) / (λS + λD), representing the proportion of failures that are either safe or detected dangerous failures.

(SIL) Safety Integrity Level Certified Practice Test

(SIL) Safety Integrity Level Certified Practice Test

SIL Functional Safety Principles & Standards 3