Functional Safety Principles & Standards Flashcards
7 cards from real SIL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Functional Safety Principles & Standards flashcards as text
In IEC 61508, what does 'systematic safety integrity' refer to?
Answer: The freedom from systematic faults caused by design errors, specification faults, or human error
Systematic safety integrity addresses freedom from faults caused by design, specification, or process errors as opposed to random hardware failures.
According to IEC 61511, which party is primarily responsible for ensuring the SIL target is correctly allocated for each safety instrumented function?
Answer: The asset owner/operator
IEC 61511 places responsibility on the asset owner/operator to define the hazards and determine SIL targets through risk assessment.
What does the Common Cause Failure (CCF) beta factor represent in a redundant SIS architecture?
Answer: The fraction of dangerous failures attributed to a single common cause affecting multiple channels simultaneously
The beta factor is the fraction of total random hardware failures assumed to be common cause failures that defeat redundancy simultaneously.
Which of the following is an example of an independent protection layer (IPL) that would typically NOT be credited in a LOPA?
Answer: A basic process control system (BPCS) action that also initiates the initiating cause
A BPCS action cannot be credited as an IPL if the BPCS failure is also the initiating cause, violating the independence requirement.
In IEC 61508, the Safe Failure Fraction (SFF) is calculated as the ratio of:
Answer: Safe failures plus dangerous detected failures to total failure rate
SFF = (λS + λDD) / (λS + λD), representing the proportion of failures that are either safe or detected dangerous failures.
What is the maximum SIL achievable by a single safety function implemented in a simplex (1oo1) architecture according to IEC 61508 Route 1H constraints?
Answer: SIL 2
Route 1H architectural constraints limit a Type B 1oo1 subsystem to SIL 2 maximum based on SFF thresholds.
Which document in the IEC 61511 lifecycle formally captures the as-built configuration of the SIS and serves as the baseline for future modifications?
Answer: As-built documentation / SIS mechanical completion record
As-built documentation captures the final installed configuration and serves as the baseline for managing future modifications under MOC procedures.