Automotive Functional Safety Interview Questions

What is SIL ?

Safety Integrity Level: The output of the Process Hazards Analysis effort is the operational definition and the assignment of a SIL rating to each safety loop.

SIL 3 is the highest rating used in the process industries.


Action that reduces the consequences of a hazardous event

What is LOPA ?

Layer of Protection Analysis : A PHA tool that starts with data developed in the Hazard and Operability analysis and accounts for each hazard by documenting and initiating cause and protection layers that prevent or mitigatre the hazard.

Final Element

Part of a safety instrumented system which implements the physical action necessary to achieve a safe state.


SIS Design Guidance for the Process Industry Sector

Safety Lifecycle – Operation Phase

  • Checklist
  • What if?
  • What if/checklist
  • FMEA (Faliure mode effect analysis)
  • Fault tree analysis
  • Event tree analysis
  • LOPA
  • IEC61511-2

    Guidelines on the application of 61511-1


    Deals with programming languages and defines 2 graphical (LD=ladder and FBD = function block diagram) and 2 textual (ST = structured text and SFC = sequential function chart)


    Safety Management System: Ensures that functional safety objectives are met and appropriate auditing processes are defined.

    Dangerous Failure

    Failure which has the potential to put the safety instrumented system in a hazardous or fail-to-function state

    IEC61508-3 ANNEX A

    provides a listing of “techniques and measures” used for software development where different development techniques are chosen depending on SIL level of software.

    What is PFDavg ?

    Probablity of failure on demand: To achieve a specific SIL, a DEVICE must have less than the specified PFDavg.

    Probablilities are calculated using a FMEDA.

    Basic philosophy behind the safety lify cycle

    Develop and document a safety plan, execute that plan, document its execution (to show that the plan has been met) and continue to follow that safety plan through decommissioning – with further appropriate documentation being generated throughout the life of the system.

    What is your approach to brand new projects? What draws your attention?

    In the initial phase, I always focus on the areas that should be included in the software development process. With each project, you must go through it anew, even it includes a new generation of software or its new variant. The first thing that you should complete is analysis of how these software changes impact the product. Based on that, I then understand whether the changes were critical to safety.

    As a rule, the subject of safety can be divided into two different categories. The first one is related to technical safety planning where we define what should happen when one of the critical functions that keeps the user safe, stops working. The second category refers to the fact that even if your initial idea is phenomenal, if the execution is lacking, the final product will not function well. This is the process aspect of product safety and it’s heavily influenced by Functional Safety. We can minimalise the process’ need for extra resources by identifying points that can be adjusted, kept intact or added. Understanding the process of developing a product and aligning it with the safety requirements is often the key to limiting the number of resources necessary for completing the project. It is also essential for fulfilling the quality requirements all at once.

    Abbreviation of IEC ?

    Based on the specific process application, a risk reduction factor (SIL rating) must be defined for each safety loop (SIF).

    The required SIL of a specific SIF is determined by taking into account the required risk reduction factor provided by that function. SIL varies for SIFs that operate continuous vs demand mode.

    ISO 26262 functional safety question

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