Safety Integrity Level Assessment/ Determination

Safety Integrity Level Assessment

Figure : Safety Integrity Level Assessment/ Determination

What is SIL Assessment/ Determination and IEC 61511 Requirements?

SIL determination is also called as Target SIL Determination or SIL Assessment or sometimes Layers of Protection Analysis [LOPA]. Here, allocation of safety functions to protection layers is assigned, SIFs are determined and for each SIF the target safety integrity requirements. The required SIL shall be derived taking into account the Probability of Failure on Demand [PFD] or Probability of Failures per hour [PFH] that is to be provided by the SIF. The standard doesn’t enforce any particular method to be used, rather it lists several methods like: Risk Matrix, Risk Graph, and LOPA.

IEC 61511-3, Annexure D, E, F details some of these methods like Risk Graph and LOPA.

Why is a SIL Assessment/ Determination Important?

A SIL determination exercise is required to know the SIFs with their integrity levels. A SIL Determination report becomes one of the key inputs for further lifecycle stages like SRS, SIS Design, etc…
For an effective SIL Determination outcome a correct Process Hazard Analysis [PHA] technique must be used e.g. Hazard and Operability [HAZOP] and the outcome must be available along with other updated key documentation like P&IDs, C&E Matrix, Tolerable Risk Matrix, etc…


By using a quantitative technique like LOPA or a qualitative technique like Risk Graph, the target SIL for each SIF can be evaluated during a brainstorming session. 

How can we support?

Our certified and competent FS professionals have extensive industry experience and they are well versed with good engineering practices used in various industries as well. They know when to use Enabling Conditions [EC] or Conditional Modifiers [CM] and how to select and evaluate IPLs [Remember – not all safeguards in a PHA become IPLs in SIL] based on the scenario under consideration and what are the appropriate PFD values to be considered/ referred to for Initiating Causes, IPLs, etc…

We can support in the following activities:

  • Prepare a Terms of Reference [ToR] document
  • Prepare/ Identify SIFs and make a SIF list
  • Provide an experienced Facilitator and Scribe for the SIL Determination session for greenfield, brownfield, revamp, de-bottlenecking projects
  • Prepare draft and final SIL Determination reports
  • Conduct re-Validation SIL Determination sessions
  • Independent Protection Layers [IPLs] scrutiny/ adequacy check

To discuss how HAZOP.EU can assist your organisation in Safety Integrity Level Assessment (Determination), please do not hesitate to contact HAZOP.EU for an informal, confidential conversation.