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  • Writer's picturePer Ståle Larsen | Principal Consultant

How to use risk-based decision support for critical, isolated operations

Updated: Jun 12, 2023


risk-based decision

Traditional quantitative risk assessment techniques based on empirical data are usually not suitable for estimating or managing risks during critical, isolated operations. In many cases, the application of Barrier Management principles, e.g. by using bowtie diagrams, will provide improved and more relevant decision support for managing major accident risk.


The traditional way of describing risk in an analytic context is probability times consequences. This approach to defining risk is narrow and may not be optimal to manage activities and enterprises. As an alternative, risk can be defined as the possible consequences of activity including the associated uncertainty.

A critical isolated operation in this context is typically recognized by the following three characteristics:

  • There are significant uncertainty and limited relevant empirical data associated with the operation;

  • It is regarded outside normal/standard operation(s);

  • There is one or more major accident hazard(s) associated with the operation.

An example of a critical isolated operation is heavy lifting operations close to critical assets or position-sensitive vessel operations.

A major accident is typically a complex chain of events involving a breach/impairment of multiple safeguards (safety barriers). Norwegian Petroleum Safety Authority (PSA / PTIL) defines a major accident as:

An acute incident, such as a major discharge/emission or a fire/explosion, which immediately or subsequently causes several serious injuries and/or loss of human life, serious harm to the environment and/or loss of substantial material assets.

Qualitative or semi-quantitative approaches such as Hazard Identification (HAZID), Hazard and Operability (HAZOP), Simultaneous Operations (SIMOPS), etc. are used as the main risk assessment methods for managing risk for operations. Such approaches are suitable for identifying and controlling large sets of specific hazard scenarios. However, these assessments are typically focusing on direct cause-consequence relationships, and do not assess the role of specific safeguards in a chain-of-event scenario. In many cases, the application of Barrier Management principles, e.g. by using bowtie diagrams, will provide better and more relevant decision support concerning the management of major accident hazards for operations.


Barrier Management in this context is founded on PSA’s regulations and supporting documents, e.g. the Barrier Memorandum from 2017. PSA defines Barrier Management as:

“Coordinated activities for establishing and maintaining barriers so that they fulfill their functions at all times.”


Key point in barrier management

Figure 1 Key point in barrier management, Ref: PSA Barrier Memorandum from 2017



The Barrier Management approach intends to strengthen the knowledge of the barriers and reduce uncertainty in barrier performance. This is achieved by establishing frameworks and initiating activities to ensure that the barriers function as intended, i.e. establishing barrier strategies for the operation. Such barrier management principles are widely used as a tool for managing major accident hazards for the asset operational phase, but less commonly used as a tool for managing such hazards associated with critical isolated operations.

Application of Barrier Management involves hazard identification and barrier analysis. The purpose is to identify the required barriers and to reduce the uncertainty by defining a framework to verify barrier performance. Typically, a workshop is arranged to both identify major accident hazards and define barriers. Further, cross-functional team collaboration is recommended to determine the required barrier functional requirements as part of the barrier strategy.



Example of a bowtie diagram

Figure 2 Example of a bowtie diagram, Ref Bow-Tie XP from CGE Risk



The Barrier Management approach is intended to improve the risk decision support by reducing uncertainty. Risk acceptance has to be evaluated based on the potential consequences of the activity and the uncertainty involved. This can be challenging and needs to be considered on a case-by-case basis. ALARP (As Low As Reasonably Practicable) principles should always apply. Risk matrices or similar can be used as support, but ultimately, the decisions should be founded on the strength of knowledge associated with the barrier performance.


ORS Consulting is supporting stakeholders in multiple sectors with barrier management using appropriate barrier management tools. Do you think your company could benefit from a barrier management approach to increase the knowledge of barriers and reduce the risk of uncertainty during critical isolated operations?

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