Enhancing QRA accuracy and reliability with EXSIM: a solution to subjectivity in explosion modelling
In this blog post, I explore how DNV's Computational Fluid Dynamics (CFD) software, EXSIM, can provide a more objective and accurate method for specifying the TNO ME curve number for representing explosions in QRA.
Quantitative Risk Assessment (QRA) is a crucial tool for managing safety in industrial settings, particularly in high-risk industries such as oil and gas, chemical, and petrochemical sectors. In the TNO Multi-Energy (ME) approach to modelling explosions – available in DNV’s QRA software, Safeti - one of the challenges faced by QRA analysts is defining curve numbers to represent the strengths of explosions in congested regions. This is an area of uncertainty, often decided by the analyst based on experience, making it subjective and potentially leading to misunderstandings and incorrect decisions about safety. In this blog post, I explore how DNV's Computational Fluid Dynamics (CFD) software, EXSIM, can provide a more objective and accurate solution for specifying the TNO ME curve number and therefore enhancing the reliability of QRA results.
The challenge of subjectivity in QRA
In a QRA, the TNO ME curve number plays a vital role in determining the explosion overpressure, which is a key factor in assessing the potential consequences of an explosion. Defining the curve number is often left to the judgment of the analyst, who may not have sufficient guidance or data to make an informed decision. This lack of objectivity can introduce uncertainty into the QRA results, affecting the overall risk management decisions.
EXSIM: a solution to subjectivity
EXSIM is a CFD software developed by DNV specifically for modelling explosions in complex geometries. One of the primary benefits of EXSIM is its ability to model the underlying physics of explosions, providing a more accurate and reliable representation of the processes occurring during an explosion event. By simulating the fluid dynamics and combustion reactions, EXSIM generates critical output data, including overpressure, which can be used to determine the appropriate TNO ME curve number for use in QRA.
A typical workflow would involve:
- Using EXSIM to model one or more representative explosion scenarios in a congested region represented by a 3D CAD geometry.
- Determine the average overpressure at the boundaries of the congested region.
- Determine the ME curve number whose peak overpressure is equal or close to the average overpressure determined above. Where the overpressure lies between the peak overpressures that correspond to the ME curve numbers, it would be conservative to use the higher ME curve number. Note that in Safeti the analyst can define non-integer ME curve numbers – that is, Safeti can interpolate between the standard ME curve numbers.
- Use this multi energy curve number to represent the explosion scenarios in your QRA.
There are alternatives to this workflow, but each workflow would have pros and cons to be considered by the analyst. The workflow suggested above is a reasonable approach.
The EXSIM advantage
By using EXSIM, the QRA analyst can define a TNO ME curve number based on detailed modelling of the explosion phenomena, effectively removing much of the subjectivity otherwise involved. This allows for a more robust and dependable QRA, with four key benefits:
- Improved accuracy: by incorporating EXSIM into the QRA process, analysts can provide a more accurate representation of explosion hazards, leading to better-informed decisions and a more precise evaluation of potential consequences.
- Increased confidence: the use of EXSIM-generated data in the QRA process instils confidence in the results, as it is based on detailed explosion modelling rather than subjective judgements.
- Consistency in decision-making: The objective approach provided by EXSIM ensures that decisions made based on QRA results are consistent across various projects, leading to improved risk management and a more comprehensive understanding of the potential hazards.
- Cost-effectiveness: By reducing the uncertainty and subjectivity in QRA, organizations can optimize their investments in risk mitigation measures, ensuring that resources are allocated more efficiently and cost-effectively.
Conclusion
EXSIM is a powerful tool that can significantly enhance the accuracy and reliability of QRA by providing a more objective and data-driven approach to defining the TNO ME curve number. By incorporating EXSIM's advanced explosion modelling capabilities, analysts can make better-informed decisions, leading to improved safety and risk management practices across high-risk industries. As the demand for accurate and reliable risk assessments continues to grow, the integration of EXSIM into the QRA process will become increasingly essential to ensure that organizations can effectively manage and mitigate the potential hazards associated with industrial operations.
In summary, EXSIM's ability to model the underlying physics of explosions and provide critical data, such as overpressure, offers a valuable solution to the challenge of subjectivity in QRA. By leveraging the benefits of EXSIM, organizations can improve the accuracy, reliability, and consistency of their risk assessments, leading to better decision-making and a safer working environment.
Author: James Pickles