The Good, the Bad, and the Really Ugly of Consequence Analysis

The growth of the technical field known as Consequence Analysis is due to the interaction of two processes. On one side is the advent of powerful commercially available software packages that allow efficient and fast analysis of complex transient phenomena, and on the other side is the need of the engineering community for more accurate information that would allow them to design, build, and operate their facilities in a safe manner but also plan for the worst case scenario. The more readily available the software packages, the more interest from the engineers. The more interest from engineers and companies, the more readily accessible, powerful and cheaper the software packages. This may sound like a perfect example of technical development, but it is important to take a step back and look at what is the reason these tools exist, i.e., what are the engineers trying to calculate, and to understand what is inside the codes used to crunch the numbers.  Like in any analytical computational code, if garbage goes in, garbage will come out.  But depending on the physics model used inside the code, a completely real scenario can be turned into a meaningless set of consequences.

These codes and tools are very powerful, but are they needed in every plant design? Are the engineers using them or those making the decision to hire a company specialized in their use, aware of the code’s underlying limitations?  What is the approach an engineering department should take when designing a new plant and trying to understand the worst case scenario consequences?  In many cases, complex analysis is driven by the tools available as opposed to practical and conservative safety needs.

By understanding what these codes do and don’t do, what they do very well and what they do very badly, the process safety professional can have a better understanding of where in his collection of tools consequence analysis would fit.

This paper presents the advantages, pitfalls, and complexity of the current consequence analysis practices through examples drawn from the authors’ experiences.  A conceptual framework for matching the complexity of tool to practical needs for consequence analysis will be provided.