Graceful Collapse – Part 2: Common Mode Failure and Resilient Performance in Complex Systems

By Douglas Owen FSI

In Part 1 of this blog series I looked at the contribution of traditional ‘predict and withstand’ defences in technical systems on their potential for resilient performance. Now in Part 2, I look at common mode failures in the context of traditional defences and resilient capabilities. These defences are :

  • Redundancy – having more than one system that can perform the same function
  • Segregation – splitting a system up
  • Diversity – having more than one system that performs the same function, but are different from one another
  • Resistance – the inherent capacity of a system to withstand whatever is thrown at it

I discuss how these failures throw an unwelcome curve ball to minimising harm in the face of unforeseen disturbances in infernally complex systems. The figure below might help you visualise how common mode failures affect traditional system defences.

Figure 1. Common mode failure effects on traditional defences in systems

I also look at how common mode failures are like a microcosm of the kind of complex failures that resilience emerged to deal with. They offer potential insight into how the performance of our systems might stack up in the face of greater, unforeseen, ‘beyond design basis’ disturbances.

You can access the full paper here: 

Dec 2016 Graceful Collapse - Part 2 - Common Mode
Dec 2016 Graceful Collapse - Part 2 - Common Mode
Dec-2016-Graceful-Collapse-Part-2-Common-Mode.pdf
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