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Atypical Scenarios – Known and Unknown Unknowns

Author : Richard Gowland – EPSC, Technical Director

03 January 2014

The Chemical Industry continues to have major accidents. 

While these might be infrequent, they continue to have large effects on the community, the environment and the economic viability of chemicals production and use. Furthermore they are a stain on our industry’s reputation and perceived value to society.  


**This paper will be presented at HazardEx 2014, contact

HazardEx 2014 conference speaker
HazardEx 2014 conference speaker

Our risk management processes aim to identify potential hazardous events, analyse them and eliminate where possible and provide sufficient control and protection for risks which remain. These processes have served us well when all the possible scenarios have been identified although ‘worst cases’ sometimes present special challenges. What remains to be accomplished is the identification of all possible scenarios. Examples such as Texas City and Buncefield show us that we either did not identify and anticipate the events which actually occurred or we assumed that they were so unlikely as to be of an acceptable likelihood or even, not worth comprehensive study.

How can we improve our ability to find and deal with ‘atypical’ scenarios? Our hazard identification methods such as Hazard and Operability and ‘What if’ studies are effective when sufficient creativity is allowed to identify what we can call‘atypical’ scenarios. The other tools such as Fault Tree Analysis, Layer of Protection Analysis and Quantitative Risk Assessment can then address a complete set of scenarios to help us manage risk comprehensively.

The European Process Safety Centre (EPSC) has a working group which has sought to find best practices which offer an improvement in scenario development which addresses these missing ‘atypical’scenarios. The results of the work are encouraging and offer a way ahead.  The work builds on strengthening and enhancing the tools we already use by adding dimensions which appear to have been missed in the past. The paper describes practical steps which when properly applied will close some of the gaps in our process risk management systems.

Richard Gowland, Technical Director EPSC
Richard Gowland, Technical Director EPSC


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