The Chemical Engineer, March 2013 by Richard Gowland
The European Process Safety Centre (EPSC) has been looking at events such as BP Texas City, Buncefield and Fukushima in or to determine whether they were so unusual that they "somehow escaped the risk management process of the responsible operators." They concluded that there is a problem because scenarios are often considered to be impossible or very unlikely when assessing risk, yet after the event we find that there was information available that could have shown the accident was credible.
The work carried out has identified four categories of events as follows:
* Known knowns
* Known unknowns
* Unknown knowns
* Unknown unknowns
We know we have processes that can be effective at capturing the first two of these, including Process Hazard Reviews (PHR) and Hazard and Operability (HAZOP), but unless we can also address the unknown knowns/unknowns we will continue to experience accidents like the ones mentioned at the start.
The paper concludes that actually there are very few unknown unknowns and hence we need to work harder and be more creative when identifying hazards and assessing risks. As a minimum we need to:
* make sure we address steady state situations comprehensively with a range of 'what if' analysis;
* cover non-steady state situations (particularly start-up and shutdown) with the same rigour, whether that involves using HAZOP or a complementary approach;
* consider worst case scenarios at a very early stage of our analysis.
"There is also much to be gained from critical task analysis and human error analysis in predicting atypical events and managing them better. They should exploit the 'known knowns,' 'known unknowns,' and 'unknown knowns;' and use a creative approach to imagine the 'unknown unknowns,' which can be studied with 'bow-tie' analysis and perhaps, controversially, a 'reverse HAZOP' where we start with the worst-case consequence and work out what can initiate or fail for the full impact to be realised."
The European Process Safety Centre (EPSC) has been looking at events such as BP Texas City, Buncefield and Fukushima in or to determine whether they were so unusual that they "somehow escaped the risk management process of the responsible operators." They concluded that there is a problem because scenarios are often considered to be impossible or very unlikely when assessing risk, yet after the event we find that there was information available that could have shown the accident was credible.
The work carried out has identified four categories of events as follows:
* Known knowns
* Known unknowns
* Unknown knowns
* Unknown unknowns
We know we have processes that can be effective at capturing the first two of these, including Process Hazard Reviews (PHR) and Hazard and Operability (HAZOP), but unless we can also address the unknown knowns/unknowns we will continue to experience accidents like the ones mentioned at the start.
The paper concludes that actually there are very few unknown unknowns and hence we need to work harder and be more creative when identifying hazards and assessing risks. As a minimum we need to:
* make sure we address steady state situations comprehensively with a range of 'what if' analysis;
* cover non-steady state situations (particularly start-up and shutdown) with the same rigour, whether that involves using HAZOP or a complementary approach;
* consider worst case scenarios at a very early stage of our analysis.
"There is also much to be gained from critical task analysis and human error analysis in predicting atypical events and managing them better. They should exploit the 'known knowns,' 'known unknowns,' and 'unknown knowns;' and use a creative approach to imagine the 'unknown unknowns,' which can be studied with 'bow-tie' analysis and perhaps, controversially, a 'reverse HAZOP' where we start with the worst-case consequence and work out what can initiate or fail for the full impact to be realised."
