40
4 Historic Failures “Statistics”
ure Mode and Effects Analyses (FMEAs) (https://www.riskope.com/2015/01/15/
failure-modes-and-effects-analysis-fmea-risk-methodology) and Probability Impact
Graphs (PIGs) remain the common practice risk assessment methodology (Oboni
and Oboni 2012) despite their know limitation and misleading aspects (Chapman
and Ward 2011; Cox 2008; FAA 2002; Hubbard 2009; NASA 2007). FMEAs lack
the finesse needed to evaluate or predict the suggested progress “toward zero failures”. Furthermore FMEAs do not help bringing any significant conclusion when
comparing alternatives, cannot measure the efficiency of the (potential) mitigative
measures implementation and compare them against themselves or even just determine if they are sufficient.
Finally, a significant number of risk studies we review do not start with a tailings
system definition (See Chap. 8), its functional analysis and they confuse hazards, risks
and consequences (Oboni et al. 2016) leading to misleading results. It is for example
rather common to see “insufficient FoS” considered as a hazard (or a risk), whereas
such deficiencies are generally the result of deliberate human choices (excessive
audacity, errors and omissions, insufficient efforts). We will take a rather extreme,
but logical, line of thinking, stating that dams failures find, in the vast majority, their
root-causes in human choices and not in natural events.
At the centre of this reasoning there is the concept of credibility threshold we
introduced at the end of the prior section. Many industries consider the limit of
credibility at around 1/100,000–1/1,000,000 (10
−5 –10
−6 ) (Comar 1987; Wilson and
Crouch 1982; Renshaw 1990), so it can be stated that any event above that limit is
not an “Act of God” (or, following modern times buzz-words a “Black Swan”) and
should therefore be foreseen and planned for. We will also note that, reportedly, the
vast majority of dam failures has occurred for other causes than “Black Swan” natural
events, but again for “chains” of gradual deviances, which become “normalized” over
time, stemming from investigations, design, construction, management and longterm monitoring.
4.2.2 Future Performance of the World-Wide Portfolio
As stated earlier, given the nature of the structures under consideration, their construction time and expected service life and closure, the effects of today’s risk mitigation
programs will only slowly become visible because the world portfolio will contain
mitigated and unmitigated (legacy) dams. During that period the public will perceive
at best a status-quo and the industry credibility and SLO will remain open to scrutiny
and criticisms (Oboni and Oboni 2014a, b; Oboni et al. 2013).
It will be very difficult to evaluate progress. Factors such as climate change,
seismicity (again, not necessarily “Black Swans”), increase in population and environmental awareness (consequence side of the risk equation) will further complicate
the situation. Thus public outcry and hostility toward the mining industry, fuelled
by the diffusion of information and communication technology, will likely increase
4 Historic Failures “Statistics”
ure Mode and Effects Analyses (FMEAs) (https://www.riskope.com/2015/01/15/
failure-modes-and-effects-analysis-fmea-risk-methodology) and Probability Impact
Graphs (PIGs) remain the common practice risk assessment methodology (Oboni
and Oboni 2012) despite their know limitation and misleading aspects (Chapman
and Ward 2011; Cox 2008; FAA 2002; Hubbard 2009; NASA 2007). FMEAs lack
the finesse needed to evaluate or predict the suggested progress “toward zero failures”. Furthermore FMEAs do not help bringing any significant conclusion when
comparing alternatives, cannot measure the efficiency of the (potential) mitigative
measures implementation and compare them against themselves or even just determine if they are sufficient.
Finally, a significant number of risk studies we review do not start with a tailings
system definition (See Chap. 8), its functional analysis and they confuse hazards, risks
and consequences (Oboni et al. 2016) leading to misleading results. It is for example
rather common to see “insufficient FoS” considered as a hazard (or a risk), whereas
such deficiencies are generally the result of deliberate human choices (excessive
audacity, errors and omissions, insufficient efforts). We will take a rather extreme,
but logical, line of thinking, stating that dams failures find, in the vast majority, their
root-causes in human choices and not in natural events.
At the centre of this reasoning there is the concept of credibility threshold we
introduced at the end of the prior section. Many industries consider the limit of
credibility at around 1/100,000–1/1,000,000 (10
−5 –10
−6 ) (Comar 1987; Wilson and
Crouch 1982; Renshaw 1990), so it can be stated that any event above that limit is
not an “Act of God” (or, following modern times buzz-words a “Black Swan”) and
should therefore be foreseen and planned for. We will also note that, reportedly, the
vast majority of dam failures has occurred for other causes than “Black Swan” natural
events, but again for “chains” of gradual deviances, which become “normalized” over
time, stemming from investigations, design, construction, management and longterm monitoring.
4.2.2 Future Performance of the World-Wide Portfolio
As stated earlier, given the nature of the structures under consideration, their construction time and expected service life and closure, the effects of today’s risk mitigation
programs will only slowly become visible because the world portfolio will contain
mitigated and unmitigated (legacy) dams. During that period the public will perceive
at best a status-quo and the industry credibility and SLO will remain open to scrutiny
and criticisms (Oboni and Oboni 2014a, b; Oboni et al. 2013).
It will be very difficult to evaluate progress. Factors such as climate change,
seismicity (again, not necessarily “Black Swans”), increase in population and environmental awareness (consequence side of the risk equation) will further complicate
the situation. Thus public outcry and hostility toward the mining industry, fuelled
by the diffusion of information and communication technology, will likely increase