36
4 Historic Failures “Statistics”
In the paper of the following year (Oboni et al. 2014) we showed quantitatively
how, over time, multiple hazards hits would significantly increase the probability of
failure of a dam and lead to intolerable future risks. The paper concluded:
Especially in the case of TDs located in areas where demographic pressure leads to settlements in the downstream areas, social and legal consequences of a failure will dramatically
increase. This will particularly be the case if the methodologies used to perform the risk
assessments prove to be in disconnect with the needs of our modern society.
Finally, at TMW 2015 (Caldwell et al. 2015) we were delighted to examine the
result of a new study of tailings dam historic failures (Bowker and Chambers 2015)
which used detailed data and actuarial techniques to define the historic rate of failures
of tailings dams after attempting to define what constitutes “serious” and “very
serious” tailings dams failures. Cumulating those dimensions, we stated:
The common practice approach of using oversimplified consequence functions (with “or”
clauses between consequences dimensions) is often used in research papers because of
scope/budget limitations, but should not be accepted for a rational world-wide approach to
decision making and tailings risks management for an industry that has significant societal
impacts like mining. Tailings accidents generate multiple direct and indirect consequences
on the environmental, human, health and safety (H&S), operational and reputational areas
and we believe it is time for the mining industry as a whole to adopt a uniform consequence
function.
Our paper concluded that:
It is comforting that the results of the “quick and dirty” 2013 (Oboni and Oboni 2013) study
reached globally comparable results to the 2015 (Bowker and Chambers 2015) very deep and
solid analytical approach. We noted that the selection of the time frame has a large influence
on the conclusions of the 2015 study and therefore we recommended these comparative
studies to be performed with constant duration (for example decade by decade) to avoid
the hazard of drawing misleading conclusions. “Averaging” over 70 years, during which so
many conditions have changed, may indeed mask decennial spikes. To prove this it is enough
to note that the accident rates have actually decreased by 15–24% from the 1990–1999 to
the 2000–2009 decades using the 2015 study’s own data.
Finally it was stated that:
The aim of zero tailings failures is impossible to achieve (with the present world dams’
portfolio). Tailings dams will continue to fail. In fact, in the long term all tailings facilities
will spiral toward significant increases of their probability of failure and, when they fail,
the tailings will run toward downstream rivers, lakes, and the ocean as they did at every
failure to date. We demonstrated that consequences are not necessarily correlated, in one
way or another, with dam height or pond volume. As in many industries the “scary stuff”
is not necessarily the riskier one. Our practice and research have shown that the probability
of failure is, or will be, often way higher in smaller structures than in major ones, simply
because more care is taken for larger structures than for “insignificant” ones.
Well documented examples such as the 1974 failure of the Bafokeng dam in
Rustenburg, SA, or the 1985 Val di Stava Dam collapse in Northern Italy are there
to show that “extreme” consequences can actually occur. We also demonstrated that
the rate of fatalities in the tailings “industry” lies way above the generally accepted
“safe” thresholds for hazardous industries. The number of existing, operational, and
4 Historic Failures “Statistics”
In the paper of the following year (Oboni et al. 2014) we showed quantitatively
how, over time, multiple hazards hits would significantly increase the probability of
failure of a dam and lead to intolerable future risks. The paper concluded:
Especially in the case of TDs located in areas where demographic pressure leads to settlements in the downstream areas, social and legal consequences of a failure will dramatically
increase. This will particularly be the case if the methodologies used to perform the risk
assessments prove to be in disconnect with the needs of our modern society.
Finally, at TMW 2015 (Caldwell et al. 2015) we were delighted to examine the
result of a new study of tailings dam historic failures (Bowker and Chambers 2015)
which used detailed data and actuarial techniques to define the historic rate of failures
of tailings dams after attempting to define what constitutes “serious” and “very
serious” tailings dams failures. Cumulating those dimensions, we stated:
The common practice approach of using oversimplified consequence functions (with “or”
clauses between consequences dimensions) is often used in research papers because of
scope/budget limitations, but should not be accepted for a rational world-wide approach to
decision making and tailings risks management for an industry that has significant societal
impacts like mining. Tailings accidents generate multiple direct and indirect consequences
on the environmental, human, health and safety (H&S), operational and reputational areas
and we believe it is time for the mining industry as a whole to adopt a uniform consequence
function.
Our paper concluded that:
It is comforting that the results of the “quick and dirty” 2013 (Oboni and Oboni 2013) study
reached globally comparable results to the 2015 (Bowker and Chambers 2015) very deep and
solid analytical approach. We noted that the selection of the time frame has a large influence
on the conclusions of the 2015 study and therefore we recommended these comparative
studies to be performed with constant duration (for example decade by decade) to avoid
the hazard of drawing misleading conclusions. “Averaging” over 70 years, during which so
many conditions have changed, may indeed mask decennial spikes. To prove this it is enough
to note that the accident rates have actually decreased by 15–24% from the 1990–1999 to
the 2000–2009 decades using the 2015 study’s own data.
Finally it was stated that:
The aim of zero tailings failures is impossible to achieve (with the present world dams’
portfolio). Tailings dams will continue to fail. In fact, in the long term all tailings facilities
will spiral toward significant increases of their probability of failure and, when they fail,
the tailings will run toward downstream rivers, lakes, and the ocean as they did at every
failure to date. We demonstrated that consequences are not necessarily correlated, in one
way or another, with dam height or pond volume. As in many industries the “scary stuff”
is not necessarily the riskier one. Our practice and research have shown that the probability
of failure is, or will be, often way higher in smaller structures than in major ones, simply
because more care is taken for larger structures than for “insignificant” ones.
Well documented examples such as the 1974 failure of the Bafokeng dam in
Rustenburg, SA, or the 1985 Val di Stava Dam collapse in Northern Italy are there
to show that “extreme” consequences can actually occur. We also demonstrated that
the rate of fatalities in the tailings “industry” lies way above the generally accepted
“safe” thresholds for hazardous industries. The number of existing, operational, and