Tailings dam risk communication

Tailings dam risk communication

May 6th, 2020

Experience shows that successful risk communications always focuses on planned control measures and precautionary actions rather than on risks. Indeed, like in many other fields, actions speak louder than words. Because actions are what matters to the public. Thus, today, we explore our experience in tailings dam risk communication.

Tailings dam risk communication

In mining, oil and gas and other industries, people demand to know what preventative actions are foreseen. That is even if it is claimed that the likelihood of an accident and associated risk is very low. Indeed, without any doubt, experience has unfortunately shown that very low likelihood events actually do occur (Fukushima and other nuclear accidents, hazmat industry, etc.). As a result, we are not mentioning tailings dams breaks or significant pipeline spills, because a rate of 1 to 4 catastrophic tailings releases per year, no one should actually talk about very low likelihood for this type of accidents.  

The considerations above may explain why the public:

  • puts more emphasis on what is done to reduce mishaps, rather than on the details of the mishaps and their potential effects,
  • cares about the skills and awareness of the operation manager more than about the risk itself, and finally
  • perceives mismanagement, incompetence, and lack of conscientiousness as the central issues in accidents.

Furthermore academic and popular literature suggest agreement that the public’s distrust of industry has developed over the past half century. Indeed that distrust likely generated as a result of repeated failures to provide adequate and/or accurate risk information to the public and, in some cases, blatant or perceived conflict of interest.

Tailings dam risk communication

Undoubtedly, media and some authors push for sensationalism, oftentimes unsupported by facts. In addition it is oftentimes the result of biased interpretation of incomplete databases or “gut feeling”. As a matter of fact, this is not a recommendable path when communicating risks. Furthermore, our experience shows that modern dams, especially the largest ones, have better investigations, design, construction, management as well as monitoring that any older structure we know. Thus, based on our experience, we see their probability of failure decrease towards value that near those of hydraulic structures of the same caliber.

We have put together a selected population of failures in the last 45 years. They occurred at medium height dams, in base and precious metals mining operations. They are, from the oldest to the most recent:

  • Bafokeng,
  • Merriespruit,
  • Corrego (Brumadinho dam),
  • Los Frailes,
  • Mount Polley,
  • Baia Mare(2000 Baia Mare cyanide spill), and finally
  • Samarco (Mariana dam disaster)

In this sample, Samarco is an exception with its 100m height, with peculiarities highlighted by forensic studies, design changes, extremely high average raise per annum. Corrego had the longest life to failure of the group (87 years), Samarco and Baia Mare the shortest.

At this date, we have no information on the:

  • duration, years, to failure for Baia Mare and Merriespruit,
  • raise history of Bafokeng, merriespruit, Los Frailes and Baia Mare, and finally
  • serious doubts on the values we have found for the average raise (m/yr) of Baia Mare and Samarco.

 Please note we would be delighted to receive help with the 3 bullets above.

Ultimately all the structures in the table had aspects of:

  • investigations,
  • design,
  • construction, and finally
  • operations and management,

leading them far astray from what would be considered an excellent large dam today.

Contrary to popular belief

The statement that larger structures failures lead to larger consequences than those of smaller structures has proven wrong in many cases. As an example, Stava failure in Italy was a 300,000m3 release with extremely serious consequences. 

Indeed, many parameters drive consequences, above and beyond the size of the dam. And the interplay of probability and consequences does not necessarily mean risks of smaller or larger dams are more or less tolerable. In addition, we unambiguously showed in a 2015 paper that the  Volume released vs. lives lost  graph, does not show any correlation.

Furthermore, the same would occur with the dam height or the run-out distance, leading to the same conclusions!

Closing remarks

Explaining what you plan, will do, and foresee to mitigate risks is at least as important as explaining how small those risks may be.

Finally, the public may be much more receptive if mitigative plans come first and the “trust us, risks are small” statement comes later, or never.

In summary:

  • Simplistic statements equating bigger dams to bigger risks are to be avoided. Because they can easily be disproved. Furthermore they do not help any constructive dialogue.
  • As structures become larger, their probability of failure should reduce toward values commonly accepted for major hydro-dams. That reduction necessitates acting on all aspects of the dam life from its inception, as all contribute to the chance of failure. In addition, the Factor of Safety (FoS) as such does not reflect any of the above necessary improvements.
  • Population increase, land use shifts, environmental constraints increase consequences of failures and therefore tend to amplify risks. Again, the probability of failure will have to shrink. That is especially considering the long-life span of tailings dams. Finally
  • the Factor of Safety does not help proper analyses and hazard evaluation of a structure.

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Category: Consequences, Mitigations, ORE2_Tailings, Probabilities, Risk analysis, Risk management, Tolerance/Acceptability, Uncategorized

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