Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014

Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014

Aug 9th, 2014

Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014

We have read public information about the tailings dam accident Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014

 Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014

Mount Polley Tailings Dam Breach

Of course, official inquiries will define causes and responsibilities.

What we intend to do with this note is to rationally discuss a few concepts linked to this event.  It seems that, like usual, in the aftermath of a catastrophe, numerous voices raise out of emotional and sometimes irrational perceptions. Issues get easily clouded.

In a paper we wrote in 2012 (see our blog and download the paper) we evaluated the world-wide rate of failures (major accidents only) of tailings dams and nuclear reactors.

We used public records and statistics from reputable sources. We noted that “major tailings accidents” are/were only fuzzily defined. Generally it seems that the bigger the outflow of material from the breached dam, the bigger the mediatic impact.

World portfolio of active tailings dams

On a portfolio of approximately 3,500 tailings dams world-wide we evaluated that in the decade 1974-1984 the rate of failure was 10-3 . That is one dam in one thousand per annum on average. In the decade around 1999 (1994-2004) the rate of failure was 2*10-4 . That is two dams in ten thousand per annum on average. Those numbers mean respectively 3.5 major dams breach on average per year (1974-1984).  Respectively 0.7 major dams breach on average per year (1994-2004).

NB: With those averages one could easily evaluate the probability of having more failures in one year. However, we will leave this aside, for the moment.

Again, we do not know if 3,500 is still correct, but we assume it is for the sake of the discussion, and there is no clear definition of what a major breach is, so we assume these are the most widely reported failures, that reach even non expert public through media exposure. The validity of the 3.5-0.7 range can easily be “verified” by looking at the Chronology of major tailings dam failures as published, for example, by Wise-Uranium in their website.

NB: As such, the decrease from 3.5 to 0.7 can be seen as an indicator of the mining industry performing overall a better job today than it did in the past. However, we will also leave this discussion to another time.

Industrial limit of credibility

Many hazardous industries (chemical, electrical, etc.) consider the limit of credibility for an accident at a probability in the range of 10-5 to 10-6. That is one in hundred thousand to one in a million. By the way, hydro dams have historic record of failure floating around the credibility threshold. Thus tailings dams are to be considered more hazardous than hydro dams. It is not possible to breach them at the end of service life: they have to stay there “forever”. Obviously, with the estimated values of the prior paragraph, major tailings dams breaches are to be considered way above credibility now, and more so, in the longer run, although long term consolidation may help a bit.

There are ways to build and manage dams that would reduce the probability of major failures to the credibility threshold. We have already demonstrated how this is possible in the short term. For the long term, including perpetual care, we are publishing a paper at the next Tailings and Mine Waste 2014.

Social and corporate risk tolerance

Finally we would like to touch on the theme of tolerance from the social and corporate point of view. Understanding social and corporate tolerance to risk is an essential skill for governance and effective leadership, one that effectively reduces knee-jerk reactions and crisis potential in the aftermath of an accident. Unfortunately, common practice approaches in the risk assessment/management arena use misleading tools such as Probability Impact Graphs (PIGs risk matrix, FMEA) that mask the reality of tolerance thresholds behind binning exercises with multicoloured (and arbitrary) matrices. Misleading risk assessments lead to wrong decisions, improper allotment of mitigative funds and anger the public.

Proper tools exist, many have already laid out the necessary rational concepts.

It is possible to get out of the rut of obsolete and misleading methods, avoiding future routs!


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Category: Consequences, Hazard, Probabilities, Risk analysis, Risk management, Tolerance/Acceptability

3 responses to “Special Issue: Mount Polley, B.C., Tailings Dam Breach, Aug. 4th 2014”

  1. MDuchene says:

    Please go out of statistics and determine which is the cause of this particular breach (storm with a lot of rain, or insufficient dam level and thickness (and process of building, which is the major cause of these breaches)) (3.5 to 0.7 per year is still too much).
    The tolerance should be zero for responsible industries.
    Michel Duchene

    • Franco says:

      Going out of statistics seems a little extreme.
      He who can count can manage.
      Without counting only gut driven decisions can be made and it will be impossible to know if they were good or mediocre decisions.

  2. Roy Wares says:

    The question that will be asked is one, whether the company and their experts misapprehended the risks and despite that, two, did they properly allocate responsibilities and duty of care to the relevant parties.

    We might disagree on risk registers but they do spell out for the public, who is, was, or was supposed to be responsible for monitoring.

    In my view, neither the company, their expert advisers and the regulators are going to escape with their professional reputations intact.

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