Standard accident theory tells us that an accident occurs when many small incidents or omissions line up. It is like a pile of Swiss cheese with hole in it: inevitably a pile of cheese with hole in it will result where holes line up and you could poke a knitting needle through the holes without penetrating the cheese. This theory explains what happened at Mt Polley. Many tiny acts and omissions lined up—and we see now the results.
It is human nature to try to simplify the explanation of bad events. There was a witch; there was an evil spell; there was an incompetent designer; there was a cash-strapped company. We seek the one party to blame–it is so much easier to do that than consider an unlikely chain of events leading to disaster.
The game of blame has started re the Mt Polley tailings disaster. The designers of the facility, Knight Piesold are being mentioned in reports. AMEC staff on site to raise the embankment are noted. Imperial Metals is called out by a former employee. The anti-government folk blame both the Provincial and Federal governments. Harper is even excoriated.
And of course those First Nations folk who resisted release of water and the BC regulators who are still reviewing the application to discharge excess water are duly noted.
Some are asking if there are insurance companies on the hook and able to pay. Many are wondering if this will become yet another taxpayer charge.
The most intelligent call I read today is the call for an independent board of experts who should be free of any constraints in assigning blame. Let us speculate what they will conclude.
The embankments were designed to hold tailings not water. The embankment was centerline construction–not a good design for a water retaining structure. The perimeter embankment have a number of sharp corners. Not a good thing as tailings and water pressure push the embankments away from each other and cracks develop and failure results. There are distinct layers of different permeability in the embankments–piping through the more permeable layer could have caused the failure. The old tailings foreman talks of a need to place five million tons of rock. Were they thinking of a toe buttress to increase stability.
Rule one in tailings management is keep the water away from the perimeter embankments. This simple rule was violated with impunity–or at most a warning from the regulators.
I am sure there are many other details that i do not know or cannot see in the videos I have examined.
Regardless the following is clear:
- It was a bad design
- It was variably constructed
- Water was held against the embankment
- It was raised without due consideration of the implication of overloading a poor structure
- None of the consultants or the inspecting regulators understood what was going on
- Imperial Metals obfuscated and delayed
- The First Nations people played a delaying game that proved fatal.
Thus we see a chain of poor decisions leading to the inevitable failure. It is not correct to place the blame on one party only. If only one party had acted with knowledge and responsibility, the dam would still be standing and I would be blogging about the most recent book I have read.
Of course all the parties are culpable and will soon enough be judged by loss of company, reputation, and a polluted living environment.
Of course Imperial Metals as the mining company must take the greater blame. They did not act proactively. There was no peer review of the tailings facility —a common enough practice these days. They skimped on expenditure. They kept pushing the limits.
I suspect the regulators had nobody in their employ trained and experienced enough to fully appreciate what was going on. They discerned that too much water against the embankment was bad, but obviously had not enough experience or insight to think what could and did happen.
The consultants left the job or kept to a narrow scope presumably defined by the mining company.
So I believe that even an independent board of experts will be forced to find as I write above, with more detail of course. It is inevitable they will find all in the chain at fault. And they will conclude it is yet another example of the basic rule: sometimes ten small faults or omission line up and the result is disaster.
I wrote about this a while back–see this link for our paper that explores these ideas in detail.