Nearly a year after Feijão tailings dam failure that killed 270 people, 11 current or past employees of Vale, including its former CEO, and five from the German consulting firm TÜV SÜD were charged with homicide. The verdicts on those cases, should they ever be delivered, are likely a long way off.

However, a judgement on the technical causes of the failure has already been rendered. In mid-December a four-member panel created by Vale and chaired by geotechnical consultant and retired University of Alberta engineering professor Peter K. Robertson issued its report on the dam failure.

The panel dismissed the theory that blasting near the dam triggered the collapse. Using simulations, it also ruled out the suggestions that discrete projects to help manage the dam – the installation of drains to lower the water level the previous summer and the drilling of a borehole on the day of the failure – were catalysts of the failure.

The catastrophic event traced back over four decades to when the facility was first conceived. “Its original design and construction was not robust,” explained Robertson in a video statement released along with the report. “Essentially, it was too wet and too steep.”

Too much water was collecting in the impoundment and not enough was migrating out. The panel also concluded that “the bonding of the tailings due to iron oxide had the effect of making the dam appear to be stronger and more robust than it actually was – without the normal signs of distress or imminent failure. Further, the internal creep movements were so small that they would not show signs of distress on the surface or be a predictor of failure.”  

In other words, the Feijão dam was on the verge of failing, but, given what little was known about the character of the impounded tailings, getting advance warning of when that might happen was not possible.

Immediately after terrible events like at Brumadinho happen, between the outrage and the demands for accountability, calm voices sometimes come through warning about the danger of jumping to conclusions. We do not, after all, have all of the information. The investigation into the Feijão collapse makes it clear we should appraise tailings facilities with that same skepticism, drawing a conclusion about their safety and integrity only after careful examination.