SAO PAULO (Reuters) – The deadly collapse of a Vale SA’s mining waste dam in Brazil was partially triggered by “a persistently high water level” that caused the structure to lose strength and stability, according to a report by a panel of experts appointed by the company’s lawyers.
The report, released by Vale on Thursday, said there was no warning the dam was unstable, and no seismic activity or explosions in the area were recorded before it burst in late January. The dam collapse unleashed an avalanche of mining waste on the Brazilian town of Brumadinho, killing at least 155 people.
The report examined technical factors leading to the disaster rather than issues of liability. It came less than four years after another dam collapse at a joint venture between Vale and BHP Group in the same region, an accident that experts also blamed on water weakening the solid materials composing the dam so that they behave more like a liquid – a phenomenon known as liquefaction.
Massive so-called tailing dams provide the most common waste disposal for mining companies, whether extracting iron ore, gold or copper. While prior experience indicates the dams rarely collapse because of a single cause, the Brumadinho disaster was set in motion by several factors, including poor internal drainage and intense rain that helped cause the excess water, the four-expert panel said.
Vale and its top executives at the time of the disaster have been assailed by politicians and prosecutors for failing to prevent the disaster, despite what critics say were ample warning signs. But the panel’s report said there were “no apparent signs of distress prior to failure.”