Collapsed dam the largest accident of the kind in 100 years

The failure of Samarco's tailings dam in November 2015—destroying Bento Rodrigues village near the town of Mariana, in Minas Gerais—is the largest release in recorded history over the last 100 years. Considering the volume of residues released—50 to 60 million cubic meters (m³)—, the accident would practically be equivalent to the sum of the world's two other largest accidents recorded—both in the Philippines. One in 1982, releasing 28 million cubic meters; and another in 1992, releasing 32.2 million cubic meters of mud. Data are part of the Bowker Associates' study— consulting about risk management for high risk heavy construction in the United States—in partnership with the geophysicist David Chambers.

But the disaster has beat not only the volume record. In terms of run out, which is the distance from the point of failure the released contents travels, Samarco's leaked sludge broke another record—so far 600 km traveled. In recorded history,  an accident in Bolivia in 1996 second the ranking, with half the mud's run out , 300 km.

There are other unprecedented numbers. According to Bowker's data collection, the companies responsible for the Brazilian disaster are being sued until now at $ 5.2 billion. Researching court records and other government data, the consultancy company found only one in recorded history post 1990 with damages as high as $1billion, in an accident in Shanxi Province, China, at $1.4 billion.

Although the exact numbers remain somewhat distorted, the dam failure at Samarco's mining company is without question the largest tailings dam failure in recorded history based on these three severity measures, pointed out Lindsay Newland Bowker, Bowker Associates coordinator. The study registers, from 1915 to 2015, a total of 129 dam failures—of the 269 known events—and forecasts, on average, one serious accident per year in the period of a decade.

Human error

All mining disasters have been caused by human error and faults for not following the best practices, the best knowledge, the best science, considers Bowker. The coordinator adds that accidents are also caused by public partners' failure. She further declared that one of the concerns is that Brazil allows the use of the upstream dams, less stable method of construction in the case of large dams. According to her, this is a deviation from the knowledge and practices generally accepted. "In the specific case of Samarco, this inherent instability was exacerbated by the tailings rate  and the increasing rate, which were well above the best global standards for dams," she added.

The study also noted another accident with dams in Brazil in September 2014 in Itabirito, also in Minas Gerais. The Herculano mining company is responsible for the works. At the time, two workers were killed and one disappeared.

The failures of Samarco and Herculano are just the two most recent examples of a government that has failed in the national mining policy. No action was taken by the government at the state or federal level to identify the problems and prevent them from happening with new sudden failures, concludes Lindsay.

This week, Undersecretary of Environmental Regulation of Minas Gerais Secretariat for Environment, Geraldo Vítor de Abreu, told the committee formed at the State Legislative Assembly to investigate the dam disaster in Mariana, that Minas Gerais government wants to ban the upstream dam system in the state.

EBC Portal tried to talk with Samarco, but so far the company has not commented on data collected by Bowker Associates' study.

Translated by Amarílis Anchieta