SÃO PAULO—Brazil’s chief police officer looking into the collapse ofValeSA’s dam in January said he was investigating whether detonations carried out by the mining company that day could have triggered the disaster, which killed about 270 people.
Luiz Augusto Pessoa Nogueira told The Wall Street Journal that internal forensic studies by the police suggest Vale may have carried out an explosion at its mine less than a mile from the dam hours before it collapsed.
“This is one of the hypotheses that we are investigating as being the trigger,” Mr. Nogueira said. He added that police also had information that there were daily detonations at the mine.
Mining specialists and the dam’s safety inspector, German certifications group TÜV SÜD, had frequently warned Vale that explosions near the 280-foot-high dam could trigger its collapse, according to internal documents reviewed by the Journal.
Vale denies conducting any detonations at the mine near the town of Brumadinho in the hours before the dam collapsed. In a statement Tuesday, the company said it carried out two explosions that day only after the dam’s rupture. It had already planned those detonations, it said, and decided to carry them out as a safety measure to eliminate explosives in the ground.
Two Vale workers from the mine told a parliamentary inquiry in Brazil on Monday that there were detonations at the site that day, but they contradicted each other on whether the explosions had occurred before or after the dam’s collapse.An investigation by the Journal in February found that employees at Brazil’s mining giant Vale and TÜV SÜD knew for months of dangerous conditions at the dam that contained mining waste. But five months after its collapse, Brazilian authorities are still trying to understand what suddenly triggered its rupture that sunny Friday in January, as workers sat down to lunch at the mine’s canteen at the foot of the dam.
Lindsay Newland Bowker, a researcher into the failure of mine-waste dams, said it was also possible the dam was in such a critical state that it didn’t need a trigger to collapse. “It was in an extremely critical condition, TÜV SÜD was unambiguous and clear in explaining this,” she said of the dam’s inspectors.
At 12:28 p.m. on Jan. 25, the dam—so seemingly solid that cows were grazing on its grassy surface—suddenly caved in, sending a tsunami of thick orange mud and debris down the valley at speeds of up to 50 miles an hour. The mud, containing sand and leftover iron-ore deposits, obliterated the mine’s canteen and offices, nearby homes and a small hotel within minutes. Most of the dead were Vale’s own workers.
Brumadinho Dam after the collapse
Internal Vale documents reviewed by the Journal show that the company had already mapped out the areas that would be affected if some of its dams burst, showing the canteen would be hit in the case of the Brumadinho site.
Mr. Nogueira, the police chief, said Vale usually carried out its daily explosions around lunchtime, between 11 a.m. and midday.
Vale declined to comment on the timing of possible explosions beyond saying that its explosions that day came after the collapse. When asked whether it carried out daily detonations at the mine, it said “detonations are part of mining activity,” adding that the company took into consideration TÜV SÜD’s recommendations in operating the mine.
The fateful dam was what is known as an upstream structure, in which the dam’s walls were formed by the mining waste itself, piled up and left to dry over several years. It is the cheapest type of dam to build, and considered by many mining experts to be the most prone to failure.
After another upstream dam that Vale jointly owned in southeast Brazil collapsed in 2015, killing 19 people, the company hired a team of experts to assess the safety of their dams. Those experts warned Vale that explosions—a normal method in mining to break rock apart for excavation—could trigger the dams’ collapse through a process called liquefaction, whereby its solid contents suddenly behave like a liquid and begin to flow.
Investigators concluded that liquefaction occurred in the 2015 disaster, and suspect it was also responsible for the latest one.
In a recent report, TÜV SÜD, the safety inspector for the dam that collapsed this year, laid out the factors that trigger liquefaction.
“To increase the safety of the dam and prevent liquefaction, it is recommended that measures should be adopted that reduce the probability of triggers occurring,” TÜV SÜD inspectors wrote. “As such, vibrations should be avoided, nearby detonations should be prohibited, and heavy machinery should not be used on the dam.”
Explosions are widely recognized as a trigger for liquefaction, mining experts said.
Washington Pirete, a Vale engineer who was part of a task force of international experts that assessed the safety of the dam in Brumadinho last year, explained in his 2010 master’s thesis how detonations could trigger liquefaction. He hasn’t responded to requests for comment since the collapse.
On the five-month anniversary of the tragedy Tuesday, some of the families of the victims were beginning to lose hope that those responsible for the tragedy will be brought to justice.
“Brumadinho was a crime, it was never an accident,” Flávia Coelho, the daughter of Olavo Coelho, a worker who was killed in the tragedy, posted on Facebook. Her father, along with several other workers, had tried to warn their bossesof dangerous conditions at the dam in the months before its collapse.
—Alistair MacDonald contributed to this article.
https://www.wsj.com/articles/blasts-probed-in-brazil-dam-burst-11561504829
