An independent investigation requested by Brazilian iron ore miner Vale SA into the causes of the Brumadinho tailings dam disaster that killed 270 people a year ago found the company knew about the problem but failed to deal with it.
An executive summary of the report published by Vale on Thursday said the company had had information dating as far back as 2003 that pointed to the fragility of the main B1 dam.
But steps taken to deal with the structural problem and heighten the dam's security were limited and ineffective, the report said.
The Brumadinho dam burst in January 2019 in Minas Gerais state, unleashing an avalanche of muddy mining waste which killed an estimated 270 people, burying many of them alive.
The internal report serves as a damning condemnation of the firm, some of its employees and various auditors. While concerns were raised at various points in time about the dam's safety, those concerns were repeatedly ignored or minimised over the course of 16 years.
In January, state prosecutors charged Fabio Schvartsman, the chief executive at the time of the burst, with homicide. A Brazilian state judge last week accepted the charges.
The investigating team concluded that the dam burst was due to structural instability caused by liquefaction, citing among other factors inadequate drainage of the reservoir and a dam that was not designed to contain liquefied material.
Australian Associated Press