BHP, the world’s largest mining company, “knew of the risks” surrounding the deteriorating condition of a Brazilian dam years before its collapse in 2015 and was “woefully negligent” in its duty to prevent the catastrophe, say lawyers representing thousands of claimants in a $5 billion damages action.

The Fundão dam near Belo Horizonte in eastern Brazil collapsed on Nov. 5, 2015, causing a mudslide that killed 19 people, displaced at least 700 more, and destroyed the nearby villages of Bento Rodrigues, Paracatu de Baixo, and Gesteira. It also devastated the Rio Doce river basin, polluting the country’s second-largest river system.

Neil Hodge is a freelance business journalist and photographer based in Nottingham, United Kingdom. He writes on insurance and risk management, corporate governance, internal audit, compliance, and legal...