Reliability in mass alert system for dam emergencies: Case study of Vale S/A

In its iron ore operations, Vale, the largest mining company in Brazil and the fourth largest mining company in the world by market value, has 77 dams considered with high potential damage in case of a failure in the stability controls. This classification follows the criteria of the sector regulatory agency in Brazil and determines that, for this class, a mass alert system is necessary for the resident population and workers immediately downstream of the dam within a region preset by legislation, considering a simulated flood area. For Vale, the mass alert system for dam emergencies is part of a critical mitigating control for a business risk analysis considering the hypothetical dam break as an unwanted material event. Therefore, both the probability of failure on demand, spurious failure, and availability of the assets of this protection barrier are important elements for this purpose, as well as the emergency response plan and the evacuation simulation of flood areas, which are part of a risk management system that require continuous verification and continuous improvement. Currently, Vale has 375 sirens, and it is planned to reach 420 sirens by the end of 2024. The purpose of this article is to present how the safety concepts applied to these systems were developed, the good practices applied from this study, and the lessons learned from the dam emergency management arising from the break of the Brumadinho dam in 2019. The reliability analyses of the systems involved and the main contributors to the Safety Critical Unavailability are presented, as well as the results of the reduction in the maintenance time and increase in system availability.