The National Dam Safety Policy - Law No. 12,344 / 2010, is the regulatory framework for dam safety in Brazil, establishing the National System for Dam Safety Information and establishes what the objectives (article 3.), The grounds and the jurisdiction to review (art. 4). Moreover, it indicates what tools and criteria for the classification of dams, which are categorized by risk, potential damage associated and by volume, based on the general rules established by the National Water Resources Council (art. 6). They are also applied to Law No. 12,608 / 2012 National -Politics Protection and Civil Defense (PNPDEC), the Law No. 9.433 / 1997 - National Water Resources Policy, the Law No. 9.984 / 2000 - creation of the National Water Agency (ANA), Law No. 6.938 / 1981 National -Politics Environment (NEP), the Mining Code - Decree-Law No. 227/1967 and the Federal Constitution of 1988. However, with regard to disaster prevention, the National Policy Dam Safety (PNSB), does not provide for the participation of Civil Defense, in what refers to the Dam Safety Action Plan, including when establishing the Emergency Action Plan (EAP), and only allows the participation of Civil Defense in emergencies, ignoring the recommendations of the Hyogo Framework for Action (2005-2015) and the current Marco Sendai Action (2015-2030), for which prevent the risk of disasters and increase the resilience of vulnerable communities should guide public policies to disasters. In this article, using bibliographic and documentary studies, as the case study - Breaking the dam of Fundão and Santarém, in the municipality of Mariana / MG, analyzes the social and environmental vulnerability to technological disaster risk, the National Policy Dam safety, and the participation of civil defense in the prevention and mitigation of disasters.