Magnetic storm activity can induce geoelectric fields in the Earth's conducting lithosphere.[28] Corresponding voltage differentials can find their way into electric power grids through ground connections, driving uncontrolled electric currents that interfere with grid operation, damage transformers, trip protective relays and sometimes cause blackouts.[29] This complicated chain of causes and effects was demonstrated during the magnetic storm of March 1989,[30] which caused the complete collapse of the Hydro-Québec electric-power grid in Canada, temporarily leaving nine million people without electricity. The possible occurrence of an even more intense storm[31] led to operational standards intended to mitigate induction-hazard risks, while reinsurance companies commissioned revised risk assessments.[32]