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During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.