In October 2007, Southern California was hit by multiple simultaneous catastrophic firesdriven by “Santa Ana” Foehn winds. Half of these fires – the largest and most destructive – havebeen attributed to power lines. Comparing scaling relations for historical fire sizes demonstratesthat power line fires tend to be larger than wildland fires from other sources. This occurs becausethe number of line faults rise rapidly as a function of wind speed while fire suppression efficiencydrops from its usual 99% to around 80% under high-wind conditions. Three physical effectscausing power line fires – tree contact, line slap, and metal fatigue – are shown to lead to anumber of ignitions that increase at least as wind speed squared, and probably as a much strongerfunction of wind speed. Current regulations are shown to be inadequate to protect againstextreme wind events, making the reoccurrence of power line conflagrations equalling or worsethan that of October 2007 inevitable barring significant additional preventative measures to betaken by utilities and regulators.
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