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