Does Compliance with Minimum Regulatory Standards Adequately Mitigate Wildfire Risk?

Transmission line design and maintenance is driven mainly by regulatory requirements, professional standards, or utility-specific provisions, all of which set minimum strength requirements for both new and replacement structures. Yet transmission line structures fail every year all around the world, demonstrating that compliance with those standards does not guarantee survival. While in the United States some frequency of failure has been considered acceptable and even expected in extreme weather events, in California the tolerance for failure is dropping, in part due to catastrophic wildland fire ignitions traced to power line failures in extreme winds. California is not alone as the consequences of power line failures elsewhere are also worsening, suggesting that the target reliability inherent in regulatory standards needs to be recalibrated. In particular, the human suffering and loss of life consequences associated with transmission line structural failure in high fire threat areas should be considered when assessing strength requirements, and the associated failure rate, for engineered structures used to support overhead lines. Regulatory requirements for power line structure strength in general, but particularly in California, are lagging behind modern, risk-based design methods being adopted elsewhere in structural engineering practice. The purpose of this paper is to progress current efforts to modernize overhead transmission line design practice in California by incorporating wildland fire risks into our structural engineering standards. We explore the history and evolution of California General Order 95 regarding minimum structural design standards and identify areas in which it could be improved. We also discuss how site-specific and risk-informed methodology should now become the best-practice for both system design and hardening.