Perhaps the most important element in the RS-Ackerman fire test is the post-fire exposure strength test. After the steel shroud is removed, the complete pole is extracted from the ground and loaded into a test fixture to complete a vertical full-scale bend test to failure, based on ASTM D1036. The bend test is intended to quantify any loss of strength resulting from the fire exposure when compared to a pole’s mean ultimate failure strength and published strength value.
Fire Mitigation Strategy
The composite pole fire test performance was exactly what SCE was seeking to identify a resilient solution in high fire threat areas to support the aggressive plan of deploying 4500 circuit miles (7242 circuit km) of covered conductor. This positioned composite poles as an integral part of SCE’s system hardening strategy.
SCE’s fire-resistant pole deployment is focused on two areas: ignition prevention and system hardening. Composite poles check both of those boxes for SCE, plus they have the ancillary benefit of woodpecker damage prevention and are environmentally benign.
The fire-resistant composite pole use strategy focuses on critical equipment poles, for additional resistance to tracking because the RS composite poles’ nonconductive material and hydrophobic surface characteristics, and woodpecker areas to which composite poles are impervious. The total composite pole deployment strategy accounts for approximately 40% of all poles in the high fire risk areas of the SCE service territory.
After the program commenced in 2018, it was not long until the composite poles were tested with wildfire exposure. The first exposure was the Tick Fire in October 2019, which burned 4615 acres (1868 hectares) in Los Angeles County and validated the performance in fires was the same as that in tests. Located in a region of largely chaparral vegetation, the adjacent wood poles burned to the ground while the composite poles emerged unscathed. On inspection of the poles, they were found intact with no structural damage to the resin and surface. The pole surface did show discoloration from the soot and ash that was flying during the fire. The poles remain in service today.
As time passed, more and more composite poles were installed in the SCE grid and exposed to fires. Time and time again, the poles mitigated the risks associated with fire threat, standing strong. More recent fires in areas with increasingly dense vegetation did prove to have a higher heat flux than the Tick Fire, resulting in some charring of the composite pole surface. The 2020 Apple Fire in Cherry Valley, California, which burned 33,424 acres (13,526 hectares) and Lake Fire in the Angeles National Forest, which scorched 31,089 acres (12,581 hectares), are prime examples. Because of the presence of trees and taller vegetation in the Apple Fire, for example, the composite poles were subjected to a high heat flux. The surface of the poles showed damage to the resin with some loose E-glass fibers. However, the poles remained standing and kept the lines off the ground, resulting in faster system restoration and a reduced outage time after the fire.
Strategy Validation
Looking to validate its choice to use composite poles in high fire threat areas, SCE wanted to verify composite pole strength after severe fire exposure in the real world. Four RS poles — one 45-ft (13.8-m) pole and three 50-ft (15.2-m) poles — that had been exposed to various actual fires were removed from service and returned to the manufacturer to undergo the vertical full-scale bend test to failure, the crucial performance verification component of the RS-Ackerman fire test method that measures both post-fire pole strength and stiffness. All four poles tested demonstrated results consistent with new poles and the manufacturer’s published pole performance parameters. The fire exposure had no impact on pole strength and stiffness.
Today, fire-exposed poles are inspected and remediation for any surface damage is being developed using a field-applied bushed coating that restores the pole surface.
