Wildfires always have been a part of our environment, particularly in the West. However, in the 21st century, the frequency and intensity of wildfires and the extensive damage caused by these blazes have prompted communities and businesses to find ways to protect against fire.
This is particularly true for utilities, who have extensive infrastructure with millions of wood utility poles frequently routed through grasslands and forests increasingly susceptible to fire. Utilities today are testing and adopting methods to protect these poles from fire, with an objective of limiting any potential fire damage and poles intact to maintain power without disruption.
Pole materials and fire
One common myth is that changing the pole material from wood to another material will solve all problems with fire. The reality is the intensity of today's fires impacts all materials, and these impacts can lead to catastrophic failures.
Utility poles today can be made of wood, steel, ductile iron, concrete or composite fiberglass. While wood burns, other materials are not impervious to fire's impacts. This is particularly important as utility poles carry significant loads from wires, transformers and other equipment. High temperatures from wildfires can easily compromise the structural integrity of any pole material, leading to failures that disrupt power.
Research into wildfires indicates temperatures in an advancing fire can reach up to 2,200 degrees F. Temperatures this high can have a significant impact on a material's structural properties. For example, steel loses strength in a predictable pattern as the temperature rises. Studies show steel begins to lose strength at about 400 degrees F. It retains just 80 percent of its strength at about 575 degrees F and retains only 50 percent of its strength at 932 degrees F.
Composite fiberglass also can lose strength when exposed to temperatures typically experienced in a wildfire. While concrete will not burn in a fire, elevated temperatures can cause both mechanical and chemical changes in the aggregate compounds as well as the rebar.
With millions of wood poles in place, utilities are focused on adding protection to existing poles, as well as incorporating protection for new poles. Fortunately, there have been new developments in technology that effectively protects poles in service.
Pole wraps have emerged as an effective and economical way to protect poles against fire. These wraps can be applied to new poles as well as those in the field. Wraps can be applied using common tools and the labor required to protect the poles is minimal compared to the labor required for replacing with poles made from other materials.
Pole wraps consist of a wire or fiberglass mesh covered with an intumescent coating. When exposed to heat, the intumescent coating expands to create a protective, insulating barrier between the fire and the wood. The wraps are durable once installed and can withstand extreme weather. The wraps also allow lineworkers to climb the wood poles with standard climbing gear, as boot gaffs can easily penetrate through the wraps into the wood pole.
Utilities in the West are using wraps such as Fire Mesh by Genics, which offers both a 23-gauge wire mesh as well as a fiberglass-based mesh, and Armorbuilt Wildfire Shield from Hexion that uses a fiberglass-based mesh. Both have undergone extensive fire testing to confirm their effectiveness in protecting poles.
The utility Southern California Edison conducted in-field fire tests on the wrap technology. Full-length poles wrapped with the Genics Fire Mesh were exposed to fire for two and three minutes, then were full-scale break tested to determine any impacts on pole strength. The results showed a less than 2 percent reduction in strength after exposure to fire.
In 2022, poles wrapped in Hexion's Armorbuilt Wildfire Shield were installed in a high intensity fire-risk area near Salinas, Calif. and subjected to a controlled burn conducted by the California Dept. of Forestry and Fire Protection. Poles located in the controlled burn endured flames as high as 45 feet and temperatures that reached up to 1,700 degrees F. Inspections conducted after the fire indicated the poles showed "no damage, superficial charring or appearance change" after the wraps were removed.
These results have been confirmed through real-world experiences. Fire-retardant-wrapped poles were in the path of the Lake Fire near Los Angeles in 2020, which burned 31,000 acres. After the fire, the wrapped poles were examined. According to the utility, the poles wrapped with the mesh were "undamaged and continued to retain the color and look of a pole which had not gone through a wildfire." The utility further concluded the poles would retain its full strength.
Crossarms and fire
The intensity of today's wildfires not only pose risks to utility poles, but also to crossarms at the top of poles. Other risks at pole tops include fires caused by transformers or shorts in electric lines.
Alternative materials for crossarms such as composite fiberglass have been promoted for their fire resistance. However, recent testing shows such claims are unsupported and underscores wood's remarkable performance when subjected to fire.
The Western Fire Center in 2022 tested both wood and composite fiberglass crossarms. Using proposed ASTM standard pole tests adapted for crossarms, sample arms of each material were exposed to a combination of heat sources. To simulate real-world conditions, the crossarms were attached to a pole stub and had 300-lb. weights suspended from each end.
In the first test, crossarms were exposed to radiant heat panels for 5 minutes, followed by exposure to a convective flame burner for an additional 5 minutes. The second test exposed the crossarms only to the convective flame burner for a total of 10 minutes. In both tests, after the radiant heat and flame exposures, the crossarms were allowed to continue to burn and self-extinguish for up to 20 minutes.
Results of the testing showed conclusively the superior fire performance of wood vs. fiberglass. In tests using both radiant panels and the flame burner, the composite fiberglass crossarm collapsed after nearly 6 minutes. Tests using only the flame burner yielded similar results, with the fiberglass arm failing after 5 minutes and 10 seconds.
Wood crossarms in both tests remained intact for the full 30 minutes. Preservative-treated wood crossarms and treated wood crossarms coated with a fire retardant were tested with similar results. The wood in the crossarm samples showed charring, but continued to hold the suspended weights with little change from pre-fire conditions.
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