Utility Poles & Fire: Surprising Findings on Wood vs. Steel
Most utility poles in North America are wood. In fact, 99% of all poles in the US are wood. It is estimated that there are 130 million wood poles in the US. Steel poles on the other hand cost 70% more than wood poles. What is the benefit of the higher price? Longer pole lifespan.
However, according to a research paper by Stephen T. Smith, PE, steel poles do not have the lifespan manufacturers claim. Specifically, in a wildfire situation wood poles and steel poles perform the same.
Wood Utility Poles Wildfire Performance
Most wildfires produces temperatures from 500°C to 1,200°C. Obviously, even treated wood poles spark up nicely and exploded into flames when the fire persists. The main condition with a wood pole is how long it is exposed to fire. The longer it is exposed to fire the more the pole will suffer. A wood pole will actually self extinguish after a fire passes. Basically, a layer of char forms on the outside of the pole that protects the interior of the pole from deterioration. At this point, the pole is not safe for the design load however. But the surprising information is that steel poles can’t handle the fire either.
Steel Utility Poles Wildfire Performance
Steel does not burst into flames at those temperatures, but from 500°C on, the integrity of the steel pole is compromised. At those temperatures steel can no longer handle the load of the wires. The design load is compromised. Furthermore, the galvanization of steel poles is compromised in fire. Down the road, those steel poles will need to be replaced sooner due to corrosion.
So in reality, wood poles perform equally as well as steel poles for wildfire situations.