Three Critical Considerations for Long-Term Utility Solutions: Part II
Utility districts across the U.S. are seeking system hardening solutions, and many are choosing to replace their framing materials with non-wood products. The case for continued use of wood solutions was made in the first of this two-part article, with focused attention given to environmental responsibility. This second-part will review two additional critical considerations: resilience and economics. Only in considering these three important areas together will the utility industry be able to move toward the long-term solutions demanded by public and governmental concerns.
Resilience: Expected Lifecycles & Weather-Related Concerns
In the face of severe weather storms and record-breaking wildfires, utility officials and customers across the U.S. are calling for all considerations to be made to reduce the likelihood of power outages. The resulting push for grid hardening has led some away from wood poles and crossarms, toward alternative materials. However, it is worth asking whether these decisions are valid, given standardized strength requirements and unproven claims for lifespan resilience among composites. There is good reason to give wood products more consideration in terms of structural resilience.
Regardless of the material, all poles and crossarms must meet minimum strength requirements, as specified under the National Electrical Safety Code for overhead line systems. Any wood pole or crossarms in service is required to meet any and all strength standards. Claims that one material is stronger than another become a moot point in regard to this code. Furthermore, whereas proponents of alternative materials are quick to suggest non-wood products offer a greater lifecycle span, such claims are often not backed by independent testing, or are yet unproven.
Proponents of composite utility products can only speculate on expected lifecycles. There has been no long-term testing of fiberglass crossarms under load duration to date, and fiberglass crossarms have only been in service since the 1990s. Likewise, proponents of steel and concrete poles claim service lives of 80 years for these products, but these materials have not been used long enough in direct burial installations to properly determine the impact of age and corrosion. Douglas fir crossarms, in contrast, offer a proven history of longevity and reliability in the utility industry, and they possess an excellent performance record in demanding environments. Millions of Douglas fir distribution crossarms and transmission framing components have been in service across the country for well over 60 years, lasting up to and exceeding 100 years in some cases.
Materials exposed to forces exceeding their design capacity are likely to fail, and that is true for any utility product. However, because of their natural variations and greater flexibility, wood poles and crossarms have proven more resilient in handling extreme loads when trees or other debris collapse into overhead power lines. In the case of utility poles, for example, steel, prestressed concrete, or composite poles are expected to have low coefficients of variation (COV), in the five percent range. In contrast, because of natural variations, wood poles have a COV in the 20 percent range. If poles of all of these materials are designed to the same load at the five percent Lower Exclusion Limit (LEL), wood poles will have substantially higher reliability when exposed to expected weather loads. This concept was fully investigated and presented in the American Society of Civil Engineers (ASCE) Manual of Practice No. 111, Reliability Based Design of Utility Pole Structures.
Compared to wood, alternative materials can be much stiffer, which can cause power poles to break at the top in extreme conditions. In severe weather conditions, where utility system components experience loads substantially above their design loads, wood poles show their unique overload capacity. Utilities seeking ways to harden their systems should reconsider wood poles designed to the higher loads, given wood’s greater natural variation, flexibility, and inherent overload capacity. For overall reliability, wood should be the material of choice in areas prone to ice storms and hurricanes.
When it comes to addressing weather related concerns, environmental degradation affects all materials. Extended exposure to sun causes fiberglass crossarms to fray, splinter, and bloom. In response, fiberglass manufacturers have developed a UV protective coating, but these delicate coatings lose their protective ability when scratched, chipped, or eroded by weather. Wood products, in contrast, won’t corrode or spall, and preservative treatment protects wood against its natural enemies: termites and fungi.
In order to take environmental impact on utility products into consideration, the American Wood Protection Association (AWPA) standards divide the U.S. into five decay zones: Zone 1 (e.g., parts of Alaska, Idaho, Montana, Utah, Nevada, Wyoming, Colorado, New Mexico, and Arizona) represents the lowest risk of decay, while Zone 5 (e.g., Hawaii, and the southeast region of the U.S.) indicates the highest level. The AWPA standards address these varying rates of risk by providing retentions that can be specified for a given preservative. Wood poles exposed to a higher decay hazard will be treated to higher preservative retentions, for example.
Preservatives integrated through pressure, combined with wood’s natural resilience, allow wood poles and crossarms to remain in service long beyond typical estimates. In a survey of data on 751,000 utility poles inspected across the U.S. between 1988 and 1999, Osmose Utilities Services determined that the application of a routine pole inspection and remediation program significantly added to the pole’s service life: by 60 percent, or 28 years on average. A 2012 Quanta Technology study on wood pole service life calculated the average expected lifetime of a wood utility pole with a routine inspection and treatment program at 96 years.
In addition to resilience, economics is another important area of consideration for utility decision makers.
Economics: Cost-Effective Solutions Across Their Lifecycle
In a year when wildfires have devastated entire regions of the West Coast, many are asking what can be done to improve preparedness, minimizing the harmful impacts of future wildfire events. Still others are asking questions about the costs involved in recovering from wildfire damage, while seeking the safest materials as cities rebuild. As city and state governments begin the important work of recovery from these devastating wildfires, it is important to consider the cost. One question that needs to be asked is whether innovation is being promoted at the expense of proven, cost-effective solutions.
Without sacrificing environmental responsibility and resiliency, wood poles and crossarms represent the most cost-effective option. Composite poles and crossarms are typically two to four times as expensive as their wood counterparts. This is true over the product’s lifetime.
A 1997 survey of all commercially available materials found that treated wood remains the most cost-effective material in terms of both initial costs and total lifecycle costs (Utility Structure Competitive Products Report Series, Report No. 5, “Life Cycle Economics,” prepared by Engineering Data Management, Inc.). When necessary, remedial treatment of wood products is simple and economical. Drilling, reframing, and adding or changing hardware can all be handled without removing the line from service. Further, wood poles allow for easy climbing–linemen can quickly attach gaffs and climb without the expense of additional tools.
Utility poles are often replaced not because of deterioration but because of a line upgrade, road widening, or land development project. Poles replaced for these reasons can be reused at other locations or recycled for non-utility applications. In fast growth areas with short duty cycles caused by frequent line upgrades, road widening, or development, wood offers an important economic advantage over alternative materials.
The reality of widespread wildfires and resulting demands put on public and private utility companies for an improved response is undeniable. However, in the face of such pressure, the answer cannot be an unquestioning call for innovation without considering the economic cost. At this critical juncture, it is worth asking, why are so many willing to move away from proven, long-term solutions, spending so much more on products with unproven benefits?
When it comes to addressing the current complexity of concerns facing utility districts, power companies, and the general public, what is needed is a long-term response to present challenges. Wood poles and crossarms remain a proven, sustainable, and environmentally responsible product. They are naturally renewable and can be produced more quickly in high- demand events. Wood utility products have been shown to be more resilient than other materials in extreme weather conditions, given wood’s natural variation and overload capacity, and wood is dramatically more cost-effective than alternative materials. For all of these reasons, treated wood products should rightly be given continued priority in today’s utility landscape.
About the Author
Ryan Pemberton is a writer, editor, and independent communications consultant. Ryan has written for a variety of industries, including energy, manufacturing, healthcare, transportation, and nonprofit organizations across the country. This article was commissioned by a leading manufacturer of wood utility products.