Utility poles are subjected to the harshest conditions that nature can dish out, from rain, ice and snow to insects and decay fungi. Preservatives infused into the poles through pressure, combined with wood's natural resilience, allow wood poles and crossarms to remain in service for 70 years or more.
Wood poles and crossarms must meet a series of standards to be used by utilities. The strength and engineering properties are defined in the ANSI O5.1, Wood Poles - Specifications and Dimemsions and CSA Standard O15-15, Wood Utility Poles and Reinforcing Studs. The standards for preservative treating of wood utility poles are set by the American Wood Protection Association (AWPA) and Canadian Standards Association (CSA) in their respective countries. American treating requirements are detailed in the AWPA Book of Standards and in Canada in CAN/CSA O80 Series-15 – Wood Preservation.
All preservatives used for utility poles are approved and regularly reviewed by the U.S. Environmental Protection Agency (EPA) and the Canadian Pest Management Regulatory Authority (PMRA).
There are five preservatives for utility poles and crossarms that are used in North America: Pentachlorophenol, or penta; Chromated Copper Arsenate, or CCA; Copper Naphthenate, or CuN; Creosote; and Ammoniacal Copper Zinc Arsenate, or ACZA. Penta, Copper Naphthenate and Creosote are oil-type preservatives and are carried into the wood via petroleum products. CCA and ACZA are waterborne preservatives and are infused in a process where water carries the preservatives deep into the wood fiber.
Most poles are preservative treated with the entire pole placed in a pressure cylinder during processing. But some Western Red Cedar poles may only have the butt, or lower portion of the pole, treated with preservatives.
The potential for deterioration of a wood pole is higher at the ground line or below, where there is more chance of exposure to water and insects. Butt-treated poles have treatment in the section that will be buried, extending just above the ground line. Western Red Cedar has a high level of natural durability, so the untreated part of the pole can withstand the elements.
The requirements for penetration and retention of preservatives in the wood for utility poles are defined under AWPA standards. The protective levels of preservative in each pole has been determined through extensive research and a long record of in-place service performance. Click below for more information on preservatives for wood utility poles.
Review a white paper on penta performance and safety
Pentachlorophenol, commonly referred to as penta, is the most commonly used preservative for utility poles and is the treatment of choice for as much as half of the wood poles used in North America. This industrial strength preservative has been used for wood treating since the 1930s and has achieved an impressive record of service performance and safe use. The light honey brown color of wood treated with penta adds to its aesthetic appeal.
Penta is very effective in resisting fungal decay and wood poles treated with penta have been known to last 70 years or more. Penta has historically been dissolved in diesel oil for pressure treating. More recently biodiesel has been used as a carrier for penta. This has virtually eliminated the offensive solvent petroleum smell of a freshly treated pole. Biodiesel is also a more sustainable alternative to petroleum-derived diesel fuel since it is produced from renewable sources such as corn and soybeans.
Penta can be burned in biomass-fed power generating facilities, thus adding to its benefits as a sustainable alternative for the preservation of wood poles.
Preservative manufacturers: KMG Chemicals
CCA is the second most common preservative used for utility poles, typically used for Southern Pine and Western Red Cedar poles. While CCA has not been used in treating residential products since 2003, it remains a popular choice for utility poles as well as agricultural products such as posts.
CCA is an effective preservative because it chemically "fixes" or bonds to the wood, reducing the chances of potential migration of the preservative into the soil or groundwater.
To improve climbability, an oil-based emulsion treatment can be added and the poles are marketed as CCA-ET treated poles. The emulsion additive allows for better climbing gaff penetration.
Preservative manufacturers: Arch Wood Protection, Koppers Performance Chemicals, Viance, LLC
Copper Naphthenate, also referred to as CuN, is an industrial strength, oil-type wood preservative with proven performance and an impressive environmental profile. It has clean handling characteristics and offers outstanding gaff penetration for climbing.
Classified by the EPA as a general use preservative, Copper Naphthenate is considered acceptable for consumer use. It is widely applied as a field treatment on end cuts or holes bored into pressure treated wood during construction.
Treatment practices for CuN-treated poles has been refined over the past two decades by manufacturers to ensure the utility poles provide a long service life in demanding conditions.
Preservative manufacturers: Nisus Corp.
Ammoniacal Copper Zinc Arsenate , or ACZA, is commonly known by its brand name Chemonite. Developed by the University of California in the 1920s, ACZA treatment is particularly effective for hard-to-treat species like Douglas Fir.
In addition to utility poles, ACZA preserved wood is often used in aquatic environments, docks, piers and applications where it will be exposed to water.
Preservative manufacturers: Arch Wood Protection
Creosote has been successfully used as a preservative for well over a century. Its most prominent and recognized application is in the production of wood railroad ties. However, it is also used extensively in wood utility poles as well as marine pilings.
Through the years, creosote-treated wood has been an economical and high performing choice for preserved wood products, offering a low total environmental impact.
Preservative manufacturers: Coopers Creek Chemical Corp., Koppers, Inc., Lone Star Specialty Products,