Utility poles are subjected to the harshest conditions that nature can dish out, from rain, ice and wind to insects and decay fungi. Preservatives integrated 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.
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 six preservatives for utility poles and crossarms that are used today in North America: Pentachlorophenol, or penta; Chromated Copper Arsenate, or CCA; Copper Naphthenate, or CuN; 4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One, or DCOI; Creosote; and Ammoniacal Copper Zinc Arsenate, or ACZA. See the publication Pole Principles - Preservatives for Wood Utility Poles
Penta, Copper Naphthenate, Creosote and DCOI are oil-type preservatives and are carried into the wood via petroleum products. CCA and ACZA are waterborne preservatives 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, often referred to as penta, is an industrial strength preservative used in wood pole treating since the 1930s. Used extensively in treating Douglas fir poles, penta has achieved a long record of service performance and safe use. The light honey brown color of wood treated with penta adds to its aesthetic appeal.
Penta is 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. Biodiesel is also a more sustainable alternative to petroleum-derived diesel fuel since it is produced from renewable sources such as corn and soybeans.
The manufacturing of penta was discontinued in 2021 and the preservative is being phased out, with the EPA discontinuing the registration.
Preservative manufacturers: None
CCA has been used in treating Southern Pine and Western Red Cedar poles for many decades. CCA has an extensive record of durable performance for utility poles and is also used to treat products used in agriculture such as posts.
CCA provides effective protection for poles 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 for utility linemen, oil-based emulsion treatments can be added to CCA, allowing for better climbing gaff penetration.
Preservative manufacturers: Arxada, Koppers Performance Chemicals, Viance, LLC
Copper Naphthenate, also referred to as CuN, is an industrial strength, oil-type wood preservative with proven performance. It has clean handling characteristics and offers good gaff penetration for climbing.
Classified by the EPA as a general use preservaitve, Copper Naphthenate also 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 have 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.
DCOI is the newest oil-type preservative available for utility poles and crossarms. DCOI has been standardized as a wood preservative by the AWPA since 1989 and ground contact uses were added in 2017.
DCOI is a thoroughly tested preservation system, offering a high performance, durable pole. Key components in the preservative are also used in Ecolife treated decking and fencing.
In addition to wood preservation, DCOI is used in water treatment, paints and coatings, adhesives, vinyl roof membranes, vinyl flooring, marine upholstery and outdoor furniture
Preservative manufacturers: Viance, LLC
Creosote has been successfully used as a preservative for well over a century. Creosote-treated utility poles have established a documented record of long-term performance and a reputation for safety and reliability.
Through the years, creosote-treated wood has been a high performing choice for preserved wood products, offering a low total environmental impact.
Creosote is supported by various multinational corporations who provide product stewardship though technical and research initiatives.
Preservative manufacturers: Coopers Creek Chemical Corp., Koppers, Inc., Lone Star Specialty Products,
Rain Carbon, Inc.
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.
ACZA-treated poles protect against the major causes of wood degradation: decay and termites (including Formosan), marine organisms, carpenter ants and woodpeckers.
Preservative manufacturers: Arxada