Pentachlorophenol (penta) has been used for utility pole treatment since the 1940s. In a review for the AWPA, Mike Freeman estimated that about 2 million poles per year are treated with penta, making it the most widely used preservative system in the country.

Penta Efficacy Review

Wood post and stake tests of penta show good performance. The south Mississippi post tests give an estimated service life of 74 years for 0.30 pcf in No. 2 fuel oil (1). This retention is only 66% of the AWPA required preservative retention for poles.

Similarly, wood stake tests in AWPA Decay Zone 5 (severe exposure) at 0.29 pcf retention had no failures after 38.5 years of exposure.

Penta Environmental Registration

Penta is also a Restricted Use Preservative like CCA and Creosote. Similar restrictions on its use and labeling have been issued by the EPA. The Registration Review on penta is underway and it is likely that its use as a wood preservative will be continued if the product is actively supported by a registrant (manufacturer) company.

Penta General

Generally, linemen prefer climbing penta poles due to the ease of gaff penetration and their cleanliness although several studies have shown the oil-based emulsion climbing additives to CCA have similar climbability characteristics. Similar to Creosote, skin contact and transfer of oil to the climber should be minimized. Penta is not conductive and and has low corrosivity. Currently there is only one North American (Mexico) chemical manufacturer of penta, and that manufacturer has stated to the industry that they plan to withdraw from the market in 2021. It is not known at this time if another penta chemical manufacturer will become available, therefore the future availability of utility poles treated with the penta wood preservative is uncertain at this time. Several treaters offer utility poles treated with penta.