Wood preservation facilities, pentachlorophenol thermal: chapter F-1

1. Production and Use

Pentachlorophenol (PCP) was first used as a wood preservative in 1936 (1). The biological properties of PCP have resulted in its use as an antimicrobial agent in industrial cooling systems and papermaking, and as a fungicide in protein-based latex paints (2). Agriculture Canada restrictions in 1981 limited the use of PCP for preservation of outdoor wood products. PCP use by the thermal process (PCPT) depends primarily on the size of the utility pole and cross-arm markets: chromated copper arsenate (CCA) has partially replaced PCP in the utility pole market, and the PCP tie market has been converted to creosote/oil treatments, leading to a decline in use since 1981 (3). PCP pressure treatments and CCA have partially replaced thermal PCP in the utility pole market. In 1993, three thermal treatment plants operated in Canada. In 2012 there are still only three PCP facilities with thermal process in Canada (4). The design and operational practices for control of PCP at thermal facilities varies. Newer facility designs reflect an increased awareness of the need for chemical control. Older facilities may compensate for design limitations through operational controls. Detailed design and operating practices are highly individualized. Table 1 provides an overview of PCP use at Canadian thermal treatment facilities.

PCP is prepared by reacting chlorine with phenol in the presence of a catalyst at high temperatures. PCP was last manufactured in Canada in 1983. It is now obtained from only one of two U.S. manufacturers, who supply it in the form of solid blocks (907 kg/2000 lbs) or liquid solution. The petroleum oils used as carriers for PCP are purchased from Canadian sources.

PCP/oil mixtures are used for the thermal treatment of wood products such as telephone and electrical utility poles, as well as cross-arms. Thermal treatments for poles may be either full length or butt treatments only with just butt treatment currently being conducted in Canada. The impregnated PCP is retained by the wood, and its bio-effectiveness protects the wood against fungi and insects. In addition to functioning as a carrier of PCP, the oil also provides extra protection against moisture content changes, providing more wood stability and resistance to splitting. For utility pole use, it has the additional advantage of providing resistance to electrical currents and facilitating the climbing of poles by line personnel.

Page details

Date modified: