Chemonite.ACZA. A Diverse Industrial Wood Preservative. Randall T. Baileys. Technical Services Representative

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Chemonite.ACZA A Diverse Industrial Wood Preservative by Randall T. Baileys Technical Services Representative Arch Wood Protection Conley, Georgia USA Presented to the Canadian Wood Preservers Association
Chemonite.ACZA A Diverse Industrial Wood Preservative by Randall T. Baileys Technical Services Representative Arch Wood Protection Conley, Georgia USA Presented to the Canadian Wood Preservers Association October 19, Chemonite.ACZA A Diverse Industrial Wood Preservative ABSTRACT: Chemonite is a registered trademark of Arch Wood Protection for the wood preservative first developed and known as ACA, then later reformulated and changed to its present form, ACZA. This ammonia based waterborne preservative has features which are attractive to consider in any selection process involving treatment of Douglas-fir round or sawn material along with any other refractory softwood species of wood common to the Western United States and Canada. The information presented is intended to describe the various specific attributes of ACZA which set it apart from other waterborne wood treating preservatives available to design architects, engineers, professional building contractors and others having a particular interest in well-established structural integrity and service performance of treated wood products. It will bring additional attributes relative to the treatment process and key differences noted from other waterborne systems, then finally, the treated product attributes which provide the diversity to allow Chemonite.ACZA to stand alone for many Industrial treated wood product applications. The paper references provide documents and studies available to support the choice of Chemonite.ACZA, including the environmental and safety aspects of chemical fixation and leach resistance, improved processing techniques available through Best Management Practices (BMP s), protection from Formosan termites, carpenter ants and woodpecker attack as well as from other biological organisms. Supporting information concerning corrosion, climb-ability and conductivity are also provided along with the most recent updates in AWPA UCS Standards. Key words: Wood Preservative, ACA, ACZA, American Wood Protection Association, Canadian Standards Association, Canadian Wood Preservation Association, Ammoniacal, Best Management Practices, Carpenter Ant, Chemonite, Climb-ability, Coastal Douglas-fir, Conductivity, Corrosion, Fixation, Formosan Termite, Industrial Wood Preservatives, Leachability, Nail-withdrawal, Refractory species, Pressure Treatment, Sterilization, Use Category System, Utility Pole, Woodpecker. INTRODUCTION The purpose of this presentation is to acquaint those in the commercial, industrial and heavy construction industries with the preservative known as Ammoniacal Copper Zinc Arsenate (ACZA or Chemonite ) and characteristics of the wood treated with this waterborne preservative. The bulk of the information provided is relative to Coastal Douglas-fir, a thick-heartwood specie known to be difficult to treat with other waterborne or oil-type preservative systems. Chemonite was specifically formulated to attain penetration into the Western refractory softwood species of woods providing a waterborne treatment capable of consistently meeting the requirements then specified in the American Wood-Preservers Association C-Standards, the Canadian Standards Association and many Building Codes as well. The original formulation of Chemonite.ACZA was known as ACA (Ammoniacal Copper Arsenate), developed and patented in the 1920 s at the University of California, then first used commercially in This preservative system experienced nearly 50 years of effective treating before a change in formulation was introduced in 1983 by J.H. Baxter & Co., the previous owner of the registered trademark preservative. The new formulation replaced half of the arsenic pentoxide with zinc oxide and the resulting preservative was recognized for environmental advantages over the previous formulation. Chemonite II, now known as Chemonite.ACZA, became a registered pesticide with the U.S. EPA and PMRA in Canada which continues to be successfully used for pressure treating beams, timbers, poles, piling, lumber, plywood, glue laminated timbers and other engineered wood products (17). 2 Chemonite.ACZA is a blend of active ingredients in a 2:1:1 ratio of copper oxide, zinc oxide and arsenic pentoxide, respectively. Historically the copper and zinc are supplied in a dry powder while the arsenic pent-oxide is liquid arsenic acid. These high quality raw materials are dissolved in aqua ammonia with the addition of ammonium bicarbonate to dissolve or burn the metals to metallic oxides in a reduction reaction. The resulting preservative provides exceptionally consistent penetration, significantly reduced surface residue, reduced corrosion properties, enhanced product appearance and improved leach resistance after fixation of the chemical takes place in the wood (23). The AWPA Standard P for Waterborne Preservatives defines both generic formulations for Chemonite (2); however, in 1999 the Canadian Institute of Treated Wood and Pest Management Regulatory Authority (PMRA) of Canada approved the use of ACZA in Canada (7) replacing ACA, and as a result, the AWPA P-4 Subcommittee having jurisdiction over the P5 Standard identified for removal without prejudice due to lack of use, the preservative ACA from the 2003 Book of Standards. At the same time, the transition into the Use Category System was initiated and is now complete with ACZA presented as a single, stand-alone preservative listed in the 2010 American Wood Protection Association Book of Standards as P22-10(3). PROPERTIES OF CHEMONITE.ACZA There are some definitive differences in the Chemonite treating process which separate it from other waterborne preservative systems. Some of these factors significantly influence the service performance of the treated product and should be taken into consideration when selecting and specifying a preservative for treatment of Coastal Douglas fir or other thin-sapwood refractory species (5). Sterilization ACZA has the ability to withstand elevated temperatures during processing and allows for treatment of green or wood seasoned before treatment. Steam conditioning of Douglas-fir poles or piling prior to treatment at allowable temperatures up to 240 F(120 C) for up to 8 hours as per ANSI 05.1 and AWPA T1-10 Section D (Table D2. Processing Limitations, Steam Conditioning for poles) and in Section E Round Timber Piles, which can be very effective in eliminating incipient decay. Preservative temperatures during the Chemonite pressure cycle normally reach 150 F (65 C), the maximum allowed by AWPA. The resulting temperature combination provides sterilization during treatment, even in large cross sectional dimension Douglas-fir materials. In addition, a Best Management Practice (BMP) for ACZA includes the use of an aqua-ammonia steaming cycle following the after-press vacuum which increases solution recovery and reduces preservative drips. This cycle subjects the treated material to ammonia vapor in the retort heated to F (88-94 C), thereby reducing surface deposits while improving fixation of chemical in the wood material with increased ammonia off-gassing taking place inside the treatment cylinder thereby lowering vapor loss to air. Fixation of chemical The recent concern for potential exposure to arsenic from treated wood has raised many questions about the safety of arsenical containing preservative treated wood. Chemical fixation and leaching are terms in the wood-treating industry related to this concern. Fixation is defined in the AWPA Book of Standards Glossary as A physical or chemical process whereby a wood preservative system is rendered leach resistant in both water and soil applications, such that the active ingredient(s) maintain fungal/insecticidal efficacy. Although it is not stated, the reference to maintaining efficacy of protection can only be possible when the active ingredient(s) are not leached from the wood in significant quantity over the exposure time. The associated term leaching is defined as The migration from wood of preservative components into surrounding environment by the movement of water (1). 3 Fixation is a property of waterborne treating chemicals that has been studied and evaluated with various levels of understanding. Many earlier studies define specific mechanisms involved in making the once water soluble chemicals become attached to the wood substance or complex with other components, thereby being insoluble in water during service exposure (23). The ACZA preservative system has some chemical fixation traits that differ from the processes associated with acid-based formulations such as CCA (chromate copper arsenate). Lebow and Morrell (14) found that during the fixation of ACZA, as ammonia levels decreased by off-gassing, precipitation of zinc arsenate occurred first. The reaction among these components may be the basis for improved arsenic fixation reported in ACZA, and zinc is normally the most leach resistant component detected in the evaluations. Copper is thought to be more directly involved with bonding reactions with the wood, which may occur at a slower rate. The ammoniacal systems use ammonia in water as the carrier to move the active ingredients throughout the cellular structure of the wood. This movement is necessary for the metallic ions to locate attachment or bonding sites in the wood (31). More ions in the matrix (higher chemical retention) make it more difficult to locate an unoccupied site for the ion to fix. Processing methods reducing the immediate loss of ammonia after treatment, such as enclosure or wrapping treated material, or increasing the ammonia available in the wood such as aqua ammonia steaming, have been successful in improving the fixation of the chemical to the wood in ACZA (16). Analytical procedures are now being developed and evaluated that will allow testing material for fixation, with more consistent and meaningful results than previously were available. These analytical tests are based on some of the theories on fixation from earlier studies (10). Fixation periods are directly related to the retention level of waterborne treatments, therefore the higher the retention of chemical in the wood, the longer it takes to fix the chemical to an equivalent level. Further reports have also shown the actual fixation process for ACZA is not directly related to drying the wood for removal of water. This was previously thought to be a key factor for fixation of all waterborne preservative systems. The ACZA process is more directly related to the off-gassing of ammonia which stabilizes metals in the wood by allowing them to form precipitates, or come out of solution and become insoluble compounds. The preservative retention level continues to affect this process, becoming much more complex when the retention is above 1.0 pcf of active ingredient. As a general rule, these higher retention materials require longer fixation periods (10, 26), but are not common retention levels for materials used above or in ground contact applications. Copper oxide is more water soluble and has been identified as the last component in many waterborne copper-based preservatives to become fixed, allowing it to be used as an indicator to determine the level of fixation obtained. Methods under development to determine chemical fixation should be of help in defining the specification necessary for material to be considered adequately fixed for shipment. The more fixed a chemical becomes, the less potential it has for leaching from wood when exposed to water and/or weathering while in service. This is a critical parameter for the future use of waterborne chemical treatment and encourages the use of BMP s by responsible wood-preserving companies (19). Leachability ACZA leaching was studied and compared to the original ACA formulation by Best and Coleman (5). Their results indicated a significant reduction in the leaching of not only arsenic but copper as well, along with reduced leaching of all components at the higher retention levels ( pcf or kg/m 3 ). Therefore, even though the fixation period is longer for higher retentions, the resulting fixation may potentially be more stable as indicated by the lower percentage of chemical leached. Analytical work is continuing to be conducted and reported by Oregon State University on soil samples to determine the amount of copper, arsenic and zinc found in soil around utility poles located in Florida, Virginia, New York and Pennsylvania to include various soil compositions. A multiple sampling grid surrounding the poles was used to provide information at distances and depths in comparison with unaffected control soils and a wood 4 sample included for each pole in the test. These data will assist in determining the potential for leaching from ACZA treated poles. An added portion of this study will evaluate samples from retaining walls and highway guardrail posts and soils in their immediate areas (18, 4). Safety The issues of fixation and leachability address environmental exposure concerns of the treated wood product during its intended use, but the human safety element created by exposure to the material must also be considered. This brief summary will approach those factors having the most direct relationship without going into intricate detail associated with the supporting information. It is important to understand the three possible routes of exposure which humans have to any chemical. These include inhalation, ingestion or absorption through the skin. Before any chemical can be a threat to human health or have toxic effects, it must enter the body. Test results at the University of California in Davis by Dr. Peoples (20) show arsenic oxides in treated wood cannot be absorbed through the skin. This eliminates one such avenue for exposure. The inhalation route of entry is confined to inhaling sawdust, surface residue or dust while working with the treated wood because these oxides are also not volatile. This means they do not evaporate into the air at normal ambient temperatures. Eating, using tobacco products or drinking without washing hands prior to performing these activities increases the risk of ingesting sawdust or surface residues from the wood and should be avoided in any circumstances. Dr. Peoples also showed that bodily fluids could only leach approximately half of the metal oxides entering the body by ingestion. The human body routinely disposes of small amounts of arsenic it absorbs from natural sources such as drinking water, seafood, and red wine. If there were small amounts ingested from treated wood, it would be eliminated from the body in this same way (21). The best protection from any exposure to wood treating chemicals is offered by following personal hygiene and safety precautions. These include using gloves to prevent splinters and contact with surface dust, wearing dust masks and eye protection when machining treated wood, and always washing before eating, drinking or using tobacco products. These are the same precautions recommended for working with untreated wood, and can greatly reduce the potential of chemical exposure from treated wood. Another safety precaution is that treated wood of any kind should not be burned as firewood in a residence or outdoor fire. Registered pesticides must be reviewed on a regular basis for re-registration with the U.S. EPA or PMRA in Canada. A requirement of this process includes data submission to confirm the safety of the treated wood. There have been four epidemiological studies on workers at arsenical wood preserving plants and carpenters extensively using treated wood. Even in these high occupational exposures there are no long-term effects from working with the preservatives or arsenical treated wood. ACZA-treated wood is a safe product and does not require any special protective clothing or equipment except the normal safety precautions used with any wood product, treated or not. The formulation change for Chemonite has made a very significant effect on the safety of ACZA in the environment and for users of the treated product for several reasons. First of all the amount of the more toxic component, arsenic, was reduced in half by replacing it with zinc (a less toxic component). Therefore, the overall toxic level of the preservative system is reduced. Zinc also acts to prevent the uptake of copper by the body if it is ingested, offering an added margin of safety. The addition of zinc to the formulation improves the fixation of arsenic by forming a less Soluble precipitate with zinc. Also, combined with the relatively low loss of copper and zinc from treated wood, this addition of zinc presents the advantage of reducing potential environmental interaction by leaching (26). The scientific evidence available supports ACZA treated wood as a very safe product to the environment and humans who have contact with it. 5 Other attributes Corrosion: The recommendation has always been to use hot-dipped galvanized fasteners or hardware when in contact with ACZA treated wood. The basis for this is to have the galvanic coating sacrificed in order to afford protection to the rest of the metal over time. This creates a surface corrosion within the first year or two of service that may cause concern for those not familiar with this process. However, several tests have indicated this initial corrosion rate is not sustained over a long period of time and does not affect the long term strength, service life or performance of the hardware. Actual test data on bolts removed after 38 years of exposure in a Portland General Electric line outside of Portland, Oregon resulted in all but one sample meeting or exceeding the rated breaking strength for the bolt size. The one exception had test results at 98.5% of the rated strength value. Other accelerated and full-size corrosion tests indicate similar results with ACZA being significantly less corrosive than the earlier ACA formulation. These tests also indicate dry or materials having lower ammonia levels are less corrosive to the galvanizing coatings than freshly treated wood, thereby supporting the need to have wood undergo fixation before shipment or use (12, 28, 30). Note: Arch recommends the use of stainless steel in marine salt water or splash zones with ACZA treated wood as well as in other extremely corrosive conditions. Specific recommendations should be obtained from an informed source for acceptable types of hardware in these exposures. Conductivity: Electrical conductivity is an appropriate concern when selecting any material as a utility pole to carry electricity. A number of studies have been conducted to evaluate and understand this particular aspect of waterborne treated wood poles. Generally speaking, even untreated wood poles will conduct electrical current when levels of moisture are above the fiber saturation point. Testing of the metal oxides used in ACZA by applying voltage to compressed pellets of the dry powder indicate these components are nonconductive. Further testing has identified water or treating solutions are the more conductive elements in treated wood, therefore any freshly treated wood pole should be considered as hot for handling purposes. Conductivity drops in a similar fashion as treated and untreated wood undergoes drying, therefore the moisture content is the critical factor, not the treatment. There is also evidence of decreasing conductivity over the service life of ACZA poles. Poles dried below fiber saturation do not induce the same level of conductivity measured before drying took place when they are subsequently re-wetted. All test results show ACZA treatment does not create a shock hazard. Because there is no consistent field test method available to accurately predict if a safety hazard exists, it is recommended that under adverse conditions, ACZA or any wet pole, should be approached and handled as if it is electrically hot (13). Woodpecker resistance: There are utility companies in the
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