CCA-Treated Timber - Despatch from the Timber Treatment Plant

CCA is a well-established water-borne preservative used to protect timber in service from all major biodeteriogens, including decay fungi, wood boring insects, termites, and marine borers. It is widely used in Australia to treat an extensive range of commodities, from poles and piles to garden furniture and fencing.

In Australia CCA preservative must conform to the Australian Standard AS1604.1-2000 Specification for preservative treatment. Part 1: Sawn and round timber, with the specifications for the main elements as shown in the box.

CCA is designed so that the copper, chromium, and arsenic react with each other and with the wood structure to become fixed as insoluble compounds. The fixation mechanism is dependent upon such factors as temperature, pH, relative humidity, and, most importantly, time. The treatment plant must take into account these factors to ensure that the chemicals are fully reacted and none of them remain unfixed in or on the surface of the timber. Such good practice minimises the risk of the elements leaching out of the timber when it enters service. The treated timber should not be allowed to leave the treatment plant yard until the CCA is well fixed.

It is very important to ensure that only fixed, surface-dry timber is delivered to the customer. As a first step in achieving this, Australia Standard AS/NZS 2843:2000. Timber preservation and plant safety code requires that CCA-treated timber be held on the drip pad for at least 48 hours (this could be longer in cooler climates). Good practice would then be to hold the drip-free treated stock in the yard for not less than 2 weeks before despatching it to the customer. This will ensure all fixation has been completed and no free preservative solution remains in or on the timber. Note that accelerated fixation processes may be used to reduce the total holding time.

Reference sources:

National Occupational Health & Safety Commission Code of Practice & Guidance Note for the Safe Handling of Timber Preservatives and Treated Timber (1989)

ANZECC Guidelines for CCA Timber Preservation Plants (1996)

AS/NZS 2843:2000 Timber Preservation Plant Safety Code 

WorkCover Authority - Investigation into the Safe Handling of CCA Treated Power Poles (1998)