Frame and truss manufacturers and builders may be concerned about the quality of MGP graded pine produced from plantation areas affected by the recent fires. There are a number of lessons that have been learnt from other major pine salvage operations – the SA Mount Gambier fire of 1983, the QLD Beerburrum fires of 1994 and the Tumut fires of 2006 were the most significant. Salvage operations have included processing logs from standing burnt trees up to about 12 months post fire, placing logs in Lake Bonney in SA where logs continued to be processed for almost 10 years, and the use of water sprinklers on log dumps for more than 3 years.
At present, there are a group of experts with direct fire salvage and processing experience from previous fire events advising affected regions on the best way to keep the large volume of fire damaged plantation logs in good condition.
But do the fires affect the quality of MGP products cut from the stored, burnt salvaged logs? The short answer is NO! This is for several reasons. Firstly, the bark on the outside of a tree is an excellent insulator and protects the wood underneath from the worst of the high temperatures. Second, the wood just under the bark has its cells full of water that cannot exceed 1000 C until all the water boils off. This is less than the kiln temperatures used to dry the wood in routine operations. In practice, the very worst I have seen from intense Mount Gambier Ash Wednesday fires was that the outer 1-2cm of wood was drier than the interior wood and had to be batched to be dried separately because it was lower in moisture content. Furthermore, it should be noted that most of the outer 1-2cm of most logs end up as chips as the tapered logs get sawn.
Perhaps the only change that will occur to wood cut from salvage logs is that over time, we expect to see an increase in the amount of blue stain that is present. Blue stain occurs when a naturally occurring microbe consumes sugars in the wood cells. The stain does NOT affect structural properties. The effects on the wood are primarily visual. There is, however, a positive effect if blue stained wood is treated. It has higher preservative solution uptake than un-stained wood.
Further confidence in MGP products from fire affected salvage logs is provided by the grading and testing of the timber in the mills. 100% of timber is subjected to the grading process that predicts strength and stiffness from the attributes of the wood. As well as the grading process, approximately 80 -200 samples per day (dependent on the number of grades at each mill) are sampled and destructively tested to determine the strength and stiffness of the batches to ensure that the grading remains accurate. If fire was affecting the structural properties, it would be found immediately, and grading thresholds would be changed to ensure that the batch exceeded the properties required for the grade.
Most producers in Australia also have the entire grading process certified by the EWPAA. This involves detailed audits every 6 months of the grading process and quality systems in place at the mill. EWPAA auditors also review batches produced during the 6 months between audits. In addition, samples are taken from more than 50% of all production runs of the main size/grade (generally 90 x 35 MGP10) and tested in the NATA accredited Timber Testing Centre laboratory. This certification program is accredited by the Joint Australian and New Zealand Accreditation System (JAS-ANZ). Customers should note that some MGP products sawn from fire salvaged timber enters the supply chain nearly every year, as small to medium fire events in pine plantations are not uncommon around Australia, and these products have been subjected to the same testing protocols that will apply now.
So, customers of MGP products have every reason to be confident that the MGP timber delivered to them meets all the requirements of the grade and will perform the same as the wood from unburnt forest. The EWPAA certification is additional assurance that the producer has also met the strict product certification requirements of the EWPAA and that all properties of MGP are being monitored for every batch.
This article was written and provided by Andy McNaught, Technical Manager of Engineered Wood Products Association Australia