There have been extensive discussions with the AWPA on the variability of retention results when the same lumber charge is sampled multiple times, and how this variability should influence the setting of requirements for conformance to retention specifications. AWPA Ul Standards specify minimum preservative retentions, with various M Standards specifying how material should be inspected at the treating plants and through third party agencies to satisfy these requirements. There have been reports of significant variability in analyzed retention results between internal plant and third party or other subsequent analyses, resulting in concern that using the current inspection procedures, some treated material may not be meeting the desired minimum retentions. The following paper provides information on: retention variability between individual boards within pilot plant and commercial treatment charges, the influence of wood density on these retentions, and how this variability can be expected to impact the accuracy and reproducibility ofcharge assays.
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