The emissions of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD and PCDF) were assessed for wood impregnated with ammoniacal copper quaternary (ACQ) and copper boron azole (CBA). The two preservatives constitute the replacements for chromated copper arsenate (CCA) treatment, which is being phased out as a consequence of health concerns relating to arsenic and chromium compounds. The gaseous emission of PCDD/F from oxidative pyrolysis of CBA contained considerable amounts of PCDD/F of up to 7500 pg TE/Nm(3). A large increase was also observed for the gaseous emission from smoldering of CBA following the oxidative pyrolysis, where 570 pg TE/Nm(3) was detected. The ash residues of CBA remaining after the CBA emissions after oxidative pyrolysis and ensuing smoldering also showed significant propensity to yield PCDD and PCDF, resulting in 3200 ng TE/kg ash. In contrast, flaming combustion of the two treated timbers did not result in the emission of significant quantities of PCDD/F. The concentrations were quantified as 3.5 and 5.2 pg TE/Nm(3) for the ACQ and CBA timber samples, and indicate no reasonable increase over that resulting from similar combustion of untreated Pinus radiata, 3.7 pg TE/Nm(3). The smoldering of ACQ and CBA ash residues after flaming combustion generated PCDD/F, with the ashes containing 5.0 and 140 ng TE/kg ash, respectively. The increase in PCDD/F formation is discussed with respect to de novo formation in the ash and the influence Eof the wood preservatives.
Proceedings of the Combustion Institute Vol. 30, p. 1237-1243