# Hazards Resulting from the Burning Wood Impregnated with Selected Chemical Compounds
## 4 Emission of Pollutants and Methods of Measurement
[64], based on the detailed pyrolysis of wood impregnated with CCA, found that, depending on the seasoning of such wood waste, there are two modes of arsenic release. CCA impregnated samples, dried for 21 days at room temperature, and ground to a particle size below 20 mesh, were pyrolysed under an N\({}_{2}\) atmosphere in the temperature range 135 to 500 \({}^{\circ}\)C, and in time from 0 to 60 min. In addition, part of the ground wood was annealed at 60 \({}^{\circ}\)C in order to achieve the complete conversion of arsenic compounds, leading to arsenic immobilisation in the wood [64]. Before the pyrolysis, it was confirmed that both of the wood samples contained the same amount of arsenic. The incorporation of CCA into the wood structure was accompanied by a reduction of Cr\({}^{+6}\) to Cr\({}^{+3}\), followed by a further reaction of reduced chromium with As\({}_{2}\)O\({}_{5}\). As a result of this reaction, the poorly soluble CrAsO\({}_{4}\) salt was formed [65; 66]. The described process was not gone through completely, and in seasoned wood some unreacted As\({}_{2}\)O\({}_{5}\) might have remained, which would have been converted to As\({}_{2}\)O\({}_{3}\) in the initial stage of pyrolysis [58]. In annealed wood, all of the arsenic is present in the form of CrAsO\({}_{4}\), decomposing into As\({}_{2}\)O\({}_{5}\), and reduced during pyrolysis to As\({}_{2}\)O\({}_{3}\), with its subsequent separation as As\({}_{4}\)O\({}_{6}\), at a temperature of about 400-500 \({}^{\circ}\)C. In order to reduce the release of arsenic during pyrolysis, CCA-impregnated wood should be carefully pyrolysed at temperatures around 300-350 \({}^{\circ}\)C only if the content of the unreacted arsenic compound is low. In the following years, CCA-impregnated wood utilisation methods were developed to reduce arsenic release through low-temperature pyrolysis [67; 68; 69], and by the incorporation of a sorbent compound [70]. [PERSON] et al. [71] found that the type of impregnation determines the method of combustion, including the burning time and the presence or absence of a flame or glow; thus, also the products of combustion. The wood test samples, which were prepared from rowan wood materials, were impregnated with Tanalith-E, Vacsol-Azure, Imersol-Aqua, and Boron compounds (Borax and Boric acid). The burning time ranged from 4.112 to 6.888 min. for samples impregnated in the sequence Vacsol Azure, Tanalith-E, Boricacid, Imersol Aqua, and Borax, and at a 3.110 min. burning time for the control samples. The highest combustion temperature was obtained for materials that were impregnated with Imersol Aqua (458.686 \({}^{\circ}\)C), and the lowest with Borax (439.023 \({}^{\circ}\)C). It was also found that boric acid reduced material losses during combustion, which indicates that boron impregnation increases the combustion temperature and provides additional fire resistance and safety [71]. The most effective preparations of refractory wood-based materials contain halogens. Thus, combustion can produce toxic and irritating gaseous products [34]. [PERSON] et al. [34] conducted research on the flammability and combustion of softwood treated with intunescent coatings that contained different ratios of industrial fillers, TiO\({}_{2}\) and Al(OH) \({}_{3}\), and/or bio-fillers, eggshells, and rice husk ash. The flame retardant effect of the samples is the result of the decomposition of the additives used, as in the case of Al(OH)\({}_{3}\), from which water vapour and Al\({}_{2}\)O\({}_{3}\) are released. The resulting aluminum trioxide contributes to the formation of a protective layer, promotes the oxidation of carbonising carbon, and increases the production of water vapour, carbon dioxide, and carbon monoxide. The amount of emissions varied, depending on the ingredients used in the coatings and the heat flux to which they were exposed [34].