# Hazards Resulting from the Burning Wood Impregnated with Selected Chemical Compounds
## 4 Emission of Pollutants and Methods of Measurement
Inorganic salts, such as (NH\({}_{4}\))\({}_{2}\)HPO\({}_{4}\) and K\({}_{2}\)HPO\({}_{4}\), when wood is doped with these, reduce the intermolecular interactions and the interactions between the chains, and change their crystallinity. However, all of the ammonium salts are possible sources of ammonia [72]. A number of alternative impregnates have been developed for wood treatment: copper boron azide (CBA), alkaline copper quaternary salts (ACQS) [73], and chlorinated pesticides, which are analogues of the naturally occurring compound pyrethrum in certain plants of the aster family, especially in Chrysanthemum cineraria folium. Protective impregnates containing these substances are approved for use. However, studies on the effects of these preparations on the emissions of combustion products have shown that they can contribute to emissions dioxins and furans--see Figure 1.  
Fires in wood impregnated with copper-based preservatives can increase the amount of PCDD/F. The formation of PCDD and PCDF during fires is favoured by low-temperature combustion with limited oxygen supply. PCDD and PCDF can be formed by different reactions depending on the degree of copper oxidation and the combustion conditions, as illustrated in detail in Table 2.  
The catalytic effect of the Cu(II) ion in the form of CuO and CuCl\({}_{2}\) was the most thoroughly tested. The experimental results indicate that Cu(II) participates in various stages of PCDD/F formation. The effectiveness of CuCl\({}_{2}\) is attributed to the propensity of copper to oxygen coupling, which reduces the temperature of exothermic oxidation by the chlorination of carbon. The catalytic efficiency of a number of CuO, CuSO\({}_{4}\), Al\({}_{2}\)O\({}_{3}\), AlCl\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), NaCl, and KCl salts in the formation of C-Cl bonds, and the promotion of carbon degradation, were also tested [79]. It has been found that copper is constantly the most effective metal for catalysing the formation of PCDD and PCDF. The mechanism can be described as the formation of carbon-chlorine bonds, followed by the oxidation of the carbon matrix and volatilisation of chlorinated aromatics [80]. The effect of the deposition of CuO on silica to increase the contact surface, which can have a positive effect on the efficiency of chlorophenol pyrolysis [75], was tested in order to increase the catalytic activity. [PERSON] et al. [1] examined the effect of a substance, called Firetex, on improving the fire resistance of copper-impregnated materials, i.e., ACQ and CuA. Samples of fir (_Abiesnordnanniana subsp. \begin{table}
\begin{tabular}{l c c} \hline
**Reaction Type** & **Catalyst** & **Reference** \\ \hline Heterogeneous condensation of 3-chlorophenol, & & \\ 3_A_-dichlorophenol, and 2,4,6-trichlorophenol & & \\ \hline PCDD formation from 2-chlorophenol according to the & & \\ \begin{tabular}{l} Eley-Rideal mechanism, and PCDD/F formation according to \\ the Langmuir-Hinshelwood mechanism \\ \end{tabular} & Copper oxide & [75] \\ \hline Pyrolysis chlorophenols with PCDD and PCDF formation & CuO dispersed on silica surfaces & [75] \\ \hline Reaction of carbon, oxygen, and chlorine sources & Copper or iron ions & [76] \\ \hline Chlorination of dibenzofuran and dibenzo-p-dioxin vapour & & \\ \
\begin{tabular}{l} at temperatures between 200 and 400 \({}^{\circ}\)C \\ \end{tabular} & & \\ \hline
\begin{tabular}{l} Decllorination of higher homologues on heating under \\ oxygen-deficient conditions \\ \end{tabular} & CuO & [78] \\ \hline \end{tabular}
\end{table} 
Table 2: Reactions that result in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Figure 1: The effect of impregnates chemistry on dioxins and furans emissions. Bornmulleriana) were treated with copper azole (Tanalith E-3492) and copper-ammonium acid (ACQ) at a concentration of 2.4% and Firetex (FT) at a concentration of 100%, in five different samples, which were characterised by different ratios of individual impregnation agents.