# Hazards Resulting from the Burning Wood Impregnated with Selected Chemical Compounds
## 2 Chemism of Wooden Materials
An effective flame retardant must have significant ignition resistance, contribute to reducing the intensity of combustion, and reduce the rate of smoke generation; and, combustion products should have as low a toxicity as possible. The features and appearance have to be suitable for the area of application and should not significantly affect the cost of the product [1; 25; 26]. Substances, such as ammonia salts, phosphorus, and boron compounds, are added to reduce the flammability of wood. Additives are implemented to change the mechanism of the pyrolysis process. Cellulose, under ideal conditions, decomposes into coal and water, and the addition of the appropriate agents lowers flammability by reducing the amount of burning pyrolysis products, thereby reducing the amount of heat released by the product. The additives react with the C6 cellulose hydroxyl group, which leads to the formation of a C5 = C6 double bond. Reactions occur through dehydration or esterification processes. Flame retardants can also slow down pyrolysis reactions and stabilise the chemical structures of wood against decomposition, such as aluminium sulphate, which, when added to wood, forms bonds between the cellulose molecules at elevated temperatures, thus preventing thermal decomposition [1; 27]. [PERSON] et al. [28] tested, for fire properties, i.e., the time to the onset of ignition, the time to the onset of glowing, the back-darkening time, the back-holing time, the burnt area, and the weight loss, involving samples of beech wood impregnated with graphene or nano-wollastonite (NW), using water-based paint. The research was conducted for improving the effects of graphene on the times to the onset of ignition and glowing. Graphene is characterised by a very low propensity to react with oxygen, and high and low thermal conductivity in the plane and cross-section. Thus, graphene has great potential for use as a flame retardant in solid wood species [28]. It should be noted that, depending on the chemical impregnation, we produce a different result in relation to the individual properties of wood and wood-like materials, including flammability, and even the combustion process itself. Paraffin, styrene, methyl methacrylate, and isocyanate, all materials that increase dimensional stability and improve hydrophobic efficiency, affect the flammability of wooden products, resulting in an enhancement to this parameter [1; 29; 30]. Impregnates, such as TiO\({}_{2}\), WO\({}_{3}\), or CaSiO\({}_{3}\), penetrate the structure of the wood and fill the pores and areolate pits, which affects both the amount of water absorbed in the equilibrium state and the kinetics of water sorption [31]. However, it should be added that fire-resistant chemicals have some negative impact on the physical and mechanical properties of wood materials [1; 29]. One of the substances used to impregnate wood is creosote, a mixture made of coal tar, consisting of inter alia, compounds from the group of phenols, cresols, and xylenols, in various ratios, depending on the production process used [32]. Creosote is commonly used in railway factories and utility poles. Copper particles that are found in impregnating agents, such as Micronised Copper Azole (MCA) and Micronised Copper Quaternary (MCQ), are so small that they fill small holes in the wood structure, and accumulate in the wood, and do not chemically bind [33]. Research conducted by [PERSON] et al. [33] showed that MCA-treated wood contained copper, primarily in the form of copper carbonate. However, it might also be present in other forms, including organocopper complexes, or in the form of particles of varying sizes [33], which affects their chemical and biological activity. Alternatives to chemicals that are used to reduce the flammability of wood include natural and environmentally friendly materials, industrial by-products, and agricultural and food waste.