Wood is a material widely used for construction purposes and – in some cases – it is the main element of building structures. In comparison with other materials, wood has a number of advantages, such as lightness, strength, resistance to impacts and vibration, simplicity in terms of processing and etc. However, one of the largest drawbacks of wood is flammability. Charring of wooden structures is the most apparent feature of combustion in case of fire in wooden buildings or buildings made of wooden structures. This property is important in identifying causes of fire; therefore it is necessary to relate charring of wooden structures with certain significant effects of fire, such as its duration or temperature. The article addresses the wood characteristics that impact on combustion and charring. It describes test methods and properties of wood samples under research. Research of charring rate of natural softwood and hardwood as a function of heating time, and regressive analysis of data were carried out. Empiric equations were derived. The calorific value of carbon residue resulting in different temperatures was determined in accordance with LST EN ISO 1716. Thermographic research of oak and pine wood was carried out in different gaseous environments. The research results were summarised in the form of conclusions.

Abstract. Wood is a material widely used for construction purposes and having quite a number of advantages. However, one of the major drawbacks of wood are its flammability. in case of fire in wooden buildings or constructions made of timber structures, the most noticeable feature of combustion is charring these structures. this property is important for identifying the cause of a fire. therefore, it is necessary to relate charring timber structures with certain significant effects of fire such as its duration or temperature. it is also particularly important to identify whether timber has been treated with fire retardant solutions before the fire break-out. the values of electrical capacitance and conductivity for the media obtained from char resulting from natural wood and that treated with fire retardant solutions and dispersed in distilled water depending on heating time have been determined. Moreover, it has been stated that the electric conductivity of char resulting from natural wood is 100 times lower, and the electrical capacitance of such char is 1000 lower than those resulting from treated wood. the regression analysis of the obtained data has been performed. the empirical equations have been derived. the results of the conducted research have been summarised. priority has been given to the application of the method evaluating electrical conductivity.

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This article describes equations derived to predict the duration of local pyrolytic charring under standard fire conditions. The equations consist of five variables: electrical capacity, electrical conductivity, calorific value, depth and rate of char. The equations are split up into two groups: one for the formation of non-impregnated carbonaceous residue, and one for impregnated carbonaceous residue during pyrolysis. This means that before predicting the local duration of charring, it is necessary to determine whether the wood has been impregnated with a fire retardant solution before the fire. Electrical conductivity and electrical capacity measurement methods were used for this purpose. The temperature of standard fire local exposure is calculated by predicting the duration of local pyrolytic charring according to the standard temperature and the time dependence of fire.