# Study of the Influence of Heat Flow on the Time to Ignition of Spruce and Beech Wood
## 2 Materials and Methods  
### Materials  
For the experimental verification, samples of spruce wood (_Picea abies_ L.) and beech wood (_Fagus sylavatia_ L.) were selected. These types of wood are among those that are commonly used in Slovakia's industrial sector [41], with beech representing hardwood and spruce representing softwood.  
Beech wood (_Picea abies_ L.) exhibits relatively high bending strength, impact toughness, and compressive strength. Due to its neutral appearance in its natural state, it can be easily colour treated on the surface. Among the advantages of its processing are its excellent ability to absorb impregnating coatings and stains, good density, hardness, and strength, flexibility that is ideal for bending, and affordability.  
Spruce wood (_Fagus sylavatia_ L.) is yellowish to yellow-brown, shiny, and has no heartwood colouring, making it generally very lightweight. Due to its prevalence as the second most common species in Slovak forests and its favourable physical and mechanical properties, spruce wood is an exceptionally important raw material for our industry.  
The wood samples were cut crosswise through the growth rings using a band saw. The prepared samples had a square shape with a side length of 165 mm and a thickness of 25 mm (Figure 1a,b).  
Surface treatment of the boards was performed by planing (with a combined wood-working machine Woodster C6 06, Woodster GmbH, Ichenhausen, Germany). Surface roughness is one of the factors influencing the ignition of samples [42]. The average density of the tested spruce wood samples was 422.9 kg\(\cdot\)m\({}^{-3}\) and beech wood was 697.2 kg\(\cdot\)m\({}^{-3}\). The determination was carried out in accordance with the standard STN EN 323:1996 [43]. The measured wood density results correspond to the wood density reported by the authors [PERSON] et al. [44] and [PERSON] et al. [45]. The variation in densities among individual wood samples depends on factors such as moisture content, position within the tree, tree age, and growth rate [46; 47; 48] (Table 1).  
Wood is a hygroscopic material in relation to the surrounding environment, capable of absorbing or releasing water in both liquid and gaseous states and changing its moisture content according to the humidity of the surrounding environment [49; 50]. Determination of the moisture content of the wood was carried out in accordance with the standard EN 322:1996 [51]. Spruce wood (_Picea excelsa_ L.) had an average moisture content of 6.4 \(\pm\) 0.5%, while beech wood (_Fagus silvatica_ L.) had a moisture content of 6.3 \(\pm\) 0.5%. Moisture content influences the time to ignition; as moisture content increases, more heat is required for the initial drying process and subsequent thermal degradation [52]. Moisture content corresponded to the moisture in the environment and was very similar between these samples.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Beech** & **Spruce** \\  & _Fagus sylvatica_**L.** & _Picea abies_**L. KARST.** \\ \hline Density (kg\(\cdot\)m\({}^{-3}\)) & 697.2 & 422.9 \\ Moisture (\%) & 6.4 \(\pm\) 0.5 & 6.3 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical parameters of samples.  
Figure 1: (a) Test sample of spruce wood; (b) test sample of beech wood.