# Study of the Influence of Heat Flow on the Time to Ignition of Spruce and Beech Wood
## 3 Results and Discussion
Subsequently, the Kruskal-Wallis test was conducted for the following variables: wood species, radiant panel power, distance, and heat flux, depending on the ignition time (Table 3 and Figure 8). Figure 8: Box plots—Multifactor Analysis of Variance (ANOVA) (95% confidence). Legend: Blue symbols represent time to ignition values for spruce, red symbols represent time to ignition values for beech. Figure 7: Dot plot: means and standard deviations, where each point on the graph represents 1 group of results. Based on the given data, it could already be proven that there was a difference between the time to ignition and distance (\(p\)-value = 0.0000, H = 37.51583) and time to ignition and heat flux (\(p\)-value = 0.0000, H = 37.69726). Multiple comparisons were then made between these variables (see Tables 4 and 5). Interpretation of the results can be based on the developed box plots (Figure 8). Figure 8 illustrates the nature of the obtained results. The first three columns represent the time to ignition values for a radiant panel power of 50 kW (labelled as 5) based on the distance of the sample from the panel. The remaining three columns present the results for a radiant panel power of 100 kW. In both cases, the trend of increasing ignition time with increasing distance from the source and decreasing heat flux intensity was confirmed. For samples of spruce at a power of 50 kW, a linear increase in time to ignition was observed (Figure 9). However, for beech samples, this dependence was observed, as ignition did not occur during the 10 min period at a distance of 200 mm. In both cases, the beech samples consistently exhibited higher time to ignition values. The red dot in the third column in Figure 8 represents a zero value, indicating that the beech samples at the distance of 100 mm with a heat flux of 64 kW\(\cdot\)m\({}^{-2}\) and a radiant panel power of 50 kW did not ignite (also indicated in Table 1). As observed from the obtained boxplots, the results exhibit a relatively wide dispersion (Figure 8 and Table 1). This phenomenon arises from the heterogeneity of the wood samples. This observation is further supported by the results obtained from measuring the density of the samples (shown in Table 1). The results for the time-to-ignition (TTI) of beech and spruce at a power of 100 kW, with heat fluxes of 92 and 62 kW\(\cdot\)m\({}^{-2}\) and distances of 100 and 150 mm (Figure 9), remain consistent. The TTI for beech is higher, but the differences are not high enough to establish a significant dependence, as indicated by the statistical analysis in Table 2. At the distance of 200 mm, flaming combustion did not occur within the 10 min time frame (Figures 10 and 11). An example of visual changes in spruce wood due to the effect of radiant heat at 5 kW power is shown in Figure 10, and that at 10 kW power is shown in Figure 11.  
[PERSON] [60] used the time to ignition for a piece of wet spruce and compared it to the time to ignition of dry wood to create a model. One of the reasons for their results is that the ignition temperature in the experiments (directly linked to the intercept heat flux) was constant for both the dry and the moist wood [13; 55; 61; 62; 63; 64]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **47—R:8.0000** & **62—R:54.750** & **64—R:28.500** & **74—R33.900** & **90—R:31.800** & **91—R:26.050** \\ \hline  
Figure 10: Visual observations of the influence of different heat fluxes on samples of spruce wood after burning at a radiant panel power of 5 kW. Legend: (**a**) image at 9 s with a heat flux of 91 kW\(\cdot\)m\({}^{-2}\), subsequently extinguished; (**b**) image of the burned sample exposed to a heat flux of 74 kW\(\cdot\)m\({}^{-2}\), burning with flames; (**c**) image represents the residue after flaming combustion under a heat flux of 64 kW\(\cdot\)m\({}^{-2}\) for 10 min. Figure 9: Example of the dependence of time to ignition on the distance of the sample from the heat source for spruce samples. Spruce is a very interesting wood material.