## 7 Results of Oak Thermal Degradation by Thermal Loading
Figure 11: _Cont._  
Figure 10: Temperature curve for oak wood samples at different distances (1D, 2D, and 3D) from the radiant heat source. The greatest weight loss was observed in spruce, which reached 18.83%. This result suggests that spruce wood is more vulnerable to heat and may undergo more significant decomposition [31]. During the measurement, sample 1S also recorded the highest temperature, reaching 491.3 \({}^{\circ}\)C. Compared to the other tested samples, the highest charred-layer thickness was observed in samples 1S and 1C. Conversely, the smallest weight loss was recorded in samples placed farthest from the radiant heat source. Specifically, cherry wood exhibited the smallest weight loss, at 2.42%. These results demonstrate the impact of distance from the heat source on the thermal degradation of wood. Based on data analysis  
Figure 11: Mutual comparison of temperature curves for wood samples from the radiant heat source: (**a**) at distance 0 mm (1S, 1 CS, 1C, and 1D); (**b**) at distance 12 mm (2S, 2 CS, 2C, and 2D); and (**c**) at distance 32 mm (3S, 3 CS, 3C, and 3D). in Excel (Figure 12), it can be concluded that as the distance from the source increases, the weight loss decreases linearly. The experiment also produced samples with a charred layer (Table 3). Visual observation reveals significant changes, which are also reflected in the quantified thickness of the charred layer. The lowest charred-layer thickness was recorded in samples 3 CS, 3C, and 3D, all showing a value of 0 mm. This issue was also addressed by [PERSON] et al. [60], who compared the thermal resistance of selected hardwoods and softwoods (spruce, fir, oak, and pine) under radiant heat exposure. In their experiment, samples were exposed to a thermal infrared emitter with a power of 1000 W for 600 s, at a distance of 30 mm. The criterion for evaluating the experiment was the relative weight loss of the tested samples. According to their results, oak samples demonstrated higher resistance to radiant heat effects and maintained a more intact shape after measurement. They observed a significant difference in weight loss for oak samples, as the weight loss occurred considerably later compared to softwoods. Upon comparing weight losses, oak samples demonstrated the lowest weight loss. These results are consistent with the measured values. The measured value for sample 1D indicates that oak was the second best-performing wood, with a weight loss of 11.07%. Additionally, the thickness of the charred layer was the smallest for all three oak samples. This suggests that wood density significantly influences resistance to thermal stress, with oak's higher density providing better resistance to thermal loads. Reference [71] also noted that the poorest results were observed in pine and spruce samples, which showed the greatest weight loss. They attribute this phenomenon to the high resin content. These samples also had the lowest density among all tested samples, aligning with the results of the experiment. Figure 12: Mutual comparison of mass loss wood samples from the various distances of radiant heat source. Legend: dark blue is spruce, light blue is red spruce, red is cherry, and green is oak. Spruce samples exhibited the greatest weight loss among all tested samples (Figure 12), a result which may be attributed to a combination of factors, such as their composition and structure [72]. Spruce wood naturally has a lower density [73], which may lead to greater susceptibility to thermal stress and subsequent weight loss. This observation is consistent with the charred-layer thickness, which was found to be greatest in the spruce samples. Red spruce showed the lowest weight loss (Figure 10), indicating its resistance to environmental factors such as moisture [74]. [PERSON] [75] conducted a similar experiment with samples of pine, spruce, fir, and larch, with a moisture content of 8 \(\pm\) 2% and dimensions of 10 \(\times\) 12 \(\times\) 150 mm. An electromagnetic radiation source was used as the initiator.