## 3 Results and Analyses
(**A**) Mass loss of specimens TP\(-\)R and TP\(-\)T; (**B**) Mass loss rate of specimens TP\(-\)R and TP\(-\)T; (**C**) Mass loss of specimens TF\(-\)R and TF\(-\)T; (**D**) Mass loss rate of specimens TF\(-\)R and TF\(-\)T.  
the TF-T specimen started to increase significantly from time 180 s until the flame was extinguished at time 600 s. On the other hand, the TF-R specimen's mass loss rate indicated a predominantly decreasing trend and started to increase slightly at time 400 s. The TP-R specimens reached the highest mass loss rate of 0.207%-s\({}^{-1}\) at 600 s, followed by the TP-T specimens (0.196%) at 470 s, the TF-T specimens (0.135%) at 390 s, and, finally, the TF-R specimens (0.082%) at 30 s.  
The dependence of the total mass loss of the thermowood on the type of material in terms of the intended use and on the side of the specimen to which the flame was applied is statistically analysed in Table 2. The ANOVA test results indicated statistically significant differences between all specimen groups concerning mass loss. Specimens exposed to flame on the radial side were statistically different from specimens exposed to flame on the tangential side; \(p\)-value = 0.095. Significant dependence related to mass loss was confirmed between the base prism and floor specimens, \(p\) = 0.0025. The ratio of the maximum value of the mass loss rate at the first peak and the time to reach this value (hereafter referred to as the fire spread rate) was highest for the TF-T specimens, with a significantly higher difference compared with the other specimens. The TP-T specimens demonstrated the second-highest \(R_{\beta}\) value. The TP-R and TF-R specimens had similar values (Table 3). All specimens reached the first peak of the mass loss rate in the same time of the 30 s. Based on the above results, it can be assumed that the thermowood specimens will have the highest fire spread rate on the tangential side, regardless of the type of material used (prism, floor). To further assess the effect of heat treatment on the mass loss and the mass loss rate, we need to consider which side will be exposed to the flame. Therefore, we were further concerned with monitoring the parameters for specimens exposed to the flame from the radial side. In this case, the mass loss and the mass loss rate for the thermally treated timber from the prism (TP-R) were significantly different for the thermally treated timber from the floor (TF-R) and the untreated timber (U-R) (Figure 6). The TF-R and U-R specimens demonstrated nearly identical mass loss and mass loss rate behaviour. For the mass loss parameter, the TP-R specimens were statistically significantly different from the U-R specimens (\(p\) = 0.01), but the TF-R specimens were not different from the U-R specimens (\(p\) = 0.31) (Tables 4 and 5). \begin{table}
\begin{tabular}{l c c c c c c} \hline  & **Df** & **Sum Sq** & **Mean Sq** & **F Value** & **Pr (\textgreater{})F** & **Influence** \\ \hline
**Exposed side** & 1 & 150.0 & 150.0 & 3.596 & 0.09451 &. \\ \hline
**Density** & 1 & 779.8 & 779.8 & 18.688 & 0.00254 & ** \\ \hline
**Exposed side:** & 1 & 243.4 & 243.4 & 5.833 & 0.04217 & * \\
**Density** & 1 & 243.4 & 243.4 & 5.833 & 0.04217 & * \\ \hline Residuals & 8 & 333.8 & 41.7 & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Multivariate analysis of variance (ANOVA) of mass loss of thermowood specimens TP-R, TP-T, TF-R, TF-T at 780 s. \begin{table}
\begin{tabular}{l c c c c c} \hline
**Specimens** & **TP\(-\)R** & **TP\(-\)T** & **TF\(-\)R** & **TF\(-\)T** & **U\(-\)R** \\ \hline
**Rfs** & 0.002736 & 0.003077 & 0.002749 & 0.003546 & 0.00288 \\ \hline \end{tabular}
\end{table} 
Table 3: Proportion of the maximum value of the first peak mass loss rate and the time to reach this. The above results demonstrate the differences in mass loss and mass loss rate of individual specimens. In particular, the TP-R and TP-T (thermowood prisms) specimens differed significantly from the other specimens.