## 3 Results and Discussion
These differences are due to the concentration of oxygen of the samples, especially regarding the Cb1-75 sample[PERSON]  
Figure 4: Differential scanning calorimetry (DSC) curves. Figure 3: Oxygen atmosphere TG and DTG curves. Figure 2: Air atmosphere TG and DTG curves. These differences in composition can also be seen in the shapes of DTG curves, as the peaks of these curves represent the volatilization of light and heavy volatiles. It means that two different stages took place during the process: Devolatilization of light volatiles and devolatilization of heavy volatiles. Figure 3 shows those different peaks more clearly, and also the stages of the process. DSC results (Figure 4) also show those different stages: The more separated were the peaks in DTG curves, the more pronounced was the change of slope seen in DSC curves. The apparent activation energy has been calculated using TGA performed with oxygen flow results, as the self-ignition risk (outlined below) is determined by using [PERSON]E_{a}\) and characteristic temperature, only available when using oxygen flow. [PERSON] et al. [47] compile a self-ignition risk classification depending on the apparent activation energy and the characteristic temperature, classifying the risk into four different categories: Low (green), medium (yellow), high (orange), very high (red)[PERSON] The obtained activation energy results were in between the 57 and 86 kJ/mol range. Charcoal samples presented higher activation energies followed by dog food. The \(E_{a}\) values obtained for biomasses were similar to [PERSON] et al. [47] results. The same conclusion for biomasses was obtained: It is easy for the biomasses to start a self-heating process, but it does not usually succeed, due to their composition [48]. Figure 5 shows a self-ignition chart, where biomasses and dog food present a high risk of self-ignition and charcoal samples low risk. This result agrees with the obtained data from TGA seen in Table 3: Biomass requires higher temperatures for self-heating than charcoal, however biomass composition usually suffocates the process, while charcoal feeds it. On the other hand, charcoal samples presented a smaller particle size, and as said before, biomass dust has different and not uniform shapes. This means that, even if charcoal is placed at the low self-ignition risk zone, its composition and particle size contributes to self-heating process, as seen in N4.2 test results. Biomass may begin the process with lower temperatures, but the available surface (related to the shape) and particle size interfere with the propagation of the process, sometimes even inhibiting it. Gas emission analysis has been carried out for all samples for two or three different particle sizes to see if there is a significant change in the initial gas emission temperature (IGET) as the granulometry changes. The gas analyzer provides the volumetric percentage of CO\({}_{2}\) and volumetric ppm\({}_{\rm v}\) (mL/m\({}^{3}\)) of CO, but even with different metrics, the procedure explained before for the temperature interval of initial emissions is valid. Figure 5: Self-ignition risk. The obtained results for the gas emission interval temperature are shown in Table 4. It can be noticed that the greater the particle sizes of the sample, the higher the temperature at which gas combustion-related emissions start in most of the samples. It means that coarse samples produce combustion-related gases at higher temperatures; in other words, granulometry affects combustion. It was also noticed that CO emissions have a lower range of temperatures than CO\({}_{2}\), which means that the CO emissions are produced before CO\({}_{2}\). It was noticed that great differences were produced between coarse and fine samples, but not so much between intermediate (<1 mm) and fine samples (<75 \(\upmu\)m). This method for gas emission evaluation does not show precisely enough the IGET, but a range, making it difficult to see the differences between coarse and fine particle size in some of the samples.