## 3 Results and Discussion
In this figure, it is possible to see the two possible results from the test: Positive (when the temperature rises) and negative (when only reaches just the oven temperature or in case the sample temperature surpasses less than 60 K the oven temperature). Charcoal brand 2 presented results more susceptible to self-heating, as only the coarse charcoal did not increase its temperature over 140 \({}^{\circ}\)C of the oven, while the other two sizes reached 400 \({}^{\circ}\)C--the temperature at which the thermal signal register gets saturated--in the first step of the experiment. The other sample (charcoal brand 1) only raised its temperature over the oven temperature when tested in particle sizes lower than 75 \(\upmu\)m. As mentioned, the figure plots the first step of the experiment when  
Figure 1: United Nations N4.2 Test for charcoal. the sample is inside a 100 mm side cubic basket at 140 \({}^{\circ}\)C, so further tests were carried out in other to fulfill the whole procedure. Charcoal samples with particle sizes lower than 75 \(\upmu\)m were exempt from classification only if transported in packages smaller than 3 m\({}^{3}\), and so was Cb2-1. As it has been said, the N4.2 test provides basic information about self-heating and requires further studies and literature data to fully assess the process. The results obtained in this test can be contrasted with data previously obtained [46] for the self-ignition temperature (SIT) of wheat dust, whose composition and particle size are similar. Those data showed that when testing a 1.5 L basket the SIT turned to be greater than 152.5 \({}^{\circ}\)C. As N4.2 oven temperature is 140 \({}^{\circ}\)C, self-ignition will not be produced, and a negative result was obtained WS-1 and WS-75 samples. The same referenced paper presents SIT for different coals (also dust), and all but one, have temperatures equal or lower than 140 \({}^{\circ}\)C, that fit the positive result of the N4.2 test for the charcoal samples. The thermogravimetry and differential scanning calorimetric analyses can only be performed with fine particle size, as the crucible's volume is 70 \(\upmu\)L. The samples tested were those with particle sizes lower than 75 \(\upmu\)m (except for dog food, whose smallest particle size is \(<\)1 mm). Even no difference between granulometric effects can be seen using those analyses; it provides information regarding self-heating and self-ignition processes: It defines the main kinetic parameters of the materials, such as the apparent activation energy (\(E_{a}\)), induction temperature when using air (\(IT_{air}\)) and oxygen flow (\(IT_{oxygen}\)), characteristic temperature (\(T_{char}\)), temperature of maximum weight loss (\(MLT\)), temperature of change of slope (\(CST\)), initial temperature of the exothermic reaction (\(IET\)), and final temperature of the exothermic reaction (\(FET\)). Those parameters can be shown in Table 3 for every sample. Biomasses present lower \(IT\) and \(T_{char}\) values than charcoal, but the N4 Div.4.2 test was negative for biomass and positive for charcoal. It means that having lower combustion induction temperature does not guarantee self-ignition processes, which is not an unusual result as it may seem: It happens because the heat transfer processes are less effective in biomasses than charcoals. Self-ignition processes are likely to succeed when testing charcoal because of the effectiveness of the heat transfer, even if its \(IT\) is great. Figures 2-4 show the TGA curves for air atmosphere, TGA curves for oxygen atmosphere, and DSC curves, respectively. TGA plots include the first derivative of the curve (DTG) as it defines the maximum weight loss temperature. It can be seen in Figures 2 and 3, that charcoals samples required higher temperatures for beginning the reaction, as shown in Table 3. Some differences may be noted when comparing the induction temperature when using air flow and oxygen flow.