## 2 Materials and Methods  
In order to obtain representative results of the analysis, the selection of polymer samples was accompanied by the inspection of the sites related to the production and use of ammonium nitrate and obtaining information from people working there. Previous experience in the preparation of test samples was also used. For the results concerning different samples to be easily comparable, the same measurement conditions were applied. Similar phenomena may be observed while testing typical explosives. For selected types of plastics, samples were taken for their most common forms applied in utility items. For example, for polyvinyl chloride, uPVC, used in construction joinery (doors, windows, facade panels, covers of electric wiring harnesses, and all types of pipes) and PVC-P (insulation of electric cables, pipes for transferring aggressive liquids, bags for such liquids, specially sealed protective clothing) were chosen. The difference between these varieties is based upon the syntactic or atactic arrangement of the polymer substituents and significant content of the plasticizer, e.g., phthalates. The test mixtures were prepared with the polymer content of 8%, 20%, 50%, and 75%. Explosion was most often observed for the content of 20% of the polymer in AN mixture. The following samples were selected:  
* PVC: A fragment of a typical water main pipe was used in the analysis. The processing was done by hand in order not to lead to undesirable changes in the structure of the material. A sample of PVC-P was also taken in a similar manner, coming from a piece of colorless tubing for transportation of liquids and gases [7]. PA: A forklift element made of PA66 was used for the analysis. The sampling and sample preparation procedure was analogous to that of uPVC. Due to the surface sorption of moisture, the sample was kept in the desiccator the entire time [8]. - PMMA: The sample used in the analysis was taken from a colorless general purpose plexiglass board [9]. - PS: The analysis used expanded polystyrene (EPS). White EPS, without dyes and modifying additives, foamed with CO\({}_{2}\)/H\({}_{2}\)O was selected [10]. Mixtures of AN with selected polymers were analyzed with the use of differential scanning calorimetry (DSC). It is one of the methods of thermal analysis of materials that allows measuring the heat flux received or supplied to the environment by a sample during its heating. This allows determining the temperatures of chemical reactions and physical changes of the material, as well as determining the thermal effects of these changes. The analysis of the course of these reactions in a function of temperature changes allows determining whether, i.e., a given reaction may take place in an explosive manner. Figure 1 presents the thermal analysis of the polymer samples used in the research in the range of 20-400 \({}^{\circ}\)C. A thermal effect was observed for each of the plastics, indicating thermal decomposition. The effect of the energy release rate was, however, several times less significant than during changes taking place in the presence of AN. Due to the high sensitivity of the research equipment and the risk of damaging the sensors, it was decided to use a relatively low mass of samples, about 5 mg. In order to map the conditions that occur on a larger scale, the prefrozen samples of AN and polymer products, cooled with liquid nitrogen (\(-196\)\({}^{\circ}\)C), were crushed by hand using an agate mortar. Thanks to this, changes in the structure of the material were avoided. Test samples with a fraction of 0.1-0.29 mm were then placed in a chamber dryer at the temperature of 28 \({}^{\circ}\)C and at 25 kPa below atmospheric pressure for 24 h. The dried material was stored in a desiccator under nitrogen atmosphere (conditioning for at least 48 h). Such measures were necessary due to the hygroscopicity of some of the analyzed substances, in particular ammonium nitrate.