Diagnostic probes for fire hazard evaluation based on thermal analysis methodology. An example of use in hot asphalt mixing operations

Abstract

The ability of thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TGA) to ‘fingerprint’ samples of varying thermal history, is demonstrated in this paper using an asphalt tank as an illustrative test system. The possibility of occurrence of smouldering fires inside such a tank is exemplified by a case study in which excessive heat build-up occurred inside the bitumen-limestone matrix. Samples collected from this tank showed essentially three types of thermal behaviour as probed by DSC and TGA. The first type was characterized by low temperature endothermic transitions and very little exothermic activity at temperatures, > 200 °C. In the second category, samples had a high unburnt (initial) bitumen content; these showed pronounced exothermic response at temperatures > 200 °C. The third type of thermal behaviour was characteristic of samples that had fire hazard potential; these showed strong low temperature exothermic response starting at ≈ 120 °C. A catalytic effect exerted by bitumen and/or limestone components (e.g. pyrophoric iron sulphide) is invoked for this response.