The interest of a detailed study of thermal signals for thermal safety assessment

Abstract

Thermal safety assessment of chemicals and chemical processes is based on the interpretation of signals as they would be obtained from a wide set of commercially available devices. Despite the large number of existing techniques devoted to thermal measurements, none of them perfectly fulfils its purpose in view. This is frequently a consequence of the important time constants ruling the heat transfer processes. For any reliable safety assessment, hazardous systems require accurate, both thermodynamic (equilibrium state) and kinetic (transfer rate of energy and matter) characterization. The heat transfer's time is constant; it gives rise to raw thermo-analytical and calorimetric results that nearly always integrate a more or less important contribution of both of these two aspects. The aim of this contribution is to point out some ways to overcome time-constant induced signal modifications and to restore the original information from raw measurements as provided by the available instrument.  For safety purposes, it is important to be fully aware of all contributions acting on the signal generation and clearly to distinguish the thermodynamic factors, which are sample size independent from the kinetic factors and which strongly depend on the sample size. Further, the importance of the effect of non-thermal potentials on the thermal behaviour needs to be assessed with regard to unexpected possible dangerous transformations. On hand of a few examples, some main aspects are illustrated with respect to possible erroneous signal interpretation, which could lead to dramatic consequences in thermal process safety assessment applications.