A predictive model for the estimation of the deflagration index of organic dusts

Among all the powder handling operations, the hazard represented by organic dusts explosions is one of the most critical, as several industrial accidents occurred during the last centuries testify. Particularly, in order to estimate the magnitude of a dust explosion, the so-called deflagration index, KSt, plays a fundamental role because it is also used to design the emergency vents aimed to protect both vessels and silos from a collapse due to an internal explosion. Nowadays Kst values are obtained by means of experimental testing, e.g. using a standard 20 L sphere, but its determination is quite expensive and time consuming. This problem is even more severe when a target dust is processed into a plant giving rise to a wide range of particles sizes; in this case, an experimental investigation of all the different granulometries would be advisable but too expensive. In this context, the aim of this work was to develop a predictive model for the evaluation of the KSt, for whatever organic dust, as it would be estimated by a standard test in the 20 L sphere using only a single thermo-gravimetric test. In order to validate the aforementioned model, eight different organic dusts (Aspirin, Cork, Cornstarch, Niacin, Polyethylene, Polystyrene, Sugar, and Wheat Flour) were tested. Preliminary results showed a good agreement between literature KSt values and model predictions. Such an achievement, once further validated on a wider range of explosive organic dusts, could lead to an improvement in the risk assessment panorama for powder handling operations by making the risk evaluation process quicker and cheaper.