Development of Speditive Explosibility Test (SET): a statistical reliable method for combustible dust explosibility investigation

Abstract

The present work of thesis investigate the explosibility sensitivity and behavior of combustible solid materials, in the form of dusts. The first phase of the work has focused on the ignition sensitivity of combustible dusts, both in form of clouds than deposed layers. Standard test methods has been used to assess ignition parameter of the samples, i.e. UNI EN 50821: 1999. MITC and MITL were measured for pure combustible dusts and for mixtures of different dusts. In particular mixtures of combustible and inert dusts were analyzed. The experimental results underlined the increase of the ignition temperature (both in clouds than in layers) the weight content of inert material increase. Extinguishing powders with chemical heat depletion effect had demonstrated to be more effective in increasing the ignition temperature with respect to inert acting with physical inertia mechanism. MITC of two combustible dusts mixture have been analyzed and results have shown the poor accuracy of the standard procedure in defining the ignition temperature, particularly when there is little difference between ignition temperatures of the pure materials. The author has attempted to reduce this lack of accuracy, inadequate when a high level of details is required (like for scientific purposes) in ignition measurements through different statistical analysis of experimental data. This study has generated a statistical approach to the investigation of dust ignition temperature with the definition of the SIT (Statistical Ignition Temperature) and the definition of a Probability Escalation Interval (PEI); within PEI ignition probability of dusts vary between 0 and 1 with respect to temperature. The results obtained show that standard methods adopted worldwide could fail in determine the MITC of dusts and bring a new, more accurate methodology a contribution on the definition of ignition concept of dusts. The statistical study could also apply to ignition criteria of the explosibility test proposed here, in order to give to SET procedures and results a more reliable statistical value. The Speditive Explosibility Test has the form of a screening procedures for defining explosibility of dust samples, with the aim of avoiding time and cost-consuming standard procedures. The test consist in different procedures derived from standards (mainly UNI EN 50821 and UNI EN 13821) which ignition conditions are modified to be as worst possible, in order to avoid marginally explosive dusts to be classified non explosible. Tests were performed on different dusts samples (by chemical composition, nature, PSD) and results were validated through explosion test in the 20 L Siwek-sphere. The test classification shows, for the majority of the samples collected, good agreement with literature standard explosibility tests. The SET could be assumed standard test for the explosibility determination of a dust. A second experimental campaign was performed on non-traditional dusts coming from textile industries. All samples PSD was analyzed and 15 over 100 total were submitted to the SET with the aim to obtain more data on explosive behavior of those type of dusts