Simplifying standards, opening restrictions part II: The significance of the ignition source on the safety characteristics of dusts in the 20 L-sphere

Abstract

The ignition behavior of chemical ignitors has been increasingly discussed in conjunction with their influence on the safety characteristics of the dust and hybrid mixture determined in the 20 L-sphere. Specifically, the turbulence generated by the ignitors and/or preconditioning of the system by a large and hot fireball. The effect of the explosion pressure generated by the chemical ignitors is included in the standards by means of the so-called pressure ratio (PR) (ASTM E1226 – 19, 2019; ASTM E1515-14, 2022) or the corrected explosion overpressure p_m (ASTM E1226 – 19, 2019; EN 14034-1, 2011). The overpressure caused by the ignitors should also be subtracted when the dusts are tested on their explosibility (ISO 80079 -20-2,; EN 14034-3, 2011; EN 14034-4, 2011).

The aim of the presented work is to show the weaknesses of the standards in the case of calculation of the corrected overpressure p_m and the pressure ratio PR with respect to the chemical ignitors′ explosion overpressure measured in the 20 L-sphere. Measurements of the explosion overpressure of the sole ignitors in the air are presented together with the influence of the dust concentration on the explosion pressures of the ignitors. Talc dust, Lycopodium Clavatum dust and their mixture (80 % by mass of talc and 20 % by mass of Lycopodium) were used for tests in air and nitrogen. The differences in the measured explosion pressures generated by the ignitors in the calculations of the pressure ratio PR and the corrected overpressure p_m were compared with calculations using the ignitors explosion overpressure calculated according to equations given by the Standards are shown. The ignition criteria given by three different standards were used as an example of ignition evaluation from the real explosion curves with different ignitors overpressures. The importance of the measurements of the real overpressures caused by the ignitors is also shown.