Dust Explosion Propagation in Small Diameter Pipes

© 2018 American Institute of Chemical Engineers In facilities handling combustible dusts, the isolation of propagating deflagrations requires great attention due to the potential catastrophic consequences of secondary dust explosions. While the ability of dust explosions to propagate is widely recognized, some misconceptions still exist. One of the common myths is that a dust explosion cannot propagate through small diameter pipes and that explosion isolation may not be required in that case. This article first presents a simplified theory of flame propagation in pipes. Dust explosion experiments performed in industrial-scale pipes smaller or equal to 4 in (or 100 mm) in diameter are then reviewed. The findings of the experiments are interpreted in the light of the simplified theory. Our study reveals that dust explosion propagation has been consistently observed in pipes with a diameter as small as 1 in. While the likelihood of flame propagation seems to decrease with pipe diameter and other “chemical” and “engineering” factors, it remains a realistic scenario and therefore should be addressed in the design and operation of powder handling systems. © 2018 American Institute of Chemical Engineers Process Saf Prog 2018.Fik

The new IEC standard for pressurised electrical equipment enclosures for areas containing combustible dust. A self-contradiction?

During the last years the International Electrotechnical Commission (IEC) has been working towards producing a series of new standards for electrical equipment to be used in areas containing combustible dusts (ExpD, ExiD, ExmD). A main objective is that the new standards shall be “harmonized” with the corresponding existing standards for explosive gas atmospheres (Exp, Exi and Exm). The ExpD standard IEC 61241-4 is the first of the new harmonized standards that has been issued. The main purpose of the present paper is to show that this new standard is self- contradictory, and that this can be traced back to basic deficiencies in the European “Atex I 00a” Directive”, which does not account for the substantial differences in the physical behaviour of gas molecules and dust/powder particles, and to corresponding deficiencies in the current standards for classification of areas containing combustible dusts