# Industrial Dust Explosions. A Brief Review
## 4 Review of Some Current Issues Related to Fighting of Dust Explosions
### Generation, Ignition and Explosion of Nm-Particle Dust Clouds  
[PERSON] [30] discussed of this topic. An increasing range of new nm-particle types are currently produced for use in various consumer products, ranging from cosmetics, sunscreens, toothpastes, pharmaceuticals, and clothing, to electronics, plastics, and tires. Over the last decades, this development has escalated. [PERSON] et al. [31] were probably amongst the first to ask whether dust clouds of nm-particles of a combustible material present an enhanced dust explosion hazard when compared with dust clouds in the air of the same materials of \(\upmu\)m size particles. More than 140 years ago, [PERSON] [32], a pioneer in dust explosion research in Germany, pointed at the close relationship between dust cohesion and dust dispersibility. [PERSON] [1] presented a highly idealized definition of an upper theoretical limit of dust/powder dispersibility. [PERSON] and [PERSON] [33] discussed the important concept of particle coagulation in dust clouds. This was re-emphasized by [PERSON] [34]. With nm size particles and explosive particle mass dust concentrations, coagulation by inter-particle collisions is extremely fast. However, as discussed below, MIEs of clouds in air of some metal powders can be significantly lower for nm particles than for \(\upmu\)m particles. Around and just after year 2000 most of the publications on production of combustible nm-particles of carbon and various metals, referred to production methods and facilities of laboratory or small pilot scales. [PERSON] et al. [35] described a method for the production of batches of up to 100 g of carbon nano-tubes. However, some years later [PERSON] et al. [36] described a pilot plant concept that is capable of producing high-purity multi-walled carbon nano-tubes at a yield of some kg/hour, which would mean 10-20 tons per year on a continuous-production basis. With such quantities, the dust explosion hazard would become a concern. It may well be that, since the paper by [PERSON] et al., genuine large-scale plants for production of various types of nm particles have become a reality. The experiments by [PERSON] et al. [37] showed that minimum electric spark ignition energies (MIEs) of dust clouds in air nm-powders of both titanium and iron were considerably lower than the MIEs of \(\upmu\)m-powders of the same materials. [PERSON] et al. [38] also found quite low MIEs (<1 mJ) for clouds in air of some nm metal powders. [PERSON] [34] suggested that this may be caused by thermal-stress break-up of particle agglomerates close to the very hot spark plasma. Existing national and international standard methods for MIE determination of dust clouds have a lower spark energy limit of about 1 mJ, Therefore, [PERSON] et al. [37] called for a new generator capable of generating synchronized electric sparks of energies <1 mJ. [PERSON] et al. [39] reported work in this direction. However, it turned out that their spark generator needed further development to become suitable for the intended purpose. This was discussed by [PERSON] and [PERSON] [40], and [PERSON] et al. [41] described an electronic solution to the problem. Using the standard 20-litre explosion bomb, [PERSON] et al. [42] determined maximum explosion pressures (P\({}_{\text{max}}\)) and maximum rates of rise of explosion pressures (dP/dt)\({}_{\text{max}}\) of three kinds of nm-particle powders. For aluminium, it was found that, down to particle sizes of the order of 1 \(\upmu\)m, both P\({}_{\text{max}}\) and (dP/dt)\({}_{\text{max}}\) increased systematically with decreasing particle size. However, when the particle size decreased further down to the genuine nm-particle region (particles smaller than 100 nm), both P\({}_{\text{max}}\) and (dP/dt)\({}_{\text{max}}\) decreased. [PERSON] [34] suggested that the reason could be very rapid coagulation of the tiny primary nm particles before the dust cloud became ignited. [PERSON] et al. [38] reported on similar results from experiments in their specially constructed two-litre closed explosion bomb.