Dust explosions containment

Where plant vessels are of small dimensions it may be economic to design them to withstand the maximum pressure generated by the dust explosion (Schofield and Abbott, 1988). The vessel may be designed to contain the explosion and be replaced afterwards or to withstand the explosion and be reusable. In both cases design of the vessel and its accompanying connections and ductwork is a specialist task. For large vessels the cost of design and construction to contain dust explosions is usually prohibitive. 

OSHA and ACGIH have not estabhshed specific airborne exposure limits for PVB and PVF resias however, some products may contain sufficient fines to be considered nuisance dust and present dust explosion potential if sufficient quantities are dispersed ia air. Unformulated PVB and PVF resias have flash poiats above 370°C. The lower explosive limit (lei) for PVB dust ia air is about 20 g/m. ... 

Inherently safer approaches to dust explosion hazard control include inerting and building equipment strong enough to contain an explosion. 

Schofield, C. and Abbott, J. A. 1988. Guide to Dust Explosion Prevention and Protection, Vol. 2 Ignition Prevention, Containment, Inerting, Suppression and Isolation. Institution of Chemical Engineers, Rugby, Warwickshire, UK. 

Contained essel explosions such as those used in gas mid dust explosion re-setuch, and explosions in internal combustion engine cylinders are examples. 

Metal catalysts on finely divided carbons can undergo dust explosions just as can the carbon itself, flour, or, as recently happened, stearic acid. The problem is circumvented easily by not dusting the catalyst, a poor practice in any case, especially when they contain noble metals. Virgin noble-metal catalysts are nonpyrophoric and can be safely held in the hand. After use, however, all catalysts containing adsorbed hydro n may ignite when dried. A used, filtered catalyst should be kepi wet and out of contact with combustible vapors and solvents. 

A several year-old 100 ml glass bottle which had originally contained 25 g of the complex hydride exploded while being opened a few hours after the previous opening to remove a portion [ 1]. No plausible explanation can be deduced, and a dust explosion seems unlikely in view of the large initiation energy required [2],... 

In buildings containing exposed explosive materials, dusts, or vapors, hardware should be nonsparking material. 

Meanwhile, in 1906, a terrible coal-dust explosion occurred at Courriere in France, in which about 1100 men lost their lives. The mine at Courriere had no methane at all and was considered to be safe, but as it turned out, it contained coal which in dust form produced a very dangerous suspension. The vast extent of this disaster aroused public indignation. It became obvious that the explosion of coal-dust may extend over a large area under ground and that this is much more dangerous than the explosion of methane which is usually localized within a small area. 

Stockpiles of milled peat are prevented from self heating and ignition by sprayed application of bitumen emulsion to form a 2—2.5 mm protective permeable film [1], The mechanism of self heating and ignition first involves aerobic microbiological processes, then chemical transformation of iron-containing minerals in the peat into pyrophoric iron compounds which later ignite the peat mound [2]. dust explosion incidents (reference 21)... 

In addition to reducing the probability of a dust explosion, it is possible to take steps to mitigate the consequences of a dust explosion, should one occur. Use of automatic vents to prevent the buildup of destructive overpressures and constructing areas with blowout partitions are examples of such steps. Also, spaces which may contain these high dust concentrations can be kept fairly open to minimize the development of turbulence in a flame front, should an explosion occur. 

As an example of dust explosion protected apparatus standard IEC 61241-4, 1st edition 2001-3, types of protection pD describes a pressurization technique the interior of this apparatus is subjected to a continuous pressure from a supply of air (not containing any combustible substances) or other inert gases while electrical components within the enclosure are energized. 

---