Explosion of Dusts, Mists and Vapors

Dust may be defined as suspension in air or other gases, of small solid particles ranging from ca 0.05 to 1000 microns in size. Mrs is usually water or other liq in the form of particles floating or falling in the atmosphere. Vapor is a term applied to a gas that is at a temp below its critical temp, which can, therefore, be condensed by pressure alone 

Some dusts, mists and vapors are combustible and when mixed with air in certain proportions they form combustible or explosive mixtures 

As examples of combustible dusts may be cited suspension in air of finely divided particles of metals (such as Mg, Al, Zr, Zn, 

which can form in plants polishing metals or in plants manufg pyrotechnics) suspensions of finely divided coal, coke or charcoal suspension of finely divided cereals ( such as of flour, rice, oats, starch, ecc) suspension of wood dust suspension of sugar dust suspension of explosive particles (such as of TNT, PA, Tetryl, etc) 

As examples of vapors may be cited those of petroleum hydrocarbons in petroleum refining plants, vapors of solvents (such as alcohol, ether, acetone, carbon tetrachloride, carbon disulfide, etc used in plants manufg expls and propints) vapors of liquid expls (such as DNB, DNT, NG, NGc, DEGDN, etc), and vapors of liquids (such as benzene, toluene or xylene) used as primary materials in the manuf of expls such as TNB, TNT or TNX. Some solid expls such as TNT evolve, when in molten condition, explosive vapors 

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Mixtures of fine combustible dusts with air in certain proportions can be ignited and they either burn or explode with velocities of propagation lower than those for explosive gases. Andreev Belyaev (Ref 2, pp 148-53) treat briefly this subject, but do not give any rates of burning. More information on expln of dusts is given under Detonation and Explosion of Dusts, Mists and Vapors Refs 1) Baum, Stanyukovich Shekhter(1959)> 384-85 2) Andreev Belyaev (I960), 139-40... 

Dust Detonation (and Explosion). See Detonation and Explosion of Dusts, Mists and Vapors in Vol 4, p D253 also in Kirk ... 

Detonation (and Explosion) of Combustible Dust-Air and Vapor-Air Mixtures. See Detonation (and Explosion) of Dusts and Mists (Vapors)... 

Prior to reading this subject, it is advisable to see "Burning (Combustion) and Deflagration of Gases, Vapors and Dusts Detonation and Explosion of Dusts and Mists (Vapors) and Detonation (or Explosion), Development (Transition) from Burning (Combustion) or Deflagration described in this Volume... 

Always ventilate spaces with normal air and never pure oxygen. Introducing a source of ignition into a space containing a flammable atmosphere will cause an explosion. Consider hazardous most liquids, vapors, gases, mist, solid materials, and dusts space. 

Category 3 Equipment in this category is intended for use in areas in which explosive atmospheres caused hy gases, vapors, mists, or air/dust mixtures are unlikely to occur or, if they do occur, are likely to do so only infrequently and for a short period only. Equipment or protective systems need to guarantee a normal level of protection. Self-certification (internal control) is allowed in this category if manufacturers have sufficient testing facilities. See Table X/3.2.2-1. 

The maximum and minimum concentrations of a gas, vapor, mist, spray, or dust in the air or other gaseous oxidant for a stable detonation to occur are the so-called upper and lower detonation limits. These limits depend on the size and geometry of the surroundings as well as other factors. Therefore, detonation limits found in the literature should be used with caution. Detonation limits are sometimes confused with deflagration limits and the term explosive limits is then used inconsiderately [40]. 

By this directive, which is the 15th individual directive according to article 16 of framework directive 89/391/EEC, minimum requirements for the protection of workers against explosive atmospheres at workplaces have been established [6-22]. It complements the earher EU directive 94/9/EC, which laid down provisions and specifications for devices and protection systems for use in explosive atmospheres [6-23]. In the case of an explosion, fife and health of workers are severely endangered as a result of uncontrolled effects of flame and pressure, the presence of noxious reaction products, and the consumption of the oxygen in the ambient air which workers need to breathe. Explosive atmosphere means a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapors, mists, or dusts, in which, after ignition has occurred, combustion spreads to the entire unburned mixture. 

The linear velocity of air flow in the tunnel bore, in shafts, and in all other underground work areas shall be at least 30 feet (9.15 m) per minute where blasting or rock drilling is conducted, or where other conditions likely to produce dust, fumes, mists, vapors, or gases in harmful or explosive quantities are present. 

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