Dust explosions prevention measures

Richard Siwek/ M S Managing Director, President, FireEx Consultant Ltd. Member, European Committee for Standardization (CENTC305) Member, Association of German Engineers (VDl 2263,3673) Member, International Section for Machine Safety (ISSA) (Dust Explosions, Preventive Explosion Protection, Explosion Protection through Design Measures)... 

The investigation of a sugar dust explosion in a Belgian factory is discussed and preventive and protective measures are described in detail [1], Sugar dust explosions and safety measures against them are reviewed [2]. 

Bartknecht, W., Prevention and design measures for protection against dust explosions, in Industrial Dust Explosions (K. L. Cashdollar and M. Hertzberg, eds.) ASTM tech. pub. 958, pp. 158-190 (1987)... 

Damaging fires are uncontrolled chemical reactions, so fire hazards involving ordinary flammable and combustible materials could be included in the above definition of chemical reactivity hazards. However, this publication seeks to supplement basic fire prevention and protection measures by addressing how to successfully manage other chemical reactivity hazards in the work environment. Consequently, the use of the term "chemical reactivity hazards" in this publication will not include explosion, fire and dust explosibility hazards involving the burning of flammable and combustible materials in air. Storage and use of commercial explosives is also outside the scope of this publication. 

In a special publication devoted to sulfide ore dust explosions, a dust explosion in a copper-zinc sulfide mine is discussed and related to causes and preventive measures [1]. Control measures [2] and prevention of secondary explosions are also discussed [3], and surveyed, including the need for further work [4], The results of experimental work on the use of limestone dust to suppress explosions in pyrites dusts are presented [5], For another special publication on ore dust explosion with numerous incidents and further studies on mechanism and control see [6], Explosibility declines in the order pyrrotite, pyrite, chalcopyrite, sphalerite, covellite, chalcocite, galena. Pyrite at 1000 g/m3 can give a peak pressure of 5.8 bar [7], Self heating of broken sulfide ore, to possible ignition, has been studied. Pyrrhotite seems primarily responsible [8],... 

CA 61, 11840 (1964). Review article on the explosive capacity of various dusts (coal ore dust, esp sulfides). Measures for the prevention of explosions are described... 

Printing Office(1946) 5 )H. W.Heinrich. Indus trial Accident Prevention A Scientific Approach5, 3rd ed, McGraw-Hill,NY( 1950) 6)National Safety Council,"Accident Prevention Manual for Industrial Operations, 2nd ed, Chicago,111(1951) 7)Underwriters Laboratories,Inc, Lists Relating to Accident Equipment , NY(1951) 8)National Fire Protection Association,"National Fire Codes for the Prevention of Dust Explosions, Bostoh(1952) 9)W.M.Kunstler,"The Law of Accidents, Oceana Publications,NY( 1954) 10)US Bureau of Mines,"Accidents from Explosives at Metal and Non-metallic Mines, JuIy(1956)(See also Safety Measures in Industry)... 

Safety from potential dust cloud explosions could include taking measures to avoid an explosion (explosion prevention) or designing plant and equipment so that in the event of an explosion people and plant are protected (explosion protection). Selection of... 

Level of personnel s knowledge and appreciation regarding the consequences of a potential dust explosion and adherence to preventive measures. 

If evolution or formation of an explosible atmosphere cannot be prevented and all sources of ignition cannot be reasonably eliminated or excluded, then the possibility of a dust cloud explosion persists. Under such conditions, explosion protection measures should be taken to protect people and minimize damage to the plant. It should be noted that explosion protection measures should be considered in addition to taking all reasonable steps to reduce the possibility of formation/spread of dust clouds and exclude potential ignition sources. Explosion protection measures include the following. 

Regardless of what type of explosion protection measure is considered, the dust cloud explosion should be prevented from propagating from the location where it originates to other locations in the plant. This is referred to as explosion isolation. Dust explosions can propagate through pipes, chutes, conveyors, etc. The first step in isolating an explosion is to avoid unnecessary connections. If this is not possible, barriers should be created in the path of the explosion. 

When speaking about explosions, preventive and constructive measures are discriminated. This is also done in the case of protection against dust explosions. When discussing the preventive measures which have the task to eliminate the chance of a possible event actually occurring, the question of substance substitution is the first to be asked. If a dust explosible substance can be replaced by one which does not have this property, this substitution is the most effective measure. The probability that this exchange is possible in practice is, however, comparatively low. 

There Is a danger of dust explosions special safety precautions are required (see Preventive Measures). 

Applies to finely dispersed particles which form explosive mixtures on contact with air. In some cases. Installation of special equipment to prevent dust explosions will be required. The risk of dust explosions can be reduced by taking measures to prevent the build-up of electrostatic charges (consult an expert). 

The handling (drying, transportation) of explosive powders is often performed under an inert atmosphere. Because of economic considerations, air is not completely excluded but is diluted by Ng or CO2 to an O2 concentration insufficient for dust explosion. The maximum permissible oxygen concentration to prevent ignition in a dust cloud is measured in a Hartmann tube or in a Godbert-Greenwald furnace by spraying the powder with the test gas mixture instead of air. 

Explain why a policy of eliminating ignition sources from a process plant handling combustible powders cannot be relied upon as the sole measure taken to prevent a dust explosion. 

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