Characteristics of Dust Explosions

The explosion characteristics of dusts of the specific type or identification varies with the size and shape of the dust particle [27]. These characteristics and a few other features [27] as well as moisture content are summarized in Table 7-31. These data are ... 

Explosion calculations, 499-504 Estimating destruction, 501 Overpressure, 502 Pressure piling, 501, 504 Relief sizing, 505 Scaled distance, 502, 503 Schock from velocity, 503 TNT equivalent, 499-504 Explosion characteristics of dusts, 515 Explosion suppression, 518 Explosion venting, gases/vapors, 504 Bleves, 504 Explosions, 482 Blast pressure. 496 Combustion, 482 Confined, 482 Damage, 498-501 Deflagration, 482 Detonation, 483... 

LABORATORY TESTING TO ASSESS EXPLOSION CHARACTERISTICS OF DUST CLOUDS... 

DEM EN 14034-4 2011-04 (2011) Determination of explosion characteristics of dust clouds— Part 4 Determination of the limiting oxygen concentration LOC of dust clouds German version EN 14034-4 2004 + A1... 

DEM EN 14034-1 2004 (2004) Determination of explosion characteristics of dust clouds— Part 1 Determination of the maximum explosion pressure pmax of dust clouds. Beuth Verlag... 

Explosion characteristics of dust clouds are generally examined by the Hartmann apparatus (Fig. 3.84) developed in USA. It consists of a vertical combustion tube of 1200 cm volume, 305 mm long and 64 mm inside dia., mounted over a brass dispersion cup. The powder sample is placed in the cup and dispersed by an air stream of 50 cm injected at a pressure of 7 bar. The ignition source is usually a pair of electrodes with a spark gap of 3 to 6 mm mounted at the lower one-third level of the tube. A wire coil igniter can also be used. 

Table 6.2 Dust explosion characteristics of combustible solids...

Explosion Characteristics of Various Dusts (Partial Listing)... 

Explosibility characteristics of coal dust clouds using... 

Use of a steel chisel to open a drum of carbide caused an incendive spark which ignited traces of acetylene in the drum. The non-ferrous tools normally used for this purpose should be kept free from embedded ferrous particles [1]. If calcium carbide is warm when filled into drums, absorption of the nitrogen from the trapped air may enrich the oxygen content up to 28%. In this case, less than 3% of acetylene (liberated by moisture) is enough to form an explosive mixture, which may be initiated on opening the sealed drum. Other precautions are detailed [2]. Use of carbon dioxide to purge carbide drums, and of brass or bronze non-sparking tools to open them are advocated [3]. The dust explosion characteristics of calcium carbide powder in air have been studied [4]. 

Explosions involving organic dusts can usually be contained in equipment that can withstand about 7-10 times the initial pressure (Lees, 1980). Thus, if the system is originally at atmospheric pressure, the maximum pressure to be expected is about 100-150 psig. Data on explosion characteristics of the actual material to be processed are usually necessary to confirm the required design pressure. 

To assess the possibility of an explosion in a facility and to select the most appropriate basis of safety, explosion characteristics of the dust(s) that are being handled/processed in the facility should be determined. 

Another phenomenological characteristic of dust explosions is the occurrence of secondary explosions. Swirled dust is a consequence of the existence of settled dust If... 

An extensive series of laboratory tests have been conducted in various countries to enable the investigation of lire and explosion characteristics of materials to be made. The testing apparatus and procedures differ from one conntry to the other, although there are some conunon points. The tests nsed to be made on a laboratory scale and the results obtained were extrapolated to full scale, always giving some uncertainty. Also, the test procedures may not reflect exactly the condition in a particular type of dryer. Therefore, it is reconunended that published data may be used carefully and individual tests on the particular dust concerned may be required. 

The similarity between the characteristics of dust and gas flames " 1 as well as the similarity between the explosion characteristics of comstarch-air mixtures and lean methane-air mixtures, which is seen from the data published and confirmed by, indicates that the process controlling the propagation of flames in these mixtures must be similar. However, this cannot be a general conclusion for all dusts because cornstarch dust is unique in its high volatile content... 

Dust explosibility characteristics Length and shape of relief pipe if existent... 

Volume of vessel (free volume V) Shape of vessel (area and aspect ratio) Type of dust cloud distribution (ISO method/pneumatic-loading method) Dust explosihility characteristics Maximum explosion overpressure P ax Maximum explosion constant K ax Minimum ignition temperature MIT Type of explosion suppressant and its suppression efficiency Type of HRD suppressors number and free volume of HRD suppressors and the outlet diameter and valve opening time Suppressant charge and propelling agent pressure Fittings elbow and/or stub pipe and type of nozzle Type of explosion detector(s) dynamic or threshold pressure, UV or IR radiation, effective system activation overpressure Hardware deployment location of HRD suppressor(s) on vessel... 

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