Page 220 - Dust Explosions in the Process Industries
P. 220

192  Dust Explosions in the Process Industries

             the high temperature, the thermal radiation from the flame is intense, which was a main
             reason for the very severe burns that the nine workers suffered.
               The investigation after the accident disclosed a small hole in a steel pipe for convey-
             ing Si powder from a mechanical sieve to a silo below.An oxygedacetylene cutting torch
             with both valves open was found lying on the floor about 1m from the pipe with the hole.
               According  to  Kjerpeseth  (personal  communication from  E.  Kjerpeseth, Elkem-
             Bremanger, Svelgen, Norway, 1990), there was strong evidence of the small hole having
             been made by the cutting torchjust at the time when the explosion occurred.At the moment
             of the explosion, part of the plant was closed down for various repair work. However, the
             dust extraction system was operating, and this may in part explain the rapid spread of the
             explosion throughout the entireplant. The interior of the perforatedpipe had probably not
             been cleaned prior to the perforation. In view of the high temperature and excessive ther-
             mal power of the cutting torch, and not least that it supplied oxygen to the working zone,
             a layer of fine dust on the internalpipe wall may well have become dispersed and ignited
             as soon as the gas flamehad burned its way through the pipe wall. The blast from the result-
             ing primary silicon dust explosion then raised dust deposits in other parts of the plant into
             suspension and allowed the explosion to propagate further until it eventually involved the
             entire silicon grinding building. The grinding plant was not rebuilt after the explosion.


             2.1 2
             TWO DEVASTATING ALUMINUM DUST EXPLOSIONS

             2.12.1
             MIXING SECTION OF PREMIX PLANT OF SLURRY EXPLOSIVE
             FACTORY AT GULLAUG,  NORWAY,  IN 1973

             The main source of information concerning the original investigation of the accident is
             Berg (personal communicationfrom E. Berg, Dyno Industries, Gullaug,Norway, 1989).
             The explosion occurred during the working hours, just before lunch, while 10 workers
             were in the same building. Five of these lost their lives, two were seriously injured, two
             suffered minor injuries, only one escapedunhurt.A substantialpart of the plant was totally
             demolished, as illustrated by Figure 2.29.
               The premix preparation plant building was completely destroyed. Debris was found
             up to 75 m from the explosion site. The explosion was followed by a violent fire in the
             powders left in the ruins of the plant and in an adjacent storehouse for raw materials.
               The explosion occurred when charging the 5.2 m3batch mixer, illustrated in Figure
             2.30. It appeared that about 200 kg of very fine aluminum flake, sulfur, and some other
             ingredientshad been charged at the moment of the explosion.The total charge of the for-
             mulation in question was 1200 kg.
               The upper part of the closed vertical mixing vessel was cylindrical, and the lower part
             had the form of  an inverted cone. The feed chute was at the bottom of the vessel. The
             mixing device in the vessel consisted of a vertical rubber-lined screw surrounded by a
             rubber-lined grounded steel tube. The powders to be mixed were transportedupward by
             the screw, and when emerging from the top outlet of the tube, they dropped to the sur-
             face of the powder heap in the lower part of the vessel, where they were mixed with other
             powder elements and eventually retransported to the top.
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