GRAIN-DUST EXPLOSIONS. 51 



of an open lamp, burned with two distinct flashes, the second one 

 spreading somewhat beyond the confines of the bin. These middUng 

 particles were too heavy to float far, and too large to burn rapidly. 



Only a few years ago a certain packer lifted the lid of a flour bin, 

 and held a lighted match within the opening to see how much flour 

 the bin contained. Apparently the flour had been drawn down par- 

 tially, leaving some piled up on one side. Set in motion by a slight 

 jar, it fell, causing a rush of air and a thick cloud of dust, which 

 was followed immediately by a long flame issuing from the opening 

 in the bin. The current of air caused by the fall of the flour was 

 evidently strong enough to prevent the flame from extending down 

 into the bin; otherwise a disastrous explosion might have resulted. 

 The flame burned the packer's face and arms to some extent, and 

 caused him to fall backward. In doing so, he let the lid of the bin 

 fall, and thus cut off the flour dust inside the bin from the flaming 

 dust outside. 



The conditions and circumstances existing just previous to each 

 of these various explosions were similar in all cases. From such 

 observations as were made the conclusion has been reached that 

 only under certain favorable conditions will a serious explosion of 

 flour dust occur. If the dust is very dense and conflned within a 

 certain volume, or if the particles forming the dust are very large, 

 the danger of a real explosion is less than in the case of the very 

 fine, starchy dust in less density, which may, however, burn very 

 rapidly. The theory is that these particles of a fine, starchy nature 

 must be separated by a layer or thin wall of air, and at the same 

 time be near enough together to ignite each other. Dense clouds of 

 dust, especially those containing coarse particles, are comparatively 

 slow burning. , . 



A dust may also be very fine, yet so widely diffused as to be in- 

 capable of ignition, even from an open light. The old-fashioned 

 dust room, sometimes merely partitioned off with fine muslin or 

 other cloth, constituted a dangerous source of fire or explosion, as 

 the dust blown from machines was held more or less in suspension 

 before settling, and, being for the most part finely divided, it would 

 be all the more dangerous should it come in contact with an open 

 light. 



