GKAIF-DUST EXPLOSIONS. 51 
of an open lamp, burned with two distinct flashes, the second one 
spreading somewhat beyond the confines of the bin. These middling 
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 confined 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 
fight. 
