50 BULLETIN 68L, U. S. DEPARTMENT OF AGRICULTURE. 
A rather curious explosion took place in a flour mill in Nebraska 
on September 22, 1911, in which the entire wall on one side above 
the second story was blown out. One end showed a bad bulge, 
but the roof remained intact, except that it sagged over the side 
from which the wall was blown out. Apparently the force of the 
explosion was exerted in one direction, or, rather, the wall on this 
side offered less resistance than the others. It is believed that the 
dust in one of the flour bins was ignited by a match struck by one 
of the workmen. 
On December 11, 1916, a large cereal mill in Ontario, Canada, 
was totally destroyed by an explosion and subsequent fire. The 
fire was started by an explosion in the feed-grinding building, and 
was ascribed to the ignition of feed dust in one of the grinding ma- 
chines. 
One of the authors witnessed several dust explosions in flour 
mills. Although these explosions were of minor importance, be- 
cause no serious consequences followed, the observations tend to 
give an idea as to the explosibility of flour dust, the conditions under 
which explosions may take place, and, in some cases, the cause of 
the initial explosion. 
At a certain mill the settlings of the dust room, into which was 
blown the dust drawn from the middlings purifiers and from the 
exhaust off the millstones, were gathered periodically into a bin and 
ground on a. small stone. This mixture was composed of very fine 
pieces of bran, fiber, larger pieces of endosperm, and a fine, impal- 
pable, starchy, flour dust. Often, when the spout became nearly 
empty and the pile above started down, the dust descended with 
sufficient force to spurt out of the opening in the spout over the 
hopper, creating a dense cloud of dust. On one occasion an open 
light was close at hand when this dust fell, and an explosion fol- 
lowed. There were three distinct explosions or flashes of the burn- 
ing dust, one following the other at intervals of a few seconds. These 
explosions were succeeded by a faint crackling sound. Each suc- 
cessive flash was wider in extent as the dust spread and diffused. 
The first enveloped only the vicinity of the spouts and millstone; 
the second, a still larger area; and the third, almost the entire area 
of the grinding floor. The first zone, composed of the heaviest and 
largest dust particles, burned the most slowly, as if partially smoth- 
ered; the next, more rapidly; and the last and largest zone, composed 
of the very lightest of the starchy particles in the state of greatest 
diffusion, burned most rapidly, and, consequently, with the greatest 
heat. This last explosion had more force than the others, and was 
more of the nature of an explosion than the other two. 
On another occasion some purified middlings were shaken down 
from the side of an empty bin, and, coining in contact with the flame 
