} 5 
10 BULLETIN 379, U. S. DEPARTMENT OF AGRICULTURE. oe 
The evidence available convinced the investigator that the explosion 
was due to ignition of smut dust by static electricity. 
In another case the owner of a machine which was destroyed stated 
that he was standing at the engine and was looking directly at the 
cylinder at the time of the explosion. He could see the cylinder 
itself, as the feeding had stopped momentarily. He observed a long 
blue spark coincident with the explosion. In other investigations 
the men in charge of the machines stated that there were large 
quantities of static electricity present around the machine preceding 
the explosions. : 
In one case the owner of the machine stated that his machine 
was very heavily charged with static electricity on the morning of 
the explosion, to such an extent that it was not possible to touch 
any metal part without getting a shock. This condition had never 
been noticed on this particular machine before. The explosion was 
violent in nature and totally destroyed the machine. — 
MILL EXPLOSIONS. 
Previous investigations relative to the causes of explosions in grain 
mills and elevators and similar plants indicated that static electricity 
was a possible factor in the production of dust explosions. 
In September, 1913, at the time investigations were being con- 
ducted in cooperation with the Millers’ Committee of Buffalo, N. Y., 
two slight explosions occurred on a dry, frosty morning in early fall, 
in two separate plants in western New York, at a time when the feed 
had been shut off from certain grinding machines. Both occurrences 
took place a considerable time after the stream of grain had stopped 
entering the machines. The possibility of static electricity being 
generated by the operation of the revolving plates of the machine 
suggested itself in a very preliminary way at the time of these explo- 
sions, and a confidential report was prepared and presented at the 
time to the Millers’ Committee. Although up to that time no record 
could be found that experiments had been conducted to determine 
whether cereal dusts could be ignited in this manner, it was found 
by experiment that sufficient static electricity could be generated by 
the friction of a very small pulley and belt to ignite natural gas 
readily. It was learned at this time that a milling company in the 
South, engaged in grinding cottonseed cake into meal, after ex- 
periencing a series of explosions, had prevented a repetition of these 
occurrences by grounding the machine by means of a wire connected 
to a rod driven into the ground near by.t This seemed to confirm 
1 Preliminary Report on the Explosibility of Grain Dusts. Cooperative Investigation by 
Millers’ Committee, Buffalo, N. Y., under the direction of Dr. George A. Hulett, Chief 
Chemist, U. S. Bureau of Mines. By David J. Price and Harold H. Brown. Pittsburgh, 
1914, 
