10 BULLETIN 319, U. S. DEPARTMENT OF AGEICULTUEE. 



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 earlj^ 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.^ 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, 



