42 BULLETIN G81, U. S. DEPAETMENT OF AGRICULTUEE. 



CARBON ARC IN DUST ROOM. 



The location of tlie arc in the dust room, at the end of the screw : 

 conveyor, did not cause an explosion (Series 4). This fact, however, | 

 merely indicates that the many conditions involved in an explosive i 

 mixture did not happen to be met in this particular case. Probably ■ 

 the dust cloud was not dense enough. In any event, it would be well i 

 to draw the following conclusion, especially in view of past explosions ; 

 in mills, and those obtained by the arc located near the grinding 

 discs of the attrition mill : 



It is always very dangerous to aUow an open flame (or an}^ source 

 of ignition) in the vicinity of a dust-laden atmosphere. 



EXPLOSIBILITY OF VARIOUS GRAINS. 



The summary of all the explosions of various materials obtained | 

 with the electric arc (except those in the demonstrations, Series 5) is ! 

 found in Table 16. From the explanation of the meanmgs of the i 

 terms of the fractions appearing in this table it would seem that each i 

 ■fraction ought to indicate the inflammability of the material. As i 

 a matter of fact, these fractions, especially those of the same series, ■ 

 serve as rough indications of the relative inflammabiUties of the 

 various materials; but too much stress should not be laid upon this j 

 point, as most of the conditions of testing were beyond control. Rela- \ 

 tive inflammability can properly be determined only by careful j 

 laboratory methods which control the many factors entering into the ' 

 question. ; 



In view of the fact that the grinding of oat huUs constitutes an 

 important part of the work done by attrition mills, it is interesting ' 

 to note that oat hulls alone (Mixtures 1, 13, and 30) were not found j 

 to be very inflammable. Only extremely fine oat huUs, or those with 

 considerable dust, were capable of giving inflammable mixtures, in i 

 spite of the fact that in series like 11 and 12 oat huUs were fed into ! 

 the mill and recirculated continuously for several hours without a , 

 resulting explosion, except in the case of Explosion 3 of Series 12. ! 



A study of Table 16, together with a knowledge of the conditions j 

 of testing, makes possible the following conclusions : 



1. Elevator dust, flour, wheat scourings, and malt sprouts seem to 

 produce explosions the most consistently. 



2. Oat huUs do not appear to give very inflammable mixtures, 

 unless they contain a considerable amount of ime dust. 



3. Every precaution should be taken to remove dust as fast as it 

 is formed, and to prevent it from coming in contact with any possible 

 source of ignition. 



