GBAIN-DUST EXPLOSIONS. 17 



dentally the mill was run several hours while oat huUs were fed 

 at as great a rate as possible. The ground oat huUs were conyeyed 

 back into the mill in order to produce as much dust as possible. 

 For over an hour the electric arc was turned on, but hot a single 

 explosion resulted. 

 Results. — 



1. During the operation of the attrition miU under severe con- 

 ditions as to rate of feeding and source of ignition no explosion 

 could be obtained with oat huUs during a period of over an hour. 



2. Out of six explosions with the dampers in service two flames 

 shot past B and D (fig. 4). 



3. In two instances with the dampers in service smoke was 

 observed issuing from the end of the conveyor, but without any 

 force. 



SERIES 12. 



Ohject. — Same as that of Series 11. 



Conditions. — Similar to those of Series 11, except that the oat 

 huUs used during the prehminary run had been fairly well dried 

 by being spread out in shallow pans, which were then placed on top 

 of radiators for a period of several days. Thus the moisture content 

 was reduced from 9.9 to 3.2 and 5.7 per cent. 



Results. — 



1. Only one explosion was obtained during the continuous grind- 

 ing of fine oat huUs. 



2. In each of the four explosions with the double damper in 

 service a flame got past the damper and in three cases extended 

 as far as D. 



3. In no instance was a, flame observed at the end of the con- 

 veyor. 



4. Smoldering lumps of ground products were found to be very 

 dangerous, in that they set fire to the wooden base of the attrition 

 miU. 



On account of the fire hazard involved in these smoldering lumps 

 of grain, special emphasis should be placed on this result of Series 12. 

 During this series of tests it was observed that smoldering lumps, 

 resulting from the explosions, were frequently brought out by the 

 screw conveyor. Some of these lumps happened to be placed on 

 several layers of asbestos paper. After several minutes it was ob- 

 served that a hole had been burned through the asbestos paper. 

 Even when this -smoldering material was buried under several inches 

 of grain it continued to burn, although not as weU. as when it was 

 spread out in a thin layer and exposed to the atmosphere. That this 

 smoldering material was to be regarded as a great source of danger 

 was very forcibly demonstrated when on the following morning it 

 ,50220°— IS— Bull. 681 3 



