48 BULLETIN 6S1^ U. S. DEPARTMENT OF AGPJCULTUEE. 



quantitative side of the problem could be takeu care of ouly by care- 

 ful laboratory investigations such as are being conducted by the 

 Bureau of Mines and the Bureau of Chemistry. The chief purposes 

 of an experimental mill, such as that installed at the college, are to 

 show that explosions can be produced in the grinding mill and propa- 

 gated a considerable distance, and to test various preventive devices 

 recommended by manufacturing concerns or by the Government. 

 Both of these purposes have been served to some extent. I 



Although it has not been demonstrated that static electricity, or'j 

 sparks emitted from foreign substances, are capable of producing \ 

 explosions in an attrition mill, it has been positively proved that 

 more intense sources of ignition, such as an open flame or electric | 

 arc, can easily ignite dust mixtures, and that the resulting explosion \ 

 can be propagated through fire traps and the screw conveyor. Con- j 

 sequently, th€ safest plan is to guard against every possible source j 

 of ignition. | 



As to the second use, only three preventive devices have thus far ' 

 been tested — a smgle revolving damper, a double revolving damper, : 

 and a rehef valve. It woidd seem, however, that the present equip- ■ 

 ment would warrant further tests of preventive measures in coopera- i 

 tion with the Government. ~ ■ 



SUMMARY OF CONCLUSIONS. i 



-i 



The final conclusions reached after studying grain-dust explosions ; 

 in an experimental attrition mill, together with the other results I 

 obtained by Government investigators, may be summarized as i 

 follows : ' 



1. Every effort should be made to collect and remove the dust 

 from the grinding mill and surrounding atmosphere. j 



2i In some cases it may be advantageous to use inert gases to ; 

 decrease the oxygen content and thus prevent the formation of an ; 

 explosive mixture of air and dust. i 



3. Every possible source of heat shoidd be eliminated where there , 

 is any danger of having a dust-laden atmospiiere. 



4. Every precaution should be taken to eliminate sparks due to i 

 static electricity.^ -. ; 



5. Greater use should be made of sheet iron on account of the ' 

 very great danger from smoldermg lumps of grain (Series 12, p. 17). ^ 



6. Revolving dampers, as installed here and elsewhere, appear to ■ 

 be of some value as preventive measures for the propagation of ; 

 explosions. 



7. The principle of the automatic relief valve should receive more ! 

 attention as a possible remedy to apply for the partial prevention of i 

 the propagation of the flame. ] 



. : . i 



I 



1 References 38 and 39, Bibliography. 



