DUST EXPLOSIONS IN GRAIN SEPAEATOES. 19 



METHODS DEVELOPED FOR PREVENTING EXPLOSIONS OR 

 EXTINGUISHING FIRES. 



GROUNDING THE SEPARATOR. 



As a result of the investigations carried on by the department 

 during the past season, it is believed that a complete system of elec- 

 trical connection from all of the moving parts to a common wire, and 

 a thorough grounding of this common wire, will prevent a large 

 percentage of the fires that are due to the presence of static elec- 

 tricity and an explosive mixture of smut dust and air. There are, 

 of course, several ways in which this wiring may be installed, and 

 the system will vary somewhat with the type of machine. 



One arrangement that is considered by the engineers of the depart- 

 ment to provide as nearly complete protection from ignition by static 

 electricity as any other is illustrated in Plate VIII. An inspec- 

 tion of this illustration will show that the common wire or conductor, 

 A, is grounded through a rod, B, which should be driven at least 3 

 feet into the ground and kept well moistened. There is a connection, 

 C, to this conductor from the shaft of the cylinder through the 

 copper brush D. This brush is in contact with the shaft itself and 

 not with the bearing. This construction is used to avoid any possi- 

 bility of insulation due to the film of oil between the shaft and the 

 bearing. The shakers are connected to the lead E. The lead F, 

 which extends over the entire sieve, connects that piece to the com- 

 mon wire. The lead G connects the metal casing of the stacker fan 

 to the wire A." The investigations in the field indicate that the mov- 

 ing parts just described are the ones on which static electricity is 

 likely to be generated. These investigations also show that there 

 were occasional collections of static electricity on the metal casing. 

 For this reason that connection has been made. The common lead 

 and its main branches are of No. 14 bare copper wire. The connec- 

 tions, particularly^ to the moving points, should be of flexible insu- 

 lated wire coiled a sufficient number of turns to permit full flexi- 

 bility. The wires should be attached to the framework of wooden 

 machines by staples, which should be of the insulated type, or there 

 should be a cushion of rubber or other material between the staple 

 and the wire, as otherwise the wire is likely to snap at that point and 

 break the circuit. 



SUCTION FAN. 



As it is necessary, in order for an explosion to occur, to have 

 present in the separator an explosive mixture of dust and air, the 

 arrangement illustrated in Plate IX is suggested as a means for pre- 

 venting the formation of such an explosive mixture. The arrange- 

 ment consists of attaching to the top of the separator, and near the 

 cylinder,- a suction fan, A. This fan exhausts from above the cylin- 



