MINE SAFETY DEVICES MANNING. 541 



mine it can not travel into a protected panel or section. The use of 

 the barriers should be supplementary to rock dusting or to the water- 

 ing method of rendering the coal dust inert. If the watering or 

 rock-dusting method fails and an explosion is propagated beyond its 

 origin, then the barriers should be effective in limiting the explosion 

 to the particular section of the mine in which it originates. 



The original barrier, invented by J. Taffanel, of France, con- 

 sisted of 10 to 15 shelves placed across the entry just beneath the 

 roof, spaced about 10 feet apart, and loaded with rock dust. This 

 barrier had two disadvantages: (1) If the explosion was light and 

 slow moving it might pass under the barrier without discharging 

 enough dust to quench the flame; and (2) the dust was exposed to the 

 mine atmosphere, and under some conditions would become wet and 

 packed, so that it was no longer in condition to be efficient in case of 

 an explosion. Accordingly, a number of different types of rock-dust 

 barriers were invented by George S. Eice, chief mining engineer of 

 the Bureau of Mines, which did not have these disadvantages. All 

 of these barriers are operated by the explosion itself through a 

 leverage system sensitive to low pressures; the dust compartments 

 are totally inclosed so that the dust is not exposed to the air current. 



The bureau has tested and found satisfactory four different types 

 of rock-dust barriers, namely, the trough barrier, the concentrated 

 barrier, the door barrier, and the rock-dust stopping. The trough bar- 

 rier and the concentrated barrier can be placed at any point in a mine 

 entry high enough to permit their erection. Each type has a swing- 

 ing board vane 100 feet beyond the barrier in each direction, these 

 vanes being connected by a wire to the operating mechanism. When 

 the explosion swings the vane it causes the barrier to dump the dust 

 into the air current, ^ach. type retains a certain amount of dust 

 near the roof so that in case there is an interval of some seconds 

 between the operation of the barrier and the passage of the flame, 

 there will still be dust in the barrier to be dislodged by the pressure 

 accompanying the flame and to (juench the flame. 



Plate 2, figure 1, shows a trough barrier in place in a mine entry. 

 The wires connecting the barrier troughs with the vane can be seen 

 on either side of the entry near the roof. When the barrier operates, 

 the bottom boards drop as shown in plate 3, and a thick shower of 

 dust falls into the entry. 



Plate 4, figure 1, shows a cloud of dust caused by the discharge 

 of the dust from one of the troughs. 



Plate 4, figure 2, shows the same cloud from a different f)oint of 

 view. 



Plate 2, figiire 2, shows a concentrated barrier after a light, 

 slow-moving explosion. Before an explosion the shelves of this 



