540 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



PREVENTION OF MINE EXPLOSIONS. 



For the past six years experimental explosion tests have been con- 

 ducted at the experimental mine of the Bureau of Mines near Bruce- 

 ton, Pa., in connection with the investigation of coal-mine explosions 

 and their prevention. As a result of these tests two recommenda- 

 tions are now being strongly made by the Bureau of Mines in con- 

 nection with the prevention of mine explosions — first, that under con- 

 ditions prevailing in the majority of the mines of the United States 

 rock dust be used for rendering mine road dust noninflammable and, 

 second, that rock-dust barriers be used at various points in the mine 

 for limiting any explosions that may occur. 



USE OF ROCK DUST TO PREA'ENT COAL-MINE EXPLOSIONS. 



Another method of rendering coal dust inert is by watering, but 

 unless the water is frequently applied it often happens that for con- 

 siderable periods the road dust of mines using this method is not in 

 satisfactoiy condition, because the water rapidly evaporates and 

 leaves the dust dry; consequently the rock-dust method is strongly 

 advocated, inasmuch as rock dust will give protection for much longer 

 periods of time than wdll the application of water. 



In the use of the rock-dust method the coal dust is removed from 

 the mine roads as completely as possible and all the surfaces through- 

 out the mine are then coated with dry pulverized rock dust. As the 

 road dust will be gradually coated with an accumulation of coal 

 dust it is desirable when the percentage of combustible dust reaches 

 a certain figure that more rock dust be distributed. This is usually 

 done by a so-called " rock-dusting machine." 



In the event of an explosion the pressure wave that travels ahead 

 of the explosion raises the road dust in a cloud and if this cloud is 

 largely composed of incombustible material it tends to blanket the 

 flame of the explosion and limit its travel. The rock-dust method has 

 been tried in one mine in Colorado for a period of about five years 

 and in three mines in Pennsylvania for periods of one to two years. 

 It is believed that the method will be extensiA-ely used in the future. 



ROCK-DUST BARRIERS. 



A rock-dust barrier consists of a number of boxes or shelves filled 

 with rock dust, which in the event of an explosion is automatically 

 dumped, resulting in the formation of a thick cloud of rock dust 

 and the blanketing of the flame. The plan of using the barriers is 

 to place them at the entrances of panels or sections of the mine, so 

 that if an explosion occurs in a panel or section so protected, it can 

 not travel beyond, or if the explosion occurs in another part of (he 



