Rock Dusting in the West

My acquaintance with rock, dusting as a preventive of wide spread explosions in coal mines dates from the fall of 1914 and the spring, summer and fall of 19.1.5 when I had an opportunity to observe the staging (both before and after) of several of the explosions in the Experimental Mine at Pittsburgh and saw violent explosions stopped by rock dust, also saw violently explosive coal dust made insensitive by use of rock dust to ignition or to propagation or spreading of an explosion. From this work I became a convert to rock dusting though I had previously been a firm believer in watering methods and am yet a firm believer that watering, methods have a well defined place in promoting the health and safety of our coal miners. In 1916, while in the Bureau of Mines service, I made an underground study and a report to the Bureau on the first extensively rock dusted mine, in the United States, the Delagua Mine of the Victor American Fuel Company near Trinidad, Colorado, there being then some ten miles of entry in that mine which had been kept well rock-dusted for at' least four years The dust used was " adobe" or surface soil screened from sweepings of the dry surface wagon roads through a screen with one-eighth inch openings, the dust giving about 20% through 200 mesh and about, 10% of approximately 1/8-inch size. The material was collected during dry weather by contract at $1.00 per ton (sacked) and was accumulated in summer and stored for winter and spring use. The dust was scattered through haulage entries by hand or by an electrically operated blower and was held on shelves along the ribs or between and on timber caps with from 1/4-inch to 2-inch thickness of the rock dust. The cost of maintaining the 10 miles of entry well dusted was about $1,500.00 per year or $150.00 per mile per year. Total cost of 'the rock dusting over a four-year period was about $6,000.00, about 2,500 tons of dust being used and 2,000,000 tons of coal produced; the above cost included about 1,200 days labor dusting at $2.50 per day, 2,500 tons of rock dust at $1.00. per ton and miscellaneous labor, material, repairs, power cost, etc., amounting to about $500.00. The cost per ton of coal produced for keeping 10 miles of entry rock dusted being about 3/10c. In addition to the rock dusting, some sprinkling was done, chiefly in the interior of the mine, costing about 2/5c per ton; and due to spilling of coal and sifting of coal .dust through loose cars on the entry floors, the floors of haulage roads were kept sprinkled between and just outside-the rails. Total cost of sprinkling and rock dusting was about .7/10c per ton much less of course than the same work would now cost. Between January, 1916, and July, 1924, my duties in the Bureau of Mines allowed me, to follow up and make underground inspections and reports on more than 20 coal mine explosions and fires in a number of states of the union and in this work a large number of samples of road, rib, and other dusts were taken to ascertain the effect of moisture, roof and floor dirt, etc., upon the propagation or the stopping of the explosion; also a large part of my work was to obtain evidence pro and con as to influences affecting the disasters and very prominent among those influences were the occurrence or use of water, water drippers, or ponds, as well as of sand, roof or floor rock or dust on floor, ribs, etc. The Dolomite explosion near Birmingham, Alabama, in November, 1922, and the Dawson No. 1 Mine Explosion at Dawson, New Mexico, in February, 1923 (at both of which I made underground inspection and report) both starting on main intake haulage road and both in mines which had fairly elaborate watering systems, convinced me that at least as far as freezing can occur on main intake air courses which also act 2s main .haulage ways, rock dusting is likely to be much more dependable than sprinkling. In making up the report on the Dawson Explosion to the Bureau of Mines (copy of which also