Discussion

MR. LITTLEJOHN: Have you any maximum length that you make your dust barriers? What I mean by that is, your entries are 10 feet wide, and I believe if I remember right, in your single track entries you had only one dust barrier to cover the full width of the. entry in your double track entries, I believe you had two-I would like to know, have you any maximum length you make these barriers? MR. CHAS. LEGER, ROYAL FUEL CO., UTAH: It is stated that they shouldn't be over 8 feet long to obtain sensitiveness. If they make them over 8 feet they are not as sensitive as they should be. They should be made short for two reasons in order to keep the sagging out and to make them as sensitive as possible. MR. DAN HARRINGTON, U. S. BUREAU OF MINES: I didn't come here to enter into any extended discussion on rock dusting or to discuss in particular the situation at Dawson. At the February meeting at Denver, we made a complete study of this matter. Since that time a report was completed and reported to the Phelps-Dodge Corporation and Mr. Moorhead probably has a copy of it, which can give you more complete information as to what we found. We found that with the adobe dusting that they have done, they had six miles of entry pretty thoroughly dusted and of all the samples we took, at least 95 percent of them showed that not only the floor but the ribs and roof were in such a condition that an explosion could not originate in any part of this entry. In other words, this entry as it was dusted was absolutely protected from ignition and propagation. The adobe they used was of material that was non-combustible. In most instances there was not more than 3 per cent of moisture in it.