 ... the 4,000-foot section or area, a pillar shall be left of sufficient width to permit the driving of the two additional passageways. Separated pairs of parallel entries entering such area, properly maintained, will fulfill the foregoing requirements;...  Bulletin - Side 231928Uten tilgangsbegrensning - Om denne boken
 | United States. Bureau of Mines - 1921 - 52 sider
...sufficient width to permit the driving of the necessary additional passageways to the area. Separatid pairs of parallel entries entering the area in question...may be waived with the approval of the Secretary of the Interior. Hoisting SEC. 20. (a) All hoisting equipment used in shafts and uan'dard1 char- slopes... | |
 | Geological Survey (U.S.) - 1938 - 56 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1939 - 826 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements ; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1967 - 414 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from, a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1959 - 664 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1949 - 566 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1970 - 436 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventillation... | |
 | 1959 - 1024 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
 | 1971 - 584 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventillation... | |
 | 1967 - 422 sider
...parallel entries entering such area, properly maintained, will fulfill the foregoing requirements; and if coal on leased land is to be mined from a mine already existing either on public domain or on private land and in the opinion of the district mining supervisor the ventilation... | |
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