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either coal or rock in coal mines permissible 15 explosives or equivalent permissible device be used exclusively, and in addition recommends that in blasting:

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(a) Each charge shall be in a hole properly drilled and stemmed with incombustible material.

(b) Each shot shall be fired separately by a permissible singleshot blasting unit, using an electric detonator or igniting equivalent of a kind specified by the Bureau for the particular permissible explosive or permissible blasting device.

(c) Before and following each shot in gassy and slightly gassy coal mines, examination for gas shall be made with a permissible flame safety lamp or permissible equivalent."

(d) If more than 12 percent of inflammable gas is found, in the quantity and by the method specified in Mine Safety Decision 9,18 the place shall be considered to be in a hazardous condition and before another shot is fired the gas shall be reduced by ventilation below the percentage and quantity specified in Decision 9.

(e) Each shot employing explosives shall be prepared and fired by or under the immediate supervision of a man having a State certificate as a mine examiner, fireboss, or foreman; and whenever conditions permit all other men than those authorized to prepare and fire shots shall be out of the mine when shot-firing with explosives is being done.

This decision, as stated in its opening words, supplements Mine Safety Decision 2 which primarily recommended the use of permissible explosives. Since the time of issuing that decision, a blasting device has been tested by the Bureau of Mines and determined to be suitable for use in gassy and dusty mines and has been termed a "permissible blasting device." This instrument consists of a reusable steel cylindrical shell which is charged with highly compressed or liquefied carbon dioxide and contains a heating element to be ignited by an electric squib within the container. A firing circuit can be established only after inserting a bayonet-locked firing plug in the end of the container. Only a permissible single-shot blasting unit should be used for firing.

Permissible explosives are "permissible" only when used in the manner prescribed in the "Schedule of Tests." This decision (12) specifies that permissibility requires the shot hole to be properly

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'Anything that has successfully passed scheduled tests and is officially approved by the United States Bureau of Mines is termed "permissible."

16 Exception: This rule would not apply where shot-firing is done electrically from the surface when all the men are out of the mine.

"Mine Safety Decision 1 relative to permissible flame safety lamps or equivalent.

18 Decision 9, paragraph 5: If the air of any unsealed place when sampled or tested in any part of that place not nearer than 4 feet from the face and 10 inches from the roof shall be found to contain:

(a) More than 12 percent of inflammable gas, the place shall be considered in a hazardous condition and require improved ventilation and

(b) If more than 22 percent of inflammable gas, the place shall be considered dangerous, and only men who have been officially designated to improve the ventilation and are properly protected shall remain in or enter said place.

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located with reference to the "burden" of the blast and that the explosive charge be stemmed with incombustible material. The charge should be fired by electrical detonator, using a permissible single-shot blasting unit, one shot at a time, except in firing electrically from the surface when all men are out of the mine, as is the practice in some of the mines of Utah and in certain other districts.

The rapid firing of a series of shots in coal mines by shot firers who may not have charged the shots, who proceed from place to place firing the groups of shots, and who do not make any inspections presents a great hazard. Where several shots are fired in one place, gas may be liberated and (or) coal dust stirred into the air by the first shots, and a subsequent shot may ignite the dust and (or) gas, as has frequently happened.

Furthermore, if one or more of the shots in a face or pillar_are what are termed "depending shots," it is impossible to foresee how much or how little coal is thrown out by the first blast, leaving too light a burden for the second blast or else so heavy a burden that it may cause a blown-out shot. No permissible explosive or blasting device so far tested and given permissibility is absolutely free under all conditions of use from the possibility of some external flame, and if there is inflammable gas in explosive proportions in an amount in excess of that given in clause 4 of Decision 12, or if there is a dense heavy cloud of coal dust present, ignition may occur which may lead to a disastrous explosion. Although this combination of circumstances is perhaps rare, it has occurred and may occur again if every precaution is not taken.

(f) Where more shots than one are to be fired in a working place of a mine it is possible that under some conditions special hazards may exist in firing shots separately and inspecting between shots; in such cases simultaneous multiple shot-firing may be allowable, when permitted by the respective State mining regulations. This condition may occur in steeply pitching workings or in working places where outbreaks of gas may be released by shot, or where the roof, draw slate, or coal is so friable that despite use of usual good timbering methods, falls are likely to occur after a shot, making it dangerous to inspect the roof and to connect the firing leads for the next shot. This possible exception making choice of a lesser hazard does not mean that the Bureau of Mines recommends simultaneous multiple shot-firing when it is at all practicable to fire safely one shot at a time with careful inspection for gas and roof conditions before and after each shot. When multiple shot-firing is necessitated by the conditions, it should be done by firing simultaneously with standard electric detonators. The use of fuse and (or) delay-action detonators, so called, is dangerous because of the possibility that a delayed shot may ignite gas or a coal-dust cloud thrown out by a previous shot.

No multiple shot-firing device for use in gassy coal mines under this exception has been approved by the Bureau of Mines at the time of completing this paper (May 1933), but an investigation is being

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conducted to determine its feasibility; meanwhile, when multiple simultaneous shot-firing is necessitated by the conditions, such available multiple shot-firing device should be selected as will give as low-tension current as possible for firing not to exceed 10 shots at a time, with duration of current of the smallest fraction of a second. Under no circumstances should the power lines be used in blasting when men are in the mine.

In section 1 of the Decision (12) emphasis is properly placed on a shot hole being properly drilled and stemmed with incombustible material. This applies to blasting with a permissible device as well as with explosive.*7

NOTE: Copies of the Mine Safety Decisions mentioned in § 25.11 may be obtained from the United States Bureau of Mines, Washington, D. C.

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**For statutory and source citations, see note to § 25.0.

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Bureau of Mines, Department of the Interior: See Chapter I. Petroleum Conservation Division, Department of the Interior: See Chapter IV. Forest Service regulations relating to mineral developments and mining in national forests: See Parks and Forests, 36 CFR 251.6, 251.12, 251.15, 251.16. General mining regulations of the General Land Office: See Public Lands: Interior, 43 CFR Parts 185, 191.

General Land Office regulations relating to mineral lands in Alaska: See Public Lands, 43 CFR Parts 66, 69–71.

Office of Indian Affairs regulations governing leases and sale of minerals on restricted Indian lands: See Indians, 25 CFR Parts 180, 183, 186, 189, 192, 195, 198, 201, 204, 207, 210, 213.

SUPPLEMENTAL PUBLICATIONS

The classification of the public lands, U.S.G.S. Bulletin 537. Director of the Geological Survey and others. 1913.

Decisions of the Department of the Interior.

Operating regulations to govern coal-mining methods and the safety and welfare of miners on leased lands of the public domain under the Act of February 25, 1920 (41 Stat. 437), Bureau of Mines. Apr. 30, 1921.

Operating regulations to govern the methods of mining oil shale, phosphate, sodium, and potash, and the safety and welfare of employees in connection therewith under the Acts approved February 25, 1920 (41 Stat. 437) and October 2, 1917 (40 Stat. 297), Bureau of Mines. Feb. 13, 1922.

Operating regulations to govern the production of oil and gas, Act of February 25, 1920 (41 Stat. 437), Bureau of Mines. June 4, 1920.

Plan for conducting work under operating regulations to govern the production of oil and gas under the Act of February 25, 1920 (41 Stat. 437), Bureau of Mines. June 4, 1920.

Operating regulations to govern the production of oil and gas under the Acts of February 25, 1920, June 4, 1920, and March 3, 1923, and under special agreement by the United States, Bureau of Mines. Mar. 3, 1923.

Operating regulations to govern the production of oil and gas under the Act of February 25, 1920 (41 Stat. 437), Act of June 4, 1920 (41 Stat. 812), and Act of March 4, 1923 (42 Stat. 1448), and under special agreement by the United States, Geological Survey. July 1, 1926.

For list of abbreviations used in this chapter, see note to 8 201.1.

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Sec.

PART 201-CLASSIFICATION OF PUBLIC COAL LANDS

Sec.

201.1 Conditions necessary for classifi- 201.2 Classification by quarter-quarter Ication of land as coal land. (a) Minimum heat value.

(b) Minimum thickness.

(c) Depth below surface varying
with thickness and heat
value; exceptions.

sections or surveyed lots. 201.3 Review of classification.

CROSS REFERENCE

General Land Office regulations relating to public mineral lands: See Public Lands: Interior, 43 CFR Parts 185, 187, 191–198.

Section 201.1 Conditions necessary for classification of land as coal land. Land shall be classified as coal land if it contains coal having:

(a) Minimum heat value. A heat value of not less than 8,000 B. t. u. on an air-dried, unwashed or washed, unweathered mine sample.

(6) Minimum thickness. A thickness of or equivalent to 14 inches for coals having a heat value of 12,000 B. t. u. or more, increasing 1 inch for a decrease from 12,000 to 11,000 B. t. u., 1 inch for a decrease from 11,000 to 10,500 B. t. u., 1 inch for each decrease of 250 B. t. u. from 10,500 to 10,000, and 1 inch for each decrease of 100 B. t. u. below 10,000.

(c) Depth below surface varying with thickness and heat value; exceptions. A depth below the surface for a bed of coal 6 feet or more thick of not more than 100 feet for each 300 B. t. u. or major fraction thereof, and for a bed of minimum thickness for that coal a depth of not more than 500 feet, and for beds of any thickness between the minimum and 6 feet a depth directly proportional to that thickness within these limits, provided that, if the coal lies below the depth limit but within a horizontal distance from the surface not exceeding 10 times the depth limit, or if its horizontal distance from the foot of a possible shaft (not deeper than the depth limit) plus 7.5 times the depth of such shaft does not exceed 10 times the depth limit, the land shall be classified as coal land; Provided further, That the depth limit shall be computed for each individual bed, except that where two or more beds occur in such relations that they may be mined from the same opening the depth limit may be determined on the group as a unit, being fixed at the center of weight of the group, no coal that is below the depth limit thus determined to be considered. (Sec. 1, 20 Stat. 394; 43 U.S.C. 31) [Regs., Feb. 20, 1913, 41 L.D. 528]

ABBREVIATIONS: The following abbreviations are used in this chapter:

I.D.

L.D.
Regs.

B. t. u.

Decisions of the Department of the Interior.

Decisions of the Department of the Interior relating to the public lands.
Regulations issued by the Geological Survey.
British thermal units.

201.2 Classification by quarter-quarter sections or surveyed lots. Classification shall be made by quarter-quarter sections or sur

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