1 Barricaded, as here used, signifies that the magazine is effectually screened from other buildings, railroad, or highway, either by natural features of the ground or by artificial barricades. These barricades shall be of such height that any straight line drawn from the top of any wall of the magazine (if the magazine has a gable roof, the line should be drawn from a point midway on the roof) to any part of the building to be protected shall pass through such intervening natural or artificial barricade. Also, any straight line drawn from the top of any wall (if the magazine has a gable roof, the line should be drawn from point midway on the roof) to any point at least 12 feet above the center of the railroad or highway to be protected shall pass through such intervening natural or artificial barricade. Where such barriers do not exist, distances should be doubled.

An artificial barricade should consist of a constructed mound of earth or sand fill, with a minimum width of 3 feet at the top. One or more of the sides may be supported by a concrete, timber, or masonry wall.

magazines containing explosives may be reduced one-half where an effectual artificial or natural barricade exists between the magazines.

Box-type magazines, when located outside a building, should be securely anchored. No magazine should be placed in a building containing oil, grease, gasoline, waste paper, or other highly flammable

FIGURE 6.-Barricaded explosives magazine, steel construction.

materials; moreover, a magazine should not be placed less than 20 feet from a stove or furnace or open fire or flame, or less than 5 feet from other sources of external heat.1 11

UNDERGROUND MAGAZINES

Storage magazines in underground mines should be at least 200 feet away from any main shaft or slope or active mine working. They should be at least 25 feet from all haulageways or other travelways and preferably in a section of the mine remote from active workings. Such a magazine should be in a separate drift or chamber and preferably offset from the entrance; magazines should be separated by at least 25 feet of solid ground. Main magazines underground that may contain rather large amounts of explosives can usually be located and constructed, according to plan, at a place where an explosion would not wreck active shafts or haulageways and kill or trap men underground. Ventilation should be so arranged that fumes from a fire or

11 Harrington, D., and Warncke, R. G., Surface Storage of Explosives: Bureau of Mines Inf. Circ. 7307, 1944, 13 pp.

explosion would not be carried through active parts of the mine or endanger men leaving the mine. In mines of any size, where explosives are kept in underground magazines, they should be at locations where an explosion would not block entry to or exit from the mine. PRECAUTIONS IN OPERATING MAGAZINES

Magazines should have natural light or be lighted by portable electric storage lamps, by protected electric systems with the switch outside, or by flood lighting from the outside. The floors should be of wood or other nonsparking material and have no metal exposed. Any explosive material that might be on the floor or on the outside of a case would be liable to detonate if struck or scraped in handling the cases. Magazines constructed of steel or covered with sheet metal should be grounded in regions where there is danger from lightning. Other precautions against fire are keeping the magazine clean and removing waste paper, sawdust, and used empty boxes so that they do not accumulate in or around any magazine. An area of 25 feet around surface magazines should be kept free of rubbish, dry grass or brush, or other easily combustible material. Smoking or the carrying of open lights or other flame into or around any magazine should not be allowed.

Storage magazines should not be heated.

Magazine floors should be swept frequently and the sweepings removed and destroyed. If magazine floors become stained with nitroglycerin, they should be scrubbed well with a stiff broom, hard brush, or mop, using a solution composed of 12 quarts of water, 32 quarts of denatured alcohol, 1 quart of acetone,12 and 1 pound of sodium sulfide (60 percent commercial). The liquid should be used freely to decompose the nitroglycerin thoroughly. If the magazine floor is covered with rubberoid or any material impervious to nitroglycerin, this portion of the floor should be swept thoroughly with dry sawdust and the sweepings taken to a safe distance from the magazine and destroyed.

AUXILIARY MAGAZINES

The main storage magazine for a mine may be on the surface or underground, but in either case one or more distributing magazines may be accessible to active workings. The main magazine for a small mine often is used as a distributing point. The mining law in certain States prohibits storage in the mine of more than 1 day's supply of explosives. Where underground storage magazines are not at a safe distance from active workings and where poisonous gases from a fire or explosion in these magazines would endanger persons in the mine, the quantity stored should be strictly limited.

Magazines used for distributing explosives and detonators should be constructed to meet the minimum standards of storage magazines. The supply kept in strictly distributing magazines should be limited to approximately 1 day's requirements. The same general provisions as to location, fire hazards, and order in the storage arrangements as are applicable to storage magazines should be observed in the operation of distributing magazines.

It may sometimes be advisable to heat distributing magazines in extremely cold climates where the place would otherwise be damp 12 E. I. duPont de Nemours & Co., Blasters Handbook: 1942, p. 70.

and cold. The source of heat should be outside the magazine, and the heat should be circulated through pipes or coils, or as warmed air. The system should be regulated to maintain a mild, evenly distributed temperature.

The safest implements for opening wooden cases of explosives are a hardwood wedge and a mallet. One approved method of opening the case is to drive the wedge against the edge of the lid to loosen it and then drive it under the lid. Another method is to split the sides of the box with the wedge on a corner at the third dovetail from the top. Any kind of metal tool used in opening a case of explosives may strike a spark from the nails that may cause the dynamite to explode. It is true that many cases of dynamite are opened by means of metal tools without accident; but the hazard is always present, and the person using the metal tool is unnecessarily exposing himself to possible death or injury. A metallic slitter may be used safely for opening fiberboard cases, provided it does not come in contact with the metallic fasteners of the case, but it would be preferable to use one made of plastic or some other nonmetallic substance.

STORAGE OF EXPLOSIVES IN WORKING PLACES

Whether explosives in any quantity are stored near the working place or are brought from distributing magazines immediately before blasting time will usually depend on variable conditions, such as distance to the working place and the regularity and sequence of the work; in some instances established custom decides the practice. Explosives should remain in the working place no longer than absolutely necessary. Thus, if mining conditions permit, the explosives should be obtained just before needed for charging or blasting. In many mines blasting is done at irregular periods, and the time required for transportation of explosives from a central magazine makes this impractical. Other conditions also arise where it is necessary to have a working supply of explosives near the working place. Keeping explosives in the working place at some point selected by the miner is undesirable, and a safe storage place should be provided. Separate boxes should be supplied for explosives and detonators; they should be strongly constructed and kept locked. The boxes should be kept in a crosscut or opening off the travelway wherever possible and in any case should be not less than 10 feet from the track and 25 feet from any trolley or power line. Detonators should be stored at a sufficient distance from explosives to preclude handling them over an open box of explosives. Explosives and detonators should be separated until it is necessary to bring them together, usually at the place and time when the primers are made up; it is not safe practice to do this in close proximity to stored explosives. Although a day's supply of detonators may be kept in a separate compartment of a storage box without undue risk if a partition of 4 inches of wood is between them and any explosives, the handling of these detonators into and out of the open box is likely to be unsafe.

Explosives, detonators, or capped fuse left over at the end of a shift should not be left in the working place or lying around in the mine. If they will be needed by the next shift, they may be kept properly in local storage boxes to avoid impractical and unnecessary handling and transportation. If left-over explosives and detonators are not expected to be used on following shifts or storage boxes are