Temporary stoppings or seals generally are constructed of brattice cloth or canvas, if available, because they can be erected quickly and can be made fairly tight. If a more substantial stopping is desired, boards covered with brattice cloth or boards with pieces of brattice cloth, stiff mud, or wood fiber packed around the edges and in cracks and holes can be used. Except where stronger stoppings are necessary, wood is generally not as desirable as brattice cloth for temporary stoppings or seals. More time is required for construction, and unless the entire surface of a wood stopping is plastered it is little, if any, tighter than a well-constructed brattice-cloth stopping. Temporary stoppings should be set from 4 to 6 feet or more inside of openings to be sealed to allow room enough to erect permanent stoppings outby the temporary stoppings.

Brattice cloth.-If it is necessary to erect a temporary stopping quickly, or if it is not essential that the stopping be especially tight, a brattice-cloth stopping can be erected as follows: Select a suitable point and set a post near each rib, wedging it securely in place. Nail a board (6 to 12 inches wide and about 1 inch thick), extending from rib to rib, across the top and bottom of the posts. Cut a piece of brattice cloth large enough to cover the opening to be closed and hold it in place. Nail the brattice cloth to the top and bottom boards and, if possible, to the ribs. Complete the stopping by shoveling fine material along the bottom. Although a stopping of this type will allow a certain amount of air leakage, it is tight enough for most purposes and can be erected in minimum time. Where time is not a serious factor and a fairly tight stopping is required, or where the stopping must withstand considerable air pressure, a more substantial one of brattice cloth should be erected (fig. 11) as follows: Select a point where the roof and ribs are solid and

well squared and pick down all loose material. Set posts about 1 foot from each rib and one or more posts (depending on the size of the opening) between the two rib posts. Be sure that the posts are set firmly and that where the floor is soft a mud cap or partial still is set under each post. Nail suitable boards across the top, center, and bottom of the posts. The boards should extend from rib to rib and the top and bottom boards should be placed as near as possible to the roof and floor. If the ribs are irregular, short boards extending from the top to the center and from the center to the bottom boards, following roughly the curvature of the ribs, should be nailed along both sides of the stopping. A piece of brattice cloth or canvas large enough to cover the opening to be sealed, allowing a small surplus on sides, top, and bottom, should be nailed to the boards. Additional layers or plies of brattice cloth, depending on the size of the opening, the air pressure against the stopping, and the thickness and type of brattice cloth, should be nailed on top of the first layer to obtain a tight fit. To close small openings around the edges of the stopping, wooden cleats (small pieces of boards) should be used to push the brattice cloth into all irregularities of the roof, ribs, and floor and should be nailed into place. To obtain maximum tightness it may be necessary to calk the edges of the stopping with pieces of brattice cloth or stiff mud or wood-fiber plaster and to shovel fine dirt against and along the bottom. With reasonable care, a bratticecloth stopping can be constructed that will allow only slight leakage of air.

Wood. If brattice cloth is not available for temporary stoppings, or a more substantial stopping is required, various kinds of boards can be used. Usually, rough boards of various widths and about 1 inch thick are used, but for a tight stopping it is advisable to use tongue-and-groove boards. A wooden stopping is erected as follows: Select a suitable place and set, firmly enough, posts in the opening to be sealed. A shallow hitch should be dug in the roof, ribs, and floor, and the boards fitted snugly into the hitch as the stopping is erected. If tongue-and-groove boards are not used and sufficient brattice cloth is available, the entire surface of the stopping should be covered with a layer of the cloth. If brattice cloth is not available, cracks or holes and places where boards are joined should be closed with stiff mud or wood-fiber plaster. In either case, the edges of the stopping should be calked with small pieces of brattice cloth, mud, or plaster. If carefully erected, a wooden stopping of this type will be fairly strong and will allow a minimum of air leakage.

PERMANENT STOPPINGS OR SEALS

The character of the permanent stoppings or seals for sealing a mine fire depends on the materials available, the length of time they are to be in use, the necessity for complete airtightness, and the strength required to withstand pressure or crushing. Permanent stoppings or seals may be built of brick, cement blocks, concrete, tile, wood plastered with wood fiber, mud and cement, or cement mortar, wood with a layer or two of brattice cloth or tarred felt between layers of planks, or pack walls of various kinds.

Permanent stoppings erected for fire seals should be well hitched in the ribs, roof, and floor and built snugly into the hitches to make

them as tight as possible. Provision should be made for collecting air samples, taking water-gage readings, and "bleeding off" excess pressure of fire gases by placing a pipe or pipes with suitable valves in one or more of the stoppings. It may be advisable, also, to pro

vide pipes and valves in some of the stoppings for the purpose of flooding or draining the fire area.

A pipe for collecting air samples may be placed anywhere in a stopping, as, after the gases are diffused, the same mixture is likely to

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FIGURE 12.-Brick stopping.

be found anywhere behind the seals. For convenience, usually the pipe is placed near the center of the stopping. The number of stoppings in which pipes should be placed for collecting air samples, etc., will depend upon the area under seal, the number of stoppings used to seal the fire, and their position.

Permanent stoppings should be patrolled regularly, inspected frequently for leaks, and all leaks closed promptly.

Brick-Stoppings or seals constructed of brick (fig. 12) usually are satisfactory; brick withstands crushing about as well as any material, and the size is well adapted to fitting into the irregularities of the ribs and roof. Brick stoppings should be 9 to 13 inches thick, according to the strength required. A strong cement mortar should be used. One part cement to two parts sand will give great strength and a 1-to-3 mixture will give a strong mortar for general use. The addition of 5 to 10 percent of hydrated lime will make the mortar

Association.

easier to work and probably quicker to set. After a brick stopping has been completed, the entire face of the stopping and the roof, ribs, and floor for a distance of several feet should be well plastered with cement mortar to prevent air leakage. The National Mine Rescue Association's 10 type of stopping is a modification of a brick stopping for fire seals (fig. 13). The important feature of this stopping is the tile section substituted for some of the bricks. This section is usually placed near the center of the stopping; it is 3 by 3 feet (or larger if desired) and made of 5- by 8- by 12-inch back-up tile. The entire stopping should be well plastered with cement mortar. As it is difficult to make an opening in a solid brick wall, the tile center should be used in all stoppings that must be removed after extinguishment of the fire through which inspection or exploration of the fire area may be made. The tile center can be knocked out easily and, if necessary, the hole may be closed quickly with other tile.

10 The National Mine Rescue Association, formerly "Smoke Eaters" Association, is composed of men who actually have worn respiratory equipment during rescue and recovery work following mine fires or explosions.