FIGURE 3.-Prop with cap piece: A, Prop ready to be driven into place; B, after being driven

QUESTION 68. What is good practice for protection against falls at the working face?

A safety prop or props should be placed within 3 or 4 feet of the face of the coal, depending on the condition of the treacherous roof material. The absence of such safety props has cost many lives. (See fig. 6 for illustration.)

FIGURE 5.-Props under firm roof and on soft bottom: A, Prop with cap piece and floor board;
B, prop with cap piece, bottom resting on shale after the fire clay has been removed

QUESTION 69. When the coal is shot down, is the safety prop liable to be knocked out?

Yes; it is often knocked out by the flying coal, and the first thing the miner should do when arriving at the face is to test the roof and replace the safety prop, and as the coal is loaded out an additional safety prop should be set, as indicated at A and B in Figure 7. Where draw slate appears over the coal, the miner should not work under it but should bar it down and place it to one side before resuming the loading of coal. If it can not be taken down, it should be well supported by timber. (See figs. 7 and 8 for illustration.)

FIGURE 6.-Safety prop and cap piece placed near working face. Distance (a) varies from 2 to 4 or more feet, depending on firmness of roof

FIGURE 7.-Plan of work when safety prop at A is liable to be knocked out by flying coal from

the blast

FIGURE 8.-Elevation and plan of timbering in 20-foot room, using props and caps. The practice in some mines is to set temporary props at A and B before the miner begins to load the coal

FIGURE 9.-Crossbar supported by props and coal rib for scaly or soft roof, 24-foot room

QUESTION 70. Is it good practice to support the ends of crossbars in niches cut into the solid coal?

Where the coal is solid, strong, and firm it is the practice in many mines to support one or both ends of a crossbar in the coal. (See figs. 9 and 16.) In parts of the mine where the coal has been affected by roof pressure or a squeeze the coal on the rib is generally unsound and must not be relied upon to support crossbars.

FIGURE 10.-Collar and props supporting roof at slip or crack in roof. Coal undercut by hand pick

QUESTION 71. What precautions should be taken when a crack or slip is discovered in the roof?

Substantial posts and crossbars should be placed under the crack or slip. The material adjoining the slip may be in the form of a cone, and where a slip is found it is advisable to keep a sharp lookout for the appearance of another slip as the coal is removed. (See fig. 10 for illustration.)

FIGURE 11.-Props with wedges under firm roof; bony gobbed along one rib

QUESTION 72. Where it becomes necessary to gob refuse such as draw slate or bony material should the gob be built around the props?

Good practice is to build the material in the form of a wall kept free from surrounding the props, although it is good practice to build the gob wall flush with the prop, as this gives some protection against props being knocked out by derailed cars. (See fig. 11.)