176 THE COLLIERY GUARDIAN. January 26, 1917. SHOT-FIRING IN BITUMINOUS MINES * By M. D. Cooper. In order to obtain first-hand d’ata in regard to the shooting down of coal in bituminous mines, the writer worked as a shot-firer, for nearly a year, in the South Main section of the No. 2 mine of the Ellsworth Collieries Company, Ellsworth, Pennsylvania, a sub- sidiary of the Lackawanna Steel Company. The established practice of the collieries in question is to undercut the coal by electric chain machines across the face of the entry or room. This is followed by replacing any posts removed by the machine runners, or the setting of new posts or timbers, as may be required. The machine cuttings being loaded into cars, the coal is spragged, and a shot-hole is drilled to the depth of the undercut. After the shot-firer has loaded the hole and fired the charge, the working place is cleaned up and timbered if necessary, the sides and face squared up, and loose material taken down. The face is again ready to be undercut. Explosives Used. Permissible explosives were used exclusively in blast- ing coal, viz., Carbonite No. 2 (a nitroglycerine explo- sive), and three different makes of ammonium nitrate explosives : Tunnelite, Red H, and Mineite 5-D. The gases resulting from the explosions of the charges caused no especial distress to the shot-firer, except on the occa- sions when a change was made from one class of explo- sive to another.- At these times the gases had an unpleasant, but not at all serious,’effect for perhaps a day. w The explosive was brought into the mine by ithe miners in small wooden boxes equipped with- grooved covers, and of sufficient size to contain nine cartridges, each 1| in. in diameter and 8 in. long. For breaking occasional rock falls in an entry, straight 40 per cent, nitroglycerine dynamite was used. All of the charges, both of permissible, explosive's and dynamite, were detonated by du Pont No. 6 electric blasting caps, equipped with Oft. iron wires. To elimi- nate all dangers that could result from careless handling, and from men attempting to load their own shot-holes before the arrival of the shot-firer, it was decided to have all of the detonators handled by the shot-firers only. When the miners called at the supply magazine to purchase their daily stock of caps, they were given Fig. 1.—Shot-firer’s Battery. checks, each good for one cap. One of the checks was in .turn given to. the shot-firer each time he fired a charge for the miner. The boxes for carrying the electric blasting caps are ‘ constructed of |in. boards, varnished inside and out, fitted with a hinged cover and lock, and with small sheet metal slots through which a shoulder strap is. run. The dimensions are such that a du Pont paper box con- taining 50 exploders, will fit snugly inside. Each shot- firer is supplied with two boxes, one being left with the supply clerk to be filled, while the other is carried into the mine for use. At the end of the shift, the shot-firer returns the box and a miner’s cap check for each deto- nator taken out of it during the shift. The lead wire used was about 110 ft. in length, of No. 14 B. & S. gauge duplex copper wire, this length being found ample for safety. However, from time; to time a short length is apt to be broken from the end nearer the charge, and to replace this loss a corre- sponding length must be spliced on. This may be neglected in some cases, as there is a tendency on the part of shot-firers to carry no more wire than is abso- lutely necessary. Here is a point of danger, often over- looked, that may well be given attention by safety inspectors. The battery used consisted of two dry cells enclosed in a suitable container (fig. 1). so arranged that the contacts were made inside, and the1 danger of accidental contact avoided. This container was devised by Mr. Andrew Boland, chief electrician of the Ellsworth Collieries Company, and proved to be especially con- venient, since it ctuld be carried in the pocket. More- over, it was doubly safe because, before the circuit was completed, it was necessary both to insert the key and press down the two contact buttons. Clay was used for tamping all shot holes. The usual procedure required the shot-firer to observe the quantity on hand in his section of the mine. When this fell below a sufficient amount, the mine foreman was notified. The latter had a mine car-load sent in by the night shift to the point designated by the shot-firer. The clay was usually unloaded in. a break-through, closed by a stopping, and conveniently located to a number of * Bulletin of the American Institute of Mining Engineers. working places.. Here the miner obtained his individual supply. If the clay proved too dry, enough water was added to make it plastic, in order that it might be worked by hand into roughly cylindrical masses about 1 in. in diameter and 6 or 7 in., in length. In the case of rock falls, the. explosive was, as a rule, placed on the upper surface of the piece to be broken, and then a shovelful of rather wet clay was packed over the charge before firing. The miners were all required to provide a tamping rod, 6 ft. long and 1 in. in diameter, obtained from among the young trees in woods near by. In addition to the materials -described above and used in the firing of shots, it was necessary, of course, to provide each shot-firer with an approved flame safety lamp, in- order to enable him to comply with the law and the rules of the mine, requiring him to test for gas. Method of Firing. The first step to be taken in an effort to safeguard the firing of shots is the selection of suitable shot-firers. The Bituminous Mine. Law of Pennsylvania provides that in the portions of a mine where locked safety lamps are used, “ the mine foreman shall employ a sufficient number of competent persons, who are able to speak the English language, to act as shot-firers, whose duty shall be to charge, tamp, and fire 'all holes properly placed by the miners, and to refuse to charge any holes not pro- perly placed.” To meet these requirements fully, it is essential that the men selected for this work -should appreciate the responsibility placed upon them, understand the proper use of explosives, and be willing and able at all times to keep constantly in mind the fact that the reason for the creation of their positions is the prevention of accidents. It has been found desirable to have, men with ffire-boss certificates.employed as shot-firers, if it is possible to obtain them, because, in the first place, a certificated man is generally competent to undertake the- work; secondly, if the regular fire boss is unable to make' his run, a man is available who is thoroughly familiar with the territory, and is able to go in and make the exami- nations as required by law. The number of shots that may be fired in one shift depends upon the extent of the section covered, the pro- portion of narrow places to wide places, and the experi- ence and ability of the shot finer. Under average con- ditions, a shot-firer ought to be able to load and fire between 40 and 50 shot^ during an eight-hour shift. This limit may be exceeded where the working places are concentrated; or, on the other hand, it may not be reached by a shot-firer who is required to visit a widely scattered group of narro w working places. Cycle of Operations. In making his rounds, the first act on the part of the shot-firer is to find whether the loader at whose place’ he has arrived is ready to have his coal shot down.. It is possible to determine this by standing in the entry and calling or whistling to the man at the face, or by going into the working place and making a. personal exami- nation. By far the best method is the latter, as it affords more frequent inspection of the working places during the shift, but when a shot-firer must cover a difficult section, it may be impossible for him to go into each place on each round. Having found that a shot is to be fired, the shot-firer is required to make a thorough examination of the condi- tion of the face. First, the safety lamp is used to make sure that there is no trace of gas present. The roof and sides are examined to see -that the required method of Fig. 2.—Locations of Shot Holes and Sprags. Undercut Undercut SECTION. ‘A.CE OF ROOM 'J Hole No.l u Hole No.2 posting or timbering has been lived up to, and that no additional timbering is required. Furthermore, two 7 ft. posts must be placed as sprags at the face in a room, or one in an entry, as shown in fig. 2. The miner must load out