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Boring Blast Holes and How to Insert Dynamite in the Showa Era (1926-1989): Dynamite, Fuse and Detonator
1964 - 1967

Showa Maito-ana Kuri to Komekata: Dai, Michibi, Pisu
[Boring Blast Holes and How to Insert Dynamite in the Showa Era (1926-1989): Dynamite, Fuse and Detonator]
38.1 x 54.2 cm Painting in Watercolors and Ink

It was in 1937 that Nittetsu Inatsuki Coal Pit introduced the auger drill for the first time in the Chikuho region. The Jack hammer had been used for mining coal until then, and it was inconvenient to manually bore blast holes. Other small scale coal pits in this region introduced this new device a few years later. A chisel with a trumpet-shaped head and one with a flat tip had been used there for boring blast holes in coalfaces by hand until then. The blast holes were usually drilled with the auger as deep as 1 meter or more and the dynamite inserted into about 10 holes was exploded together at one time. In each hole, two pieces of dynamite, a detonator, and a fuse were used. However, detonating wires were used instead of fuses in large-scale coal pits. 5 pieces or more of dynamite were sometimes inserted into each blast hole drilled in a very hard coalface with shale. In this case, two detonators were used per hole. When they were inserted into a hole, the bottom of the last piece of dynamite with a fuse and that of the other piece were put together. Clay packing was best for plugging the blast holes after inserting dynamite, but small-scale coal pits could not afford to prepare such thing. Therefore, miners in such pits plugged the blast holes with available refuse or coal dust. Plugging the holes with coal dust or straw ropes was prohibited by the law. However, the blasting done without tamping the blast holes was not effective and the miners gathered the above materials to plug the holes. They had to insert them into the blast holes with sticks or bamboo poles as a rule, but they rarely kept the rule and hastily forced them into the holes with ear-pick-shaped drags (kyuren) used for dragging out cuttings.
Once I saw about three women pit workers making the clay packing 25 millimeters in diameter and 80 millimeters in length by pressing the soft clay near the pit mouth of Inatsuki Coal Pit. Each of them pressed out the packing from a double brass cylinder with a double piston just like pressing out noodles after filling the cylinder with soft clay. They sold it at 1 rin for 10 pieces. The packing was sent down into the pit on mine cars. When the blasting was not effective, miners would say, "Hachi (hasu) utta."
Today, most coal pits use augers also for drilling into hard rock beds.

Translation Assisted by Mr. Nathan Johndro

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