THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CIX. FRIDAY, APRIL 30, 1915. No. 2835. Report on the Explosion at the Hojo Colliery, Japan. By S. MEGURO.* This detailed account of the greatest disaster in the history of Japanese mining was prepared specially for the Colliery Guardian by the inspector who investigated the cause of the accident. No less than 671 men lost their lives, and Mr. Meguro attributes the explosion to a defective safety lamp. The methods by which he has arrived at this con- clusion betray great ingenuity, and the report is a distictly original contribution to the literattire on the subject. The explosion at the above colliery, which constitutes the greatest disaster in the history of Japanese mining, occurred at about 9.30 a.m. on Tuesday, December 15, 1914. The number of persons who were killed by the explosion or died from the effects of the afterdamp was 667, and four men lost their lives while engaged in the rescue work. The Colliery. The Hojo Colliery is owned by the Mitsubishi Limited Partnership, and extends over ah area of 1,306 acres. The colliery is located at Hojo village, Tagawa district, Fukuoka prefecture, and is 34 miles distant from the port of Moji. The geological formation consists of alternate layers of shale, sandstone, and conglomerate of tertiary age, to which formation nearly all coal fields of Japan belong. As the Tagawa coal field adjoins closely the volcanic rocks of Sannodake Mountain, the carbonisation of the coal has been greatly promoted. The strike of the strata is N. 12 degs. E., and dips on the average 12 degs. to the east. The measures have been subjected to crush from the west, and are faulted in the direction of north to south. Consequently there exist many faults running north to south, and these are nearly parallel to each other. There are three groups of coal seams. The upper coal seam group contains the “ Kusaishi ” .Three-feet seam (thickness 3 ft.) and the “ Wakubuchi ” Three-feet seam (thickness 3J ft.). The middle coal seam group contains the “ Shiakunashi ” seam (thickness 2 ft.) and the “Nanaheda” Three-feet seam (thickness 2|ft.j. The lower coal seam group contains the Three-feet seam (thickness 3ft.), “Nanaheda” Five-feet seam (thickness 5|ft.), Eight-feet seam (thickness 7|ft.), “ Gosuke ” seam (thickness l|ft.), “ Banshita ” Five-feet seam (thickness 5ft.), and “Tagawa” Four-feet seam (thick- ness 31 ft.). Among the above-mentioned, the workable seams are the Eight-feet seam and Tagawa Four-feet seam. The former is chiefly worked, the latter as yet not having been worked extensively. The analyses of the Eight- feet seam coal and Tagawa Four-feet seam coal are as follow :— Eight-feet Four-feet Composition. seam. seam. Per cent. Per cent. Moisture 2'42 2-41 Volatile matter ... 26'98 39'33 Fixed carbon 67’8 50'19 Asli 5'22 7-74 Sulphur 0 37 0-33 Specific gravity ... 1 28 1-27 Calorific power ... 7,260 calories 7,447 calories The coal is non-caking. The strike of the coal seam is N. 12 degs. E., and dips 10 to 12 degs. to the east. In November 1894 this mine was purchased by Mr. N. Oki (manager of Mitsubishi Namadzuda Coal Mine), and afterwards the mine was transferred to the Mitsubishi Limited Partnership. In March 1902 the colliery com- menced sinking the first and second shafts, and finished the work in January 1908. There are two shafts, lying 180 ft. apart, one of which is 893 ft. 7 in. deep, and 14| ft. in diameter, while the other is 896 ft. 7 in. deep and 18 ft. in diameter. The * The Chief Engineer of Fukuoka Komusho (Mine Inspec- tion Office of the Japanese Department of Agriculture and Commerce). former is used for winding and as a downcast, but the latter is used for winding, drainage, and as an upcast. Both were constructed with brick ^offerings. The head- gear was constructed with iron girder frame, and the height to the top of pulley is 75 ft. from the ground. The weight of the cage is 1-7 tons, and it contains two tubs, which have- a capacity of 0-6 ton each. Ormerod detaching hooks are in use. Method of Working. From the downcast shaft bottom stretches a level to the_ eastward 270 yds. in length, called the Togo oroshi, or incline. Parallel to this level, at a distance of 40vds., there is a level called the Kuroki incline, 320 yds. long. From the upcast shaft bottom to the eastward stretches a level, 320 yds. in length, called the Oyama incline. The above three levels are the main levels, which are used for ventilation, drainage, and transportation of materials for all underground workings. They are connected with further levels and inclines. At the rise side of the upcast shaft bottom an ascend- ing gallery is driven to the westward, which is called Oyama nobori, or level, 250 yds. long. From this roads are laid off right and left. f'v. U •- Iff hl. Fig. 1.—-View of the Hojo Colliery, Japan. From the third level of the Kuroki oroshi, towards the south-east, an incline of 650 yds., which is called New Kuroki oroshi, is driven. Parallel to this incline, at a distance of 40 yds. to southward, another incline is driven of the length of 450 yds. This is called New Oyama oroshi, which is at present used for a pipe and cables lines laying. The relative position of the levels and inclines will be seen from the underground plan of the colliery (fig. 2). The method of working is the pillar and stall system. The daily output of coal is on an average 700 tons, of which 70 tons consist of shaly coal, used as boiler fuel. At present the working seams are three, namely, Eight- feet seam, Nanaheda seam, and Four-feet seam, of which the most extensively worked is the Eight-feet seam. When the pillar of the latter seam is worked, the roof, which consists of the Nanaheda seam, rapidly falls in, after which the coal of the latter seam is extracted. The number of miners employed in September 1914 was 1,640. The coal pillars are 30 yds. square, the distance between each level being determined as 100 ft., and breadth of stall 10 ft. When a fall is encoun- tered, it is customary to work out the seam in the return direction. As this mine contains so many faults, it becomes very expensive to maintain a gallery for long, and the above-described method of working comprises the utilisation of faults, the plane area inter- posed between the two faults being worked as one compartment (see fig. 3). o t. *■ / S §■ Fig. 3.—Method of Recovering Pillars. As the occurrence of sillicefied wood and partings of coal is scanty, packing materials are deficient. The coal being hard, the output per man is 80 cu. ft. Since the seam on this side of the fault is worked out in a return direction, there is no packing road (kaido). From the lower point of 55 ft. of the pillar, the coal is transferred into the lower level, and from the point of 35 ft. of the pillar, the coal is carried out into the upper level. Consequently the carrying basket is not greatly used, and the coal is carried by flat baskets (called an “ ebu ”) being scooped up by an instrument called a “ kakieta.” In the galleries coal tubs are drawn by horses or pushed by men. On the inclines the tubs are hauled by the electrical hauling engine or on the endless rope system. Although in the mine, owing to the many faults, regular incline and level cannot be laid, as a result of endeavouring to lay the rails upon the level or incline, the underground traffic became more con- venient than that in other mines. The weight of rail per ft. is 16 to 201b., and the rail gauge is 1A ft. The capacity of the coal tub is 1,5001b., or 0-45 ton, and the dead weight of the same is 1,0001b. The diameter of winding engine cylinder at upcast