1 In addition to the explosions listed, there were 21 separate major disasters, such as mine fires, falls of roof, etc., with an aggregate loss of 157 lives at bituminous mines during At anthracite mines, during the same period, 19 major disasters causing 291 deaths were reported, of which 12 accidents causing 92 deaths were due the period covered by the table. to explosions of gas. A "major disaster" is defined as an accident on which 5 or more lives were lost. 2 Includes one rescue worker. 1 ROCK-DUSTING COAL MINES The Bureau of Mines believes that had rock dusting been in general use during the years covered by the table, many of the disasters would not have happened and hundreds of lives would have been saved. In view of the large number of deaths from explosions during and since 1922, the bureau urges that the practice of rock dusting be adopted as soon as practicable in all bituminous mines in which dust constitutes a hazard. Although bureau investigators 10 years ago had satisfied themselves that rock dusting would prevent explosions, and had publicly demonstrated its efficacy at the experimental mine, the coal-mining industry of this country did not seek to adopt the practice until recently. Meantime Great Britain and France had made progress in the application of rock dusting and the mining departments of the two countries had officially approved it. Great Britain in 1920 enacted a law requiring the use of rock dust in all dry and dusty coal mines other than anthracite mines. The chief mining engineer of the Bureau of Mines was detailed to study the practice of rock dusting in European countries and the results of his findings were embodied in a report which the bureau has published as Bulletin 225. The British Government then formally proposed that the Department of the Interior and the British Department of Mines should cooperate in efforts to prevent accidents in mines, this cooperation to be more immediately directed toward research for the betterment of explosives for use in gaseous and dusty mines, investigations of electric equipment and other sources of ignition of gas or dust, and the best methods of preventing the propagation of explosions. The American Government approved this cooperation. The British Government sent Dr. R. V. Wheeler, director of research, and Mr. Henry Walker, then deputy chief and now chief inspector of mines, to the United States to confer with the scientific staff of the bureau and to determine upon a joint program of research. Later the director of the Bureau of Mines visited Great Britain where he spent several weeks in visiting mines and consulting with Government officials and mine operators. He also visited several coal mines in Belgium and France to examine the methods those countries used to lessen accidents. While the British officials were in this country they conferred with coal-mining men in various places and described the methods of rock dusting practiced in Great Britain. Afterward the bureau engineers carried on the campaign in various coal-mining districts. As a result, a great many mine operators have begun to introduce rock dusting. Probably no movement for the betterment of safety in coal mines has become effective more quickly than this widespread adoption of rock dusting. The action of the State of Utah in officially adopting rock dusting, after a disaster that killed 171 men, has been mentioned. The inspection departments of other States have informally approved it and the Mine Inspectors Institute of America gave the method hearty indorsement. The Interior Department, through the Bureau of Mines, had already required the use of rock dust under certain conditions in coal mines on the public domain. The accident-compensation insurance companies, through their national association, offer reduced rates to those mines that use the method. AVAILABILITY OF DUSTS To help coal-mine operators to obtain the most suitable dusts among those available in the different coal fields, the Bureau of Mines has made a survey of sources of limestone, gypsum, and anhydrite dust. The bureau has also made many microscopic and chemical examinations of shale dusts to determine whether shales will yield dusts suitable for rock dusting but not injurious to the health of miners. Tentative specifications have been issued for the guidance of mine operators in selecting suitable dusts, and the bureau stands ready to help any operator in making his selection. SAFE ELECTRIC EQUIPMENT Although the distribution of rock dust along the main entries and airways and the providing of enough ventilation to prevent accumulations of gas will greatly lesson the explosion hazard in gaseous or dusty bituminous mines, this hazard can not be eliminated entirely and constant vigilance on sources of ignition is necessary. The three chief sources of ignition are electricity, open lights, and nonpermissible explosives. With the rapid development of labor-saving machinery electric equipment, owing to its flexibility, has become essential to modern coal mining, but the advent of electric power in coal mines has introduced new hazards. Electric currents can cause accidents in four general ways: By shock to persons, by igniting powder, by igniting gas and coal dust, and by igniting inflammable materials such as timber and coal. The use of open-type electrical equipment which permits sparks and flame to enter gaseous and dusty mine atmospheres is a real menace. Records of the bureau show that sparks and flashes from unsafe electrical apparatus caused 26 accidents, which killed 500 men and caused great damage to property. So far as known, no disasters have been caused by equipment approved by the Bureau of Mines. The list of safe equipment approved by the bureau is being extended constantly. As a result of recent disastrous coal-mine explosions in different States, West Virginia is enforcing more rigid requirements for electric installations in mines, the State mine inspectors of Pennsylvania have made similar recommendations, and the Industrial Accident Commission of Utah has ordered that only approved electric lamps shall be used by coal miners and that no flame lamps shall be permitted in the mines except approved lamps required in testing for gas. The most forward step in safeguarding the use of electricity in coal mines is in the progress toward elimination of underground wiring. The hazard from extensive electric wiring in gaseous and dusty coal mines is so great that at least two large coalmine operators, one in West Virginia and the other in New Mexico, are planning to equip their mines electrically without permanent wiring. Recently the bureau completed an investigation which has given the mining industry a safe portable power truck, the first to be approved for use in gaseous and dusty mines. As tests proceed, it is expected that other power trucks will be approved. This truck is used to run coal-cutting machines by a storage battery, thereby eliminating the need of trolley or feeder circuits. Approved electric lamps are now almost standard equipment for gaseous and dusty mines, but more than twice as many open lamps as electric lamps are still being used in what are regarded as nongaseous mines. Mine operators are demanding safe electrical equipment for their mines, and asking for approved hoists, air compressors, pumps, and loading machines. In response the manufacturers are endeavoring to provide the operators with such equipment. In order to help this advance, the Bureau of Mines will have to do more electric testing. Otherwise the manufacturer will have to rely on his own design and construction of such apparatus as the bureau can not test with its present facilities. This will tend toward an undesirable condition that manufacturers, mine operators, and the bureau are anxious to avoid, namely, the production of socalled "flameproof" apparatus, built as carefully as the manufacturer can make it, but lacking the rigid inspection and tests given by the bureau and the assurance provided by the Government seal of safety. The bureau is far behind in meeting the demands on it for tests of mine equipment for permissibility. Ample means should be provided for carrying on the testing until safe types of all kinds of electrical equipment are generally available. SAFE EXPLOSIVES Ever since its establishment, the bureau has strongly urged the use of "permissible" explosives in all coal mines where there is any hazard from gas and dust, and the amount of "permissibles" used has steadily increased. However, while this increase has been steady, the replacement of other explosives by "permissibles" has not been as rapid as it should be, in view of the known effectiveness and greater security of "permissibles." The use of permissible" explosives is required in all gaseous or dusty coal mines on Government lands, and is favored by all State mine officials. Utah now requires the use of "permissible " explosives in all coal mines except anthracite mines. The record of coal-mine disasters in this country shows that during the years 1908 to 1923, 71 mine explosions were caused directly by use of black powder or dynamite; these explosions killed 857 men, injured 173 others, and did great damage to property. On the other hand, the Bureau of Mines does not know of one accident being directly caused by "permissible" explosives. INVESTIGATIONS OF MINE EXPLOSIONS Every mine explosion during the year was investigated by engineers of the bureau, and the operator of the mine was given a report showing the conditions and causes that, in the judgment of the bureau engineers, led to the disaster and giving recommendations as to steps that should be taken to prevent similar disasters. In addition the lessons taught by all the disasters of which the bureau has record were compiled as a report entitled "Causes of |