mine ventilation have been discussed in the same report of the chief mine inspector of Colorado, as follows:

From many years of practical experience in the various branches of underground work and under different conditions of sanitation, I feel safe in stating that the strength, speed, and durability of men working under extremely unfavorable conditions of ventilation are impaired to an extent that their normal working capacities are reduced on an average of at least 20 per cent. For example, assuming a mine, operating under extremely adverse circumstances and having a daily output of 1,000 tons and requiring an average of 50 company men, including drivers, timbermen, track layers, and laborers, at $3 per day, to haul coal and keep the mine in working order. Then if the output is kept up when 20 per cent of the efficiency of the employees is lost, due to poor ventilation, it can readily be seen that by transforming such a mine into one with first-class ventilation, the change would be accompanied by a reduction in the expense of operating equal to the advantages gained by the improvement.

Par. 1. By raising the normal capacity of the men from 80 to 100 per cent by virtue of an improvement in the air, then evidently the total amount of work done by the 50 company men in handling 1,000 tons per day could be performed with equal ease and greater comfort by 40 men. The reduction alone of 10 men at $3 each would be a clear gain of $30 per day to the operator.

Par. 2. This same rule applies also to the miners. With an increase of working power at a ratio of 8 to 10, the earning capacity of the miners would be correspondingly raised and the working area of the mine would be proportionately reduced, and still the same daily output could be maintained. Therefore, with the limitation of the working territory and increased efficiency, the amount of trackage and timbering to keep up would be cut down, the rooms would be driven and the pillars extracted in shorter time and before the roof reached an advanced stage of deterioration as well as the decay of timber. The air courses would be shortened, and consequently fewer stoppings to construct, and the friction against the air and leakages lessened, further diminishing the number of company men needed for the maintenance of the workings. This, together with the increased preservation of materials resulting from the concentration of area, would be followed by a marked reduction in the cost of operating.

Par. 3. Moreover, the lives of mules would be prolonged and the number required to do the work lessened, and, as stated before, the crumbling and falling of roof and sides would be checked and the life of the timber lengthened throughout the mine. These are important features of economy, as the amount of repairing would be curtailed and the number of company men could be further lowered, besides the danger of accidents due to the unavoidable deteriorating condition of roof and the decay of timber would be largely eliminated.

Par. 4. In a misty maine atmosphere the men can not see or hear warnings of danger as quickly, and they are not as lively to get out of the way when it approaches; therefore accidents are more frequent under such conditions than when the air is clear and good. Then, inasmuch as poor ventilation is a factor productive of accidents in this manner, it inevitably adds to the cost of production, regardless whether the accidents are unavoidable or are caused through the negli

concede, it is conclusive that a mine official who permits such unhealthy conditions to prevail on the plea of economy is grossly ignorant and robs his master of legitimate profits at the expense of the health and life of the employees under him as well as neglecting the preservation of the property.

These observations fully confirm the conclusion arrived at after an analysis of the statistical evidence, that the whole subject of mine explosions due to gas or dust requires to be dealt with in a thoroughly scientific manner. (") The tendency, fortunately, is in this direction and at no time has expert judgment been as generally applied to mine management as to-day. What is true in this respect of gas and dust explosions is equally true of fatalities resulting from the accidental explosion of powder, dynamite, premature blasts, missed shots, etc. Perhaps no class of accidents illustrates more forcibly the want of discipline, training, and successful mine experience than safety in the use of explosives, and it may be laid down as a first principle in all mine management that accidents due to this group of causes will be in almost exact proportion to the skill and intelligence of the labor employed.

EXPLOSIONS OF POWDER OR DYNAMITE.

Explosions of dynamite, or powder and blasts, including miscellaneous accidents of this nature, caused a fatality rate in the North American coal fields of 3.75 per 10,000 employed, or 11.2 per cent of the deaths from all causes. Accidents due to powder or dynamite only caused a standard or average fatality rate of 1.77, of blasts (chiefly premature explosions) 1.45, and miscellaneous causes of this nature 0.53 per 10,000 employed. Accidents due to powder and dynamite explosions are not separated in the returns and it is quite probable that common blasting powder is not always clearly distinguished from high explosives, which probably are, sometimes at least, classified as powder" explosions. The fatality rate from these causes is high and naturally there are wide variations in the rates for the different coal fields. The table which follows shows the fatality rate due to explosives for the different coal fields in the order of their importance, compared with the standard average of 3.75 for the North American coal fields as a whole.

See the special report of the Chief Inspector of Mines on the Explosion at Washington Glebe" Colliery, February 20, 1908; Parliamentary Paper Cd., 4183, London, 1908. See also Bulletin 425 of the United States Geological Survey on Explosibility of Coal Dust, by George S. Rice, Washington, 1910, which includes a bibliography on coal dust as a cause of colliery explosions.

FATAL-ACCIDENT RATES IN COAL MINING IN NORTH AMERICA DUE TO EXPLOSIVES, FOR THE PERIOD 1899 TO 1905.

As has been pointed out in the discussion of fatalities due to gas and dust explosion, the classification of accidents by causes is often of doubtful accuracy, and it is quite probable that this in part explains the extremely high rate for the Pacific coast section. In a general way, however, the rates conform to mining experience and well-known differences in methods and usage. The rate of consumption of explosives in mining in the Western States is undoubtedly higher than in the more conservative and economical mining methods of the Eastern States. The range in the fatality rates is from 1.11 in the northeastern section (Nova Scotia) to 24.55 per 10.000 for the Pacific coast States. The rates for the several States emphasize the importance of the suggestion that all returns of accidents due to explosives" require to be used with great caution. In British Columbia, for illustration, "explosions due to causes unknown" caused a fatality rate of 44.25 per 10,000, or of 47.9 per cent of the fatalities due to all causes, while explosions of powder and dynamite, specified as such, caused a rate of only 1.09. In Colorado the combined fatality rate due to explosions was 4.64, but of these 2.27 was ascribed to fire damp, 1.38 to premature shots, 0.59 to delayed shots, 0.30 to explosions of powder, and 0.10 to explosions of lamps. In Illinois the combined rate was 5.08, but of this 2.09 was due to explosions of blasts, 1.21 to explosions of powder, 1.08 to flying coal after blasts or explosions, 0.62 to blown-out shots, and 0.02 to explosions of dynamite, and the same rate due to explosion of gasoline torch. Still more varied have been the reported causes of explosions in Indiana, where the combined rate was 6.40 per 10,000, of which 1.47 was due to the explosion of powder, 1.40 to delayed shots, 0.87 to premature shots, 0.60 to "windy shots," 0.53 to "explosions of smoke" (?), 0.40 to explosion of shots through pillars, 0.33 to fire damp, and the remainder of 0.80 to miscellaneous causes. In Oklahoma the combined rate was 21.42, of which 8.81 was due to shot firing, 3.63 to windy shots, 3.28 to explosions of dynamite, 2.25 to explosions not specified, 2.07 to explosions of powder, and 1.21 to

classified. Granting probable defects in the returns, it is surprising to find that the fatality rate due to motors should be as low as 0.06 per 10,000 in the eastern coal field, which comprehends the States of Maryland, Pennsylvania, and Ohio. In Illinois, for illustration, out of 1,391 fatal accidents only 4, or 0.08 per 10,000 employed, were officially ascribed to motors, while in Ohio 19 out of 1,027, or 0.47 per 10,000 employed, were attributed to this cause. No deaths due to motors were officially reported as having occurred in the coal mines of Pennsylvania, which, no doubt, is partly due to errors in classification. For these reasons, it would serve no practical purpose to discuss the fatality rates due to motors in the different coal areas and coal mining States, but the self-evident defect in coal mining statistics clearly brings out the necessity of a uniform classification of causes to be agreed upon by the mining officials of the different States.

EXPLOSIONS OF GAS OR DUST.

Statistical defects are inherent in all classification, but they can be materially reduced by a critical examination of individual returns. Of no group of causes is this more true than of gas and dust explosions, explosions of dynamite and powder, blasts, etc. There are practical difficulties to be overcome which at times will baffle even the most skilled, for cause and effect will often be confused, and it will occasionally occur that the true but insignificant cause of a coalmining accident is overshadowed by the disastrous effect. A can of powder explodes and results in a subsequent gas and dust explosion with a considerable loss of life. Should such an explosion be classified under explosives or explosions? Or, a naked light ignites fire damp and causes a small gas explosion, which results in the explosion of an underground powder magazine, with disastrous results to life. Should such an accident be classified as gas explosion, or as a powder explosion? A compromise is necessary in such cases, but it would be of great value if definite rules governed in the statistical classification. It is due to these differences in the determination of the true cause that so many apparent errors and contradictions occur in coal-mining accident statistics and without a definite understanding among the different mine officials, a decided improvement can not be expected for many years to come.

As classified in Table XXIII of the appendix, there have been 2.571 fatal accidents due to gas and dust explosions in the coal fields of North America during the period under consideration, or 14 per cent of the fatalities due to all causes. The standard or average rate of accident frequency was 4.71 per 10,000, against 4.04 for mine cars and 1.77 for deaths due to explosions of powder or dynamite. Gas and dust explosions, therefore, are among the most important causes of mining