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fatalities and their geographical distribution is a matter of particular importance.

The rariations in rates in the different coal fields are shown in the following table:

FATAL-ACCIDENT RATES IN COAL MINING IN NORTH AMERICA DUE TO GAS

OR DUST EXPLOSION, FOR THE PERIOD 1899 TO 1908.

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The rariation in rates ranges from a minimum of 1.25 per 10,000 for the east-central section to 17.17 for the southern section. The wide range is due primarily and largely to fundamental differences in the character and depth of the coal beds in the several coal areas, which are brought out in a striking manner by reference to the tables for the different coal-mining States. Gas and dust explosions have been combined, because of the fact that dust explosions per se are probably extremely rare in coal mines, while dust explosions caused by previous gas explosions are quite common, and particularly so in some of the States of the southern and Pacifie coast fields. Coal dust, as a factor in mine explosions, has only been regarded as such within very recent years, after a number of particularly serious disasters, in which there could be no doubt that what had been a gas explosion in its inception had subsequently become an explosion of coal du-t. There is probably no more serious question to-day in many of our mining States than the increasing danger of dust explosions, due possibly to the use of coal-mining machinery and to other causes which, as yet, are not fully understood. The subject of du-t explosion is too complex to be discussed in this place, (a) but it may be pointed out that measures of prevention in

a The most important recent contribution to the subject is Bulletin 425 of the United States Geological Survey, on “The Explosibility of Coal-dust," Washington, D. ('., 1910. This bulletin includes a very complete bibliography. Reference should also be had to Bulletin 383 of the United States Geological Survey, on “ Notes on Explosive Mine Gases and Dust," by R. T. (hamberlin, 1909. Among other important recent contributions reference should be had to an article on “ The Dust Problem in Coal Mines," by Joseph Virgin, Engineering and Mining Journal, October 9, 1909; “ Coal-dust as a Factor in Mine Explosions," by Henry M. Penn, Engineering and Mining Journal, July 4, 1908; “ Equipment for the Prevention of Mine Explosions, with Special Reference to

be better understood when it is stated that heretofore the United States Geological Survey has given the details of causes of fatal accidents in only 3 specific groups, while in some of the tables in the appendix to this study the facts are given in detail in 21 groups. The practical value of the tabular analysis of coal-mining accidents, provided the facts by causes are sufficiently numerous, is, of course, in exact proportion to the detailed grouping of individual but welldefined specific causes responsible for coal-mining casualties. Much would be gained by uniformity in the method of tabulation by causes, but efforts in this direction should insist rather upon a comprehensive tabular analysis than upon condensation. (")

The importance of details is best illustrated by specific causes of modern significance, such as deaths due to mining machinery, electricity, boiler explosions, etc. (For further details of the causes of accidents by States, see Table XXIII of the appendix.)

THE FATAL-ACCIDENT RATE DUE TO PRINCIPAL CAUSES.

The rate of fatal accidents by principal causes determines with scientific accuracy the degree of risk exposure to particular hazard in mining experience. The following table is identical with the table on page 454, previously discussed, except that for each cause the rate per 10,000 exposed to risk has been calculated, instead of the percentage distribution of causes, as in the former table. Since the number of some of the causes is small, it has seemed best to use 10,000 employees exposed to risk one year, instead of the usual basis of 1,000. The table is based upon a risk exposure of 5,459,436 mine workers for one year and 18,316 fatal accidents occurring in the coal fields of North America during the decade ending with 1908, or a part thereof, since the returns for some of the States are not complete. The rates for individual coal-mining States and the details for the different coal areas, by number of casualties and the rate per 10,000, will be found in Table XXIII of the appendis.

« For suggestions for improving coal-mining accident statistics, see Engineering and Mining Journal, June 2, 1900, and subsequent issues. Among the more important works on the causes of coal mining accidents are Mining Accidents and their Prevention, by Sir Frederick Augustus Abel, New York, 1999; Explo. sions in Coal Mines, by W. N. and J. B. Atkinson, London, 1886; Essays on the Prevention of Explosions and Accidents in ('oal Mines, by Creswick, Galloway, and Hopton, London, 1574; Elements of Mining and Quarrying, by C. Le Neve Foster, London, 1903; and Practical Coal Jining, by T. H. (ockin, New York, FATAL-ACCIDENT RATE IN THE COAL MINES OF NORTII AMERICI DURING A

TEN-YEAR PERIOD, BY CAUSES.

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The average fatality rate for the North American coal field, according to this table, was 33.6 per 10,000, or 3.36 per 1,000 of persons employed one year.

FALLS OF COAL OR ROOF.

The average fatality rates by principal causes during the ten-year period 1899 to 1908, as given in the above table, may be considered the standard by which the relative frequency of accident occurrence in the different coal fields and coal-mining States can be measured. The standard rate of accident occurrence due to fall of coal and roof, slate, etc., combined was 15.67 per 10,000, but, as brought out by the following comparison, the degree of risk varies considerably in the different coal fields.

FATAL-ACCIDENT RATES IN COAL MINIXG DUE TO FALLS OF COAL, ROOF,

SLATE, ETC., DURING A TEN-YEAR PERIOD.

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This comparison is of very considerable practical significance. For the first time, the true rate of risk from a particular cause in mining operations is here precisely determined by a method which has the sanction of statistical science, and the result is startling, indeed.

The table brings out the fact that in some of the coal fields the fatality rate due to a single group of related causes; that is, fall of coal and roof, slate, etc., is as high, or higher, than the normal fatality rate due to all causes in most of the coal-mining States and Provinces of North America. Even the standard rate, of 15.67 per 10,000, or 1.57 per 1,000, is extremely high, higher, in fact, than the normal fatality rate due to all causes in the United Kingdom, Austria, and Belgium. In the far western coal area the rate has been 31.08 per 10,000, or higher than the fatality rate due to all causes for the whole American coal field. The southern, Pacific coast, and western coal areas all have decidedly higher average rates for this group of causes than the North American coal fields as a whole, while the northeastern, the east central, west central, and eastern sections experienced fatality rates due to fall of coal and roof below the standard, but in the last-named area the rate was very close to the average, so that with the exception of the northeastern and the central sections the fatality rate due to fall of coal and roof, slate, etc., must be considered high, and in some cases extremely high for the entire coal field of North America.

The variations in fatality rates due to fall of coal and roof for the different coal-mining States are, of course, much greater, but they can not be fully discussed here. By reference to Table XXIII of the appendix the facts for each State are made available in the most convenient manner, but the extremely high rates for some of the States may be briefly referred to. In Colorado the rate reached 35.15 per 10,000 out of a total rate, from all causes of accidents, of 55.99, or 62.8 per cent. In New Mexico the fatality rate due to fall of coal and roof was still higher, attaining to 40.48 per 10,000 ont of a total rate for all causes of 72.69, or 55.7 per cent. In Utah more favorable conditions prevailed, but the rate reached 21.56 per 10.000 out of a total of 133.25, or 16.2 per cent. These rates admirably illustrate the danger of reasoning exclusively from a percentage distribution of causes; for, while the fatality rate due to fall of coal and roof in Utah is considerably above the standard (15.67), it is only 16.2 per cent of the deaths from all causes, and thus apparently lower. This apparent contradiction is due to the fact that a very disastrous explosion occurred in I'tah in 1900, which increased the proportion of deaths due to this cause to 73.5 per cent of the whole number. It is evident that for an accurate understanding of the causes of coal-mining casualties, the rate of accidents by cause is required in place of the percentage distribution, but it is equally true that for many practical reasons, particularly such as govern in considerations of pre

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ACCIDENTS, TIR THE PERIOD 1899 TO 1904,

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