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The table is self-explanatory and requires no extended analysis. It is shown, for illustration, that in the eastern section (Maryland, Ohio, and Pennsylvania) falls of coal caused 10.6 per cent and falls of roof, rock, slate, etc., 38.8 per cent, a total of 49.4 per cent, against 21.2 per cent of deaths from fall of coal and 20.8 per cent of deaths from fall of roof, slate, etc., in the northeastern section (Nova Scotia). The highest percentage proportion of deaths caused by fall of coal occurred in the east central section, or 36.9 per cent, while the lowest occurred in the Pacific coast section, or 9.4 per cent. The highest percentage of deaths caused by falls of roof, slate, etc., occurred in the eastern section (Maryland, Ohio, and Pennsylvania), or 38.8 per cent, while the lowest occurred in the east central section, or 8.9 per cent. Unquestionably, some of these differences are the result of variations in the method of reporting the causes, but the differences are too pronounced to be solely due to this possible source of error. When combined the results, in order of relative importance, are as follows:

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PER CENT OF DEATHS FROM FALLS OF COAL AND OF ROOF, SLATE, ROCK,

ETC., IN COAL MINES OF NORTH AMERICA, BY GEOGRAPHICAL SECTIONS.

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There is evidently no very definite or even approximately welldefined relation between the degree of frequency of occurrence of these two closely allied and often identical causes. The most marked opposite conditions are shown to have prevailed in two coal fields not greatly different in geological characteristics or general mining methods; that is, the eastern (Maryland, Ohio, and Pennsylvania) and the east central section (Illinois and Indiana). In the former, fall of coal caused 10.6 per cent, against 36.9 per cent in the latter, so that the combined totals of 49.4 and 45.8 per cent do not vary materially. It may therefore be assumed as a reasonable probability that the two causes are often inclusive of each other, and that for statistical purposes they should be considered as a group, more or less similar in the underlying causes, conditions, and methods of mining responsible for their occurrence.

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The summary table (p. 459) brings out the local significance of other causes, which in some cases eren exceed in importance the fatality rate from fall of coal, roof, etc. Explosions due to gas or dust or the use, storage, etc., of explosives caused the largest proportionate mortality on the Pacific coast section, or 47.1 per cent. Arranged in the order of importance, the fatality percentage due to this group of causes was 39.5 per cent in the southern coal fields, 33.7 per cent in the west central section, 33 per cent in the western section, 25.2 per cent in the east central section, 18.3 per cent in the eastern section, and only 15.5 per cent in the northeastern section. The extremes in the casual occurrence of fatalities due to explosions, as would naturally be expected, were therefore of a wider range, or from 47.1 per cent to 15.5 per cent, against a range of from 49.4 per cent to 27.7 per cent for fatalities caused by falling of coal, roof, etc.

“Falling into openings” considered as a group caused 2.7 per cent of all the fatal accidents in the whole coal area, but the proportion varied between only 1 per cent in the southern section to 5.3 per cent in the northeastern. The differences are chiefly due to the

. fact that there are few deep mines or vertical mine openings in the southern coal fields, where most of the coal is mined by horizontal slopes, tunnels, etc., while in the central coal fields of Pennsylvania, for illustration, practically all the mining is by shaft. The liability to death on account of falling into openings is therefore largely governed by the methods of mining, which vary widely, according to the nature of the coal beds of the several States.

Fatal accidents caused by mine cars, railroad, and other trans; portation or hauling agencies varied from an average of 14.8 per cent for the North American coal fields as a whole to 22.9 per cent for the northeastern coal fields and 8.5 per cent for the west central section. These proportions are also governed largely by local conditions, mining methods, etc., which require to be determined by special inquiry and a thorough analysis of a large number of individual cases. The summary table gives the available information in detail, but, as previously explained, the facts must be considered with great caution and always with a due regard to the geological characteristics of the different coal fields and local variations in methods of mining, labor supply, use of coal-cutting machinery, electricity, etc.

A further consideration of the causes of fatal accidents in coal mining is made possible, at least for some of the States for which the facts are made public in more detail. As far as practicable, in the tables for the several States, all the essential facts contained in the annual reports of the state mine inspectors have been considered, which explains why for some States much more detailed returns are available than for others. The practical value of this analysis will be better understood when it is stated that heretofore the Uniteil 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. (a)

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 18,346 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.

a 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 vining Accidents and their Prevention, by Sir Frederick Augustus Abel, New York, 1859: Explo. sions in Coal Mines, by W. N. and J. B. Atkinson, London, 1886; Essays on the Preventiou of Explosions and Accidents in Coal Mines, by Creswick, Galloway, and Hopton, London, 1574; Elements of Mining and Quarrying, by C. Le Neve Foster, London, 1903; and Practical Coal Mining, by T. II. Cockin, New York,

FATAL-ACCIDENT RATE IN THE COAL MINES OF NORTII AMERIC.I 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 MINING DUE TO FALLS OF COAL, ROOF,

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

Rate per

Section.

10,000 em

ployees.

Western
Southern
Pacific coast.
Standard or average rate
Eastern..
East central.
West central.
Northeastern

34,08 21.57 21.13 15.67

15. 33 11.08 11.06 10, 44

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 34.08 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 40.18 per 10,000 out 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 ('tah 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 ['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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