DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEOKGE OTIS SMITH, DIRECTOR

BULLETIN 425

THE

EXPLOSIBILITY OF COAL DUST

BY

GEORGE S. RICE

WITH CHAPTERS BX

J. C. W. FRAZER, AXEL LARSEN, FRANK HAAS, 

AND CARL SCHOLZ

WASHINGTON

GOVERN M E N T P K I N T IN G OFFICE 

1910

CONTENTS.

Page.

Introd uctory statement...................................... ............ 9

The coal-dust, problem................................................ 9

i Acknowledgments.................................................... 10

Historical review of the coal-dust question in Europe ....................... 11

Observations in England prior to 1850................................. 11

Observations by French engineers prior to 1890........................ 12

Experiments in England between 1850 and 1885........................ 12

Experiments in Prussia............................,.............:..... 14

Experiments in Austria between 1885 and 1891......................... 16

Views of English authorities between 1886 and 1908.................... 17

German, French, and Belgian stations for testing explosives............ 19

 Altofts gallery, England, 1908......................................... 21

Second report of Royal Commission on Mines, 1909...................... 21

Recent Austrian experiments.......................................... 22

Historical review of the coal-dust question in the United States.............. 23

Grahamite explosions in West Virginia, 1871 and 1873.................. 23

Flour-mill explosion at Minneapolis, 1878.............................. 23

Explosion at Pocahontas mine, West Virginia, 1884.................... 24

Explosion at Pekay mine, Iowa, 1892.................................. 25

Proposed remedies for dust.........'................................... 26

Results of shooting off the solid....................................... 26

Great disasters of 1907.................. .............................. 27

Inaccurate reports of accidents ........................................ 28

Fatalites in 1908...................................................... 28

Inquiry by the United States Geological Survey ....................... 28

Coal dust and its origin and distribution. .................................. 29

Definition of dust .......................... I......................... 19

Ignition and propagation............................................... 30

Coal-mining methods and dust production ............................. 30

.Dust from hand and from machine undercutting........................ 31

Agencies that distribute coal dust ..................................... 33

Experiments with explosible coal dusts.................................... 34

Effect of quantity or density of dust................................... 34

Character of dust used............................................ 34

Method of procedure.............................................. 35

Method of taking samples......................................... 36

Results.......................................................... 36

Coked dusts produced by explosions............................... 38

Effect of degree of' coarseness of dust................ ^................. 38

Results of tests................................................... 38

Method of screening.............................................. 39

Distribution of dust.............................................. 40

Discussion of results............................................... 40

Character of coke produced....................................... 41

3
4 CONTENTS.

Experiments with explosible coal dusts Continued. Page.

Effect of chemical composition ........................................ 41

Past experiments................................................. 41

Investigations in the United States by Chamberlin................. 42

. Experiments of Bedson and Widdas ............................... 42

Investigation in France by Taffanel................................ 43

Comparison of Taffanel's methods with those used at Pittsburg gallery. 44

Informal tests at Pittsburg station ................................. 45

Informal tests with road dust ..................................... 48

Experiments at Pittsburg with coal dust............................... 49

Use of coal dust for tamping ...................................... 49

Experiments with coal dust in humidified air ...................... 50

Humidity of mine air..................................................... 54

Natural principles.................................................... 54

Saturated air at different temperatures............................. 54

Amount of moisture in mine air..................... I .............. 56

Effect of seasonal changes of temperature on mine air............... 57

Instruments for measuring atmospheric moisture ....................... 57

Sling psychrometer............................................... 57

Hygrometer used by the Geological Survey ........................ 58

Stationary hygrometer............................................ '58

Principle of wet and dry bulb thermometer ........................ 59

Method of making hygrometric observations in mines .................. 60

Relation of moisture content to temperature and pressure of mine air .... 61

Remedies for coal dust.................................................... 66

Review of remedies proposed ......................................... 66

Loading and cleaning up dust ; ......................................... 66

Sprinkling from water cars............................................. 67

Calcium chloride and other deliquescent salts .......................... 68

Sprinkling and washing down with hose and nozzle .................... 73

Permanent sprinklers................................................. . 74

Humidifying by steam jets..........................i................. 76

Quick-naming explosives.............................................. 78

Kockdust ........................................................... 80

Brick or concrete linings and. wet zones......:...... '. .................. 82

Tentative conclusions on the dust problem................................. 83

Factors affecting explosibility ......................................... 83

Volatile combustible matter.............................. _ ......... 83

Structure and size............................. .................... 83

Density.......................................................... 84

Moisture ........................................................ 84

ish content ..................................................... 85

Outward conditions .............................................. 85

Conditions affecting propagation of explosions.......................... 85

Amount of dust.................................................. 85

Moisture in dust and in air.... .................................... 86

Mixture with inert substances..................................... 87

Advantages and disadvantages of proposed remedies.................... 87

Force sprinklers in cars................................... ........ 87

Chemicals ....................................................... 87

Cleaning up dust washing down walls............................ 88

Permanent sprinklers zonal linings... '. ........................... 88

Use of exhaust steam sprays ...................................... 88

Stone dust r- ^ - -r ........,.,,, r .,-. TT , r ...,,.,. T ..., r ... r . r .. r .,. 91
CONTENTS. 5

Page.

Observations on manifestations of coked coal dust in mine explosions........ 92

Character of coked dust............................................... 92

Position of coked dust after an explosion............................... 94

Special features in dust explosions......................................... 97

Laboratory investigations of the ignition of coal dust, by J. C. W. Frazer.... 99

Introductory statement............................................... 99

Early experiments of Galloway....................................... 100

Ignition of dust falling on flame....................................... 100

Experiments of Vital................................................. 101

Experiments of Hall and Clark....................................... 104

Experiments of Abel................................................. 105

Experiments of Mallard and Le Chatelier.......................... ... 105

Later experiments by Galloway....................................... 110

Experiments of Thorpe............................................... 110

Reduction of pressure following explosion wave........................ 112

Experiments of Engler ............................................... 113

Lecture experiment of Bedson and Widdas............................. 113

Experiments of Holtzwart and Meyer.................................. 114

Laboratory experiments of Bedson and Widdas ........................ 117

Experiments at Lidivin, France........................................ 121

First series of experiments at Pittsburg testing station................... 124

Second series of experiments at Pittsburg testing station................ 128

Significant points in experiments...................................... 132

Coal-dust investigations at European testing stations, by Axel Larsen........ 133

Protective measures under study ...................................... 133

Apparatus and methods at Altofts and Li6vin.......................... 135

General statement................................................. 135

Instruments at Altofts........................."................... 135

Calculation of temperature at .Altofts.............................. 137

Changes in gallery at Li6vin ...................................... 137

Instruments at Li6vin ............................................ 138

Results at Altofts and Li6vin.......................................... 139

Experiments with protection zones at Lievin....................... 139

Report of work at Lievin ......................................... 139

Conditions at Altofts ............................................. 139

Experiments with protection /ones at Altofts........................ 140

Experiments at Altofts on means of ignition....................... 141

Distribution of stone dust in Altofts gallery and mine .............. 141

Future work at Altofts............................................ 142

Investigations at Frameries in Belgium............................:..-_ 143

Direction of inquiry........ .......................... ........... 143

Objections to watering roadway ................................... 143

Tests of explosives.............. .......... ....................... 146

Extension of gallery.............................................. 147

Investigations in Prussia.............................................. 147

Special preventive measures............................................. 148

Breaking coal by direct water pressure............................. 148

Kruskopf spraying process ........................................ 149

Exhaust steam as a preventive of dust explosions, by Frank Haas........... 150

Moisture in coal dust.................................................. 150

How moisture prevents explosion ................................. 150

Resistance of coal dust to mixture................................. 150

Amount of water absorbed by coal dust ........................... 151
6 CONTENTS.

Exhaust steam as a preventive of dust explosions Continued.

Moisture in coal dust Continued. Page.

Amount of water required in mine....... I........................ 151

Distribution of moisture................... ...................... 152

Exhaust steam in operation........................................... 152

Value found by accident.......................................... 152

Recording instrument ............................................ 153

Records of outside temperature and humidity.. .......°.............. 153

Moisture content of return air..................................... 154

Deficiency of water to be supplied................................. 154

Amount of heat available......................................... 156

Effect of steam on mine air ......................V................ 156

Observations of mine air v/ithout effect of steam.................... 157

Observations of effect of steam .................................... 158

Effect of heating mine air ........................................ 158

Heat radiated from surface of entries .............................. 160

Moisture carried as fog ........................................... 162

Quantity of steam needed for saturating mine air................... 162

Use of steam and water sprays in Oklahoma mines, by Carl Scholz.......'... 163

Purpose of inquiry................................................... 163

Moisture and mine air ..................... '. .... '. ...................... 164

Application of steam and water sprays................................. 165

Cost of water sprays.................................................. 167

Selected bibliography..................................................... 168

Index.............................'...................................... 183
ILLUSTRATIONS.

Page. 

PLATE I. Explosion from coal dust in gas and dust gallery No. 1, Pittsburg

testing station................................................. 34.

II. Coked dr.st from Pittsburg gallery density test with 200-mesh dust.. 38

III. Coke produced from 80 to 100 mesh dust.......................... 40

IV. Coked dust produced from 20 to 40 mesh dust..................... 40

V. Mine hygrometer with improvised sling arrangement.............. 58

VI. .,'1, A'tofta experimental gallery after explosion of dust occupying 450 

linear feet of gallery, August 11, 1908; B, Experiment 58 at

Altofts gallery, showing stone dust and smoke issuing from gallery 

as the result of an explosion of the 275-foot coal-dust zone; C, 

Experiment 99 at Altofts gallery, showing flame and smoke issuing to a distance of 160 feet from explosion of 375 feet of coal-dust 

zone ......................................................... 80

VII. Side of roadway in Altofts mine, showing method of applying stone

dust as a preventive of explosions....... ........................ 82

VIII. A, Coal-dust ignition apparatus us: d at Pittsburg; B, Apparatus used

at Piitsburg, showing ignition of dust.....____.................. 126

IX. A, Time marker, Altofts experimental gallery; /:>', Manometer,

Altofts experimental gallery................................... 134

X. A, Contact breaker, Altofts experimental gallery, before firing; B,

Contact breaker, Altofts experimental gallery, after firing........ 134'

XI. After-damp sampler, Altofts experimental gallery................. 136

XII. A, British coal-dust contact maker, before firing; /?, Same, after firing; C, Apparatus for igniting coal dust by gas flame, Altofts 

experimental gallery..................................... .... 136

XIII. A, Timbering and stone packing in Altofts gallery; J3, Stone dust on

hanging shelves in Altofts colliery.............................. 140

XIV. Radiator and steam pipe in use, Monongah No. 8 mine; B, A epray

in an entry.............................. ..................... 158

FIGURE 1. Diagrammatic sections of cannon end of gallery No. 1, Pittsburg

station................................'....................... 40

2. Curves of equal weights of water vapor per cubic foot for varying 

temperatures and relative humidities when the barometric pressure is 30 inches.............................................. 55

3. Curves of equal relative humidity for varying temperatures and

depressions of wet bulb....................................... 62

4. Curves of equal relative humidity for varying temperatures and

volumes of water carried...................................... 63

5. Coal-dust ignition apparatus of Vital............................ 101

6. C6al-dust ignition apparatus of Thorpe........................... Ill

7. Ccal-dust ignition apparatus of Engler........................... 113

8. Apparatus of Bedson and Widdas for lecture demonstration....... 114

7
8 ILLUSTRATIONS.

Page. 

FIGURE 9. Coal-dust ignition apparatus of Holtzwart and Meyer............. 114

10. First coal-dust ignition apparatus of Bedson and Widdas.......... 117

11. Later coal-dust ignition apparatus of Bedson and W'iddas......... 120

12. Coal-dust ignition apparatus used at Lievin....................... 121

13. Relative effect on flame of stone-dust zones at Lievin and at Altofts. 134

14. Dismantled present sections of Lievin gallery..................... 138

15. Device for breaking circuit in explosion gallery at Li6vin.......... 138

16. Propagation of flame in coal-dust, dustless, and stone-dust /ones.. 140

17. Elevation of apparatus for igniting coal dust by gas flame......... 142

18. Detachable section, Frameries gallery............................ 143

19: Plan of Frameries gallery, showing proposed extension ........... 144

20. Constructional details of extension to Frameries gallery........... 145

21. Device for dislodging coal by injection of water................... 149

22. Atmospheric temperature and water-vapor chart.................. 154

23. Chart of water content of outside air and return air of mine....... 155

24. Chart of temperature and relative humidity of intake air with*

exhaust stearn off and heater off............................... 157

25. Chart of temperature and relative humidity with exhaust steam on

and heater off................................................. 158

26. Plan of intake at Monongah No. 8 mine, showing arrangement of

live-steam heater and exhaust-steam pipe...................... 159

27. Chart of temperature and relative humidity.with exhaust steam on

and heater on................................................ 160

28. Progressive change of temperature of air current due to radiation.. 161
 THE EXPLOSIBILITY OF COAL DUST.

By GEORGE S. RICE.

INTRODUCTORY STATEMENT.

THE COAL-DUST PROBLEM.

This bulletin traces the growth in the belief in the explosibility

of coal dust, summarizes the experiments and mine investigations 

that have established this belief, and gives the present status of preventive measures. It has been prepared in accordance with the provisions of the acts of Congress authorizing investigations relating to 

the causes of mine explosions, and contains references to and descriptions of experiments made at the testing station of the United States 

Geological Survey at Pittsburg, Pa. This station was established, and 

equipped for the-purpose of carrying on investigations relating to 

mine explosions, fuels, and structural materials.

Only within comparatively few years has the dry dust of bituminous and lignitic coals been generally recognized as an explosive 

agent more insidious, threatening, and deadly to the miner than fire 

damp. Fire damp carries its own flag of warning the "cap" in the 

safety lamp but coal dust, though visible, does not attract attention 

until present in large quantities. Fire damp is of local occurrence, 

and except in notable and very exceptional cases is controllable by 

careful manipulation of ventilating currents. If by mischance a body 

of fire damp is ignited in a mine, the force of the explosion is terrific, 

but the effect is localized unless dry coal dust is present, or unless (as 

it very rarely happens) an explosible mixture of methane gas and air 

extends through large areas of the mine. In a dry mine dust accumulates everywhere, and the blast from the ignition and combustion 

of bituminous dust may traverse miles of rooms and entries and wreck 

structures at the entrance to the mine. The comparative potential 

destructiveness of gas and of bituminous dust is strikingly shown by 

the history of the Pennsylvania anthracite mines. These mines not 

infrequently have large inflows of gas, and the resulting mixtures of 

gas and air have sometimes been ignited, yet no such wide-sweeping 

explosions have taken place, despite the presence of dry anthracite 

dust, as have happened in excellently ventilated bituminous mines.

9
10 THE EXPLOSIBILITY OF COAL DUST.

This bulletin, as is emphasized in the body of it, should be regarded 

as a preliminary study of the coal-dust problem. The pressure of 

other work and the almost continuous use of the explosives-testing 

apparatus at the Pittsburg station for the important work of investigating the relative safety of explosives .for use in coal mines have 

limited the experiments that could be made dealing with methods 

of lessening the danger from coal dust. However, it is expected that 

opportunity will be afforded in the future to take up systematic experimenting both at the Pittsburg station and in the field along lines suggested by the results presented in this report.

ACKNOWLEDGMENTS.

The writer desires to express his thanks to Dr. J. A. Holmes, 

expert in charge of the technologic branch of the United States 

Geological Survey, for the inspiration of the studies undertaken, 

and to Mr. H. M. Wilson, chief engineer, for advice in the preparation 

and editing of the paper.

He also desires to acknowledge the great assistance given by his 

associates in the mine-accidents division, Messrs. Clarence Hall and 

J. W. Paul, Dr. J. C. Clement, Dr. J. C. W. Frazer, and the writer's 

assistants, Messrs. A. C. Ramsay and L. M. Jones.

The account of the investigations under way at experiment stations in Europe is by Mr. Axel Larsen, explosives expert, who, in 

connection with his work for the survey, visited these stations and 

examined their equipment.

The chapter on the use of steam as a preventive of dust explosions 

was prepared by Mr. Frank Haas, consulting engineer for the Con- 

"solidation Coal Company, and that on experiments with sprays in 

Oklahoma coal mines by Mr. Carl Scholz, vice-president of the Rock

Island Coal Mining Company. Cordial acknowledgment is made 

of the interest shown by both these gentlemen in the study of the 

practical aspects of preventive measures, and of their kindness in 

preparing for presentation in this bulletin the results of their 

observations. . 

The chapter on laboratory investigations of the ignition of coal 

dust, by Dr. J. C. W. Frazer, a chemist of the Pittsburg station, gives 

a review of the laboratory and other small-scale experiments that 

have been made in the past and an account of the laboratory experiments undertaken by him and to be continued, on the relative explosibility of different coal dusts collected by mining engineers in different parts of the country.

The author's indebtedness to various foreign investigators is 

shown by the numerous quotations from their published works.
THE COAL-DUST QUESTION IN EUEOPE. 11

HISTORICAL REVIEW OF THE COAL-DUST QUESTION IN

EUROPE.

OBSERVATIONS IN ENGLAND PRIOR TO 1850.

In the published account of an explosion in an English colliery, 

Wallsend,. on September 3, 1803, J. Buddle, chief of the Newcastle 

coal miners, says: "The workings were very dry and dusty, and the 

survivors who were most distant from the points of explosion were 

burnt by the shower of red-hot sparks of ignited dust which were 

driven along by the force of the explosion.' >a

Robert Bald, in Jameson's Journal for 1828,° mentions the possibility of the flame from a fire-damp explosion igniting the co'al dust 

strewn more or less thickly about the working places of a colliery.

In a book by W. N. and J. B. Atkinson, English inspectors of 

mines, entitled u Explosions in coal mines" (1886), page 132, there 

is a list of mine explosions in England prior to 1870, made from 

contemporaneous newspaper reports and inquest records. In certain 

explosions it was mentioned that coked dust was observed. Besides, 

the explosion above noted, it was reported to have been found at 

the Jarrow explosion of August 3, 1830, at the Wallsend explosion 

of June 18, 1835, at the Springwell explosion, December 6, 1837, and 

at the Thornley explosion, August 5, 1843.

Professor Faraday, the famous chemist and physicist, remarked in 

his report on the Haswell colliery explosion, September, 1844:°

In considering the extent of the fire from the moment of explosion it is not to be 

supposed that fire damp was its only fuel; the coal dust swept by the rush of wind 

and flame from the floor, roof, and walls of the works would instantly take fire and 

burn if there were oxygen enough present in the air to support its combustion; and 

we found the dust adhering to the faces of the pillars, props, and walls in the direction 

of and on the side toward the explosion, increasing gradually to a certain distance 

as we neared the place of ignition. The deposit was in some parts half an inch, in 

others almost an inch thick; it adhered together in a friable coked state. When 

examined with a glass, it presented the fused round form of burnt coal dust, and 

when examined chemically and compared with the coal itself, reduced to powder, 

was found deprived of the greater portion of the bitumen, and in some instances 

entirely destitute of it. There is every reason to believe that much coal gas was 

made from this dust in the very air itself in the mine by the flame of the fire damp 

which raised and swept it along, and much of the carbon of this .dust remained 

unburnt only from want of air.

It maybe remarked that many investigations of explosions since have 

established that coked and caked coal dust is more generally, though 

not invariably, deposited on the side of timbers and projections 

opposite to the direction from which the explosive wave approached. 

This is commented on by W. N. and J. B. Atkinson.6

o Final Kept. Accidents in Mines Coinm., 1880, p. 30. 

6 Explosions in coal mines, p. 25.
12 THE EXPLOSIBILITY OF COAL DUST.

The remarkable evidence given by Faraday on the importance of 

coal dust as an explosive agent was overlooked for many years.

OBSERVATIONS BY FRENCH ENGINEERS PRIOR TO 1890.

The final report of the accidents in mines commission (1886) gives 

the following account (p. 31) of the first French publication on this 

subject:

Although the reports of Faraday and Lyell were published in 1845, these publications appear to have remained long unknown in France, for in 1855 M. du Souich, 

chief government engineer of the Sainte Etienne Arrondissement, when referring to 

an explosion which had occurred at Firmininy, advanced as new the view that the 

deposition of crusts of light coke on the props was due to dust which had been swept 

up and transported to a distance by the violent current produced by the explosion 

and which, becoming in part inflamed, had extended and prolonged the destructive 

effects originated by the fire damp. On the occasion of two explosions in 1861 

M. du Souich again dwelt upon his views regarding the part played by coal dust 

in increasing the disastrous effects of fire-damp explosions.

In 1867 M. Verpilleaux made some experiments with coal dust 

and concluded that it is an important factor in mine explosions. 

M. Vital, in 1875, while studying the effect of an explosion in a part 

of the Campagne colliery, France, where fire damp had never been 

found, made experiments and from the results decided*that "very 

fine coal dust, rich in inflammable constituents, would increase the 

intensity of an explosion of fire damp and prolong its extent."

In 1882 M. Mallard and M. Le Chatelier, members of the French 

fire-damp commission, reported, as the result of their inquiries, that 

"they rejected the theory that coal dust was any serious danger, and 

maintained that no colliery explosion of any importance could be 

attributed with any probability to the action of coal dust." a

This unfortunate conclusion delayed recognition of the danger of 

coal dust in France for many years, and apparently the explosibility 

of coal dust did not receive general acceptance among French engineers until after the Courrieres disaster of 1906.

EXPERIMENTS IN ENGLAND BETWEEN 1850 AND 1885.

In 1870 Mr. William Galloway, former government inspector in 

Scotland, and then in charge of mines in Wales, began a special study 

of colliery explosions. He had observed that all the great explosions 

in Wales had occurred in dry and dusty mines; also the only great 

explosion in Scotland had occurred in the only dry mine" in Scotland 

known to him. In 1875 he commenced a series of coal-dust experiments in a long box or miniature gallery, and on March 2, 187'6, read 

a paper before the Royal Society in which he stated that "if coal

o Second Kept. Roy. Comm., 1894, p. 5.
THE COAL-DUST QUESTION IN EUROPE. 13

dust and air did not form an inflammable mixture a small addition 

of fire damp, which would not be inflammable alone, would become 

inflammable when coal dust is added."

In 1878 Prof. A. Freire-Marreco gave an account a of coal-dust 

experiments made in conjunction with Mr. W. Cochrane and Mr. 

Morison. They employed a box 8 feet long with a longitudinal partition, with a circulating current of air actuated by a fan. They 

arrived at the same general conclusions as Mr. Galloway.

Soon after making the experiments mentioned, Mr. Galloway 

investigated an explosion that occurred in the Llan colliery, South 

Wales, December, 1875, and reported that "coal dust had undoubtedly played the most important part in the explosion." Subsequently Mr. Galloway made further experiments and investigated 

the explosions at Pen-y-graig, Kisca, and Seaham in 1880, and as a 

result decided "that fire damp is altogether unnecessary for the 

propagation of flame with explosive effect by a mixture of dry coal 

dust and air." 6

Mr. Henry Hall, English mines inspector, in 1876 made experiments 

at St. Helens in an adit or drift which ran in from the outcrop of a 

coal seam and which was 135 feet long. Coal dust was laid on the 

floor and shots were fired at the face of the adit. Mr. Hall stated in a 

paper read before the North of England Institute of Mining and 

Mechanical Engineers that "flame traveled the length of the adit." 

The blast was very fierce "and would certainly have proved fatal to 

anyone struck by it in its course."

This was the first large-scale test of coal dust undertaken, but it 

appears to have been received with skepticism at the time. The 

prevailing impression was that some fire damp must have been 

present.

Up to 1880 the theory of the explosiveness of coal dust had made 

little progress. The British accidents in mines commission began its 

sittings in 1879, but did not make its final report until 1886. In a 

preliminary report issued in 1881 the evidence of practically all 

the expert mining witnesses, except that of Mr. Hall and Mr. Galloway, was to the effect that it was improbable that coal dust would do 

more than increase the range of a fire-damp explosion. Even Mr. 

Galloway testified (March 18, 1880) that it was necessary to have a 

slight amount of gas present to explode coal dust.

On September 8, 1880, a terrible explosion occurred at the Seaham 

mine, County of Durham, England, which attracted general, attention to the subject of coal dust. Prof. Frederick Abel was commissioned to make some experiments with coal dust. His experimental

aTrans. North of England Inst. Min. and Mech. Eng., vol. 28, p. 85. 

& Second Kept. Roy. Cornm., 1894, p. 5.
14 THE EXPLOSIBILITY OF COAL DUST.

apparatus, a long, narrow explosion box or flue, was similar to that of 

Galloway's. In his report he said: a

In the complete absence of fire damp, coal dust exhibits some tendency to become 

inflamed when passing a very large lamp flame at a very high velocity. If exposed to 

the action of a large volume of flame, as from the explosion-of gunpowder, it exhibits 

a decided tendency to propagate flame. But so far as can be determined by experiments on a moderate scale, this tendency is of a limited nature.

Professor Abel, in giving evidence at the Seaham inquest, said that 

"if coal dust alone would have exploded every colliery would have 

been wrecked long ago." 6

The Chesterfield and Derbyshire Institute of Engineers appointed 

a committee in 1880 to conduct some experiments with coal dust. 

The committee included Professor Marreco and Mr. Morison. The 

experiments were made in a miniature gallery 82 feet long, 16 inches 

wide, and 18 inches deep, connected with a chimney to produce an 

air current. Coal dust was introduced at the open end of the chamber 

and carried in by the current. A horse pistol was used to simulate a 

blown-out shot. The charge was one-half ounce of gunpowder. It 

was fired into the open end. Out of 134 tests with coal dust alone, 

ignition was obtained in 36 cases. Even when 6 per cent of gas was 

tried, no violent explosion resulted. In the opinion of the observers 

it was more of an inflammation than an explosion. 0

_ The dust for these experiments was gathered from the floor, timber, 

and sides, and in all probability was more or less mixed with stone 

dust. This may have been the cause of the inconsistency in the 

results.

In 1884 Mr. William Galloway took a more positive stand than in 

April, 1879, when he appeared before the accidents in mines commission. In his fifth paper on the subject of coal dust, communieated to 

the Royal Society in May, 1884,d he states that no earlier author than 

himself had credited coal dust with being a principal factor in mine 

explosions, relegating fire damp to a secondary place.

EXPERIMENTS IN PRUSSIA.

The Prussian fire-damp commission in 1884 conducted a series of 

experiments with coal dust and with coal dust with gas in a gallery 

which had been built at the Koenig mine at Neunkirchen, Saarbrucken. This gallery was partly constructed under a refuse pile. 

It was 51 meters (167 feet) long and elliptical in cross section, 1.72 

meters (5.6 feet) high by 1.20 meters (3.9 feet) wide. Twenty-eight 

varieties of coal dust were tested and compared, each separately tried

<* Final Kept. Accidents in Mines Comm., 1886, p. 159. 

t> Blue book on Seaham colliery explosion, 1881, p. 146. 

cTrans. Chesterfield and Derbyshire Inst. Eng., vol. 10, 1882. 

c. Roy. Soc. London, vol. 37, 1884, p. 42:
THE COAL-DUST QUESTION IN EUROPE. 15

by placing about 15 kilograms (3.3 pounds) of it along 10 meters 

(32.8 feet) of the gallery. Several means were tried of distributing 

the dust, but scattering on the floor was practically as efficient as 

any other way. The igniting charge consisted of 230 grams (0.51 

pound) of black powder placed in one of several cast-iron blocks 

or cannons at the inner end of the gallery. Clay and coal dust were 

separately used for tamping the shot. With clay for tamping, the 

flame from the explosive itself was 3 to 4 meters (6£ to 10 feet) long, 

but with the coal tamping it was from 9 to 16 meters (30 to 52£ feet) 

long. The coal used in each test was analyzed and the resultant coke 

was also analyzed. In one instance the volatile matter was reduced 

from 21.8 to 13.6 per cent.

The conclusion of the commission was as follows:*1

1. The presence of coal dust with .or without small quantities of fire damp always 

increases the length of a blown-out shot.

2. When fire damp is fully absent, the prolongation is usually limited, not exceeding 

6 to 15 meters for most varieties of dust, when clay tamping is used and when the 

sides of the bore hole do not themselves yield coal dust and gas, or 9 to 21 meters 

when dust is used for tamping or is produced from the hole itself. But there are 

coal dusts which, once ignited by a shot, burn or spontaneously give flame far beyond 

the locality strewn with the dust, and sometimes actually produce explosions when 

no fire damp is traced.

The conclusions drawn by Mr. Hilt, a member of the Prussian 

commission, were submitted to the British commission as follows: 6

1. The presence of coal dust in more or less abundance in the immediate vicinity 

of the working face gives rise to more or less considerable elongation of the flame 

projected by a blown-out shot, whether small quantities of fire damp be present in 

the surrounding air or not.

2 (a) In the complete absence of fire damp the elongation or propagation of flarne 

is generally of limited extent, however far the deposits of dust may extend in the 

mine ways.

(6) There are, however, certain descriptions of coal dust which, if ignited by a 

blown-out shot, will not only continue to carry on the flame, even to distances extending considerably beyond the confines of the dust deposits, but will also give rise to 

explosive phenomena or results,'in the complete absence of any trace of fire damp, 

which in character and effects are similar to those produced with some other dust 

in air containing 7 per cent of fire damp.

. 3 (a) All the phenomena produced by the burning of, and propagation of flame 

by, coal dust are intensified by the presence in the air of small proportions of fire 

damp, but such dusts as will per se only favor to a limited extent the propagation 

of flame from a blown-out shot, give rise only to moderately increased volumes of 

flame, in the presence of even as much as 3 per cent of gas, and are not at all capable, 

under those conditions, of carrying on flame throughout the length of a dust-strewn 

area; the latter result will, however, be produced, even with such dusts, if the proportion of fire damp in the air amounts to 4 per cent.

a Kept. Prussian commission; Preuss. Zeitschr., vol. 32, 1884, 1885; also Eng. and Min. Jour., 1885, p. 

221; also Trans. Am. Inst. Min. Eng., vol. 24, 1895, p. 901. 

b Final Kept. Accidents in Mines Comm., 1S8G, p. 43,
16 THE EXPLOSIBILITY OF COAL DUST.

According to the evidence given by Mr. William Galloway before 

the British royal commission in 1891, the Prussian investigators 

obtained inconsistent results when they attempted to classify dusts 

in the order of their relative explosibility. He said: 0

One of the dusts which they described as nonexplosive came from a colliery called 

Camphausen and they named it as quite a safe .dust. Shortly afterwards an exceedingly violent explosion occurred at Camphausen colliery killing some 200 men, and 

the government director of mines in the district wrote to me immediately afterwards 

stating that the mines were so entirely free from fire damp that he could come to no 

other conclusion but that coal dust had been the sole cause of that explosion. * * * 

It is a remarkable and noteworthy fact that the degree of explosiveness of the coal 

dust with which the members of the Prussian commission made their experiments 

appeared to be directly in proportion to the fineness of the dust, and to have little 

or no connection with their chemical composition. * * * I may state my own 

conviction that the finest dust of all kinds of coal, with the exception possibly of the 

dryest kinds of anthracite, is inflammable or explosive when mixed with air and ignited 

in large volumes.

As a further result of their tests, the Prussian commission declared 

that black powder and all other slow explosives ought to be prohibited in collieries containing fire damp, and that even dynamite 

and other high explosives, though permissible in certain cases, ought 

not to be used where accumulations of fire damp are possible in 

sufficient quantity to give a clearly perceptible blue cap on a lamp; 

and that in all cases it is desirable that the air should be tested 

within a radius of 10 yards before igniting any shot. In consequence 

of this report, shot firing was prohibited altogether in mines controlled 

by the Prussian Government, where safety lamps were used. 6

It is evident that by 1886 the serious danger of coal dust was 

realized in Germany, although the investigators were not quite 

ready to believe that coal dust would explode without fire damp 

being present. In another part of Germany, at Zwickau in Saxony, 

a testing gallery had already been erected (1883), and thenceforward, 

investigations in various parts of Germany went on more or less 

continuously, both under government supervision and by various 

mining companies.

EXPERIMENTS IN AUSTRIA BETWEEN 1885 AND 1891.

In Austria a commission on explosions in mines was appointed 

in 1885, and in 1886 a testing gallery was established at MahrischOstrau. A large number of experiments were conducted and in 

1891 the Austrian commission made its report, the substance of which 

is stated by the British royal commission as follows : c

In all, 353 experiments were made with 345 kinds of dust, generally without any 

admixture of gas. These experiments showed that, without any admixture of fire

a First Kept. Hoy. Comm. on Mines, 1891, p. 36. 

b Trans. Am. Inst. Min. Eng., 1894, vol. 24, p. 902. 

c Second Eept. Roy. Comm., 1894, p. 8.
THE COAL-DUST QUESTION IN EUEOPE. 17

damp, nearly all kinds of coal dust were ignited by a cartridge of 100 grams of dynamite 

lying loose; while many notoriously dangerous dusts were less inflammable than other 

inflammable dusts. It was further shown that a small admixture of fire damp 

notably increased the danger and sensitiveness of coal dust, so that a dust which 

is otherwise not dangerous may give rise to a disastrous explosion if there is a littlefire damp present. The fineness of the dust, as well as its dryness, greatly increases 

its sensitiveness and danger.

VIEWS OF ENGLISH AUTHORITIES BETWEEN 1886 AND 1908.

On March 15, 1886, the British accidents in mines commission, 

which had been sitting since 1879, after reviewing the coal-dust 

problem and experiments made in England and other countries, 

reported the following facts as conclusively established: a

(1) The occurrence of a blown-out shot in working places where very highly inflammable coal dust exists in great abundance may, even in the total absence of firedamp, 

possibly give rise to violent explosions, or at any rate be followed by the propagation 

of flame through very considerable areas, and even by the communication of flame 

to distant parts of the workings where explosive gas mixtures, or dust deposits in 

association with nonexplosive gas mixtures, exist.

(2) The occurrence of a blown-out shot in localities where only small proportions of 

fire damp exist in the air, in the presence of even comparatively slightly inflammable, 

or actually noninflammable, but very fine, dry, and porous dusts, may give rise to 

explosions, the flame from which may reach to distant localities where either gas 

accumulations or deposits of inflammable coal dust maybe inflamed, and may extend 

the disastrous results to other regions.

It will be observed that this report shows a. great change of sentiment from the time of the preliminary report in 1881, when the 

commission considered the explosibility of coal dust of itself as 

improbable.

In the same year W. N. and J. B. Atkinson published a book 

entitled "Explosions in Coal Mines," in which they made a special 

study of five then recent English explosions and reviewed the history 

of past explosions. They state, in unqualified language, that coal 

dust was the effective agent in most of the great mine explosions.

The reports of the accidents in mines commission in 1886, and of 

other investigations, led to an enactment by Parliament in 1887 

requiring certain precautionary measures to be used in dusty mines, 

as follows:

If the place where a shot is to be fired is dry and dusty, then the shot shall not be 

fired, unless one of the following conditions is observed, that is to say: (1) Unless the1 

place of firing and all contiguous accessible places within a radius of 20 yards are at the 

time of firing in a wet state from thorough watering or other treatment equivalent to 

watering, in all parts where dust is lodged, whether roof, floor or sides; or (2) in the 

case of places in which the watering would injure the roof or floor, unless the explosive 

is so used with water or other1 contrivance as to prevent it from inflaming gas or dust, 

or is of such a nature that it can not inflame gas or dust.

« Final Kept. Accidents in Mines Comm., 1880, p. 48. 

38970° Bull. 425 10 2
18 THE EXPLOSIBILITY OF COAL DUST.

Despite the foregoing affirmative report by the royal commission, 

there was not a general acceptance among mining men of the explosibility of coal dust in itself, so that in 1890 Mr. Henry Hall, government inspector of mines, was commissioned to make, some further 

experiments on a large scale in certain disused shafts with coal dust 

from various mines.

Some of these tests were very spectacular, notably several at the 

Big Lady pit, which was 630 feet deep and was connected by a small 

arched way with another shaft. The experimental shaft was the 

upcast. The firing charge was 1^ pounds of black powder in a cannon placed 540 feet from the surface. In the seventh test 

dust was ignited, followed by a continuous roar, and a rush of flame completely filled 

the pit mouth and ascended 60 feet into the air. This was the most violent explosion 

since the commencement of the experiment. It is difficult for anyone who did not 

witness this experiment to realize the extent of the explosion. The flame continued 

to issue from the pit for five to six seconds, followed by dense smoke. The violence 

carried away some of the woodwork 37 feet above the pit mouth.a

Mr. Hall, in his summary, states: a

These experiments conclusively prove that blasting with gunpowder in dry and 

dusty mines may cause serious disasters in the entire absence of fire damp. It is impossible to explain why many of the experiments failed to cause explosions or to ignite 

the dust, but the fact that at intervals these did occur perfectly justifies the aboveconclusion.

In February, 1891, a royal commission on explosions from coal 

dust in mines was appointed, and began hearing evidence in the following month. Its first report of evidence, without conclusions, was 

published in July, 1891. In 1892 its sittings were adjourned, pending further experiments by Mr. Henry Hall, which were conducted 

at intervals in that year and in 1893.

The commission made its second report in 1894, giving additional

evidence and their final conclusions. In reviewing the evidence they 

state: 6

The experiments made by Mr. H. Hall in 1890, 1892, and 1893 on a larger scale, 

and in shafts of mines, appear to be conclusive in the same sense, although they show 

that an explosion is not a certain consequence of every shot that blows out or emits 

flame, but depends on many circumstances affecting the condition and quantity of 

the dust, the nature and strength of the explosive, the size of the galleries or shafts, etc.

The Prussian commissioners reported that "if absolute immunity from blown-out 

shots could be obtained, the dangers which are brought about by coal dust would be 

almost entirely prevented." In their experiments they found that no shots, other 

than a blown-out shot, caused an explosion of the dust.

It is, however, the opinion of several witnesses that the danger is not confined to 

blown-out shots, but that an overcharged shot which does not blow out, or one which 

partially does the work for which it is intended, may exhibit flame and therefore 

ignite the dust. In the opinion of Mr. W. N. Atkinson, the explosions at Seaham 

in 1871 and 1880, at Elemore, at Usworth, and at Altofts were caused by shots which 

did not blow out.

a First Kept. Roy. Comin., 1891, p. 153. & Second Kept. Roy. Comm., 1894, p. 11.
THE COAL-DUST QUESTION IN EUEOPE. 19

The royal commission summarized their conclusions in the followi ' ° ing words: a

(1) The danger of explosion in a mine in which gas exists, even in very small quantities, is greatly increased by the presence of coal dust. (2) A gas explosion in a fiery 

mine may be intensified and carried on indefinitely by coal dust raised by the explosion itself. (3) Coal dust alone, without the presence of any gas at all, may cause a 

dangerous explosion if ignited by a blown-out shot or violent inflammation. To produce such a result, however, the conditions must be exceptional, and are only likely 

to be produced on rare occasions. (4) Different dusts are inflammable, and consequently dangerous, in varying degrees; but it can not be said with absolute certainty 

that any dust is entirely free from risk. (5) There appears to be no probability that 

a dangerous explosion of coal dust alone could ever be produced in a mine by a naked 

light or ordinary flame.

By the time the royal commission had issued this final report, in 

1894, the mining experts in England had became very generally convinced that coal dust was not only a factor, but the most important 

element in the great explosions occurring in collieries, and thereafter 

the experiments and investigations were directed to remedies. In 

1896 a coal-mine regulation act was passed by which power was given 

to the secretary of state to prohibit the use of dangerous explosives. 

This necessitated the testing of explosives used in mines, and to this 

end a testing station with necessary apparatus was erected at Woolwich and opened for testing June 5, 1897. As an explosive mixture 

of gas is more sensitive than coal dust, it was reasoned that an explosive that will not ignite gas would not ignite coal dust, hence the apparatus was designed primarily to determine the relative liability of the 

various explosives to ignite an explosive gas mixture.

GERMAN, FRENCH, AND BELGIAN STATIONS FOR TESTING EXPLOSIVES.

In Germany the education of the mining public to the danger of 

coal dust had gone on simultaneously with that in England. In 1894 

a station for testing mine explosives in the presence of dust and gas 

mixtures was .established at Gelsenkirchen in Westphalia by the 

mine operators and placed under the supervision of a government 

engineer. The testing gallery is 34 meters long. In cross section 

it is elliptical, 1.80 meters (5.9 feet) high and 1.35 meters (4.4 feet) 

wide. This gallery and the other apparatus for testing the explosives, also apparatus for testing safety lamps, mine motors, etc., have 

been in continuous use since the establishment of the station.

A similar station was established by the Belgian Government at 

Frameries, and the same general methods of testing explosives in the 

presence of gas and coal dust are used for the formation of a Belgian 

"permitted" list.

a Second Kept. Roy. Comm., 1894, p. 24.
20 THE EXPLOSIBILITY OF GOAL DUST.

In France, as already mentioned, the effect of the early investigation, and particularly of the French fire-damp commission, was to 

prevent acceptance of the theory of the explosiveness of coal dust 

when fire damp was not present. The effort of the French engineers 

was to prevent ignition of fire damp, and every precaution was taken 

in the French mines to this end. It was felt that if this danger could 

be guarded against, that there was practically no danger from coal 

dust. Captain Desborough, of England, in a "Report on bobbinite" 

(1907), states:

The French were, I believe, the pioneers in placing restrictions upon the indiscriminate use of explosives in gassy mines. After many valuable experiments had 

been carried out on a laboratory scale, it was decided that in gassy mines no explosives should be used whose calculated theoretical temperature of explosion exceeded 

1,500° C., which is considerably above the ignition point of a fire damp and air 

mixture.

The general good care exercised in the mines of France and the 

excellent ventilation gave France comparative freedom from the 

large mine disasters that were occurring in other countries, until the 

terrible disaster at the Courrieres mines in 1906. Although there 

was no official French report attributing the cause to coal dust, such 

was the opinion of the English investigators, Sir Henry Cunynghame 

and Mr. W. N. Atkinson, who examined the mine. They ascribe the 

initial cause to a blown-out shot in a heading, igniting coal dust, 

and state further that the propagation through the mine was 

probably through the agency of coal dust. a

As a result of the disaster the central committee of mines of France 

(comite central des houilleres de France) established a station at 

Lievin, in the Pas de Calais district, in 1907 for the study of the relative 

explosibility of different coal dusts with various percentages of fire 

damp and without fire damp. A small-scale experimental gallery 

was first erected to determine on plans for a large-size gallery. After 

a series of tests with the former, the large permanent gallery, or the first 

section of it, was erected in 1908. As at the other European stations 

there is no difficulty in causing explosions of coal dust without the 

presence of fire damp, at will, by discharging either black powder or 

dynamite from a cannon at one end of the gallery.

Some of the conclusions of M. Taffanel, the government engineer 

in charge of this station, are given in subsequent pages of this report 

(pp. 43-44). The plans are to gradually extend this gallery to a length 

of 500 meters and to investigate means for preventing or of limiting 

the explosion of coal dust. . '*

The results already reached by the Lievin station and by the testing 

stations of other countries have fully convinced the French engineers 

of the dangers of coal dust.

a Home Office report on Courrieres disaster, p. 11.
THE COAL-DUST QUESTION IN EUKOPE. 21 

ALTOFTS GALLERY, ENGLAND, 1908.

In England a new royal commission on mines was appointed in 

1906, which began hearing evidence in June of that year. This commission, while taking up all questions relating to mines, has given a 

great deal of attention to coal dust and remedial methods. It has 

issued four volumes of evidence, one in 1907, two in 1908, and one in 

1909, in which many methods for solving the coal-dust question have 

been suggested.

The general interest in the subject led the Mining Association 

of Great Britain to establish in 1908 a testing gallery of unusual 

dimensions at the Altofts colliery in Yorkshire. It is 7£ feet in 

diameter and about 900 feet long, with several right-angle turns. 

It is built of f-inch boiler plate. A concrete floor extends through it, 

also a pit car track. Unlike the other galleries, the prime purpose

is not the testing of explosives, but the study of the behavior of coal 

dust in exploding. The first tests were to demonstrate and convince 

the few who still had doubt as to the explosibility of coal dust. Some 

'of the explosions produced were very violent. In one case, where a 

longer portion (450 feet) of the gallery had been charged with coal dust 

than before or since, the resulting explosion tore off the two end sections., threw one heavy piece of boiler plate several hundred feet, 

blew out windows in houses for a mile or so around, and it is claimed 

produced a concussion that was felt 7 miles away.

After a series of preliminary demonstrations, the study of remedial 

methods has been taken up. Two plans have been tried: Having 

an intercepting zone free from coal dust, and the employment of a 

zone of stone dust. These will be discussed under other heads 

(pp. 80-83).

SECOND REPORT OF ROYAL COMMISSION ON MINES, 1909.

The second report of the royal commission on mines appeared in 

September, 1909. The coal-dust question is discussed as well as 

other dangers, and with regard to dust the commission says: a

The witnesses, who included those best qualified from scientific or practical experience to speak on the question, expressed opinions which were often widely divergent, 

as to the best means of meeting the danger of explosions, but they were generally 

agreed on two points that coal dust is liable to explosion with or without the presence 

of fire damp, under conditions which are at present to be found in most coal mines in 

this country and abroad, and that there is pressing need for the elucidation of the 

problems involved by a series of exhaustive experiments on an adequate scale. With 

regard to the first point, it was a matter of satisfaction to us that all the witnesses whom 

we consulted expressed themselves as adherent to the received opinion .on the subject 

of coal dust. In this respect we found ourselves in a better position than the commission who preceded us the royal commission on accidents in mines (1879-1886) and

Second Rept. Roy. Comm. on Mines, 1909.
22 THE EXPLOSIBTLITY OF COAL DUST.

the royal commission on coal dust (1891-1894) in that we were able to confine our attention 

to the means of dealing with coal dust without having to prove the necessity for such means. 

* * * We do not mean to convey the impression that all managers and mining engineers are fully alive to the danger of coal dust. Unfortunately, recent occurrences 

have tended to show that this is not the case. If such is the position taken by some 

managers in this country, it is the less surprising that the workmen do not all appreciate 

the danger of coal dust.

The commission, after speaking of the merits of the Altofts gallery, 

the thoroughness of its equipment, and methods in carrying on the 

tests, say:

Until these experiments are completed we are unable to make recommendation 

covering the whole question of the means of preventing coal-dust explosions.

Figures are quoted from the British "Annual Report on Mines and 

Quarries" by five-year periods, of the death rates from accidents 

underground in mines per thousand persons employed. The annual 

death rate due to explosions of fire damp or coal dust shows a regular 

decrease from the period 1851-1855, when it was 1.280 per 1,000, 

until. 1907, when it was 0.057. In other words, considering an equal 

number employed, for 22 men killed in 1851-1855 by fire damp or 

coal dust, but 1 was killed in 1907.

RECENT AUSTRIAN EXPERIMENTS.

The Vienna permanent fire-damp committee in 1908 decided to continue experiments begun some years before with coal dust in its gallery 

at Babitz, near Segengottes in the Rositz district, Austria. This 

gallery consists of part of an old mine level 293.7 meters (964 feet) 

in length, connected with the surface by three shallow shafts. Coal 

dust is introduced sometimes on shelves and sometimes through pipes 

leading from the surface, the dust being thrown into suspension by

fans. The coal dust is distributed for a distance of 10 to 90 meters 

(33 to 295 feet) from one end, where there is an explosion chamber. 

The dust is ignited by blow-out shots from a cannon or cannons 

charged with black powder, or by dynamite cartridges hung in the 

explosion chamber. The flame, in these experiments, traveled from 

50 to 180 feet beyond where the coal dust was laid, depending upon 

the character of the dust, its purity, its fineness, and its dryness. 

These experiments are still continuing, and as yet no conclusions 

have been reached.

A description of this station is given in the Colliery Guardian for 

September 24 (p. 635) and October 1 (p. 687), 1909.
THE COAL-DUST QUESTION IN THE UNITED STATES. 23

HISTORICAL REVIEW OF THE COAL-DUST QUESTION IN 

THE UNITED STATES.

GRAHAMITE EXPLOSIONS IN WEST VIRGINIA, 1871-1873.

One of the earliest recorded dust explosions in the United States 

was in a grahamite mine in Ritchie County, W. Va., on February 9, 

1871, when 4 men were killed as the result of a very violent explosion. 

The official report of the investigators was that an "explosion of 

powder (18^ cubic inches in the shot) pulverized a certain quantity 

of mineral (grahamite a hydrocarbon) and in that state it was 

easiest decomposed. The indications are that gas burned along all 

the air passages and exploded at the portal." 0

The management subsequently employed sprinklers, as much dust 

was made in running the mined mineral through chutes, but a second 

explosion, February 25,1873, also from shot firing, killed 4 men.

FLOUR-MILL EXPLOSION AT MINNEAPOLIS, 1878.

On May 2, 1878, a tremendous explosion occurred in the Washburn 

Flour Mills, at Minneapolis, completely wrecking the building and 

setting on fire 6 other flouring mills and a number of other buildings. 

Professors Peckham and Peck were commissioned by the coroner's 

jury to investigate. They made experiments in closed boxes with a 

variety of powdered substances to test their explosibility. Among 

other things, they tested various flour mixtures and coal dust. The 

powdered materials were blown into the box by bellows and ignited 

by an open light. The findings of Professors Peckham and Peck 

were to the effect that practically all finely divided highly carbonaceous material would explode under the conditions tried. Their 

report was not made public at the time, but was published in issues 

of the Chemical Engineer, March, April, and May, 1908. An abstract 

of it appeared in Mines and Minerals for September, 1908, page 55.

In an issue of the Scientific American Supplement, May 25, 1878 

(p. 1985), there was an article entitled "Dust as an explosive." 

After a general discussion of the subject, it continues:

It has been well known for a long time past that it is not alone to mixtures of the 

issuing gases with air that the explosions in colleries are to be ascribed. Finely 

divided coal is always present to a more or less extent in the air of a mine, or, if not 

present in sufficient quantity, is sure to be produced by the shock of an explosion. 

This dust furnishes a material which gives the fire power to spread from gallery to 

gallery should the mixed gases themselves be insufficient in quantity to permit 

such a spread. Indeed, it would appear that coal dust itself, when mixed with 

certain proportions of air, renders the air explosive without the presence of any of 

the gases usually evolved in coal mines; and there can be no doubt that the presence 

of coal dust renders mixtures of coal mine gas and air explosive that would otherwise be quite harmless.

aTrans. Am. Inst. Min. Eng., vol. 24, 1894, p. 195.
24 THE EXPLOSIBILITY OF COAL DUST.

Then- follow remarks about the Haswell mine explosion report of 

Lyell and Faraday, and some quotation from Galloway's papers. 

In view of the definite statements in this article, it is surprising how 

delayed the general acceptance of the coal-dust theory was in this 

country.

EXPLOSION AT POCAHONTAS MINE, WEST VIRGINIA, 1884.

On March 13, 1884, occurred the first great mine explosion of the 

bituminous fields of this country, at the Pocahontas mine, West 

Virginia. There were 114 men killed, all who were in the mine. At 

the request of the operating company, a committee was appointed 

by the American Institute of Mining Engineers, consisting of Messrs. 

J. H. Bramwell, Stuart M. Buck, and Edward H. Williams, jr. As 

soon as the mine workings were accessible, they made a careful 

examination of them. A "summary of contributing causes found by 

them is as follows: a

1. The unusual dryness of the mine.

2. The very large quantity of dust in an extremely fine state of division.

3. The constant working of the mine day and night, allowing no time for clearing 

air [of powder smoke].

4. The use of excessive quantities of powder, largely increasing the amount of dust.

5. The probable existence of small quantities of fire damp slowly given off from 

the coal.

6. The employment of incompetent and inexperienced men.

7. The almost complete stagnation of the air on the east side of the entry, owing 

to the fact that the main doors were untended and fastened open, allowing the air to 

pass up the main entry direct to the fan.

8. The failure to recognize and appreciate the previous warnings of danger given 

by occasional flashings of unusual extent, when shots were fired, indicating the need 

of special precaution.

The investigators say further: "The existence of fire damp is a

disputed point." They obtained no evidence of the previous 

existence of fire damp from the workmen of the other shifts, except 

that a miner claimed that once, when his light was in an undercutting, he observed a lengthening of the flame. The investigators comment that in general the evidence given by the former workers 

appeared to be prejudiced and therefore unreliable.

On reopening the mine after the explosion and partial flooding, no trace of fire 

damp was discovered, and none showed at the time of inspection, although the 

ventilation had been only partly restored, especially to the rise.

Their conclusion was:

We believe that the explosion was due mainly to dust, and that it originated either 

in the (3d) east headings ("at D") or very possibly in one of the rooms ("south of 

D" south of the 3d east headings). The evidence of a short northward current 

being obliterated by the stronger reaction from the close heading. We can not 

determine the initial cause, whether a blast or the accidental ignition of a small 

accumulation of fire damp.

oTrans. A.a. last. Min. Eng., vol. 13, p. 237.
THE COAL-DUST- QUESTION IN THE UNITED STATES. 25

It may be stated that after the mine was reopened fire damp was 

not detected in subsequent operations.

For some years after the Pocohontas explosion, the coal-dust problem attracted little attention in this country, and operating men were 

content to await the results of experimenting abroad. Each was 

chiefly concerned in his own part in the tremendous development 

going on in the various great bituminous fields of the country. There 

was an awakening of interest in coal dust when explosions began to 

occur in mines in parts of the western region of the interior coal 

province, particularly in Iowa. Many of these explosions were in 

shallow mines in which fire damp had never been found before the 

explosions and was not found after them. The Iowa coal is neither 

gassy rior coking in the .ordinary sense; it is high in ash, and carries 

from 12 to 14 per cent of moisture when freshly mined.

EXPLOSION AT PEKAY MINE, IOWA, 1892.

The first of the Iowa explosions occurred at the Pekay mine, February, 1892. Fortunately it was on a holiday, and only 4 men were in 

the mine. Three of these were killed, but the fourth, who was in a 

mine stable near the hoisting shaft and out of range of the explosion, 

escaped. The writer examined the mine on the morning following 

the explosion. Much violence was manifested through several 

pairs of entries and the main entries on one side. The fan was 

partly wrecked. The mine was dry and dusty. Coked particles were 

not observed, but there w.as burned dust and the flames had ignited 

kegs of powder at different points in the mine. No fire damp had 

ever been found in the .mine and none was found after the explosion. The evidence indicated that the explosion had begun in a 

certain room where three greatly overcharged shots had been discharged at or about the same time, throwing out to a distance a 

large mass of coal. No undercutting nor shearing had been done. 

What was termed "blasting off the solid " was then being introduced 

in Iowa. In the opinion of the writer, the flame of the shots ignited 

coal dust, which propagated the explosion throughout the mine.ffl

Shortly after this explosion several others occurred in Iowa, at the 

Cedar mine and elsewhere. These were also ascribed to either 

blown-out or overcharged shots "on the solid." Similar explosions, 

generally on a small scale, because the conditions were unfavorable 

for widespread explosions, occurred in the fields of southeast Kansas, 

also remarkably free from fire damp, and in the McAlester field of 

Indian Territory (now Oklahoma), where, however, the situation was 

complicated by the presence of more or less gas.

"Rice, G. S., The Pekay explosion: Trans. Illinois Min. Inst., vol. 2, 1893.
26 THE EXPLOSIBtLITY OF COAL DUST. 

PROPOSED REMEDIES FOR DUST.

The numerous accidents of this nature naturally led to a great deal 

of anxiety in the interior fields, and a great many palliatives were 

suggested and in some cases tried. There was considerable belief in 

the explosibility of coal dust, and, as it was noted that the explosions 

were usually more severe on the intake air way, it was proposed, and 

in some States was carried out under the instructions of the mining 

departments, that the fan should be slowed up or stopped at the 

shot-firing time. This was on the theory that fresh air and pressure 

increased the chance of ignition. To a small extent, sprinkling or 

wetting the floors of the roads from a tank car once or twice a week 

was practised.

An important change was then made in many of the States west of 

the Mississippi by the passage of laws requiring the shot firing to be 

done by .shot firers, the miner still drilling and charging the drill 

holes. The immediate results were not at all favorable, as the miners, 

relieved of personal risk, transferred it to the shot firers. There was 

an increasing tendency to do less and less cutting to relieve the shot, 

and to increase the already large charges of black powder. The 

effect was to cause more accidents from blown-out and overcharged 

shots, although the number of killed and injured men was decreased, 

owing to the fewer number of men exposed to the hazard. Further 

legislation followed in some States, compelling the inspection of holes 

by the shot firers before they were loaded by the miner. This measure 

very much improved the situation, resulting in a smaller number of 

killed and injured from shot firing.

RESULTS OF SHOOTING OFF THE SOLID.

East of Mississippi River, in the eastern region of the interior coal 

province, the number killed from mine explosions was relatively very 

small until a change came in the method of paying the miners, in 1897. 

Before that'time the miners had been paid on the basis of the amount 

of lump or screened coal produced. After 1897 they were paid on 

the basis of the amount of run-of-mine coal produced.' This took 

away from the miner the incentive for cutting the coal and for using 

small charges of powder, and put a premium upon shooting down the 

coal in the cheapest and easiest manner. "Shooting off the solid/' 

theretofore practiced only to a small extent, became very general, 

and with it a large increase in the amount of black powder used in the 

shots. As in the coal-mining States west of the Mississippi, this produced an immediate increase in the number of explosions and fatalities therefrom. Fortunately, the explosions were usually of limited 

character, because the natural conditions were unfavorable to widespread explosions. Nevertheless, the accidents were so frequent
THE COAL-DUST QUESTION IN THE UNITED STATES. 27

that legislation followed in Illinois requiring the employment of 

shot fixers a and inspection by them of the drill holes, and limiting the 

charge of black powder. The amount of powder used in a shot was 

difficult to control, and in some mines in Illinois the output of coal 

per keg (25 pounds) of powder fell as low as 15 tons (of 2,000 pounds).

In the meantime mines opened in the deeper-seated coals in southern Illinois found considerable gas (methane). Even where the coal 

was undercut by machine, overcharges of powder were frequently 

used, so that serious accidents resulted, in'which some or all the shot 

firers were killed. This condition still prevails (1909), but more 

care is now exercised by the shot firers in condemning bad holes, and 

a considerable number of operators are paying more attention to 

dampening coal dust along the entries by sprinkling.

In Indiana the conditions have been somewhat similar to those in 

Illinois, except that the employment of shot firers has not been compulsory, so that explosions killing a considerable number of miners 

have occurred, notably at Princeton. Very large charges of black 

powder are used in the Indiana mines. The revised state act of 1907 

fixed the limit at 6 pounds of black powder, but instances have been 

reported in which as much as 10 to 12 pounds of powder has been 

used in a single shot. Where law and local regulations allow 25-pound 

cans of powder to be in possession of the miner in the mine, and allow 

him to charge and fire his shots, there is no way of effective control 

to insure safe conditions.

In Pennsylvania, the chief coal-producing State of the country, and 

in Ohio the method of paying the miner on the screened-coal basis 

has prevailed to the present time; and in these States and in parts 

of West Virginia the system of undercutting before shooting has 

generally been adhered to except in the Connellsville coke region.

GREAT DISASTERS OF 1907.

Though numerous explosions occurred in the Appalachian field in 

Virginia, West Virginia, and Pennsylvania up to 1907, the only ones of 

the most disastrous order were those at Newburg, W. Va., in January, 

1886, Red Ash, W. Va., in 1900, Johnstown, Pa., in July, 1903, Cheswick, 

Pa.,in January, 1904, and Pocahontas,Va.,in 1906, and in the majority, 

including those cited, there was always a question whether fire damp 

was not the initial cause. However, in the propagation through the 

mine there is little question but that coal dust was the chief factor. 

The same might be said of the explosions that occurred from time to 

time in Alabama and Tennessee.

In 1907 occurred an appalling series of great wide-sweeping disasters. On January 23, at the Primero mine, Colorado, there were 24

oln mines where In shooting more than 2 pounds of l>lack powder is used in any one shot.
28 THE EXPLOSIBILITY OP COAL DUST.

deaths; on January 26, at the Penco mine, W. Va., 12 deaths; on 

January 29, at the Stuart mine, near Fayetteville, W. Va., 90 deaths; 

on February 4, at the Thomas mine, Thomas, W. Va., 25 deaths; on 

December 1, at the Naomi mine, Pa., 35 deaths; on December 6, at 

Monongah mines Nos. 6 and 8, W. Va., occurred the greatest disaster 

in the history of coal mining in the United States, 358 lives having been 

lost; on December 16, at the Yolande mine, Ala., 56 men were killed, 

and on December 19, at the Darr mine, Pa., 230 men were killed. In 

this black month of December 648 men were sacrificed chiefly from 

the effects of coal dust, which, if not the initial cause., in all cases was 

the agent carrying death. Including the powder explosions and socalled "windy shots," there were 1,148 men killed by mine explosions in the United States during 1907.a

INACCURATE REPORTS OF ACCIDENTS.

Most of the so-called "powder explosions" and "windy shots" 

are in reality dust explosions. It is true that the origin of these is 

generally from blown-out or overcharged black-powder shots, but it 

is without question coal dust that carries the flame, and death in its 

trail. In certain States it is considered that legal responsibility 

attaches, if the fatality is pronounced due to coal dust; and this fact, 

together with the knowledge in many such instances that improper 

use of powder was the initial cause has led to the use of inexact and 

ambiguous terms in reports to the several state statistical bureaus.

FATALITIES IN 1908.

In 1908 the fatalities due to mine explosions of various kinds numbered 469, according to state statistics reported to Mr. E. W. Parker, 

of the United States Geological Survey. 6 This shows a marked

improvement over the previous year.

INQUIRY BY UNITED STATES GEOLOGICAL SURVEY.

On June 10, 1907, the Secretary of the Interior transferred the 

supervision of the work of the coal-mine inspectors in New Mexico 

and Indian Territory (now included in the State of Oklahoma) to 

the United States Geological Survey. The Secretary suggested to 

the officers of the Survey that the general mining conditions in the 

Territories be investigated, with a view to lessening the number of 

mine accidents. Under the direction of J. A. Holmes, expert in 

charge of the technologic branch, an inquiry was begun into the 

nature and extent of coal-mine explosions and the methods employed 

to prevent them. In December, 1907, a brief summary of the results 

of this inquiry was published as Bulletin 333.

a Mineral Resources U. S. for 1907, U. S. Geol. Survey, 1908, pt. 2, p. 58. 

6 Mineral Resources U. S. for 1908, U. S. Geol. Survey, 1909, pt. 2, p. 56.
ORIGIN AND DISTRIBUTION OF COAL DUST. 29

The coal-dust question in this country can not be said to have 

awakened widespread interest among mining men until the terrible 

disasters of December, 1907. In response to a demand by those 

interested in coal mining-throughout the country, Congress in 1908, 

made an appropriation for the investigation of mine explosions, which 

became available July 1, 1908. The United States Geological Survey 

was charged with the investigation. A testing station was at once 

decided upon and was established at Pittsburg, Pa. The station was 

officially opened December 3, 1908, and testing of nonflaming explosives was begun soon after. Field investigations of mine conditions 

and of mine explosions were carried on, especially of the explosions 

at Marianna, Pa., and Lick Branch, W. Va., in 1908; Eend, 111., Wehrum, Pa., Eureka, Pa., Johnstown, Pa., and Herrin, 111., in 1909; and 

Primero, Colo., Drakesboro, Ky., Stearns, Ky. ; Mulga, Ala., and

Palos, Ala., in 1910. Special attention has been paid to the humidity of the mine air and the condition of the dust. At the Pittsburg testing station some experiments have been made with coal 

dust, described hereafter, and this work will be actively pursued in 

the future.

While it is probable that for several years the leading mining 

men in this country have believed in the explosibility of coal dust 

without the presence of fire damp, yet until the public demonstrations 

were given at the testing station at Pittsburg, during 1908-9, and 

reports were received of similar tests made abroad, a large proportion disbelieved. These tests were so convincing to those who 

saw them, and such general publicity has been given to them, that it 

is now exceptional to find a mining man who does not accept the 

evidence of the explosibility of coal dust. The question of the day 

no longer is "will coal dust explode?" but "What is the best method 

of preventing coal-dust explosions?"

COAL DUST AND ITS ORIGIN AND DISTRIBUTION.

DEFINITION OF DUST.

There is a diversity of opinion as to what the term "coal dust" 

means; that is, how finely must coal be divided to be termed dust. 

Some writers base the distinction on the point whether it can be 

carried to considerable distances by air currents. Coal that will pass 

through 100-mesh screens (100 wires to the linear inch) is frequently 

accepted as representing mine dust. For testing explosives at the 

Pittsburg station coal passed through 100-mesh is taken as standard. 

In the foreign galleries the practice varies between this size and coal 

that passes through 200-mesh.

For the consideration of coal dust as it effects mining, the writer 

proposes tentatively a definition based on the capacity of the dust to
30 THE EXPLOSIBILITY OF COAL DUST.

propagate flame in the incipient stages of an explosion, as determined 

at the Pittsburg station under the conditions hereafter stated. By 

this definition coal particles passing through a 20-mesh wire sieve 

(20 wires to the linear inch) will be termed dust. In the Pittsburg 

gallery tests only partial flame propagation was obtained under the 

prescribed conditions with coal that passed through the 20-mesh and 

remained on a 40-mesh sieve, but the partial propagation was sufficient to indicate that under slightly more severe conditions, namely, 

a larger initiating charge of black powder, the propagation might 

be complete. In fact, under the definition given, subsequent experiments may demonstrate that larger particles of coal than 20- 

mesh should be included.

IGNITION AND PROPAGATION.

Ignition of coal dust, as the term is applied by the writer to tests 

in the Pittsburg gallery, is an inflammation of the dust, caused by 

the flame of the explosive, with consequent extension of that flame 

more or less; and the term "propagation" is used for conditions in 

which the inflammation extends through and beyond the area in 

which coal dust has been laid along the shelves of the gallery, or beyond the area in which dust has been put into suspension by fans.

COAL-MINING METHODS AND DUST PRODUCTION.

Breaking down the coal at the face of the mine is done by one of 

the following methods: By undercutting in the underclay or coal 

itself and wedging, as in long-wall work; by undercutting or shearing 

by hand'in the coal and blasting with light shots; by the same method 

with machines; and finally by "shooting off the solid."

Of the foregoing manifestly the long-wall system will produce much 

less coal dust than any of the other systems, and its general introduction in this country would probably very much lessen the number 

of dust explosions. The system has been little used in this country, 

partly because the natural conditions are not generally favorable, 

and, where they are, because it costs more to mine a ton of coal by 

this than by the more wasteful room-and-pillar system. ' However, 

one type of the long-wall system, the "retreating" long wall, is generally applicable and is the cheapest of all methods to work, but takes 

a large investment of capital. The Wilmington and Third Vein 

fields of northern Illinois, in which the natural conditions allow the 

use of "advancing long wall," comprise the only important longwall district in the country, having an output of 5,000,000 to 

6,000,000 tons annually. No explosion has ever occurred in this 

field.

As between the methods of mining the coal at the face in room-andpillar work "shooting off the solid," and cutting the coal by hand
ORIGIN AND DISTRIBUTION OF COAL DUST. 31

or machine and then shooting we have no authoritative figures as 

to their relative production of dust.

DUST FROM HAND AND FROM MACHINE UNDERCUTTING.

In the process of cutting coal by hand and by different types of 

machines, some tests have been made by private interests and their 

results made public.

Tests of the production of dust in undercutting by hand, by chain 

machines, and by air punching machines in the Pittsburg seam were 

made by the late B. F. Jones. Mr. Jones published his results in the 

March, 1908, issue of Mines and Minerals (p. 397). The tests were 

made in three adjacent "butt" rooms in the Westmoreland mine, 

Pennsylvania. The undercutting by each process was conducted in 

a separate room, and in each case was 4 feet 3 inches deep and as 

wide as the room (15 feet). ' The height of undercutting with the 

puncher was 11 inches at the front and 3 inches at the back, and with 

the chain machine 4 to 4£ inches throughout. The seam was 6 feet 

thick.

The same total amount of coal was assumed to have been produced 

from each room (15.68 tons of 2,000 pounds). The results, reduced 

to tabular form, are as follows:

Weight of cuttings and percentage of total coal mined by different methods, as determined 

in experiments at Westmoreland mine, Pennsylvania.

Method.

Total cuttings.

Pounds.

3,436 

1,836 

4,533

Per cent.

10.95 

5.86 

14.45

Cuttings passed 

through 16-mesh.

Pounds.

755 

333 

349

Per cent.

2.40 

1.06 

1.11

Cuttings passed 

through 40-mesh.

Pounds.

394 

155 

128

Per cent.

1.250 

.494 

.408

Evidently these figures did not include the dust produced in shooting down the coal and in loading it on pit cars.

With dust defined as coal that will pass through a 20-mesh-sieve, 

these figures indicate that the amounts of dust made by the three 

cutting processes would be slightly less than 2.40, 1.06, and 1.11 per 

cent of the total coal to be produced by the undercuts.

Some tests a were made by the Fairmont Coal Company in one of 

their mines working the Pittsburg seam in the Fairmont district, 

West Virginia. The undercutting was done with electric punching 

machine and breast chain machine. One working face in which the 

coal was soft was cut by each machine, and in another part of the 

mine where the coal was harder similar cuts were made. The

o Described by C. E. Scott in Mines and Minerals, May, 1908, p. 477.
32 THE EXPLOSIBILITY OF COAL DUST.

depth of each cut was 4 feet. As it is the practice of this company 

to "block" or "snub" down the coal in the center of the room 

after cutting with a chain machine, this blocking was done in each 

instance to a height of 18 inches. The coal seam is indicated in a 

diagram in the published account as 8 feet thick.

The reported figures gave the weights of cuttings "over" and 

"through" various mesh from l|-inch to 80-mesh, and the percentage 

that each portion was of the total cuttings. In accordance with the 

definition of dust already given, only the cuttings that passed through 

20-mesh will be considered here. In the following table the percentages of the different sizes have been refigured on a basis of the 

theoretical amount of coal produced from the undercut face, assuming a uniform thickness of seam of 8 feet and 82 pounds per cubic 

foot of coal in place.

Comparative weights of cuttings and percentages of total coal in Fairmont experiments.

Through 20-mesh .... 

Through 40-mesh .... 

Through 80-mesh ....

Chain (breast) machine.

"Soft" coal (cut 20 

feet by 4 feet).

Pounds.

439 

211 

126

Per cent.

0.84 

.40 

.24

"Hard" coal (cut 

16 feet by 4 feet).

Pounds.

431 

212 

126

Per cent.

1.03. 

.50 

.30

Puncher.

"Soft"coal-(cut 20 

feet by 4 feet).

Pounds.

558 

274 

165

Per cent.

1.06 

.52 

.31

"Hard" coal (cut 

16 feet by 4 feet).

Pounds.

641 

318 

192

Per cent.

1.53 

.76 

.46

Mr. George R. Wood, in a paper read before the Coal Mining Institute of America, June 29, 1909, made some comparisons of the dust 

produced by mining machines, as reported by Mr. Randolph, formerly

with the Pittsburgh Coal Company. The results were given for dust

passed through a 40-mesh sieve only, in pounds per square foot of 

undercutting, as follows:

Pounds of dust passed through 40-mesh sieve, per square foot of undercutting, by several

methods.

Washington Coal and Coke Company mines, Connellsville region, 

Pennsylvania: 

Hand mining............................................. 1. 80

Puncher machine......................................... 4. 58

Chain machine with pick-point bits. ......................... 1.48

Pittsburgh Coal Company, Midland No. 1:

Puncher machine......................................... 6.18

Chain machine (two trials).......................,.........] '

[ 2. 51

Comparison of the results of the foregoing series of machine-dust 

and hand-dust experiments can be made on the only size in common 40-mesh. In order to compare the. weights of dust produced
ORIGIN AND DISTRIBUTION OF COAL DUST. 33

relative to the total amount mined, in compiling the following table 

the coal seam for each test was arbitrarily assumed to be 6 feet 

thick. The Fairmont percentages are refigured accordingly.

Comparative amounts of machine and hand cuttings passed through a. 40-mesh sieve, in 

percentages of total coal produced, assuming a 6-foot seam.

Chain 

machine.

0.49

ZA

.67

a. 30

1 .49

\ .51

.50

Puncher.

1.25

.70

1.01

.93

} 1.26

1.03

Hand.

0.41

.37

.39

o Chain with pick points.

The figures for the chain machines are fairly close together, also 

the two tests of hand-pick undercutting, but the results of the puncher 

tests are too divergent, even after due allowance is made for the physical character of the coal and ability of puncher machine men.

Judging from the Fairmont figures the quantity of coal dust passing through a 20-mesh sieve is double what will pass through a 40- 

mesh sieve. If we assume the limit of dangerous coal dust as 20-mesh 

(the reason for this assumption will appear later), by doubling the 

above averages we get 1.00, 2.06, and 0.78 per cent of the total coal 

as dangerous dust. If we accept these figures for a mine producing 

1,000 tons of coal per day, there would be from 15,000 to 41,000 

pounds of dust produced daily from the undercutting, besides a 

certain additional amount from shooting down, picking, and shoveling the coarse coal. If only a small fraction of the coal dust daily 

produced in the ordinary mine is left exposed in rooms and along the 

entries, and not rendered inert by natural or artificial means, the 

mine will soon contain more than sufficient dust for propagating an 

explosion.

AGENCIES THAT DISTRIBUTE COAL DUST.

While coal dust mainly comes from breaking down coal at the 

face of the mine, it is distributed through the mine in several ways:

1. By the force of the explosive used.

2. By the shoveling of coal along the face and into pit cars.

3. By the fine coal running through cracks and holes in pit cars, 

and particularly under the car door, which usually fits more or less 

loosely, and thus being distributed along tke haulage ways. 

38970° Bull. 425 10 3
34 THE EXPLOSIBILITY OP COAL. DUST.

4. By lumps of coal jolting oil the tops of'pit cars and then being 

ground up by the traffic of men and mules or horses. This condition is found particularly at sidings and at the "main bottom," 

owing to abrupt stops while the cars are moved and switched.

5. By ventilating currents, which pick up the fine "float" dust at 

the face, and more particularly from the tops of cars. The passing 

of a trip of cars, partly blocking the air way, causes a very high 

velocity past the cars, especially when they go through a single ventilation door. If the hoisting shaft is dry and is a downcast, and the 

surface screens are near the top of the shaft, the ventilating currents 

may draw considerable quantities of dust from the screens.

Dry coal dust along the passageways or entries of a mine is a great 

menace. While in this country the great majority of dust explosions 

have originated at the face from blown-out or overcharged shots, 

the propagation has been through dusty entries. If the entries were 

free from dry coal dust the explosion would be local. Again, some 

explosions have originated on the entries from igniting pockets of 

gas in poorly ventilated entries; or in shooting down the roof for overcasts, or in brushing or grading. Firing shots on roadways has 

been a frequent source of disaster in England.

The problem is not alone to treat the dust lying on the floor, but 

the fine "float" dust that lodges on walls, roof, and timbers. Every 

ledge and projection has a coating of more or less thickness of the 

purest coal dust. In the opinion of many writers, what Mr. W. N. 

Atkinson terms "upper" dust is more dangerous than the "lower" 

dust, because it is more finely divided. This will evidently depend 

on the characteristics of the dust whether it is coal dust or rock 

dust and whether the former retains its strength.

The ventilating currents have a sorting action, dropping the coarser 

particles to the floor and lodging the finer higher up.

EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS.

EFFECT OF QUANTITY OR DENSITY OF DTJST. 

CHARACTER OF DUST USED.

A preliminary series of experiments have recently been made in 

the explosion gallery at the Pittsburg station to observe the effect 

of sizing fine coal, and to determine the quantity or density of the 

finest size necessary to propagate an explosion.

All these tests were made with artificially prepared dust from a 

certain mine working the -Pittsburg seam, which provides coal of 

uniform character and chemical composition for all standardizing 

tests at the station,
U. S. GEOLOGICAL SURVEY

EXPLOSION FROM COAL DUST IN GAS AND DUST GALLERY NO. 1, PITTS
EXPERIMENTS WITH -EXPLOSIBLE COAL DUSTS. 35

The coal as prepared after grinding and screening has the following 

average proximate analysis:

Proximate analysis of coal used for tests at Pittsburg station.

Moisture.................................................... 1. 94

Volatile combustible.......................................... 35.11

Fixed carbon................................................ 57. 73

Ash.......................................................... 5.22

100. 00 

Sulphur....................................................... 1. 25

There is manifest advantage in using an artificially prepared dust 

of uniform chemical composition and known size. The use of so-called 

mine dust of unknown composition in the early experiments abroad, 

was probably the cause of inconsistency in many of the results

reported.

The coal dust for the following density tests was made by grinding 

in a ball mill the standard Pittsburg station coal until it would all 

pass through a 200-mesh sieve (200 wires to the linear inch).

METHOD OF PROCEDURE.

In these tests, six sections (40 linear feet), of the explosion gallery 

were used. The gallery 100 feet long and 6 feet 4 inches in diameter, 

may be seen in Plate I, which shows the first stage of a dust explosion. 

The near end is closed by a concrete block, in which is placed the 

cannon for simulating blown-out shots. The gallery has 15 sections, 

each 6 feet 8 inches long, with a window on the observation side in 

the middle of each section and a relief door or flap at the middle of 

the top of each section. For the density tests the following arrangement was used: A paper diaphragm was placed at the farther end 

of the sixth section. The space between the diaphragm and the 

concrete block contained 1,260 cubic feet. Air was blown into the 

bottom of the gallery and drawn out at the top by two blowers with 

5-inch inlets and outlets. These blowers, one for each three sections, 

were connected with the gallery by independent pipes. Each pipe 

formed with the gallery and its respective blower a separate circuit. 

The dust was placed in a short 6-inch pipe at the top of the gallery 

near the concrete block. A blast of compressed air ejected the dust 

from the pipe, which pointed. toward the paper diaphragm and the 

farther end of the gallery.

The fans were started at the moment of dust ejection, to cause 

circulation of the air and so keep as much of the dust in suspension 

as possible. Nevertheless, it was found, by taking samples at the 

axis of the gallery, that the greater part of the dust fell quickly to 

the floor. In eighty-five seconds only about 9 per cent remained in 

suspension, and in two hundred and seventy-five seconds about 4 per
36 THE EXPLOSIBILITY OF COAL DUST.

cent. If followed out, the curve showing the rate of fall made by 

platting the several results makes it probable that after two hundred 

and ninety seconds, the average time before the shots were fired, there 

was not in suspension at the middle of the gallery over 24- per cent of 

the original amount of dust injected.

METHOD OF TAKING SAMPLES.

The samples of the dust in suspension were gathered by a special 

device consisting of a small tube in which dried cotton served as a 

filter. This filter tube was attached to a long, thick glass tube, which 

was inserted into the gallery through a hole in a paper diaphragm 

placed over the third top relief valve of the gallery, 17 feet from the 

firing end, so that the filter tube could be placed to draw air and dust 

from the center or axial line of the gallery, and at a point where the 

end of the flame from the blown-out shot would impinge. Suction 

was produced by emptying water from a bottle of 4 liters capacity. 

The long glass tube was connected with the top of the bottle by a 

rubber hose. The water from the bottle was discharged downward 

through a rubber hose into a similar bottle below. The filter tube 

was dried and weighed before insertion and after gathering the sample 

was again dried and weighed, the difference in weight giving the 

amount of dust in suspension in 4 liters of the gallery atmosphere, 

at the average time of taking the sample. Check samples were 

taken simultaneously with duplicate apparatus. This apparatus, 

designed by Dr. J. C. W. Frazer, was found to work admirably. 

Some inconsistency in the amounts of dust in suspension was evidently due to the irregularity of the air currents and the method of' 

injecting the dust, rather than to the method of sampling. Similar 

devices for obtaining the amount of dust in mine air are described by 

Prof. Otto Brunck, of the Royal Saxon Mining School, Freiberg; 0 

and a more portable form, in which the filter tube is attached to a 

brass exhausting syringe of 200 cubic centimeters or more capacity, 

is described by Dr. J. S. Haldane in his valuable little book, "The 

investigation of mine air", (p. 57).

RESULTS.

Five tests of dust were made under the conditions named, with 

amounts varying from 2 to 5 pounds. The results are shown in the 

table below. As already stated the fans were started at once after 

the dust was injected into the gallery by the blast of compressed air. 

One minute later the first sampling of dust in suspension, in duplicate, 

was begun, and lasted approximately one minute. After an interval of 

another minute, a second sample was taken, also in duplicate. Then

? Die ch§miSQhe Untersuchung der Grupenwetter, p. 91.
EXPEBIMENTS WITH EXPLOSIBLE COAL DUSTS. 37

the fans were cut out by valves, and the shot was fired about two minutes later. The time given in the tabulation of the results is the 

period from the moment of injecting the dust to the middle point of 

the time used to take the sample.

Ignition of the dust was considered to have occurred in all five 

tests, and complete propagation in all but test G-2891, in which the 

coal-dust charge was 2 pounds, equivalent to 0.0253 ounces per cubic 

foot (or 25.3 grams per cubic meter) for the 40 lineal feet of gallery 

used in the tests.

Results of explosion-gallery experiments on explosibility rf %00-mesh dust (more, or less

in suspension').

No.

1

2 

3 

4 

5

0

Gallery 

test No.

0-2887.. 

Cr-2888..

0-2890.. 

0-2891.. 

0-2892..

0-2896..

Date of 

test 

(1909).

Sept. 7.. 

...do.....

Sept. 8.. 

...do..... 

...do....

Sept. 9..

Explosive used 

in shot.

No charge h .....

I1J- pounds (567 

\ prams) FFF 

I black powder.

.....do.......... 

.....do.......... 

.....do..........

fl| pounds (567 

\ grams) FFFF 

[ black powder.

Amount of dust 

used.

Pounds.

5*

}'

3 

2 

2j

}"

Ounces per 

cubic foot.

0. (K-08 

. 0035 

. 0381 

. 0253 

.0317

.0317

Grams per cubic meter.

69. S 

63.5 

38.1 

25. 3 

31.7

31.7

Flame 

showed (indicating its

length) at 

Doorway s 

Nos. 

1-7- 

1-5 

1-3 

1-5

1-4

Windows 

Nos. 

1-9

1-0 

1-4 

1-0

1-0

Ignition.

Yes. 

Yes. 

Yes. 

Yes.

Yes.

Propagation.

Yes. 

Yes. 

No.. 

Yes.

Yes.

Time fromstart ofteso

sample taking.

Seconds 

85 

210 

325 

97 

285 

390 

85 

275 

282 

85 

282 

390 

85 

300 

405 

85 

275 

85 

275

o

5 §'

IH 

0)

ft 0 

>>^ -^ o

°5i O

8

T3

3 

fi

Ozs.

0. 00195 

.00123 

. 00208 

.00063 

.0007 

. 00375 

.00168 

.00175 

.00243 

. 00073 

.0007 

.00298 

.00168 

. 0016 

< -. 00255 

< . 0009 

. 00275 

. 0010

"Grams per cubic meter can be obtained, approximately correct, from ounces per cubic foot by multiplying by 1,000.

'' No charge of powder fired; this test was made to observe the density of dust at successive intervals 

following injection.

c All samples were taken at door 3 except these two in test 6, which were taken at door I.

Analyses of 200-mesh dust used in experiments and of coked dust resulting from them.

Test No.

All.......

G-2892...

G-2896...

Character of sample.

.....do................................................

Moisture.

2.00

o2.00

a 2. 02

Volatile 

combustible.

34.00

14.49

13.78

Fixed 

carbon.

59.70

65.59

67. 42

Ash.

4.30

f> 17. 92

16.78

"Analyses of these coked dusts were not made until over six weeks after the test; it is probable that 

the moisture shown had been absorbed in the meantime.

& In the explosion of the coal dust, the analysis of which is given in the first line of the table, the 

quantity of ash for a given amount of the dust would remain unchanged, as in this experiment there 

was no contamination. Hence it is possible to calculate the total amount of combustible matter disappearing in the explosion and the distribution of this combustible matter between the volatile matter 

and the fixed carbon. The following result is obtained: That 89.4 per cent of the volatile matter of the 

original dust and 73.6 per cent of its fixed carbon have been consumed.
38 THE EXPLOSIBILITY OP COAL DUST.

Although the sampling showed that a very small fraction of the 

coal dust remained in suspension, the propagation of explosive wave 

was proportionate in each instance to the total amount injected into 

the gallery, indicating that a considerable part of the dust that had 

fallen to the floor before the shooting was thrown into suspension 

by the concussion of the shot and in time to assist in the propagation 

of the flame. Not all of the dust was burned and portions of it had 

not lost all of its original volatile combustible matter, but the greater 

part was moye or less coked.

COKED DUSTS PRODUCED BY EXPLOSIONS.

The coked dust produced in these tests developed some interesting 

peculiarities, as shown in Plate II. There are three types of coked 

dust. The first consists of large globular pieces, with large interior 

air cells and thin glazed walls, from one-fourth to three-fourths inch 

in diameter. The pieces of coke shown in Plate II were photographed 

on paper divided into half-inch squares, so that the actual size may 

be scaled from these squares. This type of coke was evidently produced by the flame striking a mass of floating particles, the concussion 

and heat causing them to cohere and distill their gas, the expansion 

of which within the melted mass blew it into the globular forms 

shown at the upper part of Plate II. These had time to cool and 

harden before they fell to the bottom of the gallery.

The second type of coke, shown in the middle portion of Plate II, 

consists of masses of loose particles, which have fallen while still hot, 

sticking to other masses and flattening on the floor of the gallery.

The third type, shown in the lower left corner of Plate. II, 'is not a 

true coke but scales of particles evidently caked while lying on the 

floor of the gallery. The upper side of those on squares J-4, K-4, 

show minute bubbles of coke. The lower surface on square K-3 

shows dust apparently little affected by the heat. These scales of 

caked dust are not thicker than one one-hundredth of an inch. .

EFFECT OF DEGREE OF COARSENESS OF DUST.

RESULTS OF TESTS.

A series of tests was conducted in the explosion gallery of the 

Pittsburg station to determine how coarse a coal dust may be that, 

if abundantly present, will propagate an explosion that has been 

started by ignition from a blown-out shot. The results are shown in 

the two following tables:
U. S. GEOLOGICAL SURVEY BULLETIN 425 PLATE II

12 3456

COKED DUST FROM PITTSBURG GALLERY, DENSITY TEST WITH 200-MESH DUST. 

Photographed natural size on paper divided into half-inch squares. Experiment G-2892.
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 30 

' Tests of propagation ofjlame by different sizes of coarse coal dust.

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Gallery 

test No.

0-2882..

G-2883 . .

G-28S4..

G-2885

G-2886

G-2889..

G-2894..

G-2895..

G-2963..

G-2964

0-2970..

G-2974..

G-2987..

G-2988

Date of

test

(1909).

Sept. 3

Sept. 4

...do....

...do....

...do....

Sept. 7

Sept. 9

...do....

Sept. 20

...do....

Sept. 24

Sept. 25

Sept. 27

...do....

Explosive.

Pounds.

H

H

1*

Hli

Hi*i*

H

24

2*

2*

24

24

Grams.

567

507

567

567

567

507

567

567

567

1,135

1,135

1,135

1,135

1. 135

Dust used."

Weight.

Pounds. 

10

20

10

20

10

20

10

17

14

10

10

.12

15

23

Size.

Mesh. 

20- 40

20- 40

40- 60

40- 60

60- 80

60- 80

80-100

60- 80

60- 80

60- 80

60- 80

40- 60

20- 40

20- 40

Flame showed (indicating its length)

at 

Doors 

Nos. 

(") 

(")

0

0

2- 4

2- 6

2- 7

2-14

3- 7

3-9

2-11

2-12

2- 5

2- 3

Windows 

Nos. 

1- 4

1- 5

1- 3

1- 3

1- 5

1-14

1-14

1-1.4

1-14

1-12

1-14

1-14

1- 8

1- (i

Result.

Ignition.

No... .

No.. .

No.. .

No.. .

Yes

Yes!

Yes. .

Yes.

Yes.

Yes. . Yes.

Yes. . Yes.

Yes.

Propagation.

No.

No.

No.

No.

No.

Yes.

Yes.

Yes.

Yes.

Yes

Yes!

Yes.

Partial.

Partial.

a Dust was placed on a horse in the first three sections, and on shelves in sections 2-0, except in tests 13 

and 14, in which dust was placed on shelves in sections 3-9 and 3-11, respectively. 

6 Edge of door 3.

Analyses of dust samples taken before and after tests shown in preceding table.

No.

3

5

7

12

13

Gallery 

test No.

C} 9SS9

G-28S4..

G-2886..

G-2894 . .

-2'JS / . .

Character of sample.

.....do...........................................

.....do...........................................

....do...........................................

Moisture.

2.00

2.20

2.00

2.00

«1.54

2.20

2.00

2.20

« 1.28

Volatile combustible.

OJ Cfl

33. 50

34.50

35. 00

13. 92

33. 50

12.00

33. 50

18. 18

Fixed 

carbon.

59. 70

00. 20

59. 50

58.60

65. 12

00. 20

 68. 70

60. 20

69. 62

Ash.

. 3.80

4. 10

4.00

4.40

19.42

4. 10

16. 70

4. 10

10.92

a Analyses of these coked dusts were not made until over a month after the test; it is probable that the 

moisture shown had been absorbed in the meantime.

METHOD OF SCREENING.

The coal was of the kind used for standard tests at the station, the 

average analysis of which is shown on page 35. After being crushed 

and ground, it was passed through 20, 40, 60, and 80 mesh screens, 

so that four sizes of dust remained over 40, 60, 80, and 100 mesh 

screens. Difficulty was experienced in getting each size free from 

the next smaller size, and particularly from the float dust, so that 

great care was required in screening. The float dust was eliminated 

by stirring small portions of the screened size in a deep pail, with 

the end of a hose discharging compressed air. By this means each 

size when finally finished was remarkably clean and free from other 

sizes.
40 THE EXPLOSIBILITY OP COAL DUST.

DISTRIBUTION OF DUST.

In this series of experiments, the dust of the size to be tried was 

distributed along the gallery on four narrow iron shelves on either 

side. The gross amount distributed was 1 pound per linear foot of 

gallery. This amount is much in excess of what is necessary to 

produce an explosion, so that only a relatively small part of the dust 

is active or loses its volatile matter. In addition to the dust placed 

as just described, 20 pounds was placed upon a horse 20 fee°t long and 

9 inches below the center line of the bore hole and the axis of the gallery. The dust was placed in this way to obtain ,the most extreme 

condition, such as would be found in a mine with a blown-out shot

LONGITUDINAL SECTION 

0 5 10 Feet

FIGURE 1. Diagrammatic sections of cannon end of gallery No. 1, Pittsburg station.

pointed toward a pile of coal dust. Figure 1 is a sectional outline

of part of the gallery, showing the location of the horse. 

DISCUSSION OF RESULTS.

In the first tests a charge of 1J pounds of black powder was used, 

tamped.with 2J pounds of clay. With this charge dusts larger than 

60-mesh did not even ignite (except for slight prolongation of powder 

flame in tests 1 and 2), but 80 to 100 mesh dusts and also 60 to 80 

mesh dusts in three out of four tests did ignite and propagate the 

explosion. It may be assumed that finer sizes would propagate, so. 

no tests were made of them.

A series was then tried with double the' quantity of black powder, 

or 2£ pounds, and with 2 pounds of clay tamping, which was .all that 

the depth of the bore hole would allow. The effect was notable; 60 to 

80 mesh dust propagated the explosion and so did 40 to 60 mesh dust. 

With 20 to 40 mesh dust, while there was ignition, there was only 

partial propagation, but the indications were that with a still larger
U. S. GEOLOGICAL SURVEY

3456 7

COKE PRODUCED FROM 80 TO 100 MESH DUST. 

Photographed on half-inch squares. Experiment G-2894.
U. S. GEOLOGICAL SURVEY

COKED DUST PRODUCED FROM 20 TO 40 MESH DUST. 

Unused particles shown at the bottom. Photographed on half-inch squares. Experiment G-2987.
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 41

charge of powder, increasing the concussion and heat of the initial 

explosion, complete propagation would be produced. It may be 

that in a mine still coarser sizes would propagate from very large 

shots, in view of the fact that smaller sizes are present to sustain 

the flame; but tentatively, until further tests can be made, the writer 

has accepted 20-mesh as the dividing line between what may be 

termed fine coal and what may be considered dust.

It must not be inferred that larger particles of coal may not be a 

factor in a mine explosion once fairly started. On the contrary, the 

writer believes that they are, and that in a strong explosion the coal 

walls of the passageways where struck by a fierce blast will give up 

their quota of volatile gases. The assumption as to the size (20- 

mesh) therefore refers only to the initial stage of an explosion. Heretofore such coarse dust has not generally been considered dangerous.

CHARACTER, OF COKE PRODUCED.

The coke produced in these tests presented some interesting peculiarities, as indicated in the photographs of coke from two typical 

explosions, reproduced in Plates III and IV. The first (PL III) from 

test G-2894, is the product of the explosion of "dust" finer than 80 

and coarser than 100 mesh. The globular pieces shown in the upper 

part of the picture, which are from one-half to three-fourths inch in 

diameter, resemble the coke from float dust, though more irregular 

and made up of a mass of smaller cells. The smaller particles in the 

middle of the picture (obtained by screening) are largely spherical, 

and many consist of a single cell. The finest particles, at the bottom 

of the picture, are finer cells, also fragments of larger coke cells.

Plate IV shows coke and coal particles from test G-2987, in which 

a partial propagation was obtained from "dust" finer than 20 and 

coarser than 40 mesh. Particles of this "dust" which were not used 

in the experiment are shown in the lower part of the picture. The 

large cnifnbly masses of coke in the upper part of the picture consist of individual coked and caked particles loosely stuck together 

as they were swept into little piles at the flanges of the gallery.

The piece at the top which has the same thickness as width, threefourths inch, was formed in the corner of a flange. The piece on the 

squares C-6 and 7 to G-6 and 7 shows the under side of such a mass 

with the coal particles caked or fused only enough to stick together.

. EFFECT OF CHEMICAL COMPOSITION. 

PAST EXPERIMENTS.

The effect of the chemical composition of dusts upon their relative explosibility or nonexplosibility is a problem that has been 

much discussed by mining men and by scientists from the time of 

Faraday. Experiments with dust of different chemical composition
42 THE EXPLOSIBILITY OF COAL DUST.

have been made at various times and in various countries, both in 

laboratories and on a larger scale. The earlier experiments of the 

foreign investigators, Abel, Hall, Galloway, Marreco, and others, 

and of the early European testing stations, have been mentioned on 

pages 12-19. The small-scale experiments of Professors Peckham 

and Peck, of the United States, have been referred to on page 23.

INVESTIGATIONS IN THE UNITED STATES BY CHAMBERLIN.

No large-scale systematic tests of the explosibility of coal dust had 

been made in this country before the Pittsburg station experiments 

were started; but some very interesting studies of explosive mine 

gases and dust have been made by Mr. Rollin Thomas Chamberlin.0 

The investigations relating to coal .dust were made to determine 

the part that dust took in explosions, particularly in the Monongah, Naomi, and Darr disasters. Mr. Chamberlin observed the 

enormous quantity of fine coal dust coating everything in the exploded mines. He noted that the dust was of two sorts, "uncharfed 

dust" and "charred dust," and that each took certain positions with 

reference to the obstructions in the passageways. He observed that 

the charred dust in the Monongah and Darr mines was for the most 

part on exposures facing away from the source of the explosion, but 

adds that there were many exceptions to the rule. He concluded that 

much dust was coked while in the air and deposited in a semiplastic 

condition. Laboratory experiments were made by Mr. Chamberlin 

on the loss of volatile matter in the charred dust. In these investigations he determined the amount of volatile matter contained in different coal dusts, and the amount of gas given up in the process of crushing coal to dust, and also made some investigations of the relative

inflammability of old and new dust. From the latter studies he concluded that the oxygen absorbed by dust is mainly chemically combined and that there is not enough free oxygen in the dust to play an 

important part in an explosion. He therefore inferred that "fresh 

dust is likely to prove more inflammable and more predisposed to 

start and propagate a dust explosion."

EXPERIMENTS OF BEDSON AND WIDDAS.

Abroad, during the past few years, valuable tests of the comparative sensitiveness of different dusts have been made on a laboratory 

scale by Professors Bedson and Widdas at Newcastle University, 

England. Preliminary results were given by them in two papers 

read before the North of England Institute of Mining and Mechanical 

Engineers, 1906-7. These results are discussedvfoy Dr. J. C. W. 

Frazer on pages 117-121 of this bulletin. .

a Chamberlin, R. T., Notes on explosive mine gases and dusts, with special reference to explosions in the 

Monongah, Darr, and Naomi coal mines: Bull. U. S. Geol. Survey No. 383,1909.
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 43 

INVESTIGATION IN FRANCE BY TAFFANEL.

M. J. Taffanel, in August, 1907, published the results of his first 

year's experiments at the Li6vin station. A large number of tests were 

made with the coals from the several mines of the Pas de Calais district. M. Taffanel, believing that a uniform density of dust cloud 

was necessary to obtain consistent results, arranged a closed-circuit 

gallery. (See fig. 12.) This consisted of two parallel sheet-iron pipes 

'2 feet in diameter. These pipes were 25 feet long and connected at 

the ends. In one of the pipes there was a disk fan for propelling the 

air current and mixing the dust. The four openings to the gallery 

were closed by paper diaphragms. The inclosed volume was 152 

cubic feet. In operation, the fan was started and the dust put in 

gradually, and after time had been given for circulation four or five 

times around the closed circuit at a speed of 13.16 feet per second, a

cannon charged with a half stick of dynamite, weighing 1.12 to 1.33 

ounces (32 to 38 grams), and not tamped, was fired through one of the 

paper diaphragms.

The dusts were always passed through a French 200-mesh sieve, 

equivalent to English 190 mesh. The dust put into the gallery was 

weighed and it was assumed that all was put into suspension.

The most sensitive dust was found to be that from the Courrieres 

mine. In one instance, with as low a weight of dust per cubic foot as 

0.023 ounce or 23 grams per cubic meter the flame traversed the tube 

and came out about half a yard. However, this was the only instance 

in which a flame was produced, out of three experiments tried with 

that density of dust. With this exception, it was only when as 

much as double this density, or 0.046 ounce, was used that flame 

was occasionally produced. With 0.070 ounce per cubic foot, or 70 

grams per cubic meter, explosions Were produced quite regularly with 

almost all the coals except anthracite. With this, as high a dust 

weight as 0.222 ounce per cubic foot (222 grams per cubic meter) 

were tried without producing continued flame,

Taffanel's conclusions were as follows: 0

 The experiments show, in the first place, that for most of the dusts tested it does not 

require large quantities of fine dust, once put in suspension, to form an inflammable 

cloud. A mine road where 0.1 ounce of fine dust per cubic foot [100 grams per cubic 

meter] may be collected is generally regarded as [but a] little dusty. It is important 

to observe that so far the experiments have been confined to screen dusts, which are 

purer and without doubt more inflammable than those from the mine.

We see, in the second place, that the small charge represented by half a cartridge of 

gelatin dynamite is above the "charge limit" for most of the dusts tried. This, of 

course, refers to the "charge limit" without stemming.

Finally, we remark that for the eight types of dust tested the increasing order of 

inflammability is the same as the increasing percentage of volatile matter. Strictly

o Premier essais sur I'inflammabilite' des poussieres, p. 20; Proc. South Wales Inst. Eng., vol. 26, No. 3, 

1909,p. 677.
44 THE EXPLOSIBILJTY OF COAL DUST.

speaking, it may be considered that the dusts differentiate not only by their percentage 

of volatile matter, but also by other elements of their composition, particularly by the 

percentage of ash. But the dusts tested, coming nearly all from the screens, have a 

somewhat similar percentage of ash, which causes the factor "volatile matter" to predominate. The ash intervenes in two ways: First, by its weight; the cloud densities 

indicated in the above tables are gross densities; it would be more just to compare the 

densities by reckoning only the combustible portion, after deduction of the ash and 

moisture; in the second place, the ash intervenes as an inert matter absorbing a part 

of the heat of combustion of the dust; it would be too hazardous to try to calculate this 

latter influence, which might without doubt be determined by experiment. But in 

the following table account is taken of the first influence by showing, alongside the 

gross densities, the densities calculated by deducting the ash and the moisture. This 

table places clearly in evidence the influence of the percentage of volatile matter.

Coal.

Lignite. ...................................

Percentage 

of volatile 

matter(ash 

and moisture deducted).

11.2 

11.3 

15.4 

26.6 

28.4-31.4 

30.0 

30.6 

53.3

Cloud densities from 

which inflammations 

commence.

Gross.

Oz.percu.ft.

o.iss

.070 

.040 

.038 

.023 

.030

Calculated 

(ash and 

moisture 

deducted).

Oz.percu.ft.

0.120 

.060 

. 039-. 044 

.033 

.021 

.023

Cloud densities from 

which inflammations 

always occur.

Gross.

Oz.percu.ft.

0.138 

.104 

. 07-. 074 

.092 

.058 

.040

Calculated 

(ash and 

moisture 

deducted).

Oz.percu.ft.

0.120 

.090 

. 067-. 068 

.080 

.052 

.031

« No inflammation.

By the aid of these numerical results, which, it must not be forgotten, are approximate, may be drawn the conclusion that there are great differences in inflammability, 

under the conditions of the experiments, between the three following groups: First, 

anthracite and Lens 2, not ignited; second, Dourges and Lens 1, inflammable, but 

without great effects of flame, and with a marked tendency to stifling; lastly, the four

types richest in volatile matter, which were ignited at low densities and which produced increased flames as the cloud density increased.

COMPARISON OF TAFFANEL's METHODS WITH THOSE USED AT

PITTSBURG GALLERY.

The few density tests made at the Pittsburg station (described on 

pp. 34-38) were all made with the high-volatile coal from the Pittsburg seam. While they were not numerous enough for a direct comparison with M. Taffanel's results, as given above, it would appear 

that the initiating charge of explosive was a most important factor.

M. Taffanel, in the experiments described above, used but 1.12 to 

1.33 ounces of a low-grade nitro-explosive, while in the Pittsburg 

density tests, in a much larger gallery, 1£ pounds of black powder 

was used. With this charge dust explosions were produced with as 

low a density of coal dust as 0.032 ounce of dust per cubic foot of
EXPEBIMENTS WITH EXPLOSIBLE COAL DUSTS. 45

space in the gallery (32 grams per cubic meter), as reported in the 

.table on page 37.

M. Taffanel has recently written a paper on his tests in the larger 

gallery at Li6vm.° These tests confirm those made previously, in a 

smaller gallery. He has devoted much attention to the chemistry of 

dust explosions. He finds that schist (shale) dust tends to blanket 

the effects of the coal-dust explosions, but he states that his experiments in this direction have not gone far enough to permit conclusions to be drawn therefrom. His aim, in this first series of 

experiments, unlike that of the Altofts station, which will be mentioned hereafter (p. 80), had been to find the effect of mixing this 

schist dust with the coal.

INFORMAL TESTS AT PITTSBURG STATION.

There has not yet been opportunity at the Pittsburg station for 

systematically testing in the gallery the relative explosibility of dusts 

of different chemical composition; but Clarence Hall, in charge of 

explosives testing at the station, has made a great many informal 

tests of coal dust from different parts of the United States, and has 

kept careful records of them. These records he has kindly put at the 

writer's disposal. Certain tests have been selected as typical, and 

these are given in a table below. The materials range from anthracite 

with little volatile matter to subbituminous coal with much moisture 

and volatile matter. All shots were made with black powder, except 

one with dynamite. The weight of the charge is specified in the table. 

Clay tamping was used in all these tests. The amount of coal dust 

was usually 120 pounds, of which 20 pounds was placed on a horse 

and 100 pounds distributed on side shelves running along the full 

length of the gallery, 1 pound per linear foot. When the full number 

of shelves was not used, the loading was proportionately less. The 

horse or center shelf is placed in front of and 9 inches below the 

center line of the bore hole, so that the flame of the explosive would 

touch but not directly play upon the dust. This arrangement simulates the condition in a mine where a pile of coal with dust on it lies 

in front of a blow-out shot.

The charge of coal dust averages 1.2 pounds per linear foot of 

the gallery, equal to 0.61 ounce per cubic foot, or 610 grams per 

cubic meter. According to Taffanel, the theoretical weight of coal 

dust necessary to produce a maximum explosion is about 0.111 ounce 

per cubic foot or 111 grams per cubic meter.6 Naturally this weight

oLes resultats obtenus jusqu'a ce jour dans la galerie d'essais de Lie'vin: Bulletin et comptes rendus 

mensuels de la Socidte de 1'industrie minerale, February, 1909.

6This is figuring that "the total combustion of the carbon and volatile matter, with the exclusive 

formation of carbonic acid and water vapor, would exactly absorb all the oxygen of the air" (loc. cit.). 

In reality only a portion of the volatile matter and fixed carbon is burned. See analyses of coked dusts 

jn reports of experiments, also footnote 6 to second table on p. 37.
46 THE EXPLOSIBILITY OF COAL DUST.

varies somewhat with the character of coal. a The gallery at Pittsburg is charged with dust much in excess of the theoretical amount 

to insure the most severe conditions in testing explosives, but 

repeated tests have shown that dust through a 100-mesh sieve can 

be put in suspension by the concussion of li pounds of black 

powder. if the dust is merely placed on the floor of the gallery. For 

the tests given in the table, the coal was ground until it would pass 

through a 100-mesh screen, but when road dust was tested it was 

used in the gallery as received.

No propagated explosion has been obtained with anthracite dust, 

although several tests have been made with a low- volatile anthracite 

(under 5 per cent volatile combustible matter) and with a higher 

volatile anthracite (8 .32 per cent volatile combustible matter) . However, it' must not be concluded that these tests are final; there may 

be conditions under which propagation can be obtained.

Propagation did not take place with one semibituminous dust when 

dynamite was used for the firing charge, nor in one test when black 

powder size CO was used, but in subsequent tests, with other sizes 

of black powder, complete propagation followed. The failures to 

propagate may have been accidental, but considered together with 

the slowness of propagation observed in the other tests on this coal 

they indicate that it is not so sensitive as most, bituminous coals.

With other semibituminous coals and all bituminous and subbituminous coals propagation of flame and explosion was complete. 

As these dust tests could only be made occasionally, when the gallery 

was not occupied by the more pressing testing of short-flame or socalled safety explosives, quantitative results on the relative sensitiveness of different bituminous dusts could not be attempted under 

the circumstances. But these typical tests and numerous other informal tests of the same character have demonstrated effectively the 

explosibility of coal dust.

The explosion propagative results with bituminous dusts have been 

so uniform that it is hard to understand the difficulty which early 

foreign experimenters had in obtaining consistent results, unless it 

was due to the uncertain character of the mine dust, or possibly to 

the very small charges of explosive employed.

a The theoretical quantity of the standard coal used for tests In the Pittsburg station, required for the 

complete exhaustion of the oxygen of a cubic foot of air by combination with all the combustible matter of the coal, was 0.123 ounce or 123 grams per cubic meter: This is based on the ultimate analysis of 

a sample (10556F) which was mined December 7, 1909, and analyzed. June 27, 1910. The exposure for six 

months probably increased the oxygen contents and decreased the efficiency of the coal. The ultimate 

and proximate analyses of this coal are as follows:

Ultimate analysis.

Hydrogen ................................. 5.61

Carbon ...,..........................'...... 78.00

Nitrogen.................................... 1.52

Oxygen.................................... 9. 74

Sulphur ................................... .52

Ash........................................ 4.61

100.00

Proximate analysis. ' 

Moisture................................... 2.59

Volatile matter............................ 35.34

Fixed carbon .............................. 57.46

Ash........................................ 4.61

100.00
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 47 

Explosion-gallery tests at Pittsburg station on dusts from representative coals.

Test 

No.

G--700. .

G-3043. 

G-2309. 

G-2365. 

G-2067.

G-467. . 

G-465. .

G-2110.

G-215C. 

G-2517.

G-1501. 

G-2112,

Test 

No.

G-700. .

G-3043.

G-2369. 

G-2365. 

G-2067.

G-467. .

G-465. .

G-2116. 

G-2156. 

G-2517. 

G-1501. 

G-2112.

Date of 

test 

(1909).

Jan. 30. . 

Oct. 9...

May 15. . 

...do..... 

Apr. 10..

Jan. 2... 

...do.....

Apr. 17.. 

Apr. 24..

June 19..

Mar. 20.. 

Apr. 17..

Explosive used.

500 grams FFF black powder. 

.... do --------------------

500 gra 

300 gra 

375 gra 

der. 

500 gra 

der. 

do

ms C black powder.

ms FF black powms FFF black pow375 grams FF black powder. 

.....do....................

375 grams FF potassium

nitrate powder. 

375 grams FFF black powder. 

375 grams FF black powder.

Dust on 

horse and 

shelves in 

sections 

Nos. 

1-15

1-15 

1-15 

1-15 

4- 9

4- 5

4-6 

1-15

1-15 

1-15

1-15 

4-6

Flame showed 

(indicating its 

length) at 

Doors

Nos. 

1- 6

(«) 

1-3, 11-12

1-15 

1- 9 .

1-12 

1-15

1-15 

1-15

1-15 

1-15

Source of coal dust.

Name of mine.

No. 2 Bear Valley shaft.

Connell Anthracite Mining Co. 

No. 37 B mine... 

.....do...........

Shamoki

Mine ] 

Whil 

mines. 

INo. 3 T 

and I. 

No. 7 T 

and I.

Federal 

mine. 

Sunday 

Co., N 

Oak min

Garside i

Superior 

Co. No

n mine.

Vo. 5, 

well

jnn. C. 

Co. 

2nn. C. 

Co.

Shaft 

Creek

X 114.

nine....

Coal 

.C.

Location of 

mine.

Williamstown, 

Pa.

Bernice, Pa...

Windber, Pa. . 

.....do........

S w i tchback, 

W. Va.

Whitwell, 

Tenn. .

ifllocton, Am..

Fairmont, 

W. Va. 

Longacre, W. 

Va. 

Oak Station, 

Pa. 

Saline ville, 

Ohio. 

S w e e twater, 

Wyo.

Character and place of 

sample.

Anthracite 

heading in 

View at N< 

Subanthraci 

terior of m 

Semibitumin 

-do- _-

Se 

1

Bi

Bi

Bi

Bi 

] 

B 

( 

Bi

Su 

1 

i

mibitumii 

ipple.

tuminous

tuminous

tuminous

tuminous 

 Canawha 

t u m i no 

lard" dus 

tuminous

from first 

the Little 

). 2 shaft, 

e from inne.

ous from

from dry 

coal elevator./ 

from main 

entry, g 

from tipple, 

from ribs 

and tiinbers.ff 

from interior./ 

fromtipple. 

from No. 2 

*as seam, 

us ("stant).

bbituininous from 

ace of room 1 off first 

lorth.

Windows 

Nos. 

1- 6

1-3 

1-15

1-15

1-15 1-15

1-15 

1-15

1-15 

1-15

Length 

of flame 

beyond 

dust 

zone.

Feet. 

0

0

(«) 

0 

«50

27

. 60 

(«)

«50 

(a)

(°)

60

Ignition.

Slight.

No.... 

Yes... 

No.... 

Yes...

Yes...

Yes... 

Yes...

Yes... 

Yes...

Yes... 

Yes...

Propagation.

No.

No. b 

Yes.c 

No.d 

Yes.

Yes.

Yes. 

Yes.

Yes. 

Yes.

'Yes. 

Yes.

Analyses.'

Moisture.

2.36

1.40

.77 

.77 

.84

13.18

3.41

f 2.07 

3.22

1.52

7 1.25 

1.64

1.81 

2.03 

9.63

Volatile 

combustible.

4.22

8.32

13.96 

13.96 

15.16

19.97

17.98

26. 69 

24.18

30.59

31.70 

31.54

33.52 

35.37 

34.49

Fixed 

carbon.

83.44

75.52

79.80 

79.80 

79.90

56.37

47.22

58.01 

49.34

56. 79

57. 34 

64,55

59.36 

57.00 

50.91

Ash.

9.98

14.76

5.47 

5.47 

4.10

10.48

31. 39

18.23 

23.26

11.10

9.71 

2.27

5.31 

5.60 

4.97

Sulphur.

0.49

.87 

.87 

.48

.77

1.20

. .82 

.71

2.00

2.41 

.69

1.00 

2.38 

1.05

o Not recorded.

6 This test was repeated with 40 per cent dynamite with same result. 

cThis test was repeated twice with black powder, sizes "CC" and "CCC." "CC J 

ignition, but" CCC" did. 

d This test was repeated with a similar result. 

« Flame extended 50 feet beyond end of gallery. 

/Dust placed on a horse in the tests. 

f Dust placed on shelves in the tests.

did not result in an
48 THE EXPLOSIBILITY OF COAL DUST.

INFORMAL TESTS WITH ROAD DUST.

Some informal tests were made at intervals during the past year at 

the request of various mining men. The results of a few of special 

interest are given in the table below. The last three were with road 

dusts, which had a large admixture of clay or shale. The total ash 

ranged from 30 to 57 per cent. In two tests there was complete 

propagation, but in one test, in which the combined material had a 

total of 53 per cent ash, the flame died away, reaching only half the 

length of the-gallery.

With regard to road dust, it is important to bear in mind that 

unless the shale or stone dust is very fine and is intimately mixed 

with the coal dust its presence has very little deterrent influence on the 

explosion. A concussion from a blown-out shot or a small explosion 

of fire damp does not throw the pieces of rock into the air if they 

are coarse, and therefore the dust cloud may consist only of the fine, 

pure coal dust that rises from around the rock fragments. The same 

is true of any large pieces of coal that are present. The question in 

regard to any road dust is whether there is sufficient fine coal dust 

among the coarser pieces of rock to rise and form a dust cloud of 

sufficient density to permit a propagation of flame.

. Special explosion-gallery tests with bone dust, road dust, and mixtures.

Test 

No.

GT693..

G-415..

G-491

G-1431 .

G-398

G-2962 .

Test

No.

G-693..

G-415..

G-491..

G-1431 .

G-398..

G-2962.

Date of test.

Jan. 29, 1909.......

Dec. 30, 1908.......

Jan. 9, 1909........

Mar. 13, 1909.......

Dec. 26, 1908.......

Sept. 18, 1909......

Black powder 

used.

' Size.

F.....

FFF..

FFF..

FFF..

FFF..

(»)

Weight.

Grams.

500

500

500

375

500

375

Dust on 

horse and 

shelves in 

sections 

Nos. 

0

4-6

4- 6

1-15

a4- 6

1-12

Flame showed 

(indicating its 

length) at 

Doors ^ 

Nos. 

1- 6

1-15

1-15

1- 8

2

1-15

Source of coal dust.

Name of mine.

Bear Creek No. 3..

Weaver mine.....

Penn Gas Coal Co.

No. 3.

Elkins C. and C.

Co.

Carbon mine......

Bunson Coal Co...

Location of 

mine.

Bear Creek,

Mont.

Gallup, N. Mex

Irwin, Pa.....

Elkins, W. Va.

Carbon,W. Va.

Georgetown, 111

Character and source 

of sample.

Subbituminous coal

and bone cuttings.

Subbituminous, taken

from roads.

Bituminous, taken

from roads.

Bituminous, taken

from roadway.

Coal dust and fire clay

from room 12.

1 Bituminous coal dust,

50 per cent. 

Clay, soapstone, and

coal, 50 per cent.

Vindows 

Nos. 

1-11

1-15

1-15

1- 8

1- 9

1-15

Length 

of flame 

- beyond 

dust zone.

Feet.

54

60

60

0

20

c60

Ignition.

Yes.

Yes.

Yes

Yes."

Yes.

Yes.

Propagation.

Yes.

Yes.

Yes No.'

Yes.

Yes.

Analyses.

Moisture.

8.94

9.13

2.50

1.02

2.75

10.66

6.41

Volatile 

combustible.

30.57

31.87

26.06

12.76

15.45

29.44

19.45

Fixed 

carbon.

43.49

41.42

'53.43

32.94

24.85

45.00

27.18

Ash.

17.00

17.58

18.01

53.28

56.95

14.90

46.96

Sulphur.

1.78

.59

1.24

2.14

1.48

2.29

1.49

a Dust placed on floor in sections 1-3 and not on horse.

6 Size not given.

c Flame extended 40 feet beyond end of gallery.
EXPEBIMENTS WITH EXPLOSIBLE COAL DUSTS. 49 

EXPERIMENTS AT PITTSBUEG WITH COAL DUST. 

USE OF COAL DUST FOR TAMPING.

In various parts of the country the practice of using machine cuttings ("bug dust") or other coal dust for tamping has become 

very common. Some mining men have had a theory that if coal-dust 

tamping was dampened or made wet it would be rendered harmless. 

With a view to determining this point, a number of experiments were 

made in gallery 1 at the Pittsburg station with black powder, using 

machine cuttings, dry and wet, for tamping. The wet dust was wet 

enough to pack in the hand, and in the tamping a little water was 

Squeezed out. The powder was protected from the damp dust by 

a paper' Wad. A statement of the results is given in the following 

table;

E$ptosidn-gaUery tests with machine cuttings ("buff dust") used for tamping.a

Test 

No.

G-2309 . 

0-3040. 

G-3047. 

G-3086 . 

0-3085. 

0-3082. 

0-3083.

Date of 

test 

(1909).

Sept. 11 

Oct. 14 

Oct. 14 

Oct. 23 

Oct. 23 

Oct. 21 

Oct. 21

Powdef:

Size.

FFF.. 

FFF.. 

FFF.. 

FFF.. 

FEF.. 

FFF.. 

FFF..

Weight.

Grams. 

1,134 

1,134 

1,134 

567 

667 

1,134 

1,134

Tamping.

CoHdition.

( c) Wet. .....................

Dry. ......................

Wet......................

Dry.......................

Wet......................

Weight.

Grams.

(') 

400 

400 

1,200 

1,200 

1,200 

1,200

Flame showed 

at 

Doors 

Nos. 

1-2 

(d)

W 1-3 

1-5 

1-5 

1-7

Windows 

Nos. 

1-3 

1-5 

1-3 

1-4 

1-7 

1-8 

1-10

Length 

of flame.''

Feet. 

18 

30 

18 

24 

44 

50 

64

a The dust used for tamping was bituminous coal from the Keystone mine, McDowell County, W. Va., 

with the following analysis: Moisture, 1.24 per cent; volatile matter, 14.03; fixed carbon, 73.53; ash, 

11.20; sulphur, 0.66. In all the tests with tamping the walls of the gallery were kept wet.

* Length of flame measured from the mouth of the blown-out shot to the last window showing. In 

each test the flame may have extended 6 feet farther, to a point just short of next successive window.

c No tamping used. The test was repeated with 567 and 1,701 grams of powder and the flame showed 

in the same number of windows. When clay was used, flame was seen in two windows, and occasionally 

in three.

<* Not recorded.

The first experiments were made with 2£ pounds of black powder 

(1,134 grams) and 0.9 pound (400 grams) of machine cuttings. The 

effect with wet coal tamping was nearly to double the length of the 

flame from black powder alone, but with the dry tamping for some 

unexplained reason the flame was not materially lengthened in this 

test.

Experiments were then made with 1| pounds of black powder (567 

grams) and 2.6 pounds (1,200 grams) of cuttings, wet'and dry. 

With a smaller amount of powder than in the previous tests, the length 

pf flame with the wet tamping was not quite so long as with the 

larger charge of powder but smaller amount of dust tamping, With 

the dry coal-dust tamping, the flame was two and one-half times, aslong as that of black powder alone. 

38970° Bull. 425 10 4
50 THE EXPLOSIBILITY OF COAL DUST.

A third set of experiments was tried with the same weight of coal 

tamping, but with 2$ pounds of black powder. The flame with the 

wet tamping was still more increased, being over 50 feet in total 

length, and with the dry tamping the flame was over 70 feet in 

length, causing, in fact, a limited explosion.

The length of flame from .black powder without tamping does not 

appear to increase with size of charge as far as tested (2£ pounds), 

but it appears from these tests that the flame from the coal tamping 

increases with the charge of powder used. In fact, it is possible that 

a blown-out shot with a very large charge of black powder, such as 

is sometimes used in shots in mines of trie interior coal province, that 

contains 8 pounds or more, and with coal dust for tamping, may cause a 

local dust explosion without the. presence of any external dust. This 

may happen even in a wet entry. The tests with coal tamping at 

Pittsburg were made during rainy weather and with the gallery wet 

throughout by hose.

When very small charges of black powder are used wetting coaldust tamping may make the length of flame slightly less than that 

with dry coal tamping, though the flame length would still be greater 

than that resulting with clay tamping; but when medium-size charges 

of black powder are used the heat is such that the water has little 

or no effect.

It is a reasonable conjecture, in view of the results of the experiments described above, that with larger charges of black powder 

moistening or wetting the coal-dust tamping would cause" no appreciable decrease in the flame.

The conclusion is drawn from these experiments that the use of 

coal dust or coal cuttings for tamping, whether wet or dry, is a most 

dangerous practice. With a blown-out shot in which coal dust has

been used for tamping, causing flame extending 50 to 70 feet or 

more if there is any dust along the room or entry, the chances'of an 

extended dust explosion are enormously increased.

EXPEKIMENTS WITH COAL DUST IN HUMIDIFIED AIE.

During the winter of 1908-9 experiments were made under the direction of Clarence Hall in explosion gallery 1 with standard 100-inesh. 

dust distributed on horse and shelves and a current of humidified air 

drawn through the gallery. A Koerting injector used as an exhauster 

drew the air from a relief doorway near the "face" of the gallery. 

The intake air entering a relief doorway next to the outer end of the 

gallery was warmed by steam coils and humidified by compressed air 

and water sprays. The latter were of a type much used in cotton mills, 

in which the water is mixed with compressed air to finely pulverize 

the water spray, The gallery end was closed by a paper and cloth 

jbrattjce and the intake air from the heating and humidifying box
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 51

was drawn into the gallery through the last relief doorway and a box 

conduit by the Koeting injector. The results of the experiments are 

given in the following table:

Explosion-gallery tests to show effect of humidity. 

[In all tests the explosive used was 1J pounds (507 grains) of black powder.]

Gallery 

test 

No. 

G-346

G-348

G-349

G-350

G-482

G-483

G-484

G-580

Date of test.

Dec. 19,1908

Dec. 20,1908

Dec. 20,1908

Dec. 21,1908

Jan. 4,1909

Jan. 7, 1909

Jan. 9, 1909

Jan. 19,1909

Duration 

of test.

Hrs. min.

28

1 46

10 35

24 18

48 0

48 0

CO70 0

Air current. '

& ~3F

>>s

-w C

 si

0 h

0) P(

>

131

104

120

123

112

96

132

Temperature.

<a

2

ah- f

°F

34J

61

58

59

52

53

51

44

oi

T3

2

a

O

°F

34J

39

35

34

33

21

30

Relative 

humidity.

<U d '2

d

HH

67

89

98.6

82

92.9

95

61

90

QJ O

2

3

O

67

60

73

65

77

75

81

B_

T3 

09

5

1* V

<C

 3humii f 

o

M

5

aa

fc

0

10

9

0

3

0

0

2

-4J

3 bi og

.-1 

dBQ

CJ O

5«

 22

2.2 ISO w

flj QJ

M_> .2 -3 dxi

OJ «}

2d<u o

PH

1.91

18.4

11. 03

12.71

26.19

1.78

2.15

Flame

showed (indicating its

length) at 

1

8

fc

1

o

p

1-14

1-14

1-11

1-7

4-5

2

2-14

1-14

1

g

fc

0?

&o O

.S

^

1-14

1-14

1-7

1-11

1-5

1-4

1-14

1-14

Result.

d

_o

4Ji

be i i

Yes.

Yes.

Yes".

Yes.

Yes.

Yes.

Yes.

Yes.

|

%H,

S?1PI

Yes.

Yes.

No.

No.

No.

No.

Yes.

Yes.

a The humidifier heads of the small type used in cotton mills discharged water mixed with compressed air. 

6 A few minutes.

The first experiment (G-346) was made without humidifying, to 

observe the effect of an explosion of dust in the face of a current of 

air traveling 131 linear feet per minute. The explosion was propagated through the gallery.

In the second experiment (G-348) the relative humidity of the air 

was raised to 89 per cent, and the current was maintained for one 

hour and forty-six minutes. Practically no moisture had been 

deposited by. this time, as indicated by the analysis of the coal dust, 

a sample of which was gathered from all shelves in the gallery. 

Complete ignition followed the shot.

In the third experiment (G-349) the average relative humidity 

was 98.6 per cent, and the current was kept on for sixteen hours and 

thirty-five minutes. A considerable amount of moisture was precipitated on the dust, the analysis showing the total moisture to be 

18.4 per .cent, or about 16.-5 per cent in excess of the normal content 

of the coal dust. The result of the shot was a partial propagation, 

the flame dying clown before it reached the end of the gallery.

In the fourth experiment (G-350) the relative humidity was 82 

per cent and the total moisture of the dust on the shelves 11.63 

per cent. There was also partial flame propagation in this test.

In the fifth experiment (G-482) the relative humidity was somewhat higher, but the percentage of moisture precipitated very little 

greater. The flame propagation, however, was much less, owing to 

some cause not apparent.
52 THE EXPLOSIBILITY OF COAL DUST.

In the sixth experiment (G-483) the relative humidity of the air 

was still higher, 95 per cent, and the duration of the test the same, 

forty-eight hours. More moisture was precipitated than in the 

previous experiments, the average sample of dust on the shelves 

showing 26 per cent. In this experiment there was practically no 

propagation, only a slight ignition.

In the last experiment of this group (G-580) the experiment was 

made of not raising the temperature of the intake air. This averaged 

only 44° F. The relative humidity was maintained at 90 per cent, 

and the duration of the test was seventy hours, but owing to the 

low temperature practically no moisture was deposited on the coal 

dust and complete propagation ensued, as would be expected.

Another group of experiments was made under the direction of 

the., writer during September, 1909. In these it was decided to mix 

a definite quantity of moisture with the coal dust and to humidify 

the air as far as possible with the limited volume of the sprays. 

Owing to insufficient number of sprays, the humidity could not be 

brought up to the point of depositing moisture upon the coal dust; 

therefore the propagation or nonpropagation of the explosion depended 

on the quantity of water mixed with> the coal dust. The other 

conditions were the same as in the previous series of tests, except 

that the igniting charge was 2| pounds of black powder instead of 

1£ pounds. The mixing was carefully done and occupied considerable time, as it is difficult to mix water directly with dust. 

After a stirring and kneading by hand, the wet dust was forced 

through screens to insure an even mixture. When the wet dust 

had been placed upon the shelves of the gallery, a sample was gathered 

from the dust at regular intervals through the gallery, and analyzed. 

The results of these experiments are given in the following tables:

Explosion-gallery tests to determine effect of humidity upon explosibility of coal dusts.

Gallery 

test 

No.

G-2966 

G-2967 

G-2908 

G-2969 

G-2971 

G-2972 

G-2973

Date of 

test 

(1909).

Sept. 21 

Sept. 22 

.. .do. .. . 

Sept. 23 

Sept. 24 

Sept. 25 

...do....

Relative humidity.

Outside 

air.

79 

56 

77 

46 

53 

54

Inside 

air.

78 

90 

82 

90 

71 

83 

80

Average 

velocity of 

air current.

Feet per 

minute.

85 

78 

73 

89 

78 

74 

86

Per cent of 

moisture 

in coal.

8.00 

19.20 

19.20 

29.70 

30.90 

11.80 

30.70

Flame showed (indicating its 

length) at 

Doors 

Nos. 

2-14 

2-14 2-7 

2-6 

2-3 

2-14 2-3

Windows 

Nos. 

.1-15 

1-15 

6 1-9 

ci_4 

dl-6 

1-15 1-3

Result.

Ignition.

Yes

Yes.......

Yes

Yes.......

Yes.......

Yes.......

Yes.......

Propagation.

Yes. 

Yes. 

Yes. 

No. 

No. 

Yes. 

No.

«In all tasts, 20 pounds of 100-mesh or finer dust was placed on the horse, and 1 pound per linear foot 

of gallery on the shelves. The explosive used was 2i pounds (1,134 grams) of FFF black powder Li first 

three tests and the same amount of FF black powder in the other four tests.

6 This test was made to determine the length of flame when only the horse and the first 20 feet of shelves 

were loaded with dust.

c Delayed flame showed also in windows 4 arid 5,

d Delayed flame showed also in window 5.
EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 

Analyses of coal-dust samples taken in tests shown in preceding table.

58

Test 

No.

G-29GG

G-2967

G-2968

G-29C9

G-2971

G-2972

Character of sample.

\Dust after shot. ........................................

Dust after shot. ........................................

Moisture.

8.00

0.00

19.20

5.70

19.20

15.20

29.70

25.70

30.90

27. 10

11.80

4.80

30.70

22.10

Volatile combustible.

32.00

32.50

25.50

24.00

28.00

28.50

24.50

24.50

23.50

24.00

28.00

14.50

22.50

25.00

Fixed 

carbon.

54.80

54.70

51.00

C2.00

48.30

50.90

41.60

44.20

41.20

43.10

52.40

05. 10

42.50

Ash.

5.20

6.20

4.30

8.30

4.50

5.40

4.20

5.60

4.40

5.80

7.80

15.60

4.30

7.50

In the first experiment (G-2966) the total moisture content of 

the coal was 8 per cent, which is about 6 per cent in excess of the 

normal moisture content of the standard dust. This amount was 

insufficient to prevent complete propagation of the flame throughout 

the gallery.

In the second experiment (G-2967) the moisture content was 

19.20 or 17 per cent excess moisture. This also was not sufficient 

to prevent complete propagation.

Experiment G-2968 was to observe how far the flame would, go 

under the same conditions as in the previous experiment except 

that only the first three sections of the gallery (20 feet) and the 

horse were loaded with damp dust. The flame traveled only to the 

ninth window, equivalent to 57' feet. This experiment was made 

with the same percentage of moisture (17 per cent excess) as the 

previous one.

In the fourth experiment (G-2969) the moisture content was 

raised to 29.70 per cent or 27.70 per cent excess moisture. The 

result was ignition but not propagation of the explosion, the flame 

traveling only 30 feet.

Experiment G-2971 was made with dust from the Fairmont 

'district, West Virginia. It was moistened to the extent of 30.90 

per cent, or about 29 per cent excess moisture. There was slight 

ignition, but not propagation. The dust used in this experiment 

was allowed to dry over night and after being mixed was put back 

on the shelves. The moisture content then proved to be 11.80 per 

cent, or 10 per cent of excess moisture. The result was complete 

propagation.

The final experiment (G-2973) was a repetition of the fifth experiment (G-2971). The moisture content was also practically the 

same, 30.70 per cent, or about 29 per cent excess. The result was 

ignition but not propagation.
54 THE EXPLOSIBILITY OF COAL DUST.

experiments, though limited in number, were consistent in 

results, arid indicate that slight dampness is not sufficient to prevent 

flame propagation by an explosion; that with a high volatile and pure 

coal such as that used, it is necessary to have a total moisture content 

approaching 30 per cent to insure that there will be no propagation. 

This amount of moisture does not make 100-mesh dust seem excessively wet. It can be balled up in the hand, but water is not squeezed 

out by pressure of the hand. If more moisture is added the critical 

point is reached, and with about 40 per cent of water the 100-mesh 

dust and water mixture becomes a coal mud.

These experiments, though they must be accepted as preliminary, 

give a definite figure for the percentage of moisture that makes 

coal dust relatively safe under ordinary conditions. Information 

on this point has been strangely lacking, and it is very important 

that experiments in this direction be continued.

As a pure 100-mesh coal dust was used in the experiments, a larger 

amount of moisture probably was needed to render it inert than if it 

had contained larger particles, or had been less pure, or had been mixed 

with shale dust. The tests probably represented extreme conditions.

HUMIDITY OF MINE AIR.

NATURAL PRINCIPLES. 

SATURATED AIR AT DIFFERENT TEMPERATURES.

The amount of moisture in mine air is of vital consequence in 

relation to coal dust, as well as in other respects. Aqueous vapor is 

everywhere present in the atmosphere, whether above ground or 

in the mine, varying in amount within wide limits.

The term "relative humidity" means the percentage of water 

vapor present with reference to complete saturation as 100 per cent. 

When there is complete saturation of aqueous vapor for a giveri 

temperature, the "dew point" is reached. Beyond this point of 

complete saturation, with constant temperature, additional water 

may be held mechanically in minute drops, as in fog. Hygrometric or psychrometric tables, prepared by Prof.. C. F. Marvin, are 

published and issued by the United States Weather Bureau, and are 

entitled "Psychrometric tables for obtaining the vapor pressure, 

relative humidity, and temperature of the dew point." These 

tables are calculated to small differences in temperature and relative 

humidity, so that when the difference in the wet and dry bulb thermometer readings is known the figures for the relative humidity and 

the temperature of the dew point can be read directly with little or 

no. interpolation.

The variation in the amount of water vapor at different temperatures is very striking. For example, at a temperature of 0° F. a
MINE AiS.

Cubic foot of completely saturated aqueous vapor weighs 0.481 

grain; at 32° the same saturated volume weighs 2.113 grains; at 65°, 

an ordinary mine temperature in this country, it weighs 6.782 grains; 

and at 90°, the summer temperature, it weighs 14.790 grains. This 

is shown in a graphic way in figure 2, which gives the curves of different weights of aqueous vapor per cubic foot at different temperatures 

and relative humidities.

10

10 30 40 50 60 70 80 90 100

Temperature in degrees Fahrenheit

FIGURE 2. Curves of equal weights of water vapor per cubic foot for varying temperatures and relative 

humidities when the barometric pressure is 30 inches.

It will be seen, therefore, that when the air and water vapor enter 

the mine at 0° temperature and are raised to 65° temperature in their 

course about the mine, unless moisture is picked up on the way the 

effect is to reduce the relative humidity to a remarkable degree. For 

instance, if a given space is completely saturated at 0° and contains 

0.481 grain of vapor at 65° this weight of'water would correspond 

with only 7 per cent of saturation. This effect is strikingly shown 

by the curves in figure 2.
56 THE EXPLCSIBTLFTY OP COAL DUST.

AMOUNT OF MOISTURE IN MINE AIR.

The rapidity with which water throws off vapor up to the point of 

the saturation of the adjacent space is remarkably demonstrated hi 

mines. Technically, the air has not a capacity for moisture, and 

does not become saturated with it, the aqueous vapor filling a given 

space with practically negligible reduction in the quantity of air in 

the same space. The moisture may properly be spoken of as partly 

or completely saturated, but for brevity it is usual to speak of the 

"moisture carried by mine air" or of the "relative humidity of the 

air."

Repeated observations of the amount of moisture carried by mine 

air, as measured in percentages of the amount of saturation for 

the observed temperature, have shown that the air current, after 

traveling about the mine, has a relative humidity of 80 to 100 per 

cent. In mines in this country the "return" air current near the 

outlet rarely, except in the dry climate of the Rocky Mountain region, 

shows less than 90 per cent of saturation, even in a mine that has 

appeared dry.

A group of observations made in the mines of a considerable number of States and averaged for each State are shown in the following table:

Average of'humidity observations during March and April, 1909, in dry and more or less

dusty coal mines.

State.

West Virginia. ....

Pennsylvania...... 

Total ........

Number of 

mines.

5 

3 

8 

9 

1 

9 

1 

1

39

Series of 

observations.

5 

3 

11 

14

1 

9 

1 

4

48

Temperature.

Intake.

°F. 

71 

46£ 

45J 

36 

72 

58J 

49 

48

(.3

Return.

°F. 

69 

56J 

58 

53 

70 

56 

57 

49

58£

Relative humidity.

Intake.

Per cent.

m61J 

60J 

57 

18 

63 

84 

87

Return.

Per cent. 

92^ 

93 

91 

82 

85 

94 

95£ 

91

63 90i

Water extracted 

from dust 

and walls 

per 100,000 

cubic feet, 

of air.

Gallons. 

2.27 

4.70 

4.44 

4.57 

. 9.02 

2.32 

3.04 

1.17

3.94

Water extracted 

from dust 

and walls 

in 24 

hours.a

Gallons. 

3,269 

6,768 

6,394 

6,432 

12,991 

3,341 

4,378 

1,685

5,057

a The last column is based on the assumption that the average volume of the ventilating currents of the 

mines was 100,000 cubic feet per minute.

These observations were chiefly made in March and April, 1909, 

when the conditions contrasted much less than they would in winter. 

It will be observed that the relative humidity of the return air is 

nowhere less than 90 per cent, except in the New Mexico and Colorado 

mines, where the relative humidity of the outside air is normally very 

low. Therefore the effect of air currents of a relative humidity
HUMIDITY OF MINE AIR. 57

less than 80 to 90 per cent is to dry out the walls of the passageways 

through which they pass.

Normally a coal bed is free from water. In many mines water 

seeps from the surface through troubled ground or "faults,'' arid in 

some mines artesian flows from the bottom are encountered, but » '

.ordinarily there is sufficient clayey matter in the roof and floor to 

keep out water. In most coal mines, therefore, the presence of 

moisture, except locally, depends on atmospheric conditions.

EFFECT OF SEASONAL CHANGES OF TEMPERATURE ON MINE AIR.

The warm or hot air of summer contains a large amount of moisture. 

On entering the mine the air and water vapor are cooled, usually 

below the dew point, so that precipitation takes place. The walls 

and roof of the passageways become gradually more and more moist

as.the summer progresses, and in parts of the mine the walls frequently 

become beaded with the deposited moisture. In some mines the floor 

becomes rather wet in the summer months.

On the other hand, in winter the air enters the mine at a temperature usually lower than the mine temperature, which ordinarily 

ranges in this country from 60° to 65° F. In England.and other 

European countries 0 the outside winter temperature averages higher, 

but the mine temperatures are also higher, owing to the greater 

depth of the coal beds. Hence there is the same general contrast of 

outside and inside temperatures and of relative humidities.

When the air current enters the mine at a low temperature, it carries only a small amount of moisture in the form of vapor, even 

when the relative humidity is near saturation. As the currents go 

through the mine and the walls heat up the air and vapor, the relative 

humidity falls to such an extent that the moisture contained in the 

walls of the passageways and in the dust lying along them is vaporized and carried away by the air currents. This fact has been noted 

for many years and by many observers. The danger of dry coal 

dust has been so much commented upon that it will not again be 

discussed here until the remedies are considered.

INSTRUMENTS FOB MEASURING ATMOSPHERIC MOISTURE. 

SLING PSYCHROMETER.

In the field practically the only method that can be employed to 

measure the amount of moisture in the-air, or the relative humidity, 

is by observing the temperature of evaporation, which is obtained by 

noting the difference in temperature between wet and dry bulb

a Since the body of this bulletin has been written an important series of papers entitled "Investigation 

of the drying out of mines and combating the dangers of coal dust," by Bergassessor Forstmann, has been 

published in Gliickauf (January 5 to February 12,1910). These papers treat of general investigations 

and of an elaborate series of observations recently made in mines of Germany by a government 

commission. 
58 THE EXPLOSIBILiTY OF COAL DUST.

thermometers held in a rapid current of air or swung at a rapid fate, 

The United States Weather Bureau considers that the most reliable 

instrument for measuring relative humidity by this method is a sling 

or whirled psychrometer. The standard instrument used by the 

Weather Bureau consists of a pair of thermometers mounted on a 

thin metal plate, to which a swivel handle is attached by a loose link. 

The wet-bulb thermometer projects below the dry-bulb thermometer 

and the bulb of the former is covered with a thin tight-fitting muslin 

sack which, just before the observation, is dipped into water. This 

instrument is described in the psychrometric tables issued by the 

Weather Bureau.

To make standard readings with the sling psychrometer, the speed 

of the revolving bulb must be 15 feet per second. The psychrometer 

should be whirled for fifteen or twenty seconds and then quickly read, 

the wet bulb first. This should be repeated until successive readings 

of the wet bulb agree closely.

HYGROMETER USED BY GEOLOGICAL SURVEY.

In a mine it is difficult to use the standard sling psychrometer 

without breaking it. The mining engineers .of the United States 

Geological Survey have been supplied with a psychrometer, more 

commonly called a hygrometer, in which the thermometers are 

mounted on. the hinged covers of a shallow box. Opposite the 

thermometer bulbs the covers are slotted to allow free circulation 

of air. In the use of this hygrometer as designed, the covers are 

opened wide, held firmly, and swung to and fro, facing the air current. The motion must be violent to obtain the necessary speed. 

Another method of using it has therefore been improvised by the writer.

A hole has been bored through the top of the box parallel with the face

of the hinged lids and thermometers and a long pin inserted. The 

covers are held open by a loop of string passed around the back of 

the box and attached to a pin. The instrument can thus be whirled 

like the standard sling hygrometer, with much greater ease than it 

can be swung. A picture of the instrument with this rearrangement 

is shown in Plate V. A further improvement could be.effected by 

making the box of aluminum.

STATIONARY HYGROMETER.

There are several types of stationary hygrometers in which the air 

current is produced by small fans. In another type the hair hygrometer, the rapid change that takes place in the length of a strand of 

hair with changes in the amount of atmospheric moisture has been 

utilized to move a pointer by means of a delicately adjusted lever 

arm. This pointer carries on the end an inking arrangement, so that 

it can trace a line on sectional paper wrapped on a revolving cylinder
U. S. GEOLOGICAL SURVE IULLETIN 425 PLATE V

MINE HYGROMETER WITH IMPROVISED SLING ARRANGEMENT. 

Showing method of holding for whirling.
HUMIDITY OP MINE AIR. 50

turned by clockwork. In this way a permanent and continuous 

record is obtained." This instrument is sometimes combined with a 

temperature recorder. Such combination instruments are used by 

the Fairmont Coal Company at their Monongah mine. They are 

described in the part of this bulletin by Frank Haas (pp. 150-163).

PRINCIPLE OF WET AND DRY BULB THERMOMETER. 6

The operation of the wet and dry bulb thermometer is based on 

the fact that the evaporation of water requires a certain amount of 

heat. When a current of diy or partly saturated air passes over a wet 

surface, such as the wet bulb of a thermometer, some of the water 

is evaporated and carried along by the air in the form of vapor. 

The absorption of the heat required to evaporate the water causes a 

cooling of the bulb.

The lower the relative humidity of the air, the more rapid is the 

evaporation at the surface of the wet bulb, and consequently the lower 

its temperature. As the bulb is moved through the air its temperature falls to a point where the amount of heat absorbed by evaporation is just equal to that received from the surrounding air. The 

first quantity of heat is proportional to the rate of evaporation, v. 

If we assume that the second quantity is proportional to the surface 

of the bulb, A, and to the difference in temperature between the 

surrounding air (measured by the dry bulb), and the wet surface, 

Td Tw, then. A (Td Tw) = av, where a is a constant.

Dalton found that the rate of evaporation of water is proportional 

to the surface exposed and to the difference between the pressure of 

saturated vapor at the given temperature, and the vapor pressure of 

the surrounding air, px p, and inversely proportional to the barometric pressure, H; then 

v _bA(px -p) 

where b is a constant. Hence 

or - =

Writing = c:

= Pl -cH(Td -Tw).

a Bergassessor Forstraann (Oliickauf, January 5 to February 12, 1910) states that the hair hygrometer 

tried in the recent German experiments did not give consistent results. It was therefore abandoned in 

favor of swinging wet and dry bulb thermometers. ,

6 This explanation and the calculations are given by Dr. J. K. Clement, physicist, of the United States 

Geological Survey.
60 THE EXFLOSIBILTTY OF COAL DUST.

This equation is not exact, because neither Dalton's law of evaporation nor the assumption regarding the heat received by the bulb 

from surrounding objects (Newton's law) is strictly true. The value 

of c depends on the wind velocity or the rate at which the bulb is 

moved through the air. For the Schleuder psychrometer c = 0.00069., 

As a matter of convenience, it is customary to use tables in which 

p is given as a function of (Td Tw) and Td .

METHOD OF MAKING HYGBOMETBIC OBSERVATIONS IN MINES 

AS USED BY ENGINEEBS OF THE GEOLOGICAL STJBVEY.

The observer must be equipped with a hygrometer, a small bottle 

of clean water, anemometerj barometer, watch, and tape. Before 

entering the mine he should make observations of outside atmospheric conditions, selecting, if possible, a point where he will be in the 

shade, but not where there is any steam or local heat from fires; also, 

if the shaft or mine opening is an upcast, the point must be selected 

on the windward side of it in order to obtain correct readings of the 

relative humidity. Having selected the point, the observer swings 

the hygrometer, and if there is any wind he should stand so that the 

instrument receives the wind direct; that is, his body must not 

obstruct. Having noted the depression of the wet bulb below the 

dry bulb, he reads the barometer to obtain the atmospheric pressure.

The observer, having gone underground, makes observations at 

certain stations. It is best, where possible, to select these in advance 

from the mine map. In general, it is desirable to make observations 

at the intake and return of each split in the ventilating current, and 

in particular the main return should be read as close to the outlet as 

possible.

The method of making all readings underground is the same.

After wetting the cloth covering the wet bulb the observer swings 

the hygrometer, standing sidewise to the current of air, the hygrometer facing the wind. Having repeated the reading a number of 

times, to insure that the mercury column in the wet-bulb thermometer 

is depressed as far as it will go,0 and having recorded the reading, he 

reads the barometer to obtain the mercurial pressure, which is a 

combination of the atmospheric pressure and the mine ventilation 

pressure at that point. The latter pressure is negative or positive 

according as the fan is exhausting or blowing. Then the velocity of 

the air current is obtained by means of the anemometer, and the 

volume of air is obtained by multiplying the velocity by the effective 

cross section of the passageway. The time of taking the observations 

at each station, inside and outside, should be recorded, so that the 

changes in outside atmospheric conditions can be correlated. It is

a Whea the air is below 32° F., the wet-bulb reading remains stationary for some minutes as the water 

freezes, but as the swinging is continued it will lower proportionately to the temperature and humidity.
HUMIDITY OF MINE AIR. 61

important that the cloth of the wet bulb be freshly wetted for each 

observation.

On going out of the mine it is very important that the observer 

make hygrometric and barometric readings at or near the station 

where he made readings on going into the mine and use the average 

of the two sets to compare with the underground observations or, if 

the two differ widely, prorate according to the time intervals.

Notation should be made at the different underground stations, and 

at other intervals, of the amount of dust present on floor ribs, roof, and 

timbers, also the condition of the dust in the same places as regards 

moisture. Particular note should be made of moisture drops beading 

the roof or ribs.

In the light of the preliminary experiments with moistened dust 

made at the Pittsburg station, as described on pages 50-51, it is advisable to take samples of the dust at certain points and have the moisture and ash contents determined. Such samples should be placed in 

air-tight receptacles, like glass jars with screw tops and rubber 

gaskets, at the point of taking, or in special cans, such as are used 

by the Geological Survey, sealed with insulating tape. Care will 

have to be exercised in gathering the samples, to have them representative of only that dust which is likely to be thrown into 

suspension by a violent concussion.

RELATION OF MOISTURE CONTENT TO TEMPERATURE AND 

PRESSURE OF MINE AIR.

The psychrometric tables issued by the Weather Bureau have 

already been referred to. The method of using them is explained in 

connection with the tables as published.. One table gives the temperature of the dew point in degrees Fahrenheit for various atmospheric pressures and various depressions of wet-bulb thermometer. 

This table will not ordinarily be consulted by the mine observer. The 

tables of more immediate use to him are those giving the relative 

humidity percentages.for different temperatures, pressures, and depressions of the wet-bulb thermometer and the table giving the 

"weight of a cubic foot of aqueous vapor at different temperatures 

and percentages of saturation."

The last-mentioned table has been supplemented by one appended 

below, which gives the number of gallons of water equivalent to the 

same weight of aqueous vapor in 100,000 cubic feet of air at different temperatures and different degrees of saturation. This unit, 

100,000 cubic feet of air, passing in one minute, represents an ordinary mine condition. The other unit (gallons) gives a convenient 

measure for calculating the amount of water that must be introduced 

artificially in winter to offset the amount carried out by the return 

currents. .
THE EXPLOSIBILITY OF COAL DUST.

Figure 2 gives the curves resulting from taking the different weights 

of aqueous vapor per cubic foot in grams as constants and considering 

the temperatures and different percentages of saturation as variables.

30

25

220

10

m

10 20 90 100

FIGURE 3. Curves of equal relative humidity for varying temperatures and depressions of wet bulb.

Figure 3 shows the curves derived from considering the different 

relative humidity percentages as constants and the depression of the
HUMIDITY OF MINE AIE. 63

wet-bulb thermometer and the temperature as variables when the 

barometric pressure is 30 inches.

Figure 4 shows the curves resulting from taking different percent20 30 40 50 60 70 80 90 100

Temperature in degrees Fahrenheit u

FIGURE 4. Curves of equal relative humidity for varying temperatures and volumes of water carried.

ages of saturation as constants and the temperatures and gallons of 

moisture per 100,000 cubic feet of air as variables.
64 THE EXPLOSIBILITY OF COAL DUST.

Gallons of water per 100,000 cubic feet of air for specified temperatures and percentages ofsaturation^

"-Temperature.

°F. 

-20....... _iq

-18.......

-17.......

-16.......

-15.......

-14.......

-13.......

-12.......

-11.......

-10.'......

- 9.......

- 8.......

- 7....,,.

- G....».

- 5.'..,...

- 4.......

- 3.......

 I.......

0.......

1.......

2.......

3.......

4.......

5.......

6.......

7.......

8.......

9.......

10.......

11.......

12.......

13.......

14.......

15.......

16.......

17.......

18.......

19.......

20.......

21.......

22.......

23.......

24.......

25.......

26.......

27.......

28.......

29.......

30.......

31.......

32.......

33.......

34.......

35.......

36.......

37. ......

38.......

39.......

40.......

Relative humidity (per eent) 

10.

0.028 

.030 

.032 

.034 

.035

.037 

.040 

.042 

.044 

.046

.049 

.061 

.064 

.057 

.060

.063 

.067 

.070 

.074 

.078

.082

.087 

.091 

.095 

.100 

.104

.109 

.115 

.121 

.127 

.133

.140 

.147 

.154 

.161 

.169

.177 

.185 

.193 

.202 

.211

.222 

.232 

.243 

.254 

.266

.278 

.291 

.304 

.317 

.331

.346 

.362 

.376 

.390 

.405

.421 

.437 

.453 

.470 

.488

20.

0^057 

.060 

.063 

.067 

.071

.075 

.079 

.083 

.088 

, .093

.098 

.103 

.108 

.114 

.120

.127 

.133 

.141 

.149 

.156

.165

.173 

.181 

.190 

.199 

.209

.219 

.230 

.241 

.253 

.266

.279 

.293 

.307 

.322 

.338

.353 

.370 

.386 

.404 

.423

.443 

.464 

.486 

.508 

.531

.550 

.581 

.607 

.634 

.662

.692 

.724 

.751 

.780 

.810

.841 

.873 

.906 

.940 

.976

30.

0.085 

.089 

.095 

.101 

.106

.112 

.119 

.12$ 

.132 

.139

.146 

.154 

.162 

.170 

.180

.190 

.200 

.211 

.230 

.235

.247

.260 

.272 

.284 

.299 

.313

.328 

.345 

.362 

.380 

.399

.419 

.440 

.461 

.483 

.506

.530 

.555 

.579 

.607 

.634

.665 

.696 

.728 

.762 

.797

.834 

.872 

.911 

.952 

.994

1.039 

1.085 

o 1.127 

1.171 

1.215

1.262 

l."310 

1.359 

"1.410 

1.463

40.

0.114 

.119 

.126 

.134 

.142

1149

.158 

.166 

.176 

.185

.195 

.206 

.216 

.227 

.240

.253 

.260 

.282 

.29? 

.313

.329

.346 

.362 

.379 

.398 

.418

.438 

.460 

.482 

.506 

.532

.559 

.586 

.615 

.644 

.675

.707' 

.740 

.772 

.809 

.846

.886 

.928 

.971 

1.016 

1.062

1. 112 

1.162 

1.214 

' 1. 269 

1.325

1.385 

1.447 

1.502 

1.561 

1.620

1.682 

' 1. 746 

1.812 

1.880 

1.951

50.

0.142 

.149 

.168 

.168 

.17?

.18? 

.198 

. .208 

.220 

.231

.244 

.257 

.271

.284 

.300

.-317 

.333 

,392 

,3?2 

,391

.412

,433 

.453 

.474 

.498 

.522

.547 

.575 

.603 

.633 

.665

.699 

.733 

.769 

.806 

.844

.884 

.925 

. 966 

1.011 

1.057

1.108 

1.160 

1.214 

1.270 

1.328

1.390 

1.453 

1.518 

1.586 

1.656

1.731 

1.809 

1.878 

1.951 

2.026

2.103 

2.183 

2. 265 

2.351 

2.439

60.

0. 170 

.179 

.189 

.202 

.212

.224 

' .237 

.250 

.264 

.277

.293 

.308 

.325 

.341 

.359

.38'0 

,400

,m,446

.469 

.494

.519 

.544 

.569 

.598 

.626

.656 

.689 

.723 

.759 

.797

.838 

.880 

.922 

.967 

1.013

1:060 

1.109 

1.159 

1.213 

1.268

1.329 

1.392 

1.457 

1.523 

1.593

1.667 

1.743 

1.821 

1.903 

1.987

2.077 

2.171 

2.254 

2.341 

2.431

2.524 

2.620 

2.718 

2.821 

2.927

70.

0.199 

,209 

.221 

.235 

,248

.261 

,277 

.291 

.308 

.323

.342 

.360 

.379 

.398 

.419

.443 

,466 

. ,493 

.520 

.547

.576

.606 

.634 

.664 

.697 

.731

.766 

.804 

.844 

.886 

.930

.978 

1.026 

1. 076 

1.128 

1.182

1.237 

1.294 

1.352 

1.415 

1.480

1.551 

1.624 

1.700 

1.777 

1.859

1.945 

2. 034 

2.125 

2.220 

2.318

2.423 

2.533 

2.629 

2.731 

2.836

2.944 

3.056 

3.171 

3.291

a. 415

80.

0.227 

.238 

.252 

.209 

.283

.298 

.316 

.333 

.352 

.370

.390 

.411 

.433 

.454 

.479

.506 

.533 

.563 

.594 

.626

.658

.682 

.725 

.758 

.797 

.835

.875 

.919 

.964 

1.012 

1.063

1.118 

1.173 

1.230 

1.289 

1.360

1.414 

1.479 

1.545 

.1.618 

1.691

1.772 

1.856 

1.942 

2.031 

2.124

2.223 

2.324 

2.428 

2.538 

2.650

2.770 

2.894 

3.005 

3.122 

3.241

3.365 

3.493 

3.624 

3.761

3. 902

90,

5. 856 

.268 

.284 

.302 

.319

.336 

,356 

.374

. :39'6

,416

.439 

.463 

.487 

.511 

.539

.570 

.599 

.634 

.669 

.704

.741

.779 

.815 

.853 

.896 

.940

.985 

1.034 

1.085 

1.139 

1.196

1.257 

1.319 

1.383 

1.460 

1.619

1.590 

1.664 

1.738 

1.820 

1.903

1.994 

2.088 

2.185 

2.285 

2.390

2.501 

2.615 

2.732 

2.855 

2.981

3.116 

3.256 

3.380 

3.512 

3.646

3.785 

3.929 

4.077 

4.231 

4. son

100.

0,2§4 

.298 

.315 

.336 

.354

:B

:41| 

;446

,463

 '.541 

.568 

.599

.633 

.666 

.704 

.743 

.782

.823

.865 

.906 

.948 

.996 

1.044

1.094 

1.149 

1.206 

1.266 

1.329

1.397 

1. 466 

L637 

1.611 

1. G8S

1.767

1.849 

1.931 

2.022 

2.114

2.215 

2.320 

2.428 

2.539 

2.655

2.779 

2.905 

3.035 

3.172 

- 3.312

3.462 

3.618 

3.756 

3.902 

4.051

4.206 

4. 366 

. 4. 530 

4. 701. 

4 S7S

« The table Is devised on the assumption that if the water vapor in 100,000 cubic feet of air at any given 

temperature and percentage of saturation were condensed, it would be equivalent to a certain number of 

gallons of water at that temperature. For tern peratures of 32° or under, the figures are given on the assumption that the vapor j§ equivalent to a certain volume of water a.t 32°.
HUMIDITY OP MINE AIR. 65

Gallons ofiuater per 100,000 cubic feet of air for specified temperatures and percentages of

saturation Continued.

Temperature.

41........

42........

43........

44........

AZ

40........

47........

48........

49........

50........

51........

52........

53........

54........

55........

50........

57........

58........

CQ

00

01........

02........

63........

04........

65........

06........

67........

68

09........

70........

71........

72........

73........

74........

75........

70........

77........

78........

79........

80

81........

82........

83........

84........

85........

80........

87........

88........

89........

90........

' 91........

92........

93........

94........

95........

90........

97........

98........

99........

100

Relative humidity (per cent) 

10.

0.500 

.525 

.544 

.504 

.585

.000 

.028 

.651 

.674 

.698

.723 

.749 

.775 

.802 

.831

.859 

.889 

.920 

.952 

.984

1.018 

1.053 

1.088 

1.125 

1.163

1.202 

1.242 

1.282 

1.325 

1.309

1.413 

1.459 

1.507 

1.556 

1.005

1.657 

1.710 

1.764 

1.820 

1.878

1.937 

1.997 

. 2.059 

2.123 

2.189

2.256 

2.325 

2.396 

2.469 

2.544

2.621 

2.699 

2.780 

2.863 

2.948

3.035* 

3.124 

3.216 

3.310 

3.406

20.

1.012 

1.049 

1.088 

1.128 

1.169

1.212 

1.256 

1.301 

1.348 

1.396

1.440 

1.497 

1.550 

1.605 

1.661

1.718 

1.778 

1.840 

1.903 

1.969

2.030 

2.105 

2.170 

2.250 

2.325

2.403 

2.483 

2.505 

2.050 

2.737

2.826 

2.919 

3.013 

3.111 

3.211

3.314 

3.420 

3.529 

3.640 

3.755

3.873 

3.994 

4.119 

4.246 

4.378

4.513 

4.651 

4.793 

4. 939 

5.088

5.241 

5.399 

5.560 

5.726 

5.895

0.009 

0.248 

6.431 

6.620 

6.812

30.

1.518 

1.574 

1.632 

1.692 

1.754

1.818 

1.883 

1.952 

2.022 

2.094

2.169 

2.246 

2.325 

2.407 

2.492

2.578 

2.667 

2.760 

2.855 

2.953

3.054 

3.158 

3.204 

3.375 

3.488

3.005 

3.725 

3.847 

3.974 

4.106

4.240 

4.378 

4.520 

4.667 

4.816

4.971 

5.130 

5.293 

5.461 

5.633

5.810 

5.991 

6.178 

6.370 

6.566

6.769 

6.976 

7.189 

7.40.8 

7.632

7.862 

8.098 

8.340 

8.539 

8.843

9.104 

9.372 

9.647 

9.929 

10. 217

40.

2.024 

2.098 

2. 176 

2.256 

2.338

2.424 

2.511 

2.603 

2.696 

2.792

2.892 

2.995 

3.100 

3.209 

3.322

3. 437 

3: 556 

3.680 

3.806 

3.937

4.072 

-4. 210 

4.352 

4.500 

4. 650

4.806 

4.966 

5. 130 

5.299 

5.474

5.653 

5.838 

6.026 

6.222 

6. 422

6.628 

6.840 

7.057 

7.281 

7.510

7.746 

7.988 

8.238 

8.493 

8.755

9.026 

9.302 

9.586 

9.878 

10. 176

10. 483 

10. 798 

11. 120 

11. 452 

11.791

12. 138 

12.496 

12. 862 

13. 239 

13. 623

50.

2.530 

2.623 

2.720 

2.820 

2.923

3.030 

3.139 

3.254 

3.370 

3.490

3,615 

3.744 

3.876 

4.012 

4.153

4.296 

 4.440 

4.600 

4.758 

4.922

5.090 

5.263 

5.440 

5.625 

5.813

6.008 

6.208 

6.412 

6. 624 

6.843

7.066 

7.297 

7.533 

7.778 

8.027

8.285 

8.550 

8.822 

9.101 

9.388

9.683 

9.986 

10. 297 

10. 616 

10. 944

11. 282 

11. 627 

11. 982 

12. 347 

12. 720

13. 104 

13.497 

13. 900 

14.315 

14. 739

15. 173 

15. 620 

16. 078 

16. 549 

17. 029

60.

3. 035 

3.148 

3.263 

3.383 

3.507

3.635 

3.767 

3.904 

4.044

4.187

4.337 

4.492 

4.651 

4.814 

4.984

5.155 

5. 335 

5.519 

5.710 

5.906

6.107 

6.315 

6.528 

6.749 

6.976

7.209 

7.449 

7.694 

7.949 

8.212

8.479 

. 8.756 

9.040 

9.334 

9.632

9.941 

10. 259 

10.586 

10.921 

11.206

11. 619 

11. 983 

12. 356 

12. 739 

13. 133

13.538 

13. 952 

14.378 

14. 816 

15:263

15. 724 

16. 196 

16. 680 

17. 177 

17. 686

18. 208 

18. 743 

19. 294 

19. 859 

20.435

70.

3. 541 

3.672 

3.807 

3.947 

4.092

4.241 

4.395 

4.555 

4.718 

4.885

5.060 

5.241 

5.426 

5.616 

5.814

6.014 

0.224 

0.439 

0.601 

0.890

7. 125 

7.368 

7.616 

7.874 

8.138

8.411 

8.691 

 8.977 

9.274 

9.580

9.892 

10.216 

10. 546 

10. 889 

11.238

11.598 

11.969 

12.350 

12.741 

13/143

13. 556 

13. 980 

14. 416 

14. 862 

15.322

15.795 

16. 278 

16. 775 

17. 286 

17. 807

18. 345 

18. 896 

19. 400 

20. 040 

20.034

21. 242 

21. 867 

22. 509 

23. 169 

23. 841

80.

4.047 

4.197 

4.351 

4.511

4.676

4.847 

5.022 

5.206 

'5. 392 

5.583

5.783 

5.990 

6.201 

6.418 

6.645

0.874 

7.113 

7.359 

7.613 

7.874

8.143 

8.420 

8.704 

8.999 

9.301

9.612 

9.932 

10. 259 

10. 598 

10.949

11.306 

11.675 

12.053 

12.445 

12. 843

13.255 

13.679 

14.114 

14.562 

15.021

15.492 

15. 977 

16. 475 

16. 986 

17.510

18. 051 

18. 603 

19. 171 

19. 755 

20. 351

20. 966 

21. 595 

22. 240 

22. 903 

23. 582

24, 277 

24. 991 

25.725 

20. 478 

27. 240

90.

4.553 

4.721 

4.895 

5.075 

5.261

5.453 

5.650 

5.856 

6.066 

6.281

6.506 

6.738 

0.976 

7.221 

7. 475

7.733 

8.002 

8.279 

8.564 

8.859

9. 161 

' 9.473 

9.792 

10. 124 

10. 463

10.814 

11.174 

11.542 

11.923 

12.317

12.719 

13. 135 

13.559 

14.000 

14.449

14.912 

15. 389 

15.879 

16. 382 

10.898

17. 429 

17. 974 

18.535 

19. 109 

19. 099

20. 308 

20. 929 

21.508 

22. 225 

22. 895

23.580 

24.295 

25.020 

25. 706 

26. 529

27.311 

28. 115 

28. 940 

29. 788 

30.652

100.

5.059 

5.246 

5.439 

5. 639 

5.845

6. 059 

6. 278 

6.507 

6. 740 

6.979

7.229 

7.487 

7.751 

8.023 

8.306

8.592 

8.891 

9.199 

9.516 

9.843

10. 179 

10. 525 

10. 880 

11.249 

11.626

12.015 

12.415 

12. 824 

13.248 

13. 686

14.132 

14. 594 

15.066 

15. 550 

16. 054

16. 569 

17.099 

17.643 

18.202 

18. 776

19. 365 

19.971 

20. 594 

21. 232 

21. 888

22.564 

23. 254 

23.964 

24. 694 

25.439

26. 207 

26. 994 

27. 800 

28. 629 

29. 477

30. 346 

31. 239 

32. 156 

' 33.098 

34.058

38970° Bull. 425 10-
66 THE EXPLOSIBILITY OF COAL DUST.

REMEDIES FOR COAL DUST.

REVIEW OF REMEDIES PROPOSED.

As soon as the dangers of dry coal dust became recognized, suggestions for remedies began to appear. The British accidents in 

mines commission in its final report in 1886 (p. 48) stated:

The removal of accumulating dust is practiced to some extent here and there; but 

this measure is obviously attended by many difficulties, and even if carried out as 

thoroughly as practicable, it would generally only be the main roads that could be kept 

fairly-free from dust. * * * If, however, * * * the mine ways [are kept] as 

free from dust as practicable, and the removal of the principal part of dust accumulations from the working places can be supplemented by the application of some efficient 

method of rendering the remaining dust innocuous in the presence of a blown-out 

shot, there can be no doubt that the dangers arising from coal dust will be very greatly 

reduced, if not rendered altogether insignificant.

Since the time of the foregoing report, numerous means have been 

suggested, and some tried out, to secure immunity from the coal-dust 

danger. A summary of the methods that have already been put 

forward follows: a

1. Loading and cleaning up dust.

2. Sprinkling from water cars.

3. Application of calcium chloride and other deliquescent salts.

4. Sprinkling and washing down with hose and nozzle.

5. The use of pipe lines and permanent sprinklers.

6. Humidifying the intake air current by steam sprays.

The foregoing comprise the general methods of rendering coal dust 

inert. There are other methods which contemplate the prevention 

of explosions from blown-out shots and the limiting of initial explosions. These may be summarized as follows:

7. The use of quick-flaming or short-flaming ("permissible") explosives.

8. Coating the walls and floor of the passageways with rock dust, 

either wholly or in zones.

9. Limiting the extent of explosions by the construction of brick 

or concrete linings of definite length and intervals and keeping them 

perfectly clean.

LOADING AND CLEANING TIP DUST.

Loading dust into pit cars and hauling it out of the mine does not 

require extended explanation. The method is obvious and has been 

more or less practiced in maintenance of roadways. In rooms of the 

ordinary room-and-pillar system the fine coal and dust is seldom

a Two new methods have been brought out recently in Germany. One, which aims at preventing the 

formation of dust at the face, is to force water at high pressure into the coal seam through long holes, 

drilled in advance of the face. This method does not seem applicable in room-and-pillar work. Another 

method recently patented, called the Kruskopf process, employs a viscous paste applied to all surfaces. 

It is stated that a recent experiment in a Westphalian mine showed that the " walls remained damp 

three thousand hours after the application of the paste, but they dried up within six hours when 

water was used." (Scientific American, May.21,1910.) See also p. 149.
REMEDIES FOR COAL DUST. 67

wholly loaded out. While the coal may be carefully shoveled up 

at the face, the fine coal, thrown back into the "gob" by shooting, 

usually becomes so mixed with dirt or rock that it would be difficult 

to gather it and send it out in pit cars without undue expense.

In some sections of this country the practice is to require the 

miner to leave the cuttings in the gob, particularly when the cutting 

is done in mixed coal and shale bands. This is certainly not good 

practice. It may save the quality of the screenings from injury at 

mines where there is not a washery to wash out the clay or shale, but 

it leaves a dangerous condition within the mine, increasing not only 

the chances of a dust explosion, but also the risk of gob fires.

Cleaning up fine dust after the coarser small coal has been shoveled 

out is far more difficult than the latter and is practically impossible 

on a rough uneven floor. If a broom is used, this merely moves the 

finer and more dangerous dust to other settling points. A possible 

method of sweeping which may be developed in future is the use of a 

modified form of house vacuum cleaner; though recent preliminary 

trials in England have not been successful except where the passageway was lined smoothly with brick or concrete.

SPRINKLING FROM WATER CARS.

Sprinkling the roadways by means of water cars was the earliest 

method of watering coal dust. At first the water was thrown out by 

means of a bucket from a plain tank car or let dribble from the car 

in the middle of the roadway. The latter primitive plan is still used 

in many mines. The next step was to put a sprinkling pipe on the 

rear of the water car that is, a pipe with perforations. Necessarily, 

only the roadway floor can be sprinkled with so slight a water head, 

and though this means when frequently employed prevents some dust 

from being raised by the traffic it does not reach the dangerous dust 

on the walls and timbers.

The next advance was to place a force pump on the cars, or to use 

air compressed in the top of the tank, to force the water out under 

such pressure that the roof and sides could be sprinkled as well as the 

floor. This method is much employed to-day at many of the leading 

mines. If carried out systematically and constantly it is an effectual 

method, but if used only occasionally, say once or twice a week, very 

little good is accomplished. Dust is extremely difficult to wet and 

the drops of water are not absorbed unless the dust is already more 

or less damp. If the drops remain exposed, they are quickly absorbed 

by the air currents and the road becomes dry. There are practical 

difficulties in using water cars efficiently; thus, to sprinkle each road 

once or twice a day would seriously interfere with the hauling of coal. 

On the night shift the tracks and sidings are occupied by "loads" 

and "empties," so it is difficult to get the water cars through the
68 THE EXPLOSIBILITY OF COAL DUST.

roadways, and particularly to water the partings or sidings, which 

are usually the most dusty points. It therefore requires special 

planning and efficient administration to obtain satisfactory results.

CALCIUM CHLORIDE AND OTHER DELIQUESCENT SALTS.

The rapid drying out of dust which had been sprinkled and the 

damage wrought to some mine roofs and ribs by sprinkling intermittently, led some of the early investigators to experiment with 

hygroscopic salts.

In 1879, Professor Stokes suggested the use of calcium chloride. 

Professor Abel, giving evidence before the accidents in mines commission in 1881, said:

It might possibly be desirable to try for watering purposes a solution of calcium 

chloride * * * which has been found very useful in keeping ground moist in a 

current of air.

The commission, in its final report in 1886 (p. 49) stated:

The generally elevated temperature of mines combines with the desiccating effect 

of the more or less rapidly circulating air currents to counteract the amount of pro- 

 tection obtainable even by frequent liberal watering. Hence attempts have been 

made within the last six or seven years to promote the retention of water by coal dust, 

by the application to it of hygroscopic or normally deliquescent bodies. Crude salt 

was tried in the first instance, and in 1879 Professor Stokes suggested the watering of 

the dust with a solution of calcium chloride, a highly hygroscopic salt which had been 

successfully applied in connection with street watering * * * but its trial in 

some dry deep mines in South Wales and also in the Jablin pits in France was not 

attended with success; the highly deliquescent salt actually crystallized out, consequent upon the rapid evaporation of the water in the warm air currents. Some 

amount of success appears however to have attended the application, in mines in 

North Staffordshire, of crude or refuse salt; this contains a very notable proportion 

of the magnesium chloride, which is, if anything, more hygroscopic in its character 

than the calcium salt. In an interesting discussion which followed Mr. Robert

Stevenson's communication of his favorable experience in this direction to the North 

of England Institute of Mining Engineers, the view received some support that the 

deliquescent salts would be most operative if used in admixture with sodium chloride, 

as is the case in crude or rock salt. The proportion of crude salt which Mr. Stevenson 

had found effective in maintaining the dust sufficiently moist to prevent its flying 

was 9 tons per 500 yards of 6-foot roadway, applied once weekly for the first month 

and once a month afterwards.

The method was not mentioned in the report of 1894 of the royal 

commission on accidents from coal dust in mines. It apparently 

attracted very little attention until the last few years, when the discussion of the use of salts was revived.

Mr. Henry Hall, British inspector of mines, in a recent article a 

says: . On February 22, 1908, a length of 285 feet of tunnel at St. Helens, England, was 

treated with a 40 to 45 per cent solution of calcium chloride. The floor of the tunnel

a. Coal and Coke Operator, Pittsburg, Pa., May 27,1909, p. 375.
REMEDIES FOft COAL DUST. 69

was very dusty, the dust (chiefly stone dust) rising higher than the men's knees as 

they walked along. The solution was put on with a whitewashing machine, using 

about 8 gallons of solution to 30 linear feet of road (road 9 feet wide). The surface of 

the dust was thus dampened, but under the crust there was very little effect, and dust 

raised by the traffic inby continued to travel, carried by the wind, over the treated 

portion. Considering that the dust was not removed before the application, but lay 

some 3 inches thick, the result was fairly satisfactory, and for three months the road 

could be traveled with comfort. * * * On April 14, 1908, 225 feet in the main 

return tunnel was treated with 90 gallons of 48 to 50 per cent solution of calcium 

chloride, the dust having been previously cleaned off. This application kept the 

road clear of dry dust for three months, and at the present time (August 22, 1908) the 

effect is still visible. * * * The solution when applied to side or roof had the same 

damaging effect as water. On May 28, 1908, 330 pounds of calcium chloride, previously ground to a fine powder, was sprinkled on the floor of the back brow for a distance 

of 249 feet, no dust having been removed. It was reported as being wet and no dust 

rising on the following day. The writer saw this road on July 6 and the effect was 

Still visible. Judging from this experiment, one application for every three months 

would be ample. The depth, from the surface, of this underground road is but 500 

feet. The powdered calcium chloride was thrown on dry by hand, 350 pounds being 

put on 2,241 square feet. On July 14, 282 square « feet was treated with 448 pounds 

of dry powdered calcium chloride. The dust was cleaned away from 60 feet of this 

road; the remaining 222 feet not being cleaned. This road was reported to be wet the 

next day and the writer saw it on July 16. * * * The writer saw a team brought 

out by the pony and no dust was raised. Previous to the application, dust traveled 

some 60 feet ahead of the pony. The writer saw this part again on August 6 and 

found it to be still quite satisfactory and apparently likely to continue so for some time 

longer. * * * The writer believes the cost to be about 50 shillings ($12.50) a ton 

(dry powdered calcium chloride), but there would be a great saving in labor in its 

application to the roads as compared with either plain water or any solution, and no 

capital outlay for pipes, barrels, hose, sprinklers, etc., is needed. Probably the cost 

per 100 yards by ;9 feet wide would be something like 13 shillings ($3.25), but it must 

be remembered that plain water would have to be applied almost daily, whereas the 

calcium chloride would apparently be effective for three months.

Mr. Hall then comments on the superior hygroscopic property of 

calcium chloride as compared with common salt. In conclusion he 

remarks that the test would require to be carried much further than 

he had carried them. The conditions vary much in different mines. 

So far as he had gone, the impression left on his mind was that dust 

accumulated in the main roadways at a much smaller rate than has 

been generally observed. He agreed with the observations of Mr. 

Rhodes, as to the effect of occasional spraying with water 50 or 60 

yards in advance of the sprays the conditions were generally just as 

they were before the spraying was done.

Mr. Hall gives a table of analyses of dust from the mine wHere the 

tests were made, but he does not give the moisture content. The 

most striking feature of the analyses is the high ash of the samples, 

ranging from 17 to 67 per cent. It is evident that the coal dust was 

much diluted with rock or shale dust.

a Author probably intended this to be linear feet of roadway.
70 THE EXPLOSIBILITY OF COAL DUST.

In a recent article a Mr. Joseph Virgin, the superintendent of the 

Plymouth Coal Company, Plymouth, W. Va., says:

Believing that calcium chloride would act satisfactorily * * * on February 8, 

1909, we placed 3 barrels (1£ tons) * * * on about 500 feet of heading, the latter 

being 8 feet wide; we distributed the salt like sowing seed broadcast. The dust on 

the tracks was about 3 inches deep and on the debris one-eighth inch. All was covered 

with salt * * * in twenty-four hours, the fine coal was moist, and in two days 

the dust was quite damp and would stick to the hand like wet gunpowder. The dust 

remained damp for more than a month. On April 8,1909, this heading was cleaned up.

Several mines in the Pocahontas region of West Virginia, at Marytown and near Elkhorn, and several mines in the Pittsburg district 

of Pennsylvania used calcium chloride during the winters of 1908-9 

and 1909-10 with reported favorable results.

Some tests with crude calcium chloride,6 a by-product of chemical 

manufactories, were made in the winter of 1909-10, with the cooperation of the writer, in the Catsburg mine of the Monongahela Consolidated Coal and Coke Company, working the Pittsburg seam, in 

Washington County, Pa. Two adjoining "butt" entries, very dry 

and dusty, about 2 miles in from the drift mouth, but on a split of 

air drawn from an air shaft only 2,500 feet distant, were selected 

for the experiments.

The reason for the dryness of these roads is apparent from the 

hygrometric readings, which were made on January 14, 1910. . The 

calculated results follow:

Hygrometric readings in Catsburg mine.

Return of district. .....................................

Dry bulb.

°F. 

38

47X

50

58J

Wet bulb.

' °F. 

36

48

57

Relative 

humidity.

Per cent.

83

7Q

07

91

Water per 

100,000 cu. 

ft. of air.

Gallons.

5.05

6.07

8.51

There is therefore absorbed from this one district 3.46 gallons of 

water per 100,000 cubic feet of air circulated. The volume of the 

split is 3,750 cubic feet per minute. The extraction of moisture from 

this small district, assuming that the hygrometric reading represented average winter conditions, would be 187 gallons per twentyfour hours.

Three areas were treated, each about 400 feet long, separated by 

untreated areas.

In the first, the road had been cleaned up to the level of the top of 

the ties and watered about one week before the application of calcium

a Dust problem in coal mines: Eng. and Min. Jour., October 9, 1909, p. 734.

^Composed, according to an analysis by A. C. Fieldner, chemist, of the Survey, of 5C per cent CaCls, 

11 per cent NaCl, and 32.70 per cent H20.
REMEDIES FOE COAL DUST. 71

chloride, which was made February 27. The calcium chloride was 

spread on dry to the amount of 1 pound per linear foot of the entry, 

which was from 8 to 9 feet wide. The road was ballasted with coal 

and shale fragments to the depth of the ties and from 6 to 10 inches 

deep along the sides.

In the second area the coal dust had not been cleaned or watered 

for a long time before the application, which was made on Februarj^ 

12, and the fine coal and shale dust was thick along the track and on 

the sides. This was treated with the dry calcium chloride to the same 

amount as the first section. The calcium chloride had been received 

in large drums, and was cemented in a solid mass, which had to be 

broken down by hammer to pieces about one-half inch in size and 

less. In both the dry treatments the roof and ribs were not considered. As it was a "butt" entry, the smooth, bright coal "faces" 

parallel with the road gave no lodgment for dust. The roof, which 

was shale and top coal, did not require timbering. The roads had 

been so dry that dust was raised in walking.

In the third area, also 400 feet long, the calcium chloride was 

applied February 14. It was in solution, containing 8 per cent of 

calcium chloride by weight. The entry was sprinkled by means of a 

force-pump sprinkling car, which sprinkled the top, sides, and floor. 

The total amount of calcium chloride put on was 1 pound per linear 

foot with 12£ times as much weight of water. The watering was done 

not only on the floor, but also on the ribs and roof.

On March 7 an investigation of these areas was made by the writer. 

In the first area the coal dust in the roadway was damp to the touch 

and would pack in the hand. This was eight days after treatment 

with the dry calcium chloride. There was an entire absence of dry 

dust. The sides and roof felt dry, but, as stated, these were not 

treated and had been practically free from dust.

In the second area, twenty-three days after treatment with the dry 

calcium chloride, the floor dust was damp and sticky and was more or 

less packed in the roadway. There was an entire absence of dry dust.

In the third area, treated with the wet solution February 14, the 

road dust was more or less dry. When kicked it would rise as float 

dust. It did not seem as dry as it had been before the application, but 

the effect of the calcium-chloride treatment had been practically lost. 

The ribs and roof were also dry, but as they were smooth no dust 

had collected.

Samples were gathered of the dry road dust of the three areas before 

their treatment, and on March 7 after treatment. These samples contained all sizes of fragments of coal and shale. The portion that passed 

through a 20-mesh screen was considered dust, and the remainder 

was rejected. In the samples from the areas that had been treated 

the particles were stuck together and could not be screened until air
.72 THE EXPLOSIBILITY OF COAL DUST.

dried. The moisture in the whole sample from the area treated 

eight days before (first area) was 10.57 per cent, or about 8.5 per cent 

excess over the normal moisture content of the air-dried coal. The 

moisture in the sample for the area treated twenty-three days before 

(second area) was 7.20 per cent, or about 5 per cent excess over normal. Of the former sample only 25 per cent passed through a 20- 

mesh screen; of the latter, 12 per cent. Experiments with these samples indicated that the undersize retained after preliminary drying 

three times as much water as the oversize. If this proportion also 

holds in the preliminary drying, the undersize from the first area 

contained 14 per cent of moisture and the undersize from the second 

area contained 21 per cent. The plastic condition of the samples 

indicated at least these amounts of moisture. It was the moisture in 

the finer sizes of dust, as well as the sticky nature of the salt, that 

caused the adhesive quality.

It is evident that a determination of the humidity of the air in areas 

treated with calcium chloride does not provide a test of the efficacy 

of the latter in preventing the formation of loose, dry, dangerous coal 

dust. The calcium chloride through its affinity for water draws the 

water vapor from the atmosphere. The latter would therefore show 

a deficiency (too small to be measurable) rather than an excess of 

moisture. Hence the success or failure of the treatment must be judged 

by the physical aspect of the dust or by chemical determinations supplemented by tests in an experimental gallery.

The experiments in the Catsburg mine can not be considered conclusive, but it is interesting to compare the results obtained by the dry 

and the wet treatments; the application of the dry calcium chloride 

to the floor dust appeared to be very effective, under severe conditions, inasmuch as rooms were turned off the butt entry and there 

was a constant dribbling of fresh coal along the road. The condition 

of the floor, however, was such that the new dust as it was crushed 

under foot packed down into the general mass.

At first thought it appears singular that the application of the calcium chloride in solution was less effective. The explanation may be 

that on account of the dryness of the dust the solution .quickly sank 

down into the large mass of coal dust, which was deeper than the 

thickness of the ties, and the effect on the surface was thus lost, 

whereas the dry calcium chloride, being more or less coarse, remained on the surface and absorbed the moisture from the air, 

causing a stickiness that tended to pack the dust together. It will, 

of course, be necessary to have more data before positive conclusions 

can be reached as to the advisability of the use of calcium chloride 

under varying mine conditions. If as successful as it promises to be 

on the floor or gobs of mines it would seem to be a system peculiarly 

adapted to the mines in the arid Rocky Mountain district, where
BEMEDIES FOR COAL BUS?. *75

there is a scarcity of water for wetting the dust and where an unusually large amount is needed on account of the dryness of the air.

Crude calcium chloride can be procured in granulated form. The 

price in the leading cities in 1910 varies from $14 to $18 per ton, put 

up in wood barrels. If preferred it can be procured in a 40 per cent 

solution in iron drums.

SPRINKLING AND WASHING DOWN WITH HOSE AND NOZZLE.

The method of using pipe lines through a mine with connections at 

intervals for attachment of hose was introduced in England and used 

to a slight extent after the report, in 1886, of the accidents in mines 

commission. In the same year W. N. and J. B. Atkinson published 

their book "Explosions in coal mines." In their suggestions for remedies they anticipated some of the later developments. They state 

that water tubs of the ordinary kind are ineffectual and that the use 

of water pipes, with cocks at short intervals, and .hose is a better system; and they advise that where watering causes trouble by affecting the roof or floor, the mine may be divided into sections by arching 

entries, whitewashing the arched sections, and sweeping up the bottom dust. They add: "Perhaps 100 yards (of lining) would suffice."

In Germany in consequence of the report of the Prussian fire-damp 

commission of 1885 watering, chiefly by hose sprinkling, was introduced into mines. This system has grown to the exclusion of others. 

Watering became compulsory in Germany in 1900. The mining 

department now insists that the roof and walls of the gangways be not 

merely sprinkled but washed by a stream from a hose. a

In England the use of the hose and nozzle has not become at all 

general. The mining men generally consider that it is too severe on 

the roof and walls; that heavy falls of roof and heaving of the floor 

would be caused.

In the United States the system of watering by hose and nozzle has 

been employed in the coal mines of Utah since the Scofield disaster of 

May 1, 1900, and it is now required by the Utah mining law. The 

conditions for the use of this method in the Utah field are very favorable, as the floor and roof are generally sandstone and are therefore 

not affected by the direct application of water. The method has been 

used only to a very limited extent in a few mines in Pennsylvania 

and other eastern States.

Wherever the method can be employed it is undoubtedly an efficacious one, particularly if the water pressure is good, but it requires

« About the time sprinkling was begun extensively in G ermany the worm disease called ankylostomiasis 

broke out widely among the mine workers of Westphalia. It had been known much earlier, but the fact 

that the severe outbreak occurred simultaneously with more extensive watering led to the belief that 

that practice was the sole cause. Undoubtedly humid warm air fosters the disease, but by the adoption 

of rigid sanitary precautions the epidemic was overcome and although the watering has been continued 

the disease has been almost completely stamped out.
74 THE EXPLOSIBLLITY OF COAL DUST.

constant effort and the employment of men to go continually from 

point to piont. It has the merit that water can be effectually applied 

where most needed, and it is not interfered with by the haulage system. Undoubtedly it requires a strong roof and a floor that will not 

heave from excess of water; otherwise the cost of maintaining the 

roadways is high.

PERMANENT SPRINKLERS.

The use of permanent sprinklers to dampen coal dust began in 

England shortly after the report of the royal commission of 1886. 

It is spoken of in a paper read in 1887 by Professor Abel.® He 

mentions the Harris Navigation colliery, in which "the temperature 

was reduced 6 degrees" by water sprays. He also refers to the system of water and compressed-air sprays invented by Mr. Henry 

Martin, who appeared before the royal commission in March, 1892, 

and asserted that he had employed the system since 1886 in the 

Dowlais collieries. Mr. Martin stated that the sprays used air 

compressed to 45 pounds and water under a pressure of 90 

pounds to the square inch. Tjie water was used under high pressure, 

so that if the air compressor stopped for any reason a fine spray 

might be produced with water alone. The effect of using compressed 

air was to make the spray very light, so that it would travel a long 

distance in the air current. Mr. Martin stated that the sprays were 

located 50 to 80 yards apart, although it is not strictly necessary to 

have them less than 200 yards apart. Where they were nearer 

together it was not necessary to use each one continuously. Mr. 

Martin said that the system incidentally improved the ventilation 

and temperature of the mine. They used the sprays at night but 

not during the day. He submitted a list of hygrometric readings 

taken 20 to 60 feet distant from each of the sprays to show that practically complete vapor saturation was obtained in every instance.

There does not appear to have been any wide extension of the use 

of compressed air and water sprays in mines, but the system has been 

applied in cotton mills in New England to humidify the air, both for 

the health of the employees and for the effect that it has upon the 

weaving process. In mines of the United States some attempt has 

recently been made to introduce such sprays, but as yet they have 

not been used to any considerable extent.

At the Pittsburg station, in the experiments carried on in the 

explosion gallery to try the effect of humidity in rendering coal dust 

inert, compressed air and water sprays were employed. As they 

were installed, the water has very little head, a few pounds only; the 

air is under 35 pounds compression. A very fine spray like a mist is

« Abel, Frederick, Mining explosions and their prevention, 1889, pp. 116,182.
BEMEDIES FOB COAL DUST. 75

produced. The spray heads are of the kind employed in cotton mills, 

and are too small and fragile for mine use. In mines where compressed air is available underground the system has much merit.

Plain water sprays have been much used in the coal mines of Wales. 

In certain collieries they are used continuously day and night, and the 

effect is excellent. In addition to the regular station sprays, special 

sprays have been used at the ends of partings or sidings. When a trip 

of cars leaves the siding, the spray is turned on and drenches the top 

of the car. Sprays of this kind should throw a larger volume of water 

than the station sprays. They serve a most useful purpose in washing fine dust that may have settled on top of the coal down into the 

body of the car, so that the sweeping of the ventilating current over 

the tops of the cars does not carry away fine coal.

In this country water sprays have been used only to a moderate 

extent until quite recently. In the Kock Island Coal Company mines 

in Oklahoma water sprays have been extensively, introduced by Mr. 

Carl Scholz, who has written a number of papers on the subject, 

among others one on the effect of humidity on mine explosions." 

He has contributed a chapter in this bulletin on the use of steam and 

water sprays in Oklahoma mines (pp. 163-167).

In the Alabama mines of the Tennessee Coal, Iron, and Railroad 

Company sprays have recently been extensively introduced.

In the Shoenberger mine (see pp. 76-78) of the Pittsburgh-Westmoreland Coal Company, in Washington County, Pa., water sprays 

supplement exhaust steam. The principal intake enters the mine by 

the drift road or main haulageway. At night between 1 a. m. and 

6 a. m. exhaust steam from three generator engines is allowed to enter 

with the intake air. It thoroughly saturates the air, and in the early 

morning the interior of the mine is said to be dripping with moisture. 

As the cloud of steam is very dense it is impossible to use it during 

the working hours. During this period a system of water sprays is 

used. The sprays are located about 1,500 feet from the drift mouth. 

There are 24 spray heads at intervals along a pipe about 450 feet in 

length. These sprays throw a strong, fine spray by direct water 

pressure. As they would drench men passing by, whenever an electric locomotive with a trip of cars is passing the sprays are turned 

down by manipulation of a valve in charge of a trapper boy.

Though an observation made by the writer on a cold day indicated 

that the air was saturated, by the sprays, yet as the air had not yet 

attained the degree of warmth of the mine it is a question whether 

these sprays would have been sufficient but for the exhaust steam 

supplied at night at the main intake and continuously supplied in 

an independent split of air intaking at a back opening of the mine.

"Effect of humidity on mine explosions: Trails. Am. Inst. Min. Eng., October, 1908.
76 THE EXPLOSlBlLiTY OF COAL DUST. 

HUMIDIFYING BY STEAM JETS.

The use of steam for humidifying was mentioned in the discussion 

on Sir F. Abel's paper, read in 1887.ffl Prof. Arnold Lupton said:

Perhaps one of the most ingenious ways was that of Mr. Stratton, in the Pochin pit, 

Tredegar collieries. He turned the exhaust steam of an engine into the downcast shaft 

and it had the effect of heating the air and damping it at the same time. It did very 

well in spring, summer, and autumn, but in winter it was not sufficient, because it 

would not heat the air enough, and therefore the steam was supplemented by water 

carts for laying the dust. This method of damping the air by steam was only applicable to mines of moderate depth, and consequently low temperature, say under 65° F., 

because it would make deeper mines too warm. The. steam had done no harm to the 

roads or timber at the Pochin pit and it made the mine much pleasanter.

Apparently this system made no progress in England, as there are 

only casual remarks about it from time to time in current literature.

In the United States the plan of turning the exhaust steam from 

fan engines in winter into the downcast shaft has been considerably 

used in the western coal fields for many years, but the scheme has 

been mainly used in freezing weather to prevent ice from forming in 

the downcast shaft.

There does not appear to have been any systematic use of exhaust 

steam for humidifying ventilating currents until the last few years. 

Mr. Frank Haas, consulting engineeT of the Fairmont Coal Company, 

has been an earnest advocate of this method of humidifying mine air 

to dampen coal dust and render it harmless. In an instructive 

paper b read before the West Virginia Mining Association, October 17, 

1908, he proposes humidifying the mine air as an " efficient preventive. At about that time Mr. Haas installed a system of exhaust 

steam spray for humidifying the ventilating currents of the Monongah 

mines of the Fairmont Coal Company, and carried on a series of 

observations and tests during the following winter. The results of 

these important and successful experiments are presented by Mr. 

Haas as a part of this bulletin (pp. 150-165).

In a communication dated March 8, 1910, received from Mr. H. K. 

Knopf, general superintendent of the Pittsburgh-Westmoreland Coal 

Company, he states:

I wish to advise that in the fall of 1907 we installed a system of moistening the air at 

nearly all of our mines, especially at the shaft mines. - 

At our Acme mine at Bentleyville we now-exhaust into the air shaft.all steam from 

our fan engine, and during the severest weather we have always had live steam from 

the boilers from a 2-inch line. We find that we have at this mine from 98 to 100 per 

cent of saturation at all times. The steam at this mine carries back into the workings 

between 3,000 and 4,000 feet and in two years' time with the use of steam we have had 

no trouble with the roof; in fact, the roof, in my opinion, would hold up better with a

a Mining accidents and their prevention: Proc. Inst. Civil Engineers, London, vol. 91, 1887, pp. 91-92; 

republished in book form.

6 Is dust, as such, explosive; and if so, what are the chemical reactions and the most efficient preventives? A pamphlet published by the West Virginia Mining Association.
REMEDIES FOB COAL DUST. 77

uniform condition of moisture rather than when the moisture in the mine varies as it 

.would do without having the moisture put into the air during dry, cold days.

At our Hazel Kirk No. 2 mine, which is also a shaft, we have steam from the fan 

engine and 1^-inch steam line from the boilers. At our Hazel Kirk No. 1 mine we 

have the exhaust from the fan engine and about 30 sprays, separated about 50 feet apart 

in the air way. During the daytime only a limited quantity of steam in addition to 

the moisture from the sprays goes into the mine, but at night a full amount of steam is 

turned in from the engine. At this mine we have obtained an average of 95 per cent 

moisture, and we have obtained 96 per cent of moisture even during the coldest days. 

At our Dunkirk mine we exhaust steam from the fan engine into the air shaft and we 

also have the exhaust from two or three pumps, in the mine, put into the air. All 

of the above-mentioned mines have force fans. At our Shoenberger mine we have the 

exhaust from three generator engines carried into the mine during the nighttime and 

we have a system of sprays during the daytime. At night, after the men have gone 

into the mine, the steam is turned on partially in addition to the sprays which work 

all the time. As soon as the fire bosses go into the mine in the morning, about 2 o'clock, 

a full head of steam is turned in, and shut off whenever they are ready to come out. In

addition to the steam at the front part of the mine, we also have the exhaust from the 

fan engine to the back of the mine (on a separate split), together with the sprays which 

operate substantially at the front.

Observations were made by the writer at the Shoenberger mine on 

March 8, and except in one stretch of road about 3,000 feet from the 

mouth of the mine the road dust was uniformly dampened and plastic. 

The ribs and roof were free from dust and, though not dripping, were 

damp. The relative humidities of the ventilating currents are shown 

in the following table:

Hygrometric conditions of ventilating current at Shoenberger mine, Washington County,

Pa., March 8, 1910.

Place of observation.

Main ventilating split:

2,000 feet from entrance (inby 

water sprays). 

Last cross-cut main entry, 7,000 

feet from entrance. 

Ventilating split at back of mine:

600 feet from entrance and discharge of exhaust.

Dry 

bulb.

"F.

oq

43 

55

35J

41J 

53

53?

Wet 

bulb.

"F. 

31

40

42J 

54

 tii

41* 

52

53

Relative humidity.

Per cent.

OA

QO

96 

94

63

100 

94

95

Condition of floor and ribs.

Very damp.

Floor damp, ribs and roof dampish, 

no dry dust.

Air very foggy. Walls and ribs 

dripping, floor wet.

dampish. 

Do.

It would appear from, the readings in the main ventilating split 

that the water sprays used near the main entrance were not sufficient 

to humidify the mine at the observed temperature and humidity 

of the entering air that it was the large steam exhaust at night that 

supplied the chief quantity of water, the water sprays giving some 

moisture during the day.

The exhaust steam used in the independent back split of air shows 

the efficiency of this method where it can be applied. The exhaust
78 THE EXPLOSIBILITY OF COAL DUST.

steam in the main entrance was not used during the day because the 

fog produced was so dense that it would not have been possible to 

use the road for haulage the main intake coming in on that road.

QUICK-FLAMING EXPLOSIVES.

The report of the Prussian fire-damp commission in 1885 stimulated 

the research in Germany for the development of explosives which 

would not ignite fire damp and coal dust under ordinary conditions. 

Sir F. Abel in his paper on mining accidents and their prevention in 

1887, expressed the belief that the explosives then being introduced 

in Germany, robuite, securite, and carbonite (in its original form), 

were not flameless, and he did not consider them promising means. 

He advocated inclosing the explosive in water cartridges and similar 

devices. Nevertheless, the improvement and development of the 

so-called nonflaming explosives proceeded so actively in Germany that 

by 1890 they began to be regarded as the proper explosives to be used 

in coal mines.

The report of the British royal commission in 1894 in mentioning 

"flameless explosions" says (p. 25):

Many different patent explosives have been brought to the notice of the commission. The so-called "flameless explosives" are largely in use in all parts of the 

country and as the result of practical experience are generally pronounced to be 

effective substitutes for gunpowder, and certainly very much safer. Each of these 

compositions has its advocates and each is said to be flameless or practically so. As 

far as dust is concerned, the current opinion appears to be that they are perfectly safe,, 

but there is considerable doubt as to how far the small flash or scintillation, which many 

witnesses say they display, renders them dangerous in the presence of gas.

By 1896 the agitation for better mine explosives caused the passage 

of a coal-mine regulation act in England, under which authority was 

given to prohibit the use of dangero.us explosives, and an explosives 

testing station was established at Woolwich in 1897. Since that time 

all explosives used in gaseous or dusty mines must pass the tests at 

the Woolwich station. Those that pass are placed on the list of "permitted explosives."

In Germany a station for the testing of mine explosives in the presence of gas and dust mixtures had already been opened in 1894 at 

Gelsenkirchen, Westphalia, under the direction of a government engineer. The German mining department does not allow the use of 

long-flame explosives in coal mines.

A station similar to the German one was established by the Belgian 

Government at Frameries in 1902. The Belgian mining department 

publishes lists of explosives which have passed the required tests.

Austria has a station at Mahrisch-Ostrau in which explosives are 

tested by discharge in the open gallery, not from a cannon. This 

Government also has a "permitted" list of explosives.
REMEDIES FOB COAL DUST. 79

. France does not maintain an official testing station, but the mining 

regulations require that an explosive for use in coal mines shall not 

develop sufficient heat to ignite fire damp, as determined by calculation of the chemical reactions taking place at the moment of 

explosion.

It has thus become a requirement in the coal-mining countries of 

Europe to employ only such explosives as have passed .certain tests, or 

have met certain requirements. It is fully recognized that no explosive 

has yet been produced that is absolutely free from flame, but when 

the explosive used in a shot does not exceed the amount specified as 

allowable, it has so little flame that gas and dust under ordinary conditions will not ignite from its discharge. The quantity that may be 

used of each explosive is therefore specified. It has been termed the 

" charge limit 5 ' by M. Watteyne, head of the mining department of 

Belgium, and this term has been generally adopted.

In the United States, so-called "safety 7 ' blasting powders were not 

introduced into the bituminous coal fields until about two years 

ago, although certain nonflaming explosives had been used earlier in 

special instances in some gassy mines of the anthracite region. There 

was no extensive use of such explosives until the present year 

(1909); in fact, some of the earlier explosives had been withdrawn 

from the market by the manufacturers.

Soon after the Pittsburg station was established and tried out informally, a letter was sent by the Director of the United States Geological Survey, on January 9, 1909, to the manufacturers of explosives in the United States setting forth the conditions under which 

explosives would be examined and the nature of the tests to which 

they would be subjected. By May 15, 1909, 29 explosives had been 

tested. Of these 17 passed the test requirements and were termed 

"permissible explosives." A circular was issued to this effect on 

May 15. By October 1, 1909, 14 additional explosives had passed 

the requirements and a second circular was issued reporting this fact. 

A third circular, issued May 16, 1910, listed 14 additional explosives, 

or 45 in all.

Although, as it is made clear in the circulars, no explosive is absolutely safe under all conditions, there is, nevertheless, very little 

chance of causing an explosion of fire damp or coal dust with one of 

these permissible explosives under any ordinary conditions, provided 

it is used in accordance with the conditions set forth in the circular.

The contrast between the "permissibles" and black powder is very 

strong. With equivalent quantities the flame of black powder is more 

than three times as long and has a duration from 2,500 to 3,500 times 

that of a "permissible explosive."
80 THE EXPLOSIBILITY OF COAL DUST.

By the use of "permissible explosives" the number of disasters, 

developing from blown-out or overcharged shots is reduced to a minimum. As a majority of the great mine disasters in this country 

have been caused by blown-out or overcharged shots of black powder, the general adoption of the "permissible explosives'' should 

result in a tremendous -reduction in the number of such disasters. 

There are, however, other initiating causes of great explosions, for 

instance, the ignition of any small body of fire damp. Under some 

conditions an electric arc may cause an ignition of coal dust. While 

no large-scale tests of the explosibility of coal dust by electric arc or 

hot wire have been made at the Pittsburg station, the possibility of 

such ignition is shown by the laboratory experiments conducted by 

Messrs. Bedson and Widdas in England, already referred to, and by 

the preliminary laboratory experiments of Dr. J. C. W. Frazer, an 

account of which he gives as part of this bulletin (pp. 99-133).

HOCK DTJST.

, 

The British accident in mines commission in 1886 said:

The observation recently made in Germany, in some preliminary experiments, 

that a thin layer of fine angular sand strewn over mine dust appeared to have the effect 

of preventing the communication of flame from a blown-out shot to all but the most 

inflammable dusts is worthy of'a passing notice.

Messrs. W. N. and J. B. Atkinson a suggest,' among other remedial 

measures, that " bottom dust might be rendered uninflammable by an 

adulterant like sand."

Mr. W. E. Garforth in giving testimony before the royal commission 

in 1891, in reply to a question about the Altofts explosion which 

took place October 2, 1886, said: 6

Those roads containing coal dust were affected, those containing dirt dust or only 

a sprinkling of coal dust were not affected. * * * I think you should conduct 

some experiments on the different kinds of coal dust and dirt dust. I believe dirt 

dust will really be the means of preventing an explosion on some roads. More so than 

water. .

The proposal to use stone dust to neutralize coal dust did not 

attract public attention until the Mining Association of Great Britain 

established their experimental gallery at Altofts under the direction 

of Mr. Garforth. The first experiments, beginning May 12, 1908, 

were to standardize the apparatus, and to educate the mining public 

in the explosibility of coal dust. The great size of the gallery (see 

p. 21) and the heavy explosions of coal dust that were produced 

attracted wide attention.

a Explosions in coal mines, p. 127. b First Kept. Roy. Comm., 1891, p. 125.
A. ALTOFTS EXPERIMENTAL GALLERY AFTER EXPLOSION OF DUST OCCUPYING 450 LINEAR

FEET OF GALLERY, AUGUST 11, 1908. 

The vibration of the explosion was felt at a distance of 7 miles. {From Colliery Guardian.)

B. EXPERIMENT 58 AT ALTOFTS GALLERY, SHOWING STONE DUST AND SMOKE ISSUING 

FROM GALLERY AS THE RESULT OF AN EXPLOSION OF THE 275-FOOT COAL-DUST 

ZONE.

The flame penetrated only 54 feet into a stone-dust zone of 100 feet, therefore not igniting another zone 

of coal dust at the outer end of the gallery. (From Colliery Guardian.)

C. EXPERIMENT 99 AT ALTOFTS GALLERY, SHOWING FLAME AND SMOKE ISSUING TO A

DISTANCE OF 160 FEET FROM EXPLOSION OF 375 FEET OF COAL-DUST ZONE.

Flame shows white in the view. (From Colliery Guardian.)
EEMEDIES FOB COAL DUST. 81

On June 13 an experiment (test 13) was made with a stone-dust 

zone, 158 feet long, placed on the return side of the coal-dust charge, 

369 feet long. On the intake side there was a 175-foot dustless zone. 

The flame traveled 44 feet only over the stone dust, but 110 feet on the 

dustless zone, and at this point the force was so great that it burst 

two of the boiler plates, of which the gallery was built, the flame 

finding relief upward.

Test 24, August 8, 1908, showed a penetration of flame into the 

dirt dust (ground shale) of only 155 feet, while on the opposite (return) 

side the explosion was very violent.

In test 25, August 11, 1908, a heavier loading of coal dust than 

that previously used was tried, 450 pounds over 450 feet of gallery. 

The explosion was notable for its violence, the result being thus described : a

Three boilers forming thedowncast were wrecked. [See PL VI, A.] Several pieces 

of boiler plate were blown high into the air a considerable height and distance. The 

flame shot out to great length from the downcast and the vibration of the explosion 

was felt more than 7 miles away.

In 29 experiments without interposition of a stone-dust zone, 

flames projected from the gallery averaged 156 feet in length.

Experiments with stone dust continued and in September a length 

of coal dust (367 feet) was laid between two stone-dust zones of 210 

feet each, which effectually extinguished the flame in each direction. 

This experiment was witnessed by a number of the royal commission 

on mines. b

The gallery was closed for the winter in November, resuming 

experiments in June. While no conclusions have been reached, the 

results of experiments that have been made public indicate that with 

a charge of 375 pounds of coal dust distributed over 375 feet the 

'flame of the coal-dust explosion will be extinguished by the stone 

dust after penetrating 50 to 125 feet into it, the distance depending 

on the method of application. The most effectual method tried 

was to place stone dust on noninflammable brattice cloth on the tops 

of timbers. When the explosions knocked these out the stone dust fell 

in a shower on the flame. Photographs taken after typical explosions 

are reproduced in Plate VI, B and C.

The pressure developed by one o'f the coal dust explosions was 

113 pounds per square inch at a point 375 feet from the initiating 

point of explosion. The published account says: c

The speed of travel of pressure, not necessarily the speed of travel of the flame 

* * * has shown the average speed, from the time of ignition to a point 275 feet 

distant, to be about 1,400 feet per second.

a Colliery Guardian, August 28,1908, p. 411. 

b Idem, July 30, 1909, p. 221. 

c Idem, July 30,1909, p. 219.

38970° Bull. 425 10 6
82 THE EXPLOSIBILITY OF COAL DUST.

The application of stone dust to mine passageways is now being, 

tried by Mr. Garforth in the Altofts colliery. The method adopted 

is to divide off sections of the mines by stone-dust zones of 600 feet 

in length. The roof material is ground fine and applied dry. Plate 

VII shows part of the wall in its natural condition, the other part 

treated with stone dust. The Altofts management state that stone 

dust by reason of its greater density displaces the coal dust on ledges, 

and as the angle of repose of the stone dust is greater it falls to the 

ground and is covered up by additional stone dust. The stone dust 

must be renewed at intervals depending on the rapidity with which 

coal dust gathers."

The formal report'of the committee in charge of the Altofts experiments to the royal commission will be awaited with great interest.

BRICK OB CONCRETE LININGS AND WET ZONES.

Lining sections of entries at regular intervals in a mine to limit 

the extent of an explosion has received some attention abroad. The 

ideal system is to line the passageways throughout with brick or 

concrete, and this has been done systematically in a new mine of 

the Bethune Company in the Pas de Calais district. In September, 

1908 (when it was visited by the writer), 3,500 meters (11,000 feet) 

of reenforced concrete lining had been constructed, so that a visitor 

entering the mine passed through a concrete tunnel, electrically 

lighted up to within a few hundred yards of the face. The linings 

are smooth and are easily kept clean and free from dust, so that it 

would appear impossible for an explosion originating at the face 

to penetrate any considerable distance through the gangways.

The cost of such linings is considerable, yet in a mine where the 

roof is poor, requiring much timbering, and the mine is to be longlived, the saving effected in the maintenance of the roadways will 

probably pay in a few years for the additional cost of the lining. 

The managers of the Bethune mines state that the underground 

maintenance cost in the mine mentioned is only one-fifth of the average maintenance of their other mines hi the same district.

The method of lining generally used has been to divide the mine 

up into sections and to make the length of lining sufficient to prevent 

a flame of an explosion in one section from passing through to another 

section in other words, to create a "dustless zone." Until the 

Altofts experiments were begun there was very little definite idea 

as to what length a dustless zone should have. In earlier discussions lengths from 100 to 200 yards had been suggested.

For prevention of dust explosions the importance of lining the passageways is not due to the lining as such, but to the ease of cleaning

a Colliery Guardian, October 1,1909, p. C7G,
U. S. GEOLOGICAL SURVEY

ROADWAY IN ALTOFTS MINE, SHOWING METHOD OF APPLYING STONE DU

Natural wall at left; wall treated with stone dust at right. (From Co
REMEDIES FOR COAL DUST. 83

and to the fact that it allows the free use of water without weakening 

thij roof, or the floor where there is an inverted arch as well.

Except at the Bethune mine mentioned above it has rarely, if ever, 

been contemplated to -completely line the passageways; the usual 

thought has been to employ linings to divide the mine into sections. 

In order to decrease the necessary length of dustless lining, water 

curtains have been suggested and have been experimented with to 

some extent in the gallery at Rossitz, in Austria. In 'experiments 

there with water curtains the usual flame length of dry dust without 

the curtains (147 meters) was shortened about 30 meters (97 feet), 

but the flame still penetrated a wet zone about 21 meters (68 feet). 

The conclusion was that a wet zone alone must be at least 60 meters 

(195 feet) long, but that apparently a zone supplemented by water 

curtains at either end could be shorter. These figures are somewhat 

below those indicated by the Altofts and LieVin experiments, where 

larger initial explosions were tried.

The question how long lining zones should be that are kept clean 

and free from coal dust can better be determined after the present 

series of tests at the Altofts and Lievin stations have been concluded.

TENTATIVE CONCLUSIONS ON THE DUST PROBLEM.?

FACTORS AFFECTING EXPLOSIBILITY.

t

VOLATILE COMBUSTIBLE MATTER.

That coal dust will explode under some circumstances, both in 

the presence of fire damp and without it, is now generally accepted 

by mining men. The writer fully agrees with this and takes the 

following views of the explosibility of dust and the conditions necessary for explosion.

Experiments at Pittsburg indicate that under ordinary conditions 

the dust must be from coal having at least about 10 .per cent of volatile combustible matter, though in certain foreign experiments it is 

claimed that explosions were obtained with charcoal dust.

Dusts with higher percentages of volatile combustible matter are 

more sensitive, ash, moisture contents, and size being constant. 

This view is based partly on the preliminary experiments at Pittsburg and on the results of experiments of M. Taffanel and other foreign

investigators.

STRUCTURE AND SIZE.

Physical structure and size of the dust particles are factors in the 

relative sensitiveness. In coals approaching the border line of nonexplosibility, structure and particularly size are the more important,

«It must he understood that the conclusions here stated are those of the writer and are of a tentative 

character, subject to revision as further investigation is carried on at the Pittsburg testing station and 

elsewhere.
84 THE EXPLOSIBILITY OF COAL DUST.

and affect ignition. That is, the less readily the dust gives up its 

gases the larger and more intense must be the igniting flame.

Whether or not concussion or compression of the air at the moment 

of attack by the flame is required for the ignition of the less sensitive 

dusts and the propagation of the flame is a question yet to be answered, 

but it is self-evident that the larger and heavier the particles are the 

more difficult it is for the air waves in advance of an explosion to 

bring, them into suspension where the flame can strike them.

DENSITY.

For continued propagation of flame the dust particles must be so 

close together that the burning gas enveloping one dust particle will 

cause distillation of the volatile matter of the next particle and ignite 

it. In other words, at each successive moment of inflammation 

there must be a certain density of dust for each character and size of 

dust. .

It appears to the writer that the combustion of the fixed carbon of 

an average-size particle of coal dust will not take place until the 

volatile matter of the particle has been volatilized and burned in the 

surrounding air. If this is true, the oxidation of the fixed carbon 

probably does not, except in dust particles of minutest size and 

greatest purity, take place in time to assist in the first extension of 

the flame, although it is undoubtedly an important factor in the 

succeeding moment, intensifying the flame, and hence increasing the 

violence and pressure of the explosive wave.

The analyses of burned dust from explosions, both in mines and in 

the Pittsburg gallery, show an increase in percentage of ash over the 

ash content of the original coal often considerably greater than the 

increase due to expelling the volatile matter. Such an increase

shows that there has been combustion of the fixed carbon. The 

increase in ash has been especially marked in the 200-mesh dust used 

in the Pittsburg density tests. (See p. 37.)

M. Taffanel's experiments with anthracite and those at the Pittsburg station indicate that under the conditions in the galleries used 

anthracite dust will not propagate an explosion. This supports 

the view expressed above that it is the burning volatile combustible 

gases that carry forward the initiating flame and that the combustion 

of the fixed carbon is secondary.

MOISTURE.

Moisture contained or carried in coal dust is probably converted 

to steam before gas is evolved from the dust particles, and if enough 

moisture is present the absorption of heat in this way may prevent 

sufficient heat from being imparted to adjacent dust particles to 

evolve and raise their volatile gases to the ignition point. Further-
TENTATIVE CONCLUSIONS cON THE DUST PROBLEM. 85

more, if the moisture in or surrounding each particle of dust is sufficient in quantity, the vapor therefrom will dilute the evolving gases 

or else tend to surround them with an outer incombustible envelope 

and so prevent the immediate ignition of the combustible matter 

necessary for propagation.

ASH CONTENT.

The ash content of the coal, within ordinary limits, does not appear 

to affect the explosibility of the coal dust; but if an inert dust, such as 

stone dust, is raised into the atmosphere with the coal dust by the 

advance air wave, it will affect results in two ways by separating the 

coal-dust particles with a barrier and by absorbing some of the heat of 

the impinging flame, and thus lowering the temperature below that 

necessary for the ignition of the gas distilled from the adjacent coaldust particles.

OUTWARD CONDITIONS.

The writer concludes that the outward circumstances uniier which 

coal dust will explode may be summed up as follows: Sufficient dust 

must be brought into suspension by a preliminary shock or concussion 

producing a violent air wave; or else the dust must be so minute 

that it is already suspended in a dense enough cloud at the moment 

when the flame impinges. The latter effect is produced only under 

some peculiar circumstances by which a large amount, of fine coal 

dust is thrown into a strong air current and carried to the igniting 

flame. The former effect may be produced by a heavy shock like 

that from a falling body, but is much more likely to result from 

a preliminary explosion of fire damp or, more commonly, of an 

explosive.

CONDITIONS AFFECTING PROPAGATION OF EXPLOSIONS.

AMOUNT OF DUST.

The weight of coal dust that must be thrown into suspension to 

permit propagation of an explosion depends on (a) the percentage of 

volatile combustible constituents; (&) the amount of contained and 

adhering moisture; (c) the presence of foreign substances like stone 

dust; and (cZ) the size of the dust particles, the effect of which is twofold: the smaller the particles the more easily the air concussion 

can raise them, and the more surface is exposed for the evolution 

of gas.

The minimum density of the dust cloud necessary to propagate an 

explosion evidently varies with the initial cause as well as with the 

character of the dust. Using 190-mesh bituminous dust, M. TafYanel 

obtained explosions regularly with a density of 70 grams per cubic 

meter (0.07 ounce per cubic foot), and in one instance obtained
86 THE EXPLOSIBILETY OF COAL DUST.

propagation with as low a density as 23 grams per cubic meter (0.023 

ounce per cubic foot). In the experiments at the Pittsburg station 

with 200-mesh dust from the Pittsburg.coal seam, in a much larger 

gallery, but also with far larger charges, of explosive, two propagations were obtained with as low a dust density as 32 grams per cubic 

meter (0.032 ounce per cubic foot).

Density tests with the coarser sizes have not yet been tried in the 

Pittsburg station.

MOISTURE IN DUST AND IN AIR.

The experiments with wetted dust at the Pittsburg station have 

been very instructive. The first attempt has been made to define the 

amount of water that must be present with the dust to prevent propagation. It is true that these experiments were few and were made 

with dust from the Pittsburg seam only, which is possibly more sensitive than the average bituminous dust. On the other hand, the 

igniting charge was only 1\ pounds of black powder. In the interior coal fields it is not at all uncommon for charges of 5 to 6 pounds or 

more to be used and for blown-out shots to occur with such charges. 

Hence, despite the possibly less sensitive character of the coal dust in 

these fields, the initiating cause of explosions may be greater, and it 

would not be safe to assume that a less percentage of moisture than 

that indicated by these preliminary experiments would render the 

coal dust inert.

Where there is a large amount of dry coal dust, judging from the 

Pittsburg experiments, a humid atmosphere has little effect on ignition of dust or propagation of an explosion. A long continuance of 

the humid conditions renders the coal dust moist and inert, but the 

presence of moisture in the air at the moment of explosion is not

sufficient to prevent an explosion; that is, not-enough moisture is 

carried by the mine air to reduce materially the temperature of the 

flame. Fully saturated vapor at 65° F., an ordinary mine temperature in this country, weighs 6.78 grains per cubic foot (15.5 grams 

per cubic meter). Coal dust suspended in such a saturated atmosphere in a cloud of moderate density weighs, say, 200 grams per cubic 

meter. At the figures given the weight of vapor is but 7.8 per cent 

of the weight of dust. The Pittsburg experiments with wetted dust 

showed that several times this percentage of moisture in the dust, in 

addition to a nearly saturated atmosphere, was required to prevent 

propagation.

Probably with a low dust density the relative humidity of the air 

would be an important factor in tending to prevent the initiation of 

an explosion. However, the great purpose of artificially humidifying 

mine air is that it may serve as a vehicle for carrying water to the dust.
TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 87 

MIXTUEE WITH INERT SUBSTANCES.

When the dust is abundant, the effect of high ash content, unless that 

content is excessive, is apparently not noticeable. The upper limit 

has not yet been closely defined by experiment. The effect of intimately, mixing coal dust with shale dust or stone dust has also not 

been fully determined experimentally. The few tests in this direction 

conducted at the Pittsburg station have been with "road dusts" or 

other coarse mixtures, and the tests with these indicate that the amount 

of the inert substance has to be very large, possibly equal to the amount 

of pure coal dust. The tests with finely pulverized stone dust in the 

Altofts experiments have been directed to supplanting or covering 

up coal dust in certain zones, but not to mixing stone dust with the 

coal dust.

ADVANTAGES AND DISADVANTAGES OF PROPOSED REMEDIES.

In reviewing the methods for preventing coal dust explosions or 

limiting them to certain zones the writer presents merely his own 

views and conclusions, subject to change as the investigations proceed. 

The remedial measures will be taken up in order as already given 

(pp. 66-83). The writer believes that all have more or less merit, except the water boxes or sprinkling cars of primitive type.

FORCE SPRINKLERS IN CARS.

Water cars with force sprinklers, in which the pressure is produced 

by pump or air pressure, if used frequently and thoroughly, are good. 

The great danger is that they will not be so used throughout all the 

mine, owing to their interference with the haulage of coal, and frequently owing to the lack of tracks in the air course or manways. 

When used intermittently the water-car system is useless because 

the dust is not wetted; as the drops of water do not mix with it, they 

are exposed to the air currents and quickly dry up.

CHEMICALS.

The use of calcium chloride and similar salts has not yet been 

sufficiently tested to permit a conclusion as to its effectiveness in 

preventing explosions. If it renders the dust merely dampish that 

is, not sufficiently moist to prevent explosions it may improve the 

sanitary condition and lessen the quantity of float dust. It may also 

prove to be effective in supplementing intermittent sprinkling, 

enabling the dust to absorb drops of water that would otherwise be 

taken up by the air current.
88 .THE EXPLOSIBILITY OF COAL DUST.

CLEANING UP DUST WASHING DOWN WALLS.

Cleaning up coal dust and sending it out of the mine is a plan used 

more or less under all systems, but applied only to large masses of 

dust. The plan can not reduce the quantity below the danger point.

Thorough washing down of roof and walls with hose is required by 

the mining laws in Germany, and in this country in Utah. If thoroughly and frequently done, it is undoubtedly most effective. The 

difficulty is that usually it is not done systematically and thoroughly. 

It is a system that can not be effectively applied to shaly or weak 

roofs without resulting in many falls and great cost of timbering.

PERMANENT SPRINKLERS ZONAL LININGS.

Using permanently located sprinklers, attached to pipe lines and 

running continuously, but with a flow that can be varied according 

to need, is very effective in saturating the mine air within a moderate 

distance of each sprinkler, and through this meanso gradually wetting 

the dust. One of the great merits of the system is that the sprinklers 

can be distributed where most needed; that is, where there is a tendency to produce the most dust or where the humidity of the air currents is lower than it should be. A disadvantage in some mines is 

that the moisture causes falls of roof. Some of the evidence of this 

fact is derived from trials of intermittent rather than continuous 

wetting. Nevertheless, where there is roof material that will come 

down, or fire-clay floor that will swell immediately on contact with 

water, in order to use sprinklers it may be necessary to introduce 

brick'or arched linings, sometimes with concrete floor and sump, and 

to place individual sprinklers in the lined sections. The linings would 

serve two purposes to catch any condensed water from the sprays 

and to provide a damp and dust-free zone, limiting a possible dust 

explosion from either side.

The use of more complete' zonal linings is well worthy of consideration for long-lived mines or long-lived entries (particularly the main 

entries), not alone as a dust remedy, but also for fire protection.

USE OF EXHAUST STEAM SPRAYS.

Sprays. Humidifying the intake air current with exhaust steam 

sprays is much the easiest and cheapest method of introducing moisture into a mine where the ventilating fan is run by a steam engine.

Supplementing fan steam. The quantity of steam that it is necessary to use in the fan engine for ordinary air-ventilating pressures is 

sufficient to humidify the air in moderately cold weather, but in 

extreme cold weather is insufficient. Therefore it must be supplemented by live steam or, as. suggested by Mr. Frank Haas, in order 

to insure that it is used, by passing more steam through the engine.
TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 89

The same result could be accomplished by passing the steam through 

a registering meter.

Disadvantages. The disadvantage of steam sprays is that the 

steam fogs the air current in cold weather, so that the sprays can not 

be placed on the haulage roads without considerable discomfort and 

danger of collision. It therefore seems requisite to employ a blowing 

system of ventilation, placing the steam sprays on the air way at the 

intake and throwing the return air on the main haulage road. This is 

manifestly unsafe to do in gassy mines or in mines liable to an outburst of gas, particularly if the method of haulage is electrical. The 

only alternative in such a mine is to have an additional entry for the 

return air way, making the ventilation in the haulage way "neutral" 

or passing through it a very small but sufficient supply of fresh air. 

In most old mines this is an impossible condition; therefore the 

decision as to the use of the steam-spray system must depend on 

whether the mine makes sufficient gas to prevent the return air being 

passed through the haulage way. In much the greater number of 

mines, particularly in the Middle West, there is not sufficient gas to 

prevent this being done; therefore in such mines the use of steam 

sprays appears to be one of the best S3^stems where the roof conditions permit it. A compromise method is that used at the Schoenberger mine, described on pages 76-78, in which the steam sprays are 

used in the haulage road at night only, water sprays being used on 

the day shift when coal is being hauled.

Danger to roof. It has been held by many mining men that the use 

of exhaust steam for humidifying would be especially severe on the 

roof. In the opinion of the writer this is not generally true. The 

condition of humidity obtained by its use is very uniform. Where 

humidifying is not done it is the alternate drying out and wetting 

due to the changes in weather that causes most of the trouble. The 

roof is not subjected to any more severe conditions by steam or water 

sprays than in spring when hot moist air enters the mine. Later in 

the summer during the hot weather the same high degree of moisture 

prevails, but the roof, becoming acclimated, as it were, to this condition, is not as likely to if all as during the spring, when the change of 

temperature and humidity took place. If, when cold weather comes, 

the humid condition of summer is maintained by introducing sprays, 

the roof will not be subject to violent changes in humidity.

Heating intake air. The plan of merely heating the incoming or 

intake air to produce summer temperature without introducing 

additional moisture has sometimes been proposed as a remedy. The 

fallacy of the argument will be obvious to one familiar with the 

principles of relative humidity and their application to mine air.

Heating the intake air as an aid to quick humidifying, where either 

steam or water sprays are used, has been tried more or less, with
90 THE EXPLOSIBILITY OF COAL DUST.

some diversity of opinion as to results. Mr. Frank Haas's experiments 

with heating the intake at the Monongah mine, as described by him 

on pages 158-161, indicate that there is no need of such heating. The 

walls of the passageways effectively heat the air in cold weather, so 

that the expense of artificially heating a large volume of air does not 

appear necessary, if the intake is kept humidified to the point of 

saturation as the temperature rises. Some mine operators have considered heating of great advantage.

In the use of steam sprays the steam raises the temperature of the 

incoming air to some extent, depending on the relative temperatures 

of the steam and air as well as on their relative weights for equal volumes. The lower the temperature of the external air the greater 

the weight of steam necessary to be introduced; hence the greater 

the temperature rise of the incoming air. Practically, this rise will 

range from 8° to 15° F., depending on a variety of conditions. Theoretically, if we should disregard the conductivity of the walls of the 

passageway and assume that all the steam in excess of that immediately required for saturating the incoming air is condensed, the 

rise would be very much greater. There are so many variable factors and the influence of the walls is so great that it is impossible to 

determine the rise by calculation.

Vaporization. If the steam sprays are placed at the entrance of 

the intake of the mine, when the external air is considerably colder 

than the normal temperature of the mine, the difference being 

greater than the rise resulting from the heating by the steam sprays, 

the steam in excess of the vapor capacity condenses, and some water 

falls to the ground, but as the air current moves rapidly most of it 

is carried along mechanically in the form of fog. As the air current 

travels along the mine passage and absorbs the natural heat from

the walls, its vapor capacity increases and the fog is gradually 

revaporized, thus keeping up saturation until there is total disappearance of the fog or visible moisture. If at this point the heat 

of the air current has reached that of the strata or walls, the air will 

remain practically saturated throughout the mine, but if the temperature still rises the air current no longer remains saturated, but 

has a relative humidity that decreases as the temperature rises.

Cooling effect of vaporization. When steam or water sprays are 

used, the vaporization of water or the revaporization of fog absorbs 

heat with the result of lowering or keeping down the temperature 

of the air. This result is only temporary, as the passage walls 

impart the difference in heat in a relatively short time. The 

amount of the temporary reduction or retardation of temperature under mine conditions is practically impossible to calculate on 

theoretical grounds, owing to the undetermined heating effect of 

the passage walls. Water sprays can not well be employed until 

the air has risen in temperature to about 32° F. The point in the
TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 91

mine at which this takes place when no artificial heating is done 

necessarily varies with the temperature of the incoming air. The 

sprays must therefore be arranged at intervals and turned on or 

off according to the temperature. The important point is to keep 

the air saturated as it rises in temperature. By either method of 

humidifying steam or water sprays, with' careful attention there 

is no serious difficulty in keeping the dust moist and in a relatively 

safe condition.

Effect of humid air on health. In England, where the mine temperatures are 15° to 20° F. higher than in the mines of this country, 

owing to the greater depth, fear is expressed frequently by the mining 

men that a humid condition of the air is unhealthy and enervating. 

The spreading of the intestinal disease called ankylostomiasis, 

which at one time afflicted large numbers of the German miners, was 

by some ascribed to the warm humid air of the German mines. Be 

that as it may, sanitary precautions have now largely stamped out 

the disease. Hard physical labor may be done in a saturated atmossphere at 60° to 65° F. with much less discomfort than at 75° to 85°, 

aside from that due to the greater heat, because the warmer air carries 

twice the weight of water per cubic foot. Hence conditions in this 

respect are very different in England and Germany from those in 

this country. The writer has observed no discomfort in a saturated 

or nearly saturated atmosphere at 65° F. The air of most mines in 

summer is in this condition. Only when the air is supersaturated 

or foggy does it become unpleasant.

STONE DUST.

The use of stone dust is the most recent suggestion for either preventing or limiting explosions of coal dust. As the method is only 

in the experimental state, it is too early to express any decided 

opinion. The results at Altofts appear very favorable. Not all 

the mines in this country provide a suitable stone for grinding, but 

burned dirt piles or clay or sand are nearly always available, and to 

a limited extent thoroughly burned ashes from the boiler plant.

The method is not so adaptable to room and pillar workings as 

to the long-wall system, but it may prove a valuable alternative 

remedy for coal dust where the humidifying methods are considered 

inapplicable on account of danger to the roof, or in those mines 

in the arid parts of America where water for humidifying is not 

available.

If in addition to wetting coal dust throughout a mine by one of 

the foregoing methods "permissible" explosives are used for shooting 

coal at the face, or for brushing or grading the roadways, the chances 

of starting a wide-sweeping mine explosion are reduced to a minimum. 

As a means of prevention of dust explosions, the writer would place 

the employment of permissibles at the head.
92 THE EXPLOSIBILITY OF COAL DUST.

OBSERVATIONS ON MANIFESTATIONS OF COKED COAL 

DUST IN MINE EXPLOSIONS.

CHARACTER OF COKED DUST.

The mining engineers of the Survey have made investigations of all 

the explosions of any moment that have occurred since July 1, 1908.

Of those which have been personally investigated by the writer, 

and in which dust played the most important part (though not necessarily at the origin), the most serious were those at Marianna, Pa., 

November 28, 1908, in which 156 men were lost; at the Franklin 

slope, Johnstown, Pa., October 31, 1909, in which 13 men were killed 

and 2 others seriously burned; at Primero, Colo., January 31, 1910, in 

which 75 men were killed; at Mulga, Ala., April 20, 1910, in which 35 

men were killed; and at Palos, Ala., May 6, 1910, in which 84 men 

were killed.

In these explosions the coke manifestations were strong and very 

characteristic. From a study of these and previous explosions investigated by the writer, there appear to -be five phases of coke developed 

in a mine explosion:

1. Bright splashes of coke on the open exposures, adhering to the 

ribs and to a less extent to the roof, indicating an abundance of dust 

and an intense heat, but not much movement. Such coke was found 

near the heads of entries.

2. Less friable coke or caked dust, in some places over an inch thick, 

sometimes found on the exposed surfaces of the walls and posts of 

rooms and to a lesser extent on entries facing the source of explosion. 

Such coke is found near the origin of explosions or where there have 

been secondary explosions. It indicates an abundance of dust and 

not much movement.

3. Individual particles of coke, generally bright, and in some places

close enough together to form a thin scale. This is sometimes found 

driven into crevices facing the approaching explosive blast, but 

usually is on the reverse side of timbers, projections, or rib corners. 

Such coke indicates a violent sweep of the explosive blast too strong 

to allow deposition on facing exposures, but which whips around the 

projections and deposits the semiplastic coke on the lee side.

4. Minute globules of coke as large as TV inch diameter and smaller. 

Many of these are perfectly round, and on the ulterior nearly hollow, 

with one or more cells. They are to be found on top of cars at the 

face of entries or on other surfaces on which they can be seen. Those 

globules falling to the floor are difficult to observe. Such spheres of 

coke are like tiny balloons. They do not adhere together, but have 

evidently been cooled in transit through the atmosphere. Their 

occurrence, so far as observed, is only as the result of explosions in 

mines in which the coal is of a distinctly coking nature or in which the 

bitumen is considerable, as coal of the Pittsburg seam. It would 

seem that these glowing "float globules, or other particles, might be
MANIFESTATIONS OF COKED COAL DUST. 93

important in carrying an explosion into remote corners after the 

active flame of an explosive wave has temporarily died away. Then 

should any gas be present it would be greatly compressed, so that 

when the red-hot particles penetrated the compressed gas at the head 

of an entry or other closed place they would cause its ignition, a,nd 

thus a secondary explosion would be set up.

5. The fifth kind of coke is not a coke from dust. It is formed 

where the flame of the explosion has lingered and the flame or 

adhering coked dust has ignited the coal ribs, sufficient oxygen 

being present for.the combustion to go on. This sometimes occurs 

in a room, and such a.place, if a large amount of coke has been present, 

has frequently been mistakenly considered the point of greatest intensity of the explosion.

In no place has it come to the observation of the writer that coking 

of the face or ribs has been due to the direct explosive blast; this would 

appear to be an after-effect. Generally coked dust has been caked 

while in the air, and in the plastic or semiplastic state has been thrown 

against exposed surf aces. Coke from dust is mpre likely to be found 

upon the timbers and coal ribs than upon the roof or rock ribs where 

such are exposed; but this is by no means invariably so. However, 

there does appear to be a selective action. It was peculiarly noticeable in a certain entry in the Franklin Slope mine, in which several 

slate partings with a smooth fracture showed along the ribs; the coke 

adhered conspicuously to the coal above and below each of the partings, but not to the partings themselves.

The coke or caked coal found after explosions shows a marked 

Increase in ash and decrease in volatile matter as compared with the 

average coal of the mine. Even when no coking is apparent to the 

eye there may be a considerable loss of volatile matter in the dust. 

This is indicated by a comparison of dust gathered near the shaft 

bottom at Marianna with the standard coal of the mine, as shown in 

the following tabulation:

Proximate analyses of dust and of coal from Marianna mine.

As collected:

Ash. ........................................................................

Moisture and ash free:

Standard 

coal, a

1. 80

33.14

59.00

0.00

100. 00

'Vj 97

fu m

100. 00

Dust 

heated in 

the explosion.

b 3. 99

19.56

30. 78

100. 00

29. 98

100.00-

a Sample of coal full section of seam, as mined.

6 Moisture undoubtedly absorbed after explosion; sample was gathered about ten days after it.
94 THE EXPLOSIBILITY OF COAL DUST.

Where there is actual coking the loss of volatile matter and 

increase in ash is more noticeable. The high percentage of ash 

shown in the above dust analysis is presumably due to inclusion of 

foreign matter and not to complete combustion, although that may 

have played some part.

POSITION OF COKED DUST AFTER AN EXPLOSION.

The observation of the writer has been that at the originating 

point of a coal-dust explosion, and near by, the coked particles are 

projected directly upon the exposed surfaces of props, caps, collars, 

and walls, particularly upon the upper portions toward the roof. In 

other words, the coked dust faces the originating point.

As found in mines in which the coal cokes strongly, the coked dust 

near the source of explosion is usually in thick loosely cohering 

masses, and where the dust is abundant this coke scale may be as 

much as half an inch or even an inch thick. The coking or rather 

caking through an individual scale is uniform, but the coking process 

has been carried only so far as to render the individual grains plastic 

enough to cohere and to lightly stick to surfaces. A slight touch 

will detach and break up the scale. Such coke is dull in luster and 

presents a rough granular appearance. It often contains foreign 

matter, pieces of slate, or fragments of timber.

A few loose grains or globules may adhere to the roof, but there is 

rarely a scale of coke, though such a scale is often attached to the 

bottom side of a collar.

Near the point of origin, on the reverse side of props or collars 

(facing away from the source of explosion) there are usually only a few 

scattered particles of coke, unless some reflex action has had effect.

The above-mentioned effects are those usually noted in room and 

pillar workings, in the room or in the entry where the explosion 

originated. After the explosive wave has passed from the room into 

the entry, or, if it originated in the entry, has traveled along it a 

few hundred feet, it gathers headway, and, provided it still has dry 

and pure enough coal dust to feed upon, forms thinner and more 

scattered coke scales. As the velocity of the explosive wave increases 

it no longer deposits coked dust on the facing side of props or posts, 

collars, and rib projections, except occasionally as scattered particles, 

but forms thin scales, often bright, first on the under side of 'collars, 

where there are any, then on the reverse side of timbers or projections.

At this stage coke particles may be driven into facing crevices in 

the ribs or cracks in timbers.

It is quite usual for the projections facing the origin to be coated 

with unburned dust brought out from adjacent workings, after the 

explosive wave has passed, by the suction created by the depression 

that follows the wave.
MANIFESTATIONS OF COKED COAL DUST. 95

As the explosive wave traversing the relatively narrow passageway 

becomes more intense, which it usually does if there is dry coal dust 

to feed upon, the timbers are frequently swept along by the advance 

air wave, so that their evidence is lost unless their former position 

can be definitely located.

As the explosive wave gains in velocity practically no coke is 

deposited in the main passageway traversed, and is then to be looked 

for in isolated splashes on the lee side of corners of crosscuts or 

other side openings on the coal rib or on timbers in these openings. 

Another place worth observing is the roof behind such corners, 

where careful search will sometimes disclose occasional particles 

adhering or hanging in separate globules.

In a wide-sweeping explosion that traverses the main entries 

the violence usually becomes so great that little or no coke is deposited 

there. This was notably true in the recent Primero explosion, in

which, though abundant coke showed in the rooms and cross entries, 

only a few isolated particles (on outby facing exposures) were 

observed along 1 the main slope or in the immediately adjacent openings for the inner 2,000 feet, and none at all were found by the 

author in the outer 2,000 feet traversed by the explosion. Despite 

this scarcity of coke evidence in the main slope, bodies that were 

found under a fall of rock at the mouth were burned. Also a 

brakeman who was on a motor trip of mine cars about 100 feet 

from the mouth of the slope, but who was in line with the slope, 

was slightly burned. A telephone post about the same distance 

away from the slope, but 30 feet off the direct line of it, had considerable coke scales adhering to the side facing the mouth.

The position of the scale ©n this post brings to attention the mode 

of deposition of coked particles when an explosion dies away, as in 

the instance described above. They are thrown upon the facing 

exposures. This fact was also admirably illustrated in the Primero 

explosion in a certain side entry (A-8 entry), into which a branch 

explosion wave penetrated about 1,800 feet from the main slope, and 

there died away at a wet place in the road. At this point the timbers were all standing and no violence was indicated. There was 

loose coke on the outby sides of the timbers. Several hundred feet 

out toward the main slope, where violence was shown, increasing 

toward the slope, the coke particles and scales were generally on the 

inby surfaces, or those facing away from the approach of the explosive wave. The coked dust is sometimes located on the facing side 

in very wide places, as in wide rooms where the velocity of the wave 

becomes less, from opportunity to spread laterally.

The fact that coke is not deposited where the sweep of the explosive 

wave is greatest is possibly accounted for by the extreme speed
96 THE EXPLOSIBILITY OF COAL DUST.

attained, which carries along everything loose. This action is shown 

by the scouring of the walls of the passageway. Facing edges are 

rounded off, sometimes as if by a sand blast. The coke particles 

may be reduced to fragments, and it is possible that the intensity 

of the heat may effect a more or less complete combustion of the 

fixed carbon of the dust and resultant coke.

Following such an explosion there is a continued outrush of burned 

gases, which often carry surplus dust and deposit it on the lee side 

of projections, sometimes covering the coke just deposited.

Succeeding this outrush there is a return rush to fill the vacuum 

caused by the cooling of the gases. The return wave if strong may 

pick up dust and redeposit it on the lee side of projections, or that 

side which faced the explosion.

It must be remembered that in nearly all extensive dust explosions 

an immense amount of dust is subsequently drawn out of the workings and also created by the violence of the explosion. Moreover, 

there is usually a great surplus along the pathway. In the average 

entry 6 by 9 feet in section about 7 ounces of pure coal dust per 

linear foot will if completely burned give the maximum explosive 

effect possible with the air present. (See pp. 45-46.)

Typical analyses of coke from, dust explosions, compared with analyses of the coal as mined.

Sample as received:

Ash.....................

Moisture and ash free:

Volatile matter .........

Franklin No. 2 mine,

Miller (B) seam, Johnstown, Pa.o

1.

1.28

19.88

68.11

10.73

100. 00

22. GO

77.40

2.

0.71

11.09

67.65

20.55

100. 00

14.09

85.91

3.

1.38

8.48

"52.59

37.55

100. 00

13.89

80.11

Primero mine, Las Animas County, Colo.b

4.

1.91'

32.27

<V7 01

8.61

100. 00

36.06

03.94

5.

3.47

d21.23

91 17

44.13

100. 00

40.51

59.49

6.

3.54

24.53 in r\fj

28.96

100. 00

36.34

63.66

7.

4.13

18.38

KO 10

19.37

100. 00

24.03

75.97

8.

4 QQ

19 f>8

37.11

100.00

e 21. 90

«78.10

9. .

6.62

20.49

17.23

100.00

73.09

a Samples taken following an explosion October 31,1909.

6 Samples taken after explosion January 31,1910.

cln this specimen of coke there appears to have been considerable combustion of the fixed carbon.

d Probably contains water of crystallization of clay in ash, thus affecting carbon-volatile ratio as determined by proximate method of analysis.

« This carbon-volatile ratio is interesting as indicating more complete combustion where the explosion 

died away. The ash content is also higher than that of coke samples near origin.

1. Coal from face, sample of full section as mined.

2. Thick coke scale from car bumper.

3. Coke scale adhering to rib in tenth heading.

4. Coal from face of room 2,11-A entry, sample of full section of seam as mined. (Lab. No. 10063.)

5. Road dust from room 47,7-A entry (beyond area affected by explosion). (Lab. No. 10052.)

6. Sample of dust from large mass in last crosscut, between entries 11-A and 12-A, close to their faces. 

Probably deposited by wave following the explosive wave. (Lab. No. 10051.)

7. Coked dust from prop in room 6,11-A entry. (Lab. No. 9949.)

8. Coked dust from post in 8-A entry about 1,600 feet from main slope. (Lab. No. 9947.)

9. Coked dust from prop in last crosscut between entries 11-A and 12-A. (Lab. No. 9948.)
SPECIAL FEATUEES IN DUST EXPLOSIONS. 97 

SPECIAL FEATURES IN DUST EXPLOSIONS.

At the face of headings or rooms what has been termed stalactitic 

carbon is found hanging in long threads from the roof. This is 

evidently the result of an insufficient supply of oxygen to allow 

complete combustion, and of subsequent deposition in still air.

In the typical explosion the great variation in the manifestation of 

heat is one of the curious features. At one point the heat appears 

very intense, at another there appears to be a complete dying away 

of the flame. Every observer has noticed that at certain points, 

where there can be no question that the flame has passed, blasting 

powder in cans has not been ignited. In some instances the powder 

has been upset on the ground and the grains scattered, but it has not 

always been burned. The upsetting may have been done after the 

passing of the flame by the subsequent rush of gases. It very frequently happens that an explosion passes by brattice cloth or sight 

strings (for alignment of entries) without igniting them. One obvious 

reason is that such cloths are generally damp and the time of exposure 

is momentary. Another reason is that immediately preceding the 

flame there is undoubtedly an air wave, which throws any loose canvas 

or string flat against the roof or ribs. In the majority of explosions 

it appears that the flame rarely fills the entry from side to side, but 

zigzags along, more or less in the center of the entry, striking the 

walls only here and there. ' This is also the manifestation in the 

Pittsburg gallery when mine road dust with high .ash content is used 

and the flame is partly blanketed by the excess of ash.

The belief has prevailed very generally among mining men that 

because a dust explosion is usually manifested in the intake entries the 

explosion "feeds on the fresh air" or advances against the air current. 

When it is considered that the oxygen content of the return air of the 

average mine in this country rarely shows a decrease of more than 

one-half of 1 per cent of oxygen from the normal, and that the combustion of coal dust would not be seriously affected unless the deficiency exceeded 2 or 3 per cent or possibly more, it is clear that there 

can be little real basis for this impression. In this same connection, 

the idea has also been expressed that the fan was blowing in fresh air 

for the explosion to feed upon, and that this accounted for the greater 

destruction at the intake frequently manifested. When it is considered that the speed of a dust explosion, measured over only a short 

distance from the origin, as indicated, by the Al tofts experiments, is 

1,400 feet per second, a rate presumably less than when the explosion 

is under greater headway, and, on the other hand, that the speed of 

the ventilating current would be at most one-sixtieth part of that 

rate, it is obvious that the fresh air introduced during an, explosion

38970° Bull. 425 10 7
98 THE EXPLOSIBILITY OF GOAL DUST.

can not play any part in its propagation, except by the momentary 

mechanical pressure required to overcome the inertia of the air current. The fact that a dust explosion does usually se,ek the intake 

entries is due to another cause, namely, that the fresh air has dried 

the coal dust along the roads, whereas in the return air way of mines 

of any size the air current, being saturated with water vapor, has no 

such drying effect.

The presence of the dust is the all-important thing. This was peculiarly obvious in the Primero mine explosion, where certain intake 

entries on which there was no haulage and which were free from dust 

showed no manifestation of the flame having passed through them.

In general, dust explosions are apt to die away on long stretches 

of wet ground, along which the ribs are also damp. . However, if there 

has been much dry dust in that part of the entry nearer the origin, 

the blast may carry the dust through the wet zone and in this way 

continue the explosion beyond the area where it is not fed with fresh 

dust. Just what length of wet zone is essential to stop an explosion 

depends upon the violence of the explosion wave and the amount of 

dust carried in advance. Much is yet to be learned on this and other 

points from the experiments now being made here and in other 

countries. It should always be borne in mind that though coking 

is a conspicuous result of a coal-dust explosion in coking-coal mines, 

in mines producing coals that do not coke freely, such as those in 

the interior fields, or that do not coke at all, such as the lignites of 

the far West, few signs of coke or in the latter case none at all will 

result from an explosion. In such mines the dust will show a loss in 

volatile matter and an increase in ash; the chemical analysis must 

therefore furnish the clue as to the part played by dust.

Dust from black lignite or subbituminous coals, under some conditions, has proved to very explosive. For instance, in the Gallup, 

N. Mex., subbituminous field, violent explosions have resulted from 

blown-out shots. Coals of this field do not coke at all, and the mines 

are generally free from methane.

In the absence of the coking phenomenon, an explosion of considerable magnitude must be traced by the effects of flame and of 

violence. The former are particularly erratic in dust explosions, as 

previously indicated, for often such explosions traverse long distances 

without leaving signs of heating. This is probably due to several 

causes the speed attained by the flame, the excess of dust over that 

needed for propagation, and the blanketing effect of the rock dust 

that is present. It is probable that where extreme speed is reached 

the flame darts only through the center of the dust cloud, borne by 

the advance wave. When the explosive wave reaches an enlargement 

of th§ passageway or where side passageways lead off, giving a large
INVESTIGATIONS OF THE IGNITION 0? COAL DUST. 99

volume of air space, the excess dust may have opportunity for more 

or less complete combustion, giving a sudden burst of greater energy. 

Many observers have commented on the great explosive force often 

manifested at turnouts, overcasts, and sidings.

Probably the most sensitive record of heat is provided by the hair 

of victims. On the other hand, the observation of the writer is that 

damp paper and cloth are resistant to the quick flame of the explosion. 

When combustible material like loose paper is found in the path that 

had been traversed by the explosion, careful consideration is necessary 

to determine if it might not have been brought out from its former 

resting place by the depressive wave following the cooling of the 

burned gases. In the interior fields, where the practice prevails of 

taking 25-pound kegs or cans of black powder into the mines, the 

writer has observed, after a number of dust explosions, empty kegs 

that had been drawn out from the room gobs into the entry through 

which the explosion has traversed, though the explosion evidently did 

not enter the rooms.

Coal-dust explosions show little violence near the. point of origin 

unless originating from the ignition of a considerable volume of fire 

damp or from the discharge of a large quantity of explosive.

The characteristic dust explosion increases in violence as far as the 

dry, inflammable dust extends, until the entrance of the mine is 

reached, unless there are retarding influences like long, wet areas or 

areas containing an excess of shale or rock dust.

LABORATORY INVESTIGATIONS OF THE IGNITION OF

COAL DUST.

By J. C. W. FRAZER. 

INTRODUCTORY STATEMENT.

Although perhaps laboratory experiments had no great share in 

bringing about the general knowledge of the explosive character of coal 

dust, they are a valuable means of gaining information in advance of 

experiments carried out on a scale large enough to simulate mining 

conditions. The acceptance of the theory has come about only 

through such large-scale experimental work, which has shown conclusively that coal dust alone may be the cause of serious disasters 

or may propagate and prolong a comparatively harmless explosion 

caused from some other source, so as to produce a disaster extending 

through great areas.

The object of this part of the report is to describe in some detail 

the work which has been done on a laboratory scale bearing on the 

question of coal-dust ignition and inflammation. Many of the experiments on a somewhat larger scale are excluded, but some such early
100 THE EXPLOSIBILITY OF COAL DUST.

experiments are mentioned because of their historical interest and 

some of the most recent on account of their great importance in 

furnishing quantitative data.

EAELY EXPERIMENTS OF GALLOWAY.

Galloway a was one of the first to study this question from the 

experimental side. His experiments were carried out in a wooden 

box 5.71 meters long and 0.305 by 0.0152 meters cross section, through 

which a regulated current of air was passed. A hopper placed at 

one end served to introduce the dust, which was then carried by the 

air current 2 meters to a naked flame. Twq kinds of coal dust were 

used, of the following composition:

Composition of coal dusts used in Galloway's experiments.

Carbon (C). ...............................................................................

Ash......................................................................................

1.

85.3

5.0

1.3

.6

.7

.0

0.5

22.0

2.

82.0

5.4

1.6

1.0

.8

.7

3.5

15.0

Galloway's first conclusion is thus stated by him:

The results of these experiments and others which I have since made indicate in 

a conclusive way that a mixture of air and coal dust is not inflammable at ordinary 

atmospheric pressure.

However, on investigation he concluded that suspended coal dust 

could cause the explosion of a mixture of air and amounts of methane 

too small to be explosive in the absence of the dust.

IGNITION OF DUST FALLING ON FLAME.

Marreco and Morison 6 record certain crude observations made by 

persons whose names are not given, in which the tendency of coal 

dust to inflame was studied by allowing 5 liters of the powder to 

fall from a height of 6 meters upon a strong gas flame and noting the 

effect. Some of the dusts were ignited, and flame emitting much 

heat rose at times to a height of 10 meters. Other dusts were less 

inflammable, while still others failed to ignite at all. Professor Abel 

made certain experiments on ten different samples of coal dusts in 

an apparatus similar to that used by Galloway, with results entirely 

negative.

a Proc. Roy. Soc. London, 1876, p. 168; Annales des mines,ser. 7, vol. 11,1878, p. 229; Bull.Soc. iud. miu6- 

rale, ser. 2, vol. 6, 1877; vol. 7,1878, p. 017; vol. 9, 1880, p. 157. 

6 North of England Inst. Min. and Mech. Eng., 1879, p. 92.
INVESTIGATIONS OP THE IGNITION OF COAL DUST. 101

EXPERIMENTS OF VITAL.

While investigating the cause of a certain mine explosion Vital" 

concluded that coal dust had been an important factor in the accident, and he accordingly began certain laboratory experiments to 

see if it were not possible to ignite coal dust.

His apparatus (fig. 5) consisted of three parts an explosion gallery, a gas burner of special construction, used as the source of ignition, 

and a device for measuring the violence of the explosion. The 

explosion gallery was a straight glass tube(g) 3.5 centimeters in diameter and 2 meters long. The end of this tube at which the ignition 

took place was somewhat enlarged, the opposite end somewhat constricted. Along the outside of this glass tube was pasted a strip of 

paper marked in 2-centimeter divisions in order to measure the 

distance to which the flame was propagated. Inside of the tube, at 

distances of 1.5 to 1.75 meters from the larger end, were placed small 

pieces of lead wrapped in paper to serve as indicators of the character 

of the flame traversing the tube. The ignition was brought about by

o \°\

FIGURE 5. Coal-dust ignition apparatus of Vital.

means of a specially constructed gas burner (6) situated at the larger 

end of the gallery tube. The gallery was movable, so that the flame 

from the gas burner could, at the proper instant, be directed momentarily into the larger end of the glass tube along its axis. This gas 

burner was operated by a foot bellows (/). Intervening between the 

bellows and the lamp was a glass reservoir into which the air entering 

from the bellows was directed toward the bottom; By this arrangement the gas burner could be operated by pure air by direct connection with the bellows or it could be fed by a dust-laden atmosphere 

by placing dust on the bottom of the reservoir beneath the opening 

from the bellows. At the opposite end of the gallery was placed 

the arrangement used for estimating the violence of the explosion in 

the gallery. This consisted of a light pith ball (Ji) 2 centimeters in 

diameter, the surface of which was coated with a layer of ivory black. 

This ball was placed against the open end of the gallery and rested 

against the front of a graduated circle (i), the divisions on which 

were 2 degrees each.

a Annales des mines, ser. 7, vol. 7,1875, p. 180.
102 THE EXPLOSIBILITY OP COAL DUST.

Before the apparatus was used the following facts were ascertained: 

With the gas unlighted, the air blast carrying coal dust laid a heavy 

deposit of it on a porcelain plate set a few centimeters from the end 

of the tube. With the gas lighted, burning with pure air, the burner 

gave a blue flame, scarcely visible, 5 centimeters long. When the 

blast was operated with air containing coal dust in suspension, a 

bright blue flame was obtained which showed many brilliant sparks 

of burning carbon, but did not deposit soot. With the two indicators in position, the gallery free from dust, the flame of the 

lamp fed by dust-laden air and directed into the gallery, the flame 

did not change color, but elongated about 2 centimeters. The indicators were not charred; the pendulum recoiled, but without shock.

These preliminary facts having been ascertained, the gallery was 

charged successively with dusts 1, 2, 3, and 4. When the dust-fed 

flame was directed into the tube, a red flame traversed the gallery 

rapidly, and the tube was left filled with fumes. After these were 

removed the walls were found to be covered with a coating of dust 

impregnated with water and bituminous matter. The indicators 

were burned, and the pendulum received a shock. The results of 

these experiments are given in the following table:

Results of Vital's experiments.

Observations.

Flame: 

Length.............

Color...............

Indicators: 

No.l...............

No. 2... ............

Angular motion of pendulum.

Dust 1.

1.78m.............

liant particles.

.....do.............

14°................

Dust 2.

1.46m.............

liant particles. *

11°................

Dust 3.

0.15 m... ..........

out burning particles.

.....do.............

2°.................

Dust 4.

1.73m.

liant particles.

Do. 13°.

Dusts 1 and 2 when removed from the tube had lost their black 

color and become reddish. No crystalline particles were observed, 

but globules composed largely of water were found on the inside of 

the tube. The crucible tests on these dusts before and after the 

experiments gave the results contained in the following table:

Analyses of dusts before and after ignition in Vital's experiments.

Dry dust:

Ash........................................................

Dust 1.

Before 

(a).

0.31

34.1 

24.2 

41.7

100.0

After 

(ft).

11.3

21.2 

29.7 

49.1

100.0

Dust 2.

Before 

(c).

0.29

34.8 

24.4 

*. 40.8

100.0

After 

W).

9.7

23.5 

28.2 

48.3

100.0
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 103

 The coke residues from a and c were hard and brilliant, while those 

from & and d, collected after the explosion, were found to be pulverulent. A sample of reddish dust charred by an explosion in the mine 

from which the dusts used in the experiments came gave the following 

analysis:

Analysis of coal dust charred by mine explosion.

Volatile matter.........:...................,................... 27. 2

Ash............................................................ 26.1

Fixed carbon.................................................. 46. 7

100. 0

The conclusions reached as the result of this and additional experiments were:

(1) Certain finely divided dusts, rich in gas, take fire when brought 

into the air by a blown-out shot. These dusts, being decomposed,

yield an explosive gas mixture which would take fire from the powder.

(2) The flame is instantaneous; it burns or alters the small amount 

of coal dust raised in its path and goes out.

(3) The intensity of the phenomenon is intimately connected with 

the character of the dust and becomes practically nil if the size "of 

the particles is increased to an appreciable part of a millimeter.

(4) Other things being equal, the violence of the explosion would 

depend essentially on the physical conditions which determine the 

raising of the cloud of dust and its subsequent conduct.

(5) The presence of an excess of free carbon in the powder facilitates the production of an explosion.

Certain experiments'were performed by the Societ6 de I'lndustrie 

Minerale in a gallery used for testing lamps. During the experiments 

an air current was kept circulating through the apparatus. The 

inflammation was produced by igniting 50 grams of powder contained 

in a lead cartridge, after coal dust had been placed in the gallery. 

A second series of experiments was made in a gallery constructed 

for the purpose, the length of which could be varied. In this set of 

experiments the ignition charge was 30 grams of powder placed, on 

the bottom of the gallery in a paper or lead cartridge.

In the first series of experiments it was noticed that the flame from 

the powder was elongated from 3 meters to 6£ meters. In the second 

series, when the gallery was 4 meters long and the ignition charge 

was placed 2 meters from the orifice a large flame shot out of the tube 

on the ignition of the charge; when the gallery was 8 meters long 

the flame did not emerge. Thus they were able to secure the ignition 

of the coal dust in this way, but the amount of such ignition must 

have been small, as paper was not ignited at 3 meters from the cartridge.
104 THE EXPLOSIBILITY OF COAL DUST. ' 

EXPERIMENTS OF HALL AND CLARK,

Hall and Clark a performed certain special experiments to study 

the effects of blown-out shots. They were the first to carry out 

experiments under conditions approaching those existing in mines. 

They ignited various charges of pow.der at the bottom of an inclined 

gallery along which was placed the coal dust under investigation. 

The length of the flame was determined by suspending pieces of 

inflammable cloth at regular intervals along the gallery. In many 

of their experiments the flames were voluminous.

This work is mentioned in more detail elsewhere, and is repeated 

here merely because it forms the beginning of the great amount of 

work which has been done on an extensive scale, and because it was 

repeated on a smaller scale shortly after by Marreco and Morison. 6

These investigators carried out experiments on a much smaller 

scale than those of Hall and Clark, but otherwise there was some 

similarity in their method of working. The apparatus used consisted 

of a long rectangular box divided longitudinally into two compartments by a vertical partition reaching nearly to the bottom of the 

box. One of the longitudinal chambers thus formed was 3.6 meters 

long, the other 3 meters. One end of the apparatus was closed, and 

at the second end of the longer gallery was attached a connection 

for introducing a regulated current of compressed air. The second 

end of the shorter gallery was left open. Two small cannons were 

placed at the closed end, each directed along the axis of one of the 

galleries. They were discharged electrically and the connections 

so made that they could be fired either simultaneously or one at a 

short interval after the other. The air current which came into the 

longer gallery passed under the partition and through the shorter one 

and had a velocity of 1$ to 3 meters. The charges of powder used

were not given, nor the composition of the coal.

The results of the work showed that dusts conducted themselves 

very differently under these conditions, according to their nature. 

With some the flame issued from the box, with others the flame was 

only a small fraction of the length of the box. The greatest effects 

were produced when the cannons were fired at short intervals apart, 

the first shot serving to charge the air of the second gallery with dust. 

The shot then fired into the second gallery produced more violent 

explosions. In many of their experiments the box was burst open.

As the result of these experiments they concluded that.if they had 

been able to perform their experiment on a sufficiently large scale, 

the results would have been comparable in every way with a mine 

explosion.

o Communicated to the North of England Inst. Min. and Mech. Eng., June, 1876.

6 North of England Inst. Min. and Mech. Eng., 1879, p. 85; Annales des mines, ser. 7, vol. 15,1879, p. 374.
INVESTIGATIONS OP THE IGNITION OF COAL DUST. 105 

EXPERIMENTS OF ABEL.

Abel ° attempted to secure the explosion of coal dust on a small 

scale by means of a charge of 26 grams of powder placed on the bottom 

of a wooden box, which was used as the explosion chamber. He 

judged the effect of the dust by the extent to which the flame of the 

powder was elongated by the burning of the dust. His results were 

negative, as the length of the flame was sometimes longer but sometimes shorter than the flame of the powder alone. But he concluded 

that possibly with the large flame and violent agitation from a 

blown-out shot dust alone would propagate a flame farther than the 

experiments on a small scale seemed to indicate.

EXPERIMENTS OF MALLARD AND LE CHATELIER.-

In 1882 Mallard and Le Chatelier b published the results of their

work. In the course of this work the authors undertook a study on a 

laboratory scale of many of the important conditions influencing 

the ignition and the explosive character of coal dust. This work is 

of great historical interest, because of the conclusions reached by its 

authors and the influence which these conclusions have exercised 

in the development of the coal-dust theory. The work is also of great 

scientific interest because of its scope and the number of problems 

of a fundamental character which the authors have undertaken to 

investigate. Their experimental work is prefaced by a summing up 

of the evidence in support of the theory, both the evidence furnished 

by laboratory experiments and that obtained from mine accidents 

where coal dust had been assumed to be a factor.

Their own laboratory experiments are divided in the following way:

Chapter I. The study of the phenomena presented by the mixture of coal dust and 

air containing no methane.

Chapter II. The study of the phenomena presented by mixtures of coal dust with 

air containing an amount of methane too small to form an explosive mixture.

Chapter III. The study of the phenomena presented by mixtures of coal dust with 

an explosive mixture of air and methane.

Our interest in this work, for the present, centers in Chapter I. 

This chapter is subdivided into the following six sections:

Section 1. A study of the influence of the size of the flame.

Section 2. A study of the influence of the velocity of the air current.

Section 3. A study of the influence of the size of the dust particles.

Section 4. A study of the influence of the nature of the coal.

Section 5. A study of the influence of the relative proportions of dust and air.

Section 6. The velocity of propagation of the flame.

o Annales des mines, ser. 7, vol. 20,1881, pp. 121-159. 

6 Idem, ser. 8, vol. 1,1882, pp. 5-98.
106 THE EXPLOSIBILITY OP COAL DUST.

The experiments were made in two forms of apparatus. The 

first resembled that previously used by Galloway, Morison, and 

Abel. It consisted of a wooden box, 4 meters long, 0.4 meter high, 

and 0.15 meter wide. One extremity communicated with a ventilator 

capable of giving a pressure of 5 centimeters of water. At 50 centimeters from this end was a device to regulate the flow of air, the 

velocity of the ventilator being maintained uniform. At a point 

25 centimeters farther there was placed on top of the main box or 

gallery a second box, perforated for the introduction of coal dust. 

The arrangement of the regulator with reference to the point of introduction of the dust was such that the eddy produced at the regulator 

served to disseminate the dust through the air. At 2 meters farther 

a removable glass window was placed, which permitted the introduction of a lamp and the observation of the results. The other 

end of the gallery was open to the outside air, 50 centimeters beyond 

this window. When the dust burned it gave a large flame, filling 

the whole section and extending out of the orifice.

The second form of apparatus used was simply a cubical wooden 

box of 50-centimeter dimensions. At the center was placed a gas 

flame directed downward in order to spread it out. In testing the 

dust in this form of apparatus a double handful of the dust was held 

about 1£ meters above the box, and was allowed to fall between the 

fingers in such a way as to subdivide it as much as possible. In falling the columns of descending dust carried along a considerable 

amount of air by the time the dust reached the flame, and the eddy 

produced in the box by this air kept the atmosphere charged with the 

dust. If the sample was inflammable, it ignited at the gas flame.

The sources of heat investigated by the authors were, first, the 

normal flame of the Davy lamp; second, the same after regulating 

its flame to a height of 5 centimeters; third, a large gas flame; fourth, 

a large roll of burning paper.

With finely powdered coal of an inflammable character it was 

found that in the first form of apparatus described above inflammation took place instantly when the last three sources of heat were 

used. With a normal flame of the Davy lamp flashes occurred, after 

which the whole was inflamed, the duration of this phenomenon 

being only about two seconds.

Coal dust collected in the gallery of the same mine, but less finely 

divided, took fire immediately on contact with the gas flame and roll 

of burning paper, and after the end of some seconds it ignited from 

the flame of the Davy lamp, burning 5 centimeters high. But with 

the normal flame of the Davy lamp, ignition occurred only after 

some time, or not at all.

The coarser dust collected from the floor of a gas works ignited 

after some seconds from the third and fourth sources of heat, but not
INVESTIGATIONS OF THE IGNITION OF" COAL DTJST. 107

from the others. Another sample of a different dust was found to 

be inflammable from all four sources.

The conclusion of the authors was that an inflammable mixture of 

coal dust and air required for its ignition a flame of a certain minimum 

volume, varying with the nature of the dust. The same is true of 

explosive mixture^ of gases ignited by an electric spark, a certain 

minimum spark being necessary, varying with the character of the 

gas mixture. The great difference is the enormous size of the source 

of heat necessary to ignite the dusts as compared to the electric 

spark. By increasing the size of flame above this minimum the 

rapidity of inflammation is increased and for a certain volume 

becomes practically instantaneous and nothing is gained by increasing 

the size of the flame beyond this volume. This maximum volume 

seemed to be less than a cubic decimeter for the dusts investigated.

Some indication of the effect of the size of the dust particles is

seen from the above-described experiments, in which it was found 

that the more finely divided were the dusts the more inflammable 

they became and the smaller was the size of the flame necessary for 

their ignition. Yet in many tests these authors thought that fineness of division was a secondary matter. Some coals were found 

inflammable whatever the size of the particles. This fact is not 

opposed to the principle of greater inflammability of finely divided 

coals, for the authors explain that the dusts used by them were not 

screened to a certain size, and in all samples there was a sufficient 

amount of the fine dust that remains longest in suspension to cause 

ignition on arrival at the source of heat. In this way the occurrence 

of fine dust in a sample, the average size of whose particles w.as large, 

would mask the effect that might be anticipated from the relatively 

large average size of the particles. For instance, two samples of 

dust may be very different with respect to fineness when introduced 

into the apparatus, but in the course of their passage to the flame, 

situated some distance away, the largest particles are deposited 

and only the particles smaller in size reach the flame, so that at 

this point both dust clouds are very similar as regards the size of the 

particles remaining in suspension.

The velocity of the air current which carried the dust in suspension 

was found to have a great influence on its degree of inflammability. 

One of the samples studied ceased to inflame for velocities under 1 

meter or above 4 meters. The reason appeared to the authors to be 

that with the weak air current dust was deposited from suspension 

before reaching the flame, while with currents faster than 4 meters 

the particles traversed the flame too rapidly to become ignited. .

In the course of the experiments mentioned above the authors 

established the fact that dusts of certain coals might be considered 

inflammable while others yield noninflammable dust. Many authors
108 THE EXPLOSIBILITY OF COAL DUST.

have previously attempted to connect the inflammability of the dust 

with the gaseous character of the coal from which it was derived, 

without, however, giving any experimental evidence of such connection. The authors took up this question and employed for the investigation both forms of apparatus described above, after having 

shown previously that the behavior of each dust was similar in both 

forms of apparatus. As a result of this investigation the authors 

were able to arrange the coals investigated into two groups, first, 

those whose dusts were inflammable, second, those whose dusts were 

noninflammable. These results are summarized as follows:

Percentage of volatile matter in inflammable and noninflammable dusts.

Inflammable dusts:

Sample 1.................... 32. 0

Sample 2.................... 35.0

Samples. ................... 39.0

Sample 4.................... 50. 0

Noninflammable dusts:

Sample 1...................... 19. 5

Sample 2. ................... 24.6

Samples. ................... 19.0

Sample 4. ................... 18.0

In stating their conclusion the authors say that a coal to yield 

an inflammable dust must contain 30 per cent or more volatile 

matter. The last sample investigated was a lignite, containing 50 

per cent volatile matter. It was also found to be the most inflammable of all.

In stating that a coal dust is noninflammable the authors do not 

mean that the coal dust does not burn, but that under the conditions 

of the experiment the dust suspended in the air is not capable of 

propagating the combustion much beyond the confines of the source 

of inflammation. The propagation of the flame they consider to 

be a complex function of the temperature of combustion, of inflammation, of distillation, etc. It is conceivable that this combustion

could be arrested under certain conditions and that the air and dust 

mixture would not inflame, while in other circumstances it would 

burn more or less easily. It is for an analogous reason that a mixture 

of air with methane in amounts insufficient to form an explosive 

mixture can be rendered explosive merely by raising somewhat the 

temperature of the mixture. The dusts of all coals are certainly 

combustible under the proper conditions, but only a certain number are inflammable under the conditions set by the authors. The 

proportion of volatile matter, according to the authors, is not the 

only cause of the inflammability of coal dust, as they consider that 

those volatile constituents which have already been partially 

oxidized, would be expected to be more inflammable than those same 

substances unoxidized, just as alcohol vapor is more inflammable 

than vapors of petroleum. In other words, the authors believe that 

the inflammable character of the coal dust depends not only on the 

amount of volatile matter contained in the coal, but also upon its 

character. A further influence on the inflammable nature of a
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 109

coal dust would be the ease with which the volatile matter is 

expelled.

The authors confirm the conclusions of Galloway that the amount 

of dust suspended in the air must be considerable to render the 

mixture inflammable that the dust clouds should be very dense, 

such that a thickness of 50 centimeters of the mixture in bright 

daylight intercepts completely the light from a candle placed in it. 

The authors made no special measurements in this connection, but 

conclude from their experience that Galloway was correct in assuming that the amounts of suspended dust most likely to give an 

inflammable mixture would be 1 kilogram per cubic meter of air.

Berthelot has stated that such an excess of dust is necessary 

because the only part of the dust particle that -enters into action 

is its surface, whereas in gases the mixture exploding most violently contains the constituents in proper proportions for complete 

combustion.

The authors consider that to put in suspension such a quantity 

of dust and keep it suspended would require a violent agitation in 

the air, because the density of such a mixture is nearly double that 

of the pure air, and hence only a considerable force can overcome 

the tendency of the two to separate; besides, the dust would be 

deposited soon after the cause of agitation ceased. As previously 

mentioned, the authors show that according to their experiment a 

velocity of 1 meter a second is not sufficient to keep the air charged 

to the point of inflammation.

In studying the velocity of propagation of the flame the authors 

attempted to use the same method by means of which they measured, the velocity of propagation of the flame in gas mixtures, but 

they found that in mixtures of coal dust and air not much agitated 

there was no appreciable velocity of propagation of flame, and 

conclude that if it exists it must be less than 1 centimeter. The 

propagation appears to be effected by the internal movements of the 

air instead of by conductivity or radiation.

When the air and dust mixture is agitated by considerable internal 

movements, the velocity of propagation is still small, less than 1 

meter, which shows the great difference between the velocity of 

such a flame and that in an explosive mixture of gases. In confirmation of this statement the authors call attention to the fact 

that when coal dust was ignited in their long apparatus a sheet of 

paper which covered the hole in the side of the gallery was not 

broken and was scarcely puffed out by the pressure within.

In applying their results to mining conditions the authors say 

that the accidents that can be attributed to dust alone are very 

rare, not dangerous, and that the flame does not -extend farther 

than 50 meters. The dangerous explosions occur mostly in gaseous
110 THE EXPLOSIBILITY OF COAL DUST.

mines, and whether the dust is inflammable or not the conditions 

do not permit doubting the presence of methane. Lignite mines 

which are slightly gaseous, if at all so, but which contain dusts more 

inflammable than coal dust, have never suffered from serious explosions. Further, all the accidents attributable to dust alone are caused 

by blown-out shots directed to the floor of the mine. The results 

of their experiments have confirmed these facts by showing the 

reason for them the slight inflammability of the coal dust.

According tq Galloway and to Mallard and Le Chatelier, the 

quantity of dust which must be suspended in the air to give an 

inflammable mixture is far beyond what could possibly be in the 

air even in the most dusty parts, and it requires a very violent 

agitation to bring such an amount of dust into the air and maintain 

it in suspension. Further, the authors have shown that dusts are precipitated very rapidly from the air whenever the causes which brought 

them into the air cease to operate. Their experiments on the velocity 

of propagation of the flame in air and dust mixtures show it to be 

practically zero. These two facts tend to limit the extent of a dust 

explosion, because before the flame can travel an appreciable distance 

there ceases to be a sufficient amount of dust suspended in the air to 

propagate the inflammation. They conclude, therefore, that coal 

dust alone is of very little danger in mines, but in the presence of 

small amounts of methane the danger is much increased. Coal dusts 

play an important part in mine accidents only by lowering the explosive limit of an air and methane mixture.

LATER EXPERIMENTS BY GALLOWAY.

After his first investigation on the question of the explosion of 

mixtures of air and coal dust, Galloway performed a number of 

other experiments, as a result of which he altered his first opinion, 

which was stated above in discussing his work. His first conclusion 

was that coal dust, to be a factor in mine,explosions, must be suspended in air that contains at least some methane. His later work 

led him to the conclusion that coal dust alone mixed with air would 

under the proper conditions form an explosive mixture, and that 

in all probability it figured at times as the sole cause of certain mine 

explosions.

EXPERIMENTS OF THORPE.

From this time on work on the question of coal-dust explosions 

was done on a comparatively large scale. Interest was then taken 

in the matter by several European governments, and special commissions were appointed by these to investigate the question by 

instituting experiments to demonstrate conclusively the explosive 

character of a mixture of pure air and coal dust. These experiments
INVESTIGATIONS OF THE IGNITION ,OF COAL DUST. Ill

have been discussed in another portion of this bulletin. Before 

describing certain experiments carried out under conditions which 

have been particularly well controlled attention will be called to 

several demonstrations of the explosive character of coal dust made 

on a laboratory scale as lecture experiments. A number of such 

experiments have been described, and of these one described by 

Thorpe," with which it is possible to illustrate many features of a dust 

explosion, will be taken up first.

The apparatus (fig. 6) consists of a long wooden gallery in two parts, 

A and B, which together are 3.66 meters long, each 12.7 centimeters 

square in cross section. These two parts fit into opposite sides of a 

similar gallery (C) placed at right angles to A and B and intended to 

represent a second gallery of a mine crossing the main one at right 

angles. Each of these galleries is covered for its whole length by 

a hinged top in two parts, which during the experiment are tightly 

clasped down. The box should be made of 1-inch oak and screwed 

together. A shutter (a) fits in the slot s. This end of A slips into

FIGURE 6. Coal-dust ignition apparatus of Thorpe.

a quadrangle box D, 22.86 centimeters square, which is provided 

with a door (6) and a small hole (c), through which a tube can be 

inserted.

The coal dust is put into the box D and a blank cartridge is fired 

from a small pistol through c. The dust raised by the concussion 

ignites from the flame of the powder, and the flame of the burning 

dust goes several feet out of the ends of the box. To illustrate the 

effect of a local explosion of methane, D is filled with an explosive 

mixture of methane and air, with a in place; a is then withdrawn 

and a flame applied at c. The resulting gas explosion charges the 

air with dust and ignites it, and the flame rushes along the gallery 

and shoots out at the end, being propagated the length of the gallery 

and 4 or 5 feet out into the air. The success of the experiment 

depends on the nature of the coal dust and the character of the initial 

cause. Some dusts are not brought into the air by concussion and 

the flame soon dies out. The condition of the coal dust with respect 

to dryness and fineness of division has a great influence on the character of the explosion.

o Jour. Chem, Soc., vol. 61, p. 414.
112 THE EXPLOSIBILITY OF COAL DUST.

By the use of lycopodium powder instead of coal dust one can 

show in this apparatus many .things observed in mine accidents. 

For example, it is possible now to trace an explosion to its source 

by the way the charred dust is thrown against the props in the mine. 

The deposition of dust is always on the opposite side from the explosion, because the eddies that exist at such points drive the dust to 

the rear of the object. By putting small pegs in the floor of the 

experimental gallery it can be shown that the lycopodium powder 

is swept away clean from in front of the pegs and heaped up behind 

them. It is also well known that dust explosions increase in violence 

with the distance from the source of the explosion. At the point 

of origin the disturbance is small, while a few Imndred yards away 

the violence of the explosion is remarkably greater.

: REDUCTION OF PRESSURE FOLLOWING EXPLOSIVE WAVE.

It has been said by some that mine explosions are frequently so 

violent that the diminution in pressure at places is great enough to 

draw out methane inclosed in the coal. This statement has obtained 

many believers. The only experimental evidence in regard to it was 

obtained by Greenwell.a The apparatus used for his experiment 

was a box closed at one end and open at the other. The box is 3 feet 

long, and at right angles to this and opening into it is another box 

smaller than the first and fitted with a valve on which the outside 

atmosphere acts. When a charge of dust was fired in this apparatus 

the violent outrush of air drew out some of the air in the small box 

connected to the side of the larger one, and the valve was driven in 

because of the diminished pressure produced in the small box by the 

withdrawal of a portion of the air which previously filled it at atmospheric pressure. This does not show a diminution of pressure in the

main gallery, according to the author, as the position of the side box 

would cause the withdrawal of part of the air it contained by the principle on which an injector operates. By a special manometer, which 

he devised to show that an area of low pressure exists around the 

flame of a Bunsen burner, Thorpe was able to demonstrate that no 

diminished pressure exists along the side of the gallery during an explosion, but that on the contrary there was always considerable 

pressure against the sides and top of the^box. Hence the statement 

that gas is brought into a mine from the face of the coal because of 

diminished pressure produced in certain areas during an explosion 

does not receive confirmation by this experimental work.

a Trans. Manchester Geol. Soc., vol. 10,1870, pp. 20-27.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 113 

EXPERIMENTS OF ENGLER.

In 1907 Engler" published a''description of a form of apparatus 

designed to demonstrate the explosion of coal dust on a laboratory 

scale. He showed that substances like bituminous coal, meal, and 

naphthalene, which are capable of giving gas, can be exploded by 

an electric spark. He showed also that substances such as soot and 

charcoal do not ignite in air alone, but will explode in a mixture of 

air with a small amount of combustible gas, even a mixture that 

would not ignite in the absence of the dust. Thus in air containing 

2.5 to 3.5 per cent of methane the presence of soot or charcoal dust 

brought about the explosion of the mixture, and this explosion was 

increased in violence by the use of dust from bituminous coal. A 

bituminous coal dust that does not explode when mixed with air 

will do so if the air contain a small percentage of methane. The 

apparatus which Engler used to demonstrate the explosion of coal 

dust is shown in figure 7. A is a flask of 250 to 

500 cubic centimeters capacity. A quantity of 

coal dust is put into B, a small amount of 

which can be introduced into A by elevating B. 

The wires c c lead from an induction coil, the 

spark gap being between the two platinum 

wires at a. By blowing air into Z> in jets from 

a rubber bulb the dust is brought into suspension, and as the cloud passes (a) the ignition of. 

the dust takes place, if the dust is that of the 

proper kind of bituminous coal. In a similar 

piece of apparatus filled with a mixture of air 

and 2.5 to 3.5 per cent of methane, or even less, 

no explosion takes place when the mixture is sparked in the absence of 

dust, but on introducing a small amount of a coal dust that has been 

found to be nonexplosive, and blowing it into the air as before by 

means of a rubber bulb, the contents of the vessel explode with 

great violence, and the stopper is blown out of the vessel or the 

glass flask is shattered. The same is true when soot or powdered 

charcoal is used in place of the nonexplosive coal dust.

LECTURE EXPERIMENT OF BEDSON AND WIDDAS.

A simple lecture experiment to show the inflammable character 

of finely ground coal dust is described by Bedson and Widdas. 6 

Their apparatus is shown in figure 8. It consists of two glass tubes, 

a and Ji, each 3.81 centimeters in diameter, a being 7.62 centimeters

a Chem. Zeitung, vol. 31, p. 358; Jour, fur Gasbeleuchtung und Wasserversorgung, vol. 50, p. 488.. 

6 Trans. Inst. Min. Eng., vol. 32, 1907, p. 531.

38970° Bull 425 10 8
114 THE EXPLOSIBILITY OF COAL DUST.

long and li 30.48 centimeters. The tubes a and Ji are connected by a 

collar (/) which holds in position the cotton gauze e, on which is 

placed a quantity of dust (g). Into the other end of a is fitted a 

stopper (6) through which passes the glass tube c, the 

upper end of which (d) comes a short distance below e. 

By means of an air blast blown through c, the dust is 

blown from the gauze and disseminated as a cloud, which 

is carried upward by the air blast to the open end (i) 

of the tube Ji. When a naked flame is applied to i the 

cloud of dust ignites and the flame of combustion travels 

down the tube. /

EXPERIMENTS OF HOLTZWART AND MEYER.

 I

Apparatus 

of Bedson 

and Widd a s for 

use in lectures.

In 1891° the attention of Rud. Holtzwart and Ernst 

von Meyer was directed to an investigation of the cause __ 

of explosions which had occurred frequently in factories FIGURE s. 

where lignite briquets are manufactured. The principal 

result of their work was a study of the explosive 

character of lignite dusts mixed with air. Their apparatus 

(fig. 9) consisted of an explosion tube (E) of 50 cubic 

centimeters capacity, having two platinum wires sealed through its side 

about midway the length of the tube. These wires (i i} are about 3 

to 4 millimeters apart. The spark used as the source of ignition was 

obtained from an induction coil operated by two 

strong Bunsen elements. In one end of this tube 

(fc2 ) is fitted a one-hole rubber stopper, through 

which passes a glass tube bent downward at a 

right angle. The longer limb of this tube (m) is 

immersed under water. A weighed quantity of

dust is placed against the stopcock H. A is a

glass bottle of 600 cubic centimeters capac- 

*' " fe ity; B, a bottle of 3 

liters capacity. C is a 

reservoir of water 

placed at a height of 1.5 

meters above the level

FIGUEE 9. Coal-dust ignition apparatus of Holtzwart and Meyer. °* * ne water HI _t>. In

each of the experiments performed 0.18 gram of the dust was used. Water from the 

reservoir (C) is allowed to flow into B, compressing the air contained 

in B to a pressure equal to the difference in the level of the water in

oDlngler's Polytechnisches Journal, vol. 280,1891, pp. 185 and 237.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 115

the two vessels. The screw cock c is then opened until the air contained in A is'compressed to a definite pressure indicated by the manometer D. This pressure was varied in the course of study of each 

sample. After the proper pressure was secured in A and the apparatus 

was connected up as indicated, the passage of the spark between the 

terminals i i is started. H is then quickly opened and closed and 

the character of the explosion observed. The character of the explosion is indicated somewhat by the behavior of the water closing 

the open end of m.

Eight samples of dust were tested. The results of thes'e experiments and the analyses of the dusts are given in the two following 

tables. The samples were collected from various parts of the briquetting plant, put through a fine sieve, and dried for a long time over 

sulphuric acid. To remove the last of the moisture the samples were 

heated to 60° or 70° before analysis.

Results of experiments by Holtzwart and Meyer with explosions of lignite dust.

Sample

No.

1

2

3

4

5

C

7

8

Results of tests for specified pressures of air in A in

centimeters of mercury.

2 centimeters.

2 negative, 1

very weak.

2 negative...

2 negative, 1

very weak.

2 very violent.

2 negative...

2 negative, 1

weak.

2 strong.....

2 strong, 1

negative.

3 centimeters.

1 negative, 1

weak.

2 negative...

.....do......

2 very violent.

2 negative. . .

2 rather

strong.

2 strong.....

.....do......

4 centimeters.

2 negative...

.....do......

.....do......

2 very violent.

2 negative, 1

weak.

2 rather

strong.

2 strong.....

.....do......

8 centimeters.

Negative....

.....do.... .

.....do......

2 very violent.

Negative....

2 rather

strong.

2 strong.....

.....do......

Remarks.

Tendency to explode small; in 8 experiments 6 negative.

No explosion.

Dust not inclined to explode.

In 7 experiments 6 negative.

Sample inclined to explode; in 9 experiments 7 positive.

Dust explosion very strong.

Do.

Analyses of lignite dusts used in experiments by Uoltzwart and Meyer.

6\ Ash-free ............................................

°\Ash-free. ...........................................

Ash.

15.93

14.05

9.44

6.12

7.08.

C.

56.93 

67.70 

57.72 

67.10 

60. 70 

67.09 

01.33 

65.33 

59. 50 

04.10

H2 .

5.10 

0.14 

4.73 

5.5 

5.22 

5.70 

4.00 

4.96 

4.53 

4.88

N2 .

0.93 

1.10 

.74 

.80 

1.15 

1.27 

1.11 

1.21 

1.22 

1.33

S.

4.13 

4.90 

3.16. 

., 3.68 

2.00 

2.21 

.03 

.08 

.60 

.65

02.

10.92 

20. 10 

19.00 

22. 80 

31.43 

23.07 

26. 15 

27.82 

27.01 

29.04

A glance at the above table shows a great difference in the conduct 

of the coals with respect to their inflammability. There is, however, 

no apparent connection between their explosive character and their
116 THE EXPLOSIBILITY OF COAL DUST.

elementary composition. Coal No. 4 is chemically very closely 

related to No. 5, but their conduct with respect to their explosive 

character is entirely different. It is probable that the imflammable 

character of the dust is related to the condition of the surface as well 

as to the bituminous matter of the coal. Coals Nos. 4, 6, 7, and 8 

are seen by inspection of the analyses to be very explosive, while No. 5, 

chemically very similar to these, is not explosive. Nos. 2 and 3 

were found to be nonexplosive, and No. 1 exploded only once. The 

character of the explosion could be judged by the eye. With Nos. 1 

and 3, as propagation of the flame was very slow, its passage through 

the tube could be readily followed by the eye, appearing to have a 

velocity very much like that of propagation of a flame in a mixture 

of carbon monoxide and oxygen near its explosive limit; but in 

Nos. 4, 7, and 8 the explosion was sudden, and the whole tube filled 

with a flash of light. In case of such violent explosions much gas 

escapes from the tube (m), while in weak explosions no gas escapes. 

The experimenters failed to secure an explosion of lignite dust except 

when the dust was blown in as indicated above. When the dust 

was placed in the tube E, and the tube was shaken while the spark 

was passing, no explosion was obtained even with the most explosive 

dusts. This shows the great importance which the method of 

introducing the dust can exercise on the character of the explosion. 

To the authors the character of the explosion of lignite dust under 

these conditions appeared very similar to that of an explosive gas 

mixture.

In one experiment, A and E were filled with a mixture composed 

of 10 per cent carbon monoxide and 90 per cent air. This amount 

of carbon monoxide and air was just below the explosive limit for 

these gases. A sample of coal No. 4, which was one of the most 

explosive coals investigated, was exploded in this mixture. When 

the coal was blown into the apparatus the explosion which resulted 

was not noticeably stronger than when the coal was used with air 

alone.

Their study was confined entirely to lignites, but they considered 

that a similar study of bituminous coals would be of greatest importance in furnishing data regarding the explosive character of such 

coals.

They further investigated the gases which were evolved from 

lignites when heated. Even at 400° C. the gases which were given 

off were found on analysis to be in such small amounts and of such 

nonexplosive nature that they could not be considered as a source 

of the explosions which so frequently occur in briquet ting plantsthe real cause of the explosions, according to the authors, must be 

the coal dust.
INVESTIGATIONS OF THE IGNITION OP COAL DUST. 117

LABORATORY EXPERIMENTS OF BEDSON AND WIDDAS.

Convinced of the utility of the method adopted, by Holtzwart and 

Meyer in their investigations of the explosive character of lignite 

dusts, Bedson and Widdas a undertook a similar investigation of 

mixtures of coal dust and air. The apparatus they used for this 

work differed in certain respects from that used by Holtzwart and 

Meyer. In place of the electric spark used by those authors as the 

source of ignition they substituted in certain experiments a gas flame 

or a spiral of platinum wire heated electrically. The apparatus 

shown in figure 10 consists of a bottle (a) of about 1,900 cubic centimeters capacity, closed by a three-hole rubber stopper, through 

which pass three glass tubes (Z>, c, and e). The tube 6 was connected with a foot bellows, c with an open manometer (d), and e with 

the chamber in which the explosion takes place. This chamber in 

the first form of apparatus is a cubical tin box (/) of 10.16 Centimeters 

dimension, provided with mica windows (</) at the front and back. On 

two opposite sides of the 

box are openings 3.81 

centimeters in diameter, 

provided with collars 

permitting the attachment of the glass tubes 

I and m. The glass tube 

e, communicating with 

the bottle a, is provided 

with a stopcock (p) and 

was bent downward (inside of the glass tube ra) 

at n, in front of which is placed the weighed sample of dust. Two 

other openings (h and t) into the top and bottom of / are for the 

introduction of the gas flame or other source of ignition.

The operation is carried out in the following way: A weighed 

quantity of dust is placed in front of n, in the glass tube m. The air 

in the bottle a is compressed to the desired pressure by means of the 

foot bellows connected to Z>. After placing the gas jet (q) in position 

the stopcock p is quickly opened. The outrush of air from e blows 

the dust into the air and carries it to the source of ignition^ where the 

behavior of the dust is observed through the windows. The first 

series of experiments was made on finely ground samples of lignite. 

The sources of ignition used were an electric spark, electrically heated 

platinum wire, and a small gas flame. The second series of experiments was a study of finely ground dust of each of the following 

materials: Brown coal, bituminous coal, dant (slack), charcoal, wheat 

flour, wood sawdust, lycopodium powder, metallic aluminum, and

FIGURE 10. First coal-dust ignition apparatus of Bedson and 

Widdas.

a Trans. Inst. Min. Eng., vol. 32,1907, p. 529.
118 THE EXPLOSIBILITY OP COAL DUST.

metallic magnesium. The source of ignition used in each case was a 

small gas flame, the amount of dust 1 gram. In every material 

except dant and charcoal inflammation took place.

In a second paper 0 the same authors record the results of further 

experiments on coal dust with apparatus (fig. 11), somewhat different 

from that described above. In order to secure better control of the 

conditions of ignition they substituted a coil of platinum wire for the 

gas flame and electric spark used in some of their earlier experiments. 

They could in this way obtain a considerable range of temperature, 

and could measure approximately the temperature of the coil during 

any experiment by measuring the current passing through the coil. 

Below-is given the current that was found necessary to produce 

inflammation of each of the dusts named:

Current required to produce ignition in specified dusts.

Amperes. 

Brown coal................................................... 10. 5

Busty seam, bright coal........................................ 11. 5

Hutton seam, coal...........'................................... 11. 5

Lycopodium................................................... 11. 5

Brockwell seam, cannel........................................ 12. 5

Harvey seam, splint........................................... 17. 0

A current of 17 amperes was insufficient to produce an ignition 

with anthracite or dant. The samples used in these experiments 

were passed through a 100-mesh sieve and were air dried. To show 

the effect of drying on the temperature of ignition of those same 

coals, experiments were carried out in the same way as those described 

above, except that the coals were dried. The results were as follows:

Current required to produce ignition of dried dusts.

Amperes.

Brown coal............................................... 9.8-10.0

Busty seam, bright coal.................................... 11. 0-11. 5

Hutton seam, coal.......................................... 11.0-11. 5

Brockwell seam, cannel.................................... 11. 5-12. 6

Harvey seam, splint....................................... 13. 0-15. 0

Further experiments were made on the effect of moisture by exposing the coal dusts under a bell jar over water. Brown coal dust, 

after seventy-two hours' exposure, and Hutton seam coal dust, after 

ninety-six hours' exposure, required, respectively, 12.2 and 13.5 

amperes. In another set of experiments, the freshly ground dust 

was mixed with water to a thin paste and allowed to dry for six 

days in the air. At the end of that time it was found to contain 3.1 

per cent moisture, and to require 13.5 amperes for its ignition. The 

coal was mixed with water the second time and left to dry, and on the 

fifth day it was found to contain 3.77 per cent moisture, and to require

a Trails. Inst. Min. Eng., vol. 34,1908, pp. 91-97.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 119

13.S amperes for its ignition. At the end of eight days it contained 

1.78 per cent moisture, and required 13.8 amperes for its ignition. 

The conclusion of the authors regarding the effect of moisture on the 

inflammability of coal dust is that in order to prevent an ignition of 

an inflammable dust it must be made so damp that it can not be 

blown into the air as a cloud by a jet of air, but that an increase of 

moisture tends to raise the temperature of inflammation.

It was also found that exposure to air rendered freshly ground dust 

less inflammable. A sample of dust which in the beginning required 

12.5 amperes for ignition required 14 amperes at the end of seventeen days.

Experiments were also made to test the effect of incombustible 

dusts on the inflammability of coal dust. The result of these experiments, summed up in the table below, was to show that the temperature of ignition of such a mixture was higher than that of the

coal dust alone.

Effect of mixture of sand with coal dust on current required for ignition.

Character of coal.

Do...........................................

Do. ..........................................

Do...........................................

Do...........................................

Do..... ......................................

Do...........................................

Do...........................................

Amount of 

sand to 1 

gram of 

coal.

Grams.

1

1.5

2

.5

1

1.5

3

Current 

required 

for 

ignition.

Amperes. 

12.5

13

13. 5

15.5

12.5

13

14

14

15

Remarks.

While these results afford evidence of the difference in conduct of 

different coals regarding their temperature of ignition, they give 

no measure of the relative inflammability of the dusts, as the only 

means available of judging the results was by the eye, and they 

could only be classified as no ignition, a slight puff, or a violent 

inflammation. An attempt was made by these authors to gain more 

exact information on this point with the use of the piece of apparatus 

shown in figure 11. It consists of the explosion vessel a, of 2 liters 

capacity, and provided with 3 tubulures, &, Tc, and o. In & is inserted 

a stopper, permitting connection to a coil of platinum wire (f). The 

dust is introduced through Jc in much the same way as in their first 

experiments, while o is attached to the apparatus used for registering 

the pressure developed in a by the inflammation of the dust. The 

apparatus constructed to register the pressure consists of a threenecked Wolff bottle, one opening of which is connected with the 

explosion vessel and the second with a closed manometer containing
120 THE EXPLOSIBILITY OF COAL DUST.

colored water. The third opening contains a glass tube, the upper 

end of which is closed by a short piece of rubber tubing and a pinch 

cock. Any sudden pressure generated in the explosion vessel produces a movement of the liquid in the manometer, the extent of 

which is noted by means of a scale attached to its side.

Equal weights of the same coal dust gave practically the same

pressure in the apparatus. 

Equal weights of different 

dusts, when the same current was used for ignition, 

produced quite different 

pressures. These pressures, 

the authors consider, indicate the explosive character 

of the dust mixture. Several samples of dusts were 

examined in this way; some

of these were collected from 

a mine, while others were 

ground in the laboratory. 

These are designated in the 

table below as natural and 

artificial dusts, and all were put through a screen of 100 meshes to 

the inch. The weight of dust used in each experiment was 2 grams, 

the pressure of the air used to project the dust into the vessel was 8 

inches of mercury, and the wire was heated by a current of 15 amperes. 

The results are given in the following table:

Explosive character of coal dusts of stated composition as shown in experiments by Bedson

andWiddas.

FIGURE 11. Later coal-dust ignition apparatus of Bedson 

and Widdas.

No. of experiment.

1

2 

3 

4 

5 

6 

7 

8 

9

Nature of dust.

.....do'...................

.....do...................

.....do...................

.....do...................

.....do...................

.....do...................

.....do...................

Composition of dust.

Moisture.

14. 86 

1.52 

6.08 

S.58 

1.07 

5.20 

5.01 

6.00 

4.14

Volatile 

matter.

45.77 

34. 01 

38.22 

31.89 

27.49 

29.05 

28.38 

21.70 

21.31

Fixed 

carbon.

35.87 

58.55 

52.85 

57.78 

63.72 

42.22 

37.08 

7.63 

12.06

Ash.

3.50 

0.94 

2.85 

1.81 

7.72 

23. 60 

29.60 

64.67 

62.55

Ratio of 

fixed carbon to 

volatile 

matter.

0.78 

1.50 

1.38 

1.81 

2.32 

1.45 

1.30 

.35 

.56

Ratio of 

fixed carbon and 

ash to 

volatile 

 matter.

0.81 

1.51 

1.46 

1.86 

2.59 

2.27 

2.35 

3.33 

3.50

Pressure, o

Inches.

5 

5 

2 

4 

1.5 

1.5 

0 

0

1. Ground brown coal. ' 2. Ground coal from Button seam. 3. Ground coal from Grey seam coal. 

4. Ground coal from yard seam coal. 5. Screen dust from Busty seam. 6. Dust from timber baulks 

and haulage roads in yard seam. 7. Dust from stone in roof of yard seam. 8. Dust from top and bottom 

of timber baulks and roof of Grey seam. 9. Dust from sides of haulage roads and pillar sides of Grey seam.

a The length of the sealed limb of the U tube above the level of the water in the tube is 12 inches. The 

pressure of 5 inches, therefore, would represent a compression sufficient to reduce the volume of air to 

seven-twelfths of its original volume, etc.
INVESTIGATIONS OP THE IGNITION OF COAL DUST. 121

The authors in concluding their paper call attention to the influence 

which the proportion of volatile matter in the dusts exercises on 

their inflammability and explosive character, and assert that the 

method affords a ready means of judging the character of a coal 

with respect to these qualities. They express the hope of being 

able to contribute further results of a similar character.

In some of his work Bedson has made use of a different method 

for obtaining the relative pressures produced by the explosion of 

coal dust. This is a modification of the method used by Vital in 

his experiments.

EXPERIMENTS AT LIEVIN, FRANCE.

A series of interesting experiments carried out in a comparatively 

small gallery at the Lievin station in France will next be considered. 

These experiments have been mentioned in another portion of this

ELEVATION

E 

B_________________ Y7 ____________A

ft

PLAN

FIGURE 12. Coal-dust ignition apparatus used at LitSvin.

bulletin (pp. 43-45) but they can scarcely be passed over here, because 

they embody the features of laboratory experiments together with 

those of actual mining conditions. They are, therefore, doubly 

interesting in this connection as bearing on both the quantitative 

side of the problem and its practical side. The experiments were 

performed in a small gallery (fig. 12), made of sheet-iron pipe, 0.6 

meter in diameter, and arranged so as to form two galleries parallel 

to each other and connected at each end, so that the two galleries 

formed a closed circuit in which the air is made to circulate at regulated speed by means of a ventilator (V) placed near the middle of 

one of these galleries. The length of the gallery was about 7 meters. 

At the points A, B, C, and D were openings, which were closed 

during the experiment by means of paper diaphragms. The long 

side of the gallery A-B had five observation windows, numbered 

1 to 5. Ignition was brought about by firing a cannon into the end
122 THE EXPLOSIBTLITY OP COAL DUST.

A or B, the muzzle .of the cannon having, first been placed against 

the diaphragm closing the end. In this way the ignition could be 

brought about either against or in the direction of the current of 

air in A-B. The shot was always fired with the ventilator in operation. The dust was introduced through E during the circulation of 

the current of air. " The introduction was regulated by hand, so as 

to secure uniform distribution of the dust throughout the gallery. 

The time required to introduce the dust by hand was sufficient to 

permit the circulation of the air from five to fifty times around the 

closed circuit formed by the two galleries'. The dust used throughout 

these experiments was passed through a 200-mesh sieve without 

any attempt to screen it to a certain size. The velocity of the air 

current used was from 4 to 5 meters a second, a velocity that was 

relied on as sufficient to maintain in suspension all of the dust of 

this degree of fineness. The total capacity of the apparatus was 

4.5 cubic meters, and the density of the dust was determined by the 

amount introduced considering the whole amount as suspended at 

uniform density throughout the galleries.

When the cannon was fired into the gallery devoid of dust a rapid 

flame was seen at thp first two windows, and at the same time all four 

paper diaphragms were ruptured. Identical results with a dust-laden 

air in the system indicated no inflammation. When inflammation 

occurred a red flame advanced at different velocities to various points 

of the gallery, or in some tests projected out the end opposite the cannon. Lacking the facilities for such work, the experimenters did not 

attempt to measure the velocity of propagation of the flame, but, 

judging by the eye, they were able to express the velocity as very slow, 

slow, or rapid. After each experiment the tubes were carefully

cleaned.

In the course of this work eight different samples of dusts were 

examined. By varying the density of the dust, beginning with 

densities too low for inflammation.to occur, they were able to arrange 

the dusts' in the order of their inflammability under these conditions. 

The fact was brought out by this work that the order of inflammability 

is the same as that of the content of volatile matter in the coal. The 

same conclusion, as we have seen, was reached by other investigators, 

namely, Vital, Mallard and Le Chatelier, Holtzwart and Meyer, and 

Bedson and Widdas. Further factors considered by the author as 

determining the inflammability of dust are the character of the volatile matter and the percentage of ash in the coal; but the dusts as 

prepared for use in this investigation were of somewhat similar composition with respect to ash, so that the content of volatile matter 

was found to exercise a preponderating influence, and to determine 

the order of inflammability. Attention is also called to the influence 

which the ash exercises, both by increasing the weight of the particles,
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 123

and. by furnishing inert matter which must be heated up before 

inflammation occurs. The results, summed up in a table, have been 

given in an earlier part of this bulletin (p. 44). It is seen by inspection of this table, that of the eight dusts investigated, inflammation 

was obtained in all but the anthracite and Lens 2. The inflammability of the others was found to be greater according as they contained more volatile matter. The four types richest in volatile 

matter ignited at low densities, and the violence of the inflammation 

increased with the density of the cloud of dust. The point of greatest 

interest in connection with this work is the fact that inflammation 

and propagation of the flame throughout the available length of the 

gallery took place with a comparatively low density of dust, such as 

in mining conditions would be considered as indicating a comparatively dust-free gallery.

Since the publication of the preliminary bulletin containing the

results of work done in the small gallery, further work has been done 

in this same gallery, and in one much larger. This work, however, 

is considered in another part of this bulletin (pp. 135-139).

In discussing the results of his work, Taffanel enters somewhat 

into the chemistry of dust explosions. No measurements of the 

pressure produced in the gallery, or of the velocity of propagation 

of the flame were obtained, because the necessary apparatus was 

lacking, but analyses of samples of gas taken from the gallery during 

the explosion have thrown much light on some of the problems 

involved.

Attempts to obtain samples of the gas after the explosion gave 

uncertain results because of the reentrance of fresh air. The method 

that was found satisfactory was to introduce into the gallery a closed 

glass tube, which communicated with an evacuated vessel outside of 

the gallery. By means of a detonator and instantaneous fuse, which 

was ignited by the passing flame, the closed glass tube was broken, 

and the evacuated vessel was filled with gas from the gallery in a 

fraction of a second. Analysis of this gas showed the presence of 

nitrogen, carbon monoxide, carbon dioxide, oxygen, and at times 

small quantities of methane. The distribution of the oxygen consumed between the carbon and hydrogen of the dust was obtained 

by deducting from the oxygen present in the beginning that consumed by the carbon plus that remaining free. The amount of 

carbon and hydrogen burnt per unit volume being known, and the 

amounts of the various constituents to be heated by this combustion, 

it was possible to calculate the theoretical temperature of the flame. 

This calculation gave a temperature ranging from 1,000° to 1,700° C.

The amount of carbon dioxide found, except when large amounts 

of dust were used, was much greater than the amount of carbon 

monoxide, and the absorption of heat, which takes place in the
124 THE EXPLOSIBILITY OF COAL DUST.

reduction of carbon dioxide to carbon monoxide, was not as great 

as had been expected. This is especially true in the flame itself, as 

the amount of carbon monoxide there is very small. It requires a 

certain amount of time to bring about the reduction of carbon dioxide, 

and the amount of carbon monoxide became appreciable only after 

elapse of such a period.

At first it was impossible to explain the part played by finely 

divided schist in retarding the propagation of the flame, as 100 

grams of that material should lower the theoretical temperature only 

50° C. Even after allowing for the absorption of heat that takes 

place when the chemically combined water of the schist is expelled, 

the calculated temperature was higher than the temperature in 

certain experiments in which propagation was obtained with coal 

dust alone.

The explanation given for this discrepancy is the difference in the 

screening action of coal dust and an inert dust. The effect of a dust 

cloud in front of the flame is to form a screen. With respect to coal 

dust, the greater the concentration the greater the surface of this 

screen per unit of volume, and the more favorable are the conditions 

for propagating the flame. But with a dust cloud composed partly 

of inert particles, these serve the same screening purpose, but do not 

take part in the combustion. They do not act like an excess of 

carbon, but merely by their screening effect they exercise a retarding 

influence in addition to that of the heat which they absorb in attaining the temperature of the flame.

By a careful interpretation of the analyses of gas taken during the 

explosions, it was demonstrated that certain particles of the coal 

were completely consumed, while others participated only to the 

extent of their volatile matter. For the propagation of the flame

it is necessary that the proportion of substances undergoing rapid 

combustion that is, the fine dusts and the distilled gas should be 

somewhat more than enough to make the mixture inflammable, so 

that a sufficient amount of heat shall be disengaged to raise the dust 

cloud in front of the flame to the temperature of ignition. This may 

result from the volatile matter, or from the finest coal dust, or from 

a combination of the two. These, however, are complicated questions to be dealt with only by further experimental work.

FIRST SEEIES OF EXPERIMENTS AT PITTSBURG TESTING STATION.

During the past year the writer has studied a number of coals with 

respect to their relative absorption of oxygen from oxidizing agents, 

especially standard solutions of chromic acid, with the thought that 

the amount of absorption would be indicative of the relative tendency
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 125

of the different coals to take up oxygen from the air or to undergo 

spontaneous combustion.

In this connection it seemed desirable also to determine, if possible, 

the relative inflammability of some of these same coals, and quite 

recently, with this in view, a series of experiments was carried out 

on some of the same dusts used in studying the rate of oxidation. 

The apparatus used for this work is a modification of that of Bedson 

and Widdas described above.

Plate VIII, A, shows the form of apparatus used. A is an ordinary 

2-liter aspirator bottle. B is a small filter flask of about 250 cubic 

centimeters capacity, connected at a by rubber tubing with 0, a 

glass bulb of about 150 cubic centimeters capacity, and through the 

rubber stopper with the open manometer c. D is & glass tube 6.5 

millimeters in internal diameter and 20 centimeters long, passing 

through holes in opposite sides of a box support, and set in firm and

level position with plaster of Paris.

Through a rubber stopper in the mouth of A pass two large copper 

wires, which form the terminals for the platinum coil d. Through a 

hole in the same stopper passes a glass tube 13 millimeters in internal 

diameter, which is closed at the top, and to which is sealed a side tube 

(e) of the same diameter as D. This side tube is connected closely, 

end to end, with D by means of a short rubber tube. The platinum 

coil d is made from about 120 centimeters of No. 26 platinum wire, 

is suspended in two sections from a small perforated porcelain plate, 

and is connected with the copper terminals. The porous plate serves 

not only as a support for the coil but as a protection to the rubber 

stopper above from too high heating during the experiment, and also 

tends to disseminate the dust more uniformly in the upper part of the 

flask. The platinum coil when in position hangs slightly above the 

center of the bottle.

The tube/passing through the stopper in the tubulure at the bottom of the bottle is bent at a right angle and is made funnel-shaped 

at one end. The end carrying the funnel is directed upward inside 

the bottle toward the platinum coil, and directly under and within 

about 5 centimeters of it. In this funnel is placed the coal dust 

which it is desired to examine. The funnel and the fine wire gauze 

with which it is covered aid in securing a'more complete dissemination 

of the dust when it is ejected from./. By means of a rubber tube/ 

can be connected with C. Pinchcocks are at g, Ji, and j.

The terminals of the coil d a,re connected in series with an ammeter 

arid rheostat. The relative pressure produced by the ignition of 

different dusts is measured by the distance to which a small steel ball 

Q)} is projected, when this ball is placed at a definite point in D and 

in which it fits snugly.
126 THE EXPLOSIBILITY OF COAL DUST.

Before each experiment the bottle A is thoroughly cleaned out and 

fresh air aspirated through it. Fresh air is also forced into B and 0 

through g (pinchcock ~h being also open) until the desired pressure of 

mercury is indicated in the manometer c. The cock li is then closed 

and remains closed during the remainder of the experiment. The 

stopper carrying the coil is put in place, and the tubes e and D are 

connected. The tube/, containing the coal dust, is inserted in its 

proper place and connected with C.

To secure comparable results the coil is always heated the same 

length of time, three minutes, before the dust is scattered from /. 

The same current is used each time, and is kept perfectly constant 

the entire three, minutes. With the coil used in these experiments a 

current of 6 to 7 amperes has been found satisfactory.

Just before scattering the dust the steel ball is placed exactly 

in position. At the end of the three minutes the cock j is released 

instantaneously, and the air entering A puffs the dust into the bottle 

and about the coil. It has been found better for the operator to 

replace the cock j and pinch the tube with his fingers before releasing, 

as the instantaneous release can be accomplished much more certainly in this way. The pressure in the bulb C'of 150 cubic centimeters capacity being 165 millimeters of mercury, the pressure resulting 

therefrom in A would be only about 12.7 millimeters.

With the apparatus and method of procedure described above, the 

ignition of a number of coals has been studied. In every experiment 

ignition has taken place readily, except those with anthracite, natural 

coke, and charcoal.

With a pressure in (7 of 165 millimeters of mercury, and a current of 

6 to 7 amperes, 0.04 gram of dust was found quite sufficient for producing decided inflammation with all the coals investigated, with the 

exception already noted, and with some coals even less than this 

amount was required to produce measurable results.

In the table below are given the results of experiments with 11 coals 

of varying character and from different sources. In each experiment 0.04 gram of dust was used, dust meaning coal finely ground and 

passed through a 100-mesh sieve. The current employed was 6.4 

amperes; the pressure in C'was 165 millimeters of mercury.

In the first column of the table is given the character of the coal, 

while the third column shows, in centimeters from the end of the 

barrel D, the distance to which the metal ball was projected.
U. S. GEOLOGICAL SURVEY

A. COAL-DUST IGNITION APPARATUS USED AT PITTSBURG.

11. APPARATUS USED AT PITTSBURG, SHOWING IGNITION OF DUST.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 127

Results of laboratory experiments with explosive coal dusts at Pittsburg station.

Character of coal.

Pennsylvania bituminous. . . .

ing.........................

Illinois bituminous gas coal. . .

West Virginia bituminous. ...

No. of experiment.

1 

2 

3 

1

r 3

'

\ 2 

J 1

'

2 

3 

/ 1

\ 2

Distance 

ball was 

projected.

Cm. 

318 

325 

325 

281

£i\j£,

284

277 

320 

335 

300

' 312 

302 

320 

315 

323

320

Character of coal.

New Mexico bituminous. ..... 

Kentucky cannel ......

Colorado lignite. ..............

No. of experiment.

1 '*

\ 2 

1 1

i 2

2 

3

5 

0

1 

( . 3

Distance 

ball was 

projected.

Cm. 

323 

312 

307 

317

353

339 

321 

293 

295

295 

309 

319 

312 

303

343

In the above tabulation no account is taken of the moisture or ash 

in the coals, nor of any deterioration of any of the samples that may 

have taken place before or after powdering and storing in bottles. 

As is shown in the table, lignites generally exhibited greater irregularity of results. The coals are not greatly differentiated here, probably because the heat supplied by the wire was too great in comparison with that supplied by the dust in burning, so that the differences 

of the dusts were masked.

The photograph reproduced in Plate VIII, B, was taken during one 

of the experiments. The flame observed has been in every test apparently confined to the upper half of the 2-liter bottle, as shown 

here. Consequently, the density of the mixture of dust and air at 

which the ignition occurred is not 0.04 gram of dust in 2 liters of 

air, but greater than that, 0.04 gram in less than 1 liter. Furthermore, the phenomena can not be considered as indicating indefinite 

propagation of the flame in an atmosphere containing the same 

density of dust, but only indicate propagation in the available space, 

and under the conditions of these experiments. It may be desirable 

to add that the inflammation was in all tests practically instantaneous and similar in appearance to the ignition of a slightly explosive 

gas mixture.

A great deal more work would have to be clone before any positive 

statement could be made concerning the relative behavior of different coals. The same is true with respect to the effect of variations 

in the current used, and in the pressure with which the dust is brought 

into the bottle. A definite strength of current does, however, seem 

to be required for complete ignition, and beyond that strength variation of current has no effect. The initial pressure of the ignition mixture is probably of considerable importance.
128 THE EXPLOSIBILITY OF COAL DUST.

An objection to the use of a platinum coil as a source of ignition 

is the possible catalytic action of the platinum.

It is hoped that further experiments can be performed on the 

ignition of coal dust by the use of pressure alone. It should be understood that the record given above is to be taken as a preliminary 

report of a few experiments performed under limited conditions, 

which are to a large extent repetitions of previous experiments, with 

some minor alterations of apparatus and method of manipulation.

SECOND SERIES OF EXPERIMENTS AT PITTSBURG TESTING STATION.

A second series of experiments is now in progress in which the 

pressures developed in the explosion vessel are measured by a different method. This method was adopted because the maximum 

pressure in many cases is not developed instantaneously, and the 

method previously used would on that account not give a true 

measure of the force of the explosion. The explosion vessel now in 

use is a 1,500-cubic centimeter glass globe with two tubulures on 

opposite sides. The dust is puffed into the vessel through the lower 

opening in much the same manner as in the experiments described 

above. Into the top opening is inserted a stopper carrying the same 

platinum coil used in the previous work. The measurement of the 

pressure is accomplished in the following way: A brass tube of 7 

millimeters diameter is passed vertically through the rubber stopper 

which carries the connections of the platinum coil. (See PI. VIII, A.) 

The top of this tube is ground so that a T56 -inch steel ball fits on it 

practically gastight. The pressure developed within the explosion 

vessel is measured by ascertaining by several trials the smallest 

weight which it is necessary to place on the steel ball to prevent 

it from being lifted from its position. In this way the total pressure 

exerted on a known area is obtained directly. The experiments 

have given quite concordant results, as can be seen from the table 

below:

Results of second series of experiments with explosive coal dusts at Pittsburg station. 

[Tn all tests the amount of dust used was 0.04 gram.]

Source and proximate analysis of coal dust usec 

developed in tests.

1. Bituminous coking coal from Hastings mine 

County, Colo. (Lab. No. 9780):

Ash.................................

Pressure developed, less than 454 grams per squa

and pressure

Las Animas

1.43 

33.98

57.46 

7.13 

.57 

re centimeter.

Results of tests.

Weight 

applied.

Grams. 

300 

275 

250 

225 

200 

175

Equivalent 

per sq. cm.

Grams. 

779 

714 

649 

584 

519 

454

Effect on steel 

ball.

Not lifted. 

Do. 

Do. 

Do. 

Do. 

Do.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 129 

Results of second series of experiments with explosive coal dusts at Pittsburg station Cont'd.

Source and proximate analysis of coal dust used and pressure 

developed in tests.

Results of tests.

Weight 

applied.

Equivalent 

per sq. cm.

Effect on steel 

ball.

2. Bituminous free-burning domestic coal from Chandler mine, 

Fremont County, Colo. (Lab. No. 9778):

Moisture............................ 6.49

Volatile matter...................... 35.09

Fixed carbon...................:.... 52.25

Ash................................. 5.56

Sulphur............................. .49

Pressure developed, 666 grams per square centimeter.

Grams.

250

200

 255

258

Grams. 

049 

075 

002 

070

Lifted. . 

Not lifted. 

Lifted. 

Not lifted.

3. Bituminous, noncoking steam or domestic coal, with cubical 

or round fracture, from Maitland mine, Huerfano County, 

Colo. (Lab. No. 9784):

Moisture............................ 4.74

Volatile matter...................... 38.24

Fixed carbon........................ 49,32

Ash................................. 7.70

Sulphur............................. .60

Pressure developed, 751 grams per square centimeter.

250

270

272

280

285

290

288

290

649

701

706

727

740

753

748

753

Lifted.

Do.

Do.

Do.

Do.

Not lifted. 

Lifted. 

Not lifted.

4. Noncoking, bituminous coal of "nigger head" or round formation from Ravenwood mine, Huerfano County, Colo. (Lab. 

No. 9781): 

Moisture............................ 3.49

Volatile matter...................... 37.46

Fixed carbon........................ 49.62

Ash................................. 9.43

Sulphur............................. .99

Pressure developed, less than 390 grams per square centimeter.

5. Bituminous coking coal from Delagua mine, Las Animas 

County, Colo. (Lab. No. 9785):

Moisture............................ 2.15

Volatile matter....................... 34. 45

Fixed carbon........................ 53. 42

Ash................................. 9.98

Sulphur............................. . .48

Pressure developed, 647 grams per square centimeter.

6. Bituminous coking coal from Bowen mine, Las Anirnas 

County, Colo. (Lab. No. 9779):

Moisture............................ 1.44

Volatile matter...................... 31.84

Fixed carbon........................ 50.88

Ash................................. 15.84

Sulphur............................. 3.21

Pressure developed, 652 grams per square centimeter.

7. Bituminous coking coal, high carbon, from Sun No. '2 mine, 

Fayette County, W. Va. (Lab. No. 9783):

Moisture............................ 0:96

Volatile matter...................... 21.08

Fixed carbon........................ 73.38

Ash................................. 4.58

Sulphur............................. .51

Pressure developed, 426 grams per square centimeter.

8. Bituminous coking coal from Ansted mine, Fayette County, 

W. Va. (Lab. No. 9787):

Moisture...'......................... 1.83

Volatile matter...................... 33.61

Fixed carbon........................ 58.94

Ash................................. 5.62

Sulphur............................. .74

Pressure developed, 800 grams per square centimeter.

275

260

200

150

714

675

519

390

Not lifted. 

Do. 

Do. 

Do.

250

250

240

245

250

248

649

049

023

636

649

644

Not lifted.

Do. 

Lifted.

Do.

Not liftedLifted.

250

270

200

255

252

649

701

675

662

654

Lifted. 

Not lifted.

Do.

Do.

Do.

250

230

200

150

100

170

165

163

649

597

519

390

415

441

428

423

Not lifted.

Do.

Do. 

Lifted.

Do. 

Not lifted.

Do. 

Lifted.

320

310

305

307

309

831

805

792

797

802

Not lifted.

Do. 

Lifted.

Do. 

Not lifted.

38970° Bull. 425 10-
130 THE EXPLOSIBILITY OF COAL DUST. '

Results of second series of experiments with explosive coal dusts at Pittsburg station~Cont'd.

Source and proximate analysis of coal dust used and pressure 

developed in tests.

Results of tests.

Weight 

applied.

Equivalent 

per sq. cm

Effect on steel 

ball.

9. Bituminous coal, coking, from Gem mine, Campbell County, 

Tenn. (Lab. No. 9782):

Moisture............................ 3.58

Volatile matter...................... 34.18

Fixed carbon........................ 54.98

Ash................................. 7. 26

Sulphur............................. .74

Pressure developed, less than 140 grams per square centimeter.

10. Bituminous coal, steam and domestic, from Wooldridge 

mine, Campbell County, Tenn. (Lab. No. 9780): 

Moisture............................ 2.73

Volatile matter...................... 35.85

Fixed carbon........................ 54.88

Ash................................. 6.84

Sulphur............................. 1.07

Pressure developed, 808 grams per square centimeter.

11. Bituminous coking, high carbon coal from .Ted mine, McDowell County, W. Va. (Lab. No. 10034):

Moisture............................ 1.01

Volatile matter...................... 14.52

Fixed carbon........................ 77.65

Ash................................. 6.82

Sulphur............................. .71

Pressure developed, less than 259 grams per square centimeter.

12. Bituminous coking, high carbon coal from Elk Ridge mine, 

McDowell County, W. Va. (Lab. No. 10035): 

Moisture............................ 0.97

Volatile matter...................... 17. 57

Fixed carbon........................ 77. 65

Ash................................. 3.81

Sulphur............................. .58

Pressure developed, 262 grams per square centimeter.

13. Bituminous, noncoking coal from Woodside mine, Sangamon County, 111. (Lab. No. 9774): Moisture............................ 13-13

Volatilematter...................... 35.00 

Fixed carbon........................ 41. 53

Ash................................. 10.24

Sulphur............................. 3.48

Pressure developed, 548 grams per square centimeter.

14. Bituminous, noncoking coal from Little Vermilion mine, 

Vermilion County, 111. (Lab. No. 10037):

Moisture............................ 13.92

Volatile matter...................... 33.24.

Fixed carbon........................ 45.39

Ash..............:.................. 7.45

Sulphur............................. 1.05

Pressure developed, 522 grams per square centimeter.

15. Subbituminous noncoking coal from Navajo mine, N. Mex. 

(Lab. No. 10038):

Moisture............................ 12. 65

Volatile matter...................... 33.57

Fixed carbon........................ 37.67

Ash................................. 10.11

Sulphur............................. .47

Pressure developed, 730 grams per square centimeter.

Grams. 

250 

170 

140

Grams. 

649 

441 

363

Not lifted. 

Do. 

Do.

250

300

320

310

312

649

779

831

805

810

Lifted. 

Do.

Not lifted. 

Lifted. 

Not lifted.

250

100

649

259

Not lifted. 

Do.

250

.100

120

110

105

102

649

259

311

28(5 

272 

265

Not lifted. 

Lifted. 

Not lifted.

Do.

Do.

Do.

250

225

200

210

212

649

584

519

545

550

Not lifted.

Do. 

Lifted.

Do.

Not lifted.

250

150

200

202

649

390

519

524

Not lifted. 

Lifted. 

Do. 

Not lifted.

200

230

250

260

280

285

282

519

590

649

675

727

740

732

Lifted.

Do.

Do.

Do.

Do. 

Not lifted.

Do.
INVESTIGATIONS OF THE IGNITION OF COAL DUST. 131 

Results of second series of experiments with explosive coal dusts at Pittsburg station Cont'd.

Source and proximate analysis of coal dust used and pressure 

developed in tests.

Kesults of tests.

Weight 

applied.

Equivalent 

per sq. cm.

Effect on steel 

ball.

1C. Subbituminous, noncoking coal from Weaver mine, N. Mex. 

(Lab. No. 10039):

Moisture............................ 12.14

Volatile matter...................... 38.82

Fixed carbon........................ 37.78

Ash................................. 11.26

Sulphur............................. .52

Pressure developed, GOG grams per square centimeter.

17. Subbituminous, noncoking coal from Superior mine, Wyo. 

(Lab. No. 10040):

Moisture............................ 10.45

Volatile matter...................... 38.28

Fixed carbon........................ 45.06

Ash................................. C.21

Sulphur............................. .85

Pressure developed, 718 grams per square centimeter.

18. Subbituminous, noncoking coal from Superior mine, Wyo. 

(Lab. No. 10041):

Moisture............................ 5.17

Volatile matter...................... 40.23

Fixed carbon........................ 52.77

Ash................................. 1.83

Sulphur............................. .68

Pressure developed, 769 grams per square centimeter.

19. Subbituminouf, noncoking coal from Weaver mine, N. Mex. 

(Lnb. No. 10042):

Moisture............................ 12.81

Volatile matter...................... 38.83

Fixed carbon........................ 43.06

A sh................................. 5.30

Sulphur............................. .59

Pressure developed, 782 grams per square centimeter.

Grams. 

282 

230 

240 

235 

232

Grams. 

732 

597 

623 

610 

602

Not lifted. 

Lifted. 

Not lifted.

Do.

Do.

200

225

250

260

270

280

275

278

519

584

649

675

701

727

714

722

Lifted.

Do.

Do.

Do.

Do.

Not lifted. 

Lifted. 

Not lifted.

250

300

275

290

295

300

297

649

779

714

753

766

779

771

Lifted. 

Not lifted. 

Lifted.

Do.

Do. 

Not lifted.

Do.

278

300

305

302

722

779

792

784

Lifted. 

Do.

Not lifted. 

Lifted.

The experiments recorded in the table were made on equal weights 

of the dusts, and each sample was ground to pass through a 100- 

mesh sieve. These results are interesting chiefly for two reasons. 

First, they show what degree of accuracy may be expected from this 

method of examining the explosive character of dusts. From experience it may be stated that the pressures developed in almost all of 

the tests could be measured to about 1 per cent of the total pressure 

developed. Second, the results are of most importance in showing 

the care which must be taken in preparing the dusts in order that the 

results obtained with different coals may be strictly comparable. 

Each sample of coal was ground in a ball mill, so that the whole of 

the sample passed through a 100-mesh sieve, and efforts were made 

to have them ground as nearly as possible to the same degree of fineness. But this object was not attained by any means. It was 

shown that fully 90 per cent of those dusts which developed the 

greatest pressures in the explosion vessel would pass through a 200- 

mesh sieve, whereas of some samples only about 30 per cent would
132 THE, EXPLOSIBILITY OF COAL DUST.

pass through the same sieve. To obtain comparable results it will 

be necessary to impart to all of a sample such a degree of fineness 

that the whole amount introduced into the explosion vessel will take 

part in the explosion. A series of experiments is being conducted 

on the same coals that were used in the tests described above. The 

samples used in this series were ground so that the whole passed 

through a 200-mesh sieve. The following results of experiments 

are given for comparison of the pressures developed in the previous 

experiments with the pressure developed by the same samples 

ground to pass through a 200-mesh sieve.

Comparison of pressures developed by 100-mesh and 200-mesh coal dusts of like composition.

Grams per sq.crn.

r\ i AT « n f 100-mesh............................... Less than 454 Coal No. 9780 \ __ A ,

[200-mesh.......................................... 549

n i AT nmo 1 100-mesh......................................... 666 Coal No. 9778 \ onn , ._ 1200-mesh.......................................... 703

^ i AT n_ 0 . [lOO-mesh......................................... 751 Coal No. 9784 \ . nnjt \ 200-mesh........................................... 774

n TAT n-o-, 100-mesh............................... Less than 390 Coal No. 9781 < onn , ,, 1200-mesh.......................................... 626

r. i AT oe f 100-mesh................................ J....... 647 Coal No. 9785 \ OAA , . __ 1200-mesh........................................ 667

If it is not possible to obtain dust sufficiently finely divided to get 

comparable results it will be necessary to screen the samples used for 

the tests with more than one sieve and to use in each test only dust 

whose particles are between certain sizes. This process may change 

somewhat the composition of the dust from that of the original coal 

and will not be used except as a last resort.

SIGNIFICANT POINTS IN EXPERIMENTS.

In closing this short summary of the laboratory experiments on the 

ignition of coal dust, it may be well to call attention to certain facts 

which they show. In the first place, the phenomenon of ignition is 

very complex, and for that reason it is necessary to have the proper 

conditions in order to demonstrate the ignition of coal dust on a 

laboratory scale. It has been pretty well demonstrated by these 

experiments that the order of inflammability of a coal dust is a function of the amount and character of the volatile matter which is 

expelled, the ease with which it is given up, the fineness of division 

of the dust particles, the density of the cloud, the character of the 

source of ignition, the amount of water and ash, and, finally, the 

pressure prevailing in the neighborhood of the flame. It does not 

seem that sufficient attention has been given to the last condition. 

Several facts brought out in the experiments support this statement.

Unless there is an exceptionally large amount of dust in the air, 

experience shows that ignition does not take place from a naked flame.
INVESTIGATIONS AT EUROPEAN STATIONS. 133

This fact is illustrated by the work of Galloway, arid that of Mallard 

and Le Chatelier (who used for the source of ignition different kinds 

of naked flames, and accords with the conclusions which they reached 

as a result of their work. It will be recalled, too, that Holtzwart and 

Meyer drew attention to the fact that no ignition was obtained if 

they introduced lignite dust into their apparatus, and, after establishing the spark between the terminals within, disseminated the dust in 

the air by shaking the tube. But when the dust was puffed between 

the terminals by compressed air ignition occurred. Dust explosions 

in mines and in successful experiments in galleries specially designed 

for these investigations are preceded by violent compressions simultaneously with the production of a large flaming area by the charge of 

explosive (the means of ignition always used). Attempts will be 

made to ascertain the effect of pressure alone on, coal dust suspended 

in air and in some inert gas.

COAL-DUST INVESTIGATIONS AT EUROPEAN TESTING

STATIONS.

By AXEL LARSEN. 

PROTECTIVE MEASURES UNDER STUDY.

The investigation of coal-dust explosions is naturally divided by 

two purposes: (1) Demonstration of the inflammability of coal dust, 

and (2) determination of the best means of preventing or arresting 

explosions. Inflammability may now be regarded as demonstrated. 

The second purpose, however, is likely to involve further experiments 

on a still larger scale than at Altofts in England and LieVin in France. 

Systematic scientific study of all phenomena and conditions bearing 

upon the combustion of coal dust, from the moment of its ignition 

through all subsequent stages of propagation until the highest point 

of velocity, approaching true detonation, is reached, has been generally recognized as an indispensable guide to gallery experiments; but 

it is felt that even the largest existing galleries are not long enough 

to admit of definite conclusions regarding the preventive measures 

to be adopted in actual practice.

Foremost among such measures are the so-called protection zones. 

Of these, three kinds have been experimented with, namely: Dustless, 

watered, and stone-dust zones.

The stopping power of dustless zones has proved comparatively 

slight, especially where the explosion has traveled a long distance and 

developed both high velocity and a dense "vanguard" cloud. 

Besides, it is not easy to remove coal dust completely and prevent 

its reaccumulation, even on comparatively short lengths of roadway 

in a mine.
134 THE EXPLOSIBILITY OF COAL DUST.

Watered zones are probably more effective provided the watering 

is sufficient. But such sufficiency appears to depend greatly on 

local conditions and on the character of the dust to be dealt with. 

In German mines, more particularly in the Westphalian and Saarbriicken coal fields, systematic watering has been made compulsory 

by law, and in spite of the numerous drawbacks attending its installation and upkeep, both owners and men have accepted the measure 

with growing favor. In Belgium, on the contrary, extensive watering has been considered impractical, owing to the damage said to 

be caused to walls and roof. The same is true in many English 

mines, although in Wales the watering system is extensively practiced.

Stone dust has in the experimental galleries so far given the best 

results, and its use entails but few of the disadvantages of the two 

other methods. Its efficacy as a stopping agent has been experimentally demonstrated both in England and in France, although 

the results are not entirely concordant. The dissimilarity, for 

instance, between the results in the tests depicted in figure 13 is 

remarkable, considering that the two galleries are practically alike 

and that the conditions of the tests are apparently analogous.

LIEVIN: Flame stopped

Coal dust zone 246' Stone dust 328'

ALTOFTS: ,________________________

Coal dust zone 2.75' Stone dust 1.00* 

FIGURE 13. Eelative effect on flame of stone-dust zones at Lievin and at Altofts.

Such, at least, is the impression received at the first glance. But 

it is, 6f course, quite possible that the numerous factors influencing 

an explosion may produce apparently discrepant results by acting 

in different order in different tests, and that when properly understood and accounted for such results may yet be brought into harmony. 

Indeed, if this were not credible, all. attempts to determine adequate 

lengths of protection zones in mines by extrapolation would appear 

futile.

At the time of writing this report no information could be obtained 

at either station as to any existing ratio of increase between varying 

lengths of coal dust and stone dust. But as the recording instruments 

at Altofts have shown that the pressure increases but slowly over a 

distance of 200 to 300 feet, and then suddenly rises to the maximum, 

it may be assumed that if a coal-dust zone of, say, 600 feet were 

employed for originating and propagating an explosion, the pressures 

obtained in an adjacent stone-dust zone would be very different 

from those obtained by shorter lengths of the propagating zone. 

Hence the employment of the relatively short propagating zones at
U. S. GEOLOGICAL SURVEY BULLETIN 425 PLATE IX

A. TIME MARKER, ALTOFTS EXPERIMENTAL GALLERY.

K. MANOMETER, ALTOFTS EXPERIMENTAL GALLERY.
A. CONTACT BREAKER, ALTOFTS EXPERIMENTAL GALLERY; BEFORE FIRING.

Jl. CONTACT BREAKER, ALTOFTS EXPERIMENTAL GALLERY; AFTER FIRING.
INVESTIGATIONS AT EUROPEAN STATIONS. 135

the Altofts gallery, which, owing to the limitation of strength of the 

gallery tube, have to be confined to about 367 feet, is inadequate for 

complete solution of the problem.

APPARATUS AND METHODS AT ALTOFTS AND LIEVIN. 

GENERAL STATEMENT.

The complex study of coal-dust explosions obviously involves the 

use of delicate recording instruments. Both at Altofts and at Li6vin 

the equipment in this respect, most of which has been specially 

designed, apparently leaves little to be desired.

At stations where observations have not yet been sufficiently 

extended, the selection of instruments will now be greatly facilitated 

by experience gained elsewhere. It is gratifying to acknowledge 

that the benefit of such experience is freely and willingly offered to all 

interested, both at Altofts and at LieVin.

INSTRUMENTS AT ALTOFTS.a

Measurement of pressure. The B. C. D. 6 manometer (PI. ,IX, J5) 

records the movement of a strong spring under the pressure of a coaldust explosion. In order to reduce error caused by the inertia of the 

moving parts they are made as light as possible and the amount of 

movement of the spring is as small as is convenient for accurate 

measurement. The spring itself is triangular in form and clamped 

at its base, the force acting vertically upward at its apex. With this 

form the maximum strain is the same at all cross sections of the 

spring and the inertia is also reduced, because the narrow lighter 

part of the spring moves most and the wide heavier part least.

. The pressure acts directly upon a surface of oil contained in a 

hexagonal oil box and is transmitted to a light hollow cylindrical 

plunger (closed at the bottom) moving in the oil box through a hole 

in the top. This arrangement keeps the plunger well lubricated, 

reduces leakage past it, and prevents the fine dust with which the 

gas is charged from cutting and clogging the rubbing surfaces. It 

also damps out any, rapid vibrations due to sudden shock.

The natural period of vibration of the spring is one one-hundredand-fiftieth of a second, and such vibrations do not. mask the actual 

fluctuations of pressure due to the explosion. The plunger makes 

contact with the spring by means of a loose link, one end of which 

rests in a conical depression in the bottom of the plunger and the 

other in a similar depression in the face of the spring.

a The writer is indebted to Mr. W. E. Garforth and Doctor Wheeler for the accompanying photographs 

and the following descriptions of instruments used at Altofts.

6 B. C. D., the distinguishing mark used for these instruments by the makers, stands for "British coal 

dust."
136 THE EXPLOSIBILITY OF COAL DUST.

The spring carries a fine scribing point which rests lightly against 

a smoked surface of paper fastened on a heavy drum which can be 

made to revolve by means of an electric motor; a continued record of 

the development of pressure is thus obtained.

The speed of revolution of the drum is obtained by a special 

TV-second time marker (PL IX, A). An accurate standard of 

time is obtained by measuring the time that a weight takes to fall 

from rest through a measured distance; this distance is so arranged 

that the time interval shall be exactly one-tenth second. A break 

in the electric circuit occurs at'the begininng and at the end of the fall 

of the weight, and these breaks are recorded on the surface of the 

smoked paper on the manometer drum by the movement of a light 

style attached to an electro-magnet.-

Measurement of velocity. In order to record the speed of passage 

of pressure along the experimental gallery, contact breakers are 

screwed into the top 50 feet apart. They consist of light plungers, 

which can be weighted at will to withstand from 2 to 20 pounds 

initial pressure per square inch, and which on the slightest movement upward break an electric circuit. Plate X, A, shows the position before firing and Pla_te X, B, that after firing. The breaks in 

electric current are recorded by means of a standard chronograph. 

In order to be able to record a large number of breaks (as many as 

12 have been used), and to avoid the error caused by differences in 

the latency or "lag" of the electro-magnets on the chronograph, a, 

special automatic commutator has been devised which enables all the 

breaks to be registered by one electro-magnet. An escapement 

wheel carrying the commutator brush tends to be. pulled round over 

the stops, but is held back by an anchor escapement attached to the 

armature of an electro-magnet. The circuits from the contact 

breakers on the gallery are connected through this commutator before 

passing to the chronograph. One lead of each circuit passes to the 

electro-magnet terminal and the other leads are connected, in order, 

to the numbered terminals of the stops of the commutator.

The value of this instrument depends upon the time that the 

brush takes to pass between two successive steps. This has been 

reduced to less than one-sixtieth second, so that, if the contact 

breakers on the gallery are 50 feet apart, velocities as high as 3,000 

feet a second can be determined.

Sampling of after-damp. The B. C. D. sampler (PL XI, A and 

B) consists essentially of an exhausted bottle which can be opened 

to the explosion gallery at a known time and closed at will after a 

short interval; these conditions are essential for a correct interpretation of the results obtained, - . . ...

A pipe passes through the side of "the gallery" 2 feet into the interior. 

It is closed at the inner end by a small glass bulb fastened in by
U. S. GEOLOGICAL SURVEY

AFTER-DAMP SAMPLER, ALTOFTS EXPERIMENTAL GALLERY.
U. S. GEOLOGICAL SURVEY

A. Before firing, J>. After firing. 

CONTACT MAKER USED AT ALTOFTS EXPERIMENTAL GALLERY.

C. APPARATUS FOR IGNITING COAL DUST BY GAS FLAME, ALTOFTS EXPERIMENTAL

GALLERY.

Opened by detachment of lever weight.
INVESTIGATIONS AT EUKOPEAN STATIONS. 137

sealing wax. The outer end of the pipe is screwed to the sampling 

bottle and the whole then evacuated. A small hammer head is 

fixed just over the glass end, held back by a fuse wire. On the fusing 

of this wire the hammer falls and breaks the glass, thus allowing the 

gases to enter the exhausted bottle. The same current that fuses 

the wire also releases a small weight, which, after falling a certain 

distance, pulls out a pin, thus allowing a heavy weight to fall and 

in falling to close a tap at the head of the bottle. The gases are 

afterwards withdrawn through a mercury pump for analysis. The 

time that the bottle remains open depends upon the distance that the 

small weight falls; this can be varied at will.

The time at which the bottle is opened to the gallery by the breaking of the glass bulb is determined by causing the explosion itself 

to make the electric current pass through the fuse wire; this is effected

by means of the B. C. D. contact maker shown in Plate XII, A

(before firing), and B (after firing).

CALCULATION OF TEMPERATURE AT ALTOPTS.

The temperature of explosion (T) is calculated at Altofts from 

the pressure on the assumption that T = Z+'pt; Z being the original 

temperature (absolute) of the gases, p the observed pressure, and t 

the normal temperature. For example:

Let p= 10 atmospheres; 

t = 10° C. and therefore 

Z = 10° + 273° = 283° C. 

Then T = 283+ 2,830 = 3,113° C.

CHANGES IN GALLERY AT LIEVIN.

At LieVin station an important change has, been made since last 

summer in the construction of the intake portion of the principal 

gallery. This was trapezoidal in section, buried under stone debris, 

and constructed so as to permit different kinds of timbering, the 

idea being to imitate, as far as possible the structural features of a 

roadway in the mine.

The violent dislocations of timber frames, however, and other 

heavy damage caused by the force of explosions, necessitated a 

stronger construction, and the whole of the buried part of the gallery 

(38 meters) has been replaced by boiler shells 10 millimeters in 

thickness and 2 meters in diameter. The gallery is lined with 

wooden boards and ballasted outside with debris so as to leave the 

top free. (See fig. 14.)

The gallery, which was 230 meters long in October, will be extended 

. to a total length of 400, perhaps 500 meters.
138 THE EXPLOSIBILITY OF COAL DUST.

INSTRUMENTS AT LIEVIN.

Measurement of pressures. The recording instruments for measuring pressures at Lievin comprise: (1) Spiral spring gages graduated 

to indicate £, 2, and 5 kilogram pressures per square centimeter; (2) 

copper-disk crusher gages of known pattern; and: (3) "Thomson's 

tubes," as used for taking deep soundings. The last consist of thin 

glass tubes about 20 inches long, open at one end and filled with 

chromate of silver. When placed in an iron tube containing salt

Dismantled section

FIGURE 14. Dismantled and present sections of Lie'vin gallery.

water, and inserted into the gallery, the pressure causes the water to 

mount into the glass tubes, discoloring the chromate. Although the 

pressure records obtained in this manner are not invariably trustworthy, the method is inexpensive.

Measurement of rate of propagation. The rate of propagation of 

flame is obtained by means of a number of electric circuits which are 

broken by the passing flame. The interruptions of current are 

recorded on a chronograph. The connecting wires enter the gallery 

at regular intervals through iron tubes fixed under the roof, as shown

in figure 15. The circuit is 

broken at the point marked 

x through the explosion of a 

fulminating cap.

Measurement of temperature. For measuring the 

temperature of explosion a 

thermocouple and a Le 

Chatelier galvanometer have 

been used, but for very 

violent and rapid explosions, they are not. satisfactory.

Talcing samples. The contrivance used at-Lie'vin for taking samples of the combustion gases is a simplified adaptation of the more 

elaborate instrument at Altofts, and consists of an evacuated glass 

retort ending in a long-drawn closed bent tube at the end of which a 

detonator is fixed. The flame fires the detonator and the gases rush 

into the glass vessel. By filing an indention into the glass tube at a 

suitable distance above the detonator the tube is made to break at 

that point and the entrance of fulminate combustion gases is thus 

supposed to be obviated.

FIGURE 15. Device for breaking circuit in explosion gallery 

at Lievin.
INVESTIGATIONS AT EUROPEAN STATIONS. 139

RESULTS AT ALTOFTS AND LIEVIN. 

EXPERIMENTS WITH PROTECTION ZONES AT LIEVIN.

The following is a synopsis of results obtained at the LieVin gallery 

with zones of protection against coal dust:

The gallery was divided into three zones, a, b, and c, 75, 100, and 

60 meters long, respectively.

To test the effect of a watered zone of coal dust, zone a was 

lined with fine Lievin coal dust, containing 30 per cent volatile 

matter; b with watered coal dust (2 liters per meter); and c with 

coarse coal dust. The result was slow propagation of the flame, 

visible 60 meters outside of the gallery.

In a second test a contained coal dust as before; b was dustless, 

but watered as before; and c contained coal dust as before. The

flame stopped midway of zone b.

To test the effect of stone dust, in a was placed 450 grams of coal 

dust per cubic meter, in b 450 grams per cubic meter of pure stone 

dust, and in c 900 grams of coal dust per cubic meter. As a result the 

stone-dust zone stopped the flame about midway. If the stone dust 

strewn in zone b is reduced to 225 grams per cubic meter, however, 

the flame leaps over to c.

In another test of stone dust a and c were arranged as before, while 

b contained a mixture (450 grams per cubic meter) consisting of 25 per 

cent coal dust and 75 per cent stone dust containing carbonate of lime. 

As a result the flame leaped across zone b.

REPORT OF WORK AT LIEVIN.

In a few months M. Taffanel expects to publish a full account of 

the coal-dust experiments and recent research work carried out at 

LieVin station.

CONDITIONS AT ALTOFTS.

At the Altofts station, work in the gallery is discontinued during 

the winter months. The foggy weather which generally prevails 

during that part of the year obviously produces different working 

conditions, which render uniform results difficult and frequently 

impossible. Moreover, the gallery is closely situated to three railroad 

lines, and though a system of signaling has been agreed upon with 

a view to the safety of passing trains, any serious dislocation of 

the railroad traffic in foggy weather would practically compel the 

suspension of gallery work.

During such periods of adjournment the steadily accumulating 

laboratory work and questions of equipment are attended to. As 

already mentioned, the station now possesses a set of the finest 

instruments yet produced for this particular work.
140 THE EXPLOSIBILITY OF COAL DUST.

The file of boilers originally placed in line has been shortened so as 

to leave an intake gallery of 600" feet only.

The number of experiments carried out.to date amounts to 115, 

about half of which have been "spectacular," that is, repetitions of 

phenomena regarding which those in charge were long ago satisfied, 

but which it was considered necessary, or at least desirable, to repeat 

in order to convince stanch unbelievers in coal-dus.t explosions.

EXPERIMENTS WITH PROTECTION ZONES AT ALTOFTS.

Apart from the crucial demonstrations of true coal-dust explosions 

furnished there during two seasons, much attention has been given

Flame 160'

Coal dust 275'

Coal dust 275'

Dustless150'

Coal dust 275'

Stone dust 150'

Flame 55'

Coal dust 275'

Dustless 100' Flame 150'

Coal dust 50'

Coal dust 275'

Stone dust 100'

Flame 54' C.D. SO 7

Stone dust 100'

'Flame

Cannon Coal dust 275' 22' C.D. 50' 

FIGURE 16. Propagation of flame in coal-dust, dustless, and stone-dust zones.

to the question of the relative protection afforded by dustless and 

stone-dust zones. Stone dust has been found to be the most effective.

The results of experiments typical of that particular investigation 

are shown in figure 16.

Instructive as these tests undoubtedly are, they can at best serve 

as a stimulus for gaining further knowledge, and must not be regarded 

as exhaustive; nor will they help to discover what would happen 

should the length of the coal-dust zone be doubled, or even trebled. 

This can only be determined by future experiments on a still larger 

scale.
U. S. GEOLOGICAL SURVE

E. STONE DUST ON HANGING SHELVES IN ALTOFTS COLLIERY.
INVESTIGATIONS AT EUROPEAN STATIONS. 141

By means of the present equipment, however, it has been possible 

to show that when once initiated in the presence of abundant and 

inflammatory sustenance a coal-dust explosion will travel comparatively slowly for a hundred yards, when suddenly a high temperature will develop, accompanied by corresponding concomitant 

pressures. If, after this, conditions still remain favorable to propagation, the maximum pressures and velocities will probably prevail 

undiminished until opposed by tracts of nonsupporting or screening 

material.

EXPERIMENTS AT ALTOFTS ON MEANS OF IGNITION.

In reference to the initiation of a coal-dust explosion it may here 

be mentioned that although shot firing has hitherto been resorted to 

' in the galleries, the fact that a blown-out shot is but one of several 

possible causes in practice has at last been recognized, and consequently other means of ignition are about to be attempted. When 

the writer visited Altofts he had an opportunity to see an apparatus 

designed to produce a long gas flame of sufficient volume and duration 

to ignite coal dust in suspension without setting up high pressures 

such as are caused by explosives (PI. XII, (7).

It consists of a cylinder which is filled witn" gas. At the end of the 

outlet tube there is a specially constructed valve operated by a long 

turning bar carrying a weight at each end. One of the weights is 

suspended by means of a piece of wire which forms part of an electric 

circuit with a current of sufficient tension to fuse it. When the 

weight is released in this manner, the other weight causes the bar to 

revolve and thus to open the outlet valve. A heavily weighted 

piston drops to the bottom of the gas cylinder, causing the gas to 

rush out at an adjustable pressure. The gas is simultaneously 

ignited by an electric spark inside the gallery. Figure 17 is a rough 

sketch of the apparatus.

DISTRIBUTION OF STONE DUST IN ALTOFTS GALLERY AND MINE.

In the majority of coal-dust experiments carried out at Altofts 

props and tubs have been placed in the gallery and even stone packing 

has been built in behind the timbering (PI. XIII, A).

Hanging shelves carrying an extra supply of stone dust, as used in 

the Altofts mine, were likewise provided along the stone-dust zones 

(PI. XIII, £).

Through the courtesy of Mr. Garforth, chairman of the Altofts 

Colliery Company, the writer was given the opportunity of inspecting 

the distribution of stone dust in the mine. The dust is thrown onto 

the walls of the roadways by hand, the greater part of the coal dust 

adhering to them being displaced by the process. Stone dust is also
142 THE EXPLOSIBILITY OF COAL DUST.

strewn on the floor. It was stated that every district in the mine 

was isolated by stone-dust zones 600 feet in length. The dust 

required but occasional renewal, and its application gave little or no 

trouble. The cost was said to be about 1 penny (2 cents) per linearyard of roadway with a section of 10 by 7 feet, exclusive of cost of 

crushing and grinding.

Adjustable 

weights

Drop lever termed bfrto 

broadside position so as 

to sho.w arrangement of 

 weights

«WMS«!s

FIGURE 17. Elevation of apparatus for igniting coal dust by gas flame.

FUTURE WORK AT ALTOFTS.

- Experiments at the Altofts gallery will be resumed in May, 1910. 

Meanwhile a full report on the work done to date is being prepared 

and will be published shortly.
INVESTIGATIONS AT EUROPEAN STATIONS. 143

INVESTIGATIONS AT FRAMEBIES IN BELGIUM. 

DIRECTION OF INQUIRY.

In Belgium investigations on coal dust have been chiefly directed 

to the degree of inflammability as compared with the volatile matter 

contained in the dust, and also to the liability to ignition by explosives in the absence of gas.

OBJECTIONS TO WATERING ROADWAYS.

The possibility of minimizing the coal-dust danger by watering the 

roadways has had to be at least temporarily disregarded in view of 

the prejudicial effect both on the health of the miners and on the 

economical working of the mines which that measure would unquesFIGURE 18. Detachable section, Frameries gallery.

tionably entail. The Belgian mines are deep, depths of 800 meters 

being quite common, and many workings reach a depth of 1,000 and 

1,100 meters. The temperature at that depth is about 45° C. (113° F.), 

and if charged with humidity in addition the atmosphere obviously 

would not be fit to work in. Besides, watering near the coal face, 

where it is considered to be most necessary in some cases, has been 

found to cause serious disturbances in the coal-bearing strata, and 

thus materially to raise the cost of production of coal, quite apart 

from the increased risk of fatal accidents from falls.a

"In the face of such grave objections," M. Watteyne explained, 

"we have not yet felt justified in recommending compulsory [universal] watering in Belgium."

oCoal Is extracted mainly by pick In the Belgian gassy collieries. Explosives (of permitted character) are used only in rock work. In brushing back in the passageways watering is generally done In the 

vicinity of the shot before firing it. G. S. R.
Masonry 

block

FIGURE 19. Plan of Frameries gallery, showing propose
INVESTIGATIONS AT EUROPEAN STATIONS. 145

 *<

y g O. -B

38970° Bull. 425 1C
146 THE EXPLOSIBILITY OF COAL DUST. 

TESTS OF EXPLOSIVES.

Pending future investigation of other means of preventing propagation of coal-dust explosions, due attention has at all events been 

given to means of preventing their initiation through explosives. 

A number of experiments have been conducted at Frameries with 

permitted explosives in order to test their relative safety in the presence of coal dust alone. These tests were carried out in the same 

way and under the same conditions as when testing in presence of 

fire damp, the temperature in the gallery being maintained as nearly 

as possible at 25° C.

The coal dust used for all tests was taken from one of the Agrappe 

mines, and contained 21 per cent of volatile matter. Some of the 

coal raised in Belgium contains as much as 35 per cent, but as the 

number of collieries where this coal is found is small, and the quantity of dust given off by the coal insignificant, the other quality of 

dust mentioned was chosen.

At first the practice was to bring the coal dust into a state of 

suspension, but ultimately this was found to be unnecessary, as the 

agitation caused by the shots proved sufficient.

The tests were made in the gallery at Frameries. The bore hole 

of the cannon was 55 millimeters, the charging density being kept 

within the limits of 0.4 and 0.6.

Freshly ground dust, passing through a No. 90 mesh (1,280 to the 

square centimeter), was used throughout, as it was found to be more 

inflammable than dust kept for fifteen or twenty days. The moisture, 

averaging from 0.5 to 2 per cent, was eliminated by drying the dust 

at a temperature of 30° C.

The gallery was charged with 150 grams of dust per linear meter. 

Higher .dust charges did not materially affect the "charge-limite" 

of the explosives. !

The test comprised ten shots if or each explosive and these were 

fired on different days, so as :to introduce different hygrometric 

conditions.

The result of this series of trials has led to a slight revision of the 

list of permitted explosives. Of 2.4 explosives tried, only seven proved 

less safe in coal dust alone than in gas; five of these belonged to 

the ammonium nitrate class, one to the chlorate class, and one to 

the carbonite class. i

A revised list of permitted explosives now called "Explosifs 

S. G. P." (Securite-Grisou-Poussieres), canceling all previous lists, is 

published in a ministerial circular dated October 18, 1909. The 

maximum charges are given for each explosive, 'both as to gas and 

as to coal dust; they vary from 300 to 900 grams, A minimum
INVESTIGATIONS AT EUROPEAN STATIONS. 147

length of stemming is fixed at 20 centimeters. All cartridges must 

have the exact composition printed on their wrapper. Other precautionary measures in connection with shot firing remain in force. 

Speaking of results generally, the '' charge-limite" of permitted 

explosives fell in proportion to the increase of volatile matter contained in the coal dust. When inert dust was added the "chargelimite" rose.

EXTENSION OF GALLERY.

The gallery at Frameries has now been extended to a total length 

of 80 meters in one direction. The extension is connected with the 

old gallery by a section detachably bolted to both (fig. 18). When 

the full length of gallery is not required (for example, for testing 

explosives), the connecting piece, which rests on rails, is transversely 

run out of position. The annexed plans (figs. 19 and 20) show further proposed extension and details of construction.

INVESTIGATIONS IN PRUSSIA.

According to a recent announcement, the Coal Mining Corporation, 

of Westphalia, has decided to erect a trial gallery after the Lievin 

and Altofts type for the investigation of coal-dust explosions. The 

gallery will be built at Gneisenau, near Dortmund, where land has 

been bought for the purpose, and will be under the charge of Bergassessor Beyling, the present director of the Gelsenkirchen explosives 

testing station, which will also be removed to Gneisenau. The entire 

works will be completed in the spring of 1910. The Gneisenau coaldust gallery will in all probability be of similar construction to that 

recently adopted at Lievin an upcast section of armored concrete 

and a downcast gallery of 10-millimeter plate boilers, although for 

the latter portion some mining engineers are in favor of wood construction, which could be repaired more easily and at less cost. 

There will be two parallel lengths of gallery with crosscut connections 

at varying angles. A total length of 300 meters is mentioned.

Save such work as was feasible in the short Gelsenkirchen gallery 

(34 meters), more particularly in respect to the testing of explosives, 

no special study of coal-dust explosions has proved practicable at 

Mr. Beyling's station, but the matter will be taken in hand immediately when the new station is ready.

Preliminary tests with local coal dust have shown that while dust 

containing 24 per cent of volatile matter and passing No. 150 mesh 

was regularly ignited by 160 grams of gelatin dynamite, no ignition 

of the same dust took place when the gallery had been previously 

watered.
148 THE EXPLOSIBILITY OF COAL DUST. '

SPECIAL PREVENTIVE MEASURES. 

BREAKING COAL BY DIEECT WATER PRESSURE.

'One of the recommendations contained in the report of the royal 

coal-dust commission of 1894 was as follows:

The substitution for explosive agents of similarly efficient methods of bringing 

down coal and stone which are quite free from the special dangers attending the use 

of those agents.

Attempts have frequently been made, both before and after, to 

give effect to this suggestion, but none of the methods proposed has 

so far proved successful. Certain experiments made many years ago 

at Saarbrucken at the suggestion of Herr Meissner, privy councilor 

of mines, at that time in charge of one of the state collieries in that 

district, may be cited as offering an interesting exception. This 

gentleman was, however, suddenly transferred to another sphere of 

activity, and the trials were discontinued. But recently the method 

has been again taken up in a Westphalian coal mine and put to 

practical tests with considerable success.

As the process comes under the head of "means for preventing 

coal-dust explosions/' it may fittingly be described in this report. 

Indeed, as a preventive means, it may be said to start considerably 

ahead of all other remedies proposed, inasmuch as it is directed 

against the very source of coal dust, the solid coal itself. Briefly, it 

may be described as hydrostatic injection of the coal face (in German 

'' Stoss trankung'').

Into a bore hole; preferably bored at right angles to traceable 

divisions or slips in the coal, an iron water pipe is tightly wedged 

so as to prevent any back flow. Water is then turned on and allowed 

to permeate the coal face under a pressure of about 12 atmospheres. Unless the coal is absolutely impermeable the forced endosmotic action is so quick that in about fifteen to twenty minutes loud 

"working" of the seam is heard, followed shortly afterwards by a 

rush of water from some point offering the least resistance. The 

operation is then finished and the water is turned off.

As a rule the impregnated area is about twice or three times the 

cube of the depth of the bore hole, and where the coal is naturally 

interstitial in structure the whole of the affected area may be got by 

the pick.

In the Scharnhorst mine, near Dortmund, the writer saw the 

method practically employed in a seam of schistose coal 2£ meters 

thick and dipping at an angle of 80° from the horizontal. A bore 

hole was hand drilled in three divisions of different diameters, .to 

provide the necessary "grip" for two conical wedges fixed on the
INVESTIGATIONS AT EUROPEAN STATIONS. 149

water pipe. (See fig. 21.) The pipe was inserted into the bore hole 

and sledge-rammed home. The pipe was then connected by a hose 

to the water main of the pit (now easily accessible in all dusty pits 

in Germany) and the water was turned on.

After twelve minutes loud crackings were heard from several parts 

of the coal seam, and presently the water had found an outlet some 

10 feet above the bore hole and came rushing down the coal face. 

It was stated that the one bore hole had loosened 36 half-ton cars 

of coal, all of which would be got by the pick and at about half the 

cost of blasting.

In reply to a question whether the method would prove practicable 

in less favorable conditions, it was stated that practically all seams, 

whether horizontal or perpendicular, were amenable to the treatment, 

but that not every coal could be got by pick with equal facility. 

But even if explosives had to be used afterwards, the effect of the

injection was said to be such as to eliminate danger of using them, 

as far as coal dust was concerned. The coal was rendered just moist 

enough to prevent the formation of appreciable amounts of dust at

'///i/llllllllluiiiiiilllliiilliiitiiiiiiiiiiiinii/////.

'FIGURE 21. Device for dislodging coal by injection of water.

the face, and all watering of the face could be dispensed with. The 

atmosphere in the workings never became dust-laden, hence there 

could be no clogging of lamp gauzes.

On returning toward the shaft the writer found the coal in passing 

cars clammy to the touch and haulage roads practically free from 

coal dust.

The double cone collars on the insertion pipe, are said to be an 

improvement on Herr Meissner's method, and it is understood that 

patents have been applied for.

KRUSKOPF SPRAYING PROCESS.

Another method of staying accumulations of coal dust in mines 

was mentioned to me while in Westphalia, namely, the Kruskopf 

spraying process. The inventors, Messrs. H. and E. Kruskopf, of 

Dortmund, propose to wet the walls of underground roads with a 

certain chemical solution, or to suspend similarly soaked cloths from 

the roof of haulage and main roads, with a view to preventing deposits 

of dust and to stopping coal-dust explosions.
150 THE EXPLOSIBILITY OF COAL DUST.

Although not without useful features, possibly in connection with 

protection zones, the invention has been presented in a form that is 

not likely to be adopted in practice, being too costly and of doubtful 

efficacy. The inventors refused to give particulars, owing to a pending application for American patent rights.

EXHAUST STEAM AS A PREVENTIVE OF DUST EXPLOSIONS.

By FRANK HAAS.

MOISTURE IN COAL DUST.

HOW MOISTURE PREVENTS EXPLOSION.

Exhaust steam is used to prevent coal-dust explosions on the theory 

that wet coal is more difficult to ignite than dry coal; also that a 

flame propagating through moist air suffers a greater temperature 

loss than one propagating through dry air.

To make coal dust absolutely and theoretically inert as a combustible that is, to make a mixture of such composition that it would 

not ignite or consume from heat of its own generation would require 

six or seven times its weight of water. This quantity of water is so 

large, causing, in fact, a condition practically equivalent to submergence, that its use is impossible. Fortunately the total quantity 

of heat which coal dust supplies is not the important factor in dust 

explosions, but rather the temperature of ignition. If the temperature is under control absolute safety may be attained. Before it is 

possible to ignite the combustible portion of coal dust or any other 

combustible containing water, physically or otherwise, such water 

must be evaporated.

RESISTANCE OF COAL DUST TO MIXTURE.

A very serious obstacle to complete success in preventing ignition, 

not only by introducing water by exhaust steam, but by any other 

method of application of water, is the property of coal to resist 

mixture with water, except to a very limited extent. It has been 

shown," in experiments described by the writer, that extremely fine 

coal dust, after being submerged in water and thoroughly stirred 

with it, in a way that with almost any other material would result 

in a mixture, will rise to the surface so dry that a slight breath of 

air will throw it into a cloud, leaving the water almost clear.

a Haas, Frank, Is coal dust as such explosive? Mines and Minerals, December, 1908, pp. 227-229.
EXHAUST STEAM AS A PREVENTIVE. 151 

AMOUNT OF WATER ABSORBED BY COAL DUST.

Though the writers' experiments along this line have not been completed, it has been determined that coal dust does, to a certain 

extent, absorb moisture, which for gas coal (to be hereinafter considered) amounts to about 4 per cent.

In nominally dry atmosphere, the dust which was experimented 

with contained about 1.5 per cent of water. In the return air way of 

a mine in which the air was kept moist to the point of saturation, 

dust was collected from the side walls of the entry where it had lodged 

on the small projections of the solid coal. The moisture determinations obtained for this dust were extremely various, the minimum 

moisture being 4 per cent, the maximum 42 per cent, and the average 25 per cent. As the atmospheric conditions surrounding each 

particle were practically the same, the results should have been 

uniform if the content of water so determined were one of the physical properties of the dust. As they were not uniform, however, it 

was concluded that the minimum more nearly expressed the absorptive power of the coal and that any additional water was merely 

mechanically held in contact.

Now, 4 per cent is by far too little to be considered of much consequence, hence additional water uncombined with the coal is necessary for protection against ignition. From such of the writer's 

results as are available, however, it appears that the element of time 

enters into the question, and it is apparent that the longer dust is 

exposed (within a limited period) to water or saturated air the larger 

will be the quantity of water absorbed.

AMOUNT OF WATER REQUIRED IN MINE.

If the roof, floor, and sides of any entry are covered with a film of 

water of sufficient thickness, it will not only prevent the addition of 

fuel to an explosion, but will extinguish an explosion once started. 

This latter action, as it depends largely on contact, would not be 

instantaneous, but would be effective in a comparatively short distance if the wet conditions were maintained. To demonstrate this, 

let us assume that in an. entry 10 feet wide and 6 feet high there is 

a film of water 0.025 inch thick on floor, roof, and sides. In one 

linear foot of such entry there would be 32 square feet covered by 

this film, making in all about 115 cubic inches, or 4.25 pounds of 

water. Let us suppose an explosive flame passes through this entry, 

say, at a temperature of 4,000° F. and at a pressure of 3 atmospheres. 

If the specific heat of the gases be taken at 0.3, the weight of a cubic 

foot of the gases at normal pressure and temperature would be ap-
152 THE EXPLOSIBILITY OF COAL DUST.

proximately 0.1 pound. At normal pressure and a temperature of 

4,000° F. (absolute) the water vapor would weigh roughly \ ^^ or

0.011 pound per cubic foot. At 3 atmospheres pressure the weight 

would be 0.033 pound per cubic foot. The heat units in 1 linear 

foot of entry 10 by 6 feet would be 2,376 B. t. u., since the temperature (4,000) times the weight (0.033X60) times the specific heat 

(0.3) equals 2,376.

It requires 756 B. t. u. to evaporate 1 pound of water, hence 2.376 

B. t. u. would evaporate about 3 pounds of water. If, then, a film 

of water 0.025 inch thick is maintained, which is equivalent to 4.25 

pounds of water per linear foot, to vaporize this water would absorb 

all the heat of the explosion and drop the temperature well below 

the ignition point of the coal dust.

It may be noted at this point that the smaller the area of the entry 

the less is the thickness of the film of water necessary. Hence open 

spaces in a mine should be avoided as much as possible. Mines that 

have idle rooms or unpillared sections under ventilation introduce 

an unnecessary element of danger in spite of the fact that the force 

of an explosion may be dissipated in a large opening.

DISTRIBUTION OF MOISTURE.

It is difficult or impossible to maintain or even establish a uniform film of water over the surface of the coal. Coal dust and solid 

coal so resist the contact of water that it can not be applied to them 

in better form than as "drippers" on roof and side walls. It is 

possible to provide in this form an amount of water equivalent to the 

film, but its effectiveness is not so complete. To establish such a 

condition in a mine is merely a matter of mechanical labor, but to 

maintain it requires vigilance with constant labor, or else an atmosphere either neutral or supersaturated with moisture.

EXHAUST STEAM IN OPERATION. 

VALUE FOUND BY ACCIDENT.

In connection with the following account of experiments and observations the reader should have in mind the nature of relative humidity 

and the general relations of air and water vapor.

The introduction of steam into the air current in the Fairmont 

region began about three years ago. At that time the danger from 

coal dust was not so seriously considered, and the steam was not 

introduced for the purpose of moistening the coal dust. It was rather 

for convenience to get rid of the exhaust steam from a pump and 

hoist engine rather than carry it up a shaft. The effect of the stearn
EXHAUST STEAM AS A PREVENTIVE. 153

in keeping the entry moist was observed, and when the question of 

watering the mine was more seriously considered a year or so later it 

was decided to continue to utilize the means that had been accidentally discovered.

RECORDING INSTRUMENT.

As no records of temperature and humidity of the atmosphere of 

the vicinity were available, it was necessary to produce such records 

extending over all the seasons of the year. Individual observations 

taken periodically were obviously insufficient, considering the large 

fluctuation in comparatively short times. For a recording instrument 

a hygrothermograph, manufactured in Baltimore, Md., was used. 

This instrument records both temperature and humidity for weekly 

periods. No difficulty was anticipated with regard to the temperature, but the calibration of the instrument for humidity was attempted

with considerable misgivings, as the actuating part is a hair that 

expands or contracts in direct proportion to the relative humidity of 

the atmosphere. However, the instrument was set up in a covered 

box and checked with a standard psychrometer for temperature and 

humidity at least twice a day for several weeks. It was considered 

sufficient to test the instrument at the maximum and minimum 

points of both temperature and humidity, which occurred usually 

at 8 a. m. and 4 p. m. After adjustment and thorough calibration 

this instrument and two others that were bought later gave very 

satisfactory results. While far from perfect, it is nevertheless the 

best known to the writer for continuous record and gives results well 

within the limit of error of other observations necessary for the 

investigation.

RECORDS OF OUTSIDE TEMPERATURE AND HUMIDITY.

In figure 22 is presented, together with the results of the weekly 

records from the instrument, the daily range with maximum and 

minimum of temperature and humidity of the outside air at Fairmont, W. Va., from June 1, 1908, to June 1, 1909. In this chart the 

water vapor has been calculated and recorded in gallons per 100,000 

cubic feet. This is simply a convenient figure for comparison, as 

100,000 cubic feet is ordinarily a practical unit for mine ventilation 

and is one that makes the quantities of water whole numbers rather 

than fractions. The chart shows at a glance the difference between 

the quantity of water vapor held by the atmosphere in winter and in 

summer.
1903 

jl £ JUNE JULY AUGUST SEPTEMBER - OCTOBER NOVEMBER DECEMBER JAN

o g 5 10 1520 25 5 10 15 20 25 5 10 15 20 25 5 10 15 2O 25 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25 5 1O 

FIGURE 22. Atmospheric temperature and water-vap
EXHAUST STEAM AS A PREVENTIVE. 155

will show an accumulated deficit of water 

amounting to 2,000,- 

000 gallons per year. 

Two months during 

the year the quantity 

of water taken into 

the mine by the air 

is in excess of that 

taken out. This 

period is approximately from the 

middle of June to 

the middle of August. 3

Hence it appears §

that artificial means "

w

of watering are neces- ^ 

sary during the » 

greater part of the a 

year from August g. 

15 to June 15. Dur- -g 

ing that time at least I 

2,000,000 gallons of | 

water must be sup- | 

plied. This figure, f 

of course, is based I 

only on one year's | 

observati o n s, and | 

may be greater or » 

less from year to year, f 

yet the indications g 

are that theobserva- ? 

tions in the second 

year will practically 

coincide with those 

of the first year.

In supplying the 

deficiency of water, 

the aim should be to 

cover the maximum 

deficiency for any 

period rather than 

the minimum at any 

one time. During 

the year from June

Gallons per 100,000 cubic feet
156 THE EXPLOSIBILITY OF COAL DUST.

1, 1908, to June 1, 1909, the minimum average temperature for 

one day was 21° and the minimum average content of water vapor 

per 100,000 cubic feet of air was equivalent to 1.3 gallons of water. 

The lowest weekly average temperature was 34° with a concurrent 

average humidity of 3 gallons, and the lowest monthly average 

temperature was 39° with 3 gallons of water. As the deficiency 

and excess of water in a mine are more or less cumulative, it 

would be safe to take the weekly average as a basis for calculating the 

quantity, of heat .and moisture to be supplied by artificial means.

According to the records, the temperature of the return air current 

during the coldest weather of the year was 55°, and it carried 7.2 

gallons of water per 100,000 cubic feet. If, then, sufficient heat were 

constantly supplied to raise the intake temperature from 34° to 55°, 

and sufficient water to raise the quantity from 3 to 7.2 gallons per 

100,000 cubic feet (the rate per minute), the conditions would be 

such as to provide an excess of water in the mine and keep the mine 

air saturated. Holding to a unit of 10.0,000 cubic feet per minute, we 

find that it will require 39,900 B. t. u. per minute and 4.2 gallons 

of water.

AMOUNT OF HEAT AVAILABLE.

Monongah No. 8 mine fan during these observations was making 

about 135,000 cubic feet per minute with 1^-inch water gage. By 

the common formula this required about 30 horsepower; by indicating 

the engine, however, it was found that 55 horsepower was actually 

supplied. This difference is due to the great loss in efficiency in 

running a large engine below capacity. If 55 horsepower is supplied, 

with a steam pressure of 100 pounds, and consumes 35 pounds of 

water per minute per horsepower, about 1,500 B. t. u. is used by the 

engine per minute for power and about 31,000 B. t. u. is available for

heating the air if the exhaust steam is turned into the mine. This 

amount of heat would be sufficient to increase the temperature 12°, 

or from 34° to 46°. It would also furnish 3.85 gallons of water per 

minute and would raise the water content of the air 2.8 gallons, or 

from 3 to 5.8 gallons per 100,000 cubic feet of air.

EFFECT OF STEAM ON MINE AIR.

These figures are more or less theoretical, and though both the heat 

and the water of the exhaust steam enter the mine it does not necessarily follow that all of both are available for the saturation of the 

mine air.
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FIGURE 24. Chart of temperature and relative humidity of intake air with 

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158 THE EXPLOSIBILITY OF COAL, DUST.

temperature, the humidity 

within the mine showed a 

tendency to equalize itself and 

produced a more nearly 

straight line. The fact that 

it ran higher than the humidity 

at the fan is due entirely to the 

previous wet condition.

OBSERVATIONS OF EFFECT OF 

STEAM.

A record (fig. 25) was also 

taken with the instruments in 

the same position and with the 

exhaust steam going into the 

mine. The fan instrument was 

to show the atmospheric humidity, while the instrument 

400 feet inside the mine showed 

the full effect of the steam. 

The exhaust steam was not 

turned into the mine until six 

hours after the instruments 

started recording.

The moisture made itself 

apparent immediately by saturating the air ,and holding the 

humidity at 100 per cent,

irrespective of the outside 

condition. The temperature 

showed an average increase of 

only 8°.

EFFECT OF HEATING MINE 

AIR.

It is to be noted, however, 

that the increase in temperature was greatest when the 

outside temperature was lowest. 

The amount of heat supplied 

being uniform, a constant increase in temperature should 

be expected if there were no 

disturbing elements present.
U. S. GEOLOGICAL SURVEY BULLETIN 425 PLATE XIV

.!. RADIATOR AND STEAM PIPE IN USE, MONONGAH NO. 8 MINE.

11. A SPRAY IN AN ENTRY.
EXHAUST STEAM AS A PREVENTIVE. 159

These curves, showing plainly that disturbing elements of considerable magnitude did exist, led to a separate study, which resulted in 

important conclusions, to be noted later in this paper. The principal 

fact brought out was that there was not sufficient heat supplied to 

establish a normal temperature of. 55° during this season of the year. 

To supply this deficiency of temperature it was then decided to put 

in an air preheater. This was done -by placing 1,200 feet of 2-inch 

pipe in nine coils around a coal pillar, which happened to be conveniently situated behind the fan, and between the fan and the point 

where the exhaust steam was allowed to escape into the air (fig. 26). 

In Plate XIV, A, is reproduced a photograph showing one corner of 

this radiator and the exhaust-steam pipe in operation.

An endeavor was made to measure the heat supplied by this radiator in order to get a practical figure for the size or length of pipe 

required to heat a unit volume of air. This was found very difficult

FIGURE 20. Plan of intake at Monongah No. 8 mine, showing arrangement of live-steam heater and

exhaust-steam pipe.

to accomplish, and while several methods were tried they were not 

pursued far enough for satisfactory results.

Figure 27 shows the difference in temperature and vapor contents 

between the outside air and the air 400 feet from the fan, when both 

the exhaust steam and the heater were used. The air shows complete saturation,while the temperature was raised on an average 19° F. 

A disturbing element was noted in this experiment, as in that in 

which only the exhaust steam was used. There was evidently another 

source of heat present which affected the results more than either the 

exhaust steam or the heater. It was noticed that the difference iii 

temperature was less when the instruments were moved nearer the 

intake and greater when they were moved farther away. The item 

of radiation of heat from the side walls of the entry, which at first was 

considered inappreciable, developed into the most prominent factor.
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EXHAUST STEAM AS A PREVENTIVE. 161

atmospheric temperature. The unknown factor makes the application of an equation impossible.

The fact demonstrated by these observations is that radiation from 

the side walls has considerable effect in raising the temperature of the 

air. In this particular test in 4,000 feet of mine entry over 30,000 

British thermal units had been radiated per minute, which would be 

equivalent to heat derived from burning over a ton of coal per day. 

It was the utilization of this radiated heat that led to the abandonment of the preheater. This can be done in every mine where the 

air travels over 3,000 feet at a velocity not to exceed 500 feet per 

minute before it reaches the men to be served with ventilation. For 

example, in the mine in which the observations were made, if suffiV.= Volume in cubic feet. 

H.S.^Area of exposed surface 

or radiating surface.

200 400 600 800 1000120014001600180020002200240026002800300032003400360038004000 

Distance from fan (blowing) in feet

FIGURE 28. Progressive change of temperature of air current due to radiation. Average velocity, 453 

feet per minute; volume of air, 66,432 cubic feet per minute.

cient exhaust steam were introduced at the end of the 4,000 feet the 

additional heat would raise the temperature to or above the normal 

mine temperature, even with an outside temperature of 25°. The 

conditions for complete saturation would be continuously in force, 

and the result would be a wet mine, not only theoretically wet, but 

looking and feeling wet enough to satisfy the practical man. There 

is, however, serious objection to carrying an exhaust-steam line 3,000 

or 4,000 feet into a mine, on account of the back pressure on the 

engine and the probability of adverse grades; in fact, the practical 

difficulties in the way are sufficient to condemn the method. It is 

possible, however, to avoid this objection by a sacrifice of part of the 

.moisture.

38970° Bull. 425 10 11
162 THE EXPLOSIBILITY OF COAL DUST. 

MOISTURE CARRIED AS FOG.

The capacity of air to carry water vapor is limited by its temperature, but the quantity of water that can be carried mechanically 

in the form of a fog is limited only by the velocity of the air current.

The relative proportions of water that can be carried in the form 

of vapor and as fog have not been determined. The proportions 

can very readily be determined, however, and observations were to be 

carried out on this point during the winter of 1909-10. The first 

effect of exhaust steam on air would, be the saturation of the air 

with water vapor, the remainder of the steam being deposited as 

water or carried in the form of a fog. This fog near the inlet of the 

exhaust steam is in the form of a dense white cloud, so thick as to 

hide the light of a mine lamp only a few feet away. In traveling 

with the air from the exhaust-steam intake the cloud gradually 

becomes thinner; farther in the air is clear near the side walls and 

the roof, the fog traveling in the center of the entry in the form of a 

cylinder with a revolving forward motion. The cylinder or cone 

form gradually grows less in diameter, ending in an indefinite point. 

This approximate point has been designated 'the fog line. It is 

remarkable how promptly the position of this fog line responds to 

a rise or fall of outside temperature by shifting bapkward or forward.

For practical purposes and comfort to miners it is advisable to 

keep this fog line from advancing to the working face. This can be 

done in several ways first, by reducing the volume and thereby 

the velocity of the air current; second, by increasing the number or 

area of air ways; third, by so changing the air courses that the distance to the working face is increased. Conditions in a developed 

mine where a blowing fan is used would be very unusual if no one

nor any combination of methods could be utilized to bring the fog 

line within the limits of practical application.

QUANTITY OF STEAM NEEDED FOR SATURATING MINE AIR.

In the observations made and the results obtained so far the necessary quantity of exhaust steam for a unit quantity of air has not 

been definitely determined. An approximately correct figure was 

assumed to be three-quarters of a horsepower of exhaust steam (from 

a simple reciprocating engine) for each 1,000 cubic feet of air supplied. The size of the mine does not enter into the assumption. In 

mines of small development the ratio of fan horsepower used to 

quantity of air supplied is less than that noted above as necessary 

for saturation. In mines older and of larger developed area, the 

ratio may be greater than necessary. In Monongah No. 8 mine, 

in which most of the experiments have been conducted, the ratio is 

about 0.4 or only 53 per cent of what is necessary. In order to make
USB OF STEAM AND WATEK SPKAYS. 163

up this deficiency it is intended to put a brattice immediately behind 

the fan, with sliding doors, so that the area can be contracted to a 

point where the engine will indicate 100 horsepower while still 

delivering the same quantity of air.

It has been suggested that for the additional steam live steam be 

used, thus saving the extra work of the engine or replacement by a 

large engine. The effect would be the same, but its regulation would 

not be under control, and, furthermore, there would be nothing to 

indicate whether the live steam was actually in continuous operation. 

Every fan is or should be equipped with a recording water-gage 

chart, and if the steam goes through the engine this water-gage 

chart will indicate both the quantity of air supplied and the amount 

of exhaust steam used, with sufficient accuracy for practical purposes. 

It would be much too easy for a sleepy or lazy fireman to shut off the

live-steam pipe with no one the wiser for it, and this is sufficient 

reason for putting the steam through the engine. It is true that 

steam meters could be used, but these would show only the total 

quantity supplied, and unless a recording instrument could be 

added they would fail in their purpose. Furthermore, additional 

horsepower is required only in exceptional cases, and in them only 

temporarily.

To apply the method of watering mines with exhaust steam, outlined in the preceding pages, a blowing fan is necessary. The method 

can not be applied with an exhaust fan because of the dense fog 

which necessarily occurs at the intake and for some distance in from 

the mouth of the mine. In most mines it is possible to change from 

exhaust to blowing ventilation, and if other conditions do not prevent it would pay to do so. There are strong arguments in favor 

of exhaust fans in some mines, particularly mines that were originally planned for such ventilation and worked by methods adapted 

to it. In such mines an air preheater must be used. While experiments along this line indicate that preheating can be successfully 

done, it will require constant attention for its control, besides the 

expense of erecting and maintaining the air heater.

USE OF STEAM AND WATER SPRAYS IN OKLAHOMA

MINES.

By CARL SCHOLZ. 

PURPOSE OF INQUIRY.

The writer's investigations in the Oklahoma field were begun 

because of the comparatively large number of mine fires and mine 

explosions in that district; also because of the trouble from falls 

of roofs, which add constantly to the dangers and cost of mining 

operations.
164 THE EXPLOSIBILITY OF COAL DUST.

A tabulation of the accidents in mines of the Rock Island Coal 

Mining Company resulting from explosions, mine fires; windy shots, 

and roof falls drew attention to the fact that the accidents and 

expense from roof falls diminished with the arrival of cold weather, 

but that the number of accidents from the other causes mentioned 

increased. The writer was prompted to continue his inquiry in 

this direction with a view to determining means of preventing, if 

possible, the disintegration of roofs in summer and the explosions 

and mine fires in winter.

MOISTURE AND MINE AIR.

The roof falls were ascribed to the deposits of moisture or "sweat" 

on the roof and ribs, at first near the intake, then slowly extending 

farther into the mine. With the return of cold weather the moisture 

gradually disappeared, the rate of appearance and disappearance 

varying with the local climatic conditions.

A series of observations made with thermometer and hygrometer, 

both inside and outside the mines, showed that during the summer, 

when the temperature outside averaged 85° F. for twenty-four 

hours, with a maximum of 95° or 100°, the mine temperatures 

fluctuated between 70° and 78°; and that during the winter, with a 

temperature of 40° to 50° outside, the mine temperatures ranged from 

60° to 67°, the exact temperature necessarily depending somewhat 

on the extent of the mine. In a new and less extensive mine the 

fluctuations follow more closely the outside temperature; in an 

older mine, with more extensive workings, the return air does not 

show many degrees difference between summer and winter.

At about the time that some experiments were being conducted 

in one of the mines of the Rock Island Coal Mining Company, water 

overflowed from one of the adjoining mines and flowed down a slope 

2,000 feet to the shaft of the mine under investigation. This slope 

was the intake air way of the mine. Apparently the contact of the 

air with the water tended to reduce in this mine the number of 

local dust explosions and gas ignitions from black-powder shots, 

without increasing the number of roof falls. The absence of effect 

on the roof was attributed to the uniformity of the humid condition 

of the mine air, in contrast to the former extreme changes from 

winter to summer, or during shorter intervals.

This observation led to an investigation of the relation of the 

humidity of mine air to dust explosions. Cold air entering a mine 

has a low capacity for absorbing water. As it is warmed by contact 

with the warmer mine walls its capacity for moisture increases 

rapidly, so that it draws the moisture from the mine and leaves the 

dust and timbers and faces of the coal dry. Hence in winter water 

is carried from the mine by the air current, and in summer moisture 

is deposited on the roof and walls of the mine, or the mine "sweats."
USE OP STEAM AND WATER SPEAYS. 165 

APPLICATION OF STEAM AND WATER SPRAYS.

The writer had a steam coil installed near the top of an intake 

shaft for use in cold weather, consisting of several hundred feet of 

pipe through which exhaust steam was passed. The moisture condensed from the steam was carried in with the downcast air current; heating the air to some extent and adding to its humidity. 

However, the amount of steam that could be exhausted into the 

hoisting shaft was limited by the necessity of having the atmosphere at the bottom clear of fog. This was found not to be 

sufficient. The mine continued dry within 1,000 feet of the intake. Water sprays were tried with good results, and then installed 

more extensively. As the main intake slopes were naturally more 

or less wet, the working faces farthest down the slope, but

first on the air currents, were not troubled with drying out as

were those farther along the air current. Hence it was necessary 

to place sprays at intervals for remoistening or humidifying the air, 

the places being determined by the hygrometer or wet and dry bulb 

thermometers. In general it was found that a relative humidity 

of over 85 or 90 per cent gave the working places a satisfactory degree 

of dampness. Such increased humidity lessens the chances of a dust 

explosion, both because it dampens the dust and because in the 

presence of a blown-out shot a higher temperature would be required 

for ignition of both gas and dust by reason of the higher percentage 

of water vapor in the atmosphere.

The spray heads found to be best were those of a type that will 

make as fine a spray as possible for more ready absorption by the 

air currents. They should be of such design that they will not clog 

easily. Clogging is one of the chief troubles in the use of these 

sprays, and close attention must be paid by the foremen to see that 

they are running freely. This takes only a moment's attention. A 

spray head in a heading is shown in Plate XIV, B.

On a main intake and haulage slope a different type of spray has 

been tried a short vertical pipe with a groove cut in it and holes 

perforated at intervals in the thin metal left at the back of the 

groove. These holes are easily cleaned by running a point down the 

groove. This spray pipe is placed at one side of the road and throws 

the spray against the air current.

The arrangement of sprays in the mine where the principal experiments were conducted is shown in figure 29.

An example of some of the results obtained is shown in the table 

below. The readings were taken by the ordinary dry and wet bulb 

thermometer, the air volume was determined with an anemometer, 

and the barometric fluctuations were noted at the surface, at the 

head of the most important splits, and at the foot of the upcast.
166 THE EXPLOSIBTLITY OF COAL DUST.

JLJLJLJ

ySPBAY

vLJ LJ UJ LJ LJ LJ

> oSPRflY oSPRAY

rn rn rn rn rn c

FIGURE 29. Location of sprays in entries, No. 8 mine, Hartshorne, Okla.
USE OF STEAM AND WATER SPRAYS. 167

Observations on air in mine of Rock Island Coal Mining Company in Oklahoma.

Date.

Jan. 4,1908 

Feb. 25,1009 

Sept. 14,1909

Location.

f Surface........ 

Slope 2(> "..... 

Air shaft a..... 

Surface........ 

Slope 20 «. .... 

Air shaft ...... 

Surface <>.. . ...

Slope 20 c..... 

Air shaft......

Time.

8. 50 a. m.. 

9.20 a. m.. 

10.00 a. m. 

4.17'p. m.. 

4.30p.m.. 

4.45p.m. . 

11. 40 a. m. 

12.20 p. m . 

12.50p.m.

Temperature.

°F. 

48 

05 

07 

58 

55 

68 

82 

74 

74

Relative humidity.

Per cent. 

90 

84 

85 

34 

04 

89 

30 

95 

95

Volume 

of air per 

minute.

Cubic/eel. 

1,000 

25,000 

00,000 

1,000 

20,000 

58,000 

1,000 

24,000 

63,000

Quantity of 

water per 

minute.

Gallons. 

0. 0570 

2.405 

0. 375 

. 03148 

1.3977 

0.7100 

.07104 

3. 5124 

9.219

Total water contents, 24 hours.

Downcast.

Gallons. 

4,970

2,029 

0,498

Upcast.

Gallons. 

9,180

9,003 

13,275

o Sprays in operation; roads well sprinkled. & Weather very dry. c "Sweat" disappearing rapidly.

It may be observed from the above tabulation that the method of 

exhaust ventilation was employed in this mine, the hoisting shaft 

being the intake. It is the writer's opinion that gassy or dusty mines 

are preferably ventilated with an exhausting fan. By this method 

the haulage roads have fresh air, and the following marked advantages 

result: (a) Electricity and lights are kept out of the return-air current, 

which is important if the mine makes gas; (&) the intake is under 

inspection, so that falls will be taken care of promptly; (c) in case of 

mine fires or explosions fresh air comes into the main entrance, where 

there are usually the best facilities for quick'escape.

COST OF WATER SPRAYS.

Objection has been made to the spraying system on account of 

cost of installation. While no general estimate of the necessary 

outlay can be made, as each mine has its own peculiar conditions, an 

average of 5,000 feet of 1^-inch pipe, with 6 to 10 spray heads, should 

be sufficient to saturate the air current in a mine producing 500 to 800 

tons per day. The cost of operation is slight. The labor charge is 

limited to that required for the examination of the spray heads to 

see that they are not clogged. This may be made one of the duties 

of the mine foremen.

The chief cost is in the extension of pipe lines and sprays and in 

supplying water. If the mine makes water that is not too acid to 

use, the cost of supplying water is insignificant.

A test will readily convince a mine management of the improvement 

in the atmosphere of a mine in which sprays have been introduced. 

It is purified and free from dust, and by dampening the coal dust 

one of the great sources of danger of an explosion is minimized.
168 THE EXPLOSIBILITY OF COAL DUST. 

SELECTED BIBLIOGRAPHY. 

1800-1870.

BALD, JOHN. On the fires that take place in collieries. Edinburgh New Philosophical Journal, vol. 5,1828, pp. 101-121. Notes that gas explosion might fire 

"the small dust of the roads in the mines" (p. 102).

BORGUIA, . Traite cornpletdemecanique applique'eaux arts. Paris, 1818. On 

p. 197 is a description of a Niepce engine, which had a piston impelled by the 

the explosion of a mixture of coal and resin dust.

BUDDLE, JOHN. Account of an explosion which took place in Jarrow colliery on the 

3d of August, 1830. Trans. Northumberland Nat. Hist. Soc., vol. 1, 1831, pp. 

184-205. Refers to " charred coal dust."

Du SOUICH, . In a report in 1855 as government engineer of the St. Etienne 

Department he noted the part played by dust in an explosion at the Charles pit, 

Firminy, Loire, France, August 29, 1855. First notice in France of coked dust.

FARADAY, MICHAEL, and LYELL, CHARLES. Report on the' explosion at the Haswell 

collieries. Philos. Mag., ser. 3, vol. 26, 1845, pp. 16-35. Point out evidence of 

coal dust taking part in explosion. First decided opinion on subject.

GREENWELL, G. C. Use of gunpowder in mines. Trans. Manchester Geol. Soc., vol. 

10, 1870, pp. 20-27. Notes probability of blown-out shots igniting coal dust.

HODGSON, J. Fossil fuel, collieries, and the coal trade. 1820. Describes (p. 256) 

dust cloud and coking of dust at Felling colliery explosion, 1812.

VERPILLEUX, : . Sur une systeme des portes destinies a limiter les accidents 

produits par le grisou. Bull. Soc. Ind. Min., vol. 9, 1864, p. 466. Annales des 

mines, ser. 6, vol. 12, .1867, pp. 561-566. Says fine coal dust in some mines spreads 

explosions; speaks of coked dust.

1871-1880.

BURAT, A. Les houilleres en 1872. Contains notes from Jutier, chief mining engineer of the Department of Sadne-et-Loire, dated March 21, 1872, stating belief 

that blown-out shot can ignite fine dust like that of coal from Sainte-Marie seam.

DESBIEP, P., and CHANSELLE, J. De 1'influence des poussieres charbonneuses dans 

les explosions de grisou. Bull. Soc. Ind. Min., ser. 2, vol. 4, 1875, p. 205. 

Review of discussions at meeting of society 1872-1875. Early observations of

Du Souich and other French engineers. Describes experiments made by society

in February, 1872, and March, 1875. Translation by W. Galloway in Iron,

January 26 to March 23, 1878. 

ENGINEERING AND MINING JOURNAL. Influence of coal dust on the explosiveness of

fire damp. Vol. 21, 1876, p. 199. 

FONTAINE, W. M. Notes on the West Virginia asphaltum deposits. Am. Jour. Sci.,

ser. 3, vol. 6, 1873, p. 409. Notes explosibility of grahamite dust.- 

GALLOWAY, WILLIAM. On the influence of coal dust in.colliery explosions (I). Proc.

Roy. Soc. London, vol. 24, 1876, pp. 354-372. Describes experiments with coal

dust and lamp flame. Concludes that less than 1 per cent of fire damp will make

fine dry dust inflammable.

 Influence of coal dust in colliery explosions. Erig. Min. Jour., vol. 22, Sept. 

16, 1876, pp. 158-187. Reprint from- London Mining Journal of abstract of paper 

before the Royal Society of London.

 Role des poussieres de charbon dans les explosions de grisou. Annales des 

mines, ser. 7, vol. 11, 1877, pp. 229. Translation of paper before Royal Society, 

London, 1876.

De 1'influence des poussieres charbonneuses sur les explosions dans lea

houilleres. Bull. Soc. Ind. Min., ser. 2, vol. 6, 1877, pp. 799-830.
BIBLIOGRAPHY. 169

GALLOWAY, WILLIAM. On the influence of coal dust in colliery explosions (II). 

Proc. Roy. Soc. London, vol. 28, 1878, pp. 410-421. 'Describes experiments at 

Llwynpia colliery.

 Sur les explosions des poussieres charbonneuses. Bull. Soc. Ind. Min., vol. 

1878, pp. 617-684.

 The accident at Llan colliery. Iron, vol. 11, June 8, 1878, p. 708.

 Explosion at Fowler's steam coal colliery, Pout-y-Pridd, Wales. Iron, vol. 12, 

July 13, 1878, p. 34.

De Pinfiuence des poussieres charbonneuses sur les explosions dans les houilleres. Bull. Soc. Ind. Min., ser. 2, vol. 9, 1880, pp. 157-174.

DE LA GOUPILLIERE, IlATON. Commission Charge'6 de I'e'tude des moyens propres a 

preVenir les explosions du grisou dans les houilleres, 1878. Cites opinions of De 

Souich and others on explosibility of dust.

HALL, HENRY, and CLARK, GEORGE. Mechanical effects of blown-out shots ou ventilation. Trans. North of England Inst. Min. and Mech. Eng., vol. 25, 1.876, pp. 

239-248. Describes experiments with coal dust in adit 45 yards long. Authors 

conclude dust may greatly lengthen flame of a blown-out shot. Discussion in 

vol. 26, 1877, p. 101, vol. 28, 1.879, p. 85.

MARRECO, A. FREIRE-, and MOKISON, D. P. Results of some experiments on the 

effect of coal dust in colliery explosions. Trans. Chesterfield arid Derbyshire 

Inst. Min. Civ. Mech. Eng., vol. 5, 1878, pp. 267-277. Describes experiments 

in box 8 feet long. Authors conclude that coal dust and air without any fire 

damp are inflammable by a blown-out shot. Discussion of the paper, vol. 6, pp. 

49, 203, 244, 290.

 An account of some recent experiment with coal dust. Trans. North of 

. England Inst. Min. and Mech. Eng., vol. 28, 1879, pp. 85-100. Abstract of the

paper, by Louis Dombre': Annales des mines, 7th ser., vol. 15, 1879, pp. 374-383. 

VON MEYER, ERNST. Gases inclosed in coal. Jour. Chem. Soc., vol. 25, 1872, pp.

798-801. Abstracts of paper in Journal fur praktische Chemie, ser. 2, vol. 5, pp.

144-183, 407-416.

PECK, L. W. Explosions from combustible dust, Sci. Am. Suppl. No. 16(3. 

PECKHAM, S. F. On the explosion of the flouring mills at Minneapolis, Minn., May

2, 1878, and the causes of the same. Am. Jour. Sci. and Art, ser. 3, vol. 16, 1878,

pp. 301-306. 

SCIENTIFIC AMERICAN. A great flour-mill explosion. May 18, 1878, vol. 38, p. 315.

Brief comment on explosion at Minneapolis. 

VITAL, . Recherches sur 1'inflammability des poussieres de charbon. Annales

des mines, ser. 7, vol. 7, 1875, pp. 180-197. Describes explosion at Champagnac

colliery, November 2, 1874, and experiments with dust.

1881-1890.

ABEL, F. A. Report on the results of experiments made, etc. Report to the Home 

Department, March, 1881, with appendices, on Seaham colliery explosion.

 Sur le r61e des poussieres dans les explosions de mines. Annales des mines, 

ser. 7, vol. 20, 1881, pp. 125-159.

 Some of the dangerous properties of dust. Proc. Roy. Inst. Great Britain, 

vol. 10, pt. 1, 1882, pp. 88-113. Mentions several explosions in flour mills, and 

reviews the coal-dust problem. Speaks of certain noncombustible dusts exerting 

a contact or catalytic action on gas mixtures. Discusses preventive measures.

 Some of the dangerous properties of dusts. Abstract of lecture at Royal 

Institute. Nature, vol. 26, 1882, pp. 19-22. Also Trans. Chesterfield and 

Derbyshire Inst. Eng., vol. 10, 1882, pp. 245-280.

 - Accidents in mines, Proc. Inst. Civ. Eng., vol. 90, 1887, p. 160.

 Mining accidents and their preventions. 1887.
170 THE EXPLOSIBILITY OP COAL DUST.

AGUILLON, L. Note sur les experiences enterprise's par M. Abel pour 6tudier le r61e 

des poussieres dans les explosions de mines. Annales des mines, ser. 7, vol. 20, 

1881, p. 121.

AMERICAN INSTITUTE OF MINING ENGINEERS. The Pocahontas mine explosion. 

Trans. Am. Inst. Min. Eng., vol. 13, 1884, pp. 237-249. Report of commiittee, 

Messrs. Bramwell, Buck, and Williams.

ATKINSON, W. N. Colliery explosions. Colliery Engineer, Jan. 14, 1887, p. 52.

ATKINSON, W. N. and J. B. Explosions in coal mines. London, 1886. 144 pp. 

t BRAMWELL, J. H., BUCK, S. M., and WILLIAMS, E. H., Jr. The Pocahontas mine 

explosion. Trans. Am. Inst. Min. Eng., vol. 13, 1884, pp. 237-249. Report of 

committee on explosion that killed 114 men. Explosion due mainly to dust.

CHESTERFIELD AND DERBYSHIRE INSTITUTE OF ENGINEERS. Report of committee on 

dust. Trans., vol. 10, 1882, pp. 1-44. Report of committee on dust experiments in wooden tube 82 feet long. Appendix to report contains reference to 

early observations and experiments in England and France. An excellent 

summary of literature.

COLLIERY ENGINEER. Explosiveness of coal dust. Vol. 4, November 29, 1884, p. 

605. Reprint of article in Engineering. Article refers to experiments by Prussian fire-damp commission.

 Coal dust a cause of colliery explosions. Vol. 8,1887-1888, p. 83. Notice of 

lecture by Arnold Lupton, at Yorkshire colliery.

 The Kansas mine disaster. Vol. 9, 1888-1889, p. 76. Notice of explosi&n at 

Frontenac, Kans., which killed 45 persons.

 Coal dust and colliery explosions. Vol. 9, 1888-1889, p. 80. Refers to explosion at Frontenac, Kans.

Another explosion in which coal dust plays a prominent part. Vol. 9, 1888-

1889, p. 209. Quotes testimony of W. N. Atkinson regarding an explosion at an

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BIBLIOGRAPHY. 171

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 Mining methods, air coursing, and return to haulage how the cars produce 

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 Coal dust rendered harmless. Trans., vol. 10, 1895-1896, p. 546.

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GILPIN, EDWIN. Explosions in Nova Scotian coal mines. Trans. Fed. Inst. Min. Eng., 

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GLENN, WILLIAM. Mine explosions generated by grahamite dust. Trans. Am. Inst. 

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GRIFFITH, D. Dust explosions. A peculiar explosion on a tipple at the Crested Butte 

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174 THE EXPLOSIBILITY OF COAL DUST.

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the Home Department on the disaster. Issued as a bluebook (Cd 3171). 

ATKINSON, W. N., AND HENSHAW, A. M. The Courrieres explosion. 'Trans. Inst.

Min. Eng., vol. 32, 1907, pp. 439-492. Discussion, pp. 340-348; vol. 33, pp.

124-137." 

BACHE, FRANKLIN. Explosion in coal mines and their prevention. Mining World,

October 23, 1909. Abstract of paper before the American Institute of Mining

Engineers.

38970° Bull. 425 10 12
178 THE EXPLOSIBILITY OF COAL DUST.

BARLOW, J. E. Exhaust steam as a dust precipitant. Coal and Coke Operator, 

February 11, 1909, pp. 115-116. Describes experiment with exhaust steam at 

mine taking 75,000 cubic feet of air per minute.

BEARD, J. T. Mine gases and explosions. New York, 1908, 402 pp. A descriptive 

treatise on the various factors involved in explosions.

BEDSON, P. P., AND WIDDAS, HENRY. Experiments illustrative of the inflammability 

of coal dust and air. Trans. Inst. Min. Eng., vol. 32, 1906, pp. 529-531; vol. 34, 

1907, pp. 91-97.

BREYNAERT, F. Note sur la question des poussieres dans les mines anglaises. Annales 

des mines, ser. 10, vol. 12, 1907, pp. 532-551. Review of dust problem and mine 

explosions.

CADMAN, JOHN. The ignition of coal dust by a naked light. Colliery Guardian, 

vol. 98, 1909, p. 929. Abstract of paper before the North Staffordshire Institute 

of Mining and Mechanical Engineers. Describes experiments with vertical 

gallery 12 feet long and 8 inches square.

CALLOT, TONY. The experimenting station at LieVin, France. Eng. and Min. Jour., 

vol. 88, 1909, pp. 1-5.

CHAMBERLIN, R. T. Notes on explosive mine gases and dusts, with reference to explosions in the Naomi, Darr, and Monongah mines. Bull. U. S. Geol. Survey No. 383, 

1909, 65 pp. Describes laboratory experiments to determine the gases in coals 

and considers the action of dust in mine explosions.

CHEMICAL ENGINEER. Report of S. F. Peckham on Minneapolis explosion. March, 

1908, p. 97; April,,1908, p, 146; May, 1908, p. 194. Reprint.

COLLIERY GUARDIAN. The Courrieres bluebook. Vol. 92, 1906, p. 801. Editorial 

comment on British report on Courrieres disaster. Refers to experiments on coal 

dust in France, Prussia, and England. Concludes that Courrieres explosion was 

due to dust.

 Need for coal-dust experiments. Vol. 93, 1907, p. 204. Editorial comment 

on report of Haldane, Hall, and Atkinson, to royal commission on mines; advocates experimental investigations of value of watering and of dust-free spaces.

 Tests at Altofts. Vol. 96, 1908, p. 407. Describes experiments at Altofts; 

purpose of experiment station.

 The British coal-dust experiments. Vol. 98, 1909, pp. 217-221. Mentions 

experiments at Altofts with stone dust.

 West Stanley colliery explosion. Vol. 98, 1909, pp.. 318-319. Reprint of 

official report by Redmayne and Bain.

 West Stanley colliery explosion. Vol. 98, 1909, p. 363. Review of report of

Redmayne and Bain.

British coal-dust experiments. Vol. 98, 1909, pp. 675-678.

CUNNINGHAM, J. S. Mane disasters causes and remedies. Coal, October 15,1908,

pp. 21-22. Abstract of paper before West Virginia Mining Association. General

discussion of gas and dust explosions and remedies suggested. 

CUNYNGHAME, H. H. Recent advances in means of saving life in coal mines. Lecture

before Royal Institute. Colliery Guardian, vol. 97,1909, pp. 422-424. Discusses

explosibility of coal dust and preventive measures. 

 Safety in mines. Science and Art of Mining, March, 1909. Abstract of

lecture before Royal Institute. Reviews coal-dust problem from time of Faraday. 

CUNYNGHAME, H. H., AND ATKINSON, W. N. Report on the disaster at Courrierea

mines, Pas de Calais, France. London, 1906. Bluebook issued by Home Office.

Gives description of mine and nature of explosion; rescue work, etc. 

CZAPLINSKI, , AND JiciNSKY, JARASLAV. Experiments with coal dust at the

Rossitz gallery. Colliery Guardian, September 24 and October 1, 1909, vol. 98,

pp. 635 and 687. Describes gallery and experiments with coal dust and dynamite;

influence of character of coal dust, of water screens, wet zones, and stone dust on

explosions.
BIBLIOGRAPHY. 179

DANIEL, J. Les poussieres des houilles. Paris, 1909. 76 pp. Reprint of article from 

Armales des mines.

 Les poussieres des houilles. AnnaleB des mines, ser. 10, vol. 15, February, 

1909, pp. 142-212. Discusses formation of dust; preventive measures, use of 

sprays, deliquescent salts, etc. Refers to French, English, and German practice.

DA vis, HENRY. The application of the hygrometer in coal mines. Trans. Inst. Min. 

Eng., vol. 35, 1908, pp. 285-290.

DEASON, E. J. Explosives in mines. Mines and Minerals, vol. 28, 1908, pp. 269-273. 

Reprint of article in Coal and Iron Trades Review. Describes Woolwich tests; 

experiments with dust.

DESBOROUGH, ARTHUR. Report of departmental committee on the use of bobbinite. 

London, 1907. 67 pp.

DIDIER, L. French commission on explosives and coal dust. Coal, December 10,

1908. pp. 15-16. Abstract of paper in Bull. Soc. Ind. Min. Discusses origin of 

dust and preventive measures. 

DOBBELSTEIN, 0. Durchtrankung und Lockerung des Kohlenstosses mit Hilfe vou

Druckwasser. Gliickauf, vol. 45, November 6,1909, pp. 1641-1643.

EAVENSON, N. H. Effect of humidity on mine explosions. Trans. Am. Inst. Min.

Eng., vol. 40, 1909, pp. 835-847. Gives lists of disastrous explosions at North

American coal mines. 

ENGINEER. Coal-dust experiments. Vol. 108, October 9, 1909, pp. 376-377. An

account of experiment at Altofts. 

ENGINEERING AND MINING JOURNAL. Coal-dust experiments. Vol. 88, October 30,

1909. Refers to experiments at Altofts and report of royal commission on mines. 

ENGLER, C. Einfacher Versuch z.ur Demonstration der gemischten Kohlenstaub- und

Gasexplosionen. Chem. Zeitung, vol. 31,1907, p. 358. Jour, fiir Gasbeleuchtung

und Wasserversorguug, vol."50, p. 488. 

GALLOWAY, WILLIAM. Colliery explosions and rescue appliances. London, 1908.

120 pp.

 Coal dust. Science and Art of Mining, June 12, 1909. Abstract of paper 

before Congress of Applied Chemistry. Discusses origin of dust, history of inquiry, 

preventive measures.

Colliery explosions and rescue appliances. In Practical coal mining, London,

1907. Reviews coal-dust problem, pp. 92-107.

CARFORTH, W. E. Colliery Guardian, vol. 98, July 30, 1909, p. 218. In account of 

Altofts experiments, says of Silkstone explosion, 1886, that it was first colliery 

disaster on record in which a coroner's jury returned the verdict of "death from 

an explosion of coal dust without gas."

GRAEFE, . Zur Kentniss der Kohlenstaub Explosion. Braunkohl, May 18, 

1909, pp. 125-129. Discusses explosions of dust in lignite briquet plants.

HAAS, FRANK. Is coal dust, as such, explosive; and if so, what are the chemical 

reactions and the most efficient preventatives? Paper before West Virginia Mining Association, October 17, 1908. Discusses preventive measures; advocates 

use of steam. Printed under the title, "The problem of treating coal dust in 

mines," in Eng. and Min. Jour., October 24, 1908, pp. 814-817; also under the 

title, "Is coal dust, as such, explosive?" in Coal, November 11,1908, pp. 15-17; 

also in Mines and Minerals, December, 1908, pp. 227-229.

HALDANE, J. S. The investigation of mine air. London, 1908 (?). pp.

HALL, CLARENCE, and SNELLING, W. 0. Coal-mine accidents, their causes and prevention. Bull. U. S. Geol. Survey No. 333, 1907. 23 pp.
180 THE EXPLOSIBILITY OF COAL DUST.

HALL, HENRY. The coal-dust question in Great Britain. Eng. and Min. Jour., vol. 

87, May 22, 1909, pp. 1084-1089. General review of progress of inquiry from 1844 

to-present time.

 Calcium chloride treatment of mine dust. Fuel, June 23, 1909. Describes 

experiment with CaCl 2 in a section of tunnel 285 feet long.

HANSEN, C. M. Dust explosion in the boiler room. Power and the Engineer, December 5, 1908, p. 1017. Mentions explosion of dust and soot on top of a boiler.

HARLE, RICHARD. Treatment of dust in mines, above ground and below ground. 

Trans. Inst. Min. Eng., vol. 33, 1907, pp. 254-257. Describes a spray system.

HARRINGTON, D. Spraying coal mines. Mines and Minerals, vol. 29, 1908, pp. 102- 

104. Describes sprinkler system at Sunnyside mine No. 4, Sunnyside, Utah; 

cost of construction; efficiency.

 Spraying coal dust as a colliery safeguard. Eng. and Min. Jour., January 23, 

1909, pp. 103-106. Refers to dust explosion at Winter Quarters mine, May 1, 

1900, and Sunnyside (Scofield) explosion; describes spraying methods of Utah 

Fuel Company, and cost.

HATZFELD, . Die Versuchsstation zu Lievin Gliickauf, October 9,1909, pp. 

1484-1491.

HEISE,. , and HERBST, . Bergbaukunde, 1908, p. 448.

ILLINOIS COAL OPERATORS' ASSOCIATION. Report of committee, 1905. Contends 

increased use of powder has greatly increased number of accidents.

JONES, B. F. Comparative amount of dust made in mining with puncher machines, 

chain machines, and hand mining: Mines and Minerals, March, 1908.

LEPRINCE-RINGUET, . Les experiences anglaises sur les poussieres des houilles. 

Annales des mines, ser. 10, vol. 14, 1908, pp. 115-143.

LORD, N. W. Chemistry and coal mine explosions. Fuel, November 9, 1909, pp. 

63-67. Abstract of paper before American Chemical Society. Discusses effect 

of heat of gas explosion on coal dust; benefits of moisture and of stone dust; possibility of dust explosion being a detonation.

MENTE, , and WILK, W. Zur Untersuchung des Sprengstoffe auf Ziindsicherheit im Schlagwettern und Kohlenstaub. Zeitschr. fur angewandte Chemie, 

June 11, 1909, pp. 1116-1118. Abstract of paper before Congress of Applied 

Chemistry at London. Review of progress in tests of explosives.

MINES AND MINERALS. The Yolande mine disaster. Vol. 28, 1907-1908, p. 331.

 A peculiar mine explosion, Rock Springs, Wyo. Vol. 28, 1907-1908, p. 161.

 Some characteristics of coal dust. Vol. 28, 1907-1908, p. 500.

 The Darr mine disaster. Vol. 28, 1907-1908, p. 377.

 The Monongah mine disaster. Vol. 28, 1907-1908,'pp. 324, 327, 333, 394.

 Report of the French commission on explosives and coal dust. Vol. 29, 1908, 

pp. 106-107. From report of L. Didier in Bull. Soc. Ind. Min. Gives suggestions 

for keeping down dust; does not advise sprinkling.

 British coal-dust experiments. Vol. 29, 1908, pp. 235-240. Describes gallery 

at Altofts and gives results of 26 tests with coal dust and with stone dust.

Wehrum mine explosion. Vol. 30, September, 1909, pp. 118-120. Notice of

explosion at No. 4 mine at Wehrum, Pa. Mine is classed as nongaseous and is

fairly wet. 

MANNAKEE, N. H. The barometric and temperature conditions at the time of dust

explosions in Appalachian mines. Trans. Am. Inst. Min. Eng., vol. 40, 1909,

pp. 665-667. 

NELME, H. J. The control of coal-mine explosions. Eng. and Min. Jour., vol. 87,

January 2, 1909. Believes dust can not be ignited without an explosion of fire

damp. 

OESTERREICHISCHE ZEITSCHRIFT PUR BERG- UND HUTTENWESEN. Einige Betrachtungen anlasslich der Katastrophen im Courrieres und auf Grube Reden. Vol.

55, March 16, 1907, pp. 135-139; March 23, 1907, pp. 153-157.
BIBLIOGRAPHY. 181

PAGE, W. N. Prevention of coal-dust explosions in mines. Mining World, November 

28, 1908, p. 813. An open letter to the West Virginia mine managers. Coal, 

November 26, 1908, p. 23; December 31, 1908, pp. 24-25. Dust as a'factor in 

mine explosions. Eng. and Min. Jour., December 5, 1908, p. 1108. Advocates 

slower ventilating currents; doubts possibility of moistening dust to point of 

safety in strong ventilating currents of large volume.

PARKER, E. W. Coal-mine accidents. Mineral Resources U. S. for 1906, 1907, and

1908. U. S. Geol. Survey. Accidents in coal mines in United States classified as

to cause. 

PAYNE, HENRY M. Coal dust as a factor in mine explosions. Coal, June 25, 1908,

pp. 15-17. Paper before Coal Mining Institute of America. Reviews literature. 

PECKHAM, S. F. The dust explosion at Minneapolis, May 2, 1878, and other dust

explosions. Chem. Eng., March, 1908, p. 97; April, 1908, p. 146; March, .1.908,

p. 194. Reprint. 

RAE, JOHN. Coal dust and its dangers. Fuel, November 30, 1908, p. 169. Address

before Y. M. C. A. Mining Institute, Monongahela, Pa. 

REDMAYNE, , and BAIN, . West Stanley colliery explosion. London,

1909. Official report on explosion that killed 166 persons. Explosion propagated 

by dust.

ROYAL COMMISSION ON MINES. Minutes of evidence. Vol. 1, London, 1907, 443 pp. 

Contains much testimony on coal dust, gas, accidents, etc. Vol. 2, London, 

1908, 373 pp. Vol. 3, London, 1908, 550 pp. Vol. 4, London, 1909, 573 pp.

 Second report, London, 1909, 298 pp. Coal-dust explosions, pp. 82-109. 

SCHOLZ, CARL. The settlement of dust in mines and prevention of explosions by the 

increase of humidity. Chicago, 1908, 12 pp.

 Effect of humidity on mine explosions. Trans. Am. Inst. Min. Eng., October, 

1908, pp. 551-559. Says explosions are most numerous in cold weather or following a dry season. Advocates use of sprays in intake to moisten air.

SCIENCE AND ART OF MINING. The coal-dust question. Vol. 20, November 27, 1909, 

pp. 176-177. Review of an article by Henry Hall in Eng. and Min. Jour.

STOEK, H. H. The Monongah mine disaster. Mines and Minerals, vol. 28, 1908, p. 

277.

 The Lick Branch disaster. Mines and Minerals, vol. 29, March, 1909, pp.

360-365. General description of mine, analysis of dust and gas. Report of John

Laing, D. R. Phillips, and P. A. Grady. 

STOW, AUDLEY H. Is coal dust as such explosive? Eng. and Min. Jour., vol. 87,°

January 2, 1909, pp. 17-19. Discusses chemical reactions of explosion; fineness of

''dust." 

TAFFANEL, J. French coal-dusi experiments. Proc. South Wales Inst. Eng., 1909.

 Description de la station d'essai. Comit6 central des houilleres de France, 

March, 1909, 19 pp. Description of Lie"vin station.

 Les re"sultats obtenus jusqu' a ce jour dans le galerie d'essai de Li6vin. Extract 

from Bull, and compt. rend, mensuels Soc. ind. min., Feb., 1909, pp. 18. Discusses experiments with dusts of various coals; effect of stone dust.

 Coal-dust experiments at Lie"viu. Colliery Guardian, vol. 98, July 30, 1909, 

p. 22. Brief notice of translation, by W. N. Atkinson, of two reports, dealing 

with work at Li6vin.

 French coal-dust experiments. Colliery Guardian, vol.' 98, August 13, 1909, 

pp. 315-318. Abstract from Proc. South Wales Inst. Eng., of translation by 

W. N. Atkinson of report describing equipment and methods at Lie"vin station.

 Les experiences frangaises sur les poussieres de houille. Comite" central des

houilleres de France. Notes techniques, November 15, 1909, p. 347.
182 THE EXPLOSIBILTTY OF COAL DUST.

TAFFANEL, J., AND DUNAIME, POL. Lea catastrophes minieres americaines de Monongah, Darr, et Naomi. Annales des mines, ser. 10, vol. 16, July, 1909, pp. 1-87;

August, 1909, pp. 75-210. Describes mines and mining methods and discusses

causes and courses of explosions. 

VERNER, J. Physical action of air a factor in dust explosions. Black Diamond,

August 7, 1909, pp. 12-13. Considers dust a passive factor; says records of Iowa

mines for twenty years show no dust explosions between March 12 and October 21.

Concludes heating of mine air and control of its velocity will prevent explosions. 

VIRGIN, JOSEPH. Origin of coal-mine explosions. Coal, December 17,1908, pp. 15-10.

Abstract of paper before West Virginia Coal Mining Association. Gives dust first

place as cause of explosions. 

 Facts disproving recent statement relative to mine fatalities. Eng. and Min.

Jour., vol. 87, January 2,1909, pp. 12-13. Advocates plenty of air and moistening

of air.

The dust problem in coal mines. Eng. and Min. Jour., vol. 88, October 9,

1909, p. 734. Discusses use of salt and calcium chloride, and experiments at

Plymouth, W. Va. 

WATTEYNE, VICTOR; MEISSNER, CARL; AND DESBOROUQH, ARTHUR. The prevention

of mine accidents. Bull. U. S. Geol. Survey No. 369, 1908, 11 pp. 

WATTEYNE, VICTOR, AND STASSART, S. Courrieres et La Boule; Examen comparatif

de deux grandes explosions. Annales des mines de Belgique, ser. 3, vol. 13,

1908, p. 785. Comments on Courrieres and La Boule explosions. Brief abstract

of this paper in Coal, November 12, 1908, pp. 16-17. 

 Les mines et les explosifs au septieme congres international de chimie applique'e.

Annales des mines de Belgique, vol. 4, 1909, pp. 1221-1444. Review of papers

and discussion at the congress. Coal-dust experiments (pp. 71-74) by P. P.

Bedson. Use of sprays in German mines (pp. 75-81) by Forstmann. Report on

coal-dust experiments at Rossitz gallery (pp. 183-207) by Czaplinski and Jicinsky. 

WOOD, G. R. Electricity in coal mines. Coal Min. Inst. America, June, 1909.
INDEX.

Page. 

Abel, Frederick, experiments of........... 100,105

on coal-dust explosions.................. 13-14

on explosives............................ 78

on permanent sprinklers................ 74

on steam jets............................ 7C

Accidents, incorrect report of................ 28

Acknowledgments to those assisting......... 10

After-damp, sampling of.............. 130-137,138

sampling of, apparatus for, figure showing.............................. 136

Air, dust in, measurement of................ 36

effect of steam on........................ 156

See also Mine air. 

Air, return, moisture in................... 154-156

moisture in, chart showing............... 155

Air supply, relation of, to dust explosions... 97-98 

Alabama, explosions in...................... 28

Altofts, England, conditions at............ 139-140

gallery at......................... 21,80-82,87

experiments at................ 139,140-142

temperature in...................... 137

view of............................. 80,140

instruments at.................... 135-137

views of....................... 134,136

limitations of........................ 134

Altofts mine, stone dust in................ 141-142

stone dust in, application of, views of... 82,140 

Ankylostomiasis, relation of, to watering.... 73,91

Anthracite dust; explosibility of............. 40,84

Ash, effects of............................... 85,87

Atkinson, W. N., on coal-dust explosion..... 20

Atkinson, W. N. and J. B., on coal-dust oxplosion. ......................... 11,17

on hosing............................... 73

on rock dust............................ 80

Austria, coal-dust explosions in.......... 16-17,22

explosives in............................ 78

B.

Bald, Robert, on coal-dust explosions..... 11

Bodson, P. P., and Widdas, H., apparatus

of......................... 114,117,120

experiments of............. 42,113-114,117-121

Belgium, coal-dust explosions in............ 19

explosives in............................ 78

investigations in.................. 143-144,147

Bibliography.............................. 168-182

Bituminous coal, dust from................. 9

dust from, explosion of.................. 46

Bramwell, J. H., Buck, S. M.,and Williams,

E. H., jr., on dust explosion..... 24

Brunck, Otto, on coal-dust sampling.....'... 36

Buck, S. M., Williams, E. H., jr., and Bramwell, J. H., on coal-dust explosion............................. , 24

Buddle, J., on coal-dust explosion........... 11

C.

Page. 

Calcium chloride, use of.................. 68-73,87

Catsburg mine, Pa., experiments with calcium chloride in................. 70-73

Chain machine, dust produced by........... 31-33

Chamberlln, R. T., investigations of......... 42

Charcoal dust, explosion of.................. 83

Charge limit, definition of................... 79

Charred dust, character of...........:...... 42,103

Clark, G.,and Hall, H.,experiments of... .. 104

Clement, J. K., on dry and wet thermometers. 59 

Coal dust, absorption of water by............ 151

analyses of......................... 93,102,103

chemical character of, effect of........... 41-49

definition of............................. 29-30

distribution of........................... 33-34

explosibility of, comparison of, with fire

damp........................... 9

conclusions on....................... 83-91

ignition of. Sec Ignition.

moisture in............................ 150-152

origin of................................. 30-33

removal of........................... 66-67,88

size of.......................... 29-30,41,83-84

resistance of, to moistu re................ 150

tamping with, effects of................. 49-50

Coal dust (for experiments), analyses of... 35,53,93 

character of............................. 34-35

distribution of........................... 40

precipitation of.......................... 3.5-36

preparation of......................... 131-132

screening of, method of.................. 39

Coal dust (in suspension), coarseness of, effects of................. 38-41,83-84,85

density of, effects of........ 34-38,84,85-86,108

humidifying of, effects of............. 50-54,80

measurement of......................... 36

Coal dust, coked,analyses of................. 90

characterof.............................. 92-94

deposition of......................... 11,94-96

description of........................... 38

position of............................... 94-96

views of................................. 38,40

Coal-dust explosions, causes of............... 33-34

conditions of........................... 132-137

experiments in.......'.. 21-22,29,34-47,124-133

apparatus used in................. 125-128

description of......................... 49-54

experiments with............... 21-22,29,34-47

description of........................ 49-54

fatalities from, in England............... 22

history of, in England.................... 11-22

in the United States................. 23-29

prevention of............................ 21,

26,66-83,87-91,133-135,148-167 

views of................................. 34,80

Coal mines, water in......................... 57

383
184

Page. 

Coals, noncoking, explosive dust from ....... 98

Coke, character of............................ 41

Coked dust. See Coal dust, coked.

Colorado, explosions in................... 27-28,92

Cotton mills, sprinklers in................... 74

Cunynghame, Henry, on coal-dust explosion. 20

D.

Density of dust, degree of................. 34-38,84

Desborough, A., on coal-dust explosion...... 20

Du Souich, , on coal-dust explosion ..... 12

Disasters, great, in 1007, description of....... 27-28

incorrect reports on...................... 28

Dust. Sec Coal dust; Stone dust.

Dustless zones, efficacy of.............. 133,139,140

efficacy of, diagrams showing............ 140

E.

England, coal-dust explosions in. 11-14,17-19,21-22 

explosives in............................. 78

rock dust in............................. 80

watering in.............................. 73

See also Altofts.

Engler, C., apparatus of...................... 113

experiments of........................... 113

Entries, dust in, dangers of.................. 34

heat radiation from.................... 1GO-1C2

chart showing....................... 102

See also Road dust.

Europe, coal-dust experiments in.......... 133-147

Exhaust, ventilation, advantages of......... 1C7

Explosibility, conclusions on................ 83-91

factors affecting.......................... 83-85

Explosion gallery, description of............. 35-30

figure showing............................ 40

plate showing........................... 80

tests with............................... 47-54

See also Propagation.

Explosives, regulation of........... 19-20,78-80,91

tests of........................ 143-144,140-147

Sec also Explosives, permissible.

Explosives, permissible, tests of.. 79-80,143,146-147

Explosives, quick-flaming, use of............ 78-80

Fans, preferable type of..................... 107

Faraday, M., on coal-dust explosion......... 11-12

Fatalities in Great Britain, statistics of...... 22

in United States, statistics of............ 28

Fire damp, explosibility of.................. 9

Flame, phenomena of....................... 98-99

Flour dust, explosion of..................... 23-24

Fog line, significance of..................... 102

Fogs, production of, by steam............... 89

water carried in......................... 102

Forstmann, , on hair hygrometer........ 59

Frameries, Belgium, gallery at............ 143-147

gallery at, figures showing..... 143,144,145,140 

France, coal-dust explosions in.............. 12,20

experiments in........................ 121-124

explosives in............................ 79

See also Lievin. 

Frazer, J. C. W., invention of................ 30

on coal-dust ignition................... 99-133

work of................................. 10

G. Page, 

Galleries, model, experiment.; in............ 12-22

See also Altofts gallery; Coal-dust explosion. 

Galloway, William, experiments by....... 100,110

on coal-dust explosion......... 12-13,14,1C, 100

Garforth, W. E., experiments of, on rock dust. 80-82 

Gas after explosion, character of........... 123-124

Geological Survey, U. S., investigation by... 28-29 

Germany, coal-dust explosions in........... Hi, 19 

explosives in............................ 78

watering in............................. 73

Gneisenau, Germany, gallery at............. 147

Grahamite dust, explosion of................ 23

Greenwell, G. C., experiments by........... 112

II.

Haas, Frank, on exhaust steam as a preventive. .........'............. 150-1C3

on steam jets............................ 70,90

work of.................................. 10

Haldane, J. S., on dust sampling............ 30

Hall, Clarence, work of...................... 45-48

Hall, Henry, on calcium chloride............ 08-09

on coal-dust explosion................... 13,18

Hall, H., and Clark, G., experiments of....... 104

Hand cutting, dust produced by............ 31-33

Health, effect of humidity on............... 91

Heat, manifestations of...................... 97-98

'Hilt, C., on coal-dust explosion............. 15

Holtzwart, R.,and Meyer, E. von, apparatus

of............................... 114

experiments of........................ 114-110

Hosing, use of........................ 73-74,88,143

Sec also Sprinkling. 

Humidifying, effects of...................... 88-91

fogging from............................. 89

Humidity, effects of........ 50-54,84-85, S(>, 118-119

measurement of......................... 57-01

principles of............................. 54-57

records of............................... 153

relation of, to temperature...... 54-5(1,57, G1-G5

charts showing................... 55,02,03

Sec also Saturation. 

Hygrometer, description of.................. 58-59

view of..... ............................ 58

Hygroscopic salts, use of................. OS-73,87

I.

Ignition, conditions for......... 84,118-120,132,133

definition of............................. 30

investigations of........................ 99-133

means of, experiments in................ 141

figures showing.......,...'..... 120,130,142

Illinois, long-wall system in................. 30

shot firing in............................ 27

Indiana, shot firing in....................... 27

Iowa, coal-dust explosions in..........:..... 25

J. 

Jones, B. F., experiments by................ 31 .

K.

Knopf, H. K., on steam jets ................ 70-77

Kruskopf process, description of........ 00,149-150
INDEX. 185

L. Page.

Larscri, Axel, on European experiments... 133-147

work of................................. 10

Le Chatelier, , and Mallard, , on coaldust explosion.................. 12

Licvin, France, gallery at................... 137

gallery at, experiments at\.............. 139

figure showing...................... 138

instruments at.......................... 138

 Lignite, dust from, analyses of.............. 9,115

dust from, experiments with............ 115

Lignite-briquet factories, explosions in..... 114-110

Linings, brick or concrete, effects of...... 82-83,88

Literature, lists of......................... 108-182

Long-wall system, employment of........... 30

safety of................................. 30

Lupton, Arnold, on steam jets .............. 7(1

M. 

Machine cutting, dust produced by........... 31-33

Mallard,, and Le Chatelier, , on coaldust explosion.............. 12,105-110

Marrcco, A. F., on coal-dust explosion... .13,14,100

Martin, Henry, on sprinklers................ 74

Methane, induction of, by reduced pressure.. 112 

Meyer, E. von, and Holtzwart, C., apparatus

of............................... 114

experiments of........................ 114-110

Mine air, effects of heat on................. 158-159

humidity of............. 50-57,154-159,162-163

effects of heat on............. 57,61-65,104

charts showing...... 62,03,155,157,158

See also Air. 

Minnesota, dour-dust explosion in........... 23

Moisture, distribution of..................... 152-

efficacy of, in preventing explosions.... 150-152

See also Humidity. 

Monongah mines, W. Va., coal-dust explosion

in............................... 28

Morison, D. P., on coal-dust explosion... 13,14,100

N. 

New Mexico, explosions in.................. 98

0.

Ohio, paying methods in.................... 27

Oklahoma, coal-dust explosion in............ 25

coal-mine accidents in................... 1C4

use of steam and water in........... 75,163-167

P.

Paste, use of, on mine faces.................. 66

Payment, methods of, relation of, to accidents ........................... 27

Peckham, S. F.,and Peck,L. W.,on dust explosions ......................... 23

Pekay mine, Iowa, coal-dust explosion in.... 25

Pennsylvania, cutting experiments in....... 31

disasters in........................... 27-28,92

experiments with calcium chloride in.... 70-73

paying methods in...................... 27

watering in........................ 73,75,70-78

Permissible explosives. Sec Explosives, permissible. 

Pittsburg, experiments at................... 10,29

Pocahontas mine, W. Va., explosion in...... 24-25

Powder, black, danger from................. 79-80

Page. 

Pressure, during explosion, amount of..... 127-132

effect of........................... 112,132-133

Primero mine, Colo., explosion in...... 27-28,92,95

Pressure in gallery, measurement of....... 135-136

Propagation,, definition of................... 30

factors effecting........................ 85-87

velocity of............................. 109,138

measurement of, figures showing... 134,138 

Prussia, coal-dust explosions in.............. 14-16

investigations in........................ 147

Psych remoter, description of................ 58

Puncher, dust produced by................. 31-33

R.

Remedies for coal dust, discussion of... 60-83,87-91 

Removal of dust, value of................ 66-67,88

Road dust, experiments with................ 48,87

Rock dust. See Stone dust.

Roof, effect of steam on..................... 89

S.

Saturation, relation of, to temperature....... 54-56

steam required for, amount of......... 102-163

See also Humidity. 

Scholz, Carl, on sprinklers................... 75

on use of steam and water in Oklahoma. 163-167

work of................................. 10

Scott, C. E., on dust experiments........... 31

Screening, methods of....................... 39

Seasons, effect of, on mine air....... 57,153-156,164

Shale dust, effect of, on coal dust............ 45,48

Shoenberger mine, steam jets in............. 77

Shooting off the solid, dangers from......... 26-27

method of............................... 30

Shot firing, regulation of.................... 16,26

Solid. See Shooting off the solid. 

Spraying. See Kruskopfprocess; Sprinkling. 

Sprinklers, cost of........................... 167

Sprinklers, permanent, experiments with.... 74-75

location of, in Oklahoma, figure showing. 1C6

use of............................... 74,87,165

view of.................................. 158

Sprinkling, effects of.................... 67-68,143

use of, in Oklahoma................... 165-167

See also Hosing. 

Steam, dampening by......... 76-78,88-91,150-163

dampening by, amount needed for..... 162-163 

apparatus for, plate showing ........ 158

use of, figure showing................... 159

in Oklahoma...................... 165-167

origin of........................... 152-153

See also Mine air. 

Stevenson, Robert, on deliquescent salts..... 68

Stokes, , on use of calcium chloride...... 68

Stone dust, application of..... 80-82,87,91,119,124

application of, views of................. 82,140

Stone-dust zones, efficacy of.... 134,139,140,141-142

efficacy of, diagrams showing.......... 134,140

Summer. See Seasons.

Sweeping, effect of.......................... 67

T.

Taffanel, J., on coal-dust explosions......... 20,

43-44,84,85

Taffanel's methods, comparison of, with Pittsburg experiments............... 44-45
186 INDEX.

Page. 

Tamping with coal dust, effects of............ 49-50

Temperature, effect of, on humidity. 54-56,57,61-C5

effect of, charts showing.............. 55,62,C3

records of............................... 153

chart show'ng....................... 154

Temperature in gallery, calculation of...... 137,138

records of............................... 153

Thermometer, wet and dry, theory of......... 59-CO

Thorpe, T. E.,apparatus of.................. Ill

experiments of......-..-...'.......... 110-112

U.

Undercutting, methods of................... 30

Utah, watering in........................... 73

V.

Vacuum sweeper, use of..................... 67

Vaporization, effect of....................... 90-91

Velocity of flame, measurement of........... 136

Ventilation, efficacy of...................... 9

Verpilleaux, , on coal-dust explosion..... 12

Violence, variations in....................... 99

Virgin, Joseph, on calcium chloride........... 70

Virginia, coal-dust explosions in.............. 24-25

disasters in. ............................ 27

Vital, , apparatus of, figure showing...... 101

on coal-dust explosion............. 12,101-103

Volatile matter, necessary percentage of...... 83,

108-109,121

W. Page.

Wales, sprinklers in......................... 75

Washing down. See Hosing. " Water, injection of, in mine faces........ 66,148-149

injection of, figure showing............... 149

Water pressure, coal breaking by.......... 148-149

 coal breaking by, figure showing.......... 149

Watering. See Sprinkling; Hosing.

Watteyne, V., on watering in Belgium....... 143

West Virginia, disasters in.................. 27-28

dust experiments in..................... 31-32

grahamite-dust explosion in............. 23

paying methods in...................... 27

Wet zones, efficacy of............. 83,88,98,134,139

Widdas, H., and Bedson, P. P., apparatus of.. 114,

117,120 

experiments by............. 42,113-114,117-121

Williams', E. H., jr., Bramwell, J. H., and 

Buck, S. M., on coal-dust explosion .............................. 24

AVinter. See Seasons.

Wood, G. R., on dust experiments............ 32-33

Zones, protective. See Wet zones; Dustless 

zones; Stone-dust zones.

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