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Preface

III

Introduction

1

Purpose and scope..

1

Acknowledgments

2

Use of explosives in mining...

2

History of explosives in mines...

2

Present consumption of explosives..

2

Nature and hazards of explosives....

2

Explosives accident statistics...

Common causes of explosives accidents.

5

Examples of common accidents....

5

Explosive accidents reported to National Safety Competition, 1925-35 7

Selected explosives accidents, 1940–44.

8

Underlying causes of accidents from explosives...

9

Accidents to children from blasting caps.

10

Selection of explosives..

10

Strength.......

11

Velocity

11

Resistance to moisture.

12

Density..

12

Fumes produced..

12

Stability in variable temperatures...--

12

Storage..........

13

Explosives and detonators..

13

Fuse....

14

Construction of magazines....

14

Permanent magazines for explosives.

14

Box-type magazines for explosives..

16

Detonator magazines

17

Location

18

Surface magazines......

18

Underground magazines..

21

Precautions in operating magazines..

22

Auxiliary magazines

22

Storage of explosives in working places..

23

Transportation of explosives, detonators, and fuse..

24

Requirements for vehicles carrying explosives.

24

Handling explosives

25

Transportation underground

25

Transportation for surface work.

26

Use of explosives and detonators..

32

Principles of safe blasting..

32

When and by whom shots should be fired.

33

Electrical blasting versus fuse blasting...

34

Power sources and power calculations for electric blasting.

35

Power sources

35

Ohm's law

35

Methods of connecting blasting circuits.

35

Series circuits

36

Parallel circuits

Combination circuits

37

Calculations of power for electric blasting

38

Power requirements for series circuits.

38

Power requirements for parallel circuits.

39

Safety precautions in electric blasting...

40

Safety practices

40

Stray currents

43

Static electricity

48

Precautions in using fuse....

Position of detonator in primer.

49

Requirements for primers.

49

Safety primers

52

Position of primer in borehole.

52

Loading holes

54

Hazards of excessive force in loading..

54

Use of air loaders.....

56

Use of loading tubes...

57

Use of explosives and detonators—Continued

Stemming holes

Blasting warnings and signals.......

Blockholing and mudcapping..

Chute blasting

Firing large rounds..

Long-hole drilling and blasting.

Handling misfires

Gases from explosives..

Liquid oxygen

Permissible explosives

Open-cut blasting
Detonating fuse

Disposal of deteriorated explosives and detonators.
Suggested rules for handling, storing, and delivering explosives.

General rules
Transporting explosives
Unloading explosives from cars or trucks..
Storing explosives

Suggested rules for explosives underground.
Conclusions
Questions for class discussion.
References on explosives..
List of miners' circulars..

75

77
78
79

ILLUSTRATIONS

Fig.

Page

1. Frequency rates, fatalities, and injuries from explosives. Under-

ground and open-cut metal mines, 1931-43..

5

2. Surface storage magazine, brick construction.

15

3. Underground detonator magazine.......

17

4. Barricaded explosives magazines, concrete and sand-filled construc-

tions

20

5. Barricaded explosives magazines, cinder-block construction..

20

6. Barricaded explosives magazine, steel construction.

21

7. Insulated car for transporting explosives into mine...

26

8. Detailed sketch of large insulated explosives car.

27

9. Detailed sketch of small insulated explosives car..

28

10. Steel, rubber-lined explosives car...

29

11. Mine truck for bringing explosives to a level magazine..

30

12. Plastic container for carrying electric detonators...

31

13. Fuse-capping room

32

14. Electric blasting; series connections

36

15. Electric blasting; parallel connections

37

16. Electric blasting; series-in-parallel connection

38

17. Electric blasting; parallel-in-series connection

38

18. Electric blasting; connecting leg wires to two bus wires....

41

19. Electric blasting; removing short circuit from terminals of lead

wires when connecting to firing circuit.

42

20. Electric blasting; connecting lead wire plug into the firing circuit.... 43

21. Electric blasting; miner closing the switch of the stope circuit to

connect it to the main blasting circuit...

44

22. Electric blasting; miners removing their checks from section board

as they leave area...

23. Electric blasting; after seeing that all men are out, foreman closes

firing switch on main circuit....

46

24. Preparing primers and loading holes..

50

25. Methods of preparing primers in electric blasting-

51

26. Blowing out holes with compressed air..

55

27. Loading holes in drift face...

56

28. Starting fan after blasting to clear smoke and gases from working

place

62

29. Blasting a round in an open pit..

67

30. Steel shelter for men when blasting in an open pit.

IN METAL MINES

Metal-Mine Accident-Prevention Course-Section 4

INTRODUCTION

PURPOSE AND SCOPE

2

This publication is the fourth in a series of miners' circulars covering a variety of phases of accident prevention in metal and nonmetal mines; these circulars constitute a textbook for courses of instruction on accident prevention in metal mining. They are intended to serve as a general reference to which may be added other material applicable to the district in which the course is presented. The accidentprevention course thus offered to the mining industry by the Bureau of Mines is built up from studies carried on by the Bureau and the experience and knowledge gained by Bureau engineers, to which is added information on mine safety practices made available by mine officials.

This section gives information on accidents from storing, handling, and using explosives in metal mines and discusses the precautions by which they can be prevented. The practical basis for these precautions is shown by the example of actual accidents and by their relationship to efficient blasting.

Other circulars in the series are:

Accident Statistics as an Aid to Accident Prevention in Metal Mines (Miners' Circular 51) deals with general statistics on accidents in metal and nonmetal mines, including causes, costs, and the uses of investigations and reports of all accidents.

Accidents from Falls of Rock or Ore in Metal Mines (Miners' Circular 52) discusses the prevention of accidents by the application of different mining methods to various types of ore deposits and the relative safety of these methods, especially as regards falls of rock. Causes of accidents from falling rock are described with the methods practiced to prevent them.

Hoisting and Haulage Accidents in Metal Mines (Miners' Circular 53) gives information on the hazards of hoisting and haulage and means of prevention.

Fires, Gases, and Ventilation in Metal Mines explains causes of mine fires and the measures used to prevent, control, and extinguish them ; describes gases found in mines and methods of detection, and discusses necessity for and standards of proper ventilation.

Electrical and Mechanical Hazards in Metal Mines covers accidents from these causes and their prevention. Accidents from falls of persons are also discussed in this section.

Health and Other Mine-Accident Factors in Metal Mines includes data on dust hazards, means of protection and sampling devices, protective clothing and equipment, illumination, supervision and discipline, and safety education for miners.

These seven miners' circulars do not contain all the material that may be desired on any of the various phases of accident prevention in metal mines, but it is intended that they will be inclusive enough

1 Work on manuscript completed December 1944. 2 Miners' Circulars 51, 52, and 53 have been published. The others are in preparation.

to serve as a basis for discussions. To these may be added supplementary material of particular interest in the field where the course is being presented.

ACKNOWLEDGMENTS Accident statistics in this circular were prepared with the assistance of W. W. Adams and F. J. Kennedy of the Accident Analysis Division of the Bureau. Drawings, charts, and photographs for the illustrations were prepared through the assistance of L. F. Perry and G. L. Henneman of the graphic section of the Office of Minerals Reports of the Bureau. D. O. Kennedy, P. R. Moyer, and William Eathorne reviewed the manuscript of the circular and made a number of valuable suggestions.

USE OF EXPLOSIVES IN MINING

HISTORY OF EXPLOSIVES IN MINES There are few industrial projects in which explosives are not used for one purpose or another, from removing tree stumps to tunneling through rock. Mining in all its forms makes a larger use of explosives than any of the other industries. It is said that gunpowder was first employed in 1627 for blasting rock in the mines of Austria, and by 1689 the practice had spread to Cornwall. Electric firing was first used in 1823 and was followed by the invention of safety fuse in 1831. About 1862 the successful manufacture of guncotton provided the first alternative for black blasting powder. This was followed by the introduction of dynamite in 1867 and the use of mercury fulminate in detonators about the same year. Later it was discovered that guncotton and nitroglycerin could be combined to form gelatin dynamite, and many specialized forms of explosives have been perfected.

PRESENT CONSUMPTION OF EXPLOSIVES

In 1943 metal mines of this country used approximately 31 tons of black blasting powder and 61,340 tons of high explosives; quarries and nonmetallic mines consumed a little over 1,000 tons of black blasting powder and approximately 40,034 tons of high explosives in that year.3 For the same year the consumption of explosives at coal mines was about 21,800 tons of black blasting powder and 73,100 tons of high explosives. Metal mines, nonmetal mines, and quarries used about 4.5 percent of the black blasting powder and approximately 47 percent of the high explosives sold during 1943; coal mines used approximately 94 percent of the black blasting powder and 34 percent of the high explosives; permissible explosives are included with high explosives in all of these figures. In metal mines, 99.3 percent of the explosives used were high explosives other than permissibles.

NATURE AND HAZARDS OF EXPLOSIVES Explosives are substances, or mixtures of substances, that have the property of rapid and violent change to gaseous form upon the application of shock or high temperature. With the exception of black blasting powder, commercial explosives have been modified and improved over past years to a degree that makes possible their handling,

3 Adams, W. W., and Wrenn, V. E., Production of Industrial Explosives in the United States, 1943: Bureau of Mines Tech. Paper 665, 1944, 26 pp.

storage, and use with reasonable safety so long as the utmost care is used at all times. The relative safety that can be maintained by careful observance of simple precautions is borne out by the infrequency of accidents during the storage and transportation of explosives and by the use of great quantities of explosives under properly controlled conditions without accident. The inescapable necessity for constant care to maintain safe conditions in the utilization of explosives is plainly evident in the histories of those types of explosives accidents that regularly occur.

EXPLOSIVES ACCIDENT STATISTICS

Explosives accidents have been and still are a major cause of fatalities in metal and nonmetal mines. Rock falls, haulage, and falls of persons have caused greater numbers of fatal accidents, but explosiyes accidents still rank with these as one of the serious hazards of mining. The relative percentages of fatalities and injuries from these causes for the period from 1940 to 1942 are shown in the following tabulation:

TABLE 1. Principat causes of accidents at all metal mines in the United States

[blocks in formation]

During the period 1931 to 1942, shown in tables 2 and 3, in underground metal mines the percentage of fatalities is high as compared with nonfatal injuries; 11.1 percent of the fatalities but only 0.08 percent of the injuries were caused by explosives; in the open-cut mines, fatalities of this nature were 7.6 of the total and injuries 1.5 percent. The frequency rates for fatalities and injuries are shown graphically in figure 1, from which appears a moderate lowering of both the fatal and injury rates in underground mines over the period. The fatality rate in open-cut mines is now based on such low numbers that no trend can be attributed to it, but the injury-frequency rate in these mines appears to have a downward trend. In most of these years, explosives accident rates for the open-cut mines were lower than for the underground mines.

A study 5 of the accidents from explosives in the iron mines of the Lake Superior district for the period 1940-43 showed that only 1 of 6 fatal or totally disabling accidents and only 4 of the 19 other injuries occurred in open-cut mines. Approximately 60 percent of the employment was in underground mines.

A large proportion of the explosives accidents results in fatalities and partial or total permanent disabilities, and as a type explosives

4 Adams, W. W., and Kolhos, M. E., Metal- and Nonmetal-Mine Accidents in the United States, 1940: Bureau of Mines Bull. 450, 1942, 51 pp.

Adams, W. W., and Kennedy, F. J., Metal- and Nonmetal-Mine Accidents in the United States, 1941: Bureau of Mines Bull. 457, 1944, 53 pp.

Adams, W. W., and Kennedy, F. J., Metal- and Nonmetal-Mine Accidents in tho United States, 1942: Bureau of Mines Bull. 461, 1944, 81 pp.

5 Cash, F. E., and Larsen, R. D., Accident Experience, Iron Ore Mines of the Lake Superior District, 1940-43: Bureau of Mines Inf. Circ. 7321, 1945, 9 pp.

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