ELECTRICAL ACCIDENTS IN BITUMINOUS-COAL MINES1

Coal-Mine Accident-Prevention Course-Section 6

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INTRODUCTION

PURPOSE AND SCOPE

This publication is the sixth in a series of seven miners' circulars covering various phases of accident prevention at bituminous-coal mines. These circulars constitute a textbook for courses of instruction on accident prevention in bituminous-coal mining, serving as a general reference to which may be added other material applicable to the district in which the course is presented. Other circulars in the series

are:

Accident Statistics as an Aid to Prevention of Accidents in Bituminous-Coal Mines (Miners' Circular 47).

Accidents from Falls of Roof and Coal in Bituminous-Coal Mines (Miners' Circular 48).

Accidents from Hoisting and Haulage in Bituminous-Coal Mines (Miners' Circular 49).

Explosions and Fires in Bituminous-Coal Mines (Miners' Circular

50).

Explosives Accidents in Bituminous-Coal Mines (Miners' Circular

58).

Miscellaneous Accidents in Bituminous-Coal Mines (Miners' Circular 60).

The use of electric power for haulage purposes in the bituminouscoal mines of the United States has increased from year to year since its introduction during the latter part of the nineteenth century (about 1887), a few years after trolley cars were first used for surface transportation. Later, electric power was utilized in cutting coal, pumping, drilling, ventilation, and mechanical loading.

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During 1891 only 5 percent of the underground [coal] production was cut by machines. This percentage has increased to what may now be the saturation point, about 90 percent. electric drills were first used about 1911, but the one-man portable drill did not appear until 1917. Hand augers, however, predominated until mechanical loading made it necessary to balance operations, thereby increasing the use of power drills. * *

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Loading was the last of these fundamental tasks to experience the start of replacing hand methods with machinery. Mechanical loading machines have been developing since about 1900, but little was accomplished during their first 20 years, with the result that in 1928 less than 5 percent of the underground bituminous production was loaded by machines. This had increased to more than 44 percent by 1942.2

1 Work on manuscript completed July 1945.

2 Mechanization, Inc., Mech Annual, 1943: Washington, D. C., p. 74.

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In 1943, 48.9 percent of the underground bituminous-coal production was loaded by machines, and when this circular was prepared more than half of such production was loaded mechanically. These statistics show the growth of electrically powered devices as applied to bituminous-coal mining. The trend likely will continue upward for some time to keep pace with the increase in mechanical loading.

The use of loading machines has increased rapidly during the past 20 years, and if the course made by cutting machines is followed mechanical loading will not reach the saturation point for 20 years.3

The widespread application of electric power in and about the bituminous-coal mines of the United States has been accompanied by numerous hazards. Unfortunately, in many instances safety has not kept pace with the increase in the use of electrically operated devices. This miners' circular discusses the dangers coincident with electricpower transmission and electrical-machinery installation and operation at bituminous-coal mines; it also includes recommendations for eliminating the dangers or minimizing the hazards.

During 1941, 42 fatalities and 737 nonfatal injuries occurred underground in bituminous-coal mines from the use of electric power, as compared with 51 fatalities and 931 nonfatal injuries in 1942.5 These fatal and nonfatal injuries were chargeable directly to electricity and do not include deaths and nonfatal injuries from mine explosions or fires that were known to have been caused by electricity. Mine explosions and fires originating from this source were discussed in an earlier issue of this series of miners' circulars dealing with accident prevention in bituminous-coal mining." The number of fatalities from electricity were exceeded in 1941 and 1942 by fatal accidents from falls of roof and coal, haulage, explosions of gas and coal dust, and machinery.

Numerous sources of information, predominantly publications of the Bureau of Mines, were utilized in the preparation of this circular. One of the foremost activities of the Bureau is to promote safety in mining through the activities of the Health and Safety Branch. The Electrical-Mechanical Section, through its permissibility tests and other services, has done much in the interest of safety, particularly in reducing electrical accidents. The Coal-Mine Inspection Division examines mines, including their equipment, and issues reports with recommendations to assist mine operators, officials, and mechanics to install, operate, and maintain electrical equipment and accessories so that the hazards in connection therewith will be minimized.

STATISTICS ON ELECTRICAL ACCIDENTS

Fatal and nonfatal injuries from electricity occur from several sources. Electrical-contact injuries sustained underground in the bituminous-coal mines of the United States have been classified by causes in Bureau of Mines Bulletin 4627 as follows:

3 See footnote 2.

4 Adams, W. W., and Geyer, L. E., Coal-Mine Accidents in the United States, 1941: Bureau of Mines Bull. 456, 1944, 131 pp.

Adams, W. W., and Geyer, L. E., Coal-Mine Accidents in the United States, 1942: Bureau of Mines Bull. 462, 1944, 140 pp.

6 Bureau of Mines, Explosions and Fires in Bituminous-Coal Mines. Coal-Mine AccidentPrevention Course-Section 4: Miners' Circ. 50, 1946, 107 pp.

7 See footnote 5.

a. Trolley wire.

b. Machine feed wire, junction box, or switch.

c. Haulage locomotive.

d. Power or lighting circuit.

e. Mining machine.

f. Mechanical shovel, loader, or conveyor.

g. Stationary electrical equipment (motors, switches, etc.). h. All others from electricity.

On a million man-hour basis both fatal and nonfatal injury-frequency rates from electricity show an increase in 1942 as compared with 1941. The statistics on electrical accidents do not include gas or dust explosions of electrical origin; these accidents have been discussed in section 4 of this series of miners' circulars. The 1942 accident-frequency rate, including fatal and nonfatal injuries from electricity sustained underground in bituminous-coal mines, was 1.58 per million man-hours of exposure, compared with 1.38 for 1941.

During the 20-year period 1911 to 1930, 4.6 percent (average) of all underground fatalities were caused by electricity. By 1931 mechanical loading underground had become an important factor in bituminous-coal production; in this year the underground production so loaded exceeded 10 percent of the total production. Since then it has increased almost continuously and now exceeds 50 percent of the total production. During the 12-year period 1931-42 electricity accounted for 4.8 percent of all the underground fatalities, excluding those from explosions or fires initiated by electricity. The difference between 4.6 and 4.8 percent for the periods given is small, considering the rapid growth of electrically driven machines used underground in recent years; moreover, fatal accidents from electrical causes have not shown an alarming increase in proportion to the total underground fatalities.

The situation with regard to fatalities in recent years is not good in the light of the number of mine explosions of electrical origin. For the 12-year period 1931-42 more than a third of the explosions were of electrical origin, and these accounted for more than half the number of fatalities from explosions: "

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Explosions of electrical origin were responsible for 66 (43.4 percent) deaths during the past fiscal [1943] year. This represents a marked decrease over 133 deaths from this cause during the previous year and is slightly less than the average of 69 deaths for the preceding 14 years. However, it is significant that all of the major (5) and 14 of the minor explosions were caused by electricity. The experience of 1943 bears out the statement made before in these circulars that "explosions of electrical origin will continue to occur if haphazard methods in the use of electrical equipment are continued." The shortage of trained personnel and difficulty experienced in obtaining necessary equipment and replacement parts added to the greatly increased demand for coal with rapid expansion of mechanized mining during the past year may have been major contributing factors resulting in the increased number of explosions of electrical origin. These conditions necessitate that extra precautions be taken on the part of supervisory officials to see that electrical equipment is properly operated and otherwise safeguarded. One of the main factors in the increase of explosions of electrical origin is that the demand for increased production of coal has brought about a rapid adoption of two- or three-shift operations, one of the results being that electrically operated machinery must be kept in practically continuous operation with little or no opportunity for the making of repairs unless the equipment actually breaks down and even then the

8 See footnote 6.

9 Harrington, D., and Fene, W. J., Coal-Mine Explosions and Coal- and Metal-Mine Fires in the United States During the Fiscal Year Ended June 30, 1943: Bureau of Mines Inf. Circ. 7274, 1944, 27 pp.

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repair work is hurried. In many instances permissible electrical equipment is allowed to become unsafe because a bolt or gasket has not been replaced after the machine has been repaired. * * *

The explosion record for the past 3 years should cause the coal-mining industry grave concern. Several factors contribute to this bad record, such as (1) the rapid increase in the use of electrical equipment at face regions, where gas is most likely to be found; (2) increased demand for coal to supply defense industries; (3) desire of mining-machine manufacturers and mine operators

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 FIGURE 1.-Fatal and nonfatal injuries from electrical accidents at bituminous-coal mines in the United States, 1930-42. Surface accidents include strip mining.

to obtain maximum tonnage per machine at minimum cost, which has resulted in neglect of rudimentary precautionary measures; (4) multiple-shift operation, which does not allow time for adequate maintenance of equipment, proper rockdusting, and testing for gas by fire bosses; (5) decrease in supervision owing to demands on supervisors for maximum tonnage; (6) lack of effective supervision owing to numerous causes; (7) inability to obtain adequate equipment repair and replacement parts; (8) shortage of skilled labor; and (9) failure of both miners and mining officials to show regard for safety in changing from hand-loading to mechanized methods.

10 Gaskets are approved for use on permissible machines only for a metal-to-glass joint such as a headlight on a permissible storage-battery locomotive.