wise safeguarding of transportation and of storage of explosives in mines; the employment of safer methods of blasting, such as using inert tamping material and up-to-date safeguarded electrical methods of blasting-blasting largely through shot firers when the working shift is out of the mine; and the safeguarding and use of all kinds of electrical installations found in and around mines, with particular reference to prevention of ignitions of timber or other combustible material by electric arcs or short circuits.

RECOMMENDATIONS

Other measures for the prevention of fires in mines and their more ready control include:

1. An adequate supply of water available on the surface and underground, furnished if possible through water lines extending to within 100 feet of the breasts of the various levels and drifts, with hose attachments at frequent intervals and hose stored at appropriate points. In small mines filled water barrels and fire buckets or suitable types and sizes of fire extinguishers distributed at suitable points, including shaft stations, may answer the same purpose.

2. Provision for the ready conversion of air lines into water lines. 3. The placing of containers filled with dry sand or other incombustible dust or fire extinguishers of suitable type at or near underground electrical stations and near fixed motors and transformers.

4. Regular inspection of the mine, including entrances and underground workings, for fire hazards, and written reports on such inspections.

5. Inspection of timbered stopes after each shift.

6. Regular inspection and testing of mine fire-fighting equipment. 7. Organization of mine employees for fire prevention and fire control and a written plan of action to be followed in event of fire. Regular instructions, supplemented by fire drills, of mine officials and selected employees in the duties assigned to them in event of fire.

8. Establishment of a surface and underground fire-alarm system. For informing underground workers of fire a general danger signal may be given by interruptions of the lighting circuit or by telephone, or in mines using compressed air a stench warning system may be used.

9. Use of fireproof structures only within 50 feet of any mine entrances.

10. Fireproofing of all dry-timbered shaft stations by guniting or similar method.

11. Installation of tightly closing fire doors near shafts in levels leading from shafts in every timbered mine to permit the separation of various sections of the mine in case of fire.

12. Prohibiting the storage of oil or other dangerously inflammable material within 100 feet of any mine opening.

13. Prohibiting the dumping of oily waste, papers, old hay, manure, waste carbide, and other inflammable débris into abandoned workings and keeping the mine free from empty boxes, wood chips, paper, and combustible rubbish.

14. Fireproofing of main intake shaft lining.

PRECAUTIONS AGAINST GASES FOUND IN METAL MINES 15

VENTILATION

Of importance at least equal to the taking of adequate precautions against fire in or around metal mines is the provision for adequate ventilation 16 of the mines. Efficient ventilation of metal mines consists in supplying at all times such volume of circulating air in working places as will enable the worker to exert himself in comfort at maximum physical capacity without endangering his health. In mining ventilation, fire protection and prevention, health, safety, and efficiency are closely interlocked.

Metal-mine operators rarely if ever provide for ventilation until forced to do so by some untoward condition or occurrence; coal-mine operators, however, universally provide for ventilation-they must, otherwise an explosion would ensue. There is just as much reason for providing adequate ventilation for most metal mines as for providing ventilation for coal mines.

Many metal-mine officials, technically educated as well as those without technical training, are ignorant of the principles of air circulation. Ventilation should be under constant supervision, and the man in charge should report to the highest officials of the company, as many local officials in metal mines are not in sympathy with improvements in ventilation.

Workers in metal mines, including shift and other bosses, must be educated to respect ventilating devices such as doors, regulators, overcasts, brattices, and fans as coal miners do, and to become as familiar with those devices as coal miners are. Many present-day metal miners and bosses consider ventilation a useless fad and obstruct rather than aid improvements in ventilation. Metal-mine operators should provide fan ventilation 17 from the beginning of operations to avoid dangers from explosives and other fumes and should provide fresh air to workers. Each mine should be ventilated wholly within itself; interventilation of mines is likely to be dangerous, inefficient, and unsatisfactory.

RECOMMENDATIONS

Some of the measures recommended to obtain adequate metalmine ventilation are as follows:

1. Installation of a mechanically driven fan with fireproof housing and mine connections, the fan to be capable of quickly reversing air currents and of capacity adequate to ventilate the mine properly,

16 Harrington, D., Underground Ventilation at Butte: Bull. 204, Bureau of Mines, 1923, 131 pp. Rice, G. S., and Sayers, R. R., Review of Safety and Health Conditions in the Mines at Butte Bull. 257, Bureau of Mines, 1925, 29 pp.

17 Richardson, A. S., Ventilation Problems at the Butte Mines of the Anaconda Copper Mining Co.: Min. Cong. Jour., vol. 14, May, 1928, pp. 351-354.

Pullen, J. B., Underground Ventilation Problems at the Copper Queen Mincs, Phelps Dodge Corporation, Bisbee, Ariz. Min. Cong. Jour., vol. 14, Sept mber, 1928, pp. 692–697. Mitke, C. A., Solving Ventilation Problems by Mechanical Means: Min. Cong. Jour., vol. 14, July, 1928, pp. 489-490, 495.

Richert, G. L., Mechanical Ventilation at the Minas de Matahambre: Min. Cong. Jour., vol. 14, July, 1928, pp. 491-493, 510.

Glaeser, O. A., Ventilation at the United Verde Mine: Trans. Am. Inst. Min. and Met. Eng., Yearbook, 1929, pp. 114-141; discussion, pp. 141-143.

Harrington, D., and von Bernewitz, M. W., Some Features of Ventilating Fans at 164 Coal and Metal Mines: Rept. of Investigations 2637, Bureau of Mines, 1924, 5 pp.

the air capacity to be defined further as not less than 100 cubic feet of air per minute for each person underground on any one shift, with such additional quantity as is needed to dilute adequately and render harmless any mine gases encountered.

2. Proper distribution of air to working places by such means as the driving of connections between levels; use of doors, overcasts, bulkheads, regulators, and canvas; use of auxiliary fans or blowers, electric or compressed-air driven, with canvas or other tubing.

3. Requirement that all working places in which the air temperature is above 80° F. (dry bulb) be supplied with a current of moving air by means of a blower and tubing or equivalent means.

4. Continuous operation of the surface fan while men are in the mine.

5. Maintenance of all airways so that they allow ready unobstructed passage of air.

6. Splitting of air currents systematically so that fire in one section of a mine may not necessarily fill the entire mine with asphyxial fumes.

There are records of naturally or otherwise inadequately ventilated mines filling with carbon dioxide or other gas, overcoming some of the workers, and compelling suspension of work for considerable periods of time. Upon establishment of efficient mechanical ventilation this situation has been readily controlled. During seasons when the temperature of surface air and of underground rock and water are about equal, circulation of air at certain times in mines that rely on natural ventilation is sluggish, ceases utterly, or reverses in direction. During a mine fire naturally ventilated mines are likely to be at a decided disadvantage through inability to control direction of air currents.

TEMPERATURE AND HUMIDITY

Although finely divided dust in mines is probably the chief cause of miners' consumption, it is now recognized that there may be other factors of almost equal influence, such as high temperatures and humidities, harmful gases, and lack of air movement, all of which are readily remedied by ventilation. With dry-bulb temperatures below 75° F. mine working places may be comparatively comfortable, irrespective of air movement or relative humidity. However, air heavily depleted of oxygen or impregnated with gases such as carbon dioxide, carbon monoxide, and oxides of nitrogen may be uncomfortable or unsafe; moreover, such places may be both uncomfortable and unhealthful if large quantities of finely divided dust are present. With dry-bulb temperatures above 75° F., comfort and maximum working efficiency can be attained only when the air is moving, particularly when the relative humidity is high. The exact velocity necessary is a variable dependent on the temperature and humidity. Saturated atmospheres up to nearly blood temperature may be made endurable and even to a considerable extent comfortable by providing sufficient velocity. Relative humidity, even up to the saturation point, does not appear to be harmful to health, comfort, or efficiency until this temperature is above 75° F.; if enough move

DETECTION OF GASES

17

ment is supplied, high relative humidity is not particularly harmful until the temperature is well above 90° F.18

Many accidents in metal mines are due to deficient ventilation. Failure to remove smoke and fumes after blasting prevents proper safety inspection of working places; many men have been asphyxiated in fumes from explosives. Moreover, in hot, humid, stagnant air men are likely to become dizzy or are unable to think clearly or quickly or they may faint at an inopportune time and be killed. There are instances of men having dropped dead from heart failure in such hot places. Physiological experimental work in South African mines shows that men working in stagnant air with a relative humidity of 95 per cent and a temperature of 87° F. increased the amount of work performed 46 per cent by the mere expedient of installing a small fan to move or stir the air, showing that high humidity in itself is not particularly harmful (at least until the temperature is well above 90° F.) and that air movement has a vital influence on the productive capacity of workers.

Although ventilation has generally been deemed an integral part of coal mining, metal-mine officials usually pay little or no attention to circulation of air until forced to do so by some untoward condition or accident, yet the need of efficient circulation of air is as great in metal mines as in coal mines. In coal mines the dangerous explosive gas methane, fumes from explosives, and sometimes other gases, such as carbon dioxide or nitrogen, must be removed. In metal mines there is a greater need to remove fumes from explosives, and frequently there is occasion to remove carbon dioxide, nitrogen, and other gases from strata; even the coal miner's explosive gas, methane, is occasionally found. In addition, circulating air currents are urgently needed in metal mines to reduce the excessively high_humidity and temperature so frequently found there, although these are rare in coal mines. Immense quantities of minutely fine particles of rock dust floating in the air of metal mines and largely responsible for miners' consumption 19 and some other diseases prevalent among metal miners could be almost wholly removed by adequate ventilation. The generally accepted conclusion that coal miners have a healthful occupation and live to a ripe old age and that many metal miners contract diseases, such as lead poisoning and miners' consumption, and either die early in life or are incapacitated in middle age is due almost wholly to the superior working conditions in coal mines brought about chiefly by ventilation.20

DETECTION OF GASES

The detection 21 and quantitative determination of mine gases have been described in detail in various publications referred to in footnotes.

18 Sayers, R. R., and Harrington, D., A Preliminary Study of the Physiological Effects of High Temperatures and High Humidities in Metal Mines: Public Health Report 639, 1921, 16 pp.

19 Harrington, D., and Lanza, A. J., Miners' Consumption in the Mines of Butte, Mont.: Tech. Paper 260, Bureau of Mines, 1921, 19 pp.

20 Harrington, D., Ventilation in Metal Miñes, a Preliminary Report: Tech. Paper 251, Bureau of Mines, 1921, 44 pp.

21 Forbes, J. J., and Grove, G. W., Mine Gases and Methods for Their Detection: Miners' Circ. 33, Bureau of Mines, 1929, 65 pp.

The extinguishing of a candle or match flame or the flame of a carbide lamp or flame safety lamp shows that the oxygen in the atmosphere tested is insufficient to support the flame and also indicates the presence of abnormally high percentages of nitrogen or carbon dioxide, or both. If the oxygen-deficient air hangs near the top of a raise or a high point it is probably mainly nitrogen (density 0.971) and if it is in a winze, shaft, or near the floor of a tunnel or drift it contains considerable carbon dioxide (density 1.529). The flame of a candle, match, or flame safety lamp is extinguished when the oxygen content of the air drops to about 16 per cent but the flame of a carbide lamp usually is not extinguished until the oxygen content of the air drops to between 13 and 14 per cent.

SAMPLING AIR

Air samples may be collected readily at any accessible point in a mine by the use of a vacuum bottle or by emptying a bottle filled with water in the air to be tested and then tightly sealing the bottle. The samples thus collected can be analyzed quickly with a portable Orsat apparatus for oxygen, carbon dioxide, carbon monoxide, and methane and the nitrogen determined by difference.22 The Orsat apparatus is accurate to within about 0.2 in the percentage found.

TYPES OF DETECTORS

Methane is ordinarily detected in coal mines by elongation of the flame of a flame safety lamp or by actual explosion within the lamp.23 In drifts and tunnels where the presence of methane is suspected a magnetically locked flame safety lamp or equivalent device should be used for testing. Any source of open flame will ignite methane if present in explosive proportions, and such ignition is likely to result in a severe explosion with injury or death to workers, as well as damage to property. Methane detectors 24 other than the flame safety lamp approved by the Bureau of Mines include the Martienssen, the Burrell, and the Union Carbide Co. The last is accurate to within 0.15 per cent. A continuous methane recorder has also been devised for automatically determining and continuously recording the amount of methane; for example, in a return-air current.

Hydrogen sulphide gas may be detected by its characteristic odor of spoiled eggs. If air suspected to contain hydrogen sulphide is passed through a solution of cadmium sulphate or chloride there will be a typical yellow precipitate. Even slight traces of hydrogen sulphide will tarnish a silver coin.

Sulphur dioxide is readily detected by its odor of burning sulphur matches.

Carbon monoxide gas can be detected in a number of ways. A canary or mouse usually will be overcome in quantities of carbon monoxide gas immediately harmful to man much quicker than will

22 Yant, W. P., and Berger, L. B.. Instructions in Methods of Sampling and in the Use of the Bureau of Mines Portable Orsat Apparatus for Analyzing Mine Gases: Miners' Circ. 34, Bureau of Mines, 1929, 89 pp.

23 Paul, J. W., Ilsley, L. C., and Gleim, E. J., Flame Safety Lamps: Bull. 227, Bureau of Mines, 1924, 212 pp.

24 Hooker, A. B.. Fene, W. J., and Currie, R. D., Permissible Methane Detectors: Bull. 331, Bureau of Mines, 1930, 30 pp.