15. The way in which the flame of a lamp or candle burns will show the condition of the confined air and how the oxygen is being exhausted. All flame lamps (except possibly one for part of the time) should be extinguished to save oxygen; moreover, oil, carbide, and electric batteries should not be used needlessly. Food and water, of course, should be used sparingly and thereby kept as long as possible.

16. Men behind a barricade should signal frequently by pounding on the air or water pipes, the track rails, or the back of the rock drift, or, in a coal mine, by pounding on the rib or the roof so that listeners may hear them. Generally, pounding on the rock or coal can be heard farther than pounding on pipe lines or track rails.

17. Miners should carry with them any chalk found during their retreat from gases; chalk also may be part of the working equipment of track men, fire bosses, shift bosses, etc., who may be among those entrapped. Directions for a relief party may be written on doors (see fig. 19), or an arrow may be drawn on a track rail or a pipe or a piece of board or slate or on the roof or rib to indicate the course the workers took in retreating. Under some conditions the flame of a carbide lamp will enable a mine worker to make good lettering on timber or rock. (See fig. 31.)

18. It is very important that underground employees be familiar with all escapeways, manways, and other exits in addition to those usually traveled; in many mines this is not the case, and many lives have been lost as a result of failure of the supervisory force to inform workers about this really important matter. Workers should learn, also, which entries serve for intake and return air currents; here, again, is an important safety feature very frequently neglected by both workers and bosses. A mining company should equip all parts of a mine with direction signs, which should be kept in readable condition. Often this is not done. Travel ways to emergency exits should always be kept in passable condition, reasonably free of rock falls, pools of water, and other obstacles, another safety feature neglected far too frequently.

LIFE-SUSTAINING CAPACITY OF BARRICADED CHAMBERS

A barricaded area forms a refuge chamber for the persons within, and the cubic contents of the space enclosed determines the number of men and the length of time they can remain there safely. In breathing, the men consume oxygen of the air and give off almost an equal quantity of carbon dioxide. When the proportion of carbon dioxide in the atmosphere of the enclosed space reaches 8 percent, the men will breathe very heavily and will be at the point of complete exhaustion. Actually, men have lived for 2 days in an atmosphere in which a carbide light would not burn, so that not more than 12 percent of oxygen was present. A man at rest consumes least oxygen and gives off least carbon dioxide, but if he is in a confined space the air finally will become unfit to sustain life. Experiments show that a man in a confined space needs about a cubic yard of normal air an hour. At the end of an hour this cubic yard of air will contain about 14 percent oxygen and 5 percent carbon dioxide; an oil lamp will not burn,

and an acetylene lamp will almost be extinguished. On the basis of a cubic yard of air an hour, an enclosed space 10 feet wide, 10 feet high, and 10 feet long, containing 1,000 cubic feet or 37 cubic yards of space, will support a miner 37 hours before he will begin to suffer through lack of breathable air. This minimum allowance of 1 cubic yard an hour for each man, however, does not provide for losses of oxygen through absorption by the coal or timber in the enclosed space or for the impairment of the air by flow methane or carbon dioxide from the coal or rock, and does not take into consideration the possibility that the air may not be uniformly mixed at all times and in all places, with the probability that in some places oxygen will be reduced much below the percentage required for safe breathing by man.

Some oxygen, is absorbed by the coal or ore and the timber, and absorption by timber is hastened when the region is damp or wet. In some bituminous-coal mines the rate of absorption is relatively rapid compared with that in some metal mines, and when some coal mines are sealed in whole or in part oxygen is absorbed so rapidly by the coal and timber that in 1 or 2 weeks not enough will be left to support life. Similarly, withdrawal of circulating air from some metal-mine working places results in absorption of oxygen, with replacement by carbon dioxide or other asphyxiating atmosphere in a relatively short time, in some instances only a few days.

VALUE OF BARRICADES

The miner who reads this circular naturally will wish to know whether any lives have been saved by the use of barricades and, if lives have been saved, what in general were the surrounding conditions and circumstances. One purpose of the circular is to describe briefly how numerous lives have been saved and to show where and how the barricades were built. The accompanying table summarizes the incidents discussed.

In the 42 cases of barricading listed, 876 lives were saved by barricading against the gases produced by fires or explosions; some of the 143 that died behind the barricades might have been saved had the victims used better-thought-out procedure or placed the bulkhead or barricade differently. The available information on this subject amply justifies calling attention to the usefulness of barricades after explosions or fires in mines, and all persons engaged in underground mining of any kind can well afford to give this matter careful study and

attention.

Barricades built by underground workers are described later in this circular. After reading the descriptions, the man who works underground, whether boss or laborer, should study his working conditions (knowing that nearly all underground mines have conditions such that a fire or explosion can occur), and should ascertain whether, in time of necessity, he could find material suitable for building two or more stoppings. If he is familiar with the position of doors that control the movement of air in the section of the mine in which he works (and he certainly should be), he should examine the doors and see what would be the effect of opening or closing them with regard to air conditions in the region where he works.

The first barricade recorded in the reports of the Bureau of Mines was built by entombed miners during the fire at the Cherry mine in Illinois in 1909. Accounts of this fire were published widely and at that time and for years afterward impressed many, if not most, of the miners in this country. Many of them took the lesson to heart and have surveyed their surroundings since then with the idea of erecting a barricade should the need arise. This early instance of barricading gave the idea to so many others that nearly every year additional instances occur (some successful, some not); short recital of some of the important features connected with them seems especially pertinent at this time (1940) inasmuch as very serious mine explosions seem to be increasing, especially in the bituminous-coal mines of the United States. The descriptions that follow have been divided into three groups: (1) Barricades in coal mines, (2) barricades in metal mines, and (3) other means of self-preservation.

BARRICADES IN COAL MINES

According to the records of the Bureau of Mines, barricades in coal mines have saved at least 876 lives. This number would have been larger had some of the miners listened to reason and not rushed into poisonous atmospheres, or had some of them thought of building stoppings, or had they remained within barricades until rescue workers arrived. These barricades are described briefly according to types.

BRATTICE-CLOTH BARRICADES

SAN BOIS NO. 2 (M'CURTAIN) MINE

By bratticing themselves in an emergency shelter, by closing the "creep hole" or sliding door in a stopping above a compressed-air pump, and by erecting a curtain stopping on the other side of the pump (see fig. 2) and then breathing the exhaust from the pump, 13 men saved their lives in the No. 2 mine of the San Bois Coal Co. at McCurtain, Okla., in March 1912.

The area shown in figure 2 was 27 feet long, 7 feet wide, and 72 feet high; it therefore contained about 1,400 cubic feet of space, less about 20 cubic feet which was occupied by the pump. The imprisoned men got air direct from the pipe line, which they broke at an elbow, and thus kept themselves in good condition for about 5 hours; after that time the air pressure was not strong, and all the men except one became unconscious. One man died, probably in large part from the effects of afterdamp he had breathed before the barricade was built. After about 15 hours a rescue party took down a curtain in the main slope, better air reached the men behind the brattice, and they began to revive. After 20 hours they were rescued. (Compressed air is not available in many coal mines, but this example shows what can be done if it is available, and compressed air has been used advantageously in saving lives of entrapped men during fires in metal mines.)

ECCLES NO. 6 MINE

At the time of the explosion in No. 6 mine of the New River Collieries Co. at Eccles, W. Va., 74 men were in No. 5 mine above it; of these, 8 were overcome by afterdamp, 31 were rescued, and 35 saved