11. All flame lamps should be extinguished to conserve oxygen; also, if methane is given off the flame would soon cause an explosion. It is desirable not to use candles, carbide lamps, flame lamps, or electric batteries needlessly.

12. Food and water should be conserved as long as possible.

13. A sign should be placed outside the first stopping, if more than one is built, to show that men are behind it.

14. If possible, barricades or bulkheads should be erected with a valve inclosed in the compressed-air line if compressed air is used in the mine. The valve should be opened when necessary to furnish additional air, precautions being taken, however, not to allow poisonous gases to enter the barricaded region through the compressed-air line after the compressed air fails.

15. It is very important that underground employees should be familiar with all escapeways, manways, and other exits. They should also know which entries serve for intake and return air currents. A mining company should have all parts of a mine equipped with easily read direction signs indicating the pathway to exits.

16. Many lives have been sacrificed because miners did not know the coursing of the ventilation in the particular section of the mine in which they were at work at the time of the explosion or fire.

LIFE-SUSTAINING CAPACITY OF BARRICADED CHAMBERS

A barricaded area forms a refuge chamber for the men within, and the cubic content of the inclosed space determines the number of men and length of time they can safely remain there. In breathing, the men consume oxygen from the air and give off an almost equal amount of carbon dioxide. When the proportion of carbon dioxide in the air of the inclosed space reaches 8 per cent, the men will breathe heavily and be at the point of complete exhaustion. Actually, men have lived for considerable periods in an atmosphere in which a carbide light would not burn, indicating that the air they breathed had less than 13 per cent of oxygen. A man at rest consumes less oxygen and gives off less carbon dioxide than if he were at work. In a confined space, however, the air will finally become unfit to sustain life. Experiments have shown that a man in a confined space requires approximately 1 cubic yard of air per hour. At the end of an hour this cubic yard of air will contain about 14 per cent of oxygen and 5 per cent of carbon dioxide; an oil lamp will not burn, and an acetylene lamp will be almost extinguished. On the basis of 1 cubic yard of air per hour an inclosed space which is 10 feet wide, 10 feet high, and 10 feet long and contains 1,000 cubic feet or 37 cubic yards of space will support one man for 37 hours before he begins to suffer

20855°-29-2

through lack of breathable air. This minimum allowance of 1 cubic yard per hour per man, however, does not provide for loss of oxygen through absorption by the coal or timber in the inclosed space or for the impairment of the air by methane or carbon dioxide from the coal or rock. In some bituminous coal mines the oxygen behind seals is absorbed so rapidly that in one or two weeks not enough will be left to support life.

In a metal mine a barricaded drift 250 feet long, 6 feet high, and 6 feet wide, containing 9,000 cubic feet of air, kept 29 men alive for 36 hours. In the same mine another one 130 feet long, 7 feet high, and 7 feet wide, containing 6,500 cubic feet, supported 6 out of 8 men for 50 hours; the other 2 were found dead. The 6 who were alive were all unconscious but were later revived.

VALUE OF BARRICADES

The value of barricades can not be emphasized too strongly, as they have been the means of saving hundreds of lives in coal and metal mines, and as many additional lives may be saved if men are properly instructed in their use.

The first barricade recorded in the reports of the Bureau of Mines was built by entombed miners during the fire in the Cherry mine, Cherry, Ill. This saved the lives of 20 men, who were rescued 7 days after the erection of the stoppings. Many additional lives in both coal and metal mines have since been saved by the prompt erection of barricades. Table 1 is a list of the barricades erected in coal and metal mines up to January, 1929.

TABLE 1.-Summary of barricading incidents by dates

TABLE 1.-Summary of barricading incidents by dates-Continued.

1 Add columns 7 and 11 to get total deaths in each mine; columns 10 and 11 together show how many men were behind the barricades.

* Canvas brattice.

Of these 4 were lost after leaving the barricade and were gassed, 2 died from exhaustion behind the barricade, and 19 overlooked an open manway through which gases entered the bulk headed drift.

Only partly built; men waited too long.

$1 built and another partly built, but an explosion blew down the first one.

• Second barricade unfinished; air bad from start.

71 started out from barricade too soon and was found dead; 1 horse saved.

* 2 started out from barricade too soon and were found dead; 13 horses saved.

BARRICADES IN COAL MINES

According to records of the bureau barricades in coal mines have saved a total of 496 lives. This number would undoubtedly be much larger if other miners had made an effort to erect barricades instead of rushing into poisonous atmospheres. The barricades erected will be briefly described according to type.

BARRICADES CONSTRUCTED OF BRATTICE CLOTH

1. By bratticing themselves in an emergency shelter hole, closing the sliding door in a stopping above a compressed-air pump, erecting a curtain on the other side of the pump, and then breathing the exhaust from the pump 13 men saved their lives in the San Bois mine at McCurtain, Okla.

2. At the time of the explosion in No. 5 mine at Eccles, W. Va., 74 men were in No. 6 mine above it; of these 8 men were overcome by afterdamp, 31 were rescued, and 35 saved themselves by retreating from the hot afterdamp to a sump room, where they bratticed themselves off with canvas.

3. Forty-three men saved their lives after an explosion in No. 7 mine, Clay, Ky., by placing brattices across two rise entries and opening a door, thus short-circuiting the afterdamp.

BARRICADES CONSTRUCTED OF BOARDS

1. An explosion at Layland, W. Va., killed 112 men. Of 54 that escaped 47 saved their lives by erecting board bulkheads at two different points after short-circuiting the air. All of the board stoppings were made tight by packing coal dust against the bottom and sides and by caulking the crevices between the boards with brattice cloth.

2. After an explosion of gas in No. 1 mine, Oliphant-Johnson Coal Co., near Bruceville, Ind., 42 men gathered near the face of the main entries. After opening a door to short-circuit the air current they selected a place to erect a barricade. They stretched brattice cloth across the place selected; then they made two walls 2 feet wide of timber and refuse with a 2-foot space separating the walls and filled in the space with coal and other material, using coal shovels. They were discovered and rescued about 234 hours later.

BARRICADES CONSTRUCTED OF ROCK, COAL, ETC.

1. Following the outbreak of the Cherry fire, Bureau County, Ill., 20 men built 2 barricades of stones, powder cans, and mud. The men were rescued 7 days later.

2. After an explosion in the Cross Mountain mine, Briceville, Tenn., seven men erected a barricade. These men built a gob wall and placed lighted lamps on top of it to give warning of the approach of afterdamp. When afterdamp began to come into the barricade, another wall was built 41 feet inby the first one. This barricade was made solidly of gob, and the holes between the pieces of slate were filled with hay from the mule stable. Five men were rescued, and two who had left the inclosure the day before the rescue were found dead.

3. At Dolomite, Ala., about 50 men built two stoppings of rock across an entry. Smoke leaked through, and the men went farther back and built another one. The barricade consisted of two walls of dry rock with a 2-foot space between, which was filled with fine dirt to make it tight. The men were rescued a few hours later.

BARRICADES IN METAL MINES

1. The gases from the fire in the Argonaut gold mine at Jackson, Calif., caused the death of 47 men, whose bodies were found 21 days

after the fire started behind 2 barricades. The barricades were made of spiling, chute boards (2 by 12 inch), and miscellaneous lumber. The air behind the barricades when the bodies were found analyzed 0.21 per cent carbon monoxide, 5.71 per cent carbon dioxide, and 14.18 per cent oxygen. Evidently the men were in bad air from the start and retired farther back. There they started to build a second barricade but ran out of material and were overcome.

2. A barricade saved eight men in the Pittsburgh-Idaho mine at Gilmore, Idaho, and six men in a dead end of the same level were also saved although no barricade protected them. The party of eight men went into the north drift about 100 feet, where they cut out some of the back lagging and let down considerable waste rock from the slope above. With this rock and some planks and timber they made a bulkhead two sets thick, plugging the crevices and holes with their clothing.

Comparatively few barricades have been erected in metal mines; however, the several instances of the erection of barricades have resulted in saving at least 59 lives. The example of what has been done in coal mines should be helpful to metal miners.

REFUGE CHAMBERS IN MINES

The bureau advocates that refuge chambers be built in the main sections of mines. After an explosion or during a mine fire men. might retreat to these chambers and close themselves in until rescued. Such chambers should be provided with drinking water, canned food, compressed air (if available), and, if possible, a pipe leading from the chambers to the surface. Refuge chambers of this type have been provided in some eastern bituminous coal mines. Small refuge chambers have been established in some of the coal mines of the Central States where there have been many explosions during shot firing, and these chambers have saved lives. Refuge or so-called underground safety chambers have been established in metal mines in Butte, Mont., and have been used to great advantage in the United Verde mine in Arizona to avoid dangerous fumes from blasting.

Even where refuge chambers are provided, mining companies should make a special effort to instruct underground employees in the value and procedure of erecting barricades.

Some mining companies in the bituminous fields of Pennsylvania and other States have provided equipment and material at the section foreman's offices and in the advanced workings of the mine to be