12. An oil switch controlling the powerlines of a mine failed and started a fire at the shaft collar, which spread into the mine. 13. An overloaded trolley feed cable heated and caused a fire because the circuit breaker had been fastened in. 14. A scraper motor cable was damaged by a blast, and a short circuit started a fire. 15. An electric-light bulb set fire to a rubber glove at a timber raise. OPEN LIGHTS, FLAME, AND SMOKING Open lights (candles and later carbide lamps) have caused many mine fires. But the increased use of electric cap lamps has reduced the number from this source in recent years. It is estimated that 8 to 15 percent of all recent fires in metal and nonmetallic mines have been due to smoking, carbide lamps, and open fires or flames used for various purposes. This figure does not include fires started from welding and cutting. The causes of such fires are briefly given here: 1. A shaft fire was started by a carelessly thrown cigarette. 2. A miner going off shift threw a lighted piece of paper down a chute to see how much ore was in the chute, and a fire resulted. 3. A fire was started close to the fan motor on one side of a shaft station by contact between a miner's carbide cap lamp and canvas tubing taking air from the fan. 4. A match started a fire in a station close to a timbered shaft. 5. A pumpman burning newspapers on a concrete floor in a pumproom set fire to adjacent timber. 6. A candle used for illumination was left burning by a miner and caused a fire. 7. A fire was discovered in a raise at a point where spent carbide was thrown. 8. A mechanic's helper, while welding a water line, searched for a leak in an acetylene line with an open carbide light. The timber caught fire. 9. The open-flame lamp of a man who was recovering some tools that he had hidden where there was some dry lagging came in contact with the timber and caused a costly fire. 10. A lighted carbide lamp which a powderman placed on a shelf under a large fuse box ignited the paper between the boards and started a fire. 11. Mine officials inspecting some long-abandoned pillars of ore with a view to planning their removal sat down and smoked, and about 24 hours later a fire was giving off so much smoke that the mine had to be closed until the fire could be extinguished. The fire hazards of open lights, smoking, and matches underground have led to the replacement of carbide lights by portable electric cap lamps and to restrictions on smoking. Although there are other good reasons for use of electric cap lamps, the reduction of the fire hazard has been the deciding factor in their adoption by a number of large mines. Other points regarding the use of electric lamps are discussed under illumination. WELDING AND CUTTING Available figures indicate that 12 to 20 percent of the recent metaland nonmetallic-mine fires have resulted from welding and cutting operations. These fires occurred through the ignition of wood or other flammable material at the point were the torch was used or by pieces of hot metal dropping into timber or refuse below, particularly in timbered shafts. They usually smolder and are not discovered until they have made considerable headway. The introduction and use of steel supports in underground mines, the welding and bonding of haulage rails, the practice of doing mechanical repair work underground, and the modern developments in welding and cutting technique have increased welding and cutting operations underground. The following examples are typical of fires from this cause, which are now occurring in increasing numbers. 1. A blowtorch used to thaw a frozen water pipe in a shaft set fire to decayed timbers back of the pipe; the fire smoldered several hours and then flamed and was discovered. 2. Some steelwork was being removed from the collar of a shaft, and a small piece of hot metal lodged in the timbers some distance down the shaft; fire broke out after the crew had gone and destroyed the upper part of the shaft and the entire surface plant. 3. A shaft repair crew used a cutting torch, and a hot bolthead fell down the shaft and started a timber fire. 4. Electric welding and bonding of rails set fire to ties in a mine. 5. Sparks from cutting an old air line in a shaft caused a shaft fire. 6. Sparks from welding set fire to an accumulation of oil underneath an underground crusher. 7. A fire was started in the back blocking in which a crew had been cutting rails supporting the blocking. 8. A welder from a salvage company was cutting out the bolts from the sheave-wheel bearings over a shaft. The shaft collar was partly uncovered to maintain ventilation, and hot metal ignited the shaft timbers near the collar. Information Circular 7453 10 describes 19 metal-mine fires from welding and cutting and points out precautions to be taken to prevent other fires from this cause. Welding and cutting operations in shafts and underground will continue to increase, and fire-prevention measures must be taken to safeguard the areas and operations. The danger can be lessened by wetting down the areas, making fire extinguishers a part of welding and cutting equipment, providing an extra man to watch for falling hot material and incipient fires, thoroughly cleaning and inspecting the area when the job is completed, and leaving a man to patrol the area for at least 4 hours after the welding crew leaves. SPONTANEOUS COMBUSTION Burning is rapid combination of oxygen and some other element, usually carbon or sulfur, and it is possible for a fire to start without the application of flame or external heat. Such fires have occurred underground, although they are not common, and are very difficult to handle effectively. Where conditions permit rapid oxidation and the heat so produced is not dissipated, the temperature may rise to a point at which actual burning takes place. The materials oxidized most readily are oily or greasy waste, hay, manure, carbonaceous shales, and sulfide ore. If oily waste is not confined, spontaneous combustion is probable. Punky or rotted wood is easily ignited, especially if finely divided. Occasionally, spontaneous fires are reported as having started from the oxidation of timber, but it is unlikely that solid or standing timber will ignite spontaneously unless some more readily oxidized substance is present. Sulfide ores, especially certain types, oxidize rapidly when they are in a fine state of subdivision and will burn if in close contact with burning timber. Caved material and old fills containing crushed or broken sulfides and timber present a 10 Look, Allen D., Underground Metal-Mine Fires From Cutting and Welding: Bureau of Mines Inf. Circ. 7453, 1948, 9 pp. serious fire hazard where oxygen is supplied by currents moving too slowly to dissipate the heat. Massive sulfide ore in place will rarely burn; sulfide ores, particularly copper and iron sulfides, may fire when in moving ground where they are crushed. Carbonaceous shales not only burn by spontaneous combustion but also ignite timber or other combustible material. They are most dangerous as a fire hazard when they contain pyrite or marcasite and are in moving ground. Spontaneous fires in sulfide ores or in shales rarely develop rapidly enough to cause loss of life, but their control may cost large sums of money and occasional loss of life. The exclusion, so far as possible, of sulfides from stope filling and the early removal of broken sulfide ore are advisable precautions. Adequate ventilation to dissipate heat and thereby prevent rise of temperatures in stopes having broken sulfide ore is another practical precaution. Where a fire has started but has not developed to any considerable extent, it may be practicable to load out the burning material; if not, sealing off or in a few instances slime filling of the fire area is the method used to check and limit the extension of the fire. A fire may develop in filled ground without apparent heat manifestations; such fires are very difficult to extinguish or to handle with a reasonable degree of effectiveness. Four to twenty percent of the metal- and nonmetallic-mine fires are attributed to spontaneous combustion, depending largely upon the type of ore mined. EXPLOSIVES AND BLASTING A number of instances are on record of explosives, fuse, and blasting starting fires in mines. Capped fuses spit and thrown into abandoned timbered areas have started fires. Blasting of cribs or posts in top-slicing or in cut-and-fill stopes has caused costly mine fires. Some posts caught fire from the fuse when they were blasted out in a mine using a caving system, and before the fire could be brought under control the whole mine had to be flooded. In another instance a jute sample bag was left where a spit fuse came in contact with it and started a fire. This mine now uses fire-resistant sacks for samples as well as explosives. Heavy blasting has been known to start fires and in a few instances dust explosions in high-sulfide ore when fine dust from the ore has been ignited by flame from explosives. HEATING APPLIANCES Heating appliances frequently cause mine fires in surface buildings and underground. Fires have started from small heating stoves or from heating units of all kinds, including electrical devices, used to warm oil or lunches, to dry clothing, or to heat underground stations or surface structures. Blacksmith forges, air reheaters, and steam pipes in contact with timber have started fires. A defective burner in a drying plant at a mine clogged and flared, setting fire to the plant building, which burned completely despite efforts to extinguish it. One metal mine had 3 fires in surface buildings in 5 months due to oil heaters not in proper working order. Electric heaters used underground cause fires when they are placed too close to wooden partitions or timbers. IGNITION OF FLAMMABLE DUSTS, GASES, VAPORS, AND LIQUIDS Accumulations of methane mixed with air in explosive proportions have been ignited in mines and tunnels in many sections of the United States. These ignitions have caused injury to workers but have not caused fires, except in tunneling operations where extinguishment was easy. This subject is discussed under Gases in Metal and Nonmetallic Mines. The ignition of iron-copper sulfide dust and gilsonite dust is discussed under Explosition Hazards in Metal and Nonmetallic Mines. The increasing use of diesel-powered engines in metal and nonmetallic mines presents a hazard from flammable liquids and vapors in handling fuel oil underground. There have been a number of ignitions. One of the most serious hazards at mines where electric power is not used is the ignition of vapors when gasoline is transferred from containers to the fuel tanks of gasoline-powered hoists, compressors, or power units. These fires occur most frequently at mines in outlying districts or small operations where gasoline engines find favor; vapors from the pouring of gasoline are drawn by air currents to an open flame, resulting in a fire that usually destroys the building and equipment. INCENDIARISM Actual records of incendiary fires are comparatively few, although some of the fires listed as originating from an unknown source are thought to have been due to this cause. A compilation made by the Bureau of Mines in 1923 listed 2 fires with deaths of 13 men as of incendiary origin, and in the period 1940-44, 1 metal-mine fire was listed as due to that cause. The Dolores mine fire was attributed possibly to sabotage, open lights, or smoking. MISCELLANEOUS Fires have been started from unusual sources. In one instance the sparks from a railroad locomotive set fire to the wooden headframe on the surface. Hot embers from the headframe fell into the shaft, and the timbering of the shaft was consumed by fire. In another instance spent carbide dumped into metal cans was emptied into the shaft pocket, and two or three cars of ore were dumped on top of it; ignition of the timber lining resulted. Lightning started one fire by striking the cables leading to the electric pump; the high voltage burned out the control in the underground pumproom and set fire to the wooden panel and supporting timbers. Nine percent of the fires listed in table 2 are ascribed to unknown causes. CONTROL AND EXTINGUISHMENT OF MINE FIRES FIRE-FIGHTING EQUIPMENT Every necessary precaution should be taken to prevent underground fires. Fire-fighting equipment and facilities should be provided both underground and on the surface. Crews should be trained to effectively combat all fires. Underground personnel are always endangered by surface-plant fires; their safety and to a lesser degree the preservation of property make fire prevention a most important function of every mine safety organization. Many fires have been extinguished in the incipient stage by direct attack with water, chemicals, or other smothering materials. Where possible, this method is most desirable. Failure to extinguish fires by direct method is generally due to late discovery; lack of water or other materials, equipment, or essential facilities; or improper procedure in the early stages, which permits the fire to get beyond control. Common methods of control are: 1. Direct attack with water, chemicals, or other materials. 2. Enclosing the fire area with tight seals or bulkheads. 3. Introducing inert gas, such as carbon dioxide, into the fire area. 4. Flooding the mine or affected area with water. 5. Flushing the affected area with silt or other solid material conveyed with water. WATERLINES AND WATER SUPPLY An adequate water supply and a well-laid-out distributing system are needed for the protection of mining plants against loss by fire. Fire hydrants should be placed at key places inside principal buildings, but, even more important, some should be available at such distances from buildings that a fire would not prevent their use. A standard fire stream is generally recognized as 250 gallons per minute (g. p. m.), with a 1%-inch nozzle and a pressure of 45 pounds per square inch at the nozzle; at least 2 such fire streams should be available for important structures in an emergency. The friction loss of water flowing in pipes is higher than is generally realized; with a flow of 500 g. p. m., sufficient for 2 fire streams, the friction loss per 1,000 feet in a 6-inch pipe is 15 pounds per square inch (p. s. i.), in a 4-inch pipe 100 pounds, and in a 211⁄2-inch pipe 1,020 pounds. To deliver 2 standard fire streams through 1,000-foot lengths of such pipes, the initial pressures would need to be approximately 60, 145, and 1,065 p. s. i. If water at an initial pressure of 45 p. s. i were taken through 1,000 feet of 6-inch pipe and discharged as 2 standard fire streams, the flow would be about 216 g. p. m. for each stream at a nozzle pressure of approximately 33.7 p. s. i.; if the pipe were 4 inches in diameter, the flow from each nozzle would be about 133 gallons and the discharge pressure 12.6 p. s. i.; if 21⁄2-inch pipe were used, the flow would be reduced to about 45 gallons at a nozzle pressure of approximately 1.5 p. s. i. These flow volumes and pressures are calculated from the Fire Stream Tables of the National Bureau of Fire Underwriters; no allowances are made for hose losses. Connecting fire mains to form a loop or circuit to eliminate dead ends is always recommended. The water supply should be ample to maintain hose streams which might be used for 40 or 50 minutes. Thus, two standard fire streams (500 g. p. m.) could discharge 25,000 gallons during the period that effective fire fighting would ordinarily be accomplished. Where pumping systems and mine drainage can be utilized, the time for which the hose streams can be supplied is extended. Where water supplies are limited and installations small, effective fire fighting can be done by judicious use of the waterlines available; but the handicaps are great, and the protection is limited. The cost of a satisfactory |