Firedamp Methane

The gas which occurs naturally in the coal seams is virtnally always methane it is a highly flammable, gas and forms explosive mixtures with air (5%-14% v/v methane). The explosion can then cause the combustion of the ensuing coal dust (Torrent et al., 1991) thereby increasing the extent of the hazard. 

Methane had frequently been termed (in Great Britain) marsh gas or firedamp, although the latter term should (more correctly) be confined to the flammable mixture(s) of methane and air. 

In order to render the gas harmless, it is necessary to circulate large volumes of air to maintain the proportion of methane below the critical levels. In this context, it should be noted that the permissible maximum content of methane may vary from country to country but is usually of the order of l%-2% v/v. 

Methane is produced from the coal seam either gradually or as an outburst the latter is, as the name implies, a sudden, violent discharge of short duration, usually accompanied by the displacement of large quantities of broken strata and dust. Fortunately, such outbursts are rare but firedamp (however formed) is a major hazard and, despite improvements in detection and ventilation techniques, dangerous accumulations still occur. 

To reduce the danger from flammable gas underground, long boreholes may be drilled in the strata ahead of the working face and the methane drawn out of the workings and piped to the surface, a technique known as methane drainage that is common in Europe. The extracted gas is frequently utilized on the surface and pure methane has a calorific value of 1012 Btu/ft. 

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When we consider sources of methane we have to add old methane methane that was formed millions of years ago but became trapped beneath the earth s surface to the new methane just de scribed Firedamp an explosion hazard to miners oc curs in layers of coal and is mostly methane Petroleum deposits formed by microbial decomposi tion of plant material under anaerobic conditions are always accompanied by pockets of natural gas which IS mostly methane... 

Permissible or Permitted Explosives. In many coal mines there is a continual evolution of methane (firedamp) into the air of the workings. 

Gas, Coat Mine or Firedamp. A mixture of methane (CH4) and air, usually present in "gaseous (fiery) coal mines", such as soft (bituminous) coal mines... 

Early in the present century attention was drawn to the danger created in mines by coal-dust. Until 1906 it was believed in France that this hazard could be entirely explained by the presence of firedamp, but even in the early nineteenth century it was supposed that a suspension of coal-dust in the air may also explode. Thus, as early as 1803, it was suggested in the U.S.A. that coal-dust might be involved in mine explosions [17]. In 1844, Faraday drew attention to this (according to J. Taylor and Gay [4]), and later Galloway [18] discussed the coal-dust danger. By the end of the last century the possibility of explosion was proved experimentally, but it was believed that an explosion of methane-air mixture is necessary to initiate a coal-... 

P.A. Paramonov, Ibid 1967 (63/20), 213-17 CA 69, 4083b (1968) [Safety props of coarsely dispersed AN expis contg TNT NaCl were studied with.identical compn, but at different degrees of dispersion. They were tested in a methane-air medium (9.5% methane) by expln of freely suspended ehges of different wts. The relative increase of the coarser particles of the active component in the Ammonite mixt lead to increased resistance to firedamp. An increase in the NaCI content of the coarsely dispersed expl also increased resistance to firedamp]... 

Coal Mines, Determination of Firedamp and of Coal Dust In Atmospheres of. Although many instruments have been designed to detect the presence of firedamp (or rather methane) in mine atmospheres, the principles of the flame safety lamp (Davy-type lamp) still form the basis of many detectors. The Davy lamp invented in 1815 is briefly described under COAL MINE EXPLOSIONS AND FIRES and it is stated that each US mine should have at least two Davy-type lamps to serve as detectors of firedamp or of lack of oxygen. If firedamp is present in small quantity, the flame of Davy lamp elongates and if the gas is present in considerable quantity, the lamp becomes filled with blue flame. For more definite detection of gas, the flame of the lamp is lowered until the yel part is at a minimum. Then the gas will be discernible as a small blue cap over the flame. This method is described in Refs 1, 9, 12 25. Some investigators consider that the safety lamp method of detection of firedamp is not very reliable (Ref 7)... 

Coal Mines, Determination of Firedamp and of Coal Dust in Atmospheres of. Although many instruments have been designed to detect the presence of firedamp (or rather methane) in mine atmospheres, the principles of the flame safety lamp (Davy-type lamp) still form the basis of many detectors. The Davy lamp invented in 1815 is briefly described under... 

New app for analysis of firedamp) 16) Machinenfabirik Wagener Co, GerP 824567 (1951) CA48, 10390(1954) (A firedamp recorder consisting of a methane-sensitive catalyst with a reading device incorporated into a wrist watch) 17)K.Drekopf, Brennstoff-Chemie 33, 146-51... 

Amongst the earliest experiments carried out with a view to the quantitative determination of the limits of inflammability of combustible gases were those of Davy with fire damp, wfliich is mainly methane, CH4. Owing to the importance of this gas m connection with gob fires and explosions in coal mines, several other workers have also investigated it. The value of the results, however, is restricted by the fact that firedamp, like most natural products, is subject to very considerable variation in composition.3 Even Davy recognised that it was not pure methane indeed, perfectly pure methane is not easy to prepare in quantity. The gas, as obtained from sodium acetate, may contain as much as 8 per cent, of hydrogen, as well as ethylene.4 No doubt this variation m composition is one contributory cause of the very varied results listed in the table on p. 93. 

The value for methane agrees quite well with that obtained both by Coquillon and Le Chatelier 1 for firedamp there are at least five factors concerned in the magnitude of the lower-limit mixture. These are ... 

The methane was impure, it is true, but the result closely agrees with that found by Davy with firedamp. A more thorough investigation of... 

Early on the subsurface coal mining industry learned that swamp gas or firedamp was prevalent in underground coal mines. The gas is largely methane formed from the decay and rotting of carbonaceous materials to ultimately form coal. When pressure is released (as by drilling into the coal seam) the methane-rich gas migrates to the low pressure and is produced. The composition and properties of several coal bed methane streams are shown in Fig. 20.2.15... 

Firedamp is an explosive mixture of marsh gas (methane, CH4) with air. These mixtures are explosive at normal temperatures and pressures, and the explosion is propagated over large distances if the mixture contains 5-14% methane. A methane-air mixture containing 8.5-9.5% methane is prescribed for official tests of permissibles. The danger of explosion is greatest in this concentration range. 

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