Page 1 :
FIRE DAMP EXPLOSION, The presence of sufficient amount of fire damp mixed with the air with sufficient heat and, source of ignition when get ignited results in explosion is called fire damp explosion., , Vv, , Fire damp explosion occurs more frequent than coal dust explosion in mines., , Methane burns in air when ignited with a pale blue flame but when it is mixed with, air it can explode on ignition., , The combustion and explosion take place according to the equation, , > CHa + 2(02 + 4N2) = CO2 + H2O+8N2, , Vv, , v, , > Presence of fire damp in air between 5.4 & 14.8% is explosive mixture. If a suitable, source of ignition is available with this mixture results in a explosion. The maximum, , , , , , , , MINE ENVIRONMENTAL ENGINEERING - SUMEET KISHORE, explosive violence is produced when the explosive mixture contain about 9% of fire, damp., , CAUSES OF FIRE DAMP:, , The various causes of fire damp explosion in mine may be grouped under the following, , headings., , 1, Shot-firing : Shots not properly placed causing on over charged and below out shots, with detonator wrongly placed in cartridge shots fixed without examination for fire, damp. Shots fixed where breaks exists in the hole or where in sufficient steaming has, been used or by using defective cable or exploder., , i), , . Naked light : Matches or other contrabands introduced in mine illegibly., , 3. Defective or damage safety lamp Defective or damage safety lamp : Glass broken, part assembled or lamp tempered with exposing the flame damage lamp., , 4. Electrical appliances and spark ; Electrical sparks flash is or areas arresting from, improperly in closed motors switch gear brushing of power cable owing to weak in, solution, returning of cables by falls of roof rubbing contacts bore signally wanes, unless it is made initially safe., , , , , , , 5. Friction : An intensive frictional spark at a high temperature for comparatively long, period is cable of causing an explosion such sparks high be produced by falling rock, masses on iron physites., , , , 6. Fires : Accidental fire or spontaneous combustion of coal may easily bring about, ignition of flammable fire damp air mixture in contact with them., , , , , , , 7. Foolishness of Miners :Smoking, making fire, or opening of safety lamps on the part, of miners had in the past resulted in ignition of firedamp. Explosions from such, causes reflect discredit on all concerned., , IGNITION POINT OR IGNITION TEMPERATURE, , > Itis the minimum temperature at which the methane air mixture burns in air to give, a flame., , » The ignition point of flammable firedamp-air mixture is given as 650° to 750° C., > It is not a definite temperature but depends upon the nature of source of ignition, whether flame, spark, etc., shape and size of space where ignition occurs, methane, , content, temperature of surroundings, pressure, oxygen concentration, presence of, other gases, and turbulence. The ignition point of methane in oxygen is 556° C., , , , , , , , , , , , Scanned with CamScanner

Page 2 :
Modes of emission 0, , Firedamp or meth, , f firedamp, ane entrenched in coal seam and the adjace, nt, , strata is given off in 3 ways +, , 1., , Slow emission from pores and invisible cracks in the —, or adjacent strata through their exposed surfaces. This js 4, continuous and prolonged emission., , In the form of blowers from visible cracks and Openings, in the coal or rock. These are generally short lived, bur, sometimes continue for years. Blowers are common js, Indian mines. A blower in Moonidih (1971) lasted for 2, years and gave off about 4 million m? of gas., , Sudden outbursts of firedamp, generally accompanied by, ejection of large quantities of coal or rock. Outbursts are, not common in Indian mines. There has been orty one, , case so far., Methane accumulated in the goaf area may erupt into the, workings when there is sudden fall of barometric pressure, , or major roof fall in the goaf., , Scanned with CamScanner

Page 3 :
ouee-, _ The ‘DGMS has classified all coal seams (mine-wise) into, , 3 degrees of gassiness, on the basis of gas concentration in, the general body of air in u.g. workings within the mine, boundary and the rate of emission of gas per tonne of coal, produced as follows :, , Degree % of inflammable gas in Emission of gas per t of, , general body of air coal produced, I less than 0.1 less than 1 m?, Il more than 0.1 1 to 10 m?, Il over 10 m?, , Scanned with CamScanner

Page 4 :
Layering of methane, , Formation of fairly stable layers of methane at roof level, due to, low specific gravity (only 0.553), is known as methane layering,, a The layer may be only a few centimetre thick, and in soma, cases even only lcm; thus a few cm from the roof, gas, content may be nil but at the roof level it may be even 40., 50%—in between there may be a portion within the range, , of inflammability., , = The layer is only a few metres in length., , = Ithasatendency to move along the roof towards the rise. It may, travel considerable distance from the place of its formation,, , = The gas may be emanating from cracks/crevices in the roof., Methane layers have been detected in many development, districts and even in some drifts in Indian mines., Dangers of layering, , 1. Layers are difficult to detect, and may remain undetected., , 2. A layer may lead to accumulation of gas in unexpected places., , 3. In the event of an iginition, the explosion can be transmitted to, a considerable distance, involving a number of gas, accumulations., , 4. In many cases, persons have been asphyxiated by putting, their head into the roof cavity (which is deficient in 0),, and fallen from a height resulting to fatal injuries., , 3: A roof fall may push accumulated gas to the floor level. If, it simultaneously damages a cable, passing below the, , cavity, explosion can occur. Such explosions have, occurred in Indian mines., , Removal of gas layer, , 1. A gas layer may be removed by erecting one or more, , Scanned with CamScanner

Page 5 :
FIREDAMP EXPLOSIONS 221, , hurdles at the floor level acro, , ‘ 88 the roadway to increa, velocity of air at roof level, : ., , If a jet of Compressed air may be, directed into the gas layer to produce movement and remove, the gas., , , , Floor, , Scanned with CamScanner