FIRE HAZARDS IN MINES
1. INTRODUCTION
Coal Fire is a catastrophe in true sense, endangering life, property and the resource itself. It gives rise to death, decay and destruction . The impact of coal fire comes in to picture with toxic gases, subsidence, particulate matters , destruction of floral and faunal habitats and many more, including the loss of invaluable non renewable resources. In short coal fire is affecting, air, water soil, and the entire eco system and therefore should be controlled at the earliest .
Surface and sub-surface coal fires are a wide spread problem of international magnitude. The history of coal fire in jharia coal fields can be traced back to 1916 whe the first fire was detected. Presently more than 70 mine fires are reported from this region Surface and Sub. surface fire burning through ought Jharia coal fields comprises one of the largest coal mine fires complexes in the world.
1.1 Problems faced with fire
To Check the spread of existing fire which know no control
· To Prevent new occurrence of fire and to deal effectively with those that do occur
2. 0 Proneness to Heating
The proneness to heating depends upon :
Nature of coal, including friability, moisture, iron pyrites chemical composition
etc.
Nature of adjoining strata including its thermal conductivity
Thick ness of Seams
Death of working
Geological disturbances.
Generally speaking, coal having crossing point between 120o – 140 o C, 140o – 160
o C , 160o – 190 o C, or more are respectively highly, moderately and poorly susceptible to
spontaneous heating.
3.0 Preventive Measures against Spontaneous Combustion.
Work thee seam in panel system or sectionalise the workings.,
Form large pillars and have good roof control
Aim at complete and fast extraction within incubation period.
Do not leave coal/carbonaceous shale stacked below ground or use the same in
packing.
Remove fallen coal or keep such areas sealed off by sectionalisation .
Extract highly susceptible or thick seams with stowing .
Avoid extraction of shallow coal seams by caving methods.
Blanket the subsidence cracks at surface effectively and reclaim the surface area.
Apply special sealant or sodium silicate or gunite the sides of pillars and roadways .
Keep intake and return airways for apart.
Circulate large quantities at air of low w.g.
Avoid bottle neck in air ways.
Always place doors, air crossings, stopping, booster fans etc. in strong unbroken
ground.
4.0 Causes of Mine Fires :
The causes of mine fires can be broadly classified into the following. :-
4.1 Spontaneous heating :
a) Spontaneous heating underground.
b) Spontaneous heating on surface.
c) Spontaneous heating in quarry overburden.
d) Premature collapse/crushing followed by Spontaneous heating.
4.2 Accidental fires :
a) Negligent acts i.e. dumping of hot ashes etc.
b) Bantulsi Conflagration
c) Illicit distillation, gas cutting etc.
d) Fire crossing from neighboring mines /areas.
e) Break down of insulation of electric cables.
f) Frictional fires.
g) Brattice cloth catching fire due to shot firing.
h) Explosion
i) underground. Locomotives.,
5.0 Detection of Spontaneous heating :
5.1 Sensory Indications .
There are four stages of sponteous heatings as below: Initial Stages :
a) Faint haze Produced by moisture driven off from coal coming in contact with cool air.
b) Sweating of roof , sides, timber and metal supports.
c) Typical faint odor called gob stink.
d) Increased activities and chirping of cockroaches, if present.
e) Slight discomfort and uneasiness to men near to site of heating due to increased temperature and humidity.
Intermediate Stages : It is also called Smoldering Stage and Temperature
Varies from 130 0 to 330 0 C. The Symptoms of incipient stage intensified with differences of :
a) Petrol like smell of distillation of coal.
b) Headache, increased restlessness and dulling of senses.
Heating Approaching Ignition ( Temp.> 330 0 C)
a) Gob stink i.e. tarry odor of burnt tar.
b) Smoke, incandesce or even flame may be visible.
Cooling Stage :
a) Characteristic Sour and unpleasant smell like that of stale garlic .
5.2 Chemical Indications :
CO Produce/ O2 Consumed ratio should be determined by analysis of return air.,
5.3 Hygrometric Readings :
Spontaneous heating is accompanied by progressive rise in temperature and
humidity.
5.4 Temperature Readings :
a) In solid pillars
b) In roadside packs.,
c) In coal heaps
d) Thermistors left buried in goaf and temperature readings taken,
5.5 Use of CO/multigas Detectors :
5.6 Fire Alarms/ Telemonitring Systems :
6.0 Early Detection of Spontaneous Heatings.
For early detection of spontaneous heating :
a) All underground working should be regularly & Systematically inspected by a
team of experienced people .
b) Goaf edges in Caving system should be inspected frequently,.
c) Idle day inspections.
d) Regularly and weekly monitoring of CO/O2 ratio in return airways.
e) Hygrometric reading from return air way and temperature readings from goaf as a routine.
f) Safety Consciousness among mine workers.
7.0 Combating Fires :
7.1 Fire fighting Organizations :
a) Provision of fire extinguishers, and water etc.
b) Fire Stations
c) Plans
d) Standing orders
e) Means of communication
f) Training of persons and mock re-hearsals.
8.0 Fire Control Methods :
8.1 Direct Attack :
Direct application of some extinguishing agent, on the fire can be easily applied if it is not deep seated. The dangers of fire fighting with water are the following :
a) Flames may be thrown back to the operator.
b) Adverse effect on roof of steam and heat.
c) Chances of water gas formation
d) Dangers of co-poisoning .
8.2 Digging and loading out.:
Applicable when seat of fire is easily accessible , the fire is not extensive, is in the initial stages only, no danger of fire damp explosion and roof is good. The associated dangers include out break of fire, CO poisoning .heat stroke
etc.
8.3 Trenching :
A Trench barrier is intended to confine and isolate the fire from the main body of coal, by breaking the continuity of all coal and carbonaceous shale etc.
8.4 Surface Sealing :
By Closing surface cracks and openings leading to the fires. Applicable for fire only at shallow depth of cover. For effectiveness sand blanketing should be toped with 0.5 to 1.5 m thick layer of clay, over which water patches, terraces should be maintained.
8.5 Under ground Sealing :
The chief method of controlling a fire in an under ground mine where fire has occurred due to spontaneous heating and in a goaf or old working containing huge quantities of fallen coal.
8.6 Under Ground Incombustible Barrier :
· Packing or hydraulic stowing of galleries around fire areas, with in combustible material.
· Flushing of the voids with sand etc.
· Water Infusion of the coal barrier to prevent advance transference of fire.
8.7 Flooding with water :
The success of the method defend upon inclination of coal seam, location and thickness of under ground coal barrier with respect to adjacent mine workings, presence of large fissures, and fault planes, availability of enough water, level of fire area in relation to drainage level etc.
8.8 Inert Gas Filling. :
Of late, inert gas methods of dealing with fire has gained importance. However
this method will not be able to match direct fire fighting methods in effectiveness and
economy .
In an unconfined fire, the needed gas quantities to lower the oxygen
concentration of atmosphere efficiently ( i.e. below 2% ) in next to impossible.
The inert gas injection rate should be higher than flow of hot gases from
the fire area.
The limited availability of L N in large quantities is in another drawback .
The method is costly and should be consider only when other methods are
not possible .
However it offers prevention explosive of atmosphere at any stage of fire
fighting operation.
8.9 Foam Plug Method :
The sealing of roadways from remote location by injection of expanding foams adds to range of methods available for combating mine fires and it a very flexible tool, that protects the personnel involved. The method has been successfully tried at many places including New kenda fire. Mariflex, Phenol, and formaldehyde foam was used in new kenda mine fire to isolate the fire area from rest of the mine from the surface through boreholes. The plug which was built from surface boreholes was found very effective when the sealed off area was opened and inspected .
9.0 Fittings on Fire Stoppings :
· Number plate.
· Signature plate at top.
· Thermometer with Colored Mercury
· Platform and ladder, if the stopping is high.
· Sampling pipe , 2” ddia.
· Water Seal.
· Tar trap (a drum containing sand and hard coke to absorb any smell).
· Water gauge, manometer or barrow meter.
10.0 Precautions During Sealing off :
· Maintain normal Ventilation through fire area.
· The vicinity to be heavily stone dusted.
· Suitable site selection.
a) Strong solid ground.
b) Well back from thee site of fire if slightest danger of explosion.
c) Convenient for transport of building materials.
d) Provision for further re-enforcement etc.
e) Possibility of ventilation of out bye side.
· Final Sealing off return and intake stopping simultaneously .
· Build stopping rapidly.
· Re-inforce stoppings
· Regular testing of atmosphere near stoppings
· Leave air sampling pipes.
· Provide water seal, where necessary. .
· Withdraw men, immediately after completion of both the stoppings.
· Examine both the stoppings after 24 hours, if not damaged take air samples.
· Arrange for further strengthening, plastering if necessary.
· Arrangement for speedy analysis of gas samples for CO %.
· On completion of final sealing pressure equalization at the out by faces of the stoppings
should be arranged as soon as possible.
· Organization to meet emergencies as occasioned by fire under ground should be mapped
out before hand.
11.0 Re-opening A Sealed off Area :
· Plan for the smallest possible details.
· Men and material should be well organized.
· Duties of officials to be specific and laid down in writing
· Rescue team to be summoned to deal with emergency even if not required.
· Adequate material like brattice cloth, stone dust, wooden props, ventilation appliances,
fire extinguishers should be made available.
· Only those person allowed whose presence is necessary during operation.
· Keep strict watch on movement of every person entering the mine.
· Roadways a few hundred meters out by of fire stoppings should be thickly stone dusted.
· Return air ways must be fenced off and all electrical equipment installed there in should
be isolated.
· No smoking around upcast shaft.
Routine Inspection of fire Stoppings :
· Visual general inspection
· Check plastering for cracks etc.
· Check behavior of sampling pipe ( drawing - in or out)
· Check water seal and replenish water .
· Check manometer thermometer reading.
· Check for CO, CO2 and CH4
Environmental Impact of Coal Fires. :
· Emission of noxious Gases like CO, NOx. SOx, and particulate matter.
· Emission of Greenhouses Gases such CO2 and CH4, further aggravating the global
warming problem.
· Loss of non-renewable valuable resources .
· Loss of flora and fauna.
· Subsidence causing damages to property, life, local drainage pattern, etc.
· Air pollution.
· Land degradation
· Temperature increment in surrounding areas.
· Increased production cost.
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