fire combating

Upload: sjain818574

Post on 07-Apr-2018

230 views

Category:

Documents


0 download

TRANSCRIPT

  • 8/3/2019 Fire Combating

    1/37

    Fire Combating/Fire Fighting

    While fighting fire, it is necessary tounderstand its characteristics, the wayit can develop and speed with which itcan spread, the effect of it on theventilation and conversely the effect of

    ventilation on it

  • 8/3/2019 Fire Combating

    2/37

    Effects of fire:

    Smoke generation

    -Obscure vision, choke persons &unpleasant, can cause smoke backing

    - Release of toxic gases

    Damage to roof support system &occurrence of roof falls due to excessiveheat

    Effect of heat generated on VentilationSystem

  • 8/3/2019 Fire Combating

    3/37

    Constriction (Throttle effect) Increase in volume by expansion of gases due to heat,

    release of product of combustion and release of vapoursdue to heating of mineral & rocks Opposes the ventilation in the vicinity of fire

    Buoyancy effect Reduction of density of the atmosphere on the downwind

    side due to increase temp.Effect depending upon dip direction Level- Smoke backing

    Dipping- extensive Smoke backing Rising- Reduced smoke backing

  • 8/3/2019 Fire Combating

    4/37

    Minimum Air velocity to avoid smoke backing or smoke

    roll back

    Entry Ht.,m Velocity, m/min

    Dip 0% 10% 20%

    1.2 60 72 90

    1.8 75 87 108

    2.4 84 100 126

    3.0 96 112 141

  • 8/3/2019 Fire Combating

    5/37

  • 8/3/2019 Fire Combating

    6/37

    Principles of dealing withunderground fires:

    A fire can be dealt with one of the following orcombination:

    1. Removal of combustibles: by loading out theblazing materials and/or isolating the heatedzone from the rest of the fuel feed

    2. Lowering down the temperature; Use of

    collants3. Cutting off oxygen supply: Direct method or

    indirect method

  • 8/3/2019 Fire Combating

    7/37

    Methodology adopted in fire combating dependson:

    1. Seat of fire : in roadway, roof, pillars or in goaf

    2. Magnitude of fire: Direct method of cutting offoxygen supply and loading out are notapplicable in case of large fires

    3. Approachability:4. Gassiness of the mine

    5. Ventilation situation:

    6. Availability of resources:

  • 8/3/2019 Fire Combating

    8/37

    Direct Method: to bring the fire under control by usingsuitable extinguishing agents or coolants

    Loading out: if fire is small and approachableSealing off the fire:

    a. if direct method and loading out is not effective

    b. fire is unapproachable

    c. fire is of a very large magnituded. if there exist likely danger to the personnel

    Combination:

    a. extinguishing agents along with loading out operation

    b. infusion of inert gases and introduction of coolantsimultaneously with sealing off operation

  • 8/3/2019 Fire Combating

    9/37

    Fire Combat Methods:

    The different methods of combatingunderground fires are:

    1. Loading out the fires.

    2. Cooling by water.

    3. Using extinguishers

    a. Liquid extinguishers.b. Foam type

    c. High expansion foam plug.

    d. Powder extinguishers.

    e. Halon type extinguishers.4. Infusion of inert gases.

    5. Sealing off the fires

  • 8/3/2019 Fire Combating

    10/37

    A. DIRECT METHODS:

    1. Loading out the fires:

    Removal of hot or combustible mass is one of thebest methods of liquidating the fire. But this methodcan be applied only where the seat of the fireaccessible and not much area is involved and also

    there is not much danger from emission of fire damp.Usually they are successful in shallow fires in roof,floor, pillars or barriers.

    During the loading out operation adequate ventilationfor the working personnel has to be maintained atsite even at the cost of spreading of fire. Hence quickaction is needed for success of the operation.

  • 8/3/2019 Fire Combating

    11/37

    The different action programs to be followed in successionare usually as follows:

    a. Lowering the temperature by water spraying.b. Digging out the hot mass while simultaneously

    cooling it.c. Filling up the void created from removal of solids,

    with incombustibles.d. Filing adequate roof supports to prevent collapse

    of the dug out pillars.

    The success of the above method depends much onthe prompt action in the early stage of the fire. In an

    advanced stage the danger from falls and explosionmakes the removal of burning mass difficult. If thespread of fire is faster than the removal rate of theburning mass, then the loading out method should beabandoned in favor of other methods.

  • 8/3/2019 Fire Combating

    12/37

    2. Cooling by water:

    Water is the cheapest and the most effective extinguishingagent often used as a good coolant, due to its high latentheat of evaporation.

    Water can be applied by injecting directly to the seat of fireas water jet through hoses from water mains or byspraying.The former has the advantage that it can penetrate throughthe cracks and may reach the deeper layer of the burningmass.

    Spraying on the other hand forms a water curtain andknocks down the flame easily with this method more stemcan be produced forming an insulating layer and bettercooling effect of the surrounding is achieved, thus requiresless amount of water.

    Sprinkler system also plays a very vital role in cooling bywater.

    Water mains.

  • 8/3/2019 Fire Combating

    13/37

    3. Extinguishing agents:

    Uses of extinguishers are quite effective

    in fighting out small open fire. Theseextinguishers are useful in incipient fireswhen the fire is in the initial stage.

    The usual method is to force theextinguishing agent directly into the seatof the fire. These spread over the burning

    material forming a layer or a filmseparating the air.

  • 8/3/2019 Fire Combating

    14/37

    a. Liquid extinguishers (water type): In this type, the cooling property of water may be

    improved by the addition of salt like NaHCO3, KHCO3,

    NaCl, Na2CO3, NH4Cl, Na2SiO3, Na2SO4, MgSO4, CaCl2,K2CO3, (NH4)2 HPO4 and NH4H2PO4 requiring lessamount if water. These salts may form an insulating layerand cutting off air feed to the seat of fire.

    In portable type liquid extinguishers the solution isejected by CO2 pressure. CO2 is generated by allowing

    the alkali to come in contact with H2SO4 tube, which ispunctured during operation. These extinguishers shouldbe used for fighting small fires in fabrics, coal heaps etc.the extinguisher jet is to be directed to the bottom of thefire and then reach upwards, as far as practicable, to gainadvantage of rising steam to out off air feed.

    They are however unsuitable for electrical fires, liquidfires, or far large scale fires.

  • 8/3/2019 Fire Combating

    15/37

    b. Foam type:

    Foam can float on the surface of any liquid and are ideal forextinguishing liquid fuel fires. Thick foam can isolate theburning object from surrounding air.

    6 NaHCO3 + Al2(SO4)3 = 3Na2SO4 + 2Al(OH)3 + 6CO2

    Foam can also be generated by aerating hydrolyzed proteinswith suitable surface acting agents.

    A well functioning foam extinguisher can eject the foam to adistance of 8m working at 5kg/cm2 pressure.

    They are not suitable for electrical fires, foam beingconductor of electricity.

  • 8/3/2019 Fire Combating

    16/37

    c. High expansion foam plugs:

    This method may be used to extinguish fairly

    large open fires like belt fires or roadwayfires.

    The volume of foam generated is often 1000times that of the solution sprayed (expansion

    ratio = air: water (solution) :: 1000 : 1). Itquickly fills in the entire roadways creating afoam plug and advances with the ventilationcurrent towards the seat of fire. On reaching

    the fire the water content of the foamevaporates and brings down the oxygenconcentration to such an extent so as tosuppress the combustion.

  • 8/3/2019 Fire Combating

    17/37

    Limitations:

    The use of high expansion foam is restrictedto the following situations:

    In a mine roadway with a rise steeper than 1in 10 or with dipping more than 1 in 5.

    In gallery height above 3m.

    In deep seated fires or in cases where the firegets blocked from massive roof falls.

    At places where electrical service wiringremains exposed.

  • 8/3/2019 Fire Combating

    18/37

    d. Powder extinguishers:

    Dry powder consists of small solid particles (= 40um) suspended in a gas, usuallydry nitrogen or CO2. This ensures flow as well as good stream form nozzles.Three types of dry chemicals are commonly used in dry chemicals system.

    The major constituents are sodium-bi-carbonate, potassium-bi-carbonate, andmono- ammonium-phosphate. All are effective extinguishing agent for fireson flammable liquid and combustible gases.

    Only multipurpose dry chemical is an effective agent for fires in ordinarycombustibles such as wood and paper. Being non-conductive, drychemicals may be used on fires involving live electrical equipment.

    Various additives are mixed with these base materials to improve their storage,flow, and water repellency characteristics.

    Usually a mass of powered sodium-bi-carbonate or potassium-bi-carbonate keptpreserved with a suitable additive to prevent lump formation. It is ejectedwith CO2 pressure on the seat of the fire.

    The powdered mass when applied over fire may form are inert cloud 8-10m longand 1m wide. Beside taking out heat and acting as a radiation shield thincloud acts as an inert barrier cutting off oxygen supply.

  • 8/3/2019 Fire Combating

    19/37

    e. Halon type extinguishers:They are suitable for fires in electrical installation and or liquid

    fires.

    Halons are a general name to halogenated compounds whichhave fire extinguishing properties.

    A halogenated compound is one which contains one or moreatoms of an element from the halogen series. eg. fluorine,chlorine, or bromine atom.

    The halons are chemical derivatives of methane (CH4) or

    ethane (CH3 - CH3) in which some or all hydrogen atomshave been replaced with fluorine, chlorine, or bromineatom.

    In contact with a flowing mass they vaporize and the heaviervapors of them (eg.CCl4 vapors is 5.5 times heavier thanair) drive away air from the burning surface.

    Their use, however is discouraged in underground firecombating, due to the possibility of formation of toxic gaseslike phosgene (COCl2) with TLV valve as low as 0.5 ppm.

  • 8/3/2019 Fire Combating

    20/37

    3. Infusion of inert gases:Application of inert gases in dealing with large-scale underground fireshave gained important in recent times. The inert gases commonly usedare CO2, N2 or a mixture of CO2 and N2.

    The inert gas works by cutting off oxygen feed to the fire area as wellas by taking away the heat.

    Even after sealing off an affected area, considerable leakage of aircontinues within as the fire keeps on consuming a portion of oxygen ofair in the dead space of the sealed zone, causing contraction and

    thereby creating section for leakages.

    Continued infusion of inert gases within is expected to nullify the abovetendencies of air movement to the fire.

    CO2 is better in quick replenishment of air, being 1.5 times heavierthen air. It starts filling up from floor upwards. But since it is heavier, it

    can also escape very quickly through cracks in the floor once filled up;it is difficult to flush out CO2 from roadways etc. when needed. It has tobe taken out by diluting with air.

    Besides the above stated oxygen replacement qualities of inert gasinfusion, the method is also advantageous in facilitating cooling.

  • 8/3/2019 Fire Combating

    21/37

    B. INDIRECT METHODSealing off the fires:

    Application:

    - Fires originating from spontaneous heating and/or large scaleunderground fires when other direct methods of firefightingproved unsuccessful or are considered not possible

    - If the fire is inaccessible, eg. if it is extensive or if there isdanger of fire damp explosion when dealing with it, it has to besealed off.

    It is a sure method of cutting off oxygen feed to the fire, thoughit requires a long time for extinguishing the fire.

    The aim is to prevent access of air to the fire and starve it ofoxygen. The sealing operations have to be conducted fromplaces which will not be affected by the effects of fire like heat,smoke, CO, CO2 etc.

    Time factor play an important role in sealing. Delay will causethe fire to spread over a large area and the extensive fire may goout of control resulting in abandonment of the mines.

  • 8/3/2019 Fire Combating

    22/37

    The main problems posed in sealing offfires are the leakages of air within and the

    threat from explosion. The different phases of sealing off

    operation are carried out keeping theabove problem in view. These operational

    phases for underground sealing are:i) Site selection for erecting stoppings.

    ii) Sequence of seal making.

    iii) Modus operandi of building up thestopping.

  • 8/3/2019 Fire Combating

    23/37

    i) Site Selection: The site for making the stopping should be on strong

    rock devoid of any cracks so that air leakages areminimized.

    The stoppings should be as near the fire area aspossible to minimize void volume. In case of gassymine, distance of stopping from fire depends upon theamount of gas emitted, gas emission points in between

    the fire and stopping site and on the magnitude of fire the need to build up the stoppings quickly requiring

    transport facility for material moved. Hence stoppingssite near haulage roads are preferred.

    Distance between stopping and nearest airway should

    be 10-15 m Fresh air supply to be maintained on the out bye side of

    stopping

  • 8/3/2019 Fire Combating

    24/37

    ii) Sequence of seal making: Where no risk from explosion is apparent, the stopping is first

    built on the intake side followed by building them in air split pointsand lastly the return ends are plugged.

    But in case of gassy mines plugging the intake stoppings mayhelp in building up methane concentration. Closing the return endsfirst is also not advisable, as the accumulation of combustion gasesmay be facilitated thereby. Hence ventilation has to be maintainedall through the period of building the stoppings by keeping a pipewith 300mm to 400mm diameter in the intake and return end. They

    are to be plugged simultaneously in a quick operation by eitherclosing them with sand bags or by maintaining provisions of doors.

    The underground team is withdrawn immediately after pluggingthe tunnel. There may be explosion from one hour to 24 hrs. aftersealing. American experience suggest it to occur four to six hoursafter plugging when this period has elapsed, an assessment of thecondition of stoppings are made. Necessary repair work, brickwalling even building up additional stopping may then be made asconsidered necessary.

  • 8/3/2019 Fire Combating

    25/37

    iii) Modus operandi in buildings up stoppings:

    Quickness of operation and at the same time

    leak proof ness are the two criteria that are tobe satisfied in making the stopping.

    For gassy mines it has to be explosion proof.

    It is therefore a normal practice to make two

    sets of stopping in degree I gassy mine

    - Temporary stoppings

    - Permanent stoppings.

  • 8/3/2019 Fire Combating

    26/37

    - Temporary stopping:

    These types of stoppings are quickly

    made to restrict air flow to the fire whilemaking preparation for building thepermanent stoppings.

    These stoppings could be merely ofPVC sheeting or plaster of paris mixedwith water or gypsum or simply glassfiber blocks piled one above the otheror a parachute stopping.

  • 8/3/2019 Fire Combating

    27/37

    - Permanent stopping:- Usually they are brick stopping built with cement and mortar. The thickness of

    the brick wall depends on the pressure exerted by the roof and cross section ofthe roadways.

    The stopping can be made explosion proof if needed ( higher degree ofgassines seams).

    Normally edges of the stoppings are the source of air leakage. Hence to makethem leak proof, it is a common practice to cut into roof, floor and sides. (coal1 m, Sandstone 0.15 m and Shale 0.30 m)

    Brick walls are made over them and the lining on the edges are plastered withsand and cement and with other leak proof agent, extending up to a length ofaround 1m in the roof, floor and walls. The stoppings are then checked for any

    development of cracks. Sometimes two brick walls are built at a distance of more than 4.5 m and the

    space between them is filled with sand. Such stopping are more leak-proof andstronger. These are explosion proof stoppings to be employed in Degree IIgassiness mines

    If the stopping has to withstand high pressure, a brick wall is builtconvex towards the fire side.

    For draining out water flow behind the seal, a pipe with a valve is incorporatedat the bottom of the brick walls.

    In order to collect gas samples, one or two metal pipes with taps fitted in themare kept in the seal. Pipe connections are also kept in the stopping formeasuring temperature changes and pressure fluctuation.

  • 8/3/2019 Fire Combating

    28/37

    Fittings on Stoppings:1. Water gauge

    2. Thermometer3. Sampling Pipe, 18 mm dia with a valve for

    collecting air samples behind the stopping. Itshould pass through temporary stopping if any

    and extend atleast 3 m behind it.4. 50 mm dia pipe with plug for recording

    temperature5. Water seal at the floor level for drainage

    6. Number plate7. Signature board8. Ladder if height is more than 2.0 m

  • 8/3/2019 Fire Combating

    29/37

  • 8/3/2019 Fire Combating

    30/37

  • 8/3/2019 Fire Combating

    31/37

  • 8/3/2019 Fire Combating

    32/37

  • 8/3/2019 Fire Combating

    33/37

    Iv) Inspection and control of fire

    - Maintenance of stoppings by regularinspection

    - Systematic mointoring of the fire by gas,thermal or pressure survey

    - Taking rcourse to additional measuressuch as infusion of inert gasses, floodingetc. for liquidating the fire

  • 8/3/2019 Fire Combating

    34/37

  • 8/3/2019 Fire Combating

    35/37

  • 8/3/2019 Fire Combating

    36/37

    FLOODING THE FIRE AREA OR THEENTIRE MINE Flooding a fire area is the last resort after direct

    attack and sealing have failed. A mine is floodedwhen fire (after powerful explosion) have assumedsuch proportion that all other methods of fire fightingcannot be employed due to explosion hazard and theentire mines is to be saved from destruction.

    To flood a fire area effectively, sufficient quantity ofwater must first be available and fire area must besuitably located.

    Flooding has following disadvantages: Heavy damage to the mines and equipment. Difficulty of obtaining the required amount of water in a

    short period of time.

    Possibility of generating water gas by an insufficientamount of water.

    Heavy expenditure on dewatering.

    Danger of 'water blast' during dewatering.

  • 8/3/2019 Fire Combating

    37/37

    HYDRAULIC FLUSHING

    The method can be recommended where thestrata are so broken that neither sealing nor flooding

    will be effective. Generally, the fire is sealed off withstoppings in the usual manner and then the sealedarea is flushed within a day. Water, sand-water,sand-crushed, rock-water, or sand-clay water-mixture through pipes left is the stopping.Experience had shown that the slid fill the voidscompletely and reduces where as in certain places,eliminate fire gases, cool the adjacent rocks andoffers support to the ground.

    During flushing care should be taken so that theslurry is not directed straight on to the fire seal butat a point rear if in order that water gas explosionfrom dissociation of water does not take place.