Carbon dioxide

                                                             CO2 is an excellent smothering agents for extinguishing fires.Its about 1.5 times heavier than air. It can easily be liquefied and bottled normally under pressure of approximately 150to 200 bars. 






                                                                When used on fire the liquid CO2 gas taking away some heat.The gas extinguishers the fire by smothering it is a quick clean and non - conductor of electricity. It is comparatively non-toxic& does not harm most of the materials. It does not leave any residue. It can be stored for long period and it is easily available .CO2 is very effective in enclosed areas.It cannot penetrate in to any places that cannot be reduced by other means.It does not damage delicate machinery & instruments. It can be used safely on electrical equipments & panels.CO2 is highly ashipciating and cannot be detected by smell or colour. About 9% concentration causes unconsciousness .Any compartment which has been flooded with CO2 must be fully ventilated before entering without wearing  breathing apparatus.




                                                                 When liquid Co2 is released from a pressurised storage cylinder there is an extremely rapid expansion from to gas   which produce a refrigerating effect that convert part of CO2 in to snow. This snow which has a temperature of -79 degree Celsius,soon sublimes( changes directly from solid to gas ). This sublimation produce some cooling effect but it is the smothering effect of the gas ,which is of primary importance in the extinguishing process. At normal temperature & pressure the expansion ratio of CO2 is 1:450.

Beating Out

Small fires in materiel such as textile etc.may be extinguishing by beating them out .Beating is also the method normally employed to extinguish crop and other similar fires in rural areas when water is readily not available.

Blanketing

                                                   Another method by which fire may be extinguished,especially for persons whose clothing is on fire,is by blanketing.The person should be lay down & covered or rolled in rug,coat, jacket,woolen blanket etc.Oil fires in puns and small utensils can be smothered with an asbestos blanket or similar materiel .





                                                     Fire blankets are available in two specification such as light duty & Heavy duty.Light duty fire blankets are used for extinguishing small fires.Containers of cooking oils or fires in clothing worn in people.Heavy duty fire blankets are used for industrial applications to resist penetration by molten metal while cutting or welding and to protect against radiant heat ,it can be also be used for light duty application.

Vapurising Liquids

                                The halogenated hydrocarbon used for extinguishing fires have the property of vaporizing readily when heated and are , there fore generally known as vaporizing liquids.They form a dense heavier than air ,cloud of non flammable vapor which use only blanket fire but also interferes with the chemical reaction of flame propagation in the burning materials .Vaporizing liquids are non conductors of electricity & does not damage electronic equipments.Their Great draw back is their toxicity.Some well known extinguishing media such as CTC & Methyl Bromide have been withdrawn from use due to their toxicity. Freon type vaporizing liquids are presently used as they are less toxic.The most common substance used are Bromochloro Difluro methane (BCF)Bromotri Fluro methane(BTM).



                                   Halogenated extinguishing agents are hydrocarbon in which are more halogen atoms have been replaced by atoms from the halogen series.The replacement confirms non -flammability & Flame extinguishing property to many of the resulting compounds.The use of halogenated hydro carbons as fireTextinguishing media is not permitted in accommodation and living spaces.Halon produce some adverse effect on the atmosphere.It cause depletion of the ozone layer.It is partially responsible for the noticeable warning of the earths atmosphere .Now a days Halon is almost replaced by FM 200(HEPTA FLURO PROPANE).

Extinguishing Media (SAND)

Some burning materials such as metals  ,which cannot be extinguished by the use of water,may be dealt with by means of dry earth , dry sand ,powdered graphite, powdered talc , soda ash or lime stone all of which act as a smothering agent.Dry sand may also be used  to prevent burning liquids. Such as paints & oils , from flowing down drains ,basements etc. 


*Sand should never be used for extinguishing fires in machinery  such as electronic motors.

Extinguishing media (FORM)

Liquids having a specific gravity lower than that of water are much difficult for extinguishing with the use of water. When water is put to the burning surface of a liquid, it lower the temperature momentarily and then sinks below the surface of the liquid. Form is relatively insoluble in most liquids and because of its light weight , floats on the surface of the liquids. It forms a blankets capable of covering the surface of the burning liquid & so extinguish  the fire .It also forms a radiant heat barrier , which is of importance in extinguishing oil and petrol fires.

Extinguishing media (water)

                                       Water is the cheapest and most readily available medium  for extinguishing fires of a general nature. If more water is used than what is actually required to contain and extinguish fire, the surplus will drain off or will sweep through floors & may cause more damage to goods and property than that caused by fire itself. 
*The method of using water to extinguishing a fire various according to the size of the fire.
* If  only a small quantity of water is required , portable extinguishers expelling water may be used.
* If the fire is beyond the control of hard appliances ,hose reals may be used. 
*For major fires when grater quantities of water are necessary ,high capacity pumbs may be employed.
*A variation in the application of the water used can be made by means of nozzles that produce jets or sprays. 

Steam





                                  Steam in large quantities can be used to smother in fire .In situations where it is readily available .It can be used in fixed installation. Ships & industries having individual compartment are adapting steam to fill the compartment under pressure.

Classification of Fire

Fires are classified according to the type of fuel, which are burning .Fire can be classified  in to four  they are : Solid Fire Liquid Fire and liquifiable solid fire Gaseous Fire Metal Fire.


 Fire Type                                              Fire involving            fire fighting

Class A Fire                                                Solid materials                     Cooling

Class B Fire                                                Liquids or liqufieble solids.
                                                                (Grease,wax)              Smothering


Class C Fire                                                Gas                             Starvation ,Inhibition

Class D Fire                                                Metals                         Inhibiting    

Inhibiting

                                       Checking or stopping the exothermic reaction of substances which contains oxygen within them is known as inhibiting. Certain materiel contain oxygen in themselves. Such materials when on fire cannot be extinguished by smothering as they release oxygen from them.Examples are , Gun powder, TNT and RD X etc. Such fires are due to self -sustaining ,continuous  heat producing (exothermic) chemical reactions.In such fires extinguishing is possible only by breaking the chemical chain reaction.This type of extinguishing is called Inhibiting.

Smothering

To use on metal fires such as Uranium, Plutonium and Magnesium,a powders compound TEC has been discovered .This powder ,Ternary Etetic Chloride is applied by means of a gas cartridge pressurized extinguisher.As the fusing temperature of the powder is in the range of 580 degree celcious.It shall form a crust over the burning metal and thus exclude oxygen.The vigorous discharge of an inert gas such as  Carbon dioxide, Nitrogen etc. is also smothering the atmosphere.

Smothering

Limitation or removal of oxygen from the scene of fire is known as smothering.If the oxygen content of the atmosphere in the immidiate neighbour hood of burning material can be sufficiently redused  will cease . The general procedure is to prevent the access of fresh aie  to the seat of the fire. The principle of smothering is employeed on a small scale in snuffing a candle & on a large scale in capping a burning oil well.Form & Dry chemical powders are generally used  for smothering . The powder has a cooling effect in addition to its smothering effects.To use on metal fires.

Starvation & Cooling

Starvation 

                                      Limitation or removal of fuel from the scene of fire is known as starvation. The extinction of fire by  starvation is applied in three ways.By removing combustible materiel from the neighbor hood of the fire. By removing the  fire from the neighbor hood of combustible material By subdividing the burning material.The smallest fire produced may be left to burnout easily rather than extinguishing

.Cooling

                                      limitation or removal of heat from the scene of fire is known as cooling. If the rate at which heat is generated by combustion  is less than the rate at which  it is dispersed  through  various agencies, the combustion cannot survive. There for the first step in cooling is to accelerate the speed with which heat is removed fro the fire. When the temperature of the burning mass  is reduced, the production of heat is also reduced.As heat flows from a hot body  to a cold body ,the cooling medium absorbs the heat from the fire.While pouring water on to the fire some of the water is converted to steam.The steam has produced helps to smothering.

Elements of fire & Methods of extinguishment

Elements of fire.

 It has been shown from the rectangle from combustion that four factors are essential to combustionnamely: 

 

1, The presence of combustiable substance (fuel) .

2,The presence of oxygen .

3, The attainnment & maintenance of  a certain minimum temperature(heat) .

4, The chain reaction of flame.

 Methods of extinguishment.

If one or more of these elements is limited ,the fire can be extinguished. the methods of extinguishing fire may there fore be classified as follows: 

*Starvation 

* Smothering 

*Coolinng 

*Inhibiting

Convection & Radiation

Convection:  


                                             It is ocures only in liquids and gasses.When liquid or gas is heated it expand & becomes less dense. The lighter fluid raises up and the colder liquids which is denser goes down. Thus a circulation is set up in the fire situation in a building convection currents can convey hot gasses produced by combustion through stairwells and open lift shafts there by spreading fire to the upper part of a building .As the hot gasses rise up , cold which is denser will move down towards fire and accelerate burning. 




Radiation:                    

                                              Heat may all so may transmitted in straight lines  by a meanse ,which is neither conduction nor convection. Heat from the sun passes through empty space to warm the earth.Heat from the heater placed at a height level in room can be felt underneath the heater.This method of heat transmission is named as Radiation. It does not involve any contact beetween the bodies and is independent of any material in the intervening space .All forms of radiant energy travel in a straight lines at 3*10^8 ,eter per seconds.Many fire can be caused by radiation . One of the most common fire due to radiation is cloth being ignited by placing to close to a sours of radiation.

Transmission Of Heat

Heat travels from regions of high temperature to regions of lower temperature. There are three methods by which heat may be transmitted. They are : 


*Conduction

*Convection

*Radiation.



Conduction :                       Conduction may occur in solid ,liquids or gasses ,although it is most clearly present in solids. In conduction heat energy is passed on from one molecule to another. The molecules vibrate about a mean position and pass on heat energy by colliding with their neighbors. The ability to conduct heat vapors from one materiel to another.Most of the materiel conduct heat easily and are classed as Good conductors.


                                          The best conductors heat are silver and copper.Non metallic solids, liquids and gasses are poor conductors of heat .In fire situations thermal conductivity is very important in terms of the danger of fire spread>. A plain steel door subjected to heat on one side conduct heat rapidly to the other side when compared with wooden or fiber glass door.