Reviewinfiretech 101009035616 Phpapp01 Fire

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Transcript REVIEWER IN CRIMINOLOGY    FIRE TECHNOLOGY AND ARSON INVESTIGATIONIntroduction: The development of methods and tools for using and controlling fire was critical in humanevolution and is believed to have allowed early humans to spread northward from the warmclimate of either srcin into the more severe environment of Europe and Asia. The evidence of early fire use is often ambiguous because of the difficulty in determining whether thearcheological evidence is the result of accidental fire or its deliberate use. Such evidence includefinds of occupation sites with fired or baked soils, bones or stones that have been changedthrough the application of heat, and areas containing thick layers of ash and charcoal that mighthave hearth structures.The earliest finds, in Kenya and Ethiopia, date from about 1. million years ago. !esse uivocal evidence e#ists for deliberate fire use in the $aleolithic period, beginning about %%,%%%years ago. &eolithic sites have yielded ob'ects that may have been used in fire, making drill for producing friction, heat in wood and flints for striking sparks from iron pyrites.(n legend and religion, fire is common thing. )or e#ample, in $ersian literature fire wasdiscovered during a fight of a hero with a dragon. A stone that the hero used as a weapon missedthe monster and struck a rock. !ight shone forth and human beings saw fire for the first time. (n*reek mythology, $rometheus was bestowed with god like powers when he stole the god+s fire togive it to humanity. )ire has also played a central role in religion. (t has been used as a god andrecognied as a symbol of home and family in many cultures. )ire has also been a symbol of purification and of immortality and renewal, hence the lighting of flames of remembrance. TheTemple of -esta in ome was an outstanding e#ample of the importance of fire to the omans.-esta was srcinally the goddess of the fire and her shrine was in every home. /e can only guess that pre0historic people may have gained knowledge of fire fromobserving things in nature. So the srcin of fire before the dawn of civiliation may be traced to anerupting volcano, or a forest fire, started by lighting. &o one really knows where on the earthsurface or at what stage of early history man learned how to start a fire and how to make use of it.et, today, man has had fire as2 ã source of warmth and light ã protection against enemies ã cause chemical changes to foodstuffs to suit man+s body structure ã provides processes for modifying chemicals into medicines ã provides heat to convert wood, metals, and bones into domestic tools or instrumentsfor aggression/hile the application of fire has served man+s needs its careless and wanton use e#actan enormous and dreadful toll from society in life and property. 3ence, man+s understanding of fire would enable him to develop the technology of prevention and control to a considerableadvance state 4Abis5. WHAT IS FIRE?Fire is the manifestation of rapid chemical reaction occurring between fuel and ano#idier0 typically the o#ygen in the air. Such rapid chemical reaction releases energy in the formof heat and light. Fire  is heat and i!ht resulting from the rapid combination of o#ygen, or in some casesgaseous chlorine, with other materials. The light is in the form of a a#e , which is composed of glowing particles of the burning material and certain gaseous products that are luminous at thetemperature of the burning material. THE START OF FIRE  All matters e#ist of one of the three states 6 solid, li uid and gas 4vapor5. The atoms or molecules of a solid are packed closely together, and that of a li uid is packed loosely, themolecules of a vapor are not packed together at all, they are free to move about. (n order for asubstance to o#idie, its molecules must be pretty well surrounded by o#ygen molecules. Themolecules of solids or li uids are too tightly packed to be surrounded. Thus, only vapors canburn.3owever, when a solid or a li uid is heated, its molecules move about rapidly. (f enoughheat is applied, some molecules break away from the surface to form a vapor'ust above thesubstance. This vapor can now mi#ed with o#ygen. (f there is enough heat to raise the vapor to its ignition temperature 4temperature needed to burn5, and if there is enough o#ygen present, thevapor will o#idie rapidly 6 it will start to burn.  Rkmfiles/2008/Reviewer in Fire Technology 1 REVIEWER IN CRIMINOLOGY    The start of burning is the start of a Chain Reaction  4the burning process5. -apor fromheated fuel rises, mi#es with air and burns. (t produces enough heat to release more vapor and todraw in air to burn that vapor. As more vapor burns, flame production increases. 7ore heat isproduced, more vapor released, more air drawn into the flames and more vapor burns, the chainreaction keeps increasing 6 the sie of the fire increases until fuel is consumed. CHE$ISTRY OF FIRE 8bviously, three things are re uired for combustion or fire2 F%EL 49ombustible materialsto vaporie and burn5, O&YGEN 48#ygen in air is the common o#idiing agent, to combine withfuel vapor, air contains :;< 8, =; &, 1< inert gas5, and HEAT 4to raise the temperature of thefuel vapor to its ignition temperature5. The combinations of these three elements form the so0called Fire Trian!e' The Fire Trian!e 8#ygen 3eat)uel )igure 1)igure 1 will show that if any side of the fire triangle is missing, a fire can not start or if any side of the fire triangle is removed, the fire will go off./ith the presence of the elements of fire, combustion may take place. >efore a fuel willburn, it must be changed to its vapor state. (n a fire situation, this change usually results from theinitial application of heat. The process is known as $8!S(S. ()ro)*i* 4also known asthermal decomposition5   is defined as the ?chemical decomposition of matter through the action of heat@. (n this case, the decomposition causes a change from a solid state to vapor state. (f thevapor mi#es sufficiently with air and heated to high temperature, combustion results.The combustion process is better represented by the fire tetrahedron. The Fire Tetrahedron 8#ygen3eat)uel9hain eaction)igure :The fire tetrahedron is useful in illustrating and remembering the combustion processbecause it has room for the chain reaction and because each face touches the other three faces.The basic difference between the fire triangle and the fire tetrahedron is that2 Thetetrahedron illustrates how flaming combustion is supported and sustained through the chainreaction. (n this sense, the chain reaction face keeps the other three faces from falling apart.The fire tetrahedron also e#plains the flaming mode of combustion. The modes of combustion are either )laming mode or Surface mode 4*lowing6 represented by the fire triangle5. A condensed phased combustion is called glowing combustion  Rkmfiles/2008/Reviewer in Fire Technology 2 REVIEWER IN CRIMINOLOGY     A gas0phased combustion is known as flame (f the process is confined with pressure it is called explosion (f combustion propagates at supersonic speed, it produced a detonation (RO(ERTIES OF FIRE   A'The (h)*ica +ro+ertie* 1.Specific *ravity 6 the ratio of the weight of a solid or li uid substance to theweight of an e ual volume of water.:.-apor density 6 the weight of a volume of pure gas composed to the volume of dry air at the same temperature and pressure..-apor $ressure 6 the force e#erted by the molecules on the surface of a li uid.B.Temperature 6 the measure of the degree of thermal agitation of molecules..>oiling $oint 6 the constant temperature at which the vapor pressure of the li uidis e ual to the atmospheric pressure.C.(gnitionDKindling temperature 6 the minimum temperature at which the substancemust be heated in order to initiate combustion.=.)ire point 6 the lowest temperature of a li uid in an open container at whichvapors are evolved fast enough to support combustion.;.)lash point 6 the temperature at which a flammable li uid forms a vapor0air mi#ture that ignites 4mi#ture with in the e#plosive range5.To burn a fuel 4combustible material5, its te#+erature must be raised until i!nition +oint is reached. Thus, before a fuel start to burn or before it can be ignited, it has to be e#posed to acertain degree of temperature. /hen the temperature of a certain substance is very high, itreleases highly combustible vapors known as FREE RADICALS 4combustible vapors such ashydrogen gas, carbon mono#ide, carbon dio#ide, and nitrogen5.uring the process of +)ro)*i* , the following are involved2 ã the fuel is heated until its temperature reaches its ire +oint, ã decomposition takes place 6 moisture in the fuel is converted to vapor, ã decomposition produces combustible vapors that rise to the surface of the fuel 4freeradicals5 ã free radicals undergo combustion. -'The Che#ica (ro+ertie* 1.Endothermic eactions 6 changes whereby energy 4heat5 is absorbed or isadded before the reaction takes place.:.E#othermic eactions 6 those that release or give off energy 4heat5 thus theyproduce substances with less energy than the reactants..8#idation 6 a chemical change that is e#othermic, a change in which combustiblematerial 4fuel5 and an o#idiing agent 4air5, react. E#ample of o#idation iscombustion which is the same as actual burning 4rapid o#idation5B.)lames 6 flames are incandescent 4very brightDglowing with intense heat5 gases.(t is a combustion product and a manifestation of fire when it is in its gas0phasedcombustion.  T)+e* o Fa#e*: a.>ased on 9olor and 9ompleteness of 9ombustibility of )uel1.!uminous )lame 6 is orange0red, deposit soot at the bottom of a vesselbeing heated due to incomplete combustion and has a low temperature.:.&on0!uminous )lame 6 is blue, there is complete combustion of fuel andhas relatively high temperature.b.>ased on )uel and Air 7i#ture1.$remi#ed )lame 6 is e#emplified by a >unsen0type laboratory burner where hydrocarbon 4any substance containing primarily carbon andhydrogen5 is thoroughly mi#ed with air before reaching the flame one.:.iffusion )lame 6 is observed when gas 4fuel5 alone is forced through anole into the atmosphere which diffuse in the surrounding atmospherein order to form a flammable mi#ture. The candle flame is an e#ample of   Rkmfiles/2008/Reviewer in Fire Technology 3 REVIEWER IN CRIMINOLOGY    diffusion flame governed purely by molecular diffusion, and the flame of the o#yacetylene torch. 4diffused 6 dispersed, widely spread5c.>ased on Smoothness1.!aminar )lame 6 when a particle follows a smooth path through agaseous flame.:.Turbulent )lame 6 are those having unsteady, irregular flows. As physicalsie, gas density or velocity is increased, all laminar gas flows tend tobecome turbulent. FIRE ELE$ENTS  As mentioned in part one, fire has been described as having three components2 ue,heat, and o.)!en . This triad was illustrated by the fire triangle, which symbolied, in the mostbasic terms, a chemical relationship. The additional component needed to e#plain flamingcombustion is a chemical chain reaction shown in the fire tetrahedron. THE F%ELSF%ELS /Co#0u*ti0e $ateria*1  6 fuel is matter and matter e#ist in three physical states2solid, li uid and gas. Solids melt to become li uids, and these may vaporie and become gases.The basic rule is that at high enough temperature all fuels can be converted to gases. And eachof the physical states e#hibits different physical and chemical properties that directly affect a fuel+scombustibility. )or e#ample, gasoline as a li uid does not burn, it is the vapors rising from theli uid that burn. !ikewise, wood, the most common solid fuel, is not flammable, but gives of flammable vapors 4free radicals5.)FE! is also a material that provides useful energy. )uels are used to heat and cookfood, power engines, and produce electricity. Some fuels occur naturally and others are artificiallycreated. Such natural fuels are coals, petroleum, and natural gases obtained from undergrounddeposits that were formed million years ago from the remains of plants and animals. They arecalled fossil fuels,  which account for about G%< of the energy people use today.Synthetic fuels can be made from fossil fuels, certain types of rock and sand, andbiomass.7ost fuels release energy by burning with o#ygen in the air. >ut some 6 especiallychemical fuels used in rockets 6 need special o#idiers in order to burn. &uclear fuels do not burnbut release energy through the fission 4splitting5 of fusion 4'oining together5 of atoms. Ca**i ication o Co#0u*ti0e $ateria* 1. Ca** A Fue*  6 they are ordinary combustible materials that are usually made of organic substances such as wood and wood0based products. (t includes somesynthetic or inorganic materials like rubber, leather, and plastic products. 2. Ca** - Fue*  6 materials that are in the form of flammable li uids such as alcohol,acidic solutions, oil, li uid petroleum products, etc. 3. Ca** C Fue*  6 they are normally fire resistant materials such as materials used onelectrical wiring and other electrical appliances. 4. Ca** D Fue*  6 they are combustible metallic substances such as magnesium,titanium, irconium, sodium and potassium. Genera Cate!orie* o Fue  1.Solid 9ombustible 7aterials 6 includes organic and inorganic, natural or synthetic,and metallic solid materials.:.!i uid 9ombustible 7aterials 6 includes all flammable li uid fuels and chemicals..*aseous Substances 6 includes those to#icDhaardous gases that are capable of ignition. The Soid Fue* The most obvious solid fuels are wood, paper and cloth. (ts burning rate depends on itsconfiguration. )or e#ample, solid fuels in the form of dust will burn faster than bulky materials.Types of )lammable solidsa. $yrolyable solid fuels 6 include many of the ordinary accepted combustibles2 wood,paper and so on. The vapors released by their chemical decomposition support flaming  Rkmfiles/2008/Reviewer in Fire Technology 4
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