Fire does not have a chemical composition as such, it is a result of a chemical reaction. You need to know what fuel is burning before you can think of the chemical reactions taking place. Fire is simply a form of visual energy (note: fire is not always hot!)

Fire is the same as glowing gasses. When something gets warm enoug, it is glowing. When gasses from a warm chemical or physical prosess comes out, those are called fire. It does not matter what process or what types of gass, but most often it is processes wher oxygen react with some other stuff. Please go to this site and sceoll down on the site. There you find some information about chemistry and fire. http://www.mydeltapi.com/chemistry.htm

It is the chemical composition as measured in a particular point of the fire. It depends mainly from what is burning, but also how it is burning. 1) "Chemical reaction: Fires start when a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat and is able to sustain a chain reaction. This is commonly called the fire tetrahedron. No fire can exist without all of these elements being in place. Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of oxygen and fuel. Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Fire extinguishant by the application of water acts by cooling the fuel to stop the reaction. The application of carbon dioxide starves the fire of oxygen. Other gaseous fire suppression agents, such as halon or HFC-227, interfere with the chemical reaction itself." "A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot matter, of which a very small portion is plasma. It consists of reacting gases and solids emitting visible and infrared light, the frequency spectrum of which depends on the chemical composition of the burning elements and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. For reasons currently unknown by scientists, the flame produced by exposure of zinc to air is a bright green, and produces plumes of zinc oxide. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide." Source and further information: http://en.wikipedia.org/wiki/Fire Further information: http://en.wikipedia.org/wiki/Flame 2) here a text about a 3-D measurement of the composition of fire: "2.2 Measurement Techniques We describe several techniques, apart from regular photography, for directly recovering measurements from a fire. These basic measurements, including temperature and beam deflection, can be used to infer other quantities from the fire such as density. Note that we defer a discussion of tomography for combining multiple measurements into a single field until §4.1.4. The chemical composition of fire is usually determined by analyzing peaks across a broad infrared spectrum." Source and further information: http://www.cs.toronto.edu/~hasinoff/pubs/hasinoff-thesis-2002.pdf