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1) A mechanical phenomenon wherein one substance penetrates into the inner structure of another, as in absorbent cotton or a sponge.
2) An optical phenomenon wherein atoms or molecules block or attenuate the transmission of a beam of electromagnetic radiation.
Any material used to initiate or promote the spread of a fire. The most common accelerants are flammable or combustible liquids. Whether a substance is an accelerant depends not on its chemical structure, but on its use.
The simplest ketone. A highly flammable, water soluble solvent. Flash point of 0°F. Explosive limits of 2.6% to 12.8%.
The adherence of atoms, ions or molecules of a gas or liquid to the surface of another substance. Finely divided or microporous materials having a large active surface area are strong adsorbents. Examples include activated carbon, activated alumina and silica gel.
An organic compound having a hydroxyl (-OH) group attached. The lower molecular weight alcohols, methanol (CH3OH), ethanol (C2H5OH), and propanol (C3H7OH) are water soluble.
 One of the main groups of hydrocarbons characterised by the straight or branched chain arrangement of constituent atoms. Aliphatic hydrocarbons belong to three subgroups:
  1. alkanes or paraffins, all of which are saturated and comparatively unreactive,
  2. the alkenes or alkadienes which are unsaturated (containing double [C=C] bonds) and more reactive, and
  3. alkynes, such as acetylene (which contain a triple [C=C] bond).
An aliphatic hydrocarbon having the chemical formula CnH2n+2 A normal alkane, or n-alkane is one which does not have a branched carbon backbone. An iso-alkane has a branched, rather than a straight chain, carbon backbone. Alkanes are also known as paraffins. The simplest alkanes are named as follows: CH4 methane 
C6H14 hexane 
C2H6 ethane 
C7H16 heptane 
C3H8 propane 
C8H18 octane 
C4H10 butane 
C9H20 nonane 
C5H12 pentane 
C10H22 decane 
A straight chain, unsaturated compound of the olefin series which has the generic formula ..., having at least one double [C=C] bond. (See Aliphatic).
: A functional group having the formula ... which may be attached to certain elements such as lead, silicon, or to other organic chemicals.
An unsaturated aliphatic hydrocarbon characterised by the presence of a triple [C=C] bond. The generic formula for an alkyne is .... The most important member of this group is acetylene, HCCH, the first member of the series
A solid or liquid mixture of two or more metals, or of one or more metals with certain nonmetallic elements, as in brass, bronze or carbon steel.
Pre-existing or normal environment.
An organic compound having as part of its structure a benzene ring. (See Benzene). The term 'aromatic' as used in the fragrance industry is used to describe essential oils, which are not necessarily aromatic in the chemical sense.
The crime of intentionally setting fire to a building or other property. This is a legal definition which may vary depending on the laws of a specific state.
The smallest unit of en element which still retains the chemical characteristics of that element. An atom is made up of protons and neutrons in a nucleud surrounded by electrons. A molecule of water (H20) consists of two atoms of hydrogen and one atom of oxygen.
Atomic Absorption: An analytical technique, used to determine the elemental composition and concentration of many metals and other inorganic elements. The material being analysed, generally in solution, is atomised, or broken up into individual atoms, usually by the action of extreme heat in a flame or small furnace. The ability of the atomised material to absorb characteristic wavelengths of visible or ultraviolet light is then measured using a spectrophotometer.

1) To break down into discrete atoms, usually by the application of extreme heat, as in atomic absorption, 
2) To break a liquid into tiny droplets, as occurs in fuel injected engines or in the production of aerosol sprays.
An adjustment of the signal amplifier response which results in the reduction of the electronic signal.
A mixture of two or more compounds which has a constant boiling point. The composition of the vapour above the azeotropic mixture has the same relative concentrations of compounds as does the boiling liquid. Azeotropic mixtures cannot be separated by fractional distillation.
 A hexagonal organic molecule having a carbon atom at each point of the hexagon and a hydrogen atom attached to each carbon atom. Molecules which contain a benzene ring are known as aromatic. Benzene boils at 80°C and has a flash point of 12°F (-11°C). The explosive limits are 1.5% to 8% by volume in air.
British Thermal Unit. The amount of heat energy required to raise the temperature of one pound of water one degree Fahrenheit. This is the accepted standard for the comparison of heating values of different fuels. One BTU equals 252 calories.
Normal combustion in which the oxident is molecular oxygen.
Burning Rate: The rate at which combustion proceeds across a fuel. A specialised use of this term, describes the rate at which the surface of a pool or burning liquid recedes. For gasoline, this rate is reported to be approximately ¼ inch per minute.
A fuel gas having the formula C4H10. A constituent of LP gas. One pound of liquid butane produces 6.4 cubic feet of gas. One gallon of liquid butane weighs 4.87 pounds and produces 31 cubic feet of gas. One cubic foot of butane gas produces 3266 BTUs.
The amount of energy required to raise the temperature of one gram of water one degree Centigrade. One calorie equals 0.004 BTUs. One BTU equals 252 calories.
A narrow bore glass tube. Capillary column gas chromatography employs glass tubes having an inside diameter of approximately .2 to .5 millimetres and a length of 3 to 300 metres. The walls of a capillary column are coated with an adsorbent medium (a liquid phase in which the sample dissolves).
 The element upon which all organic molecules are based. Carbon has an atomic weight of 12.00, and occurs elementally in these forms: diamond, graphite and amorphous carbon such as coal or carbon black.
Carbon Dioxide: A molecule consisting of one atom of carbon and two atoms of oxygen which is a major combustion product of the burning of organic materials. Carbon Dioxide (CO2) is the result of complete combustion of carbon. In the gaseous form, CO2 is used as a fire extinguisher. In the solid form, CO2 is known as dry ice. CO2 is heavier than air, with a vapour density if 1.53 (air = 1.00).
Carbon Disulfide: A highly flammable nonpetroleum solvent used for gas chromatography because of its relatively low signal generated in a flame ionisation detector. Carbon disulfide has the formula CS2. Reagent grade CS2 has an odour similar to rotten broccoli and can be ignited by contact with boiling water. It burns with a blue flame, providing CO2 and SO2 (sulfur dioxide). The explosive limits of CS2 are 1 to 50%. CS2 has a flash point of -22°F.
Carbon Monoxide: A gaseous molecule having the formula CO, which is the product of incomplete combustion of organic materials. Carbon monoxide has an affinity for haemoglobin approximately 200 times stronger than oxygens and is highly poisonous. CO is a flammable gas which burns with a blue flame and has explosive limits of 12% to 75%. Carbon monoxide has approximately the same vapour density as air, 0.97 air (air = 100).
Carbon Tetrachloride: A nonflammable liquid having the formula CC14, formerly used as a fire extinguisher, and still used as a solvent and cleaning agent. Carbon tetrachloride boils at 77°C.
Chain Reaction: A self-propagating chemical reaction in which activation of one molecule leads successfully to activation of many others. Most, perhaps all, combustion reactions are of this kind.
Chemical Change: Rearrangement of the atoms, ions or radicals or one or more substances, resulting in the formation of new substances, often having entirely different properties. Also known as a chemical reaction.
Chemistry: A basic science concerned with
  1. the structure and behaviour of atoms (elements);
  2. the composition and properties of compounds;
  3. the reactions that occur between substances and the resultant energy exchange and
  4. the laws that unite these phenomena into a comprehensive system.
A series of peaks and valleys printed or written on a paper chart where each peak represents a component or mixture of two or more unresolved components in a mixture separated by gas or liquid chromatography.
A chemical separation procedure which separates compounds according to their affinity for an adsorbent or absorbent material. Chromatography includes Thin Layer Chromatography (TLC), Liquid Chromatography (LC), Gas Chromatography (GC), (sometimes called Gas Liquid Chromatography or GLC) and High Performance Liquid Chromatography (HPLC).
1) A sample of material collected from a fire scene which is, to the best of the investigators knowledge, identical in every respect to a sample suspected of containing accelerant, but which does not contain accelerant.
2) A sample of suspected accelerant submitted for the purpose of comparing with any accelerant separated from a debris sample.
Combustible Liquid: A liquid which is capable of forming a flammable vapour/air mixture. All flammable liquids are combustible. Whether a liquid is flammable or combustible depends on its flash point and on the agency definition relied upon. The Coast Guard classifies all liquid having a flash point over 80°F as combustible and liquids with a flash point below 80°F as flammable. The NFPA uses 100°F.
Combustion: An exothermic chain reaction between oxidising and reducing agents, or between oxygen and fuel. combustion may occur with any organic compound, or with certain combustible elements such as hydrogen, sulfur and finely divided metals.
Component: 1) One of the elements or compounds present in a system such as a phase, a mixture, a solution or a suspension in which it may or may not be uniformly dispersed. 
2) A compound or a group of unresolved compounds represented by a peak on a chromatogram.
Compound: A chemical combination of two or more elements, or two or more different atoms arranged in the same proportions and in the same structure throughout the substance. A compound is different from a mixture in that the components of a mixture are not chemically bonded together. For example, a flask may contain two volumes of hydrogen (H2) gas and one volume of oxygen gas (O2). A different glass might contain only water vapour (H20). In the first case, two gases are mixed. In the second case, only one gas is present.
Concentration: the amount of a substance in a stated unit of a mixture or solution. Common methods of stating concentration are per cent by weight, per cent by volume, or weight per unit volume (eg: parts per million, billion, etc.).
Conduction: Passage of heat from one material to another by direct contact.
Conductivity: The ability of a material to transfer energy from one place to another. Thermal conductivity describes a substances ability to transmit heat. Electrical conductivity describes a substances ability to transmit electrical current. Conductivity is to the opposite if resistivity.
Control Sample: A sample of material which is known to be identical to a sample suspected of containing accelerant in every regard, except that the control sample does not contain accelerant. A known blank sample. In practical terms, control samples do not exist in the setting of a fire scene because 
(1) exact conditions during the fire cannot be duplicated from location to location, and 
(2) exact conditions of the substrate, ie: carpet, etc., are not known. Carpet in Room A may have had various items spilled on it during use. Carpet B (ten feet away) may be brand new. (See 
Comparison Sample)
Convection: Transfer of heat by the movement of molecules in a gas or liquid with the less dense fluid rising. The majority of heat transfer in a fire is by convection.
Corrosion: The degradation of metals or alloys due to reaction with their environment. It is accelerated by acids, bases or heats.
Cracking: A refining process involving decomposition and molecular recombination of organic compounds, especially hydrocarbons obtained by distillation of petroleum, by means of heat, to form molecules suitable for various uses such as motor fuels, solvent or plastics. Cracking takes place in the absence of oxygen.
Deflagration: Vigorous burning with subsonic flame propagation. (See Detonation).
Desorption: the process of removing an adsorbed material from the solid on which it is adsorbed.
An exothermic chemical reaction which propagates through reactive material at supersonic speed.

Diesel Fuel: Diesel Fuel consists mostly of hydrocarbons ranging from C10 to C24. The composition of diesel fuel may vary with changes in latitude or changes in season. this variability is provided by the refinery to control the volatility of the product. In order to be identified as diesel fuel, a sample extract must exhibit a homologous series of five or more consecutive normal alkanes ranging from C12 through C22. Diesel fuel has a flash point of 120 to 160°F and explosive limits of 0.7% to 5%. Many states specify a minimum flash point for diesel fuel.

Visit the Diesel T-shirt website.

Distillation: A separation process in which a liquid is concerted to a vapour and the vapour is then condensed back to a liquid. The usual purpose of distillation is separation of the compounds of a mixture. Steam distillation separates all water insoluble liquids from solids and water soluble compounds in a mixture.
Drying Oil: An organic liquid which, when applied as a thin film, readily absorbs oxygen from the air and polymerises to form a tough elastic film. Linseed, tung, soybean and castor oils are drying oils. Under certain conditions, usually involving large surface areas and insulation, such as a pile of rags soaked with drying oils, spontaneous heating may occur.
Electron: A negatively charged subatomic particle which circles the nucleus of the atom in a cloud. Most chemical reactions involve the making and breaking of bonds held together by the sharing of electrons.
Electron Capture Detector (ECD): A type of gas chromatographic detector which is sensitive to halogenated hydrocarbons and other molecules capable of easily gaining an electron. Electron capture is not generally used for hydrocarbon detection.
Element: One of 106 presently known kinds of substances that comprise all matter at and above the atomic level. (See Periodic Table)
Elution: the process of removing absorbed materials from the surface of an adsorbent such as activated charcoal. the solvent in this process is called the eluant.
Emission Spectroscopy: The study of the composition of substances and identification of elements by observation of the wavelengths of radiation emitted by the substance as it returns to a normal state after excitation by an external source. Generally used for elemental analysis.
Emulsion: A stable mixture of two or more immiscible liquids in suspension.
Endothermic Reaction: A chemical reaction which absorbs heat.
Ethane: A simple alkane having the formula C2H6. A minor component of natural gas. Its explosive range is 3% to 12.5%. Ethane has approximately the same vapour density as air.
Ethanol: Ethyl alcohol. Grain alcohol. Flammable, water soluble alcohol. Flash point of 55°F. Explosive limits of 3.3% to 19%.
Ether: Diethyl ether, ethyl ether. A highly flammable solvent which can form explosive peroxides when exposed to air. Flash point of -49°F. Explosive range of 1.85% to 48%.
Ethylbenzene: A component of gasoline, but also a major breakdown product or pyrolsis product given off when certain polymers are heated.
Eutetic: the lowest melting point of an alloy or solution of two or more substances (usually metals) that is obtainable by varying the percentage of the components. Eutetic melting sometimes occurs when molten aluminium or molten zinc comes in contact with solid steel or copper.
Evaporation: Conversion of a liquid to the vapour state. See also vaporisation.
Evaporation Rate: A measure of the quantity of a liquid converted to vapour in a unit of time. Among single component liquids, the rate varies directly with the surface area, the temperature and the vapour pressure, and inversely with the latent heat of vaporisation of the liquid.
Exothermic Reaction: A chemical reaction which evolves heat. Combustion reactions are exothermic.
Explosion: The sudden conversion of chemical energy into kinetic energy with the release of heat, light and mechanical shock.
Flammability limit. The highest or lowest concentration of a flammable gas or vapour in air that will explode or burn readily when ignited. The limit is usually expressed as a volume percent of gas or vapour in air.
: Flammability range. The set of all concentrations between the upper and lower explosive limits of a particular gas or vapour.
Extraction: A chemical procedure for removing one type of material from another. Extraction is generally carried out by immersing a solid in a liquid, or by shaking two immiscible liquids together, resulting in the transfer of a dissolved substance from one liquid to another. Solvent extraction is one of the primary methods of sample preparation in arson debris analysis.
Fire: The light and heat manifested by the rapid oxidation of combustible materials. A flame may be manifested but is not required.
Fire Point: The temperature, generally a few degrees above the flash point, at which burning is self-sustaining after removal of an ignition source.
Fire Tetrahedron: Fuel, heat, oxygen and a chemical chain reaction.
Fire Triangle: Fuel, heat and oxygen.
Flame: A rapid gas phase combustion process characterised by self-propagation.
Flame Ionisation Detector (): A nearly universal gas chromatographic detector. It responds to almost all organic compounds. An FID does not respond to nitrogen, hydrogen, helium, oxygen, carbon monoxide or water. This detector ionises compounds as they reach the end of the chromatographic column by burning them in an air/hydrogen flame. As the compounds pass through the flame, the conductivity of the flame changes, generating a signal. The is the most commonly used detector in arson debris analysis.
Flame Propagation: Travel of a flame through a combustible gas/air or vapour/air mixture.
Flammability Limit: (See Explosive Limit)
Flammability Range: (See Explosive Range)
Flammable Liquid: A combustible liquid that has a flash point below 80°F according to the Coast Guard, 100°F according to the NFPA. Liquids having a vapour pressure over 40 pounds per square inch at 100°F are classified as flammable gases. Flammable liquids are a special group of combustible liquids.
Flammable Vapour: A vapour/air mixture of any concentration within the flammability range of that vapour.
Flash Fire: A fire that spreads with unusual speed, as one that races over flammable liquid of through combustible gases.
Flash Point: The temperature at which a pool of liquid will generate sufficient vapours to form an ignitable vapour/air mixture. The temperature at which a liquid will produce its lower explosive limit in air. Flash point describes one of several specific laboratory tests. Frequently materials can be made to burn below their flash point if increased surface area or mechanical activity raise the concentration of vapour in air above the lower explosive limit.
Fractionation: The separation of one group of compounds in a mixture from another, generally by distillation.
Fuel Oil: A heavy petroleum distillate ranging from #1 (kerosene or range oil), #2 (diesel fuel), up through #6 (heavy bunker fuels). To be identified as fuel oil, a sample must exhibit a homologous series of normal alkanes ranging from C9 upward.
 (also known as Gas Liquid Chromatography): The separation of organic liquids or gases into discrete components or compounds seen as peaks on a chromatogram. Separation us done in a column which is enclosed in an oven held at a specific temperature, or programmed to change temperature at a reproducible rate. The column separates the compounds according to their affinity for the material inside the column (stationary phase). Columns can be either packed or capillary. Packed columns employ a powdery substance which may be coated with a nonvolatile liquid phase. A capillary column is a glass or quartz tube coated with a nonvolatile liquid. Gas Chromatography (GC) is the accepted method for identification of hydrocarbon mixtures normally used as accelerants, and must be performed in order to have a valid identification of petroleum distillates.
Gasoline: A mixture more than 200 volatile hydrocarbons in the range of C4 to C12 , suitable for use in spark ignited internal combustion engine. Regular automotive gasoline has a flash point of -40°F.
Headspace Concentration: A technique for concentrating all or most of the flammable or combustible liquid vapours in a sample onto a tube of charcoal, a wire coated with charcoal, a charcoal coated polymer, or some other adsorbing material which will later be desorbed in order to analyse the concentrated vapours. This is a primary form of sample preparation in arson debris analysis. This is also known as adsorption/elution, vapour concentration, or total headspace.
Heat: A mode of energy associated with and proportional to molecular motion that may be transferred from one body to another by conduction, convection or radiation.
Heptane: An alkane having the formula C7H16, flash point of 25°F and explosive limits of 1.2% to 6.7%.
Hexane: An alkane having the formula C6H14. Flash point -9°F. Explosive limits of 1.2% to 7.5%.
Homologous Series: A series of similar organic compounds, differing only in that the next higher member of the series has an additional CH2 group (one carbon atom and two hydrogen atoms) in its molecular structure. Fuel oils are characterised by the presence of an identifiable homologous series of normal alkanes.
Hydrocarbon: A organic compound containing only carbon and hydrogen.
Hydrogen: The simplest element. Atomic Number 1. Hydrogen gas has a specific gravity of 0.0694 (air = 1), so it is much lighter than air. Hydrogen is highly flammable, forming water upon combustion. Explosive limits are 4% to 75%.
Ignition: The means by which burning is started.
Ignition Temperature: The minimum temperature to which a fuel must be heated in order to initiate of cause self sustained combustion independent of another heat source.
Immiscible: Describes substances of the same phase or state of matter (usually liquids) that cannot be uniformly mixed or blended.
Incendiaries: Substances or mixtures of substances consisting of a fuel and an oxidiser used to initiate a fire.
Incendiary Fires: Fire set by human hands.
Incidental Accelerants: Flammable or combustible liquids which are usual and incidental to an area where they are detected. Gasoline is incidental to an area where gasoline powered appliances are kept. Kerosene is incidental to an area where a kerosene heater is kept. Flammable liquids may also comprise a part of a product such as insecticide, furniture polish, or paint. Additionally certain ------ containing building materials may yield ------ of fuel oil components.
Infrared Spectrophotometry (IR): An analytical technique which utilises an instrument which passes infrared radiation through a sample or which bounces infrared radiation off the surface of a sample. A very sensitive heat detecting device measures the amount of infrared radiation absorbed as the wavelength of the radiation reaching the detector is changed. IR can give useful information about the type of compounds present in a sample, but it is not capable of precisely identifying a complex mixture. Infrared is very useful in identifying single solvent accelerants. Tracerco have a wide selection of useful radiation monitors and other nucleonic instrumentation.
Intumescent Char: In plastics, the swelling and charring which results in a higher ignition point. Used in the preparation of flame retardant materials.
Ion: An atom, molecule or radical that has lost or gained one or more electrons, thus acquiring an electric charge. Positively charged ions are cations; negatively charged ions are anions.
Isomer: One of two or more forms a chemical compound which have the same number and type of each atom but a different arrangement of atoms.
Isoparaffins: A mixture of branched alkanes usually available as a narrow 'cut' of a distillation. Exxon manufactures a group of products known as 'Isopars' ranging from Isopar A through Isopar J. These solvent mixtures have a variety of uses. Gulf Oil manufactures a similar series of solvents, the most commonly available of which is Gulf Life Charcoal Starter Fluid which is roughly equivalent to Exxon's Isopar G.
Isothermal: A type of gas chromatographic analysis wherein the column is maintained at a uniform temperature throughout the analysis. (See Programming).
Kerosene (#1 Fuel Oil): Flash point generally between 100 and 150 degrees F. Explosive limits of 0.7% to 5.0%. Kerosene consists mostly of C9 through C17 hydrocarbons. In order to be identified as kerosene, a sample extract must exhibit a homologous series five consecutive normal alkanes between C9 and C17. Kerosene is the most common 'incidental' accelerant, as it is used in numerous household products ranging from charcoal lighter fluid to lamp oil to paint thinner to insecticide carriers. It is also used as jet fuel. K-1 kerosene has a low sulfur content required for use in portable space heaters.
Ketone: A type of organic compound having a carbonyl functional group (C=O) attached to two alkyl groups. Acetone is the simplest example of a ketone.
Magnesium: A silvery metal used in some metal incendiaries. The dust is highly explosive. Ignition point of 650°F.
Mass Spectrometry: A method of chemical analysis which vaporises, then ionises the substance to be analysed and then accelerates the ions through a magnetic field to separate the ions by molecular weight. Mass spectrometry can result in the exact identification of an unknown compound, and is a very powerful analytical technique, especially when combined with chromatography.
Meta-ethylitoluene (m-ethyltoluene): A component of gasoline.
Matrix: Substrate. the material from which a substance of interest is removed for analysis.
Methane: The simplest hydrocarbon and the first member of the paraffin (alkane) series, having a formula CH4. Methane is the major constituent of natural gas. Methane has a heating value of 1009 BTU/cubic foot. Its explosive limits are 5% to 15%.
Methanol: Methyl alcohol. Wood alcohol. The simplest alcohol. Methanol is water soluble and has a flash point of 54°F and explosive limits of 6% to 36.5%.
Methyl Silicone: A nonvolatile oily liquid used in gas chromatography to separate nonpolar compounds. Methyl silicone columns typically separate compounds according to their boiling point.
Methylstyrene: A common polymer pyrolysis product.
Mineral Spirits: A medium petroleum distillate ranging from C8 to C12. The flash point of mineral spirits is generally around 100°F. Mineral spirits, sometimes known as mineral turps, is commonly known as a solvent in insecticides and certain other household products. Many charcoal lighter fluids are composed almost entirely of mineral spirits.
Molecular Weight: The sum of the atomic weight of all of the atoms within a molecule. Generally, molecules of the same type have higher boiling points if the molecular weight is higher.
Molecule: The smallest particle into which a substance can be divided without changing its chemical properties. A molecule of an element consists of one atom, or two or more atoms that are alike. A molecule of a compound consists of two of more different atoms.
Monomer: The simplest unit of a polymer. Ethylene is the smallest unit of polyethylene. Styrene is the smallest unit of polystyrene.
Naphtha: Am ambiguous term which may mean high flash naphtha (mineral spirits), or low flash naphtha (petroleum, ether, low boiling ligroin) or something altogether different. Flash point and explosive limits vary. The term naphtha is so ambiguous that it should not be used.
Natural Gas: A mixture of low-molecular weight hydrocarbons obtained in petroleum bearing regions throughout the world. Natural gas consists of approximately 85% methane, 10% ethane and the balance propanes, butanes and nitrogen. since it is nearly odourless, an odorising agent is added to most natural gas prior to final sale.
Nebulize: To form a mist of fine droplets from a liquid. To atomise.
Nitrogen: A gaseous element which makes up approximately 80% of the earths atmosphere. Nitrogen is relatively inert and does not support either combustion or life. Nitrogen is usually found in the molecular N2 form.
(1) An alkane having the formula C8H18. Flash point 56°F. Explosive limits of 1% to 3.2%. 
(2) A measure of the resistance of a sample of gasoline to premature ignition (knocking). 100 octane fuel has the knocking resistance of 100% iso-octane (2, 2, 4-trimethyl pentane). Zero octane fuel has the knocking resistance of a mixture of 89% iso-octane and 11% n-heptane.
Olefin: An alkene. An organic compound similar to an alkane, but containing at least one double bond. Olefins have the formula CnH2n. The simplest olefin is ethylene, C2H4.
Organic Chemistry: the study of the carbon atom and the compounds it forms, mainly with the 20 lightest elements, especially hydrogen, oxygen and nitrogen. Some 3 million organic compounds have been identified and named.
Oxidation: Originally, oxidation meant a chemical reaction in which oxygen combines with another substance. The usage of the word has been broadened to include any reaction in which electrons are transferred. The substance which gains electrons is the oxidising agent.
Oxygen: A gaseous element which makes up approximately 20% of the earths atmosphere. It is usually found in the molecular ... form. Oxygen is the most abundant element on earth.
Pentane: An alkane having the formula C5H12, flash point of -40°F, and explosive limits of 1.4% to 8%. Pentane is frequently used to extract flammable or combustible liquid residues from debris samples.
Petroleum Distillates: By-products of the refining of crude oil. Low boiling or light petroleum distillates (LPD) are highly volatile mixtures of hydrocarbons. These mixtures are sometimes called ligroin, petroleum ether, or naphtha. LPDs are used as cigarette lighter fluid, as copier fluid, and as solvents. Medium boiling petroleum distillates (MPD) are sometimes known as mineral spirits, and are used as charcoal starters, as paint thinners, as solvents for insecticides and other products, and as lamp oils. High Boiling or Heavy petroleum distillates (HPD) are combustible liquids such as kerosene and diesel fuel. pH: A number used to represent the acidity or alkalinity of an aqueous solution. pH 7 is neutral. Acids have a pH below 7, the lower the pH, the more acidic the solution. Bases have a pH above 7. The higher the pH, the more basic of alkaline the solution.
Photoionisation Detector (PID): A type of detector used in chromatography which employs ultraviolet radiation rather than a flame to ionise compounds as they pass through a detector. Photoionisation detectors are particularly sensitive to aromatic compounds.
Polarity: The measure of an electrical charge on a molecule. Most flammable or combustible liquids are nonpolar. Many water soluble compounds, including alcohols and acetone, are polar.
Polymer: A large molecule consisting of repeating units of a monomer. Polymers may be natural, such as cellulose or synthetic such as most plastics.
A method of gas chromatographic analysis which reproducibly raises the temperature of the column so as to allow better resolution of the components over a wide range of boiling points.
Propane: An alkane having the formula C3H8. Propane is the major constituent of LP gas. Explosive limits of 2.4% to 9%. One cubic foot of propane has a heating value of 2500 BTUs.
Pseudocumene: (1, 2, 4 - trimethyl benzene) A component of gasoline.
Pyrolysis: The transformation of a substance into one or more other substances by heat alone without oxidation.
Pyrophoric Distillation: The slow drying and passive pyrolysis of wood materials.
Radiation: (1) Transfer of heat through electromagnetic waves from hot to cold.
(2) Electromagnetic waves of energy having frequency and wavelength. The shorter wavelengths (higher frequencies) are more energetic. The electromagnetic spectrum is comprised of 
a) cosmic rays, b) gamma rays, c) x-rays, d) ultraviolet rays, e) visible light rays, f) infrared, g) microwaves and h) radio waves.
Resolution: 1) In chromatography, a measure of the separation of components, 
2) in spectroscopy, a measure of the ability of the instrument to detect individual absorbance peaks.
Retention Time: The length of time required for a compound of component of a mixture to pass through a chromatographic column.
Saturation: The state in which all available bonds of an atom are attached to other atoms. Alkanes are saturated. Olefins are unsaturated.
Spalling: Destruction of a surface by frost, heat, corrosion, or mechanical causes. Concrete exposed to intense heat may spall explosively. Expansion and contraction of the concrete as well as vaporising moisture contained in the concrete contribute to this effect. It does not necessarily mean an accelerant was used.
Spectrophotometer: A light measuring device which incorporates a monchrometer to isolate and project particular wavelengths of electromagnetic radiation through a sample, and a detector to measure the amount of radiation which has passed through the sample.
Spectroscopy: An analytical technique devoted to the identification of the elements and the elucidation of atomic and molecular structure by measurement of the radiant energy absorbed or emitted by a substance in any of the wavelengths of the electromagnetic spectrum in response to excitation by an external energy source.
Spontaneous Heating: Also known as Spontaneous combustion. Initially, a slow, exothermic reaction at ambient temperatures. Liberated heat, if undissipated (insulated), accumulates at an increasing rate and may lead to spontaneous ignition of any combustibles present. Spontaneous ignition occurs sometimes in haystacks, coal piles, warm moist cotton waste, and in stacks of rags coated with drying oils such as cottonseed or linseed oil.
Styrene: Vinylbenzene. An aromatic compound having the formula C6H5C2H3. The monomer of polystyrene plastic. A common product of polymer pyrolysis.
Substrate: Matrix. The material from which a substance to be analysed is removed.
Sulfur: A nonmetallic yellow element. A constituent of black powder, sulfur burns readily when in powdered form.
Terpenes: Volatile hydrocarbons which are normal constituents of wood.
Thermal Conductivity Detector: A type of gas chromatographic detector which is sensitive to the change in the ability of the gases emerging from the column to conduct heat. A thermal conductivity (TC) detector is not as sensitive as a flame ionisation detector, but it is capable of detecting some molecules, such as water, which give no signal in FID.
Thin Layer Chromatography : A procedure for separating compounds by spotting them on a glass plate coated with a thin (about 0.01 inch) layer of silica or alumina, and 'developing' the plate by allowing a solvent to move upward by capillary action. TLC is especially used for identifying and comparing materials which are highly coloured or which fluoresce under ultraviolet light. TLC is used extensively in explosive analysis and in the comparison of gasoline dyes.
Toluene: Methylbenzene. An aromatic compound having the formula C6H5CH3. A major component of gasoline. Toluene has a flash point of 40°F and explosive limits of 1.2% to 7%.
1) Gum. The pitch obtained from living pine trees. A sticky viscous liquid. 
2) Oil. A volatile liquid obtained by steam distillation of gum turpentine, consisting mainly of pinene and diterpene. Turpentine is frequently identified in debris samples containing burned wood.
Vaporisation: The physical change of going from a solid or a liquid into a gaseous state.
Volatile: Prone to rapid evaporation. Both combustible and noncombustible materials may be volatile.
X-ray Diffraction: An analytical technique used to identify crystalline solids by measuring the characteristic spaces between layers of atoms or molecules in a crystal. X-ray diffraction can be very useful in the identification of explosive residues.
X-ray Fluorescence: A spectromphotometric analytical technique used to identify crystalline solids by measuring the characteristic spaces between layers of atoms or molecules in a crystal. X-ray diffraction can be very useful in the identification of explosive residues.
Xylene: Dimethylbenzene. An aromatic compound having the formula C6H4(CH3)2. Xylene is a major component of gasoline. A mixture of toluene and xylene is frequently used as an automotive paint thinner. Xylene is actually a mixture of three isomers, ortho, meta and para xylene, which have the methyl groups in different positions relative to each other on the benzene ring. The flash points of these isomers range from 81° to 115°F, is used to calibrate flash point testers. The explosive limits of xylene are 1.0% to 7.0%.

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