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ALLIGATORING: A term used by fire investigators in the discussion of fire spread patterns and fire point indicators. The general usage is to describe visual indications of the degree of the carbonizing process of wood when exposed to flames or sufficient heat. This results in structural deterioration of the wood. Usually, the remaining surface appearance is characterized by cracks and ridges. The term is used by some experts in conjunction with their analysis of the speed of the fire, whether or not accelerants were present. There is presently no scientific support for the reliability of estimates on this basis.
AREA OF ORIGIN: The term used by fire investigators to describe the general area where a fire may have started. It is not limited to the specific point of origin – the term is elastic and may describe an entire building in a multi-building fire.
AUTO-IGNITION TEMPERATURE: This is generally used in discussing ignition temperatures of liquid, solid, gaseous compounds or substances. It is rated at the minimum temperature to which the material must be heated to initiate or create self-sustained combustion, independent of any outside heat source. The term is also used in the discussion of spontaneous heating resulting from physical, chemical and biological reactions.
CAUSE: As used in fire investigation, identifying and describing the igniting agent or heat source of a particular fire. For example, some causes could be: “match ignited and thrown into combustibles,” “friction from electric motor belt from thrown bearings,” “incendiary origin – Molotov cocktail ignited and thrown into window of dwelling which then ignited draperies and carpet.”
CIRCUMSTANTIAL EVIDENCE: Proof of circumstances surrounding the transaction; proof of certain facts and circumstances in a given case from which a jury may infer other connected facts which usually and reasonably follow according to the common experience of mankind.
COMBUSTIBLE LIQUIDS: Liquids with a flash point at or above 100 degrees Fahrenheit are sometimes referred to as combustible liquids. When a combustible liquid is heated to or above its flash point, it may have some of the hazards of a flammable liquid.
CONDUCTION: The process by which heat is communicated from one body to another by direct contact or through intervening solid, liquid, or heat conducting medium. Some examples are: a steam pipe on contact with wood, a chimney flue in contact with attic or ceiling framing; and a pair of pliers in contact with electrical conductors that are grounded through an electrode.
CONVECTION: The process by which heat is moved by air differences, usually in a rising or circular pattern. For example, in the case of air circulation in a room, heat from a stove will move laterally if there is an obstruction to vertical movement such as a ceiling, and vertically if there is no obstruction to horizontal movement such as a wall.
DIRECT EVIDENCE: Evidence given by witnesses who testify directly concerning their own knowledge of the main facts to be proven. Eyewitnesses are a good example. “A” takes the witness stand and testifies that he saw “B” toss a burning object through the window of a dwelling and that immediately thereafter, flames burst from the window and “B” ran from the scene.
EXPLOSION: An explosion is an instantaneous decomposition of solid or liquid substance extending throughout the entire mass and accompanied by considerable disengagement of heat. The substance is partly or wholly converted into gaseous decomposition products.
FIRE COMBUSTION: As used in the discussion of combustion, fire is the process whereby substances, or individual constituents of the same, combine with oxygen accompanied by the liberation of heat. These factors are necessary to the process in the general sense; the body or supporting factor (oxygen); the substance to be consumed (fuel); and the dissemination factor (heat).
FIRE LOAD: The fire load of a space occupancy is the expected amount of combustible materials in the area or space under consideration. It can generally be expressed in the terms of the weight of the total combustibles per square foot of the occupancy in relation to their heat producing capability in calories or BTU’s. Most fuels, such as wood, fibers, petroleum products, books, papers, and furniture may be rated in BTU’s per pound and the fire load thereby generally computed. However, construction in or ventilation of the space may produce substantial variables. Predictions can only be general.
FIRE TRIANGLE: A term used in some firing training courses to illustrate the need for the three factors essential for fire: fuel, heat and oxygen. Basically, combustion depends upon the substance to be consumed, oxygen (the supporter of combustion) and the disseminating factor which is heat. The disseminating factor may result from physical, chemical or biological reactions.
FLASHOVER POINT: Initial progress of a fire may be slow or fast depending upon the characteristics of initial ignition and basic fuel. Important factors are the nature of the fuel or fabric, its surface, finish, environment, and available oxygen. If the fire continues, it may eventually reach a stage where all exposed combustible surfaces simultaneously burst into flame. This is what is generally known as flashover or flashover point and is significant in the communication of fire from space to space, even in supposedly separate areas. Flashover is a common phenomenon and is a product of fuel load, combustible surfaces, temperature, and available oxygen. The results of flashover may be mistaken by inexperienced or indifferent fire investigators as separate and distinct areas of origin. This sometimes creates the mistaken illusion that a fire was incendiary when, in fact, it was not. Flashover must also be considered in forest and wildland fires under certain conditions of weather and terrain.
FLASH POINT: The flash point is the lowest temperature at which a substance gives off vapor sufficient to form an ignitable mixture with the air near the surface of the substance. Combustion may not be continuous at the flash point, depending upon fuel, extent, and environment.
IGNITION, SPONTANEOUS: In general terms, this is the process wherein substances or compounds ignite as a result of an increase in temperature of the substance or compound without an independent outside ignition source and without drawing heat from its surroundings. It is sometimes called spontaneous combustion by laymen although it may occur over a long-term period such as unventilated, piled, green hay or other vegetable products; coal dust; charcoal; and oil painted rags. The rate of heat generation, air supply, and insulation properties of the suspect fuel and surrounding environment have definite relevance to whether or not spontaneous heating will occur in the first instance and also as to the rate of heat generation before flaming combustion may occur. In most vegetable compounds, the process may be slow. On the other hand, with unstable or rapidly oxidizing compounds, heat generation may be rapid and even explosive. The process may be luminous or nonluminous. It may occur with or without smoke.
IGNITION TEMPERATURE: Ignition temperature is generally defined as that point of minimum temperature to which a solid, liquid, or gaseous substance must be heated to initiate or cause self-continuing combustion, independent of the heating or igniting source.
POINT OF ORIGIN: In the context of fire investigation, point of origin means the precise location of initial ignition of the substance involved. Usually, the location of the heat source is indicated – match, arc, spark, or other ignition source. Point of origin is more specific than area of origin.
PYROLYSIS: Generally defined, pyrolysis is physical and chemical decomposition by heat. The phenomenon has been known for a long time, however, with the exception of its process in certain compounds, there is much to be learned. Since the organic nature and structure of commonly combustible fuels vary, the process varies.
RADIATION: As used in fire investigation, radiation is one of the three methods or media by which heat is transferred, the three methods being conduction, convection, and radiation. Radiation is the heat transfer, from one body to another, by heat rays, through intervening space, in much the same manner as light is transferred by light rays. Two examples are heat from the sun and heat from an electric heater adjacent to a wall. Radiated heat passes freely through a vacuum and through gases.
SMOKE: The vaporous matter resulting from some forms of combustion and made visible by minute particles of carbon suspended in the vapor.
SUBROGATION: As used in civil actions, the substitution of one for another so that the new party succeeds to the former’s rights or legal claims. It is frequently referred to as the doctrine of substitution. It is a device commonly used in insurance litigation, adopted or invented by equity to compel the ultimate discharge of a debt or obligation. It is the mechanism by which the equity of one man ( or party) is worked through the rights of another. The right of an insurer on payment of a loss to be subrogated pro tanto to any right of action which the insured may have had against any third person whose wrongful act or neglect caused the loss insured against by the insurer is one example.
TRAILER: A term used to describe the means utilized to extend an ignition point from a location outside an occupancy into the space where the plant or booster may be located. Trailers often connect various plants or sets inside a space to insure complete involvement within a short period of time. Flammable liquids such as kerosene and charcoal lighter fluid have been frequently used. Gasoline is seldom used as a trailer because of the rapid evaporation characteristics that makes its use unpredictable. Various types of window cord, rope, and wrapping cord have been commonly used, saturated in kerosene or other medium flash point fuels. Blasting cord has been used, particularly where explosions are desired. Arsonists occasionally improvise using oil-saturated, twisted newspaper trailers or any other tinder type fuel that insures communication through the target premises.
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