vocabulary ARSON AND EXPLOSIVES

Vocabulary for this section: I. The Chemistry of Fire Vocabulary for this section: Modus operandi oxidation Energy Combustion Heat of combustion

Exothermic reaction Endothermic reaction Ignition temperature Flash point Pyrolysis Flammable range Glowing combustion

Modus operandi: An offender’s pattern of operation. How does the arsonist do their work?

Oxidation The combination of oxygen with other substances to produce new substances. CH4 + O2  CO2 + H2O + energy Methane oxygen carbon water (heat & light) gas dioxide Notice that oxygen is a reactant and is found as a diatomic molecule…..

Not all oxidation reactions end in a fire Some are slow 4Fe + 3O2  2Fe2O3 Iron oxygen gas iron III oxide Otherwise known as “rusting”

Energy The ability to do work. The quantity of heat (a type of energy) from a chemical reaction comes from the breaking and formation of chemical bonds.

Combustion The rapid combination of oxygen with another substance accompanied by the production of heat and light.

Heat of Combustion The heat evolved when a substance is burned in oxygen (in kCal/mol or BTU/gal) These reactions are exothermic, meaning heat is liberated. The reactants have more energy than the products.

Exothermic reactions Require a HIGH IGNITION TEMPERATURE, or minimum temperature at which a fuel will spontaneously ignite.

Endothermic reaction: a chemical transformation in which heat energy is absorbed from the surroundings

Flashpoint The minimum temperature at which a liquid fuel will produce enough vapor to burn. The ignition temperature is significantly higher than the flash point. Ex: gasoline has a flash point of -50°F; however it takes an ignition temperature of 495°F to start a gasoline fire.

Pyrolysis The decomposition of organic matter by heat, or the chemical breakdown of solid material. Wood, or any other solid fuel will burn only when it is exposed to heat that is hot enough to decompose the solid into gaseous products.

Flammable Range The entire range of possible gas or vapor fuel concentrations in air that are capable of burning. Gaseous fuel and air will burn only if their composition lies within certain limits. If the fuel concentration is too low (lean) or too great (rich), combustion will not occur. The flammable range for gasoline is 1.3 to 6 percent.

Glowing combustion AKA “smoldering” is burning at the fuel-air interface. Examples are red-hot charcoal or a burning cigarette. In other words, burning without a flame

Spontaneous combustion A fire caused by a natural heat-producing process in the presence of sufficient air and fuel.

Examples Hay stored in barns if not properly ventilated can grow bacteria whose activities will generate heat. The heat can build to levels that will support combustion. Improperly vented containers containing rags soaked with certain types of oils