1. vocabulary
ARSON
AND
EXPLOSIVES

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

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

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

5. 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…..

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

7. 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.

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

10. 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.

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

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

13. 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.

14. 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.

15. 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.

16. 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

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

18. 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