Chapter 4: Chemistry and Physics of Fire

Mixable

Capable of mixing without separation.

Endothermic reaction

Reaction that absorbs heat.

Exothermic reaction

Reaction that results in the release of energy in the form of heat.

Continuity

The manner in which a fuel is spread across an area. Horizontal continuity is expressed as either uniform or patchy.

Ignition temperature

The minimum temperature to which a substance must be raised before it will ignite. The piloted ignition temperature is usually much lower than the autoignition temperature. Piloted ignition may be provided by a spark or flame or by raising the general temperature.

Rollover

A condition occurring in a structure fire where the fire extends across the ceiling consuming heated gases. Same as flameover.

Flameover

A condition occurring in a structure fire where the fire extends across the ceiling consuming heated gases. Same as rollover. Flashover A condition during a fire in a room when the contents are heated to their ignition temperature and flames break out over the entire area almost simultaneously.

Moisture content

A description of the amount of moisture contained in a natural fuel, such as brush, grass, or other natural fiber. It is usually expressed as a percentage by weight.

Black fire

A situation where heavy, dense, black smoke is being forcefully emitted by a fire.

Mixture

A substance made up of two or more substances physically mixed together.

Oxidizer

A substance that gains electrons in a chemical reaction.

Backdraft

A type of explosion caused by the sudden influx of air into a mixture of gases, which have been heated above the ignition temperature of at least one of them.

Nonmixable

Not capable of mixing; will separate.

Free radicals

An atom or group of atoms (molecule) that is unstable and must combine with other atoms to achieve stability. Fuel Anything that will burn.

Molecules

Combined groups of atoms. Molecules composed of two or more different kinds of atoms are called compounds.

Energy

The capacity for doing work.

Evaporation

The changing of liquid to a vapor.

Oxidation

The chemical combination of any substance with an oxidizer.

Pyrolysis

The chemical decomposition of matter through the action of heat.

Absolute zero

The lowest temperature that is theoretically possible. The temperature at which all molecular motion ceases. Absolute zero is expressed as −459.67°F, −273.15°C, 0K, and 0°R.

Vertical arrangement

The manner in which a fuel is arranged vertically above ground, divided into ground fuels, surface fuels, and aerial fuels.

Atmospheric pressure

The pressure of the atmosphere exerted on any point, which is 14.7 psi at sea level.

Ambient temperature

The temperature surrounding an object; air temperature.