Fuel Study Guide for McGraw-Hill's Firefighter Exams
Fuel (Combustible Matter—Solids, Liquids, And Gases)
Combustible matter may be in a solid, liquid, or gaseous state.
Solids are materials with defined volume, size, and shape at a given temperature. Examples are wood and wood products (paper, cardboard), carbon-containing materials (coal, charcoal), plastics (polyvinyl chloride, epoxies), textiles (cotton, wool, rayon), and combustible metals (magnesium, aluminum).
Wood and Wood Products
Wood and wood products are the most common solids encountered by firefighters. They are considered Class A-type materials and require water or water solutions to cool them below their ignition temperature and extinguish them. The average ignition temperature of wood is approximately 400°F. Major components are carbon, hydrogen, and oxygen.
Factors Affecting the Ignition and Combustibility of Wood and Wood Products
Many factors influence the ignition and combustibility of wood and wood products, the most important of which are cited below.
- Physical form (size, form, shape, mass)—The greater the mass in relation to surface area, the more heat energy will be required to ignite it and the slower the rate of burning will be once ignited.
- Thermal inertia—Resistance to heating, generally based on the specific gravity and density of the material, is known as its thermal inertia. Materials with a low thermal inertia (low specific gravity and density) will heat up and ignite more readily than materials with a high thermal inertia, high specific gravity, and density.
- Moisture content—Wet wood is more difficult to ignite than dry wood. Wood is very difficult to ignite when the moisture content rises above 15 percent.
- Species—Low-density softwoods (pine) will ignite at lower temperatures than high-density hardwoods (oak).
- Ignition temperature—The minimum temperature to which a material must be heated for it to ignite and be self-sustaining without an external input of heat is known as the ignition temperature.
- Piloted-ignition temperature—Ignition temperature caused with the assistance of an external (flame, spark) heat source is known as the piloted-ignition temperature. It is usually considerably lower than the ignition temperature.
- Arrangement—The term arrangement refers to the spacing of the fuel material. Tightly stacked lumber is much more difficult to ignite and will burn at a slower rate than lumber loosely arranged.
- Time—Wood and wood products must be exposed to heat for a certain period of time before combustible vapors are produced and ignite.
- Heat Source—A heat source provides heat. For wood products heat sources include steam pipes, matches, and a blowtorch.
- Rate of Heating—The rate or speed at which a substance becomes heated may be constant or sporadic.
- Oxygen—Oxygen-enriched atmospheres (greater than 21 percent in air) enhance burning, whereas oxygen-deficient atmospheres (less than 15 percent in air) will generally not support combustion.
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