Fire-Behavior-Lecture.ppt
- 2. Fire Behavior • Introduction • Physical Science – Definition – Basic Components – Fire Tetrahedron – Fire Extinguishment Theory – Classification of Fires • Other References
- 3. Introduction • Fire has been both a help and hindrance to mankind – heated homes, cooked our food, helped us to become technologically advanced • Firefighters should have a basic understanding of the science of fire and the factors that affect its ignition, growth, and spread to perform safely and effectively in any firefighting function
- 4. Physical Science • Definition – Fire is a rapid oxidation of combustible materials accompanied by the released of heat and light at various intensities. – Pyrolysis is the chemical change brought about by heat. • Basic Components: – Oxidizing Agent (Oxygen) • those materials that yield oxygen or other oxidizing gases during the course of a chemical reaction • bromates, bromine, chlorates, chlorine, fluorine, iodine, nitrates, nitric acid, nitrites, perchlorates, permanganates, peroxides
- 5. Physical Science (Cont…) – Heat • a form of energy; energy in transit • sources – chemical – chemical reactions generate heat – electrical – current flow generates heat; ex. overloading, static, lightning – mechanical – friction and compression – nuclear – fission or fusion of atoms • ways on how heat supports the combustion reaction – causes the pyrolysis or vaporization of solid and liquid fuels and the production of ignitable vapors or gases – provides the energy necessary for ignition – causes the continuous production and ignition of fuel vapors or gases so that the combustion reaction can continue
- 6. Physical Science (Cont…) – Fuel • the material or substance being oxidized or burned in the combustion process • also known as the reducing agent • forms – Solid – coal, wood, plastic, paper, cloth, wax, grease, leather, cork, etc – Liquid – gasoline, kerosene, turpentine, alcohol, paint, varnish, oil, etc – Gas – natural gas, propane, butane, hydrogen, acetylene, carbon monoxide, etc – Chemical Chain Reaction • a series of reactions that occur in sequence with the results of each individual reaction being added to the rest
- 7. Physical Science (Cont…) The Fire Tetrahedron
- 8. Physical Science (Cont…) • Fire Extinguishment Theory – Temperature Reduction – Fuel Removal – Exclusion of Oxygen – Chemical Flame Inhibition
- 9. Physical Science (Cont…) • Classification of Fire – Class A – Ordinary combustible materials • wood, paper, cloth, paper, rubber, and many plastics • can be extinguished by temperature reduction – Class B – Flammable/combustible liquids • gasoline, kerosene, alcohol, paint, varnish, etc • oxygen exclusion is the most effective extinguishing method • removal of fuel and temperature reduction can also be applied, as well as interruption of the chain reaction by dry chemical agents
- 10. Physical Science (Cont…) • Classification of Fire (Cont…) – Class C – Energized electrical fires • household appliances, computers, transformers, and overhead transmission lines • can sometimes be controlled by a non-conducting extinguishing agent such as halon, dry chemical, or CO2 • safest procedure is to de-energize high voltage circuits and fight the fire appropriately depending upon the fuel involved
- 11. Physical Science (Cont…) • Classification of Fire (Cont…) – Class D – Combustible metal fires • aluminum, magnesium, titanium, zirconium, sodium., potassium, etc • hazardous in powdered form • water and other common extinguishing agents are ineffective due to extremely high temperature • special extinguishing agents are available for control of fire in each of the metals
- 12. Physical Science (Cont…) • Mechanism of Heat Transfer – Conduction • the point-to-point transmission of heat energy • result of direct contact with a heat source
- 13. Physical Science (Cont…) • Mechanism of Heat Transfer (Cont…) – Convection • the transfer of heat energy by the movement of heated liquids or gases • there is movement or circulation of a fluid
- 14. Physical Science (Cont…) – Radiation • the transmission of energy as an electromagnetic wave without an intervening medium
- 15. Physical Science (Cont…) • Phases of Fire – Incipient • the oxygen content in the air has not been significantly reduced • fire maybe producing a flame temperature well above 1000OF (537OC), but the room temperature may be only slightly increased – Free-Burning • oxygen-rich air is drawn into the flame as convection carries the heat to the uppermost regions of the confined area • temperature in the upper regions can exceed 1300OF (700OC) • it continues to consume the free oxygen until it reaches the point where there is insufficient oxygen to react with the fuel
- 16. Physical Science (Cont…) • Phases of Fire (Cont…) – Smoldering • flame may cease to exist if the area of confinement is sufficiently airtight • burning is reduced to glowing embers • fire will continue to smolder, and the room will completely fill with dense smoke and gases of combustion at a temperature of well over 1000OF (537OC) • creates the possibility of a backdraft (an explosive ignition resulting from the combination of air with hot gases)