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Ch 5 Fire Dynamics
Fire Science
| Question | Answer |
|---|---|
| To understand how to control or predict fire behavior, FF must gain a scientific understanding of | Combustion, Fire, heat, Temperature |
| Fire | a rapid oxidation process which gas phase chemical reaction resulting in the evolution of light and heat in vary intensities |
| Combustion | A chemical process of oxidation that occurs at a rate fast enough to produce heat and light in the form of either a glow or flame |
| Heat | Form of energy associated with the motion of atoms or molecules within a fuel which is transferred from one body to another as a result of a temperature difference between the bodies |
| Temperature | Measure of the average kinetic energy of the particles in an sample of matter, expressed in terms of units |
| Fuel | A material that will maintain combustion under specified environmental conditions |
| Oxidizer | Any material that readily yields oxygen or other oxidizing gas, or that readily reacts to promote or initiate combustion of combustible materials |
| Matter | Anything that occupies space and has mass |
| Energy | Capacity to perform work, when a force is applied to an object |
| Physical change occurs when | substance remains chemically the same but change in a size, shape, or appearance |
| Chemical Reaction occurs | substance changes from one type of matter into another |
| Oxidation | chemical reaction involving the combination of an oxidizer such as oxygen in the air with other materials |
| Potential Energy | amount of energy that an object can release at some point in the future |
| Heat of combustion | Total amount of thermal energy that could be generated by combustion reaction if a fuel were completely burned. Kilojoules per gram or megajoules per kilogram |
| Rate at which fuels release energy over time depends on | Chemical composition, Density of fuel, Arrangement, Availability of oxygen |
| Kinetic Energy | energy that a moving object possesses |
| Thermal Energy | Kinetic energy associated with the random motions of the molecules of a material or object |
| Joules | Measures energy. 1 gram of water by 1 degree Celsius is 4.2J |
| BTU | British thermal Unit. measurement of heat. amount of heat to raise the temp of 1 pound of water by 1 degree F. 1055J equals 1 Btu |
| Exothermic Reaction | A reaction or process that releases thermal energy or heat |
| Endothermic reaction | A reaction or process that absorbs thermal energy or heat |
| Fire Triangle | three elements necessary for combustion to occur. remove any one and fire will be extinguished: Fuel, Oxygen, heat |
| Fire Tetrahedron | includes a chemical chain reaction, explains flaming or gas phase combustion |
| Ignition | Fuel must be in a gaseous state to burn, heat transfers to a liquid or solid the substance temperature increases, and the substance starts to convert to gaseous state |
| Pyrolysis | Chemical decomposition of a solid material by heating, precedes combustion of a solid fuel |
| Vaporization | physical change in liquids |
| Piloted ignition | Moment when a mixture of fuel and oxygen encounters an external heat source with sufficient heat or thermal energy to start the combustion reaction |
| Autoignition | without any external flame or spark to ignite the fuel gasses or vapors. Fuels surface heats to the point at which combustion occurs |
| AIT | Autoignition Temperature. minimum temperature at which a fuel in the air must be heated to start self-sustained combustion. Always higher than its piloted ignition temperature |
| Two modes of combustion | flaming and nonflaming |
| Flaming Combustion | produces visible flames above materials surface, gaseous fuel mixes with oxygen in the correct ratio and heats to ignition temperature, requires liquid or solid fuels to convert to a gas through addition of heat |
| How is a fire created | Combustion begins with ignition. heat source pyrolyzes a fuel creating fuel gases. Gas mix with oxygen and ignite creating a fire |
| Open burning | Fire burning in the open with no restrictions to its oxygen supply |
| Entrain | to draw in and transport solid particles or gases by the flow of a fluid |
| Due to buoyancy heat transfer | expands and begin to rise and move away from the fire, density of the hot combustion product is less than the surrounding air, Combustion product floats on the denser cool air surrounding the fuel creating layers of smoke and fuel gases |
| Nonflaming combustion | occurs slowly and at a lower temperature which produces a glow in the material surface |
| Products of Combustion | Materials produced and released during burning (heat and smoke) |
| What causes the most fire deaths | toxic gases found in smoke or lack of oxygen |
| Smoke is an aerosol comprised of | Gases, vapor, Solid particulates |
| Incomplete combustion | inefficient combustion of fuel; less efficient the combustion the more products of combustion are produced. produces smoke and ash |
| Complete combustion of methane in air produces | heat, Light, water vapor, CO2 |
| Structural fires involve two basic types of fuel | Natural and synthetic |
| Fire reactions with limited air supply | higher level of incomplete combustion which produces more smoke (toxic and flammable gases, Vapors, Particulates that comprise smoke) |
| Carbon Monoxide | Colorless and odorless formed by the incomplete combustion of carbon. cause of death in civilian fatalities, Chemical asphyxiant, attached to hemoglobin 200x more effectively than oxygen |
| Hydrogen cyanide | Colorless, toxic and flammable liquid until it reaches 79 degrees Fahrenheit. Gas with a faint odor similar to bitter almonds, produced by nitrogen bearing substances. 35x more toxic than CO. prevents blood cells from using oxygen targets heart and brain |
| Following materials produce HCN | Natural fibers, resins such as carbon fiber or fiberglass, Synthetic polymers, synthetic rubbers |
| materials that produce HCN are found in | Furniture, Bedding, insulation, Carpets, clothing, common building materials and household items |
| Carbon Dioxide | complete combustion of organic materials, displaces oxygen which creates an oxygen deficient atmosphere, Increased respiratory rate |
| Pressure | force per unit of area applied perpendicular to a surface 1 atm (101Kpa) at standard temp (68 degrees F, 20 degrees C) indicates the amount of pressure the atmosphere supplies to the surface of the earth |
| Gases always move from areas of | higher pressure to areas of lower pressure |
| As pressure difference between high- and low-pressure areas increase | speed with which the gases move from high to low also increases |
| Convective Flow | Heat from fire increases the pressure of the surrounding gases, Increased pressure will seek to expand and equalize the area of lower pressure. heated gases will rise and travel up and out, Cooler and fresher air will travel in toward fire |
Created by:
Jwbarnett27