C H A P T E R 6 Fire Behavior CHAPTER OVERVIEW A fire spreading through a structure is not a random event. Smoke and flame spread follow predictable patterns that are a function of the quantity, shape, and configuration of the fuel, the physical layout of the structure, ventilation in the structure, and other factors, such as how much of a head start the fire has before extinguishment begins. Understanding fire behavior and the art of reading smoke is important for more effective firefighting, but more importantly, knowing how to read a fire and helping predict what it is likely to do can literally mean the difference between life or death for the fire fighter. After students complete this chapter and the related course work, they will be able to describe the characteristics of solid, liquid, and gaseous fuels. They will understand the conditions necessary for combustion to occur, the chemistry of combustion, and the mechanisms of heat transfer. Students will also learn about the characteristics of liquid-fuel fires, gas-fuel fires, and interior structure fires. The principles of understanding how to read smoke will also be covered. The special considerations in structure fires, including flashover and backdraft, will be discussed. OBJECTIVES AND RESOURCES Fire Fighter I Knowledge Objectives After studying this chapter, you will be able to: Describe the chemistry of fire. (pp 142 143) List the three states of matter. (NFPA 5.3.10.A, pp 142 143) List the five forms of energy. (pp 143 144) Explain the concept of the fire triangle. (NFPA 5.3.11.A, p 144) Explain the concept of the fire tetrahedron. (NFPA 5.3.11.A, p 144) Describe the chemistry of combustion. (NFPA 5.3.11.A, pp 144 145) Describe the by-products of combustion. (NFPA 5.3.11.A, p 145) Explain how fires are spread by direct contact, conduction, convection, and radiation. (NFPA 5.3.12.A, pp 146 147) Describe the four methods of extinguishing fires. (p 148) Define Class A, B, C, D, and K fires. (p 148 149) Describe the characteristics of solid-fuel fires. (NFPA 5.3.11.A, pp 149 150) Describe the four phases of a solid-fuel fire: ignition phase, growth phase, fully developed phase, and decay phase. (NFPA 5.3.11.A, pp 150 152) Describe the characteristics of a room-and-contents fire during each of the four phases of a solid-fuel fire. (NFPA 5.3.10.A, 5.3.11.A, pp 152 154) Describe the conditions that cause thermal layering. (NFPA 5.3.12.A, p 155) Describe the conditions that lead to flameover. (NFPA 5.3.12.A, p 155) Describe the conditions that lead to flashover. (NFPA 5.3.12.A, p 155) Describe the conditions that lead to a backdraft. (NFPA 5.3.11.A, pp 155 156) Explain how fire behaves in an enclosed compartment. (NFPA 5.3.11.A, pp 152 154) Describe how fire behaves in modern structures. (p 156) Describe how the wind effect impacts fire behavior. (p 156) Describe the characteristics of liquid-fuel fires. (p 157) Define the characteristics of gas-fuel fires. (pp 157 158) Explain the concept of vapor density. (pp 157 158) Explain the concept of flammability limits. (p 158) Describe the causes and effects of a boiling liquid/expanding vapor explosion (BLEVE). (p 158)
2 Chapter 6 Fire Behavior Describe the process of reading smoke. (pp 158 161) Skill Objectives There are no skill objectives for Fire Fighter I candidates. NFPA 1001 contains no Fire Fighter I Job Performance Requirements for this chapter. Fire Fighter II Knowledge Objectives There are no knowledge objectives for Fire Fighter II candidates. NFPA 1001 contains no Fire Fighter II Job Performance Requirements for this chapter. Skill Objectives There are no skill objectives for Fire Fighter II candidates. NFPA 1001 contains no Fire Fighter II Job Performance Requirements for this chapter. Reading and Preparation Review all instructional materials, including Fundamentals of Fire Fighter Skills, Chapter 6, and all related presentation support materials. Review local firefighting protocols for Chapter 6. Support Materials Dry erase board and markers or chalkboard and chalk LCD projector, slide projector, overhead projector, and projection screen PowerPoint presentation, overhead transparencies, or slides Enhancements Direct the students to visit the Internet at www.firefighter.jbpub.com for online activities. Direct the students to relevant sections in the Student Workbook for application of the content introduced in this chapter. Direct the students to take practice/final examinations in the Navigate Test Prep to prepare for examinations. If you have access to any fire service memorabilia or historical materials, consider bringing them to class to augment discussions of fire service history. TEACHING TIPS AND ACTIVITIES To reinforce points about how smoke and flame spread, conduct a walking tour of a fire training building or a recent structure that caught fire. Point out smoke and burn marks that demonstrate the intensity of the fire and the degree to which smoke banked down from the ceiling toward the floor.
3 Chapter 6 Fire Behavior PRESENTATION OVERVIEW Total time: 2 hours, 48.5 minutes (with enhancements) Activity Type Time Level Pre-Lecture You Are the Fire Fighter Lecture Small Group Activity/Discussion 5 minutes Fire Fighter I I. Introduction Lecture/Discussion 12 minutes Fire Fighter I II. The Chemistry of Fire Lecture/Discussion 25.5 minutes Fire Fighter I III. Classes of Fires Lecture/Discussion 6 minutes Fire Fighter I IV. Characteristics of Solid-Fuel Fires Lecture/Discussion 28.5 minutes Fire Fighter I V. Fire Behavior in Modern Structures Lecture/Discussion 3 minutes Fire Fighter I VI. Wind Effect Lecture/Discussion 1.5 minutes Fire Fighter I VII. Characteristics of Liquid-Fuel Fires Lecture/Discussion 3 minutes Fire Fighter I VIII. Characteristics of Gas-Fuel Fires Lecture/Discussion 4.5 minutes Fire Fighter I IX. Smoke Reading Lecture/Discussion 9 minutes Fire Fighter I X. Summary Lecture/Discussion 10.5 minutes Fire Fighter I Post-Lecture I. Wrap-Up Activities A. Fire Fighter in Action B. Technology Resources Individual Activity/Small Group Activity/Discussion 40 minutes Fire Fighter I and II II. Lesson Review Discussion 15 minutes Fire Fighter I III. Assignments Lecture 5 minutes Fire Fighter I and II
4 Chapter 6 Fire Behavior PRE-LECTURE I. You Are the Fire Fighter Time: 5 Minutes Small Group Activity/Discussion Use this activity to motivate students to learn the knowledge and skills needed to understand fire behavior. Purpose To allow students an opportunity to explore the significance and concerns associated with fire behavior. Instructor Directions 1. Direct students to read the You Are the Fire Fighter scenario found in the beginning of Chapter 6. 2. You may assign students to a partner or a group. Direct them to review the discussion questions at the end of the scenario and prepare a response to each question. Facilitate a class dialogue centered on the discussion questions. 3. You may also assign this as an individual activity and ask students to turn in their comments on a separate piece of paper.
5 Chapter 6 Fire Behavior LECTURE SLIDE TEXT LECTURE NOTE I. Introduction Slides 1 7 CHAPTER 6: Fire Behavior Chapter Objectives Time: 12 Minutes Slides: 1 8 Lecture/Discussion Slide 8 Introduction Fire has been around since the beginning of time. Destruction of lives and property by uncontrolled fires has occurred since just as long. A. Fire has been around since the beginning of time. 1. We continue to depend on fires to fuel the combustion of our society. B. Destruction of lives and property by uncontrolled fires has occurred since ancient times. 1. The United States has one of the highest fire death rates in the industrialized world. 2. An average of 3,005 Americans lose their lives each year, and another 17,500 people are injured. 3. Approximately 1.3 million fires are reported each year, leading to a property loss of $11.7 billion annually. II. The Chemistry of Fire Time: 25.5 Minutes Slides: 9-25 Lecture/Discussion Slide 9 The Chemistry of Fire Understanding the conditions needed for a fire to ignite and grow will increase your effectiveness. Being well trained in fire behavior will allow the fire fighter to control a fire with less water. Slide 10 What Is Fire? Rapid chemical process that produces heat and usually light Fire is neither solid nor liquid. Solids, liquids, and gases can all burn and create flaming combustion. Slide 11 Matter Atoms and molecules Three states Solid Liquid Gas A. Introduction to the Chemistry of Fire 1. Understanding the conditions needed for a fire to ignite and grow will increase your effectiveness as a fire fighter. 2. A well-trained and experienced fire fighter can put out more fire with less water. B. What is fire? 1. Rapid chemical process that produces heat and usually light 2. Fire is neither solid nor liquid. 3. Wood is a solid, gasoline is a liquid, and propane is a gas, but they all burn and create flaming combustion. C. States of Matter 1. Matter a. Made up of atoms and molecules. b. Exists in three states: solid, liquid, and gas 2. Solids a. Have a definite shape b. Most uncontrolled fires are stoked by solid fuels. c. Expand when heated and contracts when cooled d. May change to a liquid state or a gaseous state when heated 3. Liquids a. Assume the shape of their container b. Most will turn into gases when sufficiently heated c. Have a definite volume 4. Gases a. A type of fluid that has neither independent shape nor independent volume; expands indefinitely
6 Chapter 6 Fire Behavior Slide 12 Fuel Form of energy Energy released in the form of heat and light has been stored before it is burned Slide 13 Types of Energy Chemical energy Energy created by a chemical reaction. Exothermic reactions produce heat. Endothermic reactions absorb heat. Slide 14 Types of Energy Mechanical energy Converted to heat when two materials rub against each other. Electrical energy Produces heat while flowing through a wire or another conductive material Slide 15 Types of Energy Light energy Caused by electromagnetic waves packaged in discrete bundles called photons Nuclear energy Created by nuclear fission or fusion Slide 16 Conservation of Energy Energy cannot be created or destroyed by ordinary means. Energy can be converted from one form to another. Slide 17 Conditions Needed for Fire Three basic factors required for combustion: Fuel Oxygen Heat Chemical chain reactions keep the fire burning. b. The mixture of gases in air maintains a constant composition 21 percent oxygen, 78 percent nitrogen, and 1 percent other gases. c. Oxygen is required for us to live and for fires to burn. D. Fuels 1. Fuels are a form of energy. 2. The energy released in the form of heat and light has been stored in the fuel before it is burned. E. Types of Energy 1. Regardless of the form in which the energy is stored, it can be changed from one form to another. 2. Chemical energy a. Energy created by a chemical reaction b. Some of these reactions produce heat and are referred to as exothermic reactions. c. Some of these reactions absorb heat and are referred to as endothermic reactions. d. Most chemical reactions occur because bonds are established between substances or bonds are broken as two substances are chemically separated. e. Heat is also produced whenever oxygen combines with a combustible material. f. If the reaction occurs very rapidly or within an enclosed space, the mixture can heat to its ignition temperature and begin to burn. 3. Mechanical energy a. Converted to heat when two materials rub against each other and create friction b. Heat is also produced when mechanical energy is used to compress air in a compressor. 4. Electrical energy a. Is converted to heat energy in several different ways b. Produces heat while flowing through a wire or another conductive material c. Other examples of electrical energy capable of starting a fire include heating elements, overloaded wires, electrical arcs, and lightning. 5. Light energy a. Caused by electromagnetic waves packaged in discrete bundles called photons b. Candles, light bulbs, and lasers are all forms of light energy. 6. Nuclear energy a. Created by nuclear fission or fusion b. Nuclear reactions release large amounts of energy in the form of heat. c. These reactions can be controlled or uncontrolled. F. Conservation of Energy 1. Energy cannot be created or destroyed by ordinary means. 2. Energy can be converted from one form to another. a. Chemical energy in gasoline is converted to mechanical energy when a car moves down the road. b. The stored chemical energy in the wood of the house is converted into heat and light energy during the fire. G. Conditions Needed for Fire 1. The three basic conditions required to create a fire form the fire triangle. a. A combustible fuel b. Oxygen in sufficient quantities c. A source of heat
7 Chapter 6 Fire Behavior Slide 18 Chemistry of Combustion Almost all fuels are hydrocarbons Consist of both hydrogen and carbon atoms When the fuel combines with oxygen, it produces water and carbon dioxide. Incomplete combustion produces large quantities of deadly gases Slide 19 Chemistry of Combustion Oxidation: combining oxygen with another substance to create a new compound Combustion: combining a substance with oxygen to produce heat and light Pyrolysis: decomposition of a material brought about by heat in the absence of oxygen Slide 20 Products of Combustion Smoke Toxic by-product Composed of: Particles Vapors Gases Inhalation of smoke can cause severe injuries. Slide 21 Fire Spread Direct contact Can quickly spread a fire. Many wildland fires start this way. Slide 22 Fire Spread Conduction Heat transferred from one molecule to another (direct contact) Good conductors absorb heat and transfer it throughout the object. Slide 23 Fire Spread Convection Circulatory movement in areas of differing temperatures Creates convection currents 2. A fourth factor must be added to maintain a self-sustaining fire. a. Chemical chain reactions b. Forms the fire tetrahedron H. Chemistry of Combustion 1. The smallest unit of matter is an atom. a. When atoms of one element combine chemically with atoms of another element, they produce a compound that is made up of molecules. b. Almost all fuel consists of hydrogen (H) and carbon (C) atoms (hydrocarbons). c. When the fuel combines with oxygen, it produces two by-products: water and carbon dioxide. d. Hydrocarbons often contain a wide variety of atoms besides hydrogen and carbon, resulting in various toxic by-products. e. Incomplete combustions result in the production of large quantities of deadly gases and compounds. 2. Oxidation is the process of chemically combining oxygen with another substance to create a new compound. 3. Combustion is a rapid chemical process in which the combination of a substance with oxygen produces heat and light. 4. Pyrolysis is the decomposition of a material brought about by heat in the absence of oxygen. I. Products of Combustion 1. Smoke a. The toxic by-products of combustion b. The three major components of smoke are particles (solids), vapors (aerosols), and gases. c. Unburned particles are lifted in the thermal column. d. Some partially burned particles become part of the smoke because inadequate oxygen is available to allow for their complete combustion. e. Completely burned particles are primarily ash. f. Water and oil-based droplets of water may also become part of the smoke. g. Toxic droplets can be dangerous if inhaled, and some can be poisonous if absorbed through the skin. h. Gases in smoke vary, depending on the fuel being burned. i. Common gases in smoke include carbon monoxide, hydrogen cyanide, and phosgene. j. Gases in smoke displace oxygen causing hypoxia. 2. Heat a. Temperature of the smoke will vary, depending on the conditions of the fire and the distance the smoke travels. b. The inhalation of superheated gases in smoke may also cause severe injuries in the form of severe burns of the skin and the respiratory tract. J. Fire Spread 1. By learning how fires act, fire fighters can learn how to use their suppression forces most effectively. 2. Direct contact can quickly spread a fire. a. Many ground and wildland fires are spread in this manner. 3. Conduction a. The process of transferring heat from one molecule to another b. Objects that are good conductors tend to absorb heat and conduct it throughout the object. c. Applying heat to a poor conductor will result in the heat energy staying in the area of the material to which the heat is applied. d. Materials that are good conductors are rarely the primary means of spreading a fire. 4. Convection a. The circulatory movement that occurs in a gas or fluid with areas of differing temperatures owing to the variation of the density and the action of the gravity. b. The convection currents in a fire involve primarily gases generated by the fire. c. A large fire burning in the open can generate a plume of heated gases and smoke that rises high in the air.
8 Chapter 6 Fire Behavior Slide 24 Fire Spread Radiation Transfer of heat in the form of an invisible wave Travels in all directions Not seen or felt until it strikes an object Slide 25 Methods of Extinguishment Cool the burning material Exclude oxygen Remove fuel Break the chemical reaction d. In a building, the convection currents generated by the fire rise in the room and travel along the ceiling. e. If the fire room has openings, convection may carry the fire outside the room of origin and to other parts of the building. f. Convection currents are influenced by the layout of the building. i. Air flows quickly through an open floor plan versus closed rooms. ii. Strong wind blowing through a structure will create stronger convection currents. iii. Movement of heated gases and fire influenced by wind and ventilation openings. 5. Radiation a. The transfer of heat through the emission of energy in the form of an invisible wave b. Thermal radiation from a fire travels in all directions. c. The effect of thermal radiation, however, is not seen or felt until the radiation strikes an object and heats the surface of the object. K. Methods of Extinguishment 1. Four main methods a. Cooling the burning material b. Excluding oxygen from the fire c. Removing fuel from the fire d. Interrupting the chemical reaction with a flame inhibitor 2. The method most commonly used to extinguish fires is to cool the burning material. III. The Classes of Fire Time: 6 Minutes Slides: 26-29 Lecture/Discussion Slide 26 Classes of Fire Class A Involve ordinary solid combustibles To extinguish, cool the fuel with water Slide 27 Classes of Fire Class B Involve flammable or combustible liquids To extinguish, shut off the fuel supply or use foam to exclude oxygen from the fuel A. Classes of Fire 1. The five classes of fires are: a. Class A b. Class B c. Class C d. Class D e. Class K 2. Class A fires a. Involve ordinary solid combustible materials, such as wood, paper, and cloth b. The method most commonly used to extinguish Class A fires is to cool the fuel with water to a temperature that is below the ignition temperature. 3. Class B fires a. Involve flammable or combustible liquids, such as gasoline, kerosene, diesel fuel, and motor oil b. Fires involving gases, such as propane or natural gas, are also classified as Class B fires. c. These fires can be extinguished by shutting off the supply of fuel or by using foam to exclude oxygen from the fuel.
9 Chapter 6 Fire Behavior Slide 28 Classes of Fire Class C Involve energized electrical equipment Attacking with an extinguishing agent that conducts electricity can result in injury or death. Slide 29 Classes of Fire Class D Involve combustible metals The application of water will result in violent explosions Must be attacked with special agents 4. Class C fires a. Involve energized electrical equipment b. Attacking a Class C fire with an extinguishing agent that conducts electricity can result in injury or death to the fire fighter. 5. Class D fires a. Involve combustible metals, such as sodium, magnesium, and titanium b. The application of water to fires involving these metals will result in violent explosions. c. These fires must be attacked with special agents to prevent explosions and to smother the fire. 6. Class K fires a. Involve combustible cooking oils and fats in kitchens b. Special K class extinguishers are available to handle this type of fire. IV. Characteristics of Solid-Fuel Fires Time: 28.5 Minutes Slides: 30-48 Lecture/Discussion Slide 30 Classes of Fire Class K Involve combustible cooking oils and fats Special extinguishers are available to handle this type of fire. Slide 31 Solid Fuels Most fires encountered involve solid fuels. Do not actually burn in the solid state Must be heated or pyrolyzed May change directly from a solid to a gas Wood does not have a fixed ignition temperature A. Solid Fuels 1. Most fires encountered by fire fighters involve solid fuels. 2. Solid fuels have a definite form and a defined shape. 3. Solid fuels do not actually burn in the solid state. a. Must be heated or pyrolyzed to decompose it into a vapor before it will burn. b. May change directly from a solid to a gas 4. Wood does not have a fixed ignition temperature. a. Temperature depends on the temperature at which enough flammable vapors to produce the burning reaction are produced. b. Also varies according to the manner and rate at which the heat is applied B. Solid-Fuel Fire Development 1. Progress through four phases: a. Ignition b. Growth c. Fully developed d. Decay Slide 32 Solid-Fuel Fire Development Progress through four distinct phases: Ignition Growth Fully developed Decay
10 Chapter 6 Fire Behavior Slide 33 Ignition Phase Heat ignites paper. Heat from the paper sets up a convection current, and the flame produces radiated energy. Slide 34 Growth Phase Kindling starts to burn, increasing convection of hot gases upward. Energy radiates in all directions. Major growth in an upward direction Slide 35 Fully Developed Phase Produces the maximum rate of burning Fire will burn as long as fuel and oxygen remain. Slide 36 Decay Phase Fuel is nearly exhausted. Rate of burning slows. Flames become smoldering embers. Slide 37 Key Principles of Solid-Fuel Fire Development Hot gases and flame tend to rise. Convection is the primary factor in spreading the fire upward. Downward spread occurs primarily from radiation and falling chunks of flaming material. If there is no remaining fuel, the fire will go out. 2. Ignition phase a. Heat ignites the paper. b. Heat from the paper sets up a small convection current, and the flame produces a small amount of radiated energy. c. The combination of convection and radiation serves to heat the fuel around the paper. 3. Growth phase a. Occurs as the kindling starts to burn, increasing the convection of hot gases upward b. Energy generated by the growing fire starts to radiate in all directions. c. Convection of hot gases and the direct contact with the flame cause major growth to occur in an upward direction. 4. Fully developed phase a. Produces the maximum rate of burning b. All available fuel has ignited, and heat is being produced at the maximum rate. c. A fully developed fire burning outside is limited only by the amount of fuel available. d. Lasts only as long as a large supply of fuel is available 5. Decay phase a. The period when the fire is running out of fuel. b. The rate of burning slows down because less fuel is available. c. The flames become smoldering embers, and the fire goes out because of a lack of fuel. 6. Key principles of solid-fuel fire development a. Hot gases and flame are lighter and tend to rise. b. Convection is the primary factor in spreading the fire upward. c. Downward spread of the fire occurs primarily from radiation and falling chunks of flaming material. d. If there is not more fuel above or beside the initial flame that can be ignited by convection or radiated heat, the fire will go out. e. Variations in the direction of upward fire spread will occur if (and when) air currents deflect the flame. f. The total material burned reflects the intensity of the heat and the duration of the exposure to the heat. g. An adequate supply of oxygen must be available to fuel a free-burning fire, although some parts of the flame may have a limited supply of oxygen. Slide 38 Key Principles of Solid-Fuel Fire Development Variations in the direction of fire spread occur if air currents deflect the flame. The total material burned reflects the intensity of the heat and the duration of the exposure to the heat. An adequate supply of oxygen must be available to fuel a free-burning fire.
11 Chapter 6 Fire Behavior Slide 39 Room Contents Synthetic products will usually pyrolyze to volatile products. Newer paints generally burn readily. Carpets ignite readily. Furniture has improved resistance to heat from glowing sources, but it has almost no resistance to ignition from flaming sources. Slide 40 Room-and-Contents Fire: Ignition Phase Flame begins small and localized. Convection of hot gases is the primary means of fire growth. Fire could probably be extinguished with a portable fire extinguisher. Slide 41 Room-and-Contents Fire: Growth Phase Additional fuel is drawn into the fire. Flames spread upward and outward. Radiation starts to play a greater role. Growth is limited by the fuel and oxygen available. Slide 42 Room-and-Contents Fire: Fully Developed Phase Flammable materials are pyrolyzed. Volatile gases are being released. Flashover Combustible materials ignite at once. Temperatures reach 1000 F. C. Characteristics of a Room-and-Contents Fire 1. Room contents a. The synthetic products that are so prevalent today are usually made from petroleum products and will pyrolyze to volatile products (flammable and toxic). b. Newer paints are generally emulsions of latex, acrylics, or polyvinyl, forming a plastic-like coating that will burn readily. c. If walls are not painted, they are usually covered with other flammable, plastic-based wall coatings. d. Carpets have low melting points and ignite readily. i. Smoke released from burning carpets is similar to smoke released from burning tires. e. Smoke consists of unburned fuel that burns explosively when exposed to sufficient oxygen. f. Furniture has improved resistance to heat from glowing sources, such as cigarettes, but it has almost no resistance to ignition from flaming sources. 2. Ignition phase a. The flame begins small and localized. b. As more of the contents in the wastebasket are ignited, a plume of hot gases rises from the waste basket. c. The convection of hot gases is the primary means of fire growth. d. At this point, the fire could probably be extinguished with a portable fire extinguisher. 3. Growth phase a. Additional fuel is drawn into the fire. b. The size of the fire increases. c. The plume of hot gases and flames creates a convection current that carries hot gases to the ceiling of the room. d. Flames begin to spread upward and outward. e. Radiation starts to play a greater role in the growth of the fire. f. The temperature of the room continues to increase as the fire grows. g. The growth is limited by the fuel available or by the oxygen available. h. If flames reach the ceiling they are likely to trigger involvement of the whole room. 4. Fully developed phase a. Temperatures increase to the point where flammable materials in the room are undergoing pyrolysis. b. Large amounts of volatile gases are being released. c. Flashover i. Occurs when the temperature in the room reaches a point where the combustible contents of the room ignite all at once ii. The final stage in the process of fire growth. iii. Not a specific moment, but the transition from a fire that is growing by igniting one type of fuel to another to a fire where all of the exposed fuel in the room is on fire iv. The critical temperature for a flashover to occur is approximately 1000 F. v. Fire fighters cannot survive for more than a few seconds in a flashover. d. Once the room flashes over, the fire is fully developed. e. The amount of fire generated depends on the amount of oxygen available. f. The total fire damage to the room is the result of the intensity of the heat applied and the amount of time the room is exposed to the heat. g. Fire suppression can influence the spread of fire. i. Positive pressure ventilation can force the fire into an area that may not have been involved. ii. Fire follows the path of convection currents of smoke and superheated gases.
12 Chapter 6 Fire Behavior Slide 43 Room-and-Contents Fire: Decay Phase Burning decreases to the point of smoldering fuel. May continue to produce a large volume of toxic gases Slide 44 Thermal Layering Gases rise and form layers. Thermal balance can be upset by: Water applied to a fire creating steam Steam displacing hot gases at top of the room Ventilate while attacking the fire. Avoid directing water at the ceiling. Slide 45 Flameover (Rollover) Spontaneous ignition of hot gases layered in a developing room or compartment fire Flames can extend throughout the room at the ceiling level. A sign that temperature is rising Slide 46 Flashover Caused by rising temperature during flameover Near-simultaneous ignition of combustible material Temperatures are not survivable by fire fighters. Slide 47 Backdraft Caused by introduction of oxygen in an enclosure where superheated gases and contents are hot enough but do not have oxygen to burn Requires a closed box Slide 48 Backdraft Signs and symptoms: Confined fire with a large heat build-up Little visible flame from the exterior Smoke puffing from the building Smoke that seems to be pressurized Smoke-stained windows No smoke showing Turbulent smoke Thick yellowish smoke 5. Decay phase a. Open-flame burning decreases to the point where there is just smoldering fuel. b. The amount of fuel available dwindles as the supply of the fuel becomes exhausted. c. A smoldering fire may continue to produce a large volume of toxic gases, and the compartment may remain dangerous even though the fire appears to be under control. D. Special Considerations 1. Thermal layering a. Gases rise as they are heated and form layers within a room. b. Gases are said to be in thermal balance when they are allowed to seek their own level. i. Temperatures are lowest near the floor. c. The thermal balance can be upset by fire fighters. i. Water applied to a fire creates steam, which expands and rises. ii. The steam can displace the hot gases at the top of the room, forcing them down on fire fighters (and victims). d. Fire fighters must work together to make sure the superheated gases are being vented from the fire room as they are attacking the fire. e. Fire fighters must avoid directing water at the ceiling of the fire except in special circumstances. i. Steam can cause severe burns even through PPE. 2. Flameover (rollover) a. Spontaneous ignition of hot gases that are layered in a developing room or compartment fire b. The upper layer of flammable vapor catches fire and extends throughout the room at the ceiling level. c. A sign that the temperature is rising. i. Continually rising temperature will cause the room and contents to spontaneously and rapidly ignite. d. Flashover is imminent if actions are not taken to change the condition. 3. Flashover a. Caused by rising temperature where flameover is occurring b. Near-simultaneous ignition of most of the exposed combustible material i. Flames are not limited to contents of the room. c. Occurs because the room is filled with a superheated highly flammable gas that ignites d. Temperatures can rise from 480ºF to 1110ºF in less than 3 minutes. e. Flashover temperatures are not survivable for firefighters, even with full personal protective equipment. 4. Backdraft a. Caused by introduction of oxygen into an enclosure where the superheated gases and contents are already hot enough for ignition but do not have sufficient oxygen to combust b. Require a closed box (a room or building that has a limited supply of oxygen) c. If a supply of new oxygen is introduced into the room, explosive combustion can occur, exerting enough force to cause great injury or death to fire fighters. d. Signs and symptoms of an impending backdraft: i. Any confined fire with a large heat build-up ii. Little visible flame from the exterior iii. A living fire smoke puffing from the building that looks like it is breathing iv. Smoke that seems to be pressurized v. Smoke-stained windows (an indication of a significant fire) vi. No smoke showing vii. Turbulent smoke viii. Thick yellowish smoke (containing sulfur compounds)
13 Chapter 6 Fire Behavior e. Triggered when oxygen is introduced into a room that was lacking sufficient oxygen to support a fire. i. Can occur when a window breaks or a closed door is open. f. Fire fighters must coordinate the application of water on the fire with efforts to ventilate the fire. V. Fire Behavior in Modern Structures Time: 3 Minutes Slides: 49-50 Lecture/Discussion Slide 49 Fire Behavior in Modern Structures Modern construction has altered fire behavior due to: Building construction Widespread use of plastics and petroleum-based products for furniture and accessories Slide 50 Fire Behavior in Modern Structures Fire in a modern structure progresses to the fully developed phase quickly. Fire fighters introduce a fresh supply of oxygen by opening the front door. Fire rapidly grows and spreads. A. Modern construction techniques have altered fire behavior due to two major changes: 1. Building construction a. Houses built in the last 20 to 30 years are energy and cost efficient. i. Contain insulation ii. Sealed to prevent air exchange b. Lightweight manufactured building components i. Contain highly flammable products ii. Burn hotter and faster than an older house made of wood iii. Lightweight frames fail faster than heavier wood frames of older homes. 2. Widespread use of plastics and petroleum-based products for furniture and accessories a. Contain more energy than wood and natural fiber furnishings b. Release huge quantities of thick dark smoke when burning c. Combustion requires huge amounts of oxygen to maintain the growth phase. B. Fire in a modern structure progresses to the fully developed phase quickly. 1. Encounters decreased levels of oxygen a. Growth of fire decreases along with temperature. b. Decay is due to an insufficient supply of oxygen. 2. Fire fighters introduce a fresh supply of oxygen by opening the front door. a. Fire rapidly grows and spreads. b. Prevention includes: i. Proper timing in implementing building entry ii. Ventilation iii. Application of water to the fire VI. Wind Effect Time: 1.5 Minutes Slide: 51 Lecture/Discussion Slide 51 Wind Effect Wind influences fire behavior and may affect which side of the structure to enter. Size-up of a structure fire must include a wind evaluation regardless. A. Wind influences the behavior of fire and may affect which side of the structure to enter. B. Potential wind effect may not be evident during the initial size-up. 1. Size-up of a structure fire must include a wind evaluation regardless. 2. Opening up a door or window on the side of the building in which a strong wind is blowing may result in rapid fire spread toward the opposite side of the building.
14 Chapter 6 Fire Behavior VII. Characteristics of Liquid-Fuel Fires Time: 3 Minutes Slides: 52-53 Lecture/Discussion Slide 52 Liquid-Fuel Fires A liquid must be converted to a gaseous state before it will burn. Conditions required for ignition: Fuel-air mixture within flammable limits An ignition source with sufficient energy Sustained contact between ignition source and fuel-air mixture Slide 53 Liquid-Fuel Fires Flammability is determined by compound with the lowest ignition temperature. Flash point: lowest temperature at which vapor is produced Flame point: lowest temperature at which sufficient vapors are produced A. Characteristics of Liquid-Fuel Fires 1. Liquids must be converted to a gaseous state before they will burn. 2. Three conditions must be present for a vapor and air mixture to ignite: a. The fuel and air must be present at a concentration within a flammable range. b. There must be an ignition source with enough energy to start ignition. c. The ignition source and the fuel mixture must make contact for long enough to transfer the energy to the fuel-air mixture. 3. The flammability of the mixture is determined by the compound with the lowest ignition temperature. 4. The amount of liquid that will be vaporized is related to the volatility of the liquid. a. Liquids that have a lower molecular weight will tend to vaporize more readily than liquids with a higher molecular weight. b. As more of the liquid vaporizes, the mixture may reach a point where enough vapor is present to create a flammable vapor-air mixture. 5. The flash point is the lowest temperature at which a liquid produces a flammable vapor. 6. The flame point (fire point) is the lowest temperature at which a liquid produces enough vapor to sustain a continuous fire. IIX. Characteristics of Gas-Fuel Fires Time: 4.5 Minutes Slides: 54-56 Lecture/Discussion Slide 54 Vapor Density Weight of a gas fuel Gas with vapor density less than 1 will rise. Gas with vapor density greater than 1 will settle. Knowing vapor density helps predict where the danger of ignition will be. Slide 55 Flammability Limits Below the lower flammability limit Too little fuel = too lean Above the upper flammability limit Too much fuel = too rich A. Vapor Density 1. The weight of a gas fuel 2. Measures the weight of gas compared with air 3. The weight of air is assigned the value of 1. 4. A gas with a vapor density of less than 1 will rise to the top of a confined space or rise into the atmosphere. 5. A gas with a vapor density greater than 1 is heavier than air and will settle close to the ground. 6. Fire fighters need to understand the vapor density of the escaping fuel so that they can take actions to prevent the ignition of the fuel and allow the gaseous fuel to safely escape into the atmosphere. B. Flammability Limits 1. Mixtures of flammable gases and air will burn only when they are mixed in certain concentrations. 2. If too much fuel is present in the mixture, there will not be enough oxygen to support the combustion process. 3. If too little fuel is present in the mixture, there will not be enough fuel to support the combustion process. 4. The terms flammability limits and explosive limits are used interchangeably. 5. The lower flammable limit refers to the minimum amount of gaseous fuel that must be present in a mixture for it to be flammable. 6. The upper flammable limit of carbon monoxide is 74 percent.
15 Chapter 6 Fire Behavior Slide 56 BLEVE Occurs when a vessel storing liquid fuel under pressure is heated excessively The vessel can then fail, releasing all of the heated fuel in a massive explosion. C. BLEVE 1. A BLEVE occurs when a liquid fuel is stored in a vessel under pressure. a. If this sealed container is subjected to heat from a fire, the pressure that builds up from the expansion of the liquid will prevent the liquid from evaporating. b. As heating continues, the temperature inside the vessel may exceed the boiling point of the liquid. c. The vessel can then fail, releasing all of the heated fuel in a massive explosion. d. The released fuel instantly becomes vaporized and ignited as a huge fireball. 2. The key to preventing a BLEVE is to cool the top of the tank. IX. Smoke Reading Time: 9 Minutes Slides: 57-62 Lecture/Discussion Slide 57 Smoke Reading Enables the fire fighter to learn where the fire is, how big it is, and where it is moving Fires are dynamic events. Smoke is the fuel all around you at a fire. The best place to observe patterns of smoke is outside the fire building. Slide 58 Smoke Reading Determining the key attributes of smoke Smoke volume Smoke velocity Smoke density Smoke color A. Introduction to Smoke Reading 1. Being able to read smoke enables the fire fighter to learn where the fire is, how big it is, and where it is moving. 2. Fires are dynamic events. a. What you see this minute will probably change quickly. b. The ability to read smoke gives fire fighters information that they need to mount a more effective attack on a fire and may help to save their lives or the lives of the building s occupants. 3. Smoke a. Most of the fuel in a flashover is in the form of smoke. b. Both flashovers and backdrafts are fed by superheated fuel, which takes the form of smoke. c. It is helpful to think of smoke reading as studying the fuel that is all around you at a fire. d. Composed of particles, vapors, and gases and largely comprises the fuel that will be burned when heated sufficiently in the presence of oxygen 4. The best place to observe patterns of smoke is from the outside the fire building. B. Step 1: Determining the Key Attributes of Smoke 1. The four key attributes are volume, velocity, density, and color. a. The volume of smoke gives an idea of how much fuel is being heated to the point that it gives off gas. b. The velocity (speed) at which smoke is leaving the building suggests how much pressure is accumulating in the building. i. When smoke is pushed by heat, it will rise and then slow gradually. ii. When smoke is pushed by volume, it will slow immediately. iii. Laminar smoke flow is a smooth or streamlined flow, indicating that the building and its contents are absorbing heat and pressure is not too high. iv. Turbulent smoke flow is agitated, boiling, or angry and is caused by rapid molecular expansion of the gases within the smoke and the restrictions created by the building. v. Turbulent smoke contains an immense amount of energy, and when this energy reaches a point where the smoke is heated to its ignition temperature, flashover will occur. vi. Compare the velocity of the smoke leaving different openings of the building to determine the location of the fire. c. Smoke density suggests how much fuel is contained in the smoke. i. Dense smoke can produce a powerful flashover when conditions are right. ii. Dense smoke contains many poisonous substances. d. Smoke color i. Gives some indication as to what stage the fire is in and which substances are burning
16 Chapter 6 Fire Behavior Slide 59 Smoke Reading Determine the influences on the key attributes Size of the structure Wind conditions Thermal balance Fire streams Ventilation openings Sprinkler systems Slide 60 Smoke Reading Determine the rate of change Changes in the four key attributes indicate changes in the fire. Predict the event Consider the key attributes, what influences them, and their rate of change Communicate key parts to the company officer Slide 61 Smoke Reading Through a Door Indications of a hot fire may mean you are dealing with fire in a decay phase Sign of great danger Addition of oxygen results in violent backdraft Fires can be dangerous even with little smoke. ii. Most solid materials will emit a white-colored smoke when they are first heated. iii. As materials dry out, the color of the smoke emitted changes. iv. Burning wood changes to tan or brown. v. Plastics and painted or stained substances emit a gray smoke vi. As materials become hotter, the smoke becomes blacker. vii. White smoke that is lazy or slow indicates early heating. viii. White smoke that has its own pressure indicates smoke from a hot fire that has traveled for some distance. 2. Black fire a. High-volume, high-velocity, turbulent, ultradense, black smoke b. Produces as much destruction as flames would c. Charring and heat damage to steel and concrete d. Presence indicates impending autoignition and flashover C. Step 2: Determine What is Influencing the Key Attributes 1. The following considerations must be made: a. Size of the structure b. Wind conditions c. Thermal balance d. Fire streams e. Ventilation openings f. Sprinkler systems D. Step 3: Determine the Rate of Change 1. Flames indicate what is happening now, whereas smoke gives a more complete picture of the characteristics of the fire and where it is going. 2. The changes to the four key attributes (volume, velocity, density, and color) indicate changes in the fire. E. Step 4: Predict the Event 1. To assess the size and location of the fire: a. Consider the key attributes. b. Consider the influences of the key attributes. c. Determine the rate of change. d. This information should help determine location, size, and potential for the fire. e. Communicate the key parts of these observations to the company officer. 2. One way to become more proficient in smoke reading is to review videos of fires. F. Smoke Reading through a Door 1. Indications of a hot fire may mean you are dealing with a fire in a decay phase. a. This is a sign of great danger. b. Once the fire receives oxygen, it will produce a violent backdraft. c. Fires can be dangerous even when little smoke is showing. 2. Watch what the smoke does when you open a door. a. If smoke exits through the top half of the door and clean air enters through the bottom half of the opening, then the fire is probably on the same level. This is sometimes called smoke that has found balance. b. If smoke rises and the opening clears out, the fire is probably above the level of the opening. c. If smoke thins but still fills the door, the fire is below the level of the opening. Slide 62 Smoke Reading Through a Door If smoke exits through the top half and clean air enters through the bottom half If smoke rises and the opening clears If smoke thins but still fills the door
17 Chapter 6 Fire Behavior Slide 63 Summary Fire is a chemical process. Matter exists in three states: solid, liquid, and gas. Fuels are a form of energy. Three basic conditions are needed for fire: fuel, oxygen, and heat. Smoke is the by-product of fire. Slide 64 Summary Fire can spread by direct contact, conduction, convection, and radiation. Direct contact is a flame touching a fuel. Conduction is the transfer of heat through matter. Convection is a circulatory movement in a gas or fluid. Slide 65 Summary Radiation transfers heat via invisible waves. The four principle methods of fire extinguishment are cooling the fuel, excluding oxygen, removing the fuel, and interrupting the chemical reaction. The four categories of fire are Class A, Class B, Class C, Class D, and Class K. Slide 66 Summary Most fires involve solid fuels. Solid-fuel fires develop in four phases: ignition phase, growth phase, fully developed phase, and decay phase. Growth of fires depends on room characteristics and contents. X. Summary Time: 10.5 Minutes Slides: 63-69 Lecture/Discussion A. Fire is a chemical process, producing heat and light. B. Matter exists in three states: solid, liquid, and gas. C. Fuels are a form of energy, existing in many forms, including chemical, mechanical, electrical, light, or nuclear. D. Three basic conditions are needed for fire: fuel, oxygen, and heat. E. Smoke is the by-product of fire and includes three components: particles, vapors, and gases. F. Fire can spread by direct contact, conduction, convection, and radiation. G. Direct contact is a flame touching a fuel. H. Conduction is the transfer of heat through matter. I. Convection is a circulatory movement in a gas or fluid. J. Radiation transfers heat via invisible waves. K. The four principle methods of fire extinguishment are cooling the fuel, excluding oxygen, removing the fuel, and interrupting the chemical reaction. L. The four categories of fire are: 1. Class A: solid combustible materials 2. Class B: flammable or combustible liquids 3. Class C: energized electrical equipment 4. Class D: combustible metals 5. Class K: combustible cooking oils and fats M. Most fires involve solid fuels. N. Solid-fuel fires develop in four phases: 1. Ignition phase 2. Growth phase: fire starts to burn 3. Fully developed phase: all available fuel has ignited 4. Decay phase: Burning slows due to less fuel O. Growth of fires depend on characteristics and contents of rooms. P. Special considerations of room-and-contents fires are: 1. Thermal layering: property of gas in an enclosed space 2. Flameovers: spontaneous ignition of hot gases in the upper level of a room 3. Flashovers: near-simultaneous ignition of combustible materials in an enclosed space 4. Thermal layering of gases 5. Backdrafts: oxygen being introduced to a fire in the decay phase Slide 67 Summary Special considerations of room-andcontents fires are thermal layering, flameovers, flashovers, thermal layering, and backdrafts. Modern structures are more tightly sealed, are constructed of lighter-weight materials, and contain more plastics.
18 Chapter 6 Fire Behavior Slide 68 Summary Liquid-fuel fires require fuel, air, an ignition source, and contact between fuel and the ignition. Flammable vapors are described in terms of vapor density and flammability limits. A boiling liquid/expanding vapor explosion (BLEVE) occurs in a vessel containing both boiling liquid and vapor. Q. Modern structures are more tightly sealed, are constructed of lighter-weight materials, and contain more plastics. R. Liquid-fuel fires require fuel, air, an ignition source, and contact between fuel and the ignition. S. Flammable vapors are described in terms of vapor density and flammability limits. T. A BLEVE occurs in a vessel that contains both boiling liquid and vapor. U. Fire prediction and development stage depend on assessment of smoke volume, velocity, density, and color. V. Smoke reading involves the effect of the building, weather, and ventilation. Slide 69 Summary Fire prediction and development stage depend on assessment of smoke volume, velocity, density, and color. Smoke reading involves the effect of the building, weather, and ventilation.
19 Chapter 6 Fire Behavior POST-LECTURE I. Wrap-Up Activities Time: 40 Minutes and II Small Group Activity/Individual Activity/Discussion Fire Fighter in Action and/or Fire Fighter II in Action This activity is designed to assist the student in gaining a further understanding of fire behavior. The activity incorporates both critical thinking and the application of fire fighter knowledge. Purpose This activity allows students an opportunity to analyze a firefighting scenario and develop responses to critical thinking questions. Instructor Directions 1. Direct students to read the Fire Fighter in Action and/or Fire Fighter II in Action located in the Wrap-Up section at the end of Chapter 6. 2. Direct students to read and individually answer the quiz questions at the end of the scenario. Allow approximately 10 minutes for this part of the activity. Facilitate a class review and dialogue of the answers, allowing students to correct responses as needed. Use the answers noted below to assist in building this review. Allow approximately 10 minutes for this part of the activity. 3. You may also assign these as individual activities and ask students to turn in their comments on a separate piece of paper. Technology Resources This activity requires students to have access to the Internet. This may be accomplished through personal access, employer access, or a local educational institution. Some community colleges, universities, or adult education centers may have classrooms with Internet capability that will allow for this activity to be completed in class. Check out local access points and encourage students to complete this activity as part of their ongoing reinforcement of firefighting knowledge and skills. Purpose To provide students an opportunity to reinforce chapter material through use of online Internet activities. Instructor Directions 1. Use the Internet and go to www.firefighter.jbpub.com. Follow the directions on the Web site to access the exercises for Chapter 6. 2. Review the chapter activities and take note of desired or correct student responses. 3. As time allows, conduct an in-class review of the Internet activities and provide feedback to students as needed. 4. Be sure to check the Web site before assigning these activities because specific chapter-related activities may change from time to time. II. Lesson Review Time: 15 Minutes Discussion Note: Facilitate the review of this lesson s major topics using the review questions as direct questions or overhead transparencies. Answers are found throughout this lesson plan. Fire Fighter I A. What are the three states of matter and how do they impact fire behavior? B. What is the difference between the fire triangle and the fire tetrahedron? C. What are the three methods of heat transfer? D. What are the five classes of fire?