Shasta College Fire Academy, IFSTA Chapter 5
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Why does understanding the physical science of fire help firefighters?
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It helps in predicting potential fire behavior.
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A substance that is chemically the same but has changed in size shape or appearance has undergone what kind of change?
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Physical Change
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A chemical reaction is when a substance...
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Changes from one type of matter to another.
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The energy an object can release at a point in the future is called what?
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Potential Energy
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What form of energy is possessed by a moving object?
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Kinetic Energy
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The potential chemical energy of a fuel in fire behavior is released as what?
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Heat
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All fires involve a heat-producing chemical reaction between some type of fuel and an ______.
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Oxidizer
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A chemical reaction involving the combination of an oxidizer such as oxygen in air, with other materials.
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Oxidation
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All energy can change from one type to another. (True/False)
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True
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List the 7 types of energy.
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Thermal Chemical Mechanical Electrical Light Nuclear Sound
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A ______ reaction emits energy as it occurs.
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exothermic
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What type of reaction happens as water becomes vapor during fire suppression?
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Endothermic
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Temperature increase in a fuel and sufficient heat transfer are both parts of the process of what?
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Ignition
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What form of ignition occurs without an external spark or flame to ignite fuel?
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Autoignition
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What mode of combustion produces a visible flame above a material's surface?
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Flaming
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In what mode of combustion is a smoldering glow on a material's surface produced?
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Nonflaming
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In the fire triangle removing any of the necessary elements causes the fire to do what?
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extinguish
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The autoignition temperature of a substance is always lower than its piloted ignition temperature. (True/False)
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False; Higher
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Combustion can occur without fire. (True/False)
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True
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_____ is a chemical reaction while ____ is one possible result of combustion.
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Combustion; Fire
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The fire triangle contains what three components?
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Oxygen, Fuel, Heat
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______ are materials that absorb heat but do not participate actively in the combustion reaction.
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Passive agents
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What are the 4 components of the fire tetrahedron?
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Reducing Agent Chemical Chain Reaction Oxidizing Agent Heat
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What part of the fire tetrahedron model absorbs heat but does not actively participate in the combustion reaction?
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Passive Agents
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What type of combustion occurs when gaseous fuel mixes with oxygen in the correct ratio and is heated to ignition temperature?
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Flaming
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What product of combustion is an aerosol comprised of gases vapor and solid particulates?
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Smoke
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What product of combustion binds with hemoglobin preventing oxygen distribution in the body?
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Carbon Monoxide
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Why must a firefighter use an SCBA during overhaul?
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Hazardous concentrations above short term exposure limits are present.
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What type of energy is needed to release potential chemical energy in a fuel?
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Thermal kinetic energy is needed to release it.
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_____ _____ is a chemical reaction that may increase the temperature of a material without adding external heat.
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Self heating
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What is the most common product of combustion encountered in structure fires?
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Carbon monoxide
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What is a toxic and flammable substance produced by the incomplete combustion of materials containing nitrogen that acts as a chemical asphyxiant that prevents cells from using oxygen?
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Hydrogen Cyanide
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What acts as a simple asphyxiant by displacing oxygen?
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Carbon Dioxide
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When a burning gas is mixed with the proper amounts of oxygen the flame becomes hotter and less luminous, which is caused by more complete combustion. (True/False)
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True
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What type of energy is the most common source of heat in a combustion reaction?
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Chemical Energy
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What method of electrical energy occurs when a current flows through a conductor and heat is produced?
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Resistance heating
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What method of electrical energy occurs when the flowing current exceeds the design limits of a conductor?
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Over current
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What heat transfer method is the transfer of heat through and between solids?
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Conduction
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What method of heat transfer is the transfer of energy by circulation or movement of fluid?
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Convection
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What heat transfer method is described as the transmission of energy as and electromagnetic wave without and intervening medium?
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Radiation
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Increasing the distance between the heat source and exposed surfaces reduces the effect of radiant heat. (True/False)
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True
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What type of fuel contains carbon and other elements?
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Organic
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A spark is a high temperature luminous electrical discharge across a gap or through a medium. (True/False)
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False; Arcing
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Luminous particles formed spattering away from the point of arcing are called?
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Sparking
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Knowledge of heat transfer helps firefighters do what?
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Estimate the size of a fire before attacking it and evaluate the effectiveness of the attack.
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The greater the temperature difference between the bodies the Lesser/Greater the transfer rate?
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Greater
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Heat transfer due to conduction is dependent on what three factors?
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Area being heated Temperature differences Thermal conductivity of the heated material
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_____ do not conduct heat very well because their molecules are relatively far apart.
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Gases
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Convection may only occur in one direction. (True/False)
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False; Any direction
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What method of heat is a common cause of exposure fires?
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Radiant Heat
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Heat of combustion is usually expressed in what measurements?
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Kilojoules/gram (kJ/g)
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What term describes the energy released per unit of time as fuel burns?
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Heat Release Rate
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What type of fuel is already in the physical state required for ignition?
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Gaseous
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What type of fuel will flow downhill when released on the ground?
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Liquid
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Liquids with a specific gravity greater than 1 will...
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sink below the surface
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What term indicates how easily a substance will evaporate?
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Vapor Pressure
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What term is the temperature at which sufficient vapors are being generated to sustain a combustion reaction?
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Fire point
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Wood contains more potential for heat than many plastics flammable liquids and flammable gases. (True/False)
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False
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____ is the rate at which energy is being transferred over time.
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Power
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HRR is directly related to what factor?
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Oxygen; the more available oxygen the higher the HRR
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What are the three physical states of matter fuel exists in?
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Gas Liquid Solid
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What is defined as the minimum temperature at which a liquid gives off sufficient vapors to ignite but not sustain combustion?
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Flash Point
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Liquid fuels that vaporize sufficiently to burn at a temperature under ___ F present a significant flammability hazard.
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100 F
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What effects the extent to which a liquid will give off vapor?
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Surface area exposed to the atmosphere
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Describe miscible materials.
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Mix in any proportion
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What type of fuel decomposes and then releases fuel vapors?
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Solid
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What term refers to the chemical decomposition of a substance through the action of heat?
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Pyrolysis
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Combustible products are generated more quickly as the surface to mass ratio....
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increases
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What is the primary oxidizing agent in most fires?
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Oxygen
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Describe the impact of higher oxygen concentration on combustion?
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Fires may be more difficult to extinguish and produce much more thermal energy and radiant heat
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What term defines the concentration above which combustion cannot take place?
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Upper Flammable Limit
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Pyrolysis of wood begins at temperatures below ___ F, which is lower than required for ignition of the vapors being given which is roughly ____ F to ____ F
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400; 1000; 1300
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Pyrolysis occurs in plastics much sooner than wood because there is less moisture to slow the process. (True,False)
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True
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Paneling in a horizontal position burns much more rapidly because the heated vapors rise and transfer heat more quickly. (True/False)
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False; Vertical paneling
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What is the lowest percent of oxygen that materials can ignite in?
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14%
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What form of combustion can continue at extremely low oxygen concentrations even when the surrounding environment is at a relatively low temperature?
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nonflaming
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At high ambient temperatures, what type of combustion may continue at considerably lower oxygen concentrations?
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Flaming
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Concentrations that are below lower flammable limit (LFL) are considered too ___ to burn while if they are above the upper flammable limit (UFL) they are too ____ to burn.
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Lean; Rich
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What two gases result in the combustion of methane with oxygen?
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Carbon Monoxide and Formaldehyde
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What is the impact of an extinguishing agent when trying to extinguish flaming combustion?
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It forms a stable product
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What fire development factor includes building configuration, construction materials, and contents?
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Availability and location of additional fuel
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What fire development factor includes the impact of windows, gaps in construction, and HVAC systems?
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Ventilation
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Flow path and rapid fire development can be influenced by changes in ventilation in compartment fires that are:
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Ventilation-controlled
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What thermal property of a compartment increases fire spread through the transfer of radiant heat from wall surfaces to adjacent fuel sources?
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Heat reflectivity
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What fire development factor is the total quantity of combustible contents of a building?
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Fuel Load
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What are the four stages of fire development?
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Incipient, Growth, Fully Developed, and Decay
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Why is fire development slower in a larger compartment as opposed to a smaller compartment?
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Radiant heat has a greater distance to travel to heat up other contents.
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When oxygen is sufficient in a fire it is said to be ____ _____.
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Fuel controlled
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When the available air supply is limited in a compartment the fire is considered to be what?
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Ventilation controlled
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What are the three thermal properties of a compartment?
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Insulation, Heat Reflectivity, Retention
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What thermal property maintains temperature by absorbing and releasing large amounts of heat slowly?
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Retention
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What thermal property contains heat within the compartment causing a localized increase in the temperature and fire growth?
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Insulation
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Ambient conditions can be defined as what?
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Prevailing and uncontrolled atmospheric weather conditions.
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What two common ambient conditions can slow the natural movement of smoke?
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High humidity and cold temperatures
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Cold temperatures can cause smoke to appear white and give a false impression of the interior conditions based upon the color of the smoke. (True,False)
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True
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In what stage does the process of heat transfer begin to increase the overall temperature in the room?
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Incipient
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Describe the layering of gases that are in thermal layers? Why do these gases layer?
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Hot gases tend to be in the upper layer with cooler gases below; As a gas heats it expands losing pressure causing it to rise.
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Isolated flames in a gas layer during the growth stage indicates...
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That portions of the layer are within flammable range; also known as fingering or rollover
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In what stage are burning fuels in the compartment releasing the maximum amount of heat possible for available fuel and oxygen?
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Fully Developed
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In what stage does the oxygen concentration fall to the point that flaming combustion is diminished?
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Decay
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In what aspect of fire development will the environment of a room change from a two layer condition to a single well mixed, untenable hot gas condition?
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Flashover
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What common element of flashover is not an instantaneous spread of complete involvement but happens within seconds?
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rapidity
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What two factors influence the development of fire during the incipient stage?
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Characteristics and the configuration of the fuel involved
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In what stage of fire development has the environment not been significantly influenced?
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Incipient; temperatures are only slightly above ambient
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During what stage of fire development is the environment within a compartment influenced?
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Growth Stage
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What two factors influence the development of fire during the growth stage?
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compartment configuration and amount of ventilation
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What is the term for the rapid transition from the growth stage to the fully developed stage?
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Flashover
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What factor influences the continuation of fire and heat rise in the fully developed stage?
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Ventilation
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What are the three events of rapid fire development?
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Flashover, Backdraft, Smoke Explosion
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What are the four common elements of a flash over?
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Transition in fire development, rapidity, compartment, ignition of all exposed surfaces
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What two interrelated factors determine whether a fire within a compartment will progress to flashover?
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Sufficient fuel with sufficient HRR Ventilation
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What is a smoke indicator of a possible flashover?
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Darkening Smoke
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What is a flame indicator of possible flashover?
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Isolated flames in hot gas layer
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Define rollover.
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Ignition of unburned fire gases at the top of the compartment
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Describe Backdraft.
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A result of an increase in low level ventilation prior to upper ventilation causing the fire gases to become oxygen rich.
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What is a smoke indicator for possible backdraft?
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Optically dense smoke
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What is a flame indicator for a possible backdraft?
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Little or no visible flame
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Unburned fuel gases that contact a source of ignition can cause a ____ _____
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Smoke Explosion
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Flashover typically occurs at ____ F ceiling temperature and at floor level a heat flux of approximately ___ kW/m^2
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1,100; 20
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What are the 5 common indication categories to look at for potential flashover or back draft?
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Building indicators Smoke indicators Air Flow indicators Heat indicators Flame indicators
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What flashover indicator is based on interior configuration, fuel load, thermal properties, and ventilation?
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Building Indicator
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What flashover indicator is defined as... rapidly increasing volume, turbulence, darkening color, optical density, and lowering of the hot gas level?
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Smoke Indicator
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What flashover indicator is defined as... high velocity and turbulence, bi directional movement with smoke exiting the top of a doorway and cool air entering below, or pulsing air movement?
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Air flow indicator
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What flashover indicator is defined as... rapidly increasing temperature in the compartment, pyrolysis of contents or fuel packages located away from the fire, darkened windows or hot surfaces?
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Heat indicators
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What stage of fire does backdraft most commonly occur?
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Decay stage
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What backdraft indicator is defined as... fire confined to a single compartment or void space, building contents have a high HRR?
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Building indicators
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What backdraft indicator is defined as... optically dense smoke, light colored or black becoming dense gray-yellow, with neutral plane rising and lowering like a pulsing or breathing movement?
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Smoke indicators
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What backdraft indicator is defined as... high velocity, turbulent smoke discharge, sometimes appearing to pulse or breath?
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Air flow indicators
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What backdraft indicator is defined as... high heat, smoke stained windows?
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Heat indicators
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What factors can alter the effects of a backdraft? (5 factors)
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Volume of smoke Degree of confinement Pressure Speed with which fuel and air are mixed Location that ignition occurs
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The more confined, the more violent the backdraft will be. (True/False)
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True
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During fire fighting operations water is used to...
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control burning gases and reduce the temperature of the upper layer
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When water is vaporized into steam it expands how many times?
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1,700 times
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Allowing a fire to burn until all fuel is consumed is know as...
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Fuel Removal
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What suppression method works by flooding the area with an inert gas to displace oxygen?
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Oxygen exclusion
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What suppression method is effective on gas and liquid fuels?
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Chemical flame inhibition
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What suppression method involves the introduction of air or removal of hot gases and smoke from a building?
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Ventilation
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What is the most common method of fire control and extinguishment and best method for smoldering fires?
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Cooling with water
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What temperature is water converted to steam?
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212 F
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Water absorbs significant heat as its temperature is raised but loses it effect when it is vaporized into steam. (True/False)
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False; has its greatest effect when vaporized.
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Chemical flame inhibition is relatively ineffective on what type of fire?
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nonflaming as there is no reaction to inhibit
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When can unplanned ventilation occur?
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Before or after fire suppression
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Wind speeds as low as ___ MPH can create wind driven conditions.
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10
