1. Chapter 3 — Fire Behavior

2. Chapter 3 Lesson Goal
After completing this lesson, the student shall be able to summarize physical & chemical changes & reactions that occur with fire & the factors involved in fire development

3. Combustion
Rapid oxidation of fuel that produces heat & light

4. Matter is…
anything that occupies space & has mass (weight)

5. Physical & Chemical Changes of Matter Related to Fire
Physical change
Water freezing
Water boiling
Chemical reaction
Reaction of 2 or more substances to form other compounds
Oxidation
(Continued)

6. Physical & Chemical Changes of Matter Related to Fire
Chemical & physical changes
Usually involve exchange of energy
Potential energy released & changed to kinetic energy
Exothermic reaction – may produce heat, flames & toxic smoke (Heat “exit”)
Endothermic reaction – absorbs heat energy (Heat “in”)

7. DISCUSSION QUESTION
What are some examples of physical & chemical changes of matter?

8. Flaming (Fire) Non-flaming (No fire)
Combustion — Modes
Flaming (Fire)
Non-flaming (No fire)
Oxidation involves fuel in gas phase
Requires liquid/solid fuels to be converted to gas or vaporized
When heated, liquid/solid fuels give off vapors that burn
Some solid fuels can undergo oxidation at the surface of the fuel
Examples — Burning charcoal or smoldering fabric

9. Fire Triangle
Fire Parts

10. Fire Tetrahedron
Fire Process

11. Heat as Energy Heat is a form of energy
Potential energy — Energy possessed by an object that may be released in the future
Kinetic energy — Energy possessed by a moving object

12. Temperature Temperature is a measurement of kinetic energy
When molecules move they produce heat
Faster they move, the more heat produced
Heat energy moves from objects of higher temperature to those of lower temperature
Understanding this movement is important

13. Measuring energy Not possible to measure energy directly
It is possible to measure the work it does
Work means increasing temperature of a substance
Example: mercury in a thermometer rises when heated

14. Measuring energy Measured in British thermal units (BTU)
Amount of heat required raise 1 Lb of water 1 degree Fahrenheit (F)
Measured in calories
Amount of heat required raise 1 gram of water 1 degree Celsius (C)

15. Scales Used to Measure Temperature
Celsius — Metric
Fahrenheit — Customary

16. Conversion of Energy Into Heat
Heat is the energy component of tetrahedron
Fuel is heated = temperature increases
Starting ignition
Forms of ignition

17. Forms of ignition Two forms:
Piloted ignition outside heat source used to ignite material i.e. match

18. Forms of ignition Auto ignition temperature
Temperature at which a material self-sustains combustion
Material is heated to ignition temperature
Auto ignition temperature is always higher than piloted ignition temperature
Free-burning occurs

19. Chemical Heat Energy Most common heat source in combustion reactions
Oxidation almost always results in production of heat
Self-heating

20. Electrical Heat Energy
Can generate temperatures high enough to ignite any combustible materials near heated area
Can occur as
Resistance
Overcurrent/overload
Arcing
Sparking

21. Mechanical Heat Energy
Generated by friction or compression
Movement of 2 surfaces against each other creates heat of friction
Movement results in heat and/or sparks being generated
Heat of compression generated when gas compressed
(Continued)

22. Mechanical Heat Energy

23. DISCUSSION QUESTION
What are some examples of chemical, electrical, & mechanical sources of heat energy?

24. Transfer of Heat Basic to study of fire behavior
Affects growth of any fire
Knowledge helps FFs estimate size of fire before attacking
Heat moves from warmer objects to cooler objects
(Continued)

25. Transfer of Heat
Rate related to temperature differential of bodies & thermal conductivity of material
Greater the temperature differences between bodies, greater the transfer rate
Measured as energy flow over time

26. Conduction
Transfer of heat within a body or to another body by direct contact
Occurs when a material is heated as a result of direct contact with heat source
Heat flow depends on several factors
e.g. heat flow in wood is slower than steel

27. Convection Transfer of heat energy from fluid to solid surface
Transfer of heat through movement of hot smoke & fire gases
Flow is from hot fire gases to cooler components

28. Radiation
Transmission of energy as electromagnetic wave without intervening medium
Distance between heat & surface is biggest factor
(Continued)

29. Radiation Thermal radiation results from temperature
Affected by several factors
Energy travels in straight line at speed of light, i.e. heat from the sun
Major contributor to flashover

30. Heat Transfer in Buildings
Heat can be transferred in buildings by:
Conduction
Radiation
Convection
Heat transfer by radiation

31. Passive Agents
Materials that absorb heat but do not participate in combustion
Fuel moisture = passive agent
Relative humidity & fuel moisture

32. DISCUSSION QUESTION
What is the impact of high fuel moisture on fire spread?

33. Fuel Material being oxidized in combustion process
Reducing agent: reduces or uses oxygen
Inorganic or organic; organic most common
(Continued)

34. Fuel Organic fuels: contain carbon Hydrocarbon-based Cellulose-based
Petroleum based & some plastics
Cellulose-based
Wood & paper
Inorganic fuels: do not contain carbon
Hydrogen & magnesium

35. Fuel Key factors influencing combustion process:
Physical state of fuel
Gases & liquids burn more readily than solids
Distribution or orientation of fuel
Solid fuels that are vertical burn more readily than when horizontal
Try this with a piece of paper

36. Gaseous Fuel Only gases burn
Easiest to ignite, gases are already in state ready for ignition
Methane, hydrogen, etc. most dangerous because exists naturally in state required for ignition
Has mass but no definite shape or volume

37. Gaseous Fuel Vapor density The weight of a gas compared to air
Air is 1
More than 1 will sink & collect in low points
Less than 1 will rise

38. Liquid Fuel
Has mass & volume but no definite shape except for flat surface
Assumes shape of container
Will flow downhill & pool in low areas
Must be vaporized in order to burn

39. Liquid Fuel Specific Gravity The weight of liquid compared to water
Water is 1
More than 1 will sink
Less than 1 will float

40. Liquid Fuel Characteristics
Flash point flashes & goes out
Fire point continues to burn
Surface area: how much surface area is exposed to the atmosphere
The greater the surface area, the more vapors produced

41. Liquid Fuel Characteristics
Flash point
(Continued)

42. Liquid Fuel Characteristics
Non-polar Solvents
Hydrocarbons, gasoline, diesel
Does not mix w/ water
Non-miscible, non-soluble
Lighter than water

43. Liquid Fuel Characteristics
Polar Solvents
Alcohols, acetone, esters
Readily mixes w/ water
Miscible/soluble

44. Liquid Fuel Characteristics
Firefighting considerations - Liquids lighter than water
Presents a significant challenge when using water
Volume of liquid increases as water is applied
Potentially spreading the burning fuel

45. Liquid Fuel Characteristics
Firefighting considerations - Water-soluble liquids
Presents a problem in that some water-based extinguishing agents mix w/ the burning liquid
Makes them ineffective

46. Solid Fuel Definite size & shape
React differently when exposed to heat
(Continued)

47. Solid Fuel Pyrolysis evolves solid fuel into fuel gases/vapors
As it is heated, begins to decompose below 400°F (204°C), giving off combustible vapors
(Continued)

48. Solid Fuel Commonly the primary fuel
Surface-to-mass ratio — Primary consideration in ease or difficulty of lighting
(Continued)

49. Solid Fuel
Proximity/orientation of solid fuel relative to source of heat affects the way it burns

50. Solid Fuel
Synthetic fuels such as plastic produce large amounts of toxic gases when burned
Toxic effect of smoke is not the result of any one fire gas
Fire gases can be deadly to FFs

51. Heat of Combustion/ Heat Release Rate
Heat of combustion — Total amount of energy released when a specific amount of fuel is oxidized
Usually expressed in kilojoules/gram (kJ/g)
Heat release rate (HRR) — Energy released per unit of time as fuel burns
Usually expressed in kilowatts (kW)

52. Oxygen In air, is the primary oxidizing agent in most fires
Air consists of 21% oxygen

53. Oxygen Concentrations
At normal ambient temperatures, materials can ignite/burn at concentrations as low as 14 percent
When limited, flaming combustion may diminish; combustion will continue in surface or smoldering mode
(Continued)

54. Oxygen Concentrations
At high ambient temperatures, flaming combustion may continue at much lower oxygen concentrations
Surface combustion can continue at extremely low oxygen concentrations
(Continued)

55. Oxygen Concentrations
When higher than normal, materials burn faster than normal
Fires in oxygen-enriched atmospheres are difficult to extinguish & present a potential safety hazard
Flammable/explosive range — Range of concentrations of fuel vapor & air

56. Flammable Range
Expressed as a percentage of fuel/air mixture that will ignite or explode
UEL & LEL: Upper & lower explosive limits
UFL & LFL: Upper & lower flammable limits
Terms mean the same thing

57. Flammable Range Flammable limits can change based on temperature
Higher temperatures can increase the flammable ranges
Lower temperatures can decrease the flammable ranges

58. Flammable Range Product Flammable Range Methane 5% - 15% Propane
2.1% - 9.5%
Carbon Monoxide
12% - 75%
Gasoline
1.4% - 7.4%
Diesel
1.3% - 6%
Ethanol
3.3% - 19%
Methanol
6% - 35%

59. Self-Sustained Chemical Reaction
Very complex
Example: Combustion of methane & oxygen
(Continued)

60. Flaming Combustion
Sufficient heat causes fuel/oxygen to form free radicals, initiates self-sustained chemical reaction
Fire burns until fuel/oxygen exhausted or extinguishing agent applied
Agents may deprive process of fuel, oxygen, sufficient heat for reaction

61. Surface Combustion Without flames
Example: charcoal
Distinctly different from flaming combustion
Cannot be extinguished by chemical flame inhibition
Dry chemical will not work
Must be extinguished by removing fuel, heat, or oxygen

62. Surface Combustion Without flames
Example: charcoal
Distinctly different from flaming combustion
Cannot be extinguished by chemical flame inhibition
Dry chemical will not work
Must be extinguished by working removing fuel, heat, or oxygen

63. General Products of Combustion Include Heat, Smoke, Light
Heat, smoke impact FFs most
Heat generated during fire helps spread fire
Lack of protection from heat may cause burns & other health issues
Toxic smoke causes most fire deaths

64. Common Products of Combustion
Carbon monoxide – biggest killer of people in house fires
Most common product of combustion encountered in structure fires
Chemical asphyxiant
Flammable

65. Common Products of Combustion
Hydrogen cyanide (HCN)
Commonly encountered in smoke
Acts as a chemical asphyxiant
Byproduct of the combustion of polyurethane foam, carpet & wool

66. Common Products of Combustion
Carbon dioxide (CO2)
Product of complete combustion of organic materials
Acts as a simple asphyxiant by displacing oxygen
Also acts as a respiratory stimulant, increasing respiratory rate

67. Hazards to Firefighters
Toxic effects of smoke inhalation not result of any one gas
Smoke contains a wide range of irritating substances that can be deadly
FFs must use SCBA when operating in smoke

68. Flame Visible, luminous (glowing) body of a burning gas
Becomes hotter, less luminous when burning gas mixes with proper amounts of oxygen
Product of combustion

69. Class A Fires Involve ordinary combustible materials
Primary method of extinguishment is cooling to reduce temperature of fuel to slow or stop release of pyrolysis products

70. Class B Fires Flammable/combustible liquids & gases
Gas fires are extinguished by cutting off gas supply
Liquids are extinguished with foam and/or dry chemical agents

71. Class C Fires Involve energized electrical equipment
Typical sources — Household appliances, computers, electric motors
Actual fuel usually insulation on wiring or lubricants
(Continued)

72. Class C Fires
When possible, de-energize electrical equipment before extinguishing
Any extinguishing agent used before de-energizing must not conduct electricity

73. Class D Fires Involve combustible metals
Powdered materials most hazardous
In right concentrations, metal dust can cause powerful explosions
High temperature of burning metals makes water & other extinguishing agents ineffective & dangerous
(Burning Magnesium

74. Class D Fires No single agent effectively controls Class D fires
Materials may be in a variety of facilities
Caution urged when extinguishing — Can react violently to water & may produce toxic smoke/vapors

75. Class K Fires Involve oils & greases
Require extinguishing agent specifically formulated for materials involved
Agents use saponification to turn fats & oils into soapy foam that extinguishes fire

76. Fire Development in a Compartment
Compartment — Closed room or space within building
Walls, ceiling, floor absorb some radiant heat produced by fire
Radiant heat energy not absorbed is reflected back, increasing temperature of fuel & rate of combustion
(Continued)

77. Fire Development in a Compartment
Hot smoke/air becomes more buoyant
Upon contact with cooler materials, heat is conducted, raising the temperature
Heat transfer: Process where heat is absorbed (transferred) from one body to another
Raises temperature of all materials
(Continued)

78. Fire Development in a Compartment
Heat always goes from warmer to colder
Until both bodies are the same temperature
As nearby fuel is heated, begins to pyrolize, causing fire extension
(Continued)

79. Fire Development in a Compartment

80. Fire Develops in Stages
Flashover
Incipient
Growth
Fully Developed
Decay

81. Incipient Stage
Ignition — Point when the 3 elements of fire triangle come together & combustion occurs
Once combustion begins, development is largely dependent on characteristics & configuration of fuel involved
(Continued)

82. Incipient Stage
Fire has not yet influenced environment to a significant extent
Temperature only slightly above ambient, concentration of products of combustion low
(Continued)

83. Incipient Stage
Occupants can safely escape from compartment & fire could be safely extinguished with portable extinguisher or small hoseline
Transition from incipient to growth stage can occur quite quickly

84. Growth Stage Fire begins to influence environment within compartment
Fire influenced by location of fire, layout of the compartment & amount of ventilation
(Continued)

85. Growth Stage
Thermal layering — Tendency of gases to form into layers according to temperature
Hot gases rise
Cooler gases sink
Also known as thermal balance & heat stratification
(Continued)

86. Growth Stage
Isolated flames — As fire moves through growth stage, pockets of flames may be observed moving through hot gas layer above neutral plane

87. Growth Stage
Rollover – Where unburned gases accumulate at the top of the compartment & ignites

88. Growth Stage Rollover may precede flashover
Flashover – rapid transition of fire growth to a fully developed compartment fire
Everything in the compartment ignites at once
Temperatures of flashover: 900° – 1200°F (483°-649°C)

89. Growth Stage Just prior to flashover:
Temperatures are rapidly increasing
Additional fuel packages are becoming involved
Fuel packages are giving off combustible gases
Flashover

90. Flashover Video

91. Growth Stage Factors determining flashover:
Does not occur in every compartment fire
Fuel must have sufficient heat energy to develop flashover conditions
Ventilation — A developing fire must have sufficient oxygen

92. Fully Developed Stage
Occurs when all combustible materials in compartment are burning
(Continued)

93. Fully Developed Stage
Burning fuels in compartment release maximum amount of heat possible for available fuel & ventilation, producing large volumes of fire gases
Fire is ventilation controlled

94. Decay Stage
Fire will decay as fuel is consumed or if oxygen concentration falls to point where flaming combustion can no longer be supported
Decay due to reduced oxygen concentration can follow much different path if ventilation profile of compartment changes
(Continued)

95. Decay Stage Consumption of fuel Limited ventilation
Backdraft is produced in the decay stage

96. Backdraft Video

97. Decay Stage - Backdraft
3/25/2017
Decay Stage - Backdraft
3–97

98. Decay Stage - Backdraft
3/25/2017
Decay Stage - Backdraft
Explosion that occurs when oxygen is suddenly admitted to a confined area that is very hot & filled with combustible vapors
3–98

99. Backdraft Recognition
Little or no fire
Smoke exits in puffs
Smoke stained windows
Inward drawing smoke
Grayish, yellow smoke
Confined fire area

100. Fuel Type
Impacts both amount of heat released & time over which combustion occurs
Mass & surface area are most fundamental fuel characteristics influencing development in compartment fire

101. Availability/Location of Additional Fuel
Factors that influence fire development
Configuration of building
Contents
Construction
Location of fire in relation to uninvolved fuel
Which one will have the fastest fire spread?

102. Compartment Volume & Ceiling Height
All other things being equal, a fire in a large compartment will develop more slowly than one in a small compartment
The large volume of air will support the development of a larger fire before ventilation becomes the limiting factor

103. Ventilation Influences how fire develops
Preexisting ventilation is the actual & potential ventilation of a structure
Consider potential openings that could change the ventilation profile
Size, number, & arrangement of existing & potential ventilation openings

104. Thermal Properties of Enclosure
Include insulation, heat reflectivity, retention, conductivity
When compartment well-insulated, less heat lost; more heat remains to increase temperature & speed combustion reaction
(Continued)

105. Thermal Properties of Enclosure
Surfaces that reflect heat return it to the combustion reaction & increase its speed
Some materials act as heat sink & retain heat energy
Other materials conduct heat readily & spread fire

106. Ambient Conditions Less significant factor inside structure
High humidity/cold temperatures can impede natural movement of smoke
Strong winds significantly influence fire behavior
Wind Direction?

107. Impact of Changing Conditions
Structure fires can be dynamic
Factors influencing fire development can change as fire extends from one compartment to another
Changes in ventilation likely most significant factors in changing behavior

108. Temperature Reduction
One of the most common methods of fire control/extinguishment
Depends on reducing temperature of fuel to point of insufficient vapor to burn
Solid fuels, liquid fuels with high flash points can be extinguished by cooling
(Continued)

109. Temperature Reduction
Use of water is most effective method for extinguishment of smoldering fires
Enough water must be applied to absorb heat generated by combustion
Cooling with water cannot reduce vapor production enough to extinguish fires in low flash point flammable liquids/gases
(Continued)

110. Temperature Reduction
Water can be used to control burning gases/reduce temperature of products of combustion above neutral plane
Water absorbs significant heat as temperature raised, but has greatest effect when vaporized into steam

111. Fuel Removal Effectively extinguishes any fire
Simplest method is to allow a fire to burn until all fuel consumed

112. Oxygen Exclusion
Reduces fire’s growth & may totally extinguish over time
Limiting fire’s air supply can be highly effective fire control action

113. Chemical Flame Inhibition
Extinguishing agents such as halon-repalcements & dry chemicals interrupt combustion reaction, stop flame production
Effective on gas, liquid fuels because they must flame to burn
Does not easily extinguish surface mode fires

114. Summary Many people believe that fire is unpredictable
There is no unpredictable fire behavior
Our ability to predict what will happen in the fire environment is hampered by limited information, time pressure, & our level of fire behavior knowledge
(Continued)

115. Summary
FFs need to understand the combustion process & how fire behaves in different materials/different environments
FFs need to know how fires are classified so that they can select & apply the most appropriate extinguishing agent
(Continued)

116. Summary
Most importantly, FFs need to have an understanding of fire behavior that permits them to:
Recognize developing fire conditions
Be able to respond safely & effectively to deal w/ the hazards presented by the fire