Fire Inspection and �Code Enforcement
8th Edition�Inspector I
Chapter 3 — Fire Behavior
�Learning Objective 1
Describe the various components of fire behavior.
3–1
All fires involve a heat-producing chemical reaction between a fuel and an oxidizer.
3–2
Fuel
Oxidizer (Oxygen)
Fire
When material burns, heat is generated faster than it dissipates, causing temperature to increase.
3–3
Material burns
Generates heat
Temperature increases
Theoretical foundations of physical science must be translated into fire science.
3–4
Fire Science
Chemistry
Physics
Laws related to matter
Laws related to energy
Understand the many factors that contribute to the science of fire.
3–5
Physical/chemical changes
Modes of combustion
Temperature, energy, heat
Sources of thermal energy
Heat transfer
Passive agents
Fuel
Oxidizer
Self-sustained chemical reaction
Classification of fires
Understanding the concept of fire enables inspectors to identify and mitigate hazards.
3–6
Excessive fuel loading
Improper storage
Unclean commercial cooking equipment
Knowledge of fire protection issues prepares inspectors to determine occupancy requirements.
3–7
Fire separation
Interior finish
Sprinkler coverage
Physical change occurs when substances remain chemically the same, but change in size, shape, appearance.
3–8
Water (Liquid)
Freezing temperature
Ice �(Solid)
Water (Liquid)
Heat
Steam�(Gas)
Oxidation is a chemical reaction that involves the combination of an oxidizer with other materials.
3–9
Oxidation can be slow (rust) or rapid (combustion)
Physical and chemical changes involve an exchange of energy.
3–10
Potential energy converts to
Kinetic energy
Combustion releases potential energy
Know the difference between exothermic and endothermic reactions.
3–11
Reactions that give off energy (fire) = exothermic�Reactions that absorb energy (steam) = endothermic
Know the difference between flaming and nonflaming combustion.
3–12
Produces a visible flame above material’s surface
Occurs more slowly, lower temperatures; smoldering glow
Inspectors need to know the two models of fire.
3–13
Both explain the elements of fire and how fires can be extinguished
The fire triangle is the oldest and simplest model.
3–14
The fire tetrahedron explains fires involving certain types of substances and agents needed to extinguish them.
3–15
Created after determining an uninhibited chemical reaction is needed for a fire to occur
Know the characteristics of nonflaming combustion.
3–16
Know the characteristics of flaming combustion.
3–17
Have a clear understanding of temperature, energy, and heat.
3–18
Terms should not be used interchangeably
Causes confusion
Inspectors need to know the difference
The freezing and boiling points of water provide a simple way of comparing temperature scales.
3–19
Inspectors need to understand the characteristics of energy.
3–20
It is the capacity to perform work
Work occurs when
Not possible to measure energy directly
Inspectors should know energy exists in many forms.
3–21
Chemical
Mechanical
Electrical
Light
Nuclear
Sound
Inspectors need to know energy classifications.
3–22
Potential
Kinetic
Energy can change from one to the other
Inspectors need to understand the concept of power as it relates to combustion.
3–23
It is the rate at which work is performed
Important to understanding the rate at which energy is released
Important to understanding the rate of heat transfer
The size of the fire relates to the rate at which energy is released
Inspectors should know the unit of measure for power.
3–24
Units of Measure
Standard international unit = watt (W)
1 watt = 1 joule per second (J/s)
Inspectors need to know the characteristics of heat.
3–25
Heat is energy in transit
Transfer of energy from a high-temperature substance to a low-temperature substance
“Heat” is commonly used to describe thermal energy
Heat is kinetic energy associated with the movement of atoms and molecules that comprise matter
Inspectors need to understand heat as it relates to fire behavior.
3–26
The conversion of chemical potential energy in fuel to thermal kinetic energy (heat) is the energy element in both the fire triangle and the tetrahedron
Courtesy of Dan Madrzykowski/NIST
Understand the characteristics of forms of ignition.
3–27
Inspectors need to be familiar with the two forms of ignition.
3–28
(Cont.)
Inspectors need to be familiar with the two forms of ignition.
3–29
Inspectors need to be familiar with autoignition temperature characteristics.
3–30
Minimum temperature to which a fuel in the air must be heated in order to start self-sustained combustion
Temperature always higher than its piloted ignition
Many types of energy can be transformed into thermal energy.
3–31
Chemical
Mechanical
Electrical
Light
Nuclear
Sound
Understand the characteristics of chemical energy.
3–32
Most common source of heat in combustion reactions
Potential for oxidation exists when any combustible is in contact with oxygen
Almost always produces thermal energy
Self-heating may be a result
Self-heating is both a form of oxidation and an exothermic chemical reaction.
3–33
Reaction that increases the temperature of a material without the addition of heat
Normally produced slowly by oxidation
Normally lost to the surroundings as fast as it is generated
External heat sources can accelerate the process
Understand what makes self-heating move to spontaneous ignition.
3–34
Self-heating
Heat cannot dissipate as quickly as it is being generated
Heat production is great enough to raise the temperature of the material
Air supply in and around the material is adequate to support combustion
Autoignition temperature = Spontaneous ignition
Oxidation rates increase as more heat is generated and held by the materials insulating fuels.
3–35
Rate of most chemical reactions increases as temperatures of reacting materials increase
More heat generated and absorbed by the fuel = faster reaction causing the heat generation
When heat generated by a self-heating reaction exceeds the heat being lost, material may ignite spontaneously
Electrical heating can occur in several ways.
3–36
Resistance heating
(Cont.)
Electrical heating can occur in several ways.
3–37
Overcurrent or overload
(Cont.)
Electrical heating can occur in several ways.
3–38
Arcing
(Cont.)
Electrical heating can occur in several ways.
3–39
Sparking
Mechanical energy is generated by friction or compression.
3–40
Heat of friction
Occurs when two surfaces move against each other
Results in heat and/or sparks
Heat of compression
Occurs when gas is compressed through mechanical means
Why SCBA cylinders feel warm to the touch after filling
REVIEW QUESTION
Describe and name an example of chemical, electrical, and mechanical energy.
3–41
Use knowledge of heat transfer to evaluate fire safety features.
3–42
Fire-rated walls
(Passive feature)
Sprinkler systems
(Active feature)
Structural components and interior finishes have a significant effect on heat transfer.
3–43
Drywall
Masonry
Fire doors
Fuel loads
Combustible waste and storage
Use heat transfer knowledge when considering the potential for fire spread.
3–44
Important when fire extends beyond the point of origin
For heat to transfer, objects must be at different temperatures
Rate of transfer related to the temperature differential of the objects and thermal conductivity
Greater temperature differences = Greater transfer rates
(Cont.)
Use heat transfer knowledge when considering the potential for fire spread.
3–45
Heat flux = Transfer of thermal energy
Typically measured in kilowatts per meter squared (kW/m2)
Inspectors need to know heat transfer mechanisms.
3–46
Conduction
Convection
Radiation
Conduction is the transfer of heat through and between solids.
3–47
Be familiar with the thermal conductivity temperatures of some common materials.
3–48
Know what materials delay heat transfer primarily by slowing conduction.
3–49
Insulating materials
Best commercial insulation materials
Convection is the transfer of thermal energy by the circulation or movement of a fluid.
3–50
Radiation is the transmission of energy as electromagnetic waves without an intervening medium.
3–51
Be aware that radiation is a common method of heat transfer in buildings with radiant heat systems.
3–52
Radiant heat systems are usually located under the floor of a room
Courtesy of Greg Havel
Know the factors that influence radiant heat transfer.
3–53
Nature of exposed surfaces
Distance between the heat source and exposed surfaces
(Cont.)
Know the factors that influence radiant heat transfer.
3–54
Temperature differences between heat source and exposed surfaces
Energy is an electromagnetic wave that travels at the speed of light in a straight line.
3–55
Earth
Sun
Speed of light
Energy
Radiation is a common cause of exposure fires.
3–56
As fire grows, it radiates more heat
Objects absorb energy
Convert energy to heat
Exposure fire
Exposure fire = fire ignited in fuel packages or buildings a considerable distance from the area of origin
Materials that reflect radiated energy will disrupt the transmission of heat.
3–57
Radiated heat travels through vacuums and air spaces that would disrupt heat transfer by conduction and convection
Flames have high temperature, resulting in the emission of significant radiant energy
Hot smoke in the upper layer also transmits significant energy
REVIEW QUESTION
What are the ways heat can be transferred to an object?
3–58
Know what impact passive agents can have on ignition and fire development.
3–59
Materials that absorb heat
Do not contribute fuel in the combustion reaction
Examples
Fuel is the substance that is burned in the combustion process.
3–60
In scientific terms, fuel is a reducing agent
Inorganics do not contain carbon (Hydrogen, magnesium)
Organics contain carbon and are the most common type of fuel
Understand the influences of the chemical content of fuel.
3–61
Heat of combustion
Heat release rate (HRR)
Significant to inspectors because of the widespread use of synthetics in building construction materials
Inspectors should understand heat of combustion.
3–62
Total amount of thermal energy released when a specific amount of fuel oxidizes
Usually expressed kilojoules/gram (kJ/g)
Many plastics, flammable liquids/gases contain more potential heat (thermal energy) than wood
Inspectors should understand Heat release rate (HRR).
3–63
Energy released per unit of time as a fuel burns
Usually expressed in kilowatts (kW) or megawatts (MW)
Dependent upon type, quantity, orientation of fuel
Fuel may be gas, solid, liquid: Flaming combustion requires gases and thermal energy is required to change solids/liquids into gas
Gaseous fuels can be the most dangerous of fuel types.
3–64
Methane
Hydrogen
Acetylene
Already in the state required for ignition
Inspectors should be familiar with common flammable gases.
3–65
Inspectors need to know the characteristics of gases.
3–66
Gases have mass
No definite shape or volume
Placed in a container, gas will fill the space available
Released, gas will rise or sink depending upon vapor density
Inspectors should understand gas and vapor density.
3–67
Inspectors need to know the characteristics of liquid fuels.
3–68
Have mass and volume
Assume shape of their container
When released, flow downhill
Can pool in low areas
Inspectors should understand liquids and specific gravity.
3–69
Vaporization is the transformation of a liquid to vapor or gaseous state.
3–70
Liquids must be vaporized in order to burn
Liquids must overcome the pressure exerted by the atmosphere
Liquid heated = vapor pressure and rate of vaporization increases
Rate of vaporization = vapor pressure of substance �+ amount of thermal energy applied to it
Volatility influences how easily a liquid can be ignited
Know the difference between flash point and fire point.
3–71
Solubility describes the extent to which a substance will mix with water.
3–72
Hydrocarbon fuels are lighter than water and do not mix
Polar solvents like alcohols mix readily with water
Can be expressed in qualitative terms, i.e. slightly, completely
Can be expressed as a percentage
“Miscible” materials mix in water in any proportion
Know the characteristics of solid fuels.
3–73
Have definite size and shape
Some will readily change shape and melt
Others will not
Primary fuels found in room or compartment fires
Pyrolysis occurs as solid fuels are heated and begin to decompose and give off combustible vapors.
3–74
If sufficient fuel and heat, process generates enough vapors to ignite
Must occur to generate the flammable vapors required for combustion
Pyrolysis of wood begins at temperatures below 400°F (204°C)
Similar with synthetic fuels like plastic and some fabrics
Solid fuels have a defined shape and size, which significantly affects how easy or difficult they are to ignite.
3–75
Surface-to-mass ratio = surface area of the fuel in proportion to the mass
Small fuel particles = high surface-to-mass ratio = easier to ignite
Larger fuel particles = low surface-to-mass ratio = harder to ignite
The proximity and orientation of a solid fuel relative to the source of heat also affects the way it burns.
3–76
When a solid fuel like a sheet of plywood is lying horizontally (flat), fire will consume the fuel at a relatively slow rate; the same type of material in a vertical position (standing on edge) burns much more rapidly
Know the impact of oxidizers on combustion.
3–77
Not combustible, but will support or enhance combustion
Fuels in gaseous states need oxidizers for combustion
Oxygen is the primary oxidizer
Inspectors need to be familiar with other common oxidizers.
3–78
Inspectors need to know what happens when oxygen is limited.
3–79
Materials can ignite and burn at concentrations as low as 14%
Flaming combustion will diminish
Nonflaming combustion can continue
Flaming combustion can continue at high ambient temperatures
Inspectors need to know what happens when oxygen is higher than normal.
3–80
Materials can burn more intensely
Some petroleum-based materials will autoignite
Materials that do not burn at normal oxygen levels may burn more readily
Fires more difficult to extinguish
Flammable range is the range of concentrations of fuel vapor and air.
3–81
Be familiar with the flammable ranges for some common materials.
3–82
Flammable limits are normally reported at ambient temperatures and pressures; variations in temperatures and pressure can cause the range to vary considerably.
The self-sustained chemical reaction involved in flaming combustion is complex.
3–83
Flaming combustion occurs
Free radicals form
Increases speed of oxidation
Combustion produces flammable and toxic products
Initiates the self-sustained chemical reaction
Will continue until oxygen is consumed or chemical reaction is interrupted
Be familiar with chemical flame inhibition.
3–84
Occurs when an extinguishing agent interferes with the chemical reaction
Application forms a stable product
Terminates the combustion reaction
Agents include dry chemical, Halon-replacement
Understand why smoke causes the largest percentage of fire deaths.
3–85
Aerosol comprised of gases, vapor, solid particulates
Gases are generally colorless
Vapor and particulates give smoke its colors
Generally, all smoke is toxic
Toxic effects of smoke are a result of interactions of all the toxic products present
Know the common products of combustion and their toxic effects.
3–86
(Cont.)
Know the common products of combustion and their toxic effects.
3–87
(Cont.)
Know the common products of combustion and their toxic effects.
3–88
Inspectors need to know how fires are classified.
3–89
Type of fuel involved
Type of extinguishing agent required
Classifications
Class A fires involve ordinary combustible materials.
3–90
Typically involves
Primary method of extinguishment
Class B fires involve flammable liquids and gases.
3–91
Typically involves
Primary method of extinguishment
Inspector concerns
Class C fires involve energized electrical equipment.
3–92
Typically involves
Primary method of extinguishment
Inspector concerns
Class D fires involve combustible metals.
3–93
Typically involves
Primary method of extinguishment
Inspector concerns
Class K fires involve vegetable-based oils and greases.
3–94
Typically involves
Primary method of extinguishment
Inspector concerns
REVIEW QUESTION
Describe the five classifications of fire.
#–95
�Learning Objective 2
Describe fire development.
3–96
Inspectors need to know the stages of fire development.
3–97
(Cont.)
Inspectors need to know the stages of fire development.
3–98
Developed as a result of lab studies in a single compartment
Actual conditions, with multiple compartments, may differ
Stages may not progress in order
Important for inspectors when evaluating fire extinguishing equipment
Important for inspectors when evaluating fire protection systems
A number of factors influence fire development within a compartment.
3–99
Fuel type
Availability and location of additional fuels
Compartment volume and ceiling height
Ventilation
Thermal properties of the compartment
Fuel load
The type of fuel involved in combustion affects the heat release rate (HRR).
3–100
Class B and C fuels eventually spread to contents and turn into Class A fueled fires
Surface-to-mass ratio is a fundamental characteristic influencing fire development in compartment fires
High surface-to-mass ratios are more easily ignited, burn more quickly
(Cont.)
The type of fuel involved in combustion affects the heat release rate (HRR).
3–101
Class B fires are also influenced by surface area and fuel type
Structure fires rarely involve only a single type of fuel.
3–102
Today’s homes/businesses are filled with petroleum-based materials
They produce higher HHRs and have a higher heat of combustion
Produce large quantities of solid and liquid particulates and unburned gases
Inspectors need to verify procedures to shut off Class B fuel sources.
3–103
Compartment fires can result from a flammable/combustible gas leak
May begin with a rapid ignition of gas and an explosion
Inspectors verify procedures for reducing or eliminating Class B fuel
Understand that the resulting Class A fire will continue to burn unless there is a sprinkler system in place
Many factors influence the availability and location of additional fuels.
3–104
Building configuration
Contents
Construction materials
Interior finish materials
Fuel proximity
Fire location
3–105
Number of stories above or below grade
Compartmentation
Floor plan
Openings between floors
Continuous voids or concealed spaces
Barriers to fire spread
(Cont.)
Building configuration refers to the layout elements of the structure.
3–106
These elements may contribute to fire spread or containment
May also contain fire prevention features
Building configuration refers to the layout elements of the structure.
3–107
When contents release a large amount of heat rapidly, it increases
Synthetic furnishings will begin to pyrolize rapidly
The contents of a structure are often the most readily available fuel source.
3–108
Materials include
Each type of construction is symbolized by a different quantity of fuel
The materials used to construct the building contribute to the fuel load.
3–109
In some types of buildings, the construction materials can be affected by fire
Combustible interior finishes can be a significant factor in fire spread
Rate and intensity of fire spread influenced by
Types of construction materials used in a structure also influence fuel load.
3–110
Fuels located in the upper level of adjacent compartments will pyrolize more quickly
Continuous fuels will rapidly spread the fire from compartment to compartment
Proximity and continuity of contents and structural fuels also influence fire development.
3–111
Fire located in lower levels will cause vertical extension
Fires originating in upper levels extend downward
Location of fire within the building will influence fire development.
3–112
If all other factors are equal
Greater volume of air
Increased distance radiated heat must travel from fire to contents
High ceilings may hide extent of fire development
Fire in a large compartment will develop more slowly than one in a small compartment.
3–113
All buildings exchange air inside with air outside
Compartment fires that involve the contents of a room are ventilation controlled
Ventilation in a compartment significantly influences how fire develops and spreads.
3–114
Windows can fail and doors can be left open
Available air supply will determine fire development
Fire seeks fresh air
Know how potential openings can change ventilation.
(Cont.)
3–115
Inspectors often encounter open fire doors
Know how potential openings can change ventilation.
Courtesy of Scott Strassburg
3–116
Insulation
Contains heat within the compartment
Causes localized increase in temperature and fire growth
Heat reflectivity
Increases fire spread
Transfer for radiant heat from wall surfaces to fuel sources
Retention
Maintains temperature
Absorbs and releases large amounts of heat slowly
Thermal properties of compartments contribute to rapid fire development and difficult extinguishment.
3–117
Some use the term “fire load”
Includes all of a structure’s contents and structural components
Fire protection engineers can generate an accurate estimate using mathematical equations
Inspectors may only be able to generate an estimate based on knowledge and experience
Knowledge of building construction and occupancy types are essential
The total quantity of combustible contents of a building, space, or fire area is referred to as the fuel load.
REVIEW QUESTION
List some factors that influence fire development within a compartment.
#–118
3–119
Inspectors need to understand the incipient stage of fire.
(Cont.)
Courtesy of Dan Madrzykowski/NIST
3–120
Inspectors need to understand the incipient stage of fire.
Courtesy of Dan Madrzykowski/NIST
3–121
Know the factors that influence the development of fuel-controlled fires.
3–122
Know the characteristics of the incipient stage of fire.
Fire has not yet influenced the environment significantly
Temperature is only slightly above ambient
Concentration of products of combustion is low
Occupants are more likely to escape
Fire could be safely extinguished with portable extinguisher or small hoseline
Growth from incipient stage can occur quickly
Essential to recognize the transition
3–123
Inspectors need to understand the growth stage of fire.
Courtesy of Dan Madrzykowski/NIST
3–124
Know how unconfined fires reduce flame length and vertical extension.
Draw air from all sides
Entrainment of air cools the plume
Fuel packages in the middle of the room can entrain air from all sides
Fires in fuel packages near walls can on entrain air from three sides
Fires in fuel packages in corners can only entrain air from two sides
3–125
Understand the concept of vertical extension.
Occurs when fuel packages are not located in the middle of the room
Temperatures at ceiling level affected
Wall surfaces become hot
3–126
Thermal layering of gases is the tendency of gases to form into layers according to temperature.
Hottest gases
Coolest gases
3–127
Several things impact thermal layering of gases.
Heat transfer through radiation
Heat transfer through convection
Radiation from the hot gas layer acts to heat interior surfaces, contents
Changes in flow path and ventilation
3–128
Pressure increases as the volume and temperature of the hot gas layer increases.
Causes the hot gas layer to spread downward and out through openings
As hot gases exit through top of opening, cooler air from outside enters through the bottom of opening
Pressure is neutral where two layers meet (neutral plane)
(Cont.)
3–129
Pressure increases as the volume and temperature of the hot gas layer increases.
Courtesy of Dan Madrzykowski/NIST
3–130
Isolated flames may be observed moving through the hot gas layer.
Courtesy of NIST
3–131
Rapid transition from growth stage to fully developed stage is known as flashover.
Environment of the room changes
Transition period can occur rapidly
During flashover, fire volume increases
3–132
Flashover does not occur in every compartment fire.
If a fire becomes ventilation controlled
3–133
Most fires that develop beyond the incipient stage become ventilation controlled.
Insufficient air to allow the fire to continue to develop based on fuel
If windows are intact and doors closed, becomes ventilation-controlled more quickly
Reduced HHR
Fuel will continue to pyrolize
Extremely fuel-rich smoke
3–134
Be aware of the type and amount of combustible furnishings and fuel load present during an inspection.
Decorations
Furniture
Wall coverings
3–135
Understand the fully developed stage of fire.
(Cont.)
3–136
Understand the fully developed stage of fire.
Flammable products of combustion are likely to flow
Flames will extend out of openings because there is insufficient oxygen
If no openings, unlikely fire will reach fully-developed stage
3–137
Inspectors need to know the characteristics of the decay stage of fire.
Courtesy of Dan Madrzykowski/NIST
3–138
Understand fuel consumption in the decay stage of fire.
When fire enters the decay stage
Fire can become fuel controlled
HRR will drop
Products of combustion can accumulate
3–139
Understand limited ventilation in the decay stage of fire.
HRR declines
May maintain an extremely high temperature within the compartment
Temperature drops
REVIEW QUESTION
What are the stages of fire?
3–140
�Summary
3–141
(Cont.)
�Summary
3–142