Ch. 4 - Fire Dynamics (Test 4) Flashcards
Even though there are fewer fires today than there were in the late 1970’s, there are more firefighters dying as a result of traumatic fireground injuries. ______
(+67%)
(2014-2017)
Average of 295,975 fires per year ________________.
(58% decrease)
(2014-2017)
Average of 2,728 civilian deaths ________________
(53% decrease)
Despite there being countless examples of fire being mystified, stylized or humanized but the truth is:
______________________________
Fire is insentient
Devoid of all intent and/or emotion
_________ - A rapid oxidation process, which is a chemical reaction resulting in the evolution of light and heat in varying intensities. (NFPA 921)
Fire
___________ - A self-sustaining chemical process of oxidation that occurs at a rate fast enough to produce heat and light. (i.e. a glow of a flame) – NFPA 921
Combustion
For generations, firefighters were taught that for fire to exist, only three (4) essential items needed to be present. Those elements are/were:
__________
__________
__________
Fuel
Oxidizing Agent
Heat (Activating energy)
For fire to exist, fuel, oxidizer, AND heat must interact in a such a way so as to for a _________________.
Sustained chemical reaction
The reaction we understand to be fire, is actually a _______________ reliant upon countless variables.
Complex chemical process
In the most general of terms, fuel is ______________.
Consumable matter
Matter exists in one of three physical states:
_________
_________
_________
Solid
Liquid
Gas
It’s ___________ (and density) can be altered by changes in:
-__________
and/or
-__________
-physical state
- temperature
- pressure
What happens to a substance when it changes its physical state? Does its molecular structure change? ____, only the distance between molecules changes
No
Density can be defined as:
A measure of the ___________ of a substance.
Compactness
(Density)
It affects matter’s ability to ________________ heat.
Absorb, transfer, and release
Solid fuels do not burn. They release flammable gases through _________, which is the chemical decomposition of solids through the action of heat.
Pyrolysis
Pyrolysis is ___________ by nature.
Endothermic
A few characteristics that affect solid fuels ability to generate ignitable gases.
- ______________
- ______________
- ______________ to heat source
- ______________
- ______________ of fuel
- ______________
- ______________
- Density
- Surface area to mass ratio
- Physical position/orientation
- Size and shape
- Continuity
- Ignition temperature
- Level of Exposure
Liquid fuels do not burn either. They release ignitable ashes through the process of ____________, which is the process of changing liquid matter into gaseous matter through variances in ___________________.
- vaporization
- temperature and/or pressure
A few characteristics that effect solid fuels ability to generate ignitable gases:
- ____________
- ____________
- ____________
- ____________
- ____________
- ____________
- Volatility
- Vapor Pressure
- Boiling Point
- Specific Gravity
- Solubility
- Fire Point
___________ - The ease with which a substance passes into a gaseous state at a given temperature and pressure.
Volatility
Volatility is determined by:
- ___________
- ___________
- ___________
- Flash point
- Exposed surface area
- Pressure
____________ - The lowest temperature at which a fuel will give off sufficient flammable vapors to ignite momentarily when provided with an external ignition source.
Flash point
Atmospheric pressure at sea level is: _____.
Atmospheric pressure in Salt Lake City is approx. _____.
- 7 psi
12. 5 psi
__________ - The pressure exerted by vapors at the point of __________ with its solid or liquid state (There is no net loss to evaporate).
- Vapor Pressure
- equilibrium
____________ - The temperature at which the vapor pressure of a liquid ________ atmospheric pressure.
- Boiling point
- exceeds
_________ - Water is used as a constant for comparison to other liquids and is given the relative value of one (1):
Any liquid with a density of ________ will sink.
Any liquid with a density of ________ will rise.
-Specific Gravity
- greater than one
- less than one
__________ - The relative ability of a substance to be dissolved into water.
Solubility
__________ - The lowest temperature at which a liquid fuel will produce sufficient vapors to ignite and support combustion for at least 5 seconds.
Fire point
Gaseous fuels ___________ vaporization of pyrolysis to support combustion.
Only an ___________ AND a proper mixture of an __________ is needed.
-do not require
- ignition source
- oxidizer
Characteristics that effect gaseous fuels:
- _______________
- _______________
- Vapor Density
- Flammable Limits
Any gas with a density __________ will sink.
Greater than 1.0
Any gas with a density ___________ rise.
Less than 1.0
There are only _________ gases with vapor density of less than one (1).
Fourteen (14)
Most ____________ fuel vapors are heavier than air.
Hydrocarbon
Flammable Limits: The range of flammable vapors in air, expressed by percentages; that will ignite when provided an ignition source
The area between the lower and upper limits are known as the fuel’s:
_________________
Flammable range
(Flammable Limits)
At what point an environment containing ignitable vapors may be considered _______ but still hazardous.
inert
The concept of ignitable gases acting to inert a flammable/combustible environment applies only:
- _______________
- To areas so _______________ to fuel sources as to displace or exclude all oxygen.
- To closed containers
- immediately adjacent
_____________ - A measurement of the potential fire threat of a given structure.
Fire load
Since the 1970’s, the average single-family dwelling in this country has:
- Seen a ___________ in the number of occupants living within them
- Increased in size by nearly _____
-Transitioned from primarily single-story structures to primarily 2-story structures
—____ increase in number of 2-story homes built
—____ decrease in the number of 1-story homes built
- 20% decrease
- 73%
- 143%
- 52%
How has the fire load of modern structures changed?
- Home sizes have changed
- _______________
- Structural resistance has changed
- Energy Density
- _______________
- Contents have changed
- Heat Release Rate (HRR)
(Energy Density)
______________ - The amount of heat released per unit of mass or volume until of a substance at the end of a complete combustion process.
Heat of Combustion
(Heat Release Rate [HRR])
HRR is ________________________ when describing a fire problem
The __________________________ to life
- the single most important variable
- higher the HRR the greater the threat
(Heat Release Rate [HRR])
The __________________________ to life
higher the HRR the greater the threat
These increases in energy density and heat release rates result in:
Greater __________ measurements.
heat flux
Essentially, the fuel changes are:
Greater quantities
More energy dense
Higher HHRs
……resulting in:
Greater heat flux
OR
More ___________________
Heat making more heat
Does this “Heat making more heat” mean that fires are hotter now than they were in the 1970’s?
___________
Yes & No
While today’s fire environments are:
________ hotter as a result of changes to compartmental heat loss…
The actual temperature of flaming combustion has not changed that much.
Up to 26%
Rather…
It is the _________ of these fires that has dramatically increased.
Resulting in:
- ________________
- Increased requirements for oxygen
- Drastically shortened burn times
- power (HRR)
- More rapid consumption of fuels
__________ is the most common oxidizer
Oxygen
Atmospheric air is comprised of:
__________
__________
__________
21% oxygen
78% nitrogen
1% other gases
___________ - A reactant that removes electrons from other reactants during a redox reaction.
Oxidizer
(Oxidizing Reactions)
These redox reactions can occur very slowly
—______
Very quickly
—______
- Rust
- Explosions
___________ - The complete chemical reaction of organic materials with oxygen or other oxidizing agents resulting in the formation of more stable chemical compounds.
Oxidation
Only a relatively small amount of energy is required to start the reaction resulting in a larger energy release making ______________________.
oxidation an exothermic process
___________ - A chemical reaction that releases more heat energy than it uses.
Exothermic
__________ - A chemical reaction that absorbs more heat energy than it releases.
Endothermic
Oxidation Variables:
- ___________
- ___________ of available oxidizing agent - Higher concentrations of oxidizer result in more redox reactions
- ___________ - The greater the exposed surface area, the greater the number of simultaneous redox reactions
- ___________ - Excess compounds in the atmosphere may prevent block the pathways of energy preventing or limiting the sustainment of redox reactions.
- Temperature
- Quantity
- Interface Area
- Accessibility
Accessibility– Excess compounds in the atmosphere may prevent block the pathways of energy preventing or limiting the sustainment of redox reactions. These compounds are commonly referred to as:
_______________ – Any substance occupying space and capable of absorbing heat resultant of a redox reaction.
Thermal Ballast
TRUE OR FALSE
The terms Heat and Temperature are synonymous?
False
_____________ – is a measurement of the average kinetic energy caused by the movement of molecules within a substance.
Temperature
_______ – is the form of energy that ____________________ of molecules.
- Heat
- raises the average kinetic energy
(Sources of Heat Energy) Chemical
___________ source of heat energy in combustion reactions
Most common
(Sources of Heat Energy) Chemical
Chemical heat energy is produced by ______________
oxidation reactions
Forms of Chemical Heat Energy:
- ______________
- ______________
- ______________
- ______________
- Heat of Combustion
- Heat of Solution
- Spontaneous Heating
- Heat of Decomposition
(Sources of Heat Energy) Mechanical
Forms of Mechanical Heat Energy:
________ - the force that resists the relative motion or tendency to such motion of two bodies in contact.
________ - the application of continuous force by one body on another that it is touching
- Friction
- Pressure
(Sources of Heat Energy) Nuclear
Forms of Nuclear Heat Energy
______ - a thermonuclear reaction in which nuclei of light atoms join to form nuclei of heavier atoms.
______ - the splitting of the nuclear of an atom into nuclei of lighter atoms, accompanied by the release of energy.
- Fusion
- Fission
Heat (energy) will flow from areas of higher concentration to areas of lower concentration in an attempt to balance itself out.
—This transfer will occur in several ways:
______________
______________
______________
Conduction
Convection
Radiation
____________ - Transfer of heat energy from _____________________.
- Conduction
- one material/molecule to another
Variables of Conduction:
- ______________
- ______________
- ______________
- ______________
- Thermal Conductivity (k)
- Temperature
- Mass
- Exposure
____________ - Transfer of heat energy from one point to another through _____________________.
- Convection
- the movement of liquids and/or gases
Convection is the _________________ inside a structure.
main reason for fire spread
There are two distinct mechanisms of convective heat transfer:
___________
___________
Natural
Forced
(Mechanisms of heat transfer) Natural
Velocity of flowing gas it controlled by _________________
buoyancy-induced flows
(Mechanisms of heat transfer) Forced
The velocity of flowing gas is __________________________
artificially imposed (fan, wind, fire stream)
_____________ - Fluid compounds (liquids and gases) will stratify within a given space based upon temperature and density.
Stratification
____________ - Heated fire gases and smoke will rise as long as their temperature remains higher than the surrounding atmosphere. Once either the temperatures equalize or rising gases and smoke impact the ceiling within the space, rising pressure from continued combustive by-products will force the gases and smoke to push outward along a horizontal plane and begin to bank down and stratify.
Mushrooming
____________ - Transfer of heat energy from one material to another by _______________ without the need of an intervening medium.
- Radiation
- electro-magnetic waves
Variables of Radiation:
- ___________
- ___________
- ___________
- ___________
- Color/Opacity
- Position
- Distance
- Temperature
The first phase of fire development is:
_________ - The process of initiating self-sustaining combustion
Ignition
Ignition requires:
Sufficient ______ to initiate and sustain the combustion reaction.
A source of _____ either in an immediately ignitable state or one capable of converting to this state with available heat.
An adequate supply of ______ or another oxidizing agent.
heat
fuel
oxygen
With enough heat, the available fuel gases will ignite and begin the combustion process.
The amount of heat required depends upon the fuel’s:
___________________
___________________
- Piloted Ignition Temperature
- Auto-Ignition Temperature
____________________ - The minimum temp at which a solid fuel will give off sufficient flammable/combustible vapors in air capable of sustained combustion if supplied with an external ignition source.
Piloted Ignition Temperature
______________________ - The minimum temp at which a solid fuel will give off sufficient flammable/combustible vapors in air capable of sustained combustion without an external ignition source.
Auto-Ignition Temperature
What is the temperature of Carbon Monoxide’s Auto-Ignition Temperature?
1128º F
The piloted ignition temperature is generally ____________ than the auto-ignition temperature.
significantly lower
Once the fuel has reached its ignition temperature and flaming combustion has commenced, the fire is said to be in its incipient stage. In this stage, continued growth will depend upon the following variables:
- _______________
- _______________
- _______________
- _______________
- _______________
- Compartment Design
- Location of fuel
- Fuel Composition
- Availability of Oxygen
- Time/Duration of Exposure
A fire in its Incipient State present with:
- __________________
- ____________ usually seen on windows in or near the fire compartment
- Fire that is small in size
- Little to no development of a _________ or accumulation of hot gases at the top of the compartment
- Low compartmental heat
- Condensation
- flow path
(Incipient Stage) Characteristics
- ____________________
- Heated gases rise and mix with and/or _________________
- Little if any visible smoke
- displace cooler gases
(Growth Stage)
The ease/speed at which a fire grows depends largely upon the following variables:
- _______________
- Heat
- _______________
- _______________
- Available fuel
- Compartment Design
- Air/Oxygen
(Growth Stage) Heat is:
_____________________
Heat is the driving factor in fire growth
(Growth Stage) Air/Oxygen
Fire grows in ______________ to the volume of oxidizer (air) available to it.
direct proportion
A fire in its Growth Stage will present with:
- _______________
- Condenstaion seen during the incipient stage will be replaced with _______________ and/or _________________ near the fire
- Fire that has dramatically increased in size
- Increased smoke and gas production dust to ______________
-Increased compartmental heat
- brownish black staining
- cracks in upper panes of glass
-incomplete combustion
____________ - As fire gases, near the ceiling, reach ignition temp and enter into their flammable range, flames spread through the gases in wave or snake-like patterns
Rollover
(Rollover) Increase in flames cause increases in compartmental:
- ___________
- ___________
- ___________
- Pressure
- Heat
- Heat Transfer
(Rollover)
_________ - Forces smoke and gases to extend beyond the compartment (Down the hall)
Pressure
(Rollover)
_______ - Increased flames create greater liberation of heat and light. All elements within the compartment are pushed to near auto-ignition temp.
Heat
(Rollover)
___________ - Compartment walls, ceiling, and contents are bombarded with an ever-increasing amount of heat.
Heat Transfer
If the fire/compartment cannot be/is not cooled, the fireground phenomenon ____________ will occur.
FLASHOVER
Remember, flashover is a _____________ in fire development as opposed to a truss stage
transitional phase
In order for flashover to occur, a few conditions must be present:
Ceiling temperature within the compartment must reach __________
500-600º C
In order for flashover to occur, a few conditions must be present:
Average Heat Flux to the floor of the compartment must reach __________
15-20 kW/m^2
In order for flashover to occur, a few conditions must be present:
Sufficient _________ must be available to support the increased rate of combustion
oxygen
In order for flashover to occur, a few conditions must be present:
_____________________
Once the walls and ceilings have absorbed all the heat they possibly can, they begin to_______________ back into the space, switching from _______________________.
This radiation feedback _______________________ resulting in a drastic spike in room and content temperature
- Thermal Radiant Feedback
- re-radiate heat
- endothermic to exothermic
- dramatically increases heat flux
An impending flashover will present with:
_______________ exiting through openings in the container
____________ inside the compartment with visible off-gassing of uninvolved objects
Isolated flames traveling in the hot gas layer __________ or increasing concentration of _________
- Intense turbulent smoke
- Intense heat
- ghosting
- rollover
Variables Affecting Flashover:
- _______________
- _______________
- _______________
- _______________
- Room Geometry
- Conductivity/Flammability of walls and ceiling
- Contents
- Rate of heat release
Cellulose materials release and average of __________________
Synthetic materials release between _______________________
- 9000 BTUs per pound
- 12,000 to 18,000 BTUs per pound
Rate of Heat Release - Equation based on type, quantity, and location of materials involved in fire.
________________________________
This is the single most important factor concerning flashover
A fire in its fully developed stage will present with:
Voluminous smoke:
_________ (Gray, brown, or black)
_________ through the predominant flow path
- Dark in color
- Driven by heat
A fire in its fully developed stage will present with:
A well-defined and strong flow path:
-In this state, the fire is _____________ and increasing the amount of available air will increase the size of the fire and the volume of heat.
ventilation limited
A fire in its fully developed stage will present with:
Fire that’s producing substantial heat:
_____________ (1292-2192º F)
700-1200º C
A fire in its fully developed stage will present with:
As the fire’s fully developed stage progresses,
_________________ continues to increase
the potential for collapse
Variables that effect a fully developed fire:
- Access to _________
- Its supply of _______
- _______
oxygen
fuel
Heat
(Decay) A fully developed fire that is confined or that stays compartmentalized will transition into the decay phase though one of three routes:
- ___________________________
- The amount of available ____________________________
- ________________ and transferred out through the structure
- All available fuel is consumed
- oxidizer falls below sustainable levels
- Heat balance is lost
(Decay) If the fire enters an oxidizer-induced decay phase as a result of its container:
- The fire’s heat release rate will decline in ________________ with the amount of available oxidizer
- Temperature within the compartment may ________________ (temporary)
- Fuels will continue to ______________ – releasing ignitable gases
Compartmental pressure will continue to increase.
—>Up to a ________
- direct correlation
- continue to rise
- vaporize/pyrolyze
- 3:1 ratio
Eventually, the fire will self-extinguish and minimize the hazard as long as oxygen is not reintroduced.
If, oxygen is reintroduced however, a __________ may occur.
backdraft
Backdraft definition:
The __________________ to a confined area, that is pressurized with heated flammable gases, resulting in an explosive force of significant intensity.
reintroduction of oxygen
(Backdraft) Precursors to backdraft capable environments:
- ______________
- ______________
- ______________
- Ventilation controlled states
- Available Heat
- Available Fuel
Indicators of a possible backdraft:
-Fire in a _____________ or _____________
-Smoke
——___________
——Appears to be _____________ from the structure
-Air
________ rapidly into the structure
-Doors/Windows
_____ to the touch
- ventilation controlled
- late decay state
- Issuing under pressure
- breathing of puffing
- Being drawn
- Hot
(Backdraft) Sequence of Events:
__________________ of oxygen to the confined fire space
Improper reintroduction
(Backdraft) Sequence of Events:
___________________ needs to contain an explosive mix for backdraft to occur
Only 25% of total space
(Backdraft) Sequence of Events:
Super-hearted gases ignite in an _____________________
explosive combustion process
(Results of Backdraft)
- ____________ will explosively press toward ventilation opening
- ____________ capable of breaking glass, damaging/injuring objects and personnel in its path
- _____________
- Room of backdraft origin ________________________
- Fireball/smoke
- Shockwave
- Possible collapse
- returns to fully developed state
Rollover is the _____________ an area if an effective hose stream is not in place and operating.
last sign to leave
