IFSTA CH 4 Fire Dynamics Flashcards
physical change
substance remains chemically the same but changes in size, shape or appearance (ex. freezing/boiling)
Chemical reaction
occurs when a substance changes from on type of matter into another
oxidation
chemical reaction involving the combination of an oxidizer with other materials
timeline of oxidation
potential energy
the amount of energy that an object can release at some point in the future
kinetic energy
energy that a moving object possesses
exothermic reaction
reactions that emit energy as they occur
ex. Fire, releases energy in the form of heat and sometimes light
endothermic reaction
reactions that absorb energy as they occur
ex. converting water to steam
fire triangle
Fire Tetrahedron
eliminate any of the elements in the fire triangle
the fire will be extinguished
ignition
fuels must be in a gaseous state in order to burn
pyrolysis
occurs when a solid fuel is converted into a gaseous fuel
vaporization
is the conversion of a liquid to a vapour by heat energy
piloted ignition
most common form of ignition
occurs when a mixture of fuel and oxygen encounter an external heat source with sufficient heat or thermal energy to start the combustion reaction
autoignition
occurs without any external flame or spark to ignite the fuel gases or vapours
autoignition temperature (AIT)
minimum temp at which a fuel in the air must be heated in order to start self-sustained combustion
always higher then its piloted ignition temperature
two modes of combustion
flaming and non-flaming
non-flaming combustion
occurs more slowly and at a lower temperature, producing a smoldering glow in the materials surface (fire triangle)
flaming combustion
commonly referred to as fire
produces a visible flame above the materials surface
occurs when a gaseous fuel mixes with oxygen in the correct ratio and heats to ignition temperature (fire tetrahedron)
products of combustion
often described as heat and smoke
materials produced and released during burning
incomplete combustion
smoke is a product of incomplete combustion
combustion is incomplete when any of the fuel is left after combustion has occurred
has the potential to burn
carbon monoxide
toxic and flammable product of the incomplete combustion of organic materials
colorless and odorless gas
acts as a chemical asphyxiant (frequent cause of death in civilians)
hydrogen Cyanide (HCN)
toxic flammable substance produced int he combustion of materials containing nitrogen
is a significant byproduct of the combustion of polyurethane foam used in many household furnishing
is 35x more toxic than CO
HCN prevents the body from using oxygen at the cellular level
carbon dioxide
is a product of complete combustion of organic materials
it displaces existing oxygen which creates an oxygen deficient atmosphere
pressure
is the force per unit of area applied perpendicular to a surface
gases always move from areas of higher pressure to areas of lower pressure
health effects of CO
health effects of HCN
Heat
is the thermal kinetic energy needed to release the potential chemical energy in a fuel
temperature
is the measure of heat
heat (HRR) - candle example
one candle burns at the same temperature as ten candles
however the heat release rate of the ten candles is 10x greater than on candle at the same temperature
HRR and PPE
the temperature tells you it is safe to go in but the heat transfer rate - not the temperature - tells you how long you can stay in
chemical energy
most common source of heat in combustion reactions
self-heating
a form of oxidation
is a chemical reaction that increases the temperature of a material without the addition of external heat
spontaneous ignition
ignition without the addition of external heat
electrical energy can occur in several ways, including
resistance heating
overcurrent or overload
arcing
sparking
resistance heating - electrical
electric current flowing through a conductor produces heat
overcurrent or overload - electrical
when the current flowing through a conductor exceeds its designed limits
arcing
high-temp electric discharge across a gap or through a medium
sparking - electrical
when an electric arc occurs, glowing particles can form and splatter away from the arcing point
temperature - Celsius/Fahrenheit conversion
mechanical energy
friction and compression generate mechanical energy
movement of two surfaces against each other
compressed gas
heat transfers from
warmer objects to cooler objects
Heat transfers in 3 ways
conduction
convection
radiation
conduction
transfer of heat through and between solids
a material is heated as a result of direct contact with a heat source
Convection
transfer of thermal energy by the circulation or movement of a fluid
convection - vertical movement
due to the buoyancy of smoke and fire gases
convection - lateral movement
usually the result of pressure differences between
radiation
transmission of energy as electromagnetic waves
travels in a straight line at the speed of light (ex. sun)
common cause of exposure fires
fuel
is the oxidized or burned material or substance in the combustion process
fuel in a combustion reaction is known as the reducing agent
gases
for flaming combustion to occur, fuels must be in a gaseous state
HRR in watts
vapor density
describes the density of gases in relation to air
air has a vapor density of 1
gases of a vapor density less than one will
rise
gases of a vapor density greater than 1 will
sink
liquids
have mass and volume but no definite shape
specific gravity
ratio of the mass of a given volume of a liquid compared to the mass of an equal volume of water at the same temperature
water is assigned a specific gravity of 1
specific gravity of less than 1 will
float
specific gravity of greater than 1 will
sink
flash point
is the minimum temperature at which a liquid gives off sufficient vapors to ignite but not sustain combustion in the presence of a piloted ignition source
fire point
the temperature at which a piloted ignition of sufficient vapors will begin a sustained combustion reaction
solubility
describes the extent to which a substance will mix with water
miscible
materials that are miscible in water will mic in any proportion
polar solvents
flammable liquids that have an attraction to water
will mix readily with water
solids
have a definite size and shape
surface-to-mass ratio
ratio of the surface area of the fuel to the mass of the fuel
as the ratio increases, the particles ability to ignite increases
oxygen
primary oxidizing agent in most fires
normally air consist of about 21% oxygen
flammable (explosive) range
range between the upper flammable limit and lower flammable limit in which a substance can ignite
lower explosive (flammable) limit
minimum concentration of fuel vapor and air that supports combustion
to lean to burn
upper explosive (flammable) limit
concentration above which combustion cannot take place
too rich to burn
chemical flame inhibition
occurs when an extinguishing agent, interferes with this chemical reaction, forms a stable product and terminates the combustion reaction
fuel limited
when sufficient oxygen is available for flaming combustion
incipient stage = fuel limited
ventilation-limited
have access to all the fuel need to maintain combustion
the fire does not have access to enough oxygen to continue to burn
stages of fire development
incipient stage
growth stage
fully developed stage
decay stage
three key factors that control how the fire develops
fuel properties
ventilation available
heat conservation
flammable (explosive) range photo
surface-to-mass ratio photo
incipient stage
starts with ignition (where the fire begins)
fuel-limited fire
portable extinguishers or small hose line can extinguish
ceiling jet
hot gases in the plum rise until they encounter the ceiling, then begin to spread horizontally
growth stage
a visual indicator that a fire is leaving the incipient stage is flame height
when flame reach 2.5 feet high, radiant heat begins to transfer more than convection
can become vent-limited or fuel limited
fuel package location and entrainment of air
Thermal layering
the tendency of gases to form into layers according to temperature, gas density and pressure
neutral plane
interference between the hot gas layers and cooler layer of air
net pressure is zero where the layers meet
rapid fire development
refers to the rapid transition from the growth stage or early decay stage to a ventilation-limited fully developed stage
flashover
rapid transition from the growth stage to the fully developed stage
the combustible materials and fuel gases in the compartment ignite almost simultaneously
changes from a two-layer condition to a single (untenable)
rollover
significant indicator of flash over
condition where unburned fire gases that have accumulated at the top of the compartment ignite and flames propagate through the hot gas layer or across the ceiling
four common elements of flashover
transition in fire development
rapidity
compartment
pyrolysis of all exposed fuel surfaces
fully developed stage
occurs when the heat release rate of the fire has reached its peak because of a lack of either fuel or oxygen
backdraft
an increase in ventilation such as opening door or window can result in an explosively rapid combustion of the flammable gases
occurs in a space containing a high concentration of heated flammable gases that lack sufficient oxygen for flaming combustion
fuel-limited conditions
the available fuel limits the peak heat in a fuel-limited, fully developed fire
ex. campfire
ventilation-limited conditions
lacks the oxygen available to grow
decay stage
runs out of available fuel or oxygen
flow path
composed of two regions
- ambient air flow in
- hot exhaust flow out
unidirectional due to pressure differences
smoke explosion
occurs when a mixture of unburned fuel gases and oxygen comes in contact with an ignition source
effects of firefighting operations
temperature reduction
fuel removal
oxygen exclusion
chemical flame inhibition
temperature reduction
using foam or water to cool
fuel removal
typically a tactic in wildland, liquid and gas fires
oxygen exclusion
flow path control
door control/tactical ventilation
chemical flame inhibition
using extinguishing agents other than water and foam to interrupt the combustion reaction and stop flame production
ex dry chemicals
fuel load
total quantity of combustible content of a building, space or fire area
compartments
any open space with no complete fire barrier dividing is considered a compartment
compartmentation - layout of the various open spaces in a structure
pulsing smoke
backdraft
rollover
flashover
flashover indicators
increase temperature
rollover
lowering of hot gas layer (neutral plane)
