2 types of Ignition
Piloted: the moment when a mixture of Fuel & O2 encounter an external heat source with sufficient thermal energy to start the combustion reaction
Auto Ignition: is the initiation of combustion with out spark or flame to ignite gases or vapor
Modes of Combustion
Flaming: occurs when gaseous fuel mixes with O2 in the correct ratio and heated to the ignition temp.
Non-Flaming: Occurs more slowly and at lower temperature producing a smoldering glow in the materials surface
3 forms of Energy
Mechanical: Adiabatic Compression, Friction, Friction Sparks
Electrical: Resistance Heating, Over-current/Overload, Arching, Sparking
Chemical: Self-Heating, Spontaneous Ignition
LAW OF HEAT FLOW
Heat transfer
heat is like pressure it will go from areas high temp to areas of lower temp
heat energy can be transferd in 4 ways
-Conduction: transfer of heat between solids
- Convection: TRANSFER OF THERMAL ENERGY BY THE CIRCULATION/MOVEMENT OF FLUID/GAS
- Radiation: TRANSFER OF THERMAL ENERGY as an electromagnetic wave without an intervening medium… light,radio,Xray. Factors that influence: Nature of exposed surfaces, distance between heat source and exp. surface, Temp diff. between heat source and exp surface
- Direct Flame Contact
Fuel
Fuel is the reducing agent
4 stages of fire development
Incipient
Growth
Fully Developed
Decay
3 types of rapid Fire Development
Smoke Explosion
Back Draft
Flash Over
Matter
Anything that occupies space and has mass.
Solid
Liquid
Gas(only gases will burn)
Physical vs Chemical Change
Physical: substance remains chemical the same but changes shape, size, appearance (state liquid to gas)
Chemical Change: Change from one type of matte to another like 2 types of matter are combined to form a substance
Energy
capacity to preform work
Potential & Kinetic energy
Potential: the amount of kinetic energy a an object can release in the future
Kinetic: energy possessed by a moving object
Law of Conservation of Mass
Mass and Energy my be converted from one to an other, but there is never any net loss of total mass/energy
Chemical reactions that release thermal energy
Exothermic
Chemical Reactions that absorb thermal energy
Endothermic
Pyrolysis & Vaporization
Pyrolysis: Chemical decomposition of a solid material by heating. = gases that burn
Vaporization: Physical process that changes a liquid to gaseous state
Auto Ignition Temerature
The lowest Temperature which a combustible material will ignite without an external source of ignition
Fire
Is a rapid oxidation process, which s chemical reaction resulting in the evolution of light and heat in varying intensities
Combustion
is defined as a chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either glow or flame
Products of combustion
Heat light and Smoke
Smoke
SMOKE: Suspension of heated gases and small visible particles of liquids and solids such as steam, carbon, tars and dust in air a resulting from the incomplete combustion of a fuel
- Is an Aerosol comprised of Gases, Vapor, and Solid Particulates.
smoke is a product of of incomplete combustion
Carbon Monoxide, Hydrogen Cyanide, Carbon Dioxide, Irritants
Flame
Is the visible, luminous body of a burning gas
with proper amounts of O2 the flame becomes hotter and less luminous because of a more complete combustion
Fire Triangle
Elements/Conditions needed for COMBUSTION
Fuel
Oxygen
Heat
Fire Tetrahedron
4 elements/conditions required to have FIRE Heat Fuel Oxygen Chemical Chain Reaction
HEAT
Heat is Kinetic Thermal Energy transferred from a high temp. substance to a low temp. substance
it is always in transit from open flame to exposed fuel
Temperature
is the measurement of heat
Chemical Energy: self heating
A form of oxidation, is a chemical reaction that increases the temperature of a material without the addition of external heat
Chemical Energy: Spontaneous Ignition
Initiation of combustion of a material by an internal chemical/biological reaction that has produced sufficient heat to ignite material
if heat cannot escape fast enough it will accumulate to the point where spontaneous ignition may occur
Mechanical Energy: Adiabatic Compression
Is the generation of heat when a gas is compressed
Fuel(reducing agent)
A fuel is a substance being oxidized in the combustion process.
fuel can be solid, liquid, gas; but must be in a gaseous state to burn
Heat of combustion and Heat Release Rate
Heat of combustion: is the total amount of thermal energy that could be generated by the combustion reaction if the fuel were completely burned.
Heat Release Rate: is the total amount of Heat released per unit of time and measured in kW
Specific Gravity
Ratio of MASS of a given volume of liquid compared with the MASS of equal volume of water
Vapor Pressure
the pressure of vapors escaping from a liquid;
flammable liquids with a high vapor pressure present a special hazard for ff; this is an indication of how easily they will evaporate
Flash Point
is the minimum temperature at which a liquid gives off sufficient vapors to ignite but not sustain combustion
Fire Point
is the temperature at which sufficient vapors are being generated to sustain the combustion reaction
under 38’c/100’f flammability hazard
Solubility
Describes the extent to which a substance will mix with water
materials that will mix in any proportion with water are
Miscible
Polar Solvents
liquids that will readily mix with water
Gases
all flues must be gaseous state to burn
A fuel has a LEL and UEL
LEL; Lower Explosive Limit: the lowest concentration of a combustible or flammable gas in the air that will support combustion
UEL; Upper Explosive Limit: Highest concentration of a combustible or flammable gas in the air that will support combustion
Explosive Range or Ignitable mixture
The range of vapor mixture that will ignite when subjected to an ignition source
Vapor Density
describes the density of gases in relation to air: air =1
Oxidizing Agents
is any substance that yields oxygen during a chemical reaction. An oxidizer is not combustible but will support combustion
Oxygen enriched
Oxygen Deficient
Normal 20-21%
Enriched>21%
Deficient<20%
open fire strategy
cool the fire
Compartment fire
Fuel Controlled: A fire with adequate oxygen in which the HRR and growth are determined by the characteristics of the fuel, such as quantity and geometry
Ventilation Controlled: A fire with limited ventilation in which the HRR or growth is limited by the amount of oxygen available to the fire
Thermal Layering
Tendency of gases to form into layers according to temperature
7 factors that affect fire development
- Fuel Type
- Avilablity and location of additional fuel
- Compartment volume and height of celing
- Ventilation/oxygen supply
- Thermal prperties of compartment
- Ambient weather conditions
- Fuel load
Rapid Fire Development
Smoke explosion
Backdraft
Flashover
Flashover
is a very rapid transition from local burn of contents with in a compartment to wide spread burning of all exposed fuels with in that compartment.
- can happen in as little as 90 sec.
- temp 650-1200’C
- CO has a flammable range of 12.5-74% , ignites at 610’C
- .5-2sec escape time @ 2.5’ per sec = 5’ max distance
4 precursors to flashover
Free Burning
High Temp
Heavy Dark Smoke
Rollover
4 Variables of flash over
- Compartment size
- Insulation qualities of compartment
- Ceiling height
- Ventilation: can delay(incepent,growth,) or cause(Fully developed/Decay) flash depending on stage of growth
Backdraft
explosively rapid combustion of flammable gases caused by an increase in ventilation
introduction of O2 causes fire of explosive force
5 Indicators of potential back draft
- Building:fire contained to single compartment
- Smoke: heavy dense smoke that moves or pulses
- Air flow:high velocity turbulantsmoke dischargeappering to breath/puff
- Heat: high heat, smoke stained windows, walls are hot to the touch
- Flame:little or no visible flame
Smoke Explosion
It is the ignition of a premixed pocket of fire gases and oxygen that may occur when an ignition source is introduced
- smoke color is not an indicator
- can involve cold smoke
- it involves a contained layer of flammable smoke already existing with in the flammable range
- all it requires is an ignition source
