Chapter 2 Fire Behavior Flashcards
Fire
A chemical reaction that requires Fuel, Oxygen, & Heat to occur.
A rapid chemical reaction that gives off energy & products of combustion that are very different in composition from the fuel & oxygen that combined to produce them.
Rapid self-sustaining oxidization process accompanied by the evolution of heat & light of varying intensities.
Physical Science
Study of the physical world around us and includes the sciences of chemistry & physics and the law related to matter & energy
The U.S. uses the English or Customary unit
Other use the Metric or International systems of units (SI)
Weight
The measurement of the gravitational attraction on a specific mass (customary unit LB’s)
Energy
The capacity to perform work.
Work
Transformation of energy from on form to another
(When a force is applied to an object over a distance)
(CU=”Ft lb”) (SI= “Joule”)
Joule
Unit based on a force in expressed Newtons
Types of Energy
Chemical Mechanical Electrical Heat Light Nuclear
Chemical Energy
Energy released as a result of a chemical reaction
FIRE
Mechanical Energy
Energy a object in motion possesses
Rolling Rock
Electrical Energy
Developed when electrons flow through a conductor
Heat Energy
Transferred between two bodies of differing temperatures.
(Sun & Earth)
Most common on earth
Light Energy
Visible radiation produced at the atomic level such as flame produced during the combustion reaction.
Nuclear Energy
Energy released when atoms split(Fission) or Join (Fusion).
Nuclear power plants generate power as a result of fission of uranium-235.
Fission
Atoms split
Fusion
Atoms join together
Energy exists in two states
Kinetic-energy possessed by a object in motion
Potential- Energy possessed by an object that can be released in future. (rock on cliff)
In fire, Fuel is potential chemical energy, as it burns its converted to kinetic energy in the form of heat and light.
Kinetic Energy
Energy possessed by a object in motion
Potential Energy
Energy possessed by an object that can be released.
“Rock on a cliff”
Power
Amount of energy delivered over a given period of time.
CU=”HP”) (SI=”WATTS”
Calorie
Amount of heat required to raise the temperature of 1 Gram of water 1 degree Celsius.
BTU
Amount of heat required to raise 1 Lb of water 1 degree Fahrenheit
Mechanical equivalent of heat.
Relationship between the calorie and Joule
1 Calorie= 4.187 Joules
1 BTU= 1,055 Joules
Heat can be transferred from one body to another by 3 mechanisms
Conduction
Convection
Radiation
Conduction
Point to point contact
*Heat transferred early in the development of all fires is almost entirely due to conduction
Convection
Transfer of heat energy by the movement of heated liquid of gases
- When fire grows
Radiation
Transmission of energy as a electromagnetic wave.
(Light & Radio waves, X-rays)
Travels in a straight line at the speed of light.
Energy travels @ a speed of light from the sun through space”Vacuum” & warms the earth
- Cause of most exposure fires
Matter
Anything that occupies space and has mass
Physical appearance/Properties (Mass,Size,Volume)
Physical State (Solid, Liquid, Gas, Color, Smell)
Physical appearance/Properties of matter
Mass
Size
Volume
Physical State of matter
Solid Liquid Gas Color Smell
H2O
32F Liquid
Sea level atmospheric pressure is defined as 760 mm of mercury on a barometer
Specific gravity of 1
Density
Measure of how tightly the molecules of a solid substance are packed together
(Mass/Volume)
(SI=KG/M^3) (CU=LB/FT^3)
Specific Gravity
Ratio of the mass of a given volume of liquid compared with mass of an equal volume of water.
H2O Specific gravity of 1.
Less than 1 are lighter than water. “FlOAT”
Greater than 1 are heavier than water. “SINK”
Vapor Density
Density of a gas or vapor in relation to air
Less than 1 will “RISE”
Greater than 1 will “FALL”
Chemical Reaction
Whenever matter is transformed from one state to another or a new substance is produced
Simplest of these reactions occurs when matter changes state which is called a physical change
Exp- when H2o freezes the chemical makeup stays the same.
Chemical Change
Substances are transformed into new substances with different physical & chemical properties.
Exp- When Hydrogen & Oxygen are combined to form water.
Exothermic
Reactions that give off energy
(Fire Heat/ Light)
-Oxidation, Combustion
Endothermic
Reaction that absorb energy
Liquid to gas
Oxidation
Formation of a chemical bond between oxygen and another element.
(most common is iron) Flaky red called iron oxide,rust
Very slow process- heat dissipates before noticed.
Exothermic
Combustion
Self-sustaining chemical reaction yielding energy or products that cause further reaction of the same kind.
Supported as low as 14%
Fire Tetrahedron
Oxygen (oxidizing agent) O2 most common
Fuel
Heat
Self-sustained chemical reaction
Oxygen
21% normally
Combustion supported as low as 14%
If temps in compartment fires go up, lower concentrations of o2 are need to support flaming combustion.
Research shows less than 2%
+21% is oxygen enriched ( Burn more rapidly)
31% Nomex ignites & burns vigorously. Hard to extinguish “Home care o2, Nursing homes”
Fuel
Material or substance being oxidized or burned in the combustion process.
Fuel in combustion is known as a reducing agent
Reducing Agent
Fuel in combustion
Pyrolysis
Chemical decomposition of a substance through the action of heat
Surface to mass ration
Surface area to the fuel in proportion to the mass.
Log=Low
Saw dust=High
Vaporization
Transformation of a liquid to its vapor or gaseous state.
Exp- Water left in a pan evaporates
Flammable (Explosive) Range
After fuel has been converted into a gaseous state, it must be mixed with air (oxidizer in the proper ratios) The range of concentrations of the fuel vapor & O2 is called the FR.
% by volume of gas or vapor in air for LFL & UFL
Lower Flammable Limit
Minimum concentration of fuel vapor & Air that supports combustion.
Concentration that are below the LFL are too lean to burn
Upper Flammable Limit
Concentration above which combustion cannot take place.
Above the UFL are too rich to burn
Fuel Load or Fire Load
Total amount (mass) of fuel in a compartment or specific location multiplied by the heat of combustion of materials
Typical basement fire load 5.8 (lb.sq.ft)
Heat
Energy component of fire tetrahedron
Chemical, Electrical, Mechanical, Nuclear
When heat comes in contact with fuel. Energy supports combustion reaction in many ways.
- Pyrolysis or vaporization of solid & Liquids
- Provides Energy necessary for ignition
- Continuous production & Ignition of fuel vapors or gases to continue combustion.
Chemical Heat
When any combustion is in contact with oxygen, oxidation occurs.
Most common in combustion
Heat generated when match burns
Self heating (Spontaneous Heating) is when materials increase in heat with addition of external heat.
Ignition Temperature
Minimum temperature at which self-sustained combustion occurs
Electrical Heat
Can generate temps high enough to ignite any combustible materials near the heated area.
- Current flows through a resistance (static,Lightning)
- Over current or overload ( Arching,Sparking)
Mechanical heat
Generated by friction & Compression
Movement of two surfaces against each other
Nuclear Heat
Heat Energy is generated when atoms either split (fission) or combine (fusion)
Fission heats water to drive steam turbines & produce electricity.
Fusion- sun heat is product
Fire Development
Ignition Growth Flashover (900-1200 degrees) Fully Developed Decay
Fuel Controlled
When amount of fuel available to burn is limited
Ventilation Controlled
When amount of available oxygen is limited
Heat Release Rate (HRR)
Amount of energy released over time BTU’S or KW
Flameover / Rollover
Flames move through or across the unburned gases during a fires progression
Thermal Layering
Gases form into layers according to temp
Polar Solvents
Liquids that readily mix with water
Non-polar (Hydrocarbons)
Classifications of Fires
Class A- Ordinary combustibles
Class B - Flammable & Combustible liquids
Class C- Electrical
Class D- Metals
Class A Fires
Ordinary combustibles
- wood, cloth, paper, rubber, many plastics
Class B Fires
Flammable & Combustibles
- Gas, Oil, Lacquer, Paint, Mineral Spirits, Alcohol
- Smothering or blanketing
Class C Fires
Electrical
- Household appliances, Computers, Transformers
- Halon, Dry Chemical, Carbon Dioxide
Fasters to de-energize
Class D Fires
Metals
- Aluminum, Magnesium, titanium, Zirconium, Sodium, & Potassium
- No single agent effectively controls fires in all combustible metals.