Fire Behavior

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Fire Behavior
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Combustion

• The self sustaining process of rapid oxidation of
  a fuel, which produces heat and light.

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Oxidation

• Normal air has 21 Oxygen(Nitrogen 78)
• Instantaneous oxidation Explosion
• Very Slow oxidation Rust
• Rapid oxidation Fire (Steady state, free
  burning, and smoldering fires )
• Self oxidation Organic peroxide or any oxide or
  oxalate

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Self Oxidizing Agents and Oxidizing Agents

• Bromate Bromine
• Chlorates Chlorine
• Fluorine Iodine
• Nitrates Nitric acids
• Nitrates Peroxides
• Chlorine Magnesium
• Other Combustible metals

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Fire

• Visual byproducts of combustion
• The result of a rapid combustion reaction

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What is Fire Point, Flash Point, and Ignition
Temperature?

• FIRE POINT - The temperature at which a liquid
  fuel will produce vapors sufficient to support
  continuous combustion once ignited. The fire is
  usually a few degrees above Flash point

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• FLASH POINT - The minimum temperature at which
  liquid fires gives off sufficient vapors to form
  an ignitable mixture with the air near the
  surface. At this temperature, the ignited vapors
  will flash but will not continue to burn.

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• IGNITION TEMPERATURE - The minimum temperature to
  which a fuel in air must be heated to start
  self-sustained combustion with out a separate
  ignition source.

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What Is Heat Energy?

• The movement of molecules setting matter in motion

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Categories Of Heat Energy

• Chemical
• Electrical
• Mechanical
• Nuclear
• Solar

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Chemical

• When any combustible is in contact with oxygen,
  oxidation occurs. This process almost always
  results in the production of heat.
• The heat generated when a common match burns is
  an example of Chemical Heat Energy

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Heat of Combustion

• The amount of heat generated by the combustion
  process.
• The amount of heat depends on the material being
  burned.
• This phenomenon is why some materials burn
  hotter than others

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Spontaneous or Self-Heating

• When organic materials increase in temperature
  without the help of external heat sources. e.g.
  Oil-soaked rags rolled into a ball to decrease
  ventilation.

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Materials Subject to Spontaneous Heating

• Charcoal High
  tendency
• Fish Oil
• Linseed Oil
• Brewers Grain Moderate
• Fertilizers
• Hay
• Manure
• Rags Low

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Electrical Heat Energy

• Resistance Heating - the heat generated by
  passing electrical current through a conductor
  such as wire.
• Increased when wire is not large enough for
  amount of current
• Overloaded wires
• Tightly wound conductor

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Dielectric Heating

• The result of pulsating Direct Current (DC) or
  Alternating Current (AC) at a high frequency on a
  non conductive material.

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Leakage Current Heating

• Insufficient insulation of conductor

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Arcing

• Interrupted current flow.
• Open switch
• Loose connection
• Arc welder

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Static Electricity

• The positive charge on one surface contacting the
  negative charge on another.
• Both surfaces are naturally attracted to one
  another and seek to become evenly charged. e.g.
  lightning.
• Electronic bonding/grounding is required when
  fuel is transferred from one tank to another.
  e.g. aircraft.

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Mechanical Heat Energy

• Diesel engines use heat of compression
• Rubbing two sticks together to start a fire uses
  heat of friction

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Nuclear and Solar Energy

• Splitting atoms - fission
• Combining atoms - fusion e.g. the sun

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Heat Transfer

• Heat tends to flow from hot substances to cold
  until both reach the same temperature.
• Heated air gases and liquids expand and rise
• Heat waves do not readily travel through solid
  objects

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Conduction

• A method of heat transfer of hot to cold.
• Good conductors - Aluminum, copper, and iron
• Poor conductors - Fibrous materials such as felt,
  cloth, and paper, liquids, and gases.

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Convection

• Example of heated air and liquid gases expanding
  and rising.
• Direct flame contact is a form of convection.

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Radiation

• The transmission of energy as an electromagnetic
  wave such as light waves, radio waves, or x-rays.
  Commonly called heat waves.
• Radiated heat will travel through space at the
  speed of light until it reaches an opaque object.
  In turn, the opaque object will radiate heat from
  its surface.

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The Principals of Fire Behavior

• Three types of fuel
• Solid
• Liquid
• Gas

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• For combustion to occur, all fuels must be
  transformed to a gaseous state.
• Solid fuels by Pyrolysis - the decomposition of a
  substance through the action of heat
• Liquid fuels by vaporization - generally requires
  less heat than pyrolysis.
• Gases - Do not need decomposition and the most
  difficult to contain.

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Fuel Characteristics

• Surface-to-mass ratio - solids - log vs sawdust
• Physical position - solids - vertical vs
  horizontal
• Shape assumption - liquids gases - assumes the
  shape of container
• Solubility in water - liquids
• Polar solvents - dissolve in water e.g. alcohol
• Nonpolar solvents - e.g oil, gasoline

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The Burning Process

• When the proper fuel vapor/air mixture is
  achieved, it must then be raised to its ignition
  temperature or the point which self-sustained
  combustion will continue.
• Fire burns in two basic modes - flaming and
  smoldering

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Radiative Feedback

• The radiant heat providing energy for continued
  vaporization gt self-sustain.
• Heat is fed back to the fuel creating a positive
  heat balance gt maintains combustion.

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Physiological Effects of Reduced Oxygen

• 21 - Normal
• 17 - Some impairment of muscular coordination
• 12 - Dizziness, headache, rapid fatigue
• 9 - Unconsciousness
• 6 - Death

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Phases of Fire

• Incipient
• Steady State
• Hot-Smoldering

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What is Rollover, Flashover, Flame Spread Stage,
and Clear Burning?
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How Can Flashover Be Avoided?

• Direct water toward the ceiling level and room
  contents to cool contents below ignition
  temperature.
• Avoid breaking thermal layer until required.

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Characteristics of Potential Backdraft

• Pressurized smoke exiting small openings
• Black smoke becoming gray/yellow
• Confinement and excessive heat
• Little or no visible flame
• Puffs of smoke leaving building
• Smoke stained windows
• Muffled sounds
• Rapid inward suction of air

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Thermal Layering

• Gas forming into layers according to temperature
• Other terms are Heat stratification and thermal
  balance
• Smoke is a heated mixture of air, gases, and
  particles that rise.

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Why is Thermal Layering Critical to Fire fighting?

• Hottest air and gases rise, allowing for
  ventilation and making lower levels safer for
  fire fighters
• Improper water application disrupts the thermal
  layer causing steam to circulate through all
  levels. Forced ventilation then required
• Disruption of thermal layer causes a burn hazard
  to fire fighters

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Products of Combustion

• Heat
• Flame
• Smoke
• Fire gases

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Extinguishing Methods

• Reducing Temperature
• Fuel removal
• Excluding Oxygen
• Inhibiting the Chemical Chain Reaction

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Classes of Fire

• Class A - Combustible materials
• Class B - Flammable liquids
• Class C - Electrical
• Class D - Combustible Metals