FLAME SPREAD

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FLAME SPREAD

• DEFINITION The movement of fire from one place
  to another.
• When an investigator first arrives at a fire
  scene, he begins observing fire damage around the
  perimeter of the scene.
• Mental notes and observations begin to
  materialize as to the direction the fire traveled
  from one place to another.
• Understanding the fire flow is critical to the
  investigator.

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FLAME SPREAD
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FLAME SPREAD

• To develop the fire flow pattern it is important
  to know
• What direction did the fire burn?
• Where did the fire come from?
• Where did the fire go?
• Why did the fire move the way it did?
• After he completes the exterior view, the fire
  scene itself is observed.
• Again the investigator is determining how the
  fire traveled from one point to another.

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FLAME SPREAD

• He will compare what he has observed in the scene
  with what he observed outside the scene.
• Finding where the fire stopped, or was
  extinguished now becomes the first place the
  investigator starts in tracking or following the
  flow back to the fires origin area.
• Once he develops a scenario or multiple
  scenarios, he again applies fire spread
  principles by testing and comparing scenarios
  with his flow observations that were first noted.

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FLAME SPREAD

• The ultimate objective is to be able to
  recognize, eliminate and resolve any
  contradictions as to why the damage exists as it
  does.

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FLAME SPREAD

• Definition further explained
• After ignition in the fuel-gas-air mixture, the
  flame that now evolved is either going to grow at
  some rate or stop and return to a smoldering
  stage or end.
• If the fuel-gas-air mixture stays within its
  flammable limits, the flame will begin spreading
  on the fuel surface.
• Fire can spread as a flame or in smoldering,
  however the later is much slower.

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FLAME SPREAD

• Once the fire has established, the fuel that is
  burning or a new adjacent fuel may provide a path
  for the flame.
• A flames buoyancy (or gravitational pull) in
  combination with ventilation will assist or
  oppose its travel to the new fuel.
• Ventilation can be due to meteorological wind, a
  powered fan, or even the natural drafts that are
  induced by the fire.

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FLAME SPREAD

• For the flame to spread on the fuels surface, it
  must pre-heat and start the pyrolysis in the next
  area, we will call this the target fuel region.
• The heat flux that is generated by the flames
  must be sufficient in order to pre-heat the
  target fuel region.
• Visualize the next fuel region as the target of
  the heat transfer.

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FLAME SPREAD

• A Target Fuel is a fuel that is subject to
  ignition by convection and or thermal radiation
  such as from a flame or a hot gas layer.
• It might help to think of the next region that
  the flame will travel as being in the flames
  shadow.
• If no ventilation is present the shadow will be
  short and travel will be slow unless the target
  area is vertical like a wall.

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FLAME SPREAD
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FLAME SPREAD
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FLAME SPREAD

• Many factors affect flame spread, some will be
  discussed below.
• No two fires will burn the same, except in a
  laboratory environment.
• As previously discussed, the human factor and
  environmental and fuel factors make each fire a
  unique scene.

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FLAME SPREAD

• Factors affecting flame spread - Fuel type
• Simply a fuel is any material that yields heat
  through combustion.
• The majority of these fuels are organic and
  contain carbon and some combination of oxygen,
  hydrogen and sometimes other elements such as
  nitrogen.
• The composition of these materials into various
  products through time is continuously changing as
  man finds and invents new uses and other
  products.
• Each fuel product exhibits different physical and
  chemical properties that will affect the fuels
  combustibility and how it will react with other
  materials.

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FLAME SPREAD

• Factors affecting flame spread - Fuel type
• Over the years the composition of furniture, for
  example, has changed drastically.
• For the most part, fuel weights have gotten
  lighter, however, heat release rates have
  climbed.
• The average cotton easy chair weighs between 17.7
  and 31.8 kg (39 and 70 pounds) and heat release
  rate varies between 290 and 370kW.
• While a polyurethane easy chair tips in at 12.3
  and 27.7 (27-61 pounds) and the heat release rate
  varies between 1350 and 1990 kW.
• What does the future bring?

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FLAME SPREAD

• Factors affecting flame spread - Fuel type
• With just the heat release rate changes alone we
  can see that the polyurethane chair will burn
  differently than the cotton chair.
• Flame spread, fire patterns, and fire flow will
  change due to different fuel loads.
• It is important for the investigator to recognize
  and identify materials or material residue at the
  fire scene, since different fuels can have a
  dramatically different heat release rate as shown
  in the chair comparison above.

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FLAME SPREAD

• Factors affecting flame spread - Fuel type
• Further, many fuels can spread flame much easier
  than others.
• One means of comparing interior finish materials
  is the Steiner Tunnel test, ASTM E84.
• Samples are exposed to a propane burner and the
  flame spread distance is measured down a 7.3 m
  (24 ft) tunnel.
• All materials are compared to red oak which has a
  flame spread rating of 100.
• If the material has a number higher than 100 than
  it spreads the flame further than red oak.

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FLAME SPREAD

• Factors affecting flame spread - Geometry
• Geometry is relation of properties and
  measurements of solids, surfaces, lines and
  angles.
• Geometry considerations can start on the
  molecular level of how a fuel or material is
  bound together.
• Then we want to know how that material is used
  with others to compose objects used in the home,
  auto, office and industrial.

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FLAME SPREAD

• Factors affecting flame spread - Geometry
• The geometry of objects and how they are arranged
  in proximity to each other will have an impact on
  fire spread.
• Last but not least, the containment of the
  objects or fuel load has a strong influence in
  the flame spread and fire development among
  different items in a room or structure.

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FLAME SPREAD

• Factors affecting flame spread - Material
  Geometry
• The form of individual materials that make up
  objects such as chairs, clothing, carpeting,
  appliances etc.
• Going back to our comparison of a solid piece of
  pine vs. a pile of pine saw dust or shavings.
• Even though they are composed of the same
  material, the geometry of the material will have
  a dramatic difference on the ease of ignition and
  flame spread.

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FLAME SPREAD

• Factors affecting flame spread - Material
  Geometry
• An other example would be solid cardboard vs
  corrugated cardboard.
• On a more basic level, polymers, such as
  polyurethanes, polyesters, etc have long chain
  molecules with very weak bonds holding them
  together, as opposed to celluosics, such as wool,
  wood, etc which have stronger bonds than polymers
  and require more energy to break them during the
  pyrolysis process.
• A textile with a fuzzy finish will burn easier
  than a similar material with a smooth finish.

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FLAME SPREAD

• Factors affecting flame spread - Object Geometry
• The shape of the objects and how the materials
  are used together in the construction of the
  object will influence the flame spread on the
  object.
• As noted earlier, flat objects are harder to get
  flame spread on, while inside corners or concave
  surfaces, flames can spread with ease.

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FLAME SPREAD

• Factors affecting flame spread - Object Geometry
• The shape of furniture, automobiles, decorations,
  appliances and machinery can trap heat, channel
  hot gas flow, re-radiate on itself or other
  objects to help spread the flame and affect the
  speed of fire growth.
• Where the ignition takes place on the object will
  also have an impact on the growth and development
  of the fire.

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FLAME SPREAD

• Factors affecting flame spread - Fuel Load
  Arrangement Geometry
• As we go one step further with each objects
  geometry, the distance between each object in the
  same compartment will also effect the heat
  transfer between the objects and hence, the flame
  spread and the rate of fire growth.
• A simple way to look at it is to visualize a fire
  load of 4 stuffed chairs in a given room.

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FLAME SPREAD

• Factors affecting flame spread - Fuel Load
  Arrangement Geometry
• If there is one chair at the center of each of
  the four walls, a fire in one of these chairs
  would develop slower throughout the room as
  compared to a room with all 4 of the chairs close
  to one another.
• People arrange their furniture differently and
  many times place various accessories and
  amenities in between the furniture arrangement
  that became fuel that will enhance the transfer
  of heat and fire from one point to another.

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FLAME SPREAD

• Factors affecting flame spread - Structural
  Geometry
• The geometry of the compartment or room plays an
  ever larger role in affecting flame spread and
  the rate of fire growth.
• One of the biggest factors is ventilation.
• How many openings, how large are the opening and
  where are the opening located which can provide
  the fire with fresh air.
• Windows, doors, ductwork, and even plumbing and
  wire penetrations, are all potential sources of
  ventilation.

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FLAME SPREAD

• Factors affecting flame spread- Structural
  Geometry
• The physical shape of the area, such as the
  volume, height of ceiling, the shape of the
  ceiling, the number of alcoves or closets will
  have an impact on fire development.
• Smaller spaces maximize the heat transfer between
  objects and the compartment ceiling and walls.
• Larger spaces may take longer to heat up, however
  they have a larger reserve of air to aid the
  fires growth if sufficient fuel is available.
• Open floor plans vs compartmented floor plans can
  spread smoke and fire is very different ways.

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FLAME SPREAD

• Factors affecting flame spread - Structural
  Geometry
• Type of construction will also have a dramatic
  impact on the fire growth and development.
• Combustible interior finish will add to the fuel
  load of the room.
• Non-combustible or limited combustible interior
  finishes will not contribute significantly to
  flame spread.

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FLAME SPREAD

• Factors affecting flame spread - Structural
  Geometry
• The structural elements can become a factor later
  in the fire.
• The insulation of the room or type of structure,
  i.e. masonary, wood frame, etc will affect how
  well the room will retain heat and how smoke,
  heat and fire will spread through the structure.
• Other building systems such as automatic fire
  sprinklers need to be considered.
• Once the fire moves from the compartment of
  origin, then we must consider each of the
  geometries above to determine the reasons why the
  fire destroyed or damaged the remainder of the
  structure.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow
• As a fire develops from the incipient stage, a
  circulation path also is established.
• As heat and by-products of combustion rise,
  cooler air is drawn in at the bottom.
• (Example cigarette smoke draws to a candle
  flame).
• In order for the fire to grow, it will require 15
  to 21 oxygen in the air that is being drawn in.
• Where does it come from? Compare this dilemma
  with yourself.
• Imagine locking yourself in a room or even your
  house.
• Would you run out of air?
• No, even with all the windows and doors shut
  tight, a structure is designed to breathe.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow
• Some structures breath more or less than others
  depending on how and where they are constructed.
• Structures built above ground will also breathe
  through the floor verses a structure built on a
  concrete slab.
• In a fire with this type, the investigator might
  notice evidence of high heat at floor level.
• Fires will burn more intense where there is a
  richer level of oxygen.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow
• As the fire progresses, the draft may be strong
  enough to open or even close doors, similar to a
  partially open door slamming shut when the A/C
  unit comes on.
• When the heat of the fire is sufficient to begin
  breaking windows, another ventilation source is
  now affecting the fire.
• A fire typically burns up and out.
• It will seek the easiest path in doing this.
• It doesnt like to go around sharp corners it
  will make easy curves to accomplish moving up and
  out.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow
• Once it has breached ceiling, attic and finally
  the roof, it will begin to move faster now that
  it has escaped and has a source of oxygen at the
  bottom.
• If there is any air movement on the outside, the
  fire may tend to lean in the same direction as
  the air movement.
• The fire moves forward in that direction much
  faster than against the flow.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow
• This is where the investigator first sees the
  signs of flow direction.
• Smoke, heat and fire patterns on windows and
  other openings will show him the flow direction.
• The impact of wind and weather may be subtle or
  dramatic.
• It is important for the investigator to determine
  the wind and weather conditions at the time of
  the fire.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow

• Other ventilation factors may occur at any time
  in the during the fire
• One is if there are any occupants inside the
  structure.
• They will open doors and windows in efforts to
  escape, thus again changing or altering fire
  draft conditions.
• This along with any neighbors or passerbys who
  attempt rescue or extinguishment, again opening
  doors and windows.
• Fireman also may alter draft conditions as they
  attempt rescue and/or extinguish the fire.
• Depending on their attach methodology, they may
  push or force the fire into other areas.

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FLAME SPREAD

• Factors affecting flame spread - Ventilation/fire
  flow

• CONCLUSION
•  
• With this lesson, the investigator should see how
  the many factors affect how a fire spreads
  through a structure.
• This flow from the first ignition to final
  extinguishment is what the investigator will use
  to track this flow backward to the point of
  origin and have a scenario that will be
  technically defensible.