FIRE PATTERNS

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FIRE PATTERNS

• Fire patterns are the result of a fire or its
  products of combustion interacting with adjacent
  fuels, building materials, furnishings, contents
  and/or including victims.
• V-patterns, spalling, distorted bulbs, depth of
  char, are all descriptions of damage caused by a
  fire.
• What do these patterns show?
• How do you interpret them?
• Can you be absolutely certain what caused the
  pattern to develop?

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FIRE PATTERNS

• It should be noted that there are very few
  absolutes with patterns.
• Many of the pattern development topics are
  currently the subject of research projects being
  conducted by universities and government research
  laboratories.
• Pattern analysis needs to be done, first locally,
  one section of a room or one item at a time,
  similar to studying one piece of a puzzle.

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FIRE PATTERNS

• Then globally, the whole room or structure, in an
  effort to put the puzzle pieces together.
• If the pieces dont fit dont force them.
• You must look at the totality of the incident and
  how each piece fits to come to a defensible
  conclusion.

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FIRE PATTERNSHow do they evolve?

• Qualitatively - how are the patterns formed?
• A fire produces energy and products of combustion
  and leaves behind burned or partially burned
  residue of the original fuel.
• The energy from the fire is transferred to
  surrounding surfaces via radiant heat transfer,
  convective heat transfer or a combination of
  both.
• The combination of both would occur when smoke or
  hot gas travels over a surface.
• When the hot gas is burning this is referred to
  as direct flame impingement.

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FIRE PATTERNSHow do they evolve?

• We will de-couple the fire by-products to examine
  their role in developing a fire pattern.
• The three most significant damage categories are
• Smoke
• Thermal, non-burning
• Thermal, burning
•  Fire patterns representing each of the above
  damage categories can be found at most fire
  scenes.

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FIRE PATTERNSSMOKE

• The products of combustion from burning a
  hydrocarbon based fuel in air consist of gases,
  water vapor and soot (carbon) particles.
• These products of combustion make up smoke.
• As the smoke plume rises from the fire it begins
  to cool and increase in size as it entrains
  cooler air.

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FIRE PATTERNSSMOKE

• As the smoke continues to cool, the soot
  particles provide a surface for water droplets to
  form around.
• When the smoke impinges on a cooler surface the
  water vapor/soot particles condense out on the
  surface.
• This is similar to what happens when you have a
  cold glass of lemonade on a hot humid day, the
  water vapor from the surrounding air begins to
  condense out on the outside of your relatively
  cold glass. 

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FIRE PATTERNSSMOKE

• Many of the most common combustion gases contain
  carbon.
• For example, carbon dioxide, and carbon monoxide.
• Depending on the fuel that is burning, other
  gases may contain acids, such as hydrochloric
  acid.
• Incomplete products of combustion and/or the
  acids may cause staining or have a reaction with
  a surface material that they are deposited on.

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FIRE PATTERNSTHERMAL NON-BURNING

• As we learned earlier, solids do not burn
  directly.
• When heated, the material begins to pyrolyze
  (emit combustible gases), this action of
  decomposition often causes a material to
  discolor.
• Further heating will continue the process
  typically changing the surface texture.

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FIRE PATTERNSTHERMAL NON-BURNING

• It is this process that causes the thermal
  patterns to form.
• Cellulosic materials, such as wood, cardboard,
  and cotton fabric will start to char.
• Materials such as thermoplastics, glass and wax,
  will then start to melt, disfigure and drip.

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FIRE PATTERNSTHERMAL NON-BURNING

• Additional heating may cause the materials to
  burn.
• So by this definition, the thermal patterns are
  formed by heating a material enough to cause
  discoloration, char or distortion, but not enough
  to ignite the material.
• If the heat is transferred to a wall via radiant
  heat transfer from a fire and an object such as a
  chair is blocking a portion of the wall, thus
  absorbing the heat before it reaches the wall, a
  clear line of demarcation will form at the edge
  of the chair.

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FIRE PATTERNSTHERMAL NON-BURNING

• For radiant heat transfer, the shadow of the
  item will protect the wall.
• For direct smoke plume or flame impingement, the
  item would have to have good surface to surface
  contact to prevent the heat from charring the
  wall.

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FIRE PATTERNSTHERMAL BURNING

• When the fuel is pyrolyzing at a rate that can
  produce the quantity of combustible gas necessary
  to sustain a flame and ignition occurs, the
  thermal feedback to the fuel surface from the
  burning gases increases the rate of pyrolyzation
  and consequently increasing the decomposition
  rate of the fuel.

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FIRE PATTERNSTHERMAL BURNING

• After the material is burning, significant
  changes occur to the burning surface.
• Wood for example will transition from being
  discolored at the surface to developing a char
  layer.
• As the burning continues and more volitiles are
  driven out of the wood, the char layer gets
  deeper and splits and cracks forming a char
  surface often described as alligatoring.

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FIRE PATTERNSWhat do they show?

• Fire patterns will show where smoke and/or heat
  has been transferred to a surface.
• They will provide a sense of where the hottest
  burning took place.
• clean burn area, pulled bulb
• They can indicate where the burning was
  ventilation limited or fuel rich.
• They may assist in determining a fires path of
  travel or fire flow.
• They may point you in the direction of the origin
  of the fire.

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FIRE PATTERNSPattern Catalog

• Lines of demarcation
• The boundary between an undamaged area and an
  adjacent area that has fire damage due to smoke
  or thermal effects.

photo of soot marking on wall
photo of partially burned flooring
photo of partially melted plastic
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FIRE PATTERNSPattern Catalog

• Plume
• The fire patterns formed by a plume impinging on
  a surface such as a wall, ceiling, or furnishing.

wall ceiling
walls ceiling In corner
wall ceiling
pattern on ceiling, no wall involvement
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FIRE PATTERNSPattern Catalog

• Hot gas layer
• The fire patterns formed by the hot gas layer
  contacting the ceiling and walls of a room.
• The ceiling and a portion of the walls from the
  ceiling down should be coated with soot.
• A horizontal line of demarcation will be found on
  the walls of the compartment.

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FIRE PATTERNSPattern Catalog

• Full room involvement
• Fire patterns showing thermal burn damage on
  almost all of the exposed surfaces within a room.
• This type of damage is consistent with a post
  flashover fire.
• Lines of demarcation may be found near the floor
  of open doorways or near other sources of air to
  the room.

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FIRE PATTERNSPattern Catalog

• Surface Effect
• The texture of a surface can impact the look of
  the pattern as well as the rate of heat and mass
  transfer to the surface.
• Smoke moving over a smooth wall or ceiling will
  lose less heat and soot than smoke moving over a
  rough wall or ceiling.
• The rough finish has the effect of increasing the
  surface area that the smoke is interacting with.
• If the rough surface serves as a series small
  obstructions it will slow the movement of the
  smoke.

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FIRE PATTERNSPattern Catalog

• Loss of material
• As the material burns it loses mass.
• The mass goes into the products of combustion in
  both gaseous and particulate form.
• In most cases, the loss of mass or material will
  change the appearance and shape of the burned
  object.
• Sometimes the change in the object can be related
  to the direction of fire movement or fire
  location due to the side of exposure.

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FIRE PATTERNSPattern Catalog

• Penetrations
• Holes or cracks through floors and walls can be
  used as to determine the direction of fire
  movement from one compartment to another based on
  loss of material.
•  
• ltltdiagram similar to NFPA 921 fig 4.3.3,
  comparison photo would be usefulgtgt
• (photos ron)
•  
• NFPA fig 4.3.3

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FIRE PATTERNSPattern Catalog

• Victim injury
• Another application of loss of material.
• Burns on a victim, or lack thereof, could be used
  to assist in determining fire movement.

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FIRE PATTERNSPattern Catalog

• Movement Patterns
• Typically a series of patterns, demarcations, etc
  that can be used by an investigator to track the
  movement of the fire and hot gases back to the
  origin of the heat source.
• (photos ron)
• ltltstick house thermal damage identified with
  fire flow out of doorway and window leading back
  to fuel in far corner of room.gtgt

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FIRE PATTERNSPattern Catalog

• Intensity Patterns
• Demarcation lines or patterns caused by thermal
  damage.
• In other words, using the thermal damage on an
  item or surface to estimate the intensity of the
  heat flux that the target received in a given
  area.
•  
• ltlt show a surface partly charred, melted and
  untouched annotate charred area as result of
  burning, melted (radiant heat only) and not
  enough heat to cause damage.gtgt

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FIRE PATTERNSPattern Catalog

• Wood char
• One of the most common types of damage that an
  investigator will see due to prevalence of wood
  furnishing and wood use in construction and
  finish of buildings.
• As noted in NFPA 921 (ch4.5.2), depth of char
  measurements should not be relied on to determine
  the duration of burning.
• However as discussed under ltltloss of materialgtgt,
  depth of char may provide insight into how the
  fire moved or where there was sufficient oxygen
  to sustain combustion.

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FIRE PATTERNSPattern Catalog

• Spalling
• The loss of surface material from a concrete or
  masonry surface.
• In the context of a fire environment, spalling is
  caused by exposure to high temperatures or rapid
  increases in temperature.
• It should be noted that, spalling can also be
  caused by other means such as weather and wear
  and tear.
• As the spalling occurs it can sound like popping
  or shots.
•  
• ltltspalling photo on floorgtgt

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FIRE PATTERNSPattern Catalog

• Oxidation
• Fire has been described as a rapid oxidation
  process.
• Materials which may not readily burn such as
  metals or inorganic compounds (brick, rock,
  gypsum, etc) can be oxidized by exposure to heat.
• NFPA 921 4.7 gives example for several metals.
•  
• ltltit would be great to generate photos to go with
  those examplesgtgt

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FIRE PATTERNSPattern Catalog

• Melting
• Many items in a fire environment tend to melt as
  they are being pyrolyzed, most notably plastics,
  metals and wax.
• By using Table 4.8 or other sources of melting
  temperature data the investigator can look at a
  threshold temperature range that was exceeded.
• As with everything we do in the real world there
  is uncertainty.
• In this very area, few materials are a pure
  element such as iron or lead or gold.
• Hence most of the materials in the table have a
  temperature range since the exact composition of
  the plastic or foam may not be determined.
• Further all of the factors that have to do with
  transferring the heat energy to the melted object
  come into play.

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FIRE PATTERNSPattern Catalog

• Melting
• As an example of melting, the solder on the
  thermal element of a fire sprinkler is rated to
  melt at a given temperature, it activation
  temperature.
• Given the mass of the sprinkler link, conductive
  heat losses to the sprinkler frame, supply piping
  and water in the piping, the fire gases are
  typically at a significantly higher temperature
  than the activation temperature in order to
  transfer enough heat to the link to open the
  sprinkler.
• It can be said with confidence that the gas
  temperatures exceeded the activation temperature
  in this case.

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FIRE PATTERNSPattern Catalog

• Smoke Soot
• Typically carbon particles that have condensed
  out of fire gases onto cooler surfaces.
• Smoke soot can travel great distances from the
  fire, as a result much of the damage due to smoke
  is non-thermal.

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FIRE PATTERNSPattern Catalog

• Clean burn
• Usually a non-combustible surface that has had
  direct flame impingement.
• The high heat causing by the flame contact burns
  off any soot that has been deposited in that
  area.
• Moving away from the heat of the flames, the
  surface cools off and the soot from the fire
  begins to condense or stain.

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FIRE PATTERNSPattern Catalog

• Calcination
• A physical change to plaster or gypsum board
  caused by heating the material and driving out
  (cooking off) the chemically bound water.
• For gypsum board there are other materials
  including binders, fibers which may char or
  pyrolyze.
• The calcinated areas are softer than the original
  gypsum and depth of calcination analysis can be
  used in a similar manner to depth of char for
  wood.
• Again such an analysis contains uncertainties in
  the original material condition as well as the
  measurement technique itself.
• Research is on-going in this area by Eastern
  Kentucky University.

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FIRE PATTERNSPattern Catalog

• Glass
• Glass can be a good medium for soot deposition
  and soot staining.
• Thick oily soot staining on glass is a good
  indicator of a ventilation limited fire.
• Soot on both sides of broken glass may indicate
  that the window had an opening during the fire.
• If the type of glass can be determined, melting
  temperature may prove useful.
• Crazing or other glass breakage patterns are
  usually not very useful to the investigator.

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FIRE PATTERNSPattern Catalog

• Heat shadowing
• Caused by one object protecting an area of
  another object by absorbing and/or reflecting
  radiant energy or physically blocking convective
  heat or flame from the object.
• ltltdresser against wall and carpetgtgt both
  protected

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FIRE PATTERNSPattern Catalog

• Doughnut shaped fire pattern
• Typically the result of a liquid hydrocarbon
  burning on a carpeted floor.
• The liquid is absorbed into the carpet and
  padding.
• The carpeting acts like a wick and the
  combustible vapors burn above the surface.
• While the liquid fuel remains it protects the
  carpet and padding from burning.

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FIRE PATTERNSPattern Catalog

• Doughnut shaped fire pattern
• The area just outside this ring is exposed to the
  radiant heat from the fire.
• The heat from the flames, cause thermal damage
  and potentially ignition of the exposed
  carpeting.
• These doughnut patterns have been observed to
  survive flashover and if the fire is suppressed,
  the padding under the center of the doughnut
  pattern may still have some of the flammable
  liquid in it.

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FIRE PATTERNSWHAT DONT THEY SHOW?

• Fire patterns are just pieces of the puzzle that
  you are trying to solve.
• They must be taken in context with the
  surroundings, the room and the structure.
• Ventilation plays a major role in fire growth and
  spread and therefore plays a major role in fire
  pattern development.
• Ventilation can significantly change the size,
  shape and location of a fire pattern.

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FIRE PATTERNSWHAT DONT THEY SHOW?

• Therefore it is important to determine
• if and when doors or windows were open,
• obtain weather records or observations at the
  time of the incident,
• and investigate mechanical ventilation systems to
  determine if they were operating and impacting
  the fire.

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FIRE PATTERNSWHAT DONT THEY SHOW?

• The area in a room with the most fire damage does
  not mean that is the area of origin.
• It only means that, that part of the room had
  enough fuel and enough oxygen to support more
  combustion than the rest of the room.
• The area of origin could be remote from that area.

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FIRE PATTERNSUNCERTAINITY IN ANALYSIS

• Investigators are following the scientific method
  and working hard to improve their documentation,
  measurements and analysis of a fire scene.
• Many of these measurements, such as depth of
  char, calcination depth, pattern size, etc are
  being used to make determinations about burn
  time, as well as, origin and cause.
• As with any measurement or observation there is a
  degree of uncertainty.

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FIRE PATTERNSUNCERTAINITY IN ANALYSIS

• In cases where the measurement is extremely
  repeatable, a good characterization of the
  uncertainty of that measurement can be developed
  from a set of replicate measurements.
• Unfortunately measurements/observations made at a
  fire scene rarely have something to compare to in
  order to gauge the uncertainty.
• We have all heard it said, no two fires are
  alike.
• Research is currently underway to compare burn
  patterns made under laboratory conditions to
  determine the ability to replicate the burn
  patterns and hopefully develop the ability to
  recreate burn patterns.

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FIRE PATTERNSUNCERTAINITY IN ANALYSIS

•  
• ltltphotos from similar experimentsgtgt Side reading
  NIJ 601-97 p 26
•   
• For example, depth of char or calcination
  measurements can be affected by the original
  condition of the material prior to the fire,
  non-homogeneous composition, and measurement
  technique (is the pressure exerted on the probe
  the same every time?), just to name a few.
• These uncertainties are in addition to those
  uncertainties that are associated with the fire
  behavior itself.
• This brings us back to the concept of totality.
• All of the pieces of the puzzle have to fit in
  order to mean something.
• Any one pattern or vector analysis or any other
  tool or technique by itself usually will not
  provide enough certainty to determine what
  occurred.

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FIRE PATTERNSEFFECTS OF VENTILATION

• Ventilation can dramatically change the size,
  shape, and location of the burn patterns.
• Ventilation can impact depth of char measurements
  as well as many others that an investigator might
  use because the ventilation controls where the
  fire will actually burn vs where hot gases exist.
• It will influence the spread of the fire.

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FIRE PATTERNSEFFECTS OF VENTILATION

• ltlt Comparison photos stick drawings open space
  vs closed door vs open doorgtgt)
• Also impact of doorway offset from Putorti
  ventilation paragraph) (Check USFA Pattern
  report paragraph/ santa ana report)
•  
• The impact of ventilation on fire growth and
  spread is why a fire investigator needs to be
  able to use his knowledge of fire dynamics,
  combined with an ability to read fire patterns,
  to understand the flow or movement of the fire.
• In other words the investigator must learn to
  understand the impact of ventilation and utilize
  it to his advantage in investigating the fire.

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FIRE PATTERNSCONCLUSION

• To examine the fire flow, begin where the fire
  patterns stop and work back to the origin.
• Determine where the hot gases had enough oxygen
  to burn,
• Determine where the oxygen came from and
• How it mixed with the fire gases,
• Understand where the zone(s) of combustion were
  to eliminate false origins, and
• Work back to the seat of the fire.
• Set up a fire time line.