Basic Fire and Explosion Investigation Investigation o

1
Basic Fire and Explosion Investigation

• Investigation of fires and explosions seeks their
  origins and causes using the following criteria
• Recognition of the Need
• Definition of the Problem
• Collection of the Data
• Analysis of The Data

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Chemistry and Behavior

• Fire is described as the rapid oxidation process
  with the evolution of heat and light
• Explosion is sudden conversion of potential
  energy (chemical or mechanical) into kinetic
  energy with a production and release of gases
  under pressure
• High order explosion
• Low order explosion

3
Chemistry and Behavior

• Fuels are found in three basic states solid,
  liquid and vapor
• Fuels can only be volatilized and consumed in
  vapor state
• Oxidizing agent is need to support combustion
• Oxygen is necessary for normal combustion
  process. Result of the process is carbon monoxide

4
Chemistry and Behavior

• Carbon Monoxide is most likely cause of
  backdrafts or smoke explosions
• Carbon Monoxide asphyxiation most common cause of
  death in fatal fires

5
Chemistry and Behavior

• Liquids have a flashpoint and a fire point
• Flashpoint temperature at which a liquid gives
  off sufficient vapors to form an ignitable
  mixture at its surface
• Firepoint is temperature at which liquid will
  produce vapors that will sustain combustion.
  Normally several degrees higher than flashpoint.

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Methods of Heat Production

• Chemical result of rapid oxidation
• Mechanical product of friction
• Electrical product of arcing, shorting, or
  other electrical malfunction
• Compressed Gas result of compression of
  molecules
• Nuclear product of splitting atomic particles

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Three Common Forms of Heat Transfer

• Conduction transfer of heat through direct
  contact
• Convection Transfer of heat by a circulating
  medium, usually air or a liquid
• Radiation Heat moves in invisible waves like
  sunlight or x-rays. Travels at 186 mps

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Chemical Chain Reaction

• Chemical chain reaction is a complex
• series of events that must be
• continuously and precisely reproduced
• to maintain flaming combustion.

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Chemical Chain Reaction

• Requires
• Oxidation reaction producing sufficient heat to
  maintain continued oxidation
• Fuel mass must be broken down into similar
  compounds and vaporized from mass itself, and
  combine with oxygen into flames

10
Behavior of Fire

• Point of origin where a fire begins
• Four phases of progression
• Incipient earliest phase, may last from seconds
  to hours,
• Emergent smoldering products of combustion
  become increasingly pronounced
• Free Burning Rate and intensity of open burning
  increases.

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Four Phases of Fire Progression

• Oxygen-regulated smoldering occurs when oxygen
  enriched air in phase 3 is depleted. Produces
  heavy dense smoke and gases, excess of carbon
  monoxide, and will burst into flames when fresh
  supply of oxygen is introduced. Subsequent
  explosion is called a backdraft.

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Origin and Cause Analysis

• Investigator must first evaluate areas not
  damaged or less affected by fire and find area of
  heaviest damage, known as area of origin.
• Once area of origin has been determined by fire
  patterns and physical evidence, point of origin
  can be ascertained
• Cause of fire can be identified through the
  careful analysis and inspection of heat sources

13
Origin and Cause Analysis

• Categorizations of causes of fire
• Natural, act of nature (lightning)
• Accidental, unintentional and explainable
• Undetermined, cause unknown or unable to be
  identified
• Incendiary, intentional act of setting fire

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Origin and Cause Analysis

• Determination of cause and ultimate
  responsibility of fire involves recognition of
  the degree of human intervention.
• Human intervention maybe intentional or
  accidental
• Circumstances must be evaluated equipment
  involved in fire, fuel, presence or absence of
  combustible material

15
Origin and Cause Analysis

• Possible legal actions
• Civil possible insurance claims, financial
  profit from fire, victims of fire
• Criminal components of arson, insurance fraud,
  or murder

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Stages of Investigation

• Exterior of structure evaluation
• Interior of structure evaluation
• Room (area) of origin
• Point of origin
• Determination of cause

17
Fire Safety System Assessment

• Fire Safety Systems include the following and
  should be routinely assessed
• Smoke detectors
• Heat detectors
• Fire escapes
• Fire equipment
• Federal, state and local fire codes should be
  checked for compliance

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Assessment of Fire

• Also check for
• Potential use of a possible flammable or
  combustible liquid accelerant
• Possibility of an incendiary used to start fire
• Comparison samples and charred samples should be
  taken of carpeting, flooring, etc

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Fatal Fire Investigation

• It is critical at a fire scene to
• Document scene thoroughly
• Document relationship of origin and cause of fire
  to victims
• Collect adequate samples of possible evidence
• Photograph
• Utilize autopsy to determine cause of death if a
  victim is involved to eliminate causes other than
  fire or asphyxiation

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Motor Vehicle Fires

• Knowledge of fuel source of motor vehicle is
  essential to successful investigation
• Documented physical evidence from motor vehicle
  fire will be compared with vehicle history,
  mechanical condition, owner and witness
  information and vehicle recalls

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Motor Vehicle Fires

• Investigation involves examination of
• Exterior
• Missing components and body damage
• Extent of damage to engine, passenger compartment
  and trunk/payload area
• Exterior fuel loads, tires, plastic panels, etc
  and their contribution to fire
• Position of windows doors, locking mechanisms
• Determine if fire started outside or inside
  vehicle through ventilation patterns

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Motor Vehicle Fires

• Interior Investigation
• Physical characteristics of vehicle- compartment
  barriers
• Account for missing components radios, air bag
  assemblies, etc
• Check bulkhead openings from engine to passenger
  compartment
• Examine wire bundles under dashboard

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Motor Vehicle Fires

• Interior investigation
• Any tissues, papers, combustible fuels refuse or
  items in passenger compartment should be
  evaluated
• Mechanical failures
• Electrical sources- seat and window switches
• Assess trunk area for burns
• Assess engine compartment thoroughly

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Motor Vehicle Fires

• Questions to ask concerning motor vehicle fires
• Was the vehicle being driven at time of fire, and
  if so, for how long?
• If vehicle was being operated, were there any
  prior indication of problematic conditions?
• What was first indication that problem existed?
• What was last service performed on vehicle?

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Motor Vehicle Fires

• Can a vehicle maintenance history be obtained?
• When was last time vehicle was fueled and total
  amount of fuel?
• If vehicle was not being operated and parked,
  when was last time it was driven? By whom?
• Can other keys to vehicle be accounted for?
• If vehicle was parked, where was it parked?
• What personal items were in the vehicle (cell
  phones, stereo equipment, radar detector)?
• What was last known mileage of vehicle?

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Collection of Fire Evidence

• Fire evidence is defined as any finite or
  tangible materially that is legally obtained in
  an effort to prove the cause of a fire
• Four recognized methods of removing evidence
• Exigent circumstances
• Consent of property owner
• Administrative search warrant
• Criminal Search warrant

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Evidence Containers

• Three containers for placement of evidence for
  fire investigation include
• New Metal Paint Cans inexpensive, several sizes,
  but may corrode over time
• Glass jars several sizes, but breakable. No glue
  should be used to seal jars solvent will
  interfere with later testing of materials
• Special evidence bags easily stored, sealable,
  inexpensive, variety of shapes and sizes tear
  easily