Fire Cause Determination
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Knowledge
Objectives
(1 of 2)• Discuss the use of the process of elimination when determining fire cause.
• Explain the roles source and form of heat of ignition play in fire cause.
• Discuss identification of the first fuel ignited.
• Discuss identification of the ignition source.
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Knowledge
Objectives
(2 of 2)• Discuss the potential oxidizing agents at a fire scene.
• Explain the use of the scientific method in cause determination.
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Skills
Objectives
• Identify the first fuel ignited.
• Identify the ignition source.
• Use the scientific method in cause determination.
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Introduction
• Fire cause determination identifies: –Ignition sources
–First fuel ignited
–Oxidizing agent
–Human actions
• Also considers:
–Circumstances, conditions, agencies
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Process
of
Elimination
(1 of 2)• Fire investigator:
–Considers all reasonable ignition sources
–Employs scientific method to test hypotheses of
origin and cause
–Uses evidence gathered during investigative
Process
of
Elimination
(2 of 2)• There may be a clearly defined point of origin but no identifiable ignition source.
Inappropriate Use of the Process of
Elimination
• Simply eliminating “known” potential ignition sources in area of origin is:
–Insufficient to say fire was intentionally set
–Also insufficient to say fire was accidental
• There must be evidence of the ignition source for the hypothesis to be tested.
–Sometimes evidence is not physical.
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Source and Form of Heat of Ignition
• Source of ignition energy is at or near point of origin
–Must have sufficient temperature and energy to
raise fuel to ignition temperature
•This involves generation, transmission, and heating (thermal inertia).
• Consider interviewing those who knew contents of room of origin
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First
Fuel
Ignited
• Identify the first fuel that sustains combustion beyond ignition source.
• Consider configuration of fuel:
–With like fuels, one with a higher surface‐to‐mass
ratio will require less thermal energy to ignite.
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Ignition
Source
• Was obviously at point of origin when fire started
–Postfire physical evidence of it may remain.
–It may also have been destroyed or removed.
• Ignition source for ignitable vapors can be
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Oxidizing
Agent
• Is generally just the oxygen in the air
• Fire intensity can be enhanced by the addition of other oxidants.
–e.g., medical oxygen cylinders, pool sanitizers
Ignition
Sequence
• Events that brought ignition source and fuel together
–Establishes cause and
responsibility
The Scientific Method in Cause
Determination
(1 of 2) • Determining cause follows the accurateidentification of origin.
• Data must be collected and analyzed.
• Cause hypotheses can then be developed and tested for each individual heat source.
16
The Scientific Method in Cause
Determination
(2 of 2)• Appropriate way to apply scientific method is to attempt to disproveeach hypothesis
• Hypotheses that cannot be disproved may be possible or probable.
16
Data
Collection
• Essential data:
–Identification of fuels (fuel analysis)
–Potential ignition sources (ignition source analysis)
–Unusual oxidants in area of origin
• Information from persons with knowledge of the area can be helpful.
• Prefire photographs can also be useful.
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Data
Analysis
(1 of 5)• Data analysis can be done once all potential initial fuels, ignition sources, oxidants, and relevant circumstances have been identified.
• Investigator must not jump to conclusions
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Data
Analysis
(2 of 5)• Separate hypothesis must be tested for each fuel/ignition source/oxidant combination
• Ignition sequencemust be identified
–Ignition source can sometimes be logically inferred
Data
Analysis
(3 of 5)• Certain evidence supports the inference of a reliable ignition sequence:
–Diffuse fuel ignitions
–Multiple origins
–Trailers
–Witnessed ignitions
–Presence of ignitable liquids
Data
Analysis
(4 of 5)• Factors to consider:
–How and when initial fuel came to origin
–How and when oxidant came to be present
–How and when competent ignition source came to
be present
–How and when competent ignition source
transferred heat to initial fuel
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Data
Analysis
(5 of 5)• Factors to consider (cont’d):
–What acts or omissions brought together the fuel,
oxidizer, and ignition source.
–How initial fuel ignited subsequent fuels to result
in fire spread
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Cause
Hypotheses
• Using scientific method, investigator forms opinions based on fire cause hypothesis
• Investigator assigns a level of certainty: –Probable—more likely true than not
–Possible—feasible but not probable
• Do not confuse these terms with the term “probable cause” used in criminal investigations.
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Summary
(1 of 4)• In any investigation of a fire cause, the investigator will need to consider all reasonable ignition sources and use the scientific method to test his or her application to the investigation at hand.
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Summary
(2 of 4)• The source of the ignition energy will be at or near the point of origin.
• Identification of the first fuel ignited is an important part of the hypothesis testing.
Summary
(3 of 4)• The investigator should identify the ignition sequence or the events that brought the ignition source and the fuel together, thus establishing the fire cause and responsibility.
Summary
(4 of 4)• The investigator may establish one of two levels of certainty based on his or her confidence in the data collected.
–Probable
