Knowledge Objectives (2 of 2) Skills Objectives. Introduction. Process of Elimination (1 of 2) 12/20/2013

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1 Fire Cause Determination 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. Knowledge Objectives (2 of 2) Discuss the potential oxidizing agents at a fire scene. Explain the use of the scientific method in cause determination. Skills Objectives Identify the first fuel ignited. Identify the ignition source. Use the scientific method in cause determination. Introduction Fire cause determination identifies: Ignition sources First fuel ignited Oxidizing agent Human actions Also considers: Circumstances, conditions, agencies 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 1

2 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. 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 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. 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 difficult to identify 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 Residue of chemical oxidants may remain after the fire. Collect, test, document Consider their role in the fire. 2

3 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 accurate identification of origin. Data must be collected and analyzed. Cause hypotheses can then be developed and tested for each individual heat source. The Scientific Method in Cause Determination (2 of 2) Appropriate way to apply scientific method is to attempt to disprove each hypothesis Hypotheses that cannot be disproved may be possible or probable. 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. 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 Data Analysis (2 of 5) Separate hypothesis must be tested for each fuel/ignition source/oxidant combination Ignition sequence must be identified Ignition source can sometimes be logically inferred when physical evidence is lacking 3

4 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 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 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. 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. 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. 4

5 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 Possible 5