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Arson Dr. Walker
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The Chemistry of Fire Combustion Reactions
Write all The Chemistry of Fire Combustion Reactions Hydrocarbon (or alcohol) + Oxygen Water + Carbon Dioxide Examples C3H8 + 5 O CO2 + 4 H2O (propane) 2 C8H O CO H2O (octane) 4 C2H6O + 5 O CO H2O (ethanol)
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Write all Fire Triangle
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Temperature Measure of the kinetic energy of matter
Write all Temperature Measure of the kinetic energy of matter More kinetic energy, more motion, higher temperature
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The Chemistry of Fire Combustion Reactions
Write all The Chemistry of Fire Combustion Reactions These are exothermic, meaning they give off energy Heat and light result from combustion (the fire)
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More Vocabulary Ignition Temperature Flash Point
Write bold More Vocabulary Ignition Temperature The temperature needed to start a fire of a substance Ethanol = 425 C Gasoline = 536 C Flash Point The lowest temperature where enough fluid can evaporate to form a combustible concentration of gas Ethanol = 54 F Gasoline = - 45 F
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Notes on Flash Point All liquids exist in an equilibrium with vapor
Write bold Notes on Flash Point All liquids exist in an equilibrium with vapor Why puddles of water evaporate Why you smell volatile liquids Gasoline Alcohol Solvents (nail polish remover, etc.) Fuel must be in the vapor phase to burn No vapor, no fire Solvents below flash point (no vapor) will not burn!!
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Equilibrium All liquids exist in an equilibrium with vapor
The vapor pressure remains constant because every molecule which escapes (like A) is immediately replaced by another molecule reentering from the vapor (like B). Any given molecule spends some of its time in the vapor and some in the liquid.
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Write all Pyrolysis During a fire, breakdown of particles of a solid to form gaseous particles. Wood burning – pyrolysis of cellulose
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Air-Fuel Mixtures Flammable Range
Write all Air-Fuel Mixtures Flammable Range Reported as the ratio of volume of fuel vapor to air expressed as a percentage. 14.7 : 1 is standard air:fuel ratio (6.8 % fuel) Lower percentage fuel(> 6.8%) = lean mixture Higher percentage fuel (< 6.8%) = rich mixture
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Air-Fuel Mixtures Lean mixtures Less fuel, more air
Write all Air-Fuel Mixtures Lean mixtures Less fuel, more air Burn hotter (typically) Better economy, poorer performance Rich mixtures More fuel, less air Burn cooler (typically) Less economy, better performance More harmful byproducts Carbon monoxide, carbon deposits (soot) No absolutes, dependent on engine design
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Write all Extinguishing Fires Therefore, to kill a fire, you must deny the fire one or more of these three things. You may: Exclude oxygen from the fire. Cover frying pan for a grease fire Remove the fuel on which the fire is feeding. Alcohol fires during cooking go out when the alcohol is burned up Lower the temperature.
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Classes of Fires Dependent upon the fuel Class A Wood, paper, etc.
Write all Classes of Fires Dependent upon the fuel Class A Wood, paper, etc. Leave ash as residue Put out by lowering temperature below ignition temperature
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Classes of Fires Dependent upon the fuel Class B
Write all Classes of Fires Dependent upon the fuel Class B Accelerants - Flammable liquids (gasoline, etc.) and gases Extinguish by creating a barrier between the fuel and the oxygen, such as layer of foam. Can’t use water – insoluble with fuel, so the fuel (and fire) are splattered
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Classes of Fire Dependent upon the fuel Class C
Write all Classes of Fire Dependent upon the fuel Class C Electrical in nature (faulty wiring) Special techniques and agents required to extinguish, most commonly carbon dioxide or dry chemical agents Can’t use water – conducts electricity
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Classes of Fire Dependent upon the fuel Class D
Write all Classes of Fire Dependent upon the fuel Class D Flammable metals (sodium, potassium, etc.) Burn in Water!!! Extinguish with special powders based on sodium chloride or other salts; also clean dry sand
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Classes of Fire Dependent upon the fuel Class K
Write all Classes of Fire Dependent upon the fuel Class K Fires that involve cooking oils, grease or animal fat Distinguished from liquid accelerants like gasoline
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Extinguishers
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Speed Speed of a fire is most affected by oxygen supply
Write all Speed Speed of a fire is most affected by oxygen supply Fires that burn at supersonic speed become explosions In most explosions, the oxygen is delivered by a chemical oxidizer, not by atmospheric oxygen
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Stages of Fire Stage 1 – Ignition
Write bold Stages of Fire Stage 1 – Ignition Fuel, oxygen and heat join together in a sustained chemical reaction Can be controlled by extinguisher at this stage Note: Different sources will use different terms for the stages of fire. The terms here are from
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Stages of Fire Stage 2 – Growth
Write bold Stages of Fire Stage 2 – Growth With the initial flame as a heat source, additional fuel ignites
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Stages of Fire Stage 3 – Fully developed
Write bold Stages of Fire Stage 3 – Fully developed Fire has spread over much if not all the available fuel Temperatures reach their peak, resulting in heat damage Oxygen is consumed rapidly.
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Stages of Fire Stage 4 – Decay
Write bold Stages of Fire Stage 4 – Decay Fire becomes less intense and cooler as available fuel and/or oxygen is consumed
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How Fire Spreads Conduction Convection Radiation
Write all How Fire Spreads Conduction Transfer of heat through direct contact Convection Diffusion of heated gas/liquid from hot to cold areas Radiation Travel of heat through electromagnetic waves
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Other Circumstances Flashover
Write bold Other Circumstances Flashover Sudden, simultaneous ignition of all fuel sources in an enclosed space How it happens Hot gases rise to ceiling and radiate outwards Heat radiates downward All combustible material rises above ignition temperature and burst into flames ( around 1000 degrees) Even protected fire personnel are unlikely to survive a flashover
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Write all More on Flashover Flashover can cause several traits that can mislead investigators Hotter than usual flames can melt metal Can mimic accelerant pour patterns Can leave “v” patterns
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Fire and Glass Evidence
Write all Fire and Glass Evidence “Crazed” glass High degree of branching in cracks Caused by water from firehoses quickly cooling hot glass Previously believed it was caused by heat generated by use of accelerant
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Other Circumstances Backdraft How it Happens
Write all Other Circumstances Backdraft Explosion that occurs when oxygen is introduced into area with hot gases How it Happens Oxygen is consumed by fire Visible flames disappear as solid fuel smolders, room fills with hot gases Re-introduce oxygen, get explosion
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Fire Investigation Why investigate?
Write all Fire Investigation Why investigate? To determine the origin and cause of the fire. Determine if the cause was accidental or intentional. If accidental, prevent further fires from occurring. If intentional, process the crime scene and develop a suspect
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Arson Facts Arson is difficult to prove.
Write bold Arson Facts Arson is difficult to prove. Approximately 25% of all fires are arson related. 15% are closed by arrests 2% result in convictions Juveniles account for 55% of arson related fires.
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Arson Costs All arson fires are crimes against people.
Write bold Arson Costs All arson fires are crimes against people. All require the response of firefighters, police, paramedics and investigators. Arson property loss exceeds $2 billion dollars annually.
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Common Motives Vandalism Revenge Serial arsonist Insurance Fraud
Write bold Common Motives Vandalism Revenge Business competitors Ex-spouse or love interest Serial arsonist Thrill seekers, sexual gratification Many times, arsonists escalate to murder (Berkowitz, etc.) Hero complex Set fire, gain attention for putting it out Insurance Fraud Burn down building to receive insurance money
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Write all Legal Considerations Fire is considered an emergency (exigent circumstances) Fire personnel do not need a warrant to collect evidence at the scene If fire personnel leave the scene, they need a warrant to return
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Developing an arson suspect
Determine the fire was arson. Eliminate all possible natural and accidental causes. If there was an arson fire, who had the motive and opportunity? Not all arson has a clear motive
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Investigative Procedure
Write all Investigative Procedure Interviews with firefighters, witnesses and occupants Examination of the structure or vehicles exterior Check all alibis Check clothing, possessions for traces of accelerants (flammable liquids)
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Observations Condition of windows Smoke and flame patterns
Blown out, melted? Smoke and flame patterns Property outside the structure People watching Photograph and document all you see Presence of keepsakes/collectibles/electronics in debris
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Investigative Procedure
Write bold Investigative Procedure Search for suspicious items Candles, cigarettes, matches, Molotov cocktails, electrical/mechanical devices Look for streamers burn trails left behind where the arsonist has laid down accelerant to aid in spreading the fire
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Investigative Procedure
Write all Investigative Procedure Determine point of origin Where the fire started in the building Most damage Fires burn upward, outward Collect soot and debris from point of origin Traces of accelerant may still be present Collect in airtight container to avoid further evaporation
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Investigative Procedure
Write bold Investigative Procedure Check objects around the point of origin to see if they belong. Soot or ashes that are unusual in color are collected. Sprinklers and alarms are checked to determine if they have been tampered with. An accelerant container is likely nearby (because arsonists are typically lazy/stupid) if it was used. Check windows/doors for forced entry.
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Write bold Equipment Combustion meter (aka “sniffer”) – used to detect accelerants on site A sniffer has a wand that draws air with an internal pump. The air is pumped over a catalyst-coated resistance element. When the air contains any combustible vaporlike gasoline, it burns as it passes over the element. This raises the resistance, altering the electrical balance and causing the dial to move and an audible alarm to sound
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Equipment Accelerant Canines
Write bold Equipment Accelerant Canines Trained to detect the presence of ignitable substances. Useful in expediting a scene search where ignitable liquids are suspected. Plus - In many cases, a dog’s nose can be more sensitive than a piece of equipment. Dogs will alert, usually by sitting down when they detect substances containing petroleum products. Minus: Require a great deal of training for the animal…and the handler
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Equipment Gas Chromatography (GC)
Write bold Equipment Gas Chromatography (GC) Debris + solvent is filtered and injected into machine Machine vaporizes sample which travels through tube Smaller compounds travel faster than the heavier ones, separating mixture
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Equipment Gas Chromatography (GC)
Write bold Equipment Gas Chromatography (GC) A data readout is produced showing the order that the chemicals were detected and the relative amounts. Primarily used to detect accelerants Merely pouring gas is enough to detect gasoline residue in clothing, even if it isn’t spilled
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