Module 5 : Fire Investigations

Several Types of Fires Investigated (Main 4)

Liability, Negligence, Arson, Accident

Arson investigations often present…..

complex and difficult circumstances to investigate

Arson (3 examples of why its difficult to investigate)

-thoroughly planned -criminal not present during -destruction is extensive

Arson forensics mostly limited to: (3)

- detecting point of origin - identifying relevant chemical materials collected at scene - reconstructing and identifying igniter mechanisms.

Fire causes: (3 general)

Accidental, Arson, Spontaneous Combustion

Fire causes: Accidental:

Faulty wauring, overheated electrical motors, improperly maintained heating systems, cigarettes

Fire causes: Arson: 2 types of arson

Chemical and non-chemical

Fire causes: Arson: chemical accelerants

gasoline, kerosene, etc (leave chemical traces)

Fire causes: Arson: nonchemical caused

pile of combustible

Fire causes: Spontaneous Combustion: nonchemical caused

natural heat producing process ignites a fire in a poorly ventilated area

Chemically, fire is a type of…

oxidation, the combination of oxygen with other substances to produce new substances

What is Combustion?: Not all oxidation reactions proceed in a manner that one associates with a fire; e.g.,…..

rusting (rate of reaction matters!!!).

What is Combustion?: Oxidation is associated with….

energy release, e.g., heat and/or light.

What is Combustion?: All oxidation reactions:

more energy is liberated than is required to initiate the reaction. • Exothermic reactions

Chemistry of rusting formula

Fe + H2O +O2 = Fe2O3H2O

To initiate and sustain a fire requires:

fuel (vapor)

• sufficient oxygen to combine with fuel

• heat to initiate combustion

• sufficient heat generated to sustain reaction

Fire Triangle (Tetrahedron)

fire

To start fire: what must be reached first….

minimum temperature needed to spontaneously ignite fuel, known as ignition temperature, must be reached.

Heat involved when a substance burns is known as….

heat of combustion.

Once combustion starts enough energy in the form of heat and light (flame) is liberated, a portion of which is used to….

sustain the fire (e.g., maintain chain reaction (fire tetrahedron) called the fire point temperature

A fuel achieves a reaction rate with oxygen sufficient to produce a flame only when it is in…..

the gaseous state

A liquid burns when the temperature is….

high enough to vaporize the fuel

The flash point is the….

lowest temperature at which a liquid produces enough vapor to burn.

A solid such as wood burns only when exposed to…

heat hot enough to decompose into gaseous products (pyrolysis).

Glowing combustion or smoldering is….

burning at the fuel-air interface, such as a cigarette, the embers of a wood fire, or a charcoal fire.

Flash point

The lowest temperature at which a volatile liquid can vaporize to form an ignitable mixture in air but cannot sustain combustion

Ignition Temperature

(Fire Point) Minimum temperature to which a substance must be heated before it will continue to burn independent of the source of heat

Will fuel in liquid state will not burn?

No!

flash point indicates how easily…

chemicals burn

materials with higher flash points are….

less flammable or hazardous than those with lower flash points

Important: The flash point is NOT the temperature at which the vapour will spontaneously ignite. The vapour must be exposed to a….

heat source at or above its Auto-ignition temperature which is the minimum temperature required to ignite a gas or vapour in air without a spark or flame being present.

What is the autoignition temperature?

The temoerature at which the vapor of flammable material ignites in air without an ignition source

What is gasolines flash point and autoignition temperature ?

flash point : 43 celsius

Autoignition temperature: 280 celsius

What is the difference between flammable and combustible?

Flammable : flash point 60 celsius >

Combustible: flash point 60 celsius <

Arson Types/Categories (6)

Vandalism, Profit Motivated, Crime Concealment, Sabotage, Revenge, Excitement

Arson Types/Categories: Vandalism

geared towards group/culture

Arson Types/Categories: Profit Motivated

e.g., insurance fraud, competition

Arson Types/Categories: Crime Concealment

cover up evidence/murder

Arson Types/Categories: Sabotage

means of protest/political

Arson Types/Categories: Revenge

means to “get even”

Arson Types/Categories: Excitement

pleasure of watching fire burn

Examine fire scene for signs of arson as soon as….

the fire has been extinguished

Most arsons started with…

petroleumbased accelerants (gasoline/kerosene)

Fire Scenes: Focus on finding….

fire’s origin, most productive in search for accelerants / ignition devices as indicators of arson

Fire Scenes:Evaluation of….

fire patterns and physical evidence (e.g.,Heaviest fire damage)

Locating Fire Origin (4 things to consider)

Fire moves up (V-shaped pattern)

Streamers

lower burning liquids flow down •

Accelerant search

Accelerant search through….

vapor detectors, trained canines

Arson Indicators (5)

evidence of separate, unconnected fires

• irregularly shaped pattern on floor from pouring accelerant

• Fire moves in an upward direction, probable origin lowest point showing most intense characteristics of burning.

Evidence of severe burning found on the floor (as opposed to the ceiling) of a structure is indicative of a flammable liquid/accelerant.

• Discovery of an ignition device:

The most common igniter is a…….

match

The most common igniter is a match, but arsonists can construct many other types of devices to start a fire, including…

burning cigarettes, firearms, ammunition, a mechanical match-striker, electrical/timed sparking devices, and a “Molotov cocktail.”

Fortunately, combustible liquids are rarely….

entirely consumed during a fire

What are some examples of arson myths? (3)

alligatoring effect, crazing of glass, depth of char

Fire Scene Evidence Collection • point of origin:

ash and soot, along with porous materials may contain excess accelerant collected and stored in airtight containers (new paint cans or widemouth glass jars, never use plastic containers).

Fire Scene Evidence Collection: traces of flammable liquid residues may be located with…

a vapor detector (sniffer) or a trained canine.

Fire Scene Evidence Collection: • materials suspected of containing volatile liquids must be accompanied by a….

thorough sampling of similar but uncontaminated control specimens from another area of the fire scene, called a substrate control.

Accelerants (3 general categories)

Solid, liquid, gas

Accelerants: Solid

paper, fireworks, flares, black powder

Accelerants: Gaseous

butane, propane, natural gas (these don’t leave residue)

Accelerants: Liquid

Petroleum distillates – petroleum products – Non-petroleum products – methanol, acetone, turpentine

Dog Accelerant detection training:….

detect and alert to the scent of accelerants, introducing dog to accelerants (gasoline, diesel fuel and lighter fluid, but also butane, kerosene, propane, solvents) and teaching the dog to alert to scent. Learn to discriminate between scent of accelerants and other scents (burnt wood or plastic).

Lab Recovery of Flammable Residues: recover accelerant residues from fire-scene debris by….

heating airtight container

Lab Recovery of Flammable Residues: any volatile residue in the debris is…

driven off and trapped in the container’s enclosed airspace (headspace)

Lab Recovery of Flammable Residues: vapor or headspace is removed with a…

syringe

Lab Recovery of Flammable Residues: Vapor injected into gas chromatograph, separated into its components, and each….

peak is recorded on the chromatogram.

Lab Recovery of Flammable Residues: vapor concentration technique….

a charcoal strip is placed in the airtight debris container when it is heated.charcoal strip absorbs much of the vapors during heating. • strip is washed with a solvent to recover the accelerant vapors • solvent is then injected into the gas chromatograph for analysis

Gas Chromatograph:

gas chromatograph most sensitive/reliable instrument for detecting and characterizing flammable residues/accelerants.

Gas Chromatograph: gas chromatograph separates the…

hydrocarbon components and produces a chromatographic pattern characteristic of a particular petroleum product.

comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, may be able to identify….

the accelerant used to initiate the fire. Chromatographic pattern of the unknown compared to patterns produced by known petroleum products

Gas Chromatography: Interpretation can be….

difficult in reality and difficult to quantify

Analysis of Fire Debris Evidence

Chromatogram – Retention time and intensity • Pattern matching to standards – Weathering