Fire Debris Analysis

Forensic Crime ScienceEisenhower High School

Fire

Arson - The crime of maliciously, voluntarily, and willfully setting fire to the building, buildings, or other property of another or of burning one's own property for an improper purpose, as to collect insurance.

Arson – The crime of starting an illegal fire.

Transfer Types of Heat

Conduction

Convection

Radiation

Direct Flame Contact

Fire: rapid oxidation with evolution of heat and light.

Fuel Heat Oxygen Uninhibited chemical

chain reaction

Four components of fire:

Fuel: can be solid, liquid or gas Fuel can only consumed in the vapor state Therefore, solids and liquids must first be

“vaporized”

Four components of fire:

Burning takes place at the surface of solids and liquids.

Heat: Temperature Oxygen: found in air; can be used up in closed in

spaces.

Four components of fire:

Chemical Chain Reaction must: The oxidation reaction (burning) must produce

enough heat to maintain burning The fuel mass must be vaporized and drawn up

into the flame.

Cause of Fire: Unintentional Intentional

Natural Accidental

Who investigates the fire?

Often, the Fire Department will have an investigative team to determine the cause/origin of a fire. (major events = ATF)

Fire Debris

• Fire debris is submitted to laboratories for analysis by the fire marshal, crime scene investigators, forensic scientists, and insurance investigators.

• Investigators determine the best locations at the scene to collect samples, based on suspicious details.

Suspicious Circumstances• The presence of: a)combustibleb) increase the rate of combustion

• These are frequently detected by canines trained to detect ignitable liquids by smelling the fire debris.

• Investigators can also detect the presence of these liquids from pour patterns that remain on the burnt substrate after the fire.

Pour Patterns

• Pour patterns often are characterized by intermixed light, medium, and heavy burning in a puddle shape that corresponds to the shape of the original pool of the ignitable liquid.

Other indicators of ignitable liquid

– unnatural flame movement (downward or too fast)

– gapping of wood or floor seams (caused by pooling of liquid)

– damage with no identifiable point of origin

– burned out flooring beneath appliances and furniture

– Inverted cone shaped burn patterns on vertical surfaces

First the point of origin is determined: Where the fires starts Usually contains the most damage.

Fire Investigation:

Once point of origin is determined, the cause of the fire is determined.

Fire Debris Samples

• Sample areas likely to contain traces of ignitable liquid:– lowest regions of burned area– insulated areas within the pattern– porous substrates in contact with the pattern• cloth• paper products• wood

– seams or cracks– lightly burned edges of the pattern

What evidence can be collected?

Paper/Trash – not much evidence Accelerant – rapid start Chemical device (road flares, propellant) Electronic device for delayed ignition

Unburned portions of chemical and electronic devices may be left behind.

Collection of Fire Debris

• Once an appropriate area has been identified for sampling, samples are collected for later analysis.

• Samples are collected in a tightly sealed container (glass jar or metal can).

Even in a large fire, accelerant residues of flammable liquids may be left behind.

Collection of Evidence

Common: gasoline, kerosene, fuel oil Rarer: alcohol, paint thinner

Unusual burn pattern may suggest use of liquid accelerant.

Along with sample from point of origin, a control sample should be collected. (material from a different room/location)

Collection of Evidence

Carpet fibers (synthetics) may be “petroleum” based.

Obviously, evidence collection documented with photos, sketches, etc.

Accelerant remains can be detected by tracing the point of origin or canine use.

Collection of Evidence

Object containing accelerant must be packaged in air tight container.

Containers for Evidence

Metal cans: airtight, but old cans might rust

Glass Jars: rubber or glued liners may interfere with results.

Special airtight plastic evidence bags: must be properly sealed

Collection of Samples

• Sample should fill 2/3 of the container.

• Top 1/3 of container is used for sampling headspace.

Passive Headspace Sampling• In passive headspace sampling the container is

heated to volatilize any ignitable liquids remaining in the sample.

A Activated charcoal is suspended in the headspace

to absorb the volatilized liquid.

• The charcoal is then removed from the sample container and the liquid is removed from it by solvent extraction.

Solvent Extraction

• Carbon disulfide is frequently used in solvent extraction because it produces excellent desorption of most accelerants.

• It also produces a low detector response when analyzed by a gas chromatograph using a flame ionizer detectorr.

• Unfortunately, carbon disulfide is a health hazard because it can cause nervous system damage.

GC-MS

• After the solvent is extracted it is analyzed with a gas chromatograph and a mass spectrometert(GC-MS).

• The liquid is injected into the GC and carried through the instrument by an inert carrier gas (called the mobile phase).

• The liquid then permeates a column (long thin tubing) which binds the liquid to a polymer coating on the inside (called the stationary phase). This separates the liquid components by volatility.

Gas Chromatography separates components and Mass Spectrometry identifies the components.

Analysis of Accelerants

GC-MS• More volatile components move faster through the

column.

• The components come off of the column separately during the elution step and enter the mass spectrometer.

• The mass spectrometer separates each component based upon the mass-to-charge ratio of their particles.

• The mass spectrum of the sample is then compared to a library of known compounds to identify the compound in the sample.

Presumptive Testing

• GC-MS analysis can be time consuming and expensive.

• A presumptive test can be performed quickly in the field to indicate the presence of an ignitable liquid.

• Colorimetric gas detection tubes are used for this purpose

Presumptive Testing

• Colorimetric gas detection tubes are filled with a compound designed to react with a specific compound of interest (gasoline, diesel fuel, etc.)

• To perform the test, both ends of the glass tube are broken off.

• Air from the scene is drawn through the tube with a pump

Presumptive Testing

• In the presence of specific vapors, the compound within the tube will change color.

• The concentration of the compound may be estimated but this technique is not very accurate.

Presumptive Testing

• If the presumptive test is positive, then samples will be collected for GC-MS analysis.

• In some labs, this is used for preliminary screening of samples.

• http://www.cbsnews.com/videos/arson-investigation/ criminal homicide arson

• http://www.youtube.com/watch?v=jeztKycHSf0 fire investigations

• http://www.youtube.com/watch?v=sdKjHB9sb7o anatomy of a fire scene

• http://www.youtube.com/watch?v=bwuxi_aW39A job of fire investigator