FUEL

OXYGENHEAT

The air we breathe is about 21% oxygen.  Fire requires an atmosphere with at least 16% oxygen. 

The Chemistry of Fire

The Chemistry of FireCombustion -

The Chemistry of Fire

A fuel will produce a flame only when it is in the gaseous state.

Flashpoint:

Pyrolysis:

The Chemistry of Fire

Accelerant Flashpoint (oC)Acetone -20Gasoline -46Kerosene 52-96Mineral Spirits 40-43Turpentine 32-46

BASIC METHOD OF A FIRE INVESTIGATION

Point of Origin (POO)◦ Defined as where the fire

originated.◦ Cause of fire may be near

the POO.◦ Fire usually burns longer

at POO.◦ If accelerants or ignition

devices used, they may be present at the POO.

◦ Multiple POO’s MAY indicate arson.

◦ “V” patterns usually point to the POO.

◦ Extensive ceiling damages may be present above the POO.

Interior Examinationo Work backward in

relation to fire travel and from least to most damage.

o Ceiling damage may lead to POO.

o In accidental fires, floor damage is limited in respect to the ceiling damage.

Fire investigation

Char Patterns – Created by very hot fires that burn very quickly and move fast along its path, so that there can be sharp lines between what is burned and what isn't.

patterns

V-Patterns -

Inverted Cone Pattern:

Alligatoring Pattern:

Spalling Pattern:

Streamer Pattern:

Arc Damage Pattern:

Pool or plant:

Glass –

Chimney Effect - Since fire burns upwards, there can be a "chimney effect" If the roof is not entirely burnt, and the fire investigator finds such a hole, the origin of the fire could be directly underneath.

Colour of smoke – Determine what type material was burning.

Colour of flames – Indicates at what temperature the fire was burning.

Melting points of metals: Each metal has a unique melting point

What clues might a fire investigator gain from these photographs?

Fire investigation

•

What are Common Motives for Arson?

General Arson Indicators

Arson indicators: what do you think?Owner Occupant Indicators

Arson indicaters: What do you think?Arson Indicators CommercialVehicle

Indicators

Large amounts of damage Unusual burn patterns High heat stress Multiple sites of origin “Sniffers” Portable detectors Human smell at 1 part /10

million Portable gas chromatographs Chemical tests Canines Detect change in oxygen level

on a semiconductor

Dogs can detect 0.01µL of 50% evaporated gasoline 100% of the time.

0.01µL is about the size of a thousandth of a drop.

Arson investigation

A portable hydrocarbon detector

Evidence of Accelerants

Vehicle Fires

often bodies will be part buried in debris and often difficult to recognize.

If fire threatens to destroy evidence and the body needs to be removed, the following details should be noted;o Location of the body, Position of the body, the nature

and position of article around the body

Carbon Monoxide asphyxiation most common cause of death in fatal fires

Discovering BodiesArson investigation

Evidence ContainersThe evidence container should have the following:

Methods for Isolating and Concentrating Accelerants

Burn injuries to the hands, face, legs or hair

of a suspect/witness.

Symptoms of ignitable liquid use

Clothing Items Impact or transfer patterns - actions

Investigating suspects

Methods for Isolating and Concentrating Accelerants

A. Steam DistillationB. Solvent ExtractionC. Head Space AnalysisD. Vapor Concentration on CharcoalE. Solid Phase Extraction

HW. Read each of the types of analysis

Steam Distillation

Solvent ExtractionIt relies on variations in the solubilities of different compounds in different substances. A solvent will be chosen that does not mix with the compound in which the substance of interest is currently dissolved, so that, when left undisturbed, they will form two separate layers, as with oil and water. It is also important that the compound to be extracted should have greater solubility in the solvent that has been added, and that this should not dissolve any unwanted substances in the original mixture.

Once added, the two liquids may be shaken together for a time then allowed to stand for a while, so that they separate out. The choice of solvent to be used will depend on the chemical and physical properties of all the substances in the mixture. The process may need to be carried out in several stages, using different solvents.

Heat container (paint can) and stick syringe through top and pull gas into syringe

Limited to sample by size of syringe and concentration present in headspace at that time

Head Space Method

Failure of Head Space Method

A liquid or solid sample is placed into a vial, sealed, and heated to a specific temperature.  All of the components that are volatile at or below the pre-set temperature escape from the sample to form a gaseous "headspace" above the sample.After a certain period of time, the headspace gas is extracted from the vial and injected into a gas chromatograph which separates the various components of the sample based on size and/or polarity.

A charcoal coated strip is placed into the container while the container is enclosed and heated to 60ºC for one hour

As the accelerant vaporizes the charcoal absorbs it The strip is then washed with a small volume of carbon

disulfide and the solvent is injected into the GC/MS 100x more sensitive than headspace analysis

Vapor Concentration Method

At the suspect point of origin of a fire, ash and soot, along with porous materials which may contain excess accelerant, should be collected and stored in airtight containers, leaving an airspace to remove samples.

A separation process by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties. Solid phase extraction can be used to isolate analytes of interest from a wide variety of matrices, including urine, blood, water, beverages, soil, and animal tissue.The result is that either the desired analytes of interest or undesired impurities in the sample are retained on the stationary phase. The portion that passes through the stationary phase is collected or discarded, depending on whether it contains the desired analytes or undesired impurities.

Solid Phase Extraction (SPE)

http://www.youtube.com/watch?v=BCjF50wrzn4

Methods for Isolating and Concentrating Accelerants

Catalytic Combustion Detectors: The most common flammable vapor detector operates on the catalytic combustion principle.

Flame Ionization Detector: In the flame ionization detector the sample gas is mixed with hydrogen and the mixture is burned.

Gas Liquid Chromatograph: The portable gas liquid chromatograph (GLC) is one of the most common detectors in arson investigations.

Infrared Spectrophotomer: Infrared spectophotometers can achieve high specificity to flammable liquids and high sensitivity.

Ultraviolet Fluorescence: This procedure consists of illuminating the darkened fire scene with an ultraviolet lamp.

Laser ablation: This process allows the removal material from a small sample’s surface by irradiating its surface with a laser beam.

Accelerant lab testing

In the laboratory, the gas chromatograph is the most sensitive and reliable instrument for detecting and characterizing flammable residues.

The vast majority of arsons are initiated by petroleum distillates such as gasoline and kerosene.

The gas chromatograph separates the hydrocarbon components and produces a chromatographic pattern characteristic of a particular petroleum product.

By comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire.

Gas Chromatography

Can tell what type of hydrocarbon is present such as: benzene, toluene, xylenes, alcohols, methane, pentane, butane, ethane, hexane, etc.

Arson labs often use a method called gas chromatography/mass spectrometry detector (GC/MSD) to determine the composition of the accelerants or explosives found.

GCMS

The vial is automatically injected on the gas chromatograph / mass selective detector (GC/MSD).

The GC will separate all of the sample’s components. The MSD will identify the sample’s components.

Gas Chromatography

Gas Chromatography

The problem with gas chromatography and mass spectrometry, however, is that in order to analyze evidence, you have to destroy it.

Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma.

Laser Ablation

Laser ablation etches off only a tiny slice of a sample with a needlelike light beam and cooking it in a plasma furnace equipped with a mass spectrometer especially sensitive to trace elements.

No Ignitable Liquids Were Detected

Ignitable Liquids Were Detected

Example:Sample contains a medium petroleum distillate (MPD), some types are paint thinner and mineral spirits.

Sample contains a mixture of gasoline and a heavy petroleum distillate (HPD). Some types of HPD are diesel fuel and heating oils.

We can look at this in four ways… No ignitable liquids were

used. Ignitable liquids were used

to start the fire, but have totally been consumed.

Ignitable liquids are still present; however, not in the collected sample.

Ignitable liquids are still present in the collected sample; however they are too dilute to be detected.

Accelerant lab testing

Furnishings and Clothing:◦ Are they natural fibers – cotton, linen, wool?◦ Are they synthetic – polyester, polypropylene, nylon,

acrylic, or ???◦ Are they thermoplastic, or thermosetting, or

elastomers?◦ Melting points? Ignition temperatures?◦ What volatile products do they generate?◦ Foam – polyurethane, polyether, or latex?◦ Are there fire retardants present?

Further lab analysis

General type of fuel may help identify or exclude competent ignition sources.

Is the Fuel First Ignited Cellulosic?◦ Cellulosic: Derived from Plants

Wood Paper Cotton Linen Cardboard Susceptible to smoldering Crumbly grey/black ash on burning White smoke

Cellulosic fuels are susceptible to hot surface/glowing ember ignition

Further lab analysis

Is the Fuel First Ignited Synthetic? Most Synthetics are petroleum derivativeso Nylono Polyethyleneo Polystyreneo Polyester

Rarely ignitable by smoldering/hot surface source Easily ignited by open flame Tend to melt and shrink away from heat Most do not sustain smoldering combustion

Further lab analysis

Synthetics:◦ May be thermoplastic – melts without degrading◦ May be thermosetting (resin) – degrades, chars, may

smolder Other fuel types:

◦ Elastomers (rubbers): Synthetic or natural◦ Leather – Wool – Silk: Proteinaceous (from animals)