Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations

Presentation on theme: "FUEL OXYGENHEAT The air we breathe is about 21% oxygen. Fire requires an atmosphere with at least 16% oxygen. The Chemistry of Fire."— Presentation transcript:

1 FUEL OXYGENHEAT The air we breathe is about 21% oxygen. Fire requires an atmosphere with at least 16% oxygen. The Chemistry of Fire

2 Combustion -

3 The Chemistry of Fire

4 A fuel will produce a flame only when it is in the gaseous state. Flashpoint: Pyrolysis: The Chemistry of Fire AccelerantFlashpoint ( o C) Acetone-20 Gasoline-46 Kerosene52-96 Mineral Spirits40-43 Turpentine32-46


6 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 Examination o 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

7  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

8  V-Patterns -

9  Inverted Cone Pattern:

10  Alligatoring Pattern:

11  Spalling Pattern:  Streamer Pattern:

12  Arc Damage Pattern:  Pool or plant:

13  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

14 What clues might a fire investigator gain from these photographs? Fire investigation

15 What are Common Motives for Arson?

16 General Arson Indicators Arson indicators: what do you think? Owner Occupant Indicators

17 Arson indicaters: What do you think? Arson Indicators Commercial Vehicle Indicators

18  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

19 Vehicle Fires

20  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 Bodies Arson investigation

21 Evidence Containers The evidence container should have the following: Methods for Isolating and Concentrating Accelerants

22 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

23 Methods for Isolating and Concentrating Accelerants A.Steam Distillation B.Solvent Extraction C.Head Space Analysis D.Vapor Concentration on Charcoal E.Solid Phase Extraction HW. Read each of the types of analysis

24 Steam Distillation

25 Solvent Extraction It 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.

26  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.

27  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.

28 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)

29 Methods for Isolating and Concentrating Accelerants

30  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

31  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.

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

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

34 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.

35 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

36  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

37  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

38 Is the Fuel First Ignited Synthetic?  Most Synthetics are petroleum derivatives o Nylon o Polyethylene o Polystyrene o 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)

Download ppt "FUEL OXYGENHEAT The air we breathe is about 21% oxygen. Fire requires an atmosphere with at least 16% oxygen. The Chemistry of Fire."

Similar presentations

Ads by Google