Warm-Up December 1, 2014 What is combustion? What are the three types of heat transfer?
Objective SWBAT identify the point of origin and be able to interpret identifying marks of accelerants in the debris of a fire.
Agenda 1.OKC Bombing Documentary 2.Debris of Fire 3.Arson 4.Burn Patterns 5.Exit Slip
The Problem with Arson One of the fastest growing crimes in US Arson for its own sake – pyromania Arson to cover up other crimes such as murder or embezzlement Not hard to determine if a fire is arson Difficult to determine who caused the fire
What Is Fire? Essentially a combustion reaction with a fuel, oxygen and sufficient temperature. This is the fire triangle. 2C 8 H O 2 = 18H 2 O + 16CO 2 An explosion and a fire involve the same process. – The only difference is the speed of the reaction. – Combustion may cause an explosion if confined
The Fire Triangle oxygen heat fuel
Types of Fires Burning or flaming fire – Sufficient oxygen and fuel – Flames and smoke visible Smoldering fire – Oxygen deprived – Can burst into explosive flame if oxygen is suddenly supplied
OKC Documentary 6. Why did the FBI dismiss John Doe 2 and what do the body shop witnesses say? 7. Why was McVey already in jail? 8. Why does Jones think that the FBI stopped searching for John Doe 2? 9. Why does Jones think that McVey and Nicholls could not have been the mastermind behind the bombing? 10. What were comparisons with the 1993 World Trade Center bombing? 11. Why is there a theory that Islamic terrorists were involved?
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Suspicious Circumstances The presence of: –ignitable liquid (combustible) –accelerants (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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Suspicious Circumstances 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
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Fire Debris Sampling 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
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Collecting 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).
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Collecting Fire Debris Sample should fill 2/3 of the container. Top 1/3 of container is used for sampling headspace.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. Passive Headspace Sampling In passive headspace sampling the container is heated to volatilize any ignitable liquids remaining in the sample. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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 ionization detector. Unfortunately, carbon disulfide is a health hazard because it can cause nervous system damage.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. GC-MS After the solvent is extracted it is analyzed with a gas chromatograph – mass spectrometer (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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved. 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.
20/20 Arson Video
Arson Deliberately set. Also sometimes called an incendiary fire May involve the use of an accelerant Accelerant is a substance that causes a fire to start that would not ordinarily start or to burn faster than in the absence of the accelerant. These are usually fuels such as gasoline
Conditions for a Fire A fire must have: – Oxygen – Fuel – Sufficient heat to get the fire started Deprive the fire of one of these and it will cease or won’t start
Conditions for a fire Generally only gases (vapors) will burn. Solids and liquids will not burn Sufficient heat is required to vaporize some of the fuel and break oxygen molecules apart into oxygen atoms Fire will produce enough heat to continue vaporization and keep fire going
Investigating the Fire Scene Done by fire scene investigator Search for point(s) of origin Possible causes: – Accidental (leave the stove on, accidental malfunction in appliance) – Natural (lightening) – Deliberate (Use an accelerant, deliberately sabotage an appliance)
The Point of Origin Crucial piece of evidence in determining type of fire Often most intense location of burning Usually at a low point in the building-may be buried under tons of rubble Smoke or damage often shows “V” pattern
Determination of Arson Eliminate all natural and accidental causes: leaves only arson Multiple points of origin Fire trail Presence of accelerant in debris Presence of accelerant in observation of fire: thick black smoke
The Role of an Accelerant The accelerant supplies the heat needed to get substances into the vapor phase so they can burn. Presence of an accelerant does not necessarily mean that fire is arson. Absence of an accelerant does not rule out arson.
Finding Accelerants Find point of origin Look for absorbent materials Use fire dog – capable of sniffing out miniscule quantities of accelerants Look for fire trails
Accelerants Accelerants are any liquid, solid or gaseous material that will sustain or enhance flammability. Liquid materials are commonly used because of ease of ignition and familiarity of use. Accelerants are nearly exclusively derived from hydrocarbons. Straight chain hydrocarbons are the backbone of the oil industry. Hydrocarbons are molecules made up of the elements hydrogen and carbon. Octane is a term familiar to all. It consists of a hydrocarbon having 8 carbons. Examples: – Gasoline – Kerosene – Diesel – Lighter fluids – Charcoal starters – Automobile additives – Camping fuels
Evidence of Accelerants Large amounts of damage Unusual burn patterns High heat stress Multiple sites of origin “Sniffers” Portable gas chromatographs Chemical tests Canines Portable detectors Detect change in oxygen level on a semiconductor Guides to the best place to collect samples
Role of the Crime Laboratory Lab does not determine if fire is arson or not Examines debris to determine if an accelerant may be present Isolates and identifies accelerants This may support the fire scene investigator in determination of arson
Methods of Isolating and Concentrating Accelerant Residues Heated headspace Purge and trap
Heated Headspace Closed container Samples headspace over residue Henry’s law - heating drives equilibrium to vapor Favors volatile components
Headspace Analysis syringe headspace ~~~~~~~~~~~~ fire debris
Purge and Trap Closed container Uses charcoal strip or charcoal tube to trap accelerants Uses vacuum or positive pressure with inert gas to force accelerant vapor through charcoal trap
Purge and Trap vacuum headspace ~~~~~~~~~~~~~~ Fire debris
Analysis of Residues Uses GC or GC/MS for comparisons – MS has advantage of identifying particular compounds which are present in certain accelerants Analyst should have own library of knowns for comparison
GC of Gasoline
50% Evaporated Gasoline
Gasoline Residue
Furniture Polish
Cases Dentist who liquidated his assets Smoldering fire Body in the trunk of the car
Dentist Who Liquidated His Assets Dentist had failing practice in deteriorating neighborhood Had offer to relocate practice with partner but needed $$$$$$$$$$ to get started Used gasoline to make fire trail to each room in office Building destroyed but witness saw him leave building before fire started Convicted of arson
Smoldering Fire Man catches wife fooling around and decides to set trap for her. He seals up all windows and doors to house and sets a fire in living room Fire flames first and then, having used up oxygen, settles into glowing, smoldering fire.
Smoldering Fire He expects wife to come home from work and enter house. This will cause influx of oxygen into house and rekindle the fire explosively, killing her instantly She has an auto accident on the way home and is delayed. Meanwhile a neighbor smells smoke and calls fire department They arrive at scene and recognize that whole house is sealed up and enter very carefully. Husband is charged with arson and attempted murder
Burn Patterns p p
Homework Fire Debris Pre-Lab due Tuesday
Exit Slip December 1, 2014 Go to m.socrative.com and enter Question: What are common accelerants and how can you identify that one has been used in a fire?