warm-up december 1, 2014 what is combustion? what are the three types of heat transfer?

Warm-UpDecember 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.

2C8H18 + 25O2 = 18H2 O + 16CO2

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 Documentary6. 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.www.CrosscuttingConcepts.com

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:– 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.


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.


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


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


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).


Collecting Fire Debris

• 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.

• 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 ionization detector.

• 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 – 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.


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.

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 headspacePurge 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

http://www.interfire.org/res_file/patterns.asp



Homework

Fire Debris Pre-Lab due Tuesday

Exit SlipDecember 1, 2014

Go to m.socrative.com and enter 417101 Question: What are common accelerants

and how can you identify that one has been used in a fire?

warm-up december 1, 2014 what is combustion? what are the three types of heat transfer?

Documents

crosscutting concepts

ignitable liquids

traces of ignitable

insurance investigators

combustion reaction

comfire debrisfire debris

crime scene investigators

john doe