Arson, Fire, and Explosives: Key Concepts and Analysis

Fire

Rapid oxidation process producing heat and light.

Explosion

Sudden conversion of potential energy into kinetic energy.

Arson

Deliberate act of setting fire to property.

Oxidation

Combination of oxygen with substances producing new substances.

Exothermic Reactions

Reactions releasing more energy than required to start.

Ignition Temperature

Minimum temperature to spontaneously ignite fuel.

Heat of Combustion

The heat involved when a substance burns

fire is a what?

chain reaction

what are the components of the Fire Tetrahedron?

heat, fuel, oxygen, and chemical chain reaction.

Flashpoint

Lowest temperature at which a liquid can ignite.

Fire Point

Temperature at which a liquid continues to burn.

Flammable Liquids

Liquids igniting below 100 ºF temperature.

Combustible Liquids

Liquids igniting above 100 ºF temperature.

what are the methods of heat production

chemical, mechanical, electrical, nuclear

Chemical Chain Reaction

Continuous oxidation producing sufficient heat to sustain fire.

Incipient Phase

Earliest fire phase lasting seconds to days depending on the fuel or ignition source

Emergent Smoldering

the products of combustion become increasingly pronounced

What happens during the Free Burning Phase?

The rate and intensity of open burning increase.

How does the intensity of a fire change with temperature during the Free Burning Phase?

The intensity of the fire doubles with each 18°F (10°C) increase in temperature.

What are the three methods of heat transfer?

Convection, conduction, and radiation.

Can you get out during the free burning period?

No

Oxygen-regulated Smoldering Phase

Final phase with depleted oxygen; high heat remains.

Might not be a flame, but there still a lot of heat there

Backdraft

reintroducing oxygen to a room that just had a fire

what happens with a backdraft?

occurs at an explosive rate due to the extreme temperatures being fueled by the new oxygen

- Kills a lot of people

- IF there is a fire in a room with a closed door, DON'T OPEN IT.

Pyrophoric Chemicals

React upon exposure to air with low activation energy.

what is origin in origin and cause analysis?

Evaluation of fire patterns and physical evidence

- Heaviest fire damage

what is cause in origin and cause analysis?

Accidental

Natural

Incendiary

Undetermined

Spoliation

Intentional or negligent destruction or alteration of evidence

Which comes first during physical examination

Exterior then interior

exterior examination

Document the fire conditions and patterns

Document utilities

interior examination

Least to heaviest amount of damage

Potential Ignition Sources

Electrical equipment (outlets, lighting, appliances) heating sources (primary and secondary sources)

accelerant

Samples from point of origin + char control

Line of Demarcation

Black and clear area

above the line of demarcation...

the Potentially Combustible smoke follows the path of less resistance

what is the most commonly used liquid accelerant?

gasoline

Accelerants

Substances used to increase fire intensity.

solid accelerants

paper, fireworks, flares, black powder

liquid accelerants

Petroleum distillates - petroleum products

Non-petroleum products - methanol, acetone, turpentine

how do porous materials relate to liquid acclerants

Porous materials harbor liquid accelerants

Detecting Accelerants

Canine

Chemical color tests

Portable instruments and sensors

Volatility

Speed at which a substance evaporates post-fire.

Fire Investigation

Process of determining origin and cause of fire.

Fatal Fire Investigation

Examining evidence related to fire-related fatalities.

- loss of evidence

critical documentation

victim proximity to origin

postmortem investigation

Identification - medical or physical examination or autopsy

arson is what?

hard to prove

who does the collection of fire debris evidence

Fire investigation teams and or Arson task force

what are some sample collection

Importance of controls

Containers: Paint cans

Arson Task Force

Specialized team for investigating suspected arson cases.

ASTM

Standards for testing fire debris evidence.

GC-FID

Gas chromatography method for analyzing liquid accelerants.

GC-MS

Gas chromatography-mass spectrometry for chemical analysis and liquid accelerants

sample preparation

Cold or heated headspace, extraction, purge and trap, charcoal strip/SPME

pattern matching to standards

Spalling (occurs concrete burns)

Vapor Concentration

Method for recovering accelerants from fire debris.

Apparatus for Accelerant Recovery by Vapor Concentration

The vapor in the enclosed container is exposed to charcoal, a chemical absorbent, where it is trapped for later analysis.

What distinguishes an explosion from combustion?

The speed at which the reaction occurs

Low Explosives

Burn quickly (1000 m/s)

low explosives

Decompose relatively slowly (1,000 m/s) and produce propelling or throwing action which makes them suitable for ammunition or skyrocket propellants

High Explosives

burn slow

Primary - shock and/or heat sensitive

Secondary - more stable

high explosives

Detonate almost instantaneously at rates of 1,000- 8,500 m/s

What are primary explosives?

Explosives that are ultra-sensitive to heat, shock, or friction.

What are primary explosives used for?

They provide the major ingredients found in blasting caps or primers used to detonate other explosives.

What are secondary explosives?

Explosives that are relatively insensitive to heat, shock, or friction.

How do secondary explosives behave when ignited in small quantities in the open air?

They will normally burn rather than detonate.

Black Powder

Mixture of nitrate, charcoal, and sulfur.

Smokeless Powder

Nitrated cotton or nitroglycerin-based explosive.

RDX

most popular and powerful of the military explosives, often in C-4 form.

What does TATP stand for?

Triacetone triperoxide

What is TATP?

A homemade explosive made from acetone and peroxide in the presence of an acid

Which type of organizations have used TATP?

Terrorist organizations

Triacetone triperoxide

Its existence has led to the banning of most liquids on commercial aircraft

What is one of the first and most famous explosives?

Nitroglycerin which was invented in 1847

What must be systematically searched at a bomb site?

The entire bomb site must be systematically searched.

What should be given great care during the collection protocol at a bomb site?

Recovering any trace of a detonating mechanism or any other item foreign to the explosion site.

What must be collected for laboratory examination at the origin of an explosion?

Objects located at or near the origin of the explosion.

What is often found at the origin of an explosion?

A crater.

What must be preserved from the interior of a crater for laboratory analysis?

Loose soil and other debris.

How should materials collected for laboratory examination be stored?

In sealed air-tight containers.

What information must be included on the labels of collected materials?

All pertinent information.

How should debris and articles collected from different areas be packaged?

In separate air-tight containers.

What can happen if explosives are stored in plastic containers?

Some explosives can diffuse through plastic and contaminate nearby containers.

Sealed Containers

Used for preserving collected explosive evidence.

Explosives Analysis

Laboratory methods for identifying explosive materials.

Microscopic Examination

Detailed analysis of explosive residues under a microscope.

Color Screening Tests

Visual tests for identifying explosive materials.

Immunoassays

Tests using antibodies to detect specific explosives.

IR Spectrophotometry

Technique for analyzing chemical compounds using infrared light.

Ion Mobility Spectrometry (IMS)

Technique for detecting explosives based on ion movement.

Chemical Color Tests

Tests identifying substances based on color changes.

Field-deployable Devices

Portable tools for on-site explosive analysis.