Forensics Chapter 12: Arson, Fire, and Explosives

Definition of Fire

Rapid Oxidation Process with the evolution of hear and light

Definition of Explosion

Sudden Conversion of potential energy (chemical or mechanical) into kinetic energy with a production and release of gases under pressure

What are the two sub-definitions of explosion?

high-order and low-order

Which kind of explosion has a rapid pressure rise?

High-order explosion

Which explosion is characterized by shattering the confining structure?

High-order explosion

Which kind of explosion has a slow rate of pressurization?

Low-order explosion

Which kind of explosion is characterized by pushing or dislodging the confining structure or container?

Low-order explosion

What are the four components of the fire tetrahedron?

Fuel, heat, oxygen, and uninhibited chemical chain reactions

What is fuel?

Any substance that will burn or support combustion.

Although the fuels may exist in three different states, they can only be _____ and ____ in the vapor state

Volatilized and consumed

In wood, what is it that actually burns?

The vapor coming off the wood

What is required to support combustion?

An oxidizing agent.

What is the most common oxidizing agent?

the oxygen in the earth's atmosphere

How much oxygen is in normal atmospheric air?

21%

The higher the _______ the less _____ is required for combustion.

ambient temperature, oxygen

What is the primary cause of death in fatal fires?

carbon monoxide asphyxiation

What is the ignition temperature of carbon dioxide?

1128 degrees Farenheit

Methane's density is ____ than air, and propane's density if _____ than air

Less than, More than

What is the lower limit of flammable explosive range of gas?

the percentage of gas to air when the gaseous air diffuses into air and ignites or explodes

What is the higher limit of flammable explosive range of gas?

the percentage at which the mixture is too concentrated to ignite.

What are the three indicators of volatility of liquid fuel?

Liquids boiling point, flashpoint, and fire point

What is a flashpoint?

the temperature at which a liquid gives off sufficient vapors to form an ignitable mixture at its surface

what is the fire point?

the temperature at which a liquid produces capors that will sustain combustion

Temperatures below 100 degrees Fahrenheit classify

flammable liquids

Temperatures above 100 degrees Fahrenheit classify

combustible liquids

what it the tetrahedron component necessary to increase the temperature of the fuel in the presence of oxygen and cause ignition

heat

what are the five basic methods of heat production

chemical, mechanical, electrical, compressed gas, and nuclear

What method of heat production is the result of rapid oxidation?

chemically produced heat

_____ heat is the product of friction

mechanical

_____ is the product of arcing, shorting, or other malfunction

Electrical heat

when a gas is ______ the molecular activity is greatly increased

compressed

__ __ is the product of splitting or atomic particles

nuclear energy

what are the most common forms of heat transfer?

conduction, convection, and radiation

____ is the transfer of heat through direct contact

conduction

_____ entails the transfer of heat by a circulating medium, usually air or liquid

convection

____ moves in invisible waves and rises much like sunlight or x-rays

radiation/radiated heat

What must happen to continue and precisely reproduced to maintain flaming combustion?

(1): the oxidation reaction must produce sufficient heat to maintain continued oxidation

(2): the fiel mass must be broken down into similar compounds and vaporized from the mass itself, and in turn, these unburned vapors must combine with available oxygen and be continuously drawn up into the flame

A fire extends horizontally and vertically from its _____

area of origin

What are the four phases in a fire's progression?

Incipient, Emergent smoldering, Free Burning, Oxygen-regulated smoldering

What is the earliest phase and what does it depend on?

incipient, depends on fuel or ignition source

In what phase does the products of combustion become increasingly pronounced

emergent smoldering

in which phase of fire does the rate and intensity of open burning increase?

free bruning

in which phase of fire does the oxygen enriched air in the room during the third phase is depleted?

oxygen-regulated smoldering

typically, the heaviest fire damage occurs at or near the ____

area of origin

What are the four classifications of cause of a fire?

1. accidental or explainable

2. natural, act of nature

3. Intentional act of setting a fire

4. undetermined, cause unknown, unable to be identified

subrogation is defined as

the legal action of substituting once creditor for another

what is spoilation

the intentional or negligent destruction or alteration of evidence

What is overhaul?

it happens when the inspection of and movement or removal of debris in an effort to discover concealed embers or flames that might rekindle the fire results in getting rid of potential evidence.

What is an accelerant?

flammable material that is used to start a fire

solid accelerants include

paper, fireworks, highway flares, and black powder

gaseous accelerants could be

butane, propane, and natural gas

What are the two categories of liquid accelerants

petroleum distillates, and non=petroleum products

petroleum distillates are derived from ___ and also called __ or ____

crude oils/hyrdocarbons/petroleum hydrocarbons

the ____ of an accelerant is an important consideration in the combustion process

volatility

What ways can the presence of an accelerant

trained dogs, chemical color tests, and portable instruments and sensors

the utmost concern in a fatal fire is __

the potential loss of physical evidence

usually if a fatality is involved the ____ will be summoned

Fire Prevention Bureau

when an investigator believed the cause of the fire could potentially be incendiary what should happen?

samples of the burn materials around the point oforigin should be removed and tested to identify the potential traces of accelerants

A Control or comparison samples is

the same material removed from a different room or different area of the room than where the fire originated

what is the most common container used to collect fire debris evidence

unlined paint cans

what is the primary tool used to detect and identify liquid accelerants

Gas chromatography coupled to either a flam ionization detector or a mass spectrometer

What are the methods of sample preparation for introduction into GC?

Cold headspace, Heated Headspace, extraction, purge-and trap, charcola strip/solid phase microexctraction

What happens in cold headspace sample introduction

can is punctured and syringe is used to withdraw a headspace sample that is injected into gc

what happens in heated headspace sample introduction

prior to syringe introduction, the can is heated

what happens in extraction sample introduction?

the accelerant is extracted from the sample using a solvent or steam

what happens in purge-and-trap sample introduction?

inlet and outlet holes are put in the can lid. a stream of filtered air is pumped in through the inlet and a charcoal trap is placed on the outlet. the can may be heated and vapors are trapped on the charcoal. the trapped compounds can be removed using heat of solvent extraction.

what happens in strip/solid phase extraction?

a charcoal strip or other adsorptive material is lowered into the can or places on an inlet drilled into the can. a vacuum can be used to draw a sample through the trap or a steam of filtered air can be pumped into the can to force headspace to flow our through the trap. the can may be heated with a thermometer inserted in the can to monitor the temperature

a detonation is initiated by

pressure

___ high explosives are shock and or heat sensitive

primary

___ high explosives are much more stable and are usually detonated by the shock generated from a primary explosive

secondary

____ explosives decompose at a much faster rate than __ explosives

high/low

one of the oldest and most famous explosives is

nitroglycerin

what are the two ingredients in dynamite

nitroglycerin and diatomaceous earth

what are common screening techniques for explosives in airports?

ion mobility spectrometry and x-ray scanning methods