Forensic Science Chapter 12 - Forensic Aspects of Fire Investigation

True

True or False: Arson investigations often present complex and difficult circumstances to investigate due to the fact that the perpetrator has thoroughly planned the act, is not present during the act, and the destruction is so extensive.

False

True or False: The criminalist's function is NOT rather limited to detecting and identifying relevant chemical materials collected at the scene and reconstructing and identifying igniter mechanisms.

oxidation

Chemically, fire is a type of _________, which is the combination of oxygen with other substances to produce new substances.

ignition temperature

To start fire, the minimum temperature needed to spontaneously ignite fuel, known as ________ __________, must be reached.

heat of combustion

The heat evolved when a substance burns.

rate or speed

An additional factor, besides the liberation of energy, needed to explain fire is the ____ or _____ at which the oxidation reaction takes place.

gaseous state

A fuel will achieve a reaction rate with oxygen sufficient to produce a flame only when it is in the what?

vaporize it, decompose

A liquid burns when the temperature is high enough to ________ __ (flash point), while a solid must be hot enough to _________ into gaseous products (pyrolysis).

fuel-air interface

Glowing combustion or smoldering is burning at the ____-___ _________, such as a cigarette.

spontaneous combustion

___________ __________, which is rare, is the result of a natural heat-producing process in poorly ventilated containers or areas.

Fuel, oxygen, heat

To initiate and sustain combustion the following is required:

1. A ____ must be present

2. ______ must be available in sufficient quantity to combine with the fuel

3. ____ must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction

Conduction, radiation, convection

The three mechanisms of heat transfer are conduction, radiation, and convection.

• __________ is the movement of heat through a solid object.

• _________ is the transfer of heat energy by electromagnetic radiation.

• __________ is the transfer of heat energy by the movement of molecules within a liquid or gas.

Fire

Produced when a substance undergoes rapid oxidation involving heat and light.

Fire Triangle

Shows the three elements needed to produce and sustain a fire.

Flash Point

The lowest temperature to which a substance must be heated in order for the substance to give off vapors which will burn when exposed to a flame or ignition source.

Point of Origin

The location where the fire started.

Burn Patterns

Noticeable patterns created by the fire as it burns.

Accelerants

Substances, such as gasoline, paint thinner, and alcohol, that accelerate the burning process.

Arson

A fire started deliberately.

Fire Triangle

Represents the three elements needed for fire to occur: heat, fuel, and oxygen.

True

True or False: Fuel can be any combustible material in any state of matter - solid, liquid, or gas.

vapor or gas

Most solids and liquids become a _____ or ___ before they will burn.

21%, 16%

The air we breathe is about ___ oxygen. Fire requires an atmosphere with at least ___ oxygen.

Heat

The energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur.

Point of Origin

Burn patterns and other damage can help determine the point of origin, or the location where the fire started.

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.

V-Patterns

Fire burns up, in a V-shaped pattern, so a fire that starts at an outlet against a wall leaves a char pattern that points to the origin.

which side of the door the fire was on

A char pattern on a door would help an investigator determine what?

the use of an accelerant and its path

A char pattern on the floor would help investigators determine what?

hotter than normal

A very narrow V-shape might indicate a fire that was what? (such as one helped along by an accelerant)

slow burning

A wide V-shape might indicate a fire that was what?

pool of origin

A U-shape could indicate that there was a "____ __ ______" rather than a point of origin, such as might be caused by, say, a puddle of gasoline.

Heat Shadows

Occur when heavy furniture shields part of a wall; can help determine the origin point.

Glass

Glass fragments, windows, and light bulbs can provide clues to a fire.

the direction of the fire

Light bulbs tend to melt toward the heat source, so the "direction of melt" can indicate what?

shattered or cracked glass

The _________ __ _______ _____ of the windows can provide indications as to how a fire burned.

dark soot layer

A ____ ____ _____ on the glass could indicate a slow, smoldering fire.

abnormal pattern of cracking

Clear glass with an ________ ______ __ ________ could imply a very hot fire, possibly due to an accelerant.

Chimney Effect

Since fire burns upwards, there can be a "chimney effect" where the fire ignites at a point, the super heated gases rise upward and form a fireball, which continues straight up to burn a hole in the ceiling. If the roof is not entirely burnt, and the fire investigator finds such a hole, the origin of the fire could be directly underneath.

Color of Smoke

Determine what type material was burning

Color of Flames

Indicates at what temperature the fire was burning.

Interview witnesses, determine the point of origin, and determine the heat source(s)

What are 3/7 fire investigation basics?

Heating systems, electrical appliances, and lightning

What are three things that could cause accidental fires?

Odors, two or more points of origin, charred floors

What are three things that could point to

non-accidental fires?

55%

According to the FBI Crime Index, juvenile and adult arson cause an annual average of 560,000 fires, 750 deaths, 3,700 injuries, and $1.5 billion in property loss. ___ of all arson arrests in the US are children under 18.

Crime concealment, revenge or spite, and monetary gain

What are three common motives for arson?

juveniles

Fires set by _________ are usually the result of a child or teenager experimenting with fire with a lack of understanding of the consequences. Others fires may be started by troubled children as a "cry for help" or as acts of vandalism.

Children themselves

These tragic events are not isolated incidents. In a typical year, in the U. S., 300 people are killed and $190 million in property is destroyed in fires set by children. ________ __________ are usually the victims of these fires accounting for 85 of every 100 lives lost.

report suspicious persons and activities that may result in arson, install and properly maintain fire alarms in your homes and encourage others around you to do the same

What are two things that you can do to help prevent arson or arson damage?

As soon as the fire has been extinguished

The arson investigator needs to begin examining a fire scene for signs of arson when?

petroleum-based accelerants

Experience shows that most arsons are started with what?

the requirement to obtain a search warrant

The necessity to begin an immediate investigation even takes precedence over what?

the fire's origin

The search of the fire scene must focus on finding ___ ____'_ ______, which may be most productive in any search for an accelerant or ignition device.

separate and unconnected, streamers, severe burning

Some telltale signs of arson include evidence of ________ and ___________ fires, the use of "_________" to spread the fire from one area to another, and evidence of ______ _______ found on the floor as opposed to the ceiling of a structure, due to a flammable liquid.

upward, intense

Normally, a fire has a tendency to move in an ______ direction, and thus the probable origin will most likely be the lowest point showing the most _______ characteristics of burning.

True

True or False: Fortunately, combustible liquids are rarely entirely consumed during a fire.

airtight containers

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 ________ __________, leaving an airspace to remove samples.

vapor detector

Traces of flammable liquid residues may be located with a what? (sniffer)

uncontaminated

It is important that a sampling of similar but _____________ control specimens be collected.

search for igniters

A ______ ___ ________ such as matches, an electrical sparking device, or parts of a "Molotov cocktail" must also be conducted.

oxygen combines with a fuel

When a fire occurs, ______ ________ ____ _ ____ to produce noticeable quantities of heat and light (flames).

initiated and sustained

If combustion is to be _________ ___ _________, a fuel must be present, oxygen must be available, heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction.

gaseous state

A fuel will achieve a reaction rate with oxygen sufficient to sustain a fire only when it is in the what?

gas chromatograph

In the laboratory, the ___ _____________ is the most sensitive and reliable instrument for detecting and characterizing flammable residues.

gasoline and kerosene

The vast majority of arsons are initiated by petroleum distillates such as what?

chromatographic pattern

The gas chromatograph separates the hydrocarbon components and produces a ______________ _______ characteristic of a particular petroleum product.

known flammable liquids

By comparing select gas chromatographic peaks recovered from fire-scene debris to _____ _________ _______, a forensic analyst may be able to identify the accelerant used to initiate the fire.