Arson and BAC Review
Revised BAC
BAC - (time in hours x 0.015)
gas chromatograph
In the laboratory, the ___ _______________ is the most sensitive and reliable instrument for detecting and characterizing flammable residues.
control specimens
It is important that a sampling of similar but uncontaminated ________ ___________ be collected.
Pour Patterns
pool of ignitable liquid which can leave an irregular pattern
pyrolysis
A solid must be hot enough to decompose into gaseous products. (When heat converts solids and liquids into gas)
thermal plume
as gases are heated and become buoyant they flow upward and form a _______ ______
Victims of fire effects
carbon monoxide poisoning presence of soot pugilistic posture
Relevant Chemical Materials
criminalist's function is limited to detecting and identifying ________ _________ _________ collected at the scene and reconstructing and identifying igniter mechanisms.
Fire, gases, and smoke move because of
differences in temperature, density, and pressure
True arson indicators
multiple points of origin Trailers: combustible material used to spread fires Ignition device evidence of other crimes accelerant containers eye witness ignitable liquids
% of alcohol in drink(s) =
proof / 2
Fire induced injuries can cause:
pugilistic posture can cause breaks in joints muscles can contract enough to break bones Skull can fracture due to the heat
Crazed glass
rapid cooling of glass can cause small fractures.
Collection Procedure
should be collected and stored in airtight containers, leaving an airspace to remove samples.
Flashover
spontaneous ignition without a spark or flame.
80% proof
standard (14 grams)
Backdraft
sudden increase in oxygen after the fire starts to extinguish
what starts a fire?
the combination of oxygen and fuel gases
what would happen in a closed room without an outside air supply?
the oxygen in the room depletes and combustion stops
Alligatoring
the pattern of crevices formed by the burning of a wooden structure. Burns so hot, material forms blisters.
Heat
the thermal energy that produces fuel gases and causes ignition
ceiling jet
thin layer of hot gases spread along the ceiling
Synthetic and man-made fuels
type of fuel that releases the most smoke and can generate the most soot
legal limit of BAC
0.08
r for females
0.55
r for males
0.68
Fire Scene Procedures
The arson investigator needs to begin examining a fire scene for signs of arson as soon as the fire has been extinguished.
hydrocarbon components
The gas chromatograph separates the _________ ____________ and produces a chromatographic pattern characteristic of a particular petroleum product.
heat of combustion
The heat involved when a substance burns is known as the.
fire's origin
The search of the fire scene must focus on finding the ______ _______.
Petroleum
The vast majority of arsons are initiated by ___________ distillates such as gasoline and kerosene.
Glowing combustion or smoldering
________ ________ or _________ is burning at the fuel-air interface, such as that of a cigarette.
Spontaneous combustion
(rare) the result of a natural heat-producing process in poorly ventilated containers or areas.
Alcohol consumed (grams) =
(total mass of the drink (grams) x % of alcohol in a drink) / 100
igniters
A search for __________, such as matches, an electrical sparking device, or parts of a "Molotov cocktail" must also be conducted.
To initiate and sustain combustion, the following is required:
1. A Fuel must be present. 2. Oxygen must be available in sufficient quantity to combine with the fuel. 3. Heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction.
Four Stages of Fire Development
1. Ignition (heat, oxygen, and fuel combine to create fire) 2. Growth (fuel will continue to burn as long as oxygen is available) 3. Full Development (all combustible items are ignited with enough oxygen) 3. Decay (longest stage when fire goes out)
1 lbs = _____ grams
454
gaseous state.
A fuel will achieve a reaction rate with oxygen sufficient to produce a flame only when it is in the _______ _______
flash point
A liquid burns when the temperature is high enough to vaporize it.
Arson
A perpetrator that has thoroughly planned a fire, is not present during the act, and the destruction is extensive.
BAC formula
Alcohol consumed (grams) ------------------------------ x 100 = Body Weight (grams) x r
Spurious arson indicators
Alligatoring Narrow V pattern Crazed glass pour patterns spalling of concrete melted metal
rate or speed
An additional factor needed to explain fire, besides the liberation of energy, is the ____ __ ______ at which the oxidation reaction takes place.
Collection of Evidnence
At the suspected point of the origin of a fire, ash and soot, along with porous materials that may contain excess accelerant
chromatographic peaks
By comparing select gas _____________ _____ recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire.
V Pattern
Could indicate where the fire started (V-shaped)
petroleum-based accelerants
Experience shows that most arsons are started with
Rollover
Gases ignite, rise, and set the ceiling on fire.
ignition temperature
To start a fire, the minimum temperature needed to ignite fuel spontaneously must be reached.
vapor detector (sniffer)
Traces of flammable liquid residues may be located with a _____ ________
The necessity to begin an immediate investigation takes precedence even over the requirement to obtain a search warrant. T/F
True
Spalling of Concrete
Under intense heat, parts of the concrete fall.
Continuous pumping of fresh air can cause
flashover
when the ceiling jet reaches the walls, a hot gas layer forms and pressure __________
increases
Effect of ventilation
introduces new oxygen sources and can cause the fire to grow
Fire
is a type of oxidation, which is the combination of oxygen with other substances to produce new substances.
Ventilation
is the exchange of hot fuel gases and air in which hot gases flow out (exhaust) and cooler air enters (intake)
Conduction
is the movement of heat through a solid object.
Radiation
is the transfer of heat energy by electromagnetic radiation.
Convection
is the transfer of heat energy by the movement of molecules within a liquid or gas.