NOTES ON CRIME DETECTION AND INVESTIGATION
CDI-6: FIRE TECHNOLOGY AND ARSON INVESTIGATION
FIRE
- a rapid, self-sustaining oxidation process accompanied by the evolution of heat and light of varying intensity
- an active chemical reaction that takes place between fuel, heat and oxygen in the form of light and noticeable
heat
- a chemical reaction; the rapid oxidation of a fuel producing heat and light
- an oxidation taking place with a rate rapid enough to produce heat and light
TECHNOLOGY
- the branch of knowledge that deals with industrial arts and sciences
- the application of such knowledge that is used to produce the material necessity of society
ELEMENTS OF FIRE OR TRIANGLE OF FIRE
FUEL
- anything that will burn when heated with sufficient oxygen
OXYGEN
- aids in combustion; comes from the atmosphere we breath; the atmosphere contains: 21% oxygen, 78% nitrogen
and 1% impurities
HEAT
- source of ignition
TRIANGLE OF FIRE
For many years, the fire triangle (oxygen, fuel and heat) was taught as the components of fire. While this simple
example is useful, it is NOT technically correct.
TETRAHEDRON OF FIRE
- a geometric representation of what is required for fire to exist, namely, fuel, an oxidizing agent, heat, and an
uninhibited chemical reaction
FIRE TETRAHEDRON
- Oxygen (oxidizing agent)
- Fuel
- Heat
- Self-sustained chemical reaction
Each component of the tetrahedron must be in place for combustion to occur. Remove one of the four
components and combustion will not occur. If ignition has already occurred, the fire is extinguished when one of
the components is removed from the reaction.
OXYGEN (Oxidizing Agent)
- a colorless, odorless gas and one of the compositions of air which is approximately 21% percent by volume
-
Oxygen sources: Oxygen requirements:
1. 21% of normal oxygen 1. 12% no fire
2. 78% nitrogen 2. 14% flash point
3. 1% other gases 3. 21% fire point
FUEL
- the material or substance being oxidized or burned in the combustion process.
Fuel sources
1. Solid
- molecules are closely packed together
2. Liquid
- molecules are loosely packed
3. Gas
- molecules are free to move
HEAT
- the energy component of the fire tetrahedron
- when heat comes into contact with a fuel, the energy supports the combustion reaction
- heat energy is measured in units of Joules (J), however it can also be measured in Calories (1 Calorie = 4.184 J)
, 55 131 Human skin receives a second degree burn injury
62 140 A phase where burned human tissue becomes numb
72 162 Human skin is instantly destroyed
100 212 Water boils and produces steam
140 284 Glass transition temperature of polycarbonate
230 446 Melting temperature of polycarbonate
250 482 Charring of natural cotton begins
300 572 Charring of modern protective clothing fabrics begins
600 1112 Temperatures inside a post-flashover room fire
Types of Energy (common sources of heat)
1. Chemical Energy
2. Electrical Energy
3. Nuclear Energy
4. Mechanical Energy
CHEMICAL ENERGY
- the most common source of heat in combustion reactions
When any combustible is in contact with oxygen, oxidation occurs. The reaction of this process results in
the production of heat.
ex. Heat generated from burning match, self heating (spontaneous heating)
ELECTRICAL ENERGY
- can generate temperature high enough to ignite any combustible material near the heated area
Examples:
1. over current or overload
2. arcing
3. sparking
4. static
5. lightning
NUCLEAR ENERGY
- generated when atoms either split apart (fission) or combine (fusion)
Ex.
1. fission heats water to drive steam turbines and produce electricity
2. solar energy is a product of a fusion reaction
MECHANICAL ENERGY
- an energy created by friction and compression
1) Heat of friction - the movement of two surfaces against each other, thus producing sparks
2) Heat of compression - heat is generated when a gas is compressed in a container or cylinder
SELF-SUSTAINED CHEMICAL REACTION
Combustion is a complex reaction that requires a fuel (in the gaseous or vapor state), an oxidizer, and heat
energy to come together in a very specific way. Once flaming combustion or fire occurs, it can only continue when enough
heat energy is produced to cause the continued development of fuel vapors or gases. Scientists call this type of reaction a
“chain reaction”.
A chain reaction is a series of reactions that occur in sequence with the result of each individual reaction being
added to the rest.
FIRE DEVELOPMENT
When the four components of the fire tetrahedron come together, ignition occurs. For a fire to grow beyond the
first material ignited, heat must be transmitted beyond the first material to additional fuel packages.
Stages of Fire
- Ignition
- Growth
- Flashover
- Fully-developed
- Decay
IGNITION
- describes the period when the four elements of the fire tetrahedron come together and combustion begins
CDI-6: FIRE TECHNOLOGY AND ARSON INVESTIGATION
FIRE
- a rapid, self-sustaining oxidation process accompanied by the evolution of heat and light of varying intensity
- an active chemical reaction that takes place between fuel, heat and oxygen in the form of light and noticeable
heat
- a chemical reaction; the rapid oxidation of a fuel producing heat and light
- an oxidation taking place with a rate rapid enough to produce heat and light
TECHNOLOGY
- the branch of knowledge that deals with industrial arts and sciences
- the application of such knowledge that is used to produce the material necessity of society
ELEMENTS OF FIRE OR TRIANGLE OF FIRE
FUEL
- anything that will burn when heated with sufficient oxygen
OXYGEN
- aids in combustion; comes from the atmosphere we breath; the atmosphere contains: 21% oxygen, 78% nitrogen
and 1% impurities
HEAT
- source of ignition
TRIANGLE OF FIRE
For many years, the fire triangle (oxygen, fuel and heat) was taught as the components of fire. While this simple
example is useful, it is NOT technically correct.
TETRAHEDRON OF FIRE
- a geometric representation of what is required for fire to exist, namely, fuel, an oxidizing agent, heat, and an
uninhibited chemical reaction
FIRE TETRAHEDRON
- Oxygen (oxidizing agent)
- Fuel
- Heat
- Self-sustained chemical reaction
Each component of the tetrahedron must be in place for combustion to occur. Remove one of the four
components and combustion will not occur. If ignition has already occurred, the fire is extinguished when one of
the components is removed from the reaction.
OXYGEN (Oxidizing Agent)
- a colorless, odorless gas and one of the compositions of air which is approximately 21% percent by volume
-
Oxygen sources: Oxygen requirements:
1. 21% of normal oxygen 1. 12% no fire
2. 78% nitrogen 2. 14% flash point
3. 1% other gases 3. 21% fire point
FUEL
- the material or substance being oxidized or burned in the combustion process.
Fuel sources
1. Solid
- molecules are closely packed together
2. Liquid
- molecules are loosely packed
3. Gas
- molecules are free to move
HEAT
- the energy component of the fire tetrahedron
- when heat comes into contact with a fuel, the energy supports the combustion reaction
- heat energy is measured in units of Joules (J), however it can also be measured in Calories (1 Calorie = 4.184 J)
, 55 131 Human skin receives a second degree burn injury
62 140 A phase where burned human tissue becomes numb
72 162 Human skin is instantly destroyed
100 212 Water boils and produces steam
140 284 Glass transition temperature of polycarbonate
230 446 Melting temperature of polycarbonate
250 482 Charring of natural cotton begins
300 572 Charring of modern protective clothing fabrics begins
600 1112 Temperatures inside a post-flashover room fire
Types of Energy (common sources of heat)
1. Chemical Energy
2. Electrical Energy
3. Nuclear Energy
4. Mechanical Energy
CHEMICAL ENERGY
- the most common source of heat in combustion reactions
When any combustible is in contact with oxygen, oxidation occurs. The reaction of this process results in
the production of heat.
ex. Heat generated from burning match, self heating (spontaneous heating)
ELECTRICAL ENERGY
- can generate temperature high enough to ignite any combustible material near the heated area
Examples:
1. over current or overload
2. arcing
3. sparking
4. static
5. lightning
NUCLEAR ENERGY
- generated when atoms either split apart (fission) or combine (fusion)
Ex.
1. fission heats water to drive steam turbines and produce electricity
2. solar energy is a product of a fusion reaction
MECHANICAL ENERGY
- an energy created by friction and compression
1) Heat of friction - the movement of two surfaces against each other, thus producing sparks
2) Heat of compression - heat is generated when a gas is compressed in a container or cylinder
SELF-SUSTAINED CHEMICAL REACTION
Combustion is a complex reaction that requires a fuel (in the gaseous or vapor state), an oxidizer, and heat
energy to come together in a very specific way. Once flaming combustion or fire occurs, it can only continue when enough
heat energy is produced to cause the continued development of fuel vapors or gases. Scientists call this type of reaction a
“chain reaction”.
A chain reaction is a series of reactions that occur in sequence with the result of each individual reaction being
added to the rest.
FIRE DEVELOPMENT
When the four components of the fire tetrahedron come together, ignition occurs. For a fire to grow beyond the
first material ignited, heat must be transmitted beyond the first material to additional fuel packages.
Stages of Fire
- Ignition
- Growth
- Flashover
- Fully-developed
- Decay
IGNITION
- describes the period when the four elements of the fire tetrahedron come together and combustion begins
