Chapter 6 - Fire Behavior
The mixture of gases in air maintains a constant composition of
21% oxygen, 78% nitrogen, and 1% other gases such as carbon dioxide
Note
A building that is fully involved in a fire radiates a tremendous amount of heat and energy in all directions. The radiant heat from a large building fire can travel several hundred feet to ignite and unattached building
Combustion
A chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either a glow or flame
Thermal column
A cylindrical area above a fire in which heated air and gases rise and travel upward
Fire tetrahedron
A geometric shape used to depict The four components required for a fire to occur: fire, oxygen, heat, and chemical chain reaction
Fire triangle
A geometric shape used to depict the three components of which a fire is composed: fire, oxygen, and heat
Liquid
A liquid will assume the shape of the container in which it is placed. Most liquids expand when heated and will turn into gases when sufficiently heated, cannot be compressed and does not have a definite volume
Fire
A rapid, persistent chemical reaction that releases both heat and light
Endothermic
A reaction that absorbs heat or require heat to be added
Exothermic
A reaction that results in the release of energy in the form of heat
Hypoxia
A state of in adequate oxygenation of the blood and tissue sufficient to cause impairment of function
Matter
A substance made up of atoms and molecules and exists in three states: solid, liquid, and gas
Note
According to recent statistics from the NFPA 3,005 Americans lost their lives and almost 17,500 Americans were injured as a result of fire in 2011.
Note
Actual fires burn without an adequate supply of oxygen, which results in incomplete combustion and produces a variety of toxic byproducts. These by products are collectively called smoke
Note
Almost all fuels consist of hydrogen and carbon Adams; hence they are called hydrocarbons
Note
Almost all of the gas is produced by a fire are toxic to the body, including carbon monoxide, hydrogen cyanide, and Phosphene.
Note
Another example of light energy is the radiant energy we received from the sun
Note
Approximately 1.3 million reported fires, leading to property losses totaling $11.7 billion, occur annually
Extinguishment of a class C fire
Attacking a class C fire with and extinguishing agent that conducts electricity can result in injury or death to the firefighter. Once the power is cut to a class C fire, the fire is treated as a class a or class B fire depending on the type of material that is burning
Note
Because a solid is rigid, only a limited number of molecules are present on its surface, the majority of molecules are cushioned or insulated by the outer surface of the solid
Note
Both uncontrolled explosions and controlled reactions release radioactive material, which can cause injury or death.
Note
Carbon monoxide is deadly in small quantities and was used to kill people in gas chambers. Hydrogen cyanide was also used to kill convicted criminals in gas chambers. Phosphene was used in war war one as a poisonous gas to disable soldiers
The following toxic gases are commonly found in smoky environment
Carbon monoxide, hydrogen chloride, hydrogen cyanide, carbon dioxide, Phosgene, Ammonia and chlorine
Chemical energy
Chemical energy is the energy created by a chemical reaction. Some chemical reactions produce heat, exothermic; others absorb heat, endothermic
Class a fires
Class A fires involve ordinary solid combustible materials such as wood, paper, and cloth. Natural vegetation is also considered to be part of class A.
Extinguishment of Class B fires
Class B fires can be extinguished by shutting off the supply of fuel or by using foam to exclude oxygen from the fuel
Class B fires
Class B fires, involve flammable or combustible liquids such as gasoline, kerosene, diesel fuel, and Motor oil. Fires involving gases such as propane or natural gas are also classified as class B fires.
Class C fires
Class C fires involve energized electrical equipment. They are listed in a separate class because of the electrical hazard they present.
Class D fires
Class D fires involve combustible metals such as sodium, magnesium, and titanium. These fires are assigned to a special class because the application of water two fires involving these metals will result in violent explosions
Extinguishment of class D fires
Class the fires must be attacked with special agents to prevent explosions and to smother the fire and remove the supply of oxygen to the fire
Note
Cold makes most solids more brittle, whereas heat makes them more flexible.
Combustion
Combustion is a rapid chemical process in which the combustion of a substance with oxygen produces heat and light
Methods of extinguishment
Cooling the burning material, excluding oxygen from the fire, removing fuel from the fire, and interrupting the chemical reaction with a flame inhibitor
Note
Decomposition of gases in smoke will vary greatly, depending on the amount of oxygen available to the fire at that instant. The composition of the substance being burned also influences the composition of the smoke
Note
Electrical energy is converted to heat energy in several different ways.
Types of energy
Energy exist in the following forms: chemical, mechanical, electrical, light, and nuclear.
Note
Fire is characterized by the production of a flame, which can be seen in many different colors, depending on what is burning and how much is being produced.
Note
Fire is neither solid nor liquid, but rather is the byproduct of combustible vapors being consumed during a chemical process
Classes of fire
Fires are generally categorized into want to five classes: class a, class B, classy, class D, and class K.
Fire spread
Fires grow and spread by for primary mechanisms: direct contact, Conduction, convection, and radiation
Note
First, a combustible fuel must be present. Second, oxygen must be available insufficient quantities. Third, a source of ignition, heat, must be present. A fourth factor, a chemical chain reaction, must result from the first three elements to produce and maintain a self sustained fire
Note
Fuel, oxygen, and heat must interact in such a way as to create a self-sustaining chemical chain reaction to keep the combustion process going
The three basic elements needed for combustion to occur
Fuel, oxygen, and heat.
Fuels
Fuels are a form of energy. The energy released in the form of heat and light has been stored in the fuel before it is burned
Note
Heat is also produced when mechanical energy is used to compress air in a compressor
Note
Heat is also produced whenever oxygen combines with a combustible material
Electrical energy
Heat that is produced by electricity
Convection
Heat transfer by circulation within a medium
Conduction
Heat transfer to another body or within a body by direct contact. Example: heat transferring down a steel beam
Note
Hydrocarbon fuels are very complex molecules that contain a wide variety of Adams besides hydrogen and carbon
Note
Hydrocarbon fuels plus oxygen equals water and carbon dioxide
Reaction for combustion
Hydrocarbon fuels plus oxygen equals water plus carbon dioxide plus loght plus heat
Note
If the reaction occurs very rapidly or within an enclosed space, the mixture can be heated to its ignition temperature and can begin to burn
Note
If two substances have the same ignition temperature, it will be easier to ignite the substance that is a poor conductor then it is to ignite the substance that is a better conductor
Light energy
Light energy is caused by electromagnetic waves packaged in discrete bundles called photons. This energy travels as thermal radiation, a form of heat
Note
Materials that are good conductors are rarely the primary means of spreading fire
Mechanical energy
Mechanical energy is converted to heat win two materials rub against each other and create friction
Note
Metals generally have a greater ability to conduct heat then Wood does, where as a substance such as fiberglass has almost no ability to conduct heat or fire
Note
Most chemical reactions occur because of bonds are established between two substances or bonds are broken as two substances are chemically separated
Note
Most uncontrolled fires are fed by solid fuels. In structure fires, the building and most of the contents are solids.
Nuclear energy
Nuclear energy is created by splitting the two nucleus of an Adam into two smaller nuclei (nuclear fusion) or by combining two small nuclei into one large nucleus (fusion)
Note
Nuclear energy is stored in radioactive materials and convert to e electricity by nuclear power generating stations
Note
Nuclear reactions release large amounts of energy in the form of heat. These reactions can be controlled, as in a nuclear power plant, or uncontrolled, as in an atomic bomb explosion
Note
Objects that are good conductors tend to absorb heat and conduct it through out the object. For example, heat applied to a steel beam will be readily conducted along the beam
Note
Oil-based or lipid compounds can cause great harm to a person when they are in hailed, some toxic droplets calls poisoning if absorbed through the skin
Note
One method of extinguishing a fire by interrupting the chemical reaction with the flame inhibitor, is with halon type extinguishers. Halogenated fire extinguishers are often used on electronics and computer systems
Solids
One of the three phases of matter; a material that has three dimensions and is firm in substance
Direct contact
Putting fire on the fuel directly. Example: embers from a wildland fire dropping on to dry Pineneedles
Pyrolysis
Pyrolysis is the decomposition of a material brought about by heat in the absence of oxygen
Radiation
Radiation is the transfer of heat through the admissions of energy in the form of invisible waves. Example: the heat and energy radiated from the sun
Note
Regardless of the form in which the energy is stored, it can be changed from one form to another.
Note
Smoke consist mainly of unburned forms of hydrocarbon fuels
Note
Smoke contains large amounts of potential energy that can be released violently under the right conditions
Smoke
Smoke includes three major components: particles, which are solids, vapors, which are finally suspended liquids, and gases
Note
Smoke particles include unburned, partially burned, and completely burnt substances.
Note
The US has the 8th highest mortality rate from fires among the 25 developed countries that keep fire statistics
Plume
The column of hot gases, flames, and smoke rising above a fire; also called convection column, thermal updraft, or thermal column
Note
The combustion process is and exothermic reaction, because it releases heat energy
Convection current
The convection currents in a fire involve primarily gas is generated by heat. The heat of the fire warms the gases and particles in the smoke forming a circulatory movement Column created by the action of gravity called a plume
Pyrolysis
The destructive distillation of organic compounds in an oxygen free environment that converts the organic matter into gases, liquids, and char
Note
The energy produced during combustion is an example of chemical energy
Note
The greater the flow of electricity and the greater the resistance of the material, the greater the amount of heat produced
Note
The inhalation of superheated gases in smoke may also cause injury in the form of severe burns of the skin and the respiratory track
Conversions of energy
The law of conversion of energy states that energy cannot be created or destroyed by ordinary means. Energy can, however, be converted from one form to another
Thermal radiation
The means by which heat is transferred to other objects. Thermal radiation from a fire travels in all directions. The effects of thermal radiation, however, is not seen or felt until the radiation strikes and object and heats The surface of the object
Extinguishment of class a fires
The method most commonly used to extinguish class a fires is too cool the fuel with water to a temperature that is below the ignition temperature
Note
The method most commonly used to extinguish fires is too cool for the burning material
Ignition temperature
The minimum temperature it takes a substance to ignite
Note
The most important fact to remember about conductivity and fire spread is that poor conductors may ignite more easily but, once ignited, do not spread fire through conduction.
Oxidation
The process in which oxygen combines chemically with another substance to create a new compound. It is a reaction with oxygen either in the form of the element or in the form of one of its compounds
Note
The process of oxidation can be very slow; it can take years for oxidation to become evident. Flow oxidation does not produce easily measurable heat
Note
The production of large quantities of heat and light is an integral part of combustion
Atom
The smallest particle of an element, which can exist alone or in combination
Note
The temperature of smoke will vary depending on the condition of the fire and the distance the smoke travels from the fire
Note
The unburned particles are lifted in the thermal call them produced by the fire. Some partly burned particles become part of the smoke because in adequate oxygen is available to allow for their complete combustion. Completely burned particles are primarily ash
Note
We can describe the chemical reaction of combustion simply by considering the fuel to contain carbon and hydrogen. When this fuel combines with oxygen, it produces two by products, water and carbon dioxide
Note
When Adams of one element combine chemically with atoms of another element, they produce a compound that is made up of molecules. For example an atom of oxygen combines chemically with two atoms of hydrogen the resulting compound is water H2O
Note
When light energy is hot enough, it can sometimes be seen in the form of visible light. If it is of a frequency that we cannot see, the energy may be filled as heat but not seen as visible light
Note
When water is applied to a fire, small droplets may also be suspended in the smoke or Hayes that forms
Gas
a gas is a type of fluid that has neither independent shape nor independent volume but rather tends to expand in definitely
