FIRE BEHAVIOR

FIRE CHEMISTRY Without reference, define simple facts about fire chemistry.

FIRE CHEMISTRY Fire- is a rapid chemical reaction that produces: Heat Light For fire to occur all four elements of the fire Tetrahedron must be in place.

FIRE CHEMISTRY The Fire Tetrahedron is the flaming mode of combustion.

FIRE CHEMISTRY This model consists of four elements: Oxygen (Oxidizing agent) Fuel (reducing agent) Heat (temperature) Self-sustained chemical reaction

Self sustained chemical reaction Fire Tetrahedron (Reducing agent) Fuel (Oxidizing agent) Oxygen Self sustained chemical reaction Heat (Temperature)

FIRE CHEMISTRY Oxidizing agents - are those materials that yield oxygen or other oxidizing gases during the course of a chemical reaction.

FIRE CHEMISTRY Oxidizers are not combustible, but they support combustion when combined with a fuel. For purposes of discussion the oxygen in the air around us will be considered the primary oxidizing agent.

FIRE CHEMISTRY Normally air consists of 21% oxygen. Combustion is supported at oxygen levels as low as 14%.

FIRE CHEMISTRY Atmospheres with oxygen concentrations greater than 21% are said to be oxygen enriched.

FIRE CHEMISTRY Fires in oxygen enriched atmospheres present severe safety risks for firefighters operating in them.

FIRE CHEMISTRY Potential oxygen enriched facilities include: Industrial occupancies Hospitals, nursing homes, or clinics Private dwellings where occupants have oxygen

FIRE CHEMISTRY Common chemical oxidizers include: Permanganates Nitrates Chlorates

FIRE CHEMISTRY Fuel (reducing agent)- is the material being oxidized or burned in the combustion process and exists in three forms:

FIRE CHEMISTRY Solid: Has a definite shape and size. The molecules have a very little mobility.

FIRE CHEMISTRY Liquid: A substance that assumes the shape of its container. The molecules flow feely, but substantial cohesion prevents them from expanding as a gas would.

FIRE CHEMISTRY Gas: volume, that tends to assume the shape of A compressible substance, with no specific volume, that tends to assume the shape of its container. Molecules move about rapidly in this state.

FIRE CHEMISTRY Fuels must be in their vapor state to burn.

FIRE CHEMISTRY Solids fuel gases evolve from solid fuels by pyrolysis.

FIRE CHEMISTRY Pyrolysis is the chemical decomposition of a substance through the action of heat. Pyrolysis is the process of a solid producing gases that burn.

FIRE CHEMISTRY Liquids: vaporization. Fuel gases are evolved from liquids by vaporization.

FIRE CHEMISTRY Vaporization is the changing from a liquid to a gaseous state. The rate of vaporization depends on the liquid involved and heat.

FIRE CHEMISTRY Gases: Are in the natural state required for ignition. No pyrolysis or vaporization is needed.

FIRE CHEMISTRY The following are factors that affect the ignitability of both solid and liquid fuels.

FIRE CHEMISTRY Solid fuels have a definite shape and size. The primary consideration is surface-to-mass ratio.

FIRE CHEMISTRY As the ratio increases, the fuel particles become smaller and more finely divided. As the surface area increases, heat transfer is easier speeding up the pyrolysis process.

FIRE CHEMISTRY The position of a solid fuel affects its ignitability and flame spread. In the vertical position, fire spread will be rapid. Fire spread is due to increased heat transfer.

FIRE CHEMISTRY Liquid fuels will assume the shape of the ground and will flow to low.

FIRE CHEMISTRY Firefighters must consider the density of a liquid fuel before they use water for extinguishment.

FIRE CHEMISTRY The density of liquids in relation to water is known as specific gravity. Water is given a value of one.

FIRE CHEMISTRY A specific gravity less than one is lighter than water and a specific gravity greater than one is heavier than water.

FIRE CHEMISTRY Solubility of a liquid fuel in water is also an important factor.

FIRE CHEMISTRY Solubility is the ability of a substance to mix with water.

FIRE CHEMISTRY Alcohol’s (polar solvents) – dissolve in water. Hydrocarbon liquids (non-polar solvents) – will not dissolve in water and float.

FIRE CHEMISTRY The volatility or ease with which a liquid gives off vapor influences its ignitability.

FIRE CHEMISTRY All liquids give off vapors through simple evaporation. Liquids that give off large amounts of vapors are dangerous because they are easily ignited.

FIRE CHEMISTRY Vapor density is of concern with ignitable liquids and gaseous fuels.

FIRE CHEMISTRY Air is given a value of one. Gasses assume the shape of their container.

FIRE CHEMISTRY If a gas is heavier than air it will hug the ground and will move with terrain and wind (propane). Gases lighter than air (methane) will rise and dissipate.

FIRE CHEMISTRY The concentration of oxygen in relation to a fuel directly affects its combustibility. Gases must mix with air (oxidizer) in the proper ratio to burn.

FIRE CHEMISTRY The Flammable (explosive) Range – percentage of a substance mixed with air that will burn once its ignited.

FIRE CHEMISTRY The Upper Flammable Limit – maximum concentration of gas in air that will allow combustion to occur. Concentrations above this are “too rich” to burn.

FIRE CHEMISTRY The Lower Flammable Limit – is the lowest percentage of fuel/oxygen mixture required for combustion. (farthest away from the fuel) Any mixture with a lower percentage is “too lean.”

Flammable Explosive Range Too Rich F V u a e p l o r Flammable Explosive Range Upper Flammable Limit O x y g e n Too Lean Lower Flammable Limit

FIRE CHEMISTRY The mixture of fuel and oxygen must be within the Flammable Range to burn. Oxygen concentrations below 21% affect fire production and life safety.

FIRE CHEMISTRY HEAT – is the energy component of the fire tetrahedron.

FIRE CHEMISTRY HEAT: Causes pyrolysis of solid fuels and vaporization of liquid fuels. Incites the production of ignitable vapors or gases. Provides the energy necessary for ignition.

FIRE CHEMISTRY Self-sustained Chemical Reaction – occurs when sufficient heat energy produces the continual development of fuel vapors or gases.

FIRE CHEMISTRY A series of reactions that occur in sequence, with each individual reaction being added to the rest is called a chain reaction.

FIRE CHEMISTRY Vapors mix with an oxidizer and heat in a specific way creating fire. Heat continues the development of fuel vapors.

FIRE CHEMISTRY As fuel vapors mix with oxygen while being heated, flaming combustion propagates itself.

FIRE CHEMISTRY Self-sustained chemical reaction and related rapid growth are factors that distinguish fire from slower oxidation reactions such as: Rusting of iron Yellowing of paper

FIRE CHEMISTRY Examples of uncontrolled, runaway chain reactions include : Forest fires Nuclear bombs

FIRE CHEMISTRY The following definitions are used to describe the combustion process or pertain to fire behavior:

FIRE CHEMISTRY Flash Point – Minimum temperature at which a liquid gives off enough vapors to form an ignitable mixture with air near the liquid’s surface.

FIRE CHEMISTRY Fire Point – Temperature at which a liquid fuel produces sufficient vapors to support combustion once the fuel is ignited. The fire point is a few degrees above the flash point. Also called burning point.

FIRE CHEMISTRY Ignition temperature – Minimum temperature to which a fuel in air must be heated in order to start self-sustained combustion independent of the heating source.

FIRE CHEMISTRY British Thermal Unit (BTU) – Amount of heat energy required to raise the temperature of one pound of water one degree Fahrenheit.

Heat Transfer OBJECTIVE: Without reference, define the methods of heat transfer and identify heat sources.

Heat Transfer Heat transfer involves numerous laws of physics. One natural law is the Law of Heat Flow:

Heat Transfer Heat tends to flow from a hot substance to a cold substance. The colder of two objects in contact will absorb heat until both objects are the same temperature.

Heat Transfer Conduction is the point to point transmission of heat energy.

Heat Transfer Heat can be transferred through the direct contact of two objects (I.e. pipes in a structure). In the early stages of fire, heat transfer is primarily due to conduction. Fire spread is low.

Heat Transfer Not all materials have the same heat conductivity.

Heat Transfer Convection is the transfer of heat by the movement of heated liquids or gases. Heated air or vaporized liquids will expand and rise. Heat rises to the highest point and spreads outward until it runs out of ceiling space, then travels back toward the floor.

Heat Transfer Radiation is the transfer of heat energy by electromagnetic waves.

Heat Transfer Radiated heat will travel until it reaches an opaque object. As an object is exposed to heat radiation, it will radiate heat from its surface. Radiation is the cause of most exposure fires.

Heat Transfer Heat is proportional to molecular movement. Heat is described as “matter in motion” caused by movement of molecules.

Heat Transfer When matter is heated, the speed of the molecules increases, and the temperature also increases. Anything that sets the molecules in faster motion produces heat in that material.

Heat Transfer There are many forms of heat found in nature; however, we will discuss four basic categories of heat energy: Chemical Mechanical Electrical Nuclear

Heat Transfer Chemical Heat Energy is energy released as a result of a chemical reaction such as combustion. The materials may come in contact with each other and react.

Heat Transfer Heat of Combustion Spontaneous Heating The following are sources of chemical heat energy: Heat of Combustion Spontaneous Heating Heat of Decomposition Heat of Solution

Heat Transfer Electrical Heat Energy is energy developed when electrons flow through a conductor.

Heat Transfer Sources of electrical heat energy include: Leakage current heating Resistance heating

Heat Transfer Mechanical Heat Energy is energy an object in motion possesses such as a fan belt turning on a pulley, or a piston compressing a gas in a cylinder.

Heat Transfer Nuclear Heat Energy is energy generated when atoms are either split apart (fission) or combined (fusion).

Fire Conditions OBJECTIVE: Without reference, describe thermal layering and recognize fire conditions, their hazards, and appropriate actions.

Fire Conditions There are four products of combustion when fuels burn:

Fire Conditions Heat – responsible for the spread of fire and firefighter injuries such as: Damage to the respiratory tract Heat Exhaustion Dehydration Burns

Fire Conditions Light or Flame – is the visible, luminous body of burning gas. A loss of light is caused by a more complete combustion of the carbon. Although flame is a product it is not present in a smoldering fire.

Fire Conditions Smoke – causes most deaths in fires and contain a variety of materials. Smoke generated in a fire contains narcotic gases.

Fire Conditions The most common narcotic (asphyxiant) gases are: Carbon Monoxide (most easily detected in the blood) Hydrogen cyanide Carbon dioxide

Fire Conditions Fire Gases – are found in smoke, but the exact type of gas generated during burning varies from fuel to fuel.

Thermal Layering Thermal Layering of Gases is the tendency of gases to form into layers, according to temperature.

Thermal Layering The hottest gases tend to accumulate at the highest levels. The smoke mixture of air, gases, and particles rise or fall into thermal layers according to their vapor density.

Thermal Layering Understanding thermal layering is critical to safe firefighting activities. The lower level is safer for firefighters.

Thermal Layering A lack of coordinated ventilation and proper hose streams can cause: Smoke and steam to circulate Disruption to the thermal balance Unnecessary burns to firefighters

Phases of Fire The Phases and Conditions of Fire must be recognized by a firefighter to promote safe and effective fire ground operations.

Phases of Fire The Ignition Phase is the earliest phase of a fire.

Phases of Fire Ignition can be a result of a flame (piloted) or caused when the material reaches its ignition temperature (non-piloted).

Phases of Fire The fire is small and limited to fuel first ignited.

Phases of Fire Hazards during the Ignition Phase are minimal to firefighters . Oxygen content is still high, but the fire is producing water vapor, carbon dioxide, small quantities of sulfur dioxide, and carbon monoxide.

Phases of Fire Actions for the Ignition Phase: Attack the seat of the fire Ventilate to get rid of smoke and hot gases

Phases of Fire The Growth Phase – total involvement is possible.

Phases of Fire During Growth Phase there is sufficient oxygen and fuel for fire growth. Oxygen in the room is drawn into the flame. Heat is carried to the uppermost regions of the confined area.

Phases of Fire The temperature in the plume is still moderate due to the air that is drawn into the plume. Once the air is recycled the temperature rises quickly

Phases of Fire Hazards during the Growth Phase: Heat and fire spread out laterally from the top down and ignite all material in the upper levels of the room.

Phases of Fire In the early portion of the Growth Phase flame spread is predominate. Temperatures in the upper regions can exceed 1,300 degrees.

Phases of Fire Actions for a Growth Phase fire include: Ventilate overhead to relieve the structure of superheated smoke and gases.

Phases of Fire Use hose lines to extinguish or control the fire, and protect firefighters. Use a combination attack to advance and make a direct attack on the seat of the fire.

Phases of Fire A Flashover Phase is the transition between the Growth and Fully Developed phases and is not a specific event such as ignition.

Phases of Fire During Flashover flames flash over the entire surface of the room. The actual cause of a Flashover is the build up of heat from the fire.

Phases of Fire All the contents of the fire area gradually reach their ignition temperature. Once the ignition temperature of contents is reached simultaneous ignition occurs, and the area becomes fully involved.

Phases of Fire Hazards during Flashover include: High temperatures Total fire involvement (room or area) Once it happens it cannot be stopped

Phases of Fire Appropriate actions for a flashover include: Ventilate overhead to relieve the structure of superheated smoke and gases. Use sufficient size hose lines to extinguish or control the volume of fire, and protect firefighters.

Phases of Fire The Fully Developed Phase occurs when all combustible materials in the compartment are involved in fire.

Phases of Fire Hazards during the Fully Developed Phase include: The burning fuels are releasing the maximum amount of heat.

Phases of Fire The heat released depends on the number and size of the ventilation openings. Hot unburned gases are likely to begin flowing from the compartment of origin into adjacent spaces or compartments.

Phases of Fire Appropriate actions for a Fully Developed fire include: Ventilate overhead, (possibly the only way to control the fire). Coordinate overhead ventilation and hose streams.

Phases of Fire Decay Phase – the final phase of fire development.

Phases of Fire The rate of heat release begins to decline as available fuel is consumed. The fire begins to become fuel controlled as with the ignition phase.

Phases of Fire The fire starts to diminish. Temperatures within the compartment begin to decline.

Conditions of Fire A Flameover/Rollover Condition takes place when flames move through the unburned gases during a fire’s progression.

Conditions of Fire The Flameover Condition is limited to the involvement of only the fire gases.

Conditions of Fire May occur during the Growth Stage when a hot gas layer forms at the ceiling. Superheated vapors ignite.

Conditions of Fire A flame front rolls across the ceiling. Hazards occur when flames move through or across unburned gases.

Conditions of Fire Appropriate actions for a Flameover Condition include:

Conditions of Fire Ventilate first to relieve the structure of unburned gases. Firefighters must remain low (12” to 24”)

Conditions of Fire Cool the heated products overhead and gases by advancing hose lines to attack the seat of the fire. A Flameover may be avoided by directing water towards the ceiling level and the room contents to cool material below their ignition temperatures.

Conditions of Fire A Backdraft Condition is the result of a confined fire that is late in the Fully Developed or Decay Phase.

Conditions of Fire During a Backdraft Condition unburned carbon particles and other flammable products are available for combustion.

Conditions of Fire A Backdraft Condition is a combination of high heat from Fully Developed burning and no oxygen common in the Decay Phase.

Conditions of Fire The signs of a Backdraft are: Pressurized smoke exiting small openings Black smoke becoming dense gray/yellow Confinement and excessive heat Little or no visible flame Smoke leaving the building in puffs or at intervals Smoke-stained windows

Conditions of Fire Hazards during the Backdraft Condition pose a serious risk to firefighters. Any introduction of oxygen will cause an explosion followed by a flame front.

Conditions of Fire The pressure from a Backdraft explosion can scatter debris and cause serious injury or death to personnel in the area. A Backdraft can be the most hazardous condition a firefighter will ever face.

Conditions of Fire Appropriate actions for a Backdraft Condition include: Size-up the scene prior to any action. Wear proper protective clothing and SCBA. Ventilate at the highest point to release fire gases and smoke prior to entry.

Summary

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