Ch 5 - Fire Behavior

Heat

A form of energy characterized by the vibration of molecules and is capable of starting and supporting chemical changes and changes of state (i.e changing a liquid to a gas). Measured in BTUs in the English system and Joules in the metric system (77)

Radicals

A highly reactive molecular fragment that, when attached to another molecular fragment or hydrocarbon backbone, will impart specific properties to the new compound. (76/1100)

Dielectric Heating

A method of heating non-conductive materials (like a microwave) (82).

Ignitable Liquids

A more commonly accepted term for all liquids that burn (78). A flash point is the minimum temperature at which an ignitable liquid gives off sufficient vapor to form an ignitable mixture with air near the surface of the liquid or within a test vessel.

Entrainment

A process where air (oxygen) is drawn into a fire (86).

How does NFPA 921 define fire?

A rapid oxidation process with the evolution of light and heat in varying intensities (76).

Endothermic Reactions

A reaction between combustibles that absorbs heat (77/1084).

Incipient Fire

A small and limited fire (86).

Oxidizer

A substance that either is oxygen, a substance that contains oxygen and gives it up readily, or another substance that will support combustion. Also known as an oxidizing agent (76/1097).

Fire Tetrahedron

A three dimensional fire triangle illustrating the interrelationship of the chemical chain reaction in the combustion process (77/1086).

Why is it a good reason to be very careful with aluminum ground ladders around wires?

Aluminum conducts electrical current (81).

Specific Heat

Amount of heat that a substance absorbs as the temperature of the substance increases. It's expressed as "the amount of thermal energy required to raise unit mass of a substance by one degree" (80).

What needs to be known in order to attack and control fire?

An understanding of fire including how fire occurs, how a fire grows and spreads, and how a fire can be controlled and ultimately extinguished (76).

Cloud-to-cloud lightning

As clouds connect, electrons flow and cause lightning between them (82).

Why is it critical for ventilation to be closely coordinated with fire attack and the application of fire streams?

Because trapped occupants and/or firefighters will be rapidly exposed to excessively high temperatures due to thermal layering (87).

Fire Development

Before any fuel can be ignited, the fuel must be heated to a point where the fuel emits ignitable vapors. Gasoline's flash point is -45F (86).

BLEVE

Boiling Liquid Expanding Vapor Explosion. An event in which a container of liquefied flammable gas fails and the resulting release allows the content to expand to hundreds of times their liquefied volume. When ignited, the rapidly expanding vapor violently explodes (84/1078)

Ventilation-Controlled Fire

Can be controlled by ventilation

Chemical Heat Source / Spontaneous Ignition

Combustion is a form of chemical heat energy. Spontaneous Ignition- the initiation of combustion of a material by an internal chemcial or biological reaction that has produced sufficient heat to ignite the material (rags or clothes made of cotton soaked with oils. As fibers break down from the oils, a process takes place causing heat, and ignite) (81)

What has been heralded as the most important discovery known to humankind?

Fire (some call it a 'beast' (76)) (75).

Flammable and Combustible Liquids

Flammable - liquids with a flash point below 100F. Combustible - liquids with a flash point at or above 100F. (Europe's differentiation point is 140F. (78).

Gas

Flammable gases n most ambient temperature and pressures have already vaporized and only need the introduction of an ignition source to burn if they are within their flammable limits. If there is too little gas, the mixture is too lean and ignition will not occur. If there is too much gas, the mixture will be too rich and will not ignite (79).

What is NFPA 921?

Guide for Fire and Explosion Investigations (76)

What does the word Latent mean?

Hidden (80).

Heat Release Rate (HRR)

How much heat is being generated over a period of time. Firefighters need to know the HRR so they can apply the correct volume of extinguishing agent to combat and extinguish the fire. Heat generation is discussed in BTUs or Jouls/second (usually called Watts). (77)

Flammable or Explosive Limits

If the ambient atmosphere is oxygen-depleted, no ignition can occur. The air at sea level has approximately 20.8% oxygen, which is enough to support ignition and combustion (79). If the fuel vapor is between the LEL and UEL, ignition will occur. Different gases have different ranges of LEL and UEL.

Ignition

Ignition occurs the instant when an ignition source units with a ignitable vapor in an oxygen-sufficient environment, resulting in a chemical chain reaction, and a fire begins to burn (86).

Four stages of fire development

Ignition, growth, full development, decay (86).

Who is able to fight a radioactive fire?

Individuals specially trained and properly protected against radiation exposure. PPE will offer no protection (83).

Lower Explosive Limit (LEL)

LEL - The mixture is classified as too lean and will not ignite. If a flammable mixture is present but below the LEL, it's best to ventilate and supply fresh air to further dilute the mixture and keep it from reaching its threshold point (79).

Liquids

Liquids that can't burn can absorb heat, boil and evaporate. Some of these liquids can be extinguishing agents, such as water (78).

Thermal Conductivity- low and high

Low thermal conductivity- good insulators sense they inhibit the transfer of heat. Examples: fiberglass and mineral wool. High thermal conductivity- poor insulators sense they allow the transfer of heat. Examples: metals (84).

Induction heating

Process of heating an electrically conducting object (usually a metal) by electromagnetic induction, where currents are generated within the metal and resistance leads to heating of the metal (82).

What mode of heat transfer will facilitate flashover more than the others?

Radiation will facilitate flashover more than Convection and Conduction (85).

Measurements of Heat

Rankine- An abolute temperature scale. The same size as a Fahrenheit degree. Absolute zero (-460F is 0R) Freezing point 492R and boiling point 672R. (1100) Kelvin- Absolute temperature scale where zero is assigned the value zero. One Kelvin is the same size as a Celsius degree. Freezing point of water = 273.15K and boiling point=373.15K (1092) Fahrenheit- Normal freezing=32F, Boiling is 212F (1085). Celsius-Normal freezing=0C, Boiling is 100C (1079). Heat- Measured in BTUs in the English system and Joules in the metric system (77)

Exothermic Reactions

Reactions between various combustibles and oxygen in the air that release heat (77).

Resistance / Ohms

Resistance

Vapor densities of gases lighter than air

See table of page 81.

3 states of matter

Solids, liquids, gases. Matter can change by heating or cooling, applying pressure or releasing pressure (76).

Fire

Sometimes called a process. Fire creates heat and light in varying intensities. Fire requires oxygen to burn (76).

Smoke, defined by NFPA 921

The airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion, together with the quantity of air that is entrained or otherwise mixed into the mass (85).

Latent Heat of Vaporization

The amount of heat absorbed by a liquid that passes to a gaseous form. Water has an extremely high heat of vaporization, which makes it an ideal extinguishing agent (80).

Pyrolysis

The chemical decomposition of matter by heat (84/1099).

Conductor

The denser a substance is, the better conductor it is (metals are good conductors of electricity) (81).

Surface-area-to-mass ratio

The greater the ratio, the easier it is for the solid to absorb the heat, reach its ignition temperature and ignite. (example - block of wood, versus wood shavings versus wood dust) (78).

Latent Heat

The thermal energy absorbed when a substance is converted from a solid to a liquid or from a liquid to a gas (80).

What relates to the density and the mass of a substance?

The tighter arrangement of molecules and the greater quantity of molecules (78).

Extinguishment of Fire

Walter M Haessler concepts on a series of tests to better explain how fires burned and how fire could be put out in the early 1960s (76).

Thermal Balancing

What some firefighters refer to thermal layering (87).

Rollover (Flameover)

When gases and smoke ignite at the ceiling and flames travel over the heads of anyone in the room who are staying low (87-88). Dangers are that the fire can get behind a firefighter, blocking egress path.

Conduction

When heat is transferred by direct contact between solid objects (steam pipe from a building's heating system that comes in contact with a wooden structural member) The more dense and heavier, the better conductor it is. Also depends on the mass of the object and the quantity of heat being released. All matter is thermally conductive and will absorb, hold and transmit heat. (84).

Sublimation

When matter changes phases directly from solid to a gas (76).

Pyrolyze

When solids decompose (77). This creates Pyrolystates.

Decay

When the fire diminishes in size because the fuel package has been mostly consumed and the HRR drops significantly. Glowing embers will be the final indicator that the fire is about to cease (89-90).

What are the factors that determine if heat transfer can cause the fire to grow and spread?

-Amount of heat being generated over a particular period of time. -Item or substance being heated (combustibility and physical state). -Distance between the fire and the item being heated. -Ability of the item being heated to retain the heat and reach its ignition temperature. (83)

Four commonly accepted sources of heat

-Chemical -Electrical -Mechanical -Nuclear (81)

3 modes by which heat is transferred

-Conduction -Convection -Radiation (83)

Flashover Warning Signs

-Flames licking overhead (rollover) -Rapid buildup of heat in a room or compartment -Appearance of smoke or gases coming off all contents, including carpet. -Flames emerging from doors and windows as thee are the places where gas fuel can find a lot of oxygen (88).

Backdraft Warning Signs

-Smoke puffing from the building; sometimes the building appears to be "breathing". -Smoke churning in window glass. -Window glass appears as if its being pulled in. -Lack of any visible flame -Air rushes in when any opening or vent is created. (88).

Static Electricity Discharge - reasons

1) Contact and separation between dissimilar solids 2) Flowing powders 3) Flowing liquids or gases (82).

Vapor Density

Comparing the weights of vapors and gases with the weight of air. This is not the same as Specific Gravity, as vapor density measures vapors and gases NOT liquids. Air is the standard against which all other vapors and gases are compared and has a value of 1. Vapors greater than 1 will drop to the ground and less than 1 will float. There are only 13 known gases lighter than air (80).

Compression

Compression can generate heat, especially if the compression is done under pressure at a rapid pace. (SCBA, if filled up too rapidly, will cause the air to warm. Once it cools, there will be less air than initially thought) (82).

Deflagrations and Detonation Explosions

Deflagrations - The combustion zone (blast wave) moves slower than the speed of sound. (i.e. Natural gas and dust explosions). Typically do not have the "shattering effect of the more powerful detonation. Detonation - The combustion zone moves faster than the speed of sound. (i.e. TNT) (90).

Fire Triangle

Each side of the triangle represents what's needed for fire to start. The three sides were fuel, heat, oxygen. If you remove one of the three sides, the fire would stop (76).

Flow of Electricity

Electrical power flows from a generating facility (power plant), through transmission and distribution conductors (power lines) to a service cable into a distribution panel. The panel has a main or service disconnect and either fuses or circuit breakers that function as over-current protection devices (81).

Matter

Matter is classified as organic or inorganic. Organic Matter - consists of those substances that contain carbon (76). Organic can burn (77). Inorganic Matter - Matter that does not contain carbon (76). Inorganic cannot burn (77).

Where must oil-soaked rags be stored?

Metal Containers to prevent spontaneous ignition (81).

Are heat and temperature the same thing?

No (77)

Fully Developed fire

Once the fire has involved an entire compartment or space (87).

What are the two types of matter that exist in two states only?

Oxygen and Helium (77)

Switch-controlled circuits

Power will not flow to the outlet or electric device unless a switch is turned on. For example, a switch-controlled light. Other circuits have electricity at the receptacle or outlet. As soon as a plug is inserted, electrical power flows into the appliance or device (81).

Growth

The heat from the fire will heat transfer and spread to surrounding combustibles. Factors that affect the fire's ability to grow and spread include: -Factor #1: Amount of available oxygen. If the oxygen falls below 16% in the atmosphere, the fire has a more difficult time burning (causing more carbon monoxide). If it falls below 8%, the fire will not sustain. -Factor #2: Amount of fuel that is available to burn. (fire in a fireplace. Once the logs are consumed, the fire goes out). -Factor #3: Relative size of the space where the fire is to the involved fuel and its distance from other surrounding combustibles. -Factor #4: Insulating value for the ceiling and walls. The better insulated, the less head will pass through. Heat will be radiated back to the fire and the surrounding combustibles (86-87).

Thermal Layering

The layering of heat and smoke when fire occurs in a room or enclosed space, with the highest temperatures and more dense smoke at the ceiling and lower temperatures and less dense smoke near the floor (87/1106).

Ignition Temperature

The minimum temperature at which combustion can be initiated under specific test conditions (78).

Specific Gravity of Common Liquids TABLE

The only liquids heavier than water (greater than 1.0) are: - Carbon Disulfide - Carbon Tetrachloride - Mercury - Milk (80). (**think 2 Carbons and 2 'M's)

Flashover

The point where all contents reach their ignition temperature and the ignitable vapors ignite, causing the entire compartment to become involved. Flashover occurs when thermal layer reaches temperatures of about 900-1100F (88).

Atomization

The process that breaks a liquid into a mist; yet its physical state is still a liquid even though the liquid is in finely divided particles. When an ignitable liquid is atomized, there is maximized surface-to-mass ratio that permits rapid vaporization as the liquid is heated (78). (i.e. aerosol can)

What does Amps measure?

The quantity or volume of electrical current (81). Specific wire diameters (wire gauges) are rated for maximum number of amps it can safely carry (82).

Density

The ratio of mass to volume of an object or substance. The greater the density of the object or substance, the more heat energy is needed to cause ignition (80). (i.e. harder to light a block of wood because of its density compared to a piece of paper)

Specific Gravity

The ratio of the weight density of the substance to the weight density of another substance, usually water. Water is the benchmark that other liquids are measured against. Heavier liquids will sink, lighter will rise. Water is valued at 1, with specific gravity less than 1 will float on water, gravity greater than 1 will sink (80).

Smoke

The soot, or Carbon particles, are the predominant solid particulate. Multitude of gases are produced including carbon monoxide and hydrogen cyanide (the predominant substances that cause the most deaths in a fire) (85).

Explosions, per NFPA 921

The sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure. These high pressure gases then do mechanical work such as moving, changing or shattering nearby materials" (90).

Backdraft (Smoke Explosion)

The sudden reintroduction of oxygen to the compartment or space to a oxygen-deprived fire. The fast reappearance of flames will result in an explosive manner and has the power to blow our windows and doors, even push walls. Vertical vent at the highest point over the fire can reduce the buildup of superheated gases and minimize or prevent the possibility of backdraft (89).

Fire point of an ignitable liquid

The temperature at which sufficient vapors are present to ignite and have sustained combustion (79).

Radiation

The transfer of heat through space by light waves. Light waves range from ultraviolet to infrared and contain electromagnetic energy that travels outward in all directions. Radiation can travel through space, and transparent items such as clear glass and water curtains. As the object absorbs the radiated heat, they in turn give off radiated heat (making them more of a hazard than conduction or convection with respect to fire spread). Example: The warmth felt on a person's face when looking at a fire place. When they look away, their face begins to immediately cool. (85)

Convection

The transfer of heat via a fluid medium, either liquid or air. Flames and heated gases passing over a material's surface will transfer heat through convection. Many objects are ignited in this way (84).

Thermally Thin and Thermally Thick

Thermally Thick - When a material is exposed to a heat flux on its front face, appreciable temperature rise has not yet occurred on its back face. Thermally Thin - At a given instant the material's back face is at a temperature close to that of the front face (78).

Nuclear Heat source

Two forms of nuclear heat energy- fusion and fission. Nuclear material is radioactive and unstable. Fusion- nuclear heat energy is generated when atoms are combined. As of now, nuclear fusion cannot be controlled and has no commercial use. Fission- nuclear heat energy is generated when atoms are split apart. During this process, heat energy is released. In a controlled setting, fission is used to heat water to drive turbines and produce electricity.

Upper Explosive Limit (UEL)

UEL - The Mixture is classified as too rich and will not ignite (79).

Mechanical Heat

Usually developed by friction when two items are rubbed together (rubbing hands together).