Physical Change
A substance remains chemically the same but changes in size, shape, or appearance (water freezing and boiling)
Chemical Reaction
A substance changes from one type of matter into another, such as two or more substances combining to form compounds. (oxidation)
Combustion
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.
Fire
A rapid oxidation process resulting in the evolution of light and heat in varying intensities
Heat
A form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state. Kinetic energy transferred from a high temperature substance to a low temperature substance.
Temperature
Measure of a material's ability to transfer heat energy to other objects. Average kinetic energy of the particles in a sample of matter.
Fuel
A material that will maintain combustion under specified environmental conditions.
Oxidizer
Any material that readily yields oxygen or other oxidizing gas, or that readily reacts to promote or initiate combustion.
Matter
Anything that occupies space and has mass.
Energy
Capacity to perform work; occurs when a force is applied to an object over a distance, or when a chemical, biological, or physical transformation is made in a substance.
Oxidation
Chemical process that occurs when a substance combines with an oxidizer such as oxygen in the air (rust on metal)
Potential Energy
Stored energy possessed by an object that can be released in the future to perform work once released.
Kinetic Energy
The energy possessed by a body because of its motion.
Joules (J)
Defined in terms of mechanical energy. 4.2 joules are required to raise the temperature of one gram of water one degree Celsius.
British Thermal Unit (BTU)
The amount of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit.
Exothermic Reaction
Chemical reaction that releases thermal energy or heat (combustion).
Endothermic Reaction
Chemical reaction that absorbs thermal energy or heat (converting water from a liquid to a gas (steam)).
Pyrolysis
The chemical decomposition of a solid material by heating, preceding combustion. Occurs quicker in plastics than wood due to the lack of moisture.
Vaporization
Physical process that changes a liquid into a gaseous state.
Ignition
The process of igniting self-sustained combustion.
Piloted Ignition
When a mixture of fuel and oxygen encounters an external heat source with sufficient heat or thermal energy to start the combustion reaction.
Autoignition
Initiation of combustion by heat but without a spark or flame.
Autoignition Temperature (AIT)
The lowest temperature at which a combustible material ignites in air without a spark or flame. Always higher than the piloted ignition temperature of a substance.
Nonflaming Combustion
Occurs more slowly at a lower temperature producing a smoldering glow in the material's surface.
Flame
Visible, luminous body of burning gas emitting radiant energy including light of various colors given off by burning gases or vapors during the combustion process.
Fire Triangle
heat, oxygen, and fuel
Fire Tetrahedron
Fuel, heat, oxygen, and self-sustaining chemical chain reaction.
Passive Agent
Materials that absorb heat but do not participate actively in the combustion process.
Products of Combustion
Materials produced and released during burning. Heat and Smoke.
Smoke
Aerosol comprised of gases, vapor, and solid particulates. Product of incomplete combustion.
Carbon Monoxide (CO)
Colorless, odorless, flammable gas formed by the incomplete combustion of carbon. Combines with hemoglobin 200 times faster than oxygen does, decreasing the blood's ability to carry oxygen.
Hydrogen Cyanide (HCN)
Colorless, toxic, flammable gas produced by the combustion of nitrogen. Odor similar to almonds. Byproduct of polyurethane foam combustion commonly used in furniture and bedding.
Carbon Dioxide (CO2)
Colorless, odorless, heavier than air gas that does not support combustion. Product of complete combustion of carbon. Displaces oxygen and also increases respiratory rate.
Irritants
Cause breathing discomfort and inflammation of eyes, respiratory tract, and skin. Include hydrogen chloride, formaldehyde, and acrolein.
Self-Heating
Result of exothermic reactions, occurring simultaneously in some materials whereby heat is generated at a rate sufficient to raise the temperature of the material.
Spontaneous Ignition
Initiation of combustion of a material by an internal chemical or biological reaction that has produced sufficient heat to ignite the material.
Resistance Heating
When electric current flows through a conductor and heat is produced.
Overcurrent or Overload
Current flowing through a conductor exceeds its easing limits; unintended resistance heating.
Arcing
A high-temperature luminous electric discharge across a gap or through a medium.
Mechanical Energy
Generated by friction or compression of a gas.
Heat Flux
Measure of the rate of heat transfer to a surface, measured in kilowatts per meter squared. Related to the temperature differential of the bodies and the thermal conductivity of the solid material.
Conduction
Heat transfer though direct contact of. Insulation slows the conduction of heat from one solid to another.
Convection
Transfer of thermal energy through a fluid (liquid or gas). Generally upward because smoke are heated and buoyant, or laterally from areas of high pressure to low pressure.
Flow Path
Flow of heat determined by difference in pressure, from high pressure to low pressure.
Radiation
Transfer of heat as an electromagnetic wave without a medium. As the temperature of the heat source increases, the radiant energy increases by a factor to the fourth power.
Reducing Agent
The fuel that is being oxidized or burned during combustion.
Organic Fuels
Contain carbon. Can be either hydrocarbons: gasoline, fuel oil, and plastics. Or cellulose-based: wood and paper.
Heat of Combustion
Total amount of heat released when a specific amount of that fuel is burned. (BTUs per pound)
Heat Release Rate (HRR)
Total amount of heat released per unit of time.
Power
Rate at which energy is being transferred over time. Measured in watts (J/s)
Vapor
The gaseous state of a fuel that would normally exist as a liquid or a solid at standard temperature and pressure
Vapor Density
Density of gases in relation to air. Air=1. Vapor Density less than 1 will rise. Vapor Density greater than 1 will sink.
Specific Gravity
Ratio of the mass of a given volume of liquid compared with water. Water=1. Less than 1 will float on the surface of water. Greater than 1 will sink to the bottom.
Flammable Liquids
Most have specific gravity less than 1. Any liquid having a flash point below 100 degrees F and a vapor pressure not exceeding 40 psi absolute.
Atmospheric Pressure
14.7 psi at sea level.
Vapor Pressure
Measure of the tendency of a substance to evaporate. High vapor pressure, greater tendency to evaporate.
Volatility
Ease with which a liquid gives off vapor. Influences ease of ignition.
Flash Point
Minimum temperature at which a liquid gives off sufficient vapors to ignite, but not sustain combustion.
Fire Point
Temperature at which sufficient vapors are being generated to sustain the combustion reaction.
Solubility
Extent to which a substance will mix with water.
Miscible
Materials that are capable of being mixed in all proportions.
Hydrocarbon Fuels
Lighter than water and do not mix with water. Gasoline, diesel, and fuel oil.
Polar Solvents
Will mix readily with water. Alcohols, Methanol and ethanol.
Combustible Liquid
Liquid having a flash point at or above 100 degrees F and below 200 degrees F.
Surface Are to Mass Ratio
The greater the ratio, the greater the ability to be ignited.
Oxygen
Primary oxidizing agent. Not combustible but supports combustion. At 31% atmospheric oxygen, Nomex will ignite and burn vigorously.
Oxygen Concentrations
Air is 21% oxygen. Materials can ignite and burn at as low as 14%. Less than 19.5% is considered deficient. Greater than 23.5% is considered enriched and an increased fire risk.
Flammable (Explosive) Range
Range of concentrations of the fuel vapor and air in which combustion can occur. Below Lower Flammable Limit=too lean to burn. Above Upper Flammable Limit=too rich to burn.
Self-Sustained Chemical Reaction
During combustion, fuel molecules break apart forming free radicals that can then combine with oxygen in the air and produce more heat, thus breaking apart more fuel molecules.
Chemical Flame Inhibition
Extinguishment of a fire by interruption of the chemical chain reaction using dry chemicals, halogenated agents, and Halon-replacement agents.
Fuel-Controlled Fire
Sufficient oxygen is available and the fire development is determined by the characteristics and configuration of the fuel.
Ventilation-Controlled Fire
The available air supply limits fire development in a compartment.
Insulation
Contains heat within the compartment causing a localized increase in temperature and fire growth
Heat Reflectivity
Increases fire spread through the transfer of radiant heat from wall surfaces to adjacent fuel sources
Retention
Maintains temperature by absorbing and releasing large amounts of heat slowly.
Ambient Conditions
Common, prevailing, and uncontrolled atmospheric weather conditions both inside or outside the structure.
Fuel Load
The total quantity of combustible contents of a building, space, or fire area. Expressed in heat units of the equivalent weight in wood.
Incipient Stage
Starts with ignition, radiant heat warms adjacent fuels, a plume of hot gases rises to the ceiling and spreads horizontally transferring heat to other materials. Occupants can safely escape and the fire can be safely extinguished with a portable extinguis
Ceiling Jet
Thin layer of flowing hot gases that develops under a horizontal surface as a result of plume impingement and the flowing gas being forced to move horizontally.
Fuel Packages
During the growth stage, when the fuel package is not in the middle of the room, the combustion zone expands vertically and a higher plume results.
Thermal Layering
Outcome of combustion in a confined space in which gases tend to form layers, according to temperature, with the hottest gases found at the ceiling and the coolest gases at floor level.
Growth Stage
Fire begins to influence the environment within the compartment and has grown large enough for the compartment configuration and amount of ventilation to influence it.
Flashover
A rapid transition from the growth stage to the fully developed stage. All combustible surfaces in the enclosed space become ignited almost simultaneously.
Fully Developed Stage
Occurs when all combustible materials in the compartment are burning. The fire becomes ventilation-controlled and releases the maximum amount of heat possible for the available fuel and oxygen.
Decay Stage
Occurs when all of the fuel is consumed or if the oxygen concentration falls below a certain point. If decay occurs due to lack of ventilation, a change in ventilation can quickly bring back flames.
Flashover Indicators
Smoke indicators are rapidly increasing volume, turbulence, darkening color, optical density, lowering of the hot gas level, and pulsing air movement. Pyrolysis of contents located away from the fire, darkened windows, hot surfaces, isolated flames in the
Rollover
A condition where the unburned fire gases that have accumulated at the top of a compartment ignite and flames propagate through the hot-gas layer or across the ceiling. Contributes to and usually precedes flashover.
Backdraft
Explosive burning of heated gases that occurs when oxygen is introduced into a compartment that has a high concentration of flammable gases and a depleted supply of oxygen. Occurs in the decay stage.
Backdraft Indicators
Neutral plane rising and lowering, high velocity, turbulent smoke discharge, sometimes appearing to pulse or breathe, smoke-stained windows, and little or no visible flame.
Smoke Explosion
Smoke within its flammable range contacts an ignition source and results in an explosively rapid combustion.
Temperature Reduction
Water can be used to extinguish fire by cooling. Water converts to steam at 212 degrees F and expands approx. 1,700 times.
Fuel Removal
May be appropriate to allow fuel to be consumed when fires involve pesticides or flammable liquids.
Oxygen Exclusion
Foam or carbon dioxide can be used to extinguish fire by displacing the oxygen from the fuel.
Tactical Ventilation
Planned, systematic, and coordinated removal of heated air, smoke, gases or other airborne contaminants from a structure, replacing them with cooler and/or fresher air to meet the incident priorities of life safety, incident stabilization, and property co