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Ablation - Removal of material by erosion, evaporation, or reaction for short-term protection against high temperatures.
Accelerant - Substance used to initiate and develop a fire. Flammable liquids are the most common accelerants.
Adiabatic Process - Physical or chemical process without the loss or gain of heat.
Anoxia - Strictly, absence of molecular oxygen in living tissue cells; often used to indicate reduction of the oxygen content of the blood below physiological levels.
Arrhythmia - Absence of rhythm, applied especially to any variation from the normal rhythm of the heart beat.
Asphyxia - Unconsciousness resulting from anoxia or hypoxia and increased carbon dioxide in blood and tissue. See suffocation.
Auto Ignition Temperature (AIT)- (Also called Autonomous Ignition Temperature) Temperature at which a material ignites in air or other oxidant at a specified pressure without the aid of a spark or flame. The minimum AIT is determined by an ASTM test method. AIT relates to external heating whereas spontaneous ignition temperature relates to self heating.
Bladder Cell - Tank formed by a flexible bag which is contained in a rigid cavity.
Blast Pressure - Overpressure (side-on) and dynamic pressure of an explosion.
BLEVE - Boiling-Liquid-Expanding-Vapor Explosion that occurs when a pressure vessel with a superheated liquid or a liquefied gas is heated and bursts. The rate of pressure build-up is greater than pressure relief due to venting. This increase pressure coupled with reduced structure strength due the external heating (particularly with surfaces adjacent to the vapor phase) may result in rupture of the container. A BLEVE is particularly hazardous if the fluid is flammable.
Bonding - Permanent joining of metallic parts to form an electrically conductive path which will assure electrical continuity and capacity to conduct safely any current likely to be imposed.
British Thermal Unit (Btu) - Amount of heat required to raise the temperature of 1 pound of water 1oF.
Burn - Undergo combustion or effect of fire.
Burn Degree - Burns of the first degree show hyperemia (redness); of the second degree, vesication (blistering); of the third degree, necrosis of skin and underlying tissues (charring).
Burning Rate - Rate at which a solid or liquid is burned, measured in the direction normal to the surface. Also, regression rate.
Burning Velocity - Rate at which a combustion wave propagates into unburned gas. For premixed flames, the velocity depends only on the initial conditions in the cold gas (temperature, pressure, and composition). Also, burning rate, flame velocity, and propagation velocity.
Calorie - Amount of heat required to raise the temperature of 1 gram of water 1oC.
Calorific Value - Heating value or heat of combustion of a combustible material in oxygen.
Carboxyhemoglobin - Product of reaction between hemoglobin and carbon monoxide.
Combustible - Capable of burning. In fire practice, the term usually refers to materials that will burn under normal conditions.
Combustible Liquid - Liquid having a flash point at or above 100oF according to NFPA classification code.
Combustion - Rapid oxidation or other chemical reaction of a material which produces heat and luminous or nonluminous burning.
Conflagration - Fire of large extent.
Cool Flame - Weak luminous hydrocarbon flame (e.g., <500oC) of fuel-rich air mixture. The chemistry involves peroxy radicals and is related to two-stage ignition.
Decomposition Flame - Flame of a combustible that can propagate without an oxidant.
Deflagration - Subsonic gaseous combustion process propagating through unreacted material by conduction, convection and radiation, with flame front and reaction products traveling in opposite directions.
Detonation - Supersonic combustion process propagating into unreacted material with flame front or shock front and reaction products traveling in the same direction.
Diffusion Flame - Nonpremixed laminar flame, the propagation of which is governed by the interdiffusion of the fuel and oxidizer. A candle flame is a typical example.
Enthalpy - Heat content of a substance or system.
Equivalence Ratio - Ratio of combustible/oxidant concentration to the stoichiometric ration for complete combustion.
Explosion - Rapid release of pressure or energy. Effect of a rapid exothermic combustion reaction occurring in an enclosed space, characterized by a catastrophic buildup of pressure and resulting shock wave.
Explosion Limit - Highest or lowest concentration of a flammable gas or vapor in air or oxygen that will propagate flame when ignited.
Explosion Pressure - Maximum pressure of explosion reaction at constant volume.
Explosion-proof Equipment - Equipment in an enclosure that is capable of with-standing an internal explosion of a specified gas or vapor and of preventing possible ignition of a surrounding flammable atmosphere.
Explosion Suppression - A method, device, or system to effectively extinguish an explosion.
Explosive - Substance capable of sudden high velocity reaction with the generation of high pressures. High energy explosives generate detonations.
Explosive Mixture - Combustible-oxidant mixture that is potentially explosive or capable of propagating flame.
Extinguishing Agent - Substance used to put out a fire by cooling the burning material, inhibiting chemical reaction and/or blocking the supply of oxygen.
Fire - Rapid oxidation or other reaction of fuel resulting in heat and light emission.
Fire Classes - For purposes of identification of hazards and to facilitate the control and extinguishment of fires, the NFPA classifies fires and hazards by type of fuel or combustible:
Class A - Ordinary combusitlbes such as wood, cloth, papar, rubber, and certain plastics.
Class B - Flammable or combustible liquids, flammable gases, greases, and similar materials.
Class C - Energized electrical equipment.
Class D - Combustible metals, such as magnesium, titanium, zirconium, sodium, or potassium.
Fire Load - Potential heat release of combustible materials in a given space, expressed in terms of Btu/sq.ft. (British thermal units per square foot) or, in the case of ordinary combustible materials such as wood and paper, in terms of lbs./sq.ft. (pounds per square foot). A fire load of less than about 80,000 Btu/sq.ft. (10 lbs./sq.ft.) is considered to provide a low fire severity in the space; 80,000-160,000 Btu/sq.ft. (10-20 lbs./sq.ft.), a moderate fire severity; and over 160,000 Btu/sq.ft. (over 20 lbs. /sq.ft.) a high fire severity.
Fire Point - Lowest temperature at which a liquid gives off sufficient flammable vapor to produce sustained combustion after removal of the ignition source.
Fireproof - A condition in which structure, equipment, wiring, controls, or piping is capable of performing its intended function under the most severe conditions of fire likely to occur at its location.
Fire Resistance Rating - Length of time, in hours, that a building material or assembly (beam, girder, or truss; column, floor, or floor-ceiling; roof or roof-ceiling, or wall or partition) will withstand the effects of a standard fire exposure and meet specific conditions of aceptance, in accordance with the "Standard Methods of Fire Tests of Building Construction and Materials," ASTME-119, U.L. 263 or NFPA 251.
Fire Retardant - Substance or treatment, such as monoammonium sulfate, that reduces the combustibility of a material.
Fire Stop - Fire resistance or noncombustible material or construction installed at appropriate intervals in concealed spaces to prevent or restrict the spread of fire or smoke through walls, ceilings, and the like.
Fire Suppression System - A method, device, or system to detect fire or ignition and to extinguish the fire in sufficient time to prevent aircraft structural damage and/or debilitation of personnel.
Fire Triangle - Three factors necessary for combustion: fuel, oxygen, and heat. NOTE: A fire tetrahedron has been proposed to account for chemical chain reaction in combustion processes.
Flame Front - Temperature and compositional microstructure associated with flames; plane along which combusion starts.
Flame Proofing - Surface treatment or impregnation of wood products, textiles, and other materials with fire-retardant chemicals.
Flame Propagation - Spread of flame from region to region in a combustible material, especially in a combustible vapor-air mixture.
Flame Resistant - Property of a material that does not conduct flame or continue to burn when an ignition source is removed.
Flame Retardant - Flame inhibiting chemical compound, such as inorganic salts, Lewis acids, or free radical inhibitors, used on surfaces as well as in bulk to reduce the flammability of a product or structure.
Flame Speed - Velocity of propagating flame measured relative to the observer.
Flame Speed Rate - Propagation velocity of flame over a surface of combustible material.
Flame Temperature - Intensity of heat of a flame. Maximum temperature of combustion products in constant pressure or constant volume reaction.
Flammability Limits - Maximum and minimum concentrations of combustible gas in air or oxygen that are capable of propagating flame at a specified temperature and pressure.
Flammable - Capable of burning with a flame. Easily ignited or highly combustible.
Flammable Liquid - According to NFPA, liquid that has a flash point below 100oF and a vapor pressure not exceeding 40 psia at 100oF.
Flashback - Propagation of a flame from an ignition source back to a supply of flammable gas or liquid.
Flash Fire - Fire that spreads with extreme rapidity.
Flash Point - Minimum temperature at which a liquid vaporizes sufficiently to form an ignitable mixture with air. NFPA has divided liquids into flash point classes; Class I is called flammable and Classes II and III combustible liquids:
Class I - Liquids having flash points below 37.8oC (100oF).
Class IA- Those having flash points below 22.8oC (73oF) and B.P. below 37.8oC.
Class IB- Those having flash point below 22.8oC and B.P. at or above 37.8oC.
Class IC- Those having flash point at or above 22.8oC and below 37.8oC.
Class II- Liquids having flash points at or above 37.8oC and below 60oC (140oF).
Class III- Liquids having flash points at or above 60oC.
Fuel Tank Inerting - A method or system utilizing noncombustible gases such as nitrogen to preclude flammable fuel and air mixtures, and thus prevent fire and explosion.
Glowing Combustion - Oxidation of solid material with light emission but without a visible flame.
Ground - Conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth; resistances <1 ohm acceptable for electrical hazards and <106 ohms for electrostatic hazards.
Heat Capacity - Heat required to raise the temperature of a unit quantity of material one degree.
Heat of Combustion - Heat evolved in the complete combustion of a mole or unit mass of material.
Hot Gas Ignition Temperature - Lowest temperature required for ignition of a substance by a jet of hot gas in some specified environment.
Hot Spot - Particularly active part of a fire.
Hot Surface Ignition Temperature - Lowest temperature required for ignition of a substance by a hot surface in some specified environment.
Hypergolic - Ability of substances to ignite spontaneously when mixed with each other.
Hypoxia - Oxygen want or deficiency in living tissues.
Ignition - Initiation of combustion as evidenced by glow, flame or explosion.
Ignition Delay - Time to ignition from the instant reactants are mixed or exposed to a heat source.
Ignition Energy - Quantity of heat or electrical energy that must be absorbed by a substance to ignite in some specified environment.
Ignition Temperature - Lowest temperature at which a substance can sustain combustion in air or oxygen at a specified pressure.
Incandescence - Emission of light by a substance due to its high temperature.
Induction Period - Time required by combustibles before oxidation and burning can proceed independently of heat or energy input.
Inerting Agent - Inert subestance like nitrogen or helium which can prevent formation if ignitable mixtures.
Inhibition - Reduction of a fire or flame by the introduction of a chemical which interferes with the flame reactions. Examples are freons and sodium bicarbonate.
Intrinsically Safe Electrical Equipment - Equipment and wiring that is not capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific mixture of gas or vapor in air in its most easily ignited concentration (NFPA 493-1975).
Intumescent Paint - A coating applied as a paint to a surface to protect it from flame or heat; produces an insulating, fire-resistant foam upon exposure to heat.
Isothermal Process - Physical or chemical process without a temperature change.
Jet Fuels - Jet aircraft fuels can be classed as low or high volatility petroleum mixtures. The low volatility grades are typically kerosenes, such as Jet A, Jet A-1, JP-8, and JP-5. The high volatility grades are blends of kerosene and aviation gasoline (Av gas) such as JP-4, Jet B, and AVTAG. Specific NATO designation, product description, commonly used nomenclature and applicable specifications are as follows:
| Nato Code Number | Product Description | Common Nomenclature/Specification |
| F-34 | Aviation Turbine Fuel: Kerosene Type + Fuel System Icing Inhibitor | JP-8 (Mil-T-83133), AVTUR (D.Eng.RD2453) |
| F-35 | Aviation Turbine Fuel: Kerosene Type | Jet A-1 (ASTM D1655), AVTUR (D.Eng.RD2494) |
| F-40 | Aviation Turbine Fuel: Wide-Cut Type | JP-4 (Mil-T-5624), Jet B (ASTM D1655), AVTAG (D.Eng.RD2454) |
| F-44 | Aviation Turbine Fuel: High Flash Type | JP-5 (MilT-5624), AVCAT (D.Eng.RD2452 |
Note: Jet A is very similar to Jet A-1. Both fuels have a 100 oF (Min.) flash point temperature for safety reasons. Jet A has a freeze point of -40 oF whereas Jet A-1 has a freeze point of -53 oF. For this reason Jet A is more available and therefore more widely used. The commercial fuels in the US are not required to have the anti-static additive and generally do not have the additive.
Kindling Temperature - The lowest temperature at which a substance ignites. Also, ignition temperature.
LC50 - Caluclated concentration, usually atmospheric, of a chemical that is expected to produce death in 50 percent of the biological specimens exposed; median lethal contration.
LD50 - Calculated dose of a chemical or other agent that is expected to produce death in 50 percent of the biological specimens exposed to it.
Limit Flame Temperature - Lowest temperature at which flame can be sustained by a combustible mixed with air; flame temperature of lower limit of flammability.
Limiting Oxygen Index (L.O.I.) - The lowest oxygen concentration in an oxygen-nitrogen mixture at which a substance will continue to burn by itself.
Lower Limit of Flammability - Lowest concentration of a flammable vapor or gas mixed with an oxidant (e.g., air) that will propagate flame at a specified temperature and pressure.
Mach Number - Ratio of the speed of a body to the speed of sound in the surrounding atmosphere.
Mass Fire - Fire involving many buildings or structures or a large forest fire.
Noncombustibility - Property of a material to withstand high temperature without ignition.
Nonflammable - Not liable to ignite or burn when exposed to flame.
Oxygen Index - Limiting Oxygen index.
Physical Explosion - Explosions without any combustion or chemical reaction.
Preburn Time - Period between ignition and start of extinguishment (of fire).
Premixed Laminar Flame - Flame in which the fuel and oxidizer are mixed prior to combustion and the flow is laminar, e.g., Bunsen burner flame.
Pyrolysis - Irreversible chemical decomposition due to an increase in temperature without oxygen reaction.
Pyrophoric - Capable of autoignition upon contact with ambient air.
Quenching distance (gap) - Minimum gap or wall separation distance below which ignitions of flammable mixtures are quenched in tubes or channels.
Radiation - Thermal or optical radiation (UV or IR) of the heat or fire source.
Ramp Fire - Any fire of an aircraft while it is on the ground, i.e., before takeoff or after successful landing and including when under construction or repair-maintenance-storage.
Rate of Heat Release - Amount of heat released by a burning body in unit time.
Reid Vapor Pressure - Vapor pressure of fluid at 100oF (38oC) in a bomb where initial liquid volume is ~1/4 the air volume.
Seat of fire - Main body of fire; fire area producing most of the heat.
Self-extinguishing - Incapable of sustained combustion in air after removal of external heat or flame.
Self-ignition - Ignition resulting from self or spontaneous heating. Also, spontaneous ignition.
Shock Wave Compression - Nonisentropic adiabatic compression in a wave traveling greater than local sound velocity.
Smoke - Fine (0.01 to 5 micron) dispersion in air of particles of carbon and other solids and liquids of incomplete combustion.
Smoldering - Combustion without flame but usually with incandescence and moderate smoke.
Smother - To extinguish a fire by blocking the oxygen supply or limiting it to a point below that required for combustion.
Specific Heat - Heat capacity of a substance per unit mass.
Spontaneous Combustion - Combustion of a substance through slow oxidation or other self-heating at ambient temperature.
Spontaneous Heating - Self-heat buildup by oxidation or fermentation. May lead to spontaneous ignition.
Spontaneous Ignition - Initiation of combustion of a material by spontaneous heating. Similar to auto ignition where the material is heated by its surroundings.
Stoichimetric Mixture - Mixture of combustible and oxidant for complete combustion.
Suffocation - Interference with the entrance of air into the lungs and resultant asphyxia.
Synergism - Combined action or effect of two or more agents that is greater than the sum of their individual actions.
TNT Equivalent - Energy release of a system expressed as an equivalent mass of TNT with an assumed heat of detonation of 1100 cal./g.
Temperature Limits of Flammability - Extreme limits of temperature within which saturated fuel vapor- air mixtures are flammable.
Threshold Limit Value (TLV) - Airborne concentration of a particular substance used to define conditions under which nearly all workers may be repeatedly exposed for a working lifetime (8 hours/day, 5 days/week) without adverse effect (value established by American Conference of Governmental Industrial Hygienists).
Toxicity - Harmful effect on a biological system caused by a chemical or physical agent.
Triboelectrification - Generation of static electricity by friction of flowing fluids and solids.
Turbulent Flame - Flame propagation under turbulent flow conditions. Example: jet engine flame.
Upper Limit of Flammability - The highest concentration of a flammable vapor or gas
mixed with an oxidant (e.g., air) that will propagate flame at a specified temperature and
pressure.