Glossary of Technical Terms

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z 
A
Accelerant - A fuel, often an ignitable liquid, used to initiate a fire or increase the rate of growth or spread of fire.
Accidental fire - Fire for which the cause does not involve a human act with the intent to ignite or spread a fire.
ACFM - Actual cubic feet per minute.
Action levels - Indicator of the level of a toxic or harmful substance and/or activity which requires medical surveillance, industrial hygiene monitoring, or biological monitoring. Action levels are used by OSHA and NIOSH to express a health or physical hazard.
Activation energy - The minimum energy that colliding fuel and oxygen molecules must possess to permit chemical interaction.
Active crown fire - A fire where a solid flame develops in the crowns of trees, and the surface and crown phases advance as a linked unit and are dependent on each other.
Acute exposure - A single exposure to a toxic substance which may result in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day. The toxic effect may be temporary and reversible, or may be permanent (disability or death).
Adiabatic cooling - Occurs when pressure is decreased on an adiabatic system, allowing it to expand, causing it to do work on its surroundings. When the pressure applied on a parcel of air is reduced, the air in the parcel is allowed to expand; as the volume increases, the temperature falls as its internal energy decreases.
Adiabatic heating - The heating of a gas caused by its compression.
Administrative controls - Work procedures, written safety policies, rules, supervision, laboratory testing, schedules, and training that are implemented to reduce or remove the duration, frequency, and severity of exposure to hazardous chemicals or situations.
Advancing fire - (also known as forward fire or a run) That portion of a wildland fire with rapid fire spread and higher intensity that is normally burning with the wind and/or up slope.
Aerosol - A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 micrometers (µm) and residing in the atmosphere for at least several hours. Aerosols may be of either natural or anthropogenic (human) origin.
Air contaminant - An airborne particulate, dust, mist, gas, fume, odor, smoke, vapor, pollen, carbon, acid, soot, or any combination thereof.
Ambient air - Background, environmental or surrounding air (American Meteorological Society).
AMS - American Meteorological Society
Angle of char - Standing fuels that are burned at an angle that indicates the direction of fire spread. This is one of the eleven categories of fire pattern indicators.
Arson - The act of maliciously and intentionally or recklessly starting a fire or causing an explosion.
Ash - The solid residue that remains after combustion is complete.
Asphyxiation - Injury or death caused by the replacement of oxygen in the environment by another gas or vapor.
B
Backburn - A method to reduce the amount of flammable material during a bushfire by setting a fire along the inner edge of a fire line to consume the fuel in the path of a wildfire or change the direction of the fires convection column.
Backdraft - A backdraft is an explosion caused by the inrush of air from any source or cause, into a burning enclosure, where combustion has been taking place in a shortage of air. A fire needs oxygen, or an oxidizer, in order to burn. Generally, this is not a problem since the atmosphere contains sufficient oxygen to allow a fire to burn. However, if the fire is burning in a closed confined area or space, the fire will consume the available oxygen and generate large amounts of carbon monoxide along with an assortment of other fire gases. These products of incomplete combustion accumulate in the compartment and create an extremely hazardous condition. A backdraft event generally occurs when a fire is smoldering. As oxygen levels drop, visible flames start to diminish because the fire is being starved of oxygen. The confined space can become charged with superheated gases and smoke. The temperature increases, the gases expand and the pressure builds within the confined space. If oxygen is reintroduced into this confined environment, the hot vaporized fuel bursts into flames and the pressurized gases will ignite with explosive force. The explosive force at which the backdraft occurs is a result of the amount of superheated gas in the space and the amount of oxygen introduced. A backdraft is an air-driven event.
Bacteria - One celled microorganisms which do not have a nuclear membrane.
Biological Oxygen Demand (BOD) - Refers to the amount of oxygen that would be consumed if all the organic materials in a 1-liter water sample were oxidized by bacteria and protozoa. It is generally a good measure of the organic contamination level of a water supply.
Barometer - An instrument for measuring atmospheric pressure.
Berm - A ridge of soil and/or debris along the outer edge of a fire line.
Binary explosive - Two substances which are not explosive until they are mixed together.
Black powder - A low explosive typically consisting of potassium nitrate, charcoal and sulfur.
Blasting Agent - Any material or mixture, consisting of a fuel and oxidizer, intended for blasting.
Boiling point - The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced.
Bomb - A device that contains an explosive, chemical material and/or incendiary that is designed to explode.
Brisance - The shattering effect of the sudden release of energy in an explosion.
C
Candling - Burning aerial canopy of one single tree from ground up.
Catabolism - The production of energy in a living organism by the degradation of complex organic compounds to form simpler ones.
Chain reaction - A series of reactions in which each reaction is initiated by the energy produced in the preceding reaction.
Chemical sensitization - Sensitization to chemicals can be defined as changes in the organism, usually the immunochemical system, by exposure to a chemical such that further chemical exposure leads to recognition by the organism. Such recognition will lead to a response that is marked by a greater reaction at lower doses than what would be observed in non-sensitized individuals.
Chronic exposure - continuous or repeated contact with a chemical and/or toxic substance over a long period of time (months or years). Over time, the exposure of some chemicals can build up in the body and/or cause long-term health effects. The toxic effect may be temporary and reversible, or may be permanent (disability or death).
Closed cup flash point testing - This type of test is conducted inside a sealed vessel and the ignition source is introduced into the vessel. The substance is not exposed to the elements outside of the vessel, which can have an interfering effect on the results of the test. This, in turn, also leads to lower flash points, because the heat is trapped inside. Because it is lower, the flash point is also safer for widespread use, and as such is more generally accepted.
CO2 - Carbon dioxide
Code of Federal Regulations (CFR) - A compilation of the general and permanent rules published in the Federal Register by the Executive departments and agencies of the Federal Government of the United States of America.
Control of fire - When firefighters and/or other resources completely surround and leave no open line on the fire perimeter.
Combustible dust - Finely divided solid particles that present a dust fire or dust explosion hazard when dispersed and ignited in air.
Combustion - A combustion reaction involves a substance combining with an oxidizer, releasing a large amount of heat (exothermic) and produces a flame. The heat produced can make combustion self-sustaining. An oxidizer is a compound that takes electrons in a reaction and can promote or initiate combustion. Oxygen and chlorine are examples of oxidizers. When oxygen is available in sufficient amounts, complete combustion occurs. If a hydrocarbon undergoes complete combustion, carbon dioxide and water vapor are produced. Combustion reactions can be oxygen starved or can involve excess oxygen. In an oxygen starved combustion reaction, a combustion reaction has a limited oxygen supply and incomplete combustion occurs. In an environment of combustion in excess air, the amount of oxygen supplied to the combustion reaction is more than is needed for complete combustion and can lead to a hotter, faster burning fire.
The products of incomplete combustion (PICs) are different than the products of pyrolysis. Some of the products of incomplete combustion (PIC) of a hydrocarbon are gasses such as carbon monoxide, methane and polyaromatics because there is not enough oxygen to completely oxidize the hydrocarbon. Carbon in the form of soot or ash can also be a a product of incomplete combustion. Typically, a mixture of unreacted carbon char and ash remains in the products of pyrolysis. Char is a porous carbon structure that remains after the bonds are broken in the pyrolytic reaction and all the hydrogen and oxygen, along with some carbon is removed as a gas. Char is often defined as the solid residue after pyrolysis. Pyrolytic carbon is a material similar to graphite which is produced by the pyrolysis of carbon containing compounds at very high temperatures.
Condensate - Any material that has been condensed from the vapor state to the liquid state.
Conduction - The transfer of heat energy in materials (usually solids) via molecular scale vibrations and collision interactions.
Confined space - An area that is large enough and also configured so a person can bodily enter and perform assigned work but which has limited or restricted means for entry or exit and is not designed for continuous human occupancy.
Convection - The transfer of heat energy through gasses and liquids by the amount and mixing of those fluids.
Covalent bond - A chemical bond in which electrons are shared approximately equally by two atoms.
Cupping - A concave or cup-shaped depression on grass stem ends, small stumps, and terminal ends of brush and tree limbs. The cupped sides typically face the area of fire origin. This is one of the categories of fire pattern indicators.
Curling - Heat exposure causes foliage leaf to dry out and shrink on the surface that is exposed to the heat. The shrinkage causes the edges to curl in towards the source of the heat, folding in the direction the fire is coming from. This is one of the categories of fire pattern indicators.
Cryogenic liquid  A refrigerated, liquefied gas that has a boiling point colder than -90°C (-130°F) at atmospheric pressure.
D
Daubert Challenge - A Daubert Challenge is a particular type of motion made to the judge either before or during litigation, in an effort to exclude the introduction of unqualified expert witness testimony to the judge or jury during trial.
Decontamination - The act of removing contaminants from protective clothing and equipment by a physical, chemical, or combined process.
Decontamination Area - An area located on the upwind edge of the Hot Zone used to decontaminate personnel and equipment. All personnel coming out of the Hot Zone must pass through the Decontamination Area for decontamination.
Dermal exposure - - Many chemicals can cause direct effects at the point of contact with the skin. Some chemicals can be absorbed into the body through the skin. Dermal exposure to hazardous agents can result in a variety of occupational diseases and disorders, including occupational skin diseases (OSD) and systemic toxicity. Chemicals can also come in contact with the eyes as dusts, mists, gases, vapors or splashed liquids. Some chemicals can be absorbed through the eyes causing harmful effects elsewhere in the body. Certain acids and other chemicals can be adsorbed through the skin and damage both the nervous and/or the lymph system.
Detonation - Combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.
Dimer - A molecule composed of two identical monomers and joined by a chemical bond.
Dimerization - A chemical reaction that joins two monomer molecular subunits, resulting in the formation of a single dimer. Some dimerization reactions have no byproduct, others may have a small molecular byproduct such as a carbon dioxide molecule.
DOT - An acronym for the United States Department of Transportation.
E
Ecosystem - A community of organisms together with their physical environment.
Electron affinity – The amount of energy absorbed or given off when an atom accepts an electron.
Electronegativity – A measure of the tendency of an atom to attract a bonding pair of electrons.
Ember - A particle of solid material that emits radiant energy due either to its temperature or the process of oxidation on its surface.
Emergency decontamination - The physical process of immediately reducing contamination of individuals in potentially life-threatening situations.
Emissivity - The ratio of radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.
Empirical data - Factual data that is based on actual measurement, observation or direct sensory experience.
Endothermic reaction - A chemical reaction that absorbs energy (usually heat) from its surrounding environment. This type of reaction requires energy (usually heat) to proceed.
Equivalence ratio - For a particular fuel-oxidant mixture, the fuel oxidant ratio of a particular mixture divided by the fuel oxidant ratio of the stoichiometric mixture.
Exotherm - A compound that gives off energy (heat) during its formation. It may also be used to refer to the heat released during an exothermic reaction.
Exothermic reaction - A chemical reaction that releases energy. The energy released is by heat or light. The energy needed to initiate the chemical reaction is less than the energy released and therefore, it gives net energy to its surroundings.
Expansion ratio - Ratio of burned gas volume to initial volume for a low-speed (constant pressure) flame. Expansion is responsible for flame-induced flow.
Explosion - The sudden conversion of potential energy (chemical, mechanical, or nuclear) into kinetic energy that produces and violently releases gas.
Explosion prevention - Methods used to prevent an explosion by controlling either the air, fuel, ignition source or a combination of these.
Explosive material - Any material that can act as fuel for an explosion.
Exposure pathway - The route a substance takes from where it began (source) to its end point.
Olfactory bulb –A structure found on the front of the brain in vertebrates essential for the sense of smell. It is responsible for transmitting smell information from the nose to the brain.
F
Ferromagnetic materials - Materials, such as iron, cobalt, and nickel, which have an abnormally high magnetic permeability.
Fingers of a fire - Long, narrow tongues projecting from the main body of a fire, usually occurring on rapidly running fires.
Fire analysis - According to NFPA 921, the process of determining the origin, cause, development, responsibility, and, when required, failure analysis of a fire or explosion.
Fire barrier - Any obstruction to the spread of fire. This is typically an area devoid of combustibles.
Fire dynamics - The study of how chemistry, physics, fire science, material science, and the engineering disciplines of fluid mechanics and heat transfer, interact to influence fire behavior.
Fire extent – Spatial area affected by a wild land fire. Typically expressed as extent per fire and/or total extent in a given period of time.
Fire intensity – Refers to the heat release rate of a fire.
Fire patterns - The visible or measurable physical effects that remain after a fire.
Fire progression – The spread of the fire from one location to another.
Fire return interval – Time between two successive fires in a specified area.
Fire seasonality - A period of time that fires can typically occur, or that they are likely to be of high intensity or burn large areas of land.
Fire severity – Degree to which a site (ecosystem) has been altered by fire or successional processes disrupted by fire.
Fire suppression - All of the work of extinguishing a fire, beginning with its discovery.
Fire tetrahedron - Four elements must be present for a fire to occur- fuel, heat, an oxidizing agent (usually oxygen) and a chemical chain reaction.
Fire vector – The direction of fire spread identified as one of the three categories: advancing, lateral and backing.
First fuel ignited - The fuel that is first set on fire by the heat of ignition. May also be referred to as “material first ignited.”
First ionization energy - The energy required to remove the outer most electron from a neutral atom in the gas phase.
Flame arrestor - A device that prevents the transmission of a flame through a flammable gas/air mixture by quenching the flame on the surfaces of an array of small passages through which the flame must pass.
Flame burning velocity - Defined by NFPA as the burning velocity of a laminar flame under specified conditions of composition, temperature and pressure for an unburned gas.
Flammable - A flammable liquid is defined as a liquid whose flash point does not exceed 100°F, when tested by closed‐cup test methods, while a combustible liquid is one whose flash point is 100°F or higher when tested by closed‐cup methods.
Flammable limit - Applies generally to vapors are defined as the concentration range in which a flammable substance can produce a fire or explosion when an ignition source (such as a spark or open flame) is present. The concentration is generally expressed as percent fuel by volume.
Flammable range - The range of concentrations of a gas or vapor between the upper and lower flammable limits that will burn or explode if an ignition source is introduced.
Flanks of a fire – Part of the fires perimeter that is roughly parallel to the main direction of spread.
Flashover - Flashover, in contrast with backdraft, is a temperature driven event. A flashover is the rapid transition to a state of total surface involvement in a fire of combustible materials within an enclosure, the point between the growth phase and the fully developed phase of a fire. It requires that the fire’s energy is radiated back to the contents to produce a rapid rise in temperature and simultaneous ignition. A flashover occurs when there is a good supply of air that allows the accumulated unburned fuel to heat up to its auto ignition temperature.
Flash point - The flash point is the lowest temperature at which a substance vaporizes into a gas, which can be ignited with the introduction of an external source of fire.
Flow path – The movement of heat and smoke from the higher pressure fire area towards the lower pressure.
Foliage freeze – Green vegetation of trees that appears windswept and “frozen”. This is due to the heat of the fire that causes green vegetation to soften while wind and/or gravity bend the foliage in the direction of the wind. Heat from the fire removes moisture from the vegetation, drying and freezing it into a fixed position consistent with the wind direction at the time of fire passage. This is one of the categories of fire pattern indicators.
Fuel limited fire - A fire in which the heat release rate and fire growth are controlled by the quantity and characteristics of the fuel.
G
Gas - One of four main states of matter that is composed of molecules in constant, random motion. Unlike a solid, a gas has no fixed shape and will take on the shape of the available space.
Gasometer - An apparatus used to measure gas, or the flow of gas, particularly in a laboratory setting.
Gas Chromatograph - A gas chromatograph (GC) is an analytical instrument that measures the content of various components in a sample. The analysis performed by a gas chromatograph is called gas chromatography.
Glowing combustion - Luminous burning of solid material without a visible flame.
Grass fire - Any fire in which the predominant fuel is grass or grass-like.
Grounding wire - Grounding wires serve as an alternate path for the current to flow back to the source, rather than go through anyone touching a dangerous electrical box or appliance
Ground visibility - Horizontal visibility observed at ground level.
H
Hazardous - As defined by OSHA Standard 1910.1200, a hazardous chemical is one which is a physical hazard or a health hazard.
Hazmat Incident - Actual or potential unplanned release of a hazardous material.
HAZWOPER - Name given to the 29CFR 1910.120 regulation entitled Hazardous Waste OPeration and Emergency Response.
Heartcut - The various components of a mixture have different molecular sizes, molecular weights and boiling temperatures.  Because they have different boiling temperatures, they can be separated by a process called fractionation and heart cutting.
Heat (v.) - The flow of energy from a warm object to a cooler object.
Heat energy - A form of energy created by the motion of atoms and molecules.
Heat sink - A material that has the ability to absorb and store heat and release it after the environment cools, or to transfer heat from one location to another.
I
ICS - An acronym for Incident Command System
Ignition device - Object used to set something on fire or to begin burning.
Incident Commander (IC) - The officer in charge of all activities at an incident.
Ingestion Exposure - Chemicals can be ingested through the mouth (swallowed). Ingestion can result from consuming contaminated food or drinks, hand-to-mouth contact, or smoking cigarettes that have come into contact with a chemical. Ingested materials can be absorbed anywhere along the gastrointestinal tract; the major absorption site is the small intestine. Once absorbed, they eventually enter the blood stream by one of several means, and circulate throughout the body.
Inhalation exposure - For most chemicals in the form of vapors, gases, mists or fine particulates, inhalation (breathing) is the major route of entry. Contaminants that enter the respiratory system through inhalation may harm the tissues of the respiratory tract or lungs. Once inhaled into the body, chemicals can enter the bloodstream and circulate throughout the body, causing harm. Inhalation exposure can be either chronic exposure or acute exposure.
Ion - An atom or molecule which has gained or lost one or more of its valence electrons, giving it a net positive or negative electrical charge.
Ionization - The process by which a molecule or atom acquires a negative or positive charge by gaining or losing electrons to form ions.
Ionization energy - The amount of energy it takes to detach one electron from a neutral atom. This energy is typically expressed in the units of energy/mole.
J
Job hazard analysis - A technique that focuses on the job tasks as a way to identify work hazards before they occur.
Joule (symbol J) - The joule is the derived unit of energy in the International System of Units. It is the energy exerted by a force of one newton acting to move an object through a distance of one meter. In terms of dimensions- 1 J = N m = kg m/s^2* m=kg m^2/s^2
K
Kerosene - Kerosene is a hydrocarbon fuel distilled from petroleum. It is a fuel used for heating, cooking and as a component of jet engine fuel. Kerosene's chemical and physical properties make it different from other fuels. Kerosene is an odorless liquid at room temperature with a clear to pale yellow color. However, when kerosene burns, it gives off a strong smoke odor. Kerosene boils at very high temperatures ranging from 175 -325 Celsius (347-617 Fahrenheit). At room temperature, kerosene has a density of 0.80 grams per milliliter. Kerosene is insoluble in water, but it does mix with other petroleum solvents. The auto-ignition temperature of kerosene is 229 C (444 F) and its flash point ranges from 37.8 -85 C (100 -185 F), depending on the pressure the kerosene is under.
Kilopascal (kPa) - A unit of pressure measurement. One kPa is approximately the pressure exerted by a 10-g mass resting on a 1-cm² area. 101.3 kPa = 1 atm. There are 1,000 pascals in a kilopascal.
Knot - Nautical miles per hour equal to 1.15 miles per hour (mph).
L
Lower Explosive Limit (LEL) - The minimum concentration of a particular combustible gas or vapor necessary to support its combustion in air. Below this level, the mixture is too “lean” to burn.
M
Markstein length - The length that measures the effect of curvature on a flame. The larger the Markstein length, the greater the effect of curvature on burning velocity.
Markstein number - The Markstein length divided by the flame thickness.
Marine incident - Any fire, explosion, hazardous material, utility, or other type of emergency incident on or in the vicinity of a marine vessel and/or facility to which an emergency response team can be expected to respond.
Methane - A chemical compound with the formula CH4. It is a colorless, odorless, flammable gaseous hydrocarbon with a wide distribution in nature. It is the principal component in natural gas and is formed by the anaerobic decomposition of organic matter. Methane has a boiling point of −161 °C (−257.8 °F) at a pressure of one atmosphere. As a gas it is flammable over a wide range of concentrations (5.4–17%) in air at standard pressure.
Minimum Ignition Energy (MIE) – Minimum energy needed to ignite combustible vapor, gas or dust particles.
Mist - A dispersion of fine liquid droplets in a gaseous medium.
Monomer - A simple compound whose molecules can join together to form polymers.
N
Native species - A species which is a part of the original flora or fauna of a subject area.
NFPA - National Fire Protection Association
NIMS - The National Incident Management System. A federally mandated program for the standardizing of command terminology and procedures.
NIOSH - The National Institute for Occupational Safety and Health, NIOSH, is part of the U.S. federal government's Centers for Disease Control and Prevention (CDC). NIOSH is the only federal Institute responsible for conducting research and making recommendations for the prevention of work-related illnesses and injuries.
Nonflammable - Material that is unlikely to burn when exposed to flame under most conditions.
Non-flaming combustion – Mode of combustion that produces a smoldering glow in a materials surface.
NRTL - Nationally Recognized Testing Laboratory
O
Odor adaptation - The process by which one becomes accustomed to an odor.
Odorant - A substance capable of eliciting an olfactory response. For example, mercaptan is an odorant added to natural gas. It’s sulfur smell helps humans detect natural gas leaks.
Odor recognition threshold - The concentration at which 50% of a human panel can identify an odor such as ammonia.
Offshore flow - Wind blowing from land onto water.
Olfactory bulb – A structure found on the front of the brain in vertebrates essential for the sense of smell. It is responsible for transmitting smell information from the nose to the brain.
Onshore flow - Wind blowing from a body of water toward/onto land.
Open cup flash point testing - This type of testing is performed by placing the substance into a vessel which is open to the outside atmosphere. The temperature is gradually raised, and an ignition source is passed over the top of it at timed intervals. Once the substance “flashes” or becomes ignited, it has reached its flash point.
Open flame - A visual flame that is typically free burning.
Organic matter - Also called total organic matter (TOM). The portion of the soil, or other sample, that includes plant and animal residues at various stages of decomposition, cells and tissues of soil organisms.
OSHA - The U.S. Occupational Safety and Health Administration, OSHA, is a federal government agency in the U.S. Department of Labor. OSHA was created by the Occupational Safety and Health (OSH) Act of 1970. The primary goals of OSHA are to save lives, prevent injuries and protect the health of America's workers.
P
Parts Per Million (PPM) - PPM is a way of expressing very dilute concentrations of substances. PPM means out of a million (1/1000000). One ppm is equivalent to one milligram of substance per liter of water (mg/l) or 1 milligram of a substance per kilogram of soil (mg/kg).
Permissible Exposure Limit (PEL) - Permissible exposure limits are set by OSHA to protect workers against the adverse effects of exposure to chemical substances. PELs are legal limits and OSHA can enforce their use and any non-compliance in the United States.
Percent by volume - Defined as the volume of the solute divided by the sum of the volumes of the other components multiplied by 100%. This is typically used for mixtures of liquids.
Personal Protective Equipment (PPE) - Equipment and/or clothing that is required to mitigate the risk of injury or exposure to hazardous conditions encountered in the performance of duties.
pH - pH stands for percentage of hydrogen and is a measure of acidity or alkalinity of water soluble substances. pH tells you whether a solution is acidic, basic or neutral. Acidic solutions are present when the values for pH are between zero and 7. A solution is basic (or alkaline) when the values for the pH are between 7 and 14. A solution is considered neutral when the pH is 7.
Phlegmatization - The process of mixing inert dusts with combustible dusts to reduce or eliminate the explosion hazard.
Plume - The column of hot gases, flames, and smoke rising above a fire; also called convection column, thermal up draft, or thermal column.
PM - Particulate matter.
PM 2.5 - Fine inhalable particles with diameters that are generally 2.5 micrometers and smaller.
PM 10 - Inhalable particles with diameters that are generally 10 micrometers and smaller.
Point of origin - A specific physical location within the area of origin where a heat source and the fuel interact, resulting in a fire or explosion.
Polymer - A large molecule composed of repeating structural units.
Polymerization - The chemical reaction in which a monomer combines with itself to form a long-chained molecule called a polymer.
Propagation of fire - The spreading of fire from one point to another point.
Pyrolysis - Pyrolysis is the process of heating organic material at high temperatures in the absence of oxygen or any other oxidizer. The term pyrolyze is used when subjecting a substance to pyrolysis. Pyrolysis involves the simultaneous change of chemical composition and physical phase, and is irreversible. Pyrolysis is not combustion and the compounds produced by pyrolysis are generally different than those produced by combustion or incomplete combustion. Pyrolysis has been used since ancient times for turning wood into charcoal. Charcoal is obtained by heating wood in the absence of air until its complete pyrolysis (carbonization) occurs, leaving only carbon and inorganic ash.
Pyrophoric - A substance which can ignite spontaneously in air at or below 55 °C (130 °F).
Q
Quadrangle - USGS mapping unit which defines and area in terms of longitude and latitude distance. Commonly, a scale of 1-24,000 quadrangles is used and is 7.5’ longitude x 7.5’ latitude.
Quenching - The cessation of combustion due to either heat transfer and mass transfer to the surface or aerodynamics effects like strain fields and rapid mixing.
Quenching distance - A characteristic length scale associated with laminar flame quenching during propagation in a narrow channel or tube.
R
Radiation feedback – The heat which radiates back to the fire.
Recommended Exposure Limits (RELs) - The REL is a level that National Institute for Occupational Safety and Health (NIOSH) believes would be protective of worker safety and health over a working lifetime if used in combination with engineering and work practice controls, exposure and medical monitoring, posting and labeling of hazards, worker training and personal protective equipment. RELs are not legally enforceable.
Relative humidity – Ratio of the amount of water vapor in the air to the amount the air could hold when saturated at the same temperature and pressure.
Risk - A measure of the chances that damage to life, property, or the environment will occur if a hazard occurs. Risk includes consideration of the severity of the damage and is often stated as a probability or range of probabilities.
Rubber - Factice vs. Synthetic - Factice is vulcanized vegetable oil and is typically a springy type solid of friable consistency. Vulcanizing from the manufacturers point of view is applying heat at a given temperature for a given time to cure the product so it takes up its shape. Curing involves the chemical reactions which occur in the rubber mixture to produce the crosslinking. Heating can be done in the mold using steam, or in autoclaves, ovens, typically using hot gases. One of the uses of factice is an additive as a processing aid in the manufacture of synthetic rubber. As a processing aid factice reduces tackiness of compounds during roll operations, improves processability and shortens mixing time, gives dimensional stability and smooth surface to compounds and can reduce die swell and shrinkage. As a softener and a dry plasticizer, factice can be useful to make low-hardness rubber products, absorbs liquid plasticizers and oils, prevents blooming, improves oil and solvent resistance. The two types of rubber in common use today are natural and synthetic. Natural rubber comes from the rubber tree (Hevea brasiliensis). Synthetic rubber is made by man from petrochemical feedstocks. Crude oil is the principal raw material. Polybutadiene synthetic rubber is widely employed in tire treads. Polybutadiene rubber generally consists of polybutadiene, and an elastomer (elastic polymer) built up by chemically linking multiple molecules of butadiene to form giant molecules, or polymers. 1,3-butadiene is a an industrial chemical with the formula C4H6. 1,3-Butadiene is typically a reactive colorless gas produced by the dehydrogenation of butane or butene or by the cracking of petroleum distillates. The gas is dissolved in hydrocarbon solvents and polymerized to polybutadiene. Polybutadiene rubber is sometimes notated as PBR.
Route of exposure - The way a chemical comes into contact with an organism (such as a person). Possible routes of exposure include inhalation, ingestion, and dermal contact.
S
SCFM - Standard cubic feet per minute.
Scientific Method - Principles and procedures for the systematic pursuit of knowledge involving the recognition and formulation of a problem, the collection of data through observation and experiment, and the formation and testing of hypotheses.
Scorching - The early partial combustion of a surface that is commonly from exposure to a heat source.
Self-Accelerating Decomposition Temperature (SADT) - The lowest temperature that a mass of material, capable of an exothermic decomposition reaction may occur with substance as packaged.
Soot - The term 'soot' refers specifically to the fine, black, carbonaceous (carbon-containing) particles produced by incomplete combustion of an organic material.
Sooting - Airborne particles in the form of a complex mixture of organic compounds resulting from the incomplete combustion of a hydrocarbon adheres to the exposed surfaces of an object such as rocks, metal, and sometimes vegetation.
Spalling – When heat allows moisture in concrete to expand, causing the concrete to crack and/or break away from a structure.
Spill fire - The ignition and subsequent combustion of a flammable or combustible liquid inadvertently released from a container.
Spontaneously combustible - Materials that can undergo combustion and burn without the addition of heat or a flame.
Standpipe system - An assembly of pipes and fittings that coveys water from the water service pipe or fire service main within the building for firefighting purposes.
Starvation of a fire - The process of depriving the fire of fuel (i.e. combustible materials).
Strong acid - An acid that early completely ionizes in solutions. Examples of strong acids are hydrochloric acid and sulfuric acid.
T
Temperature - A measure of the degree of molecular motion of a material compared to a reference point. Temperature is measured in degrees Farenheit (melting point of ice = 32 º F, boiling point of water = 212 º F) or degrees Celsius (melting point of ice = 0 º C, boiling point of water = 100 º C).
Threshold Limit Value (TLV) - Threshold Limit Values are the maximum average airborne concentration of a hazardous material to which healthy adult workers can be exposed during an 8-hour workday and 40-hour workweek—over a working lifetime—without experiencing significant adverse health effects. Threshold limit values are recommendations set by the American Conference of Governmental Industrial Hygienists.
Transpiration - The loss of water from plants through leaves and other parts.
Troposphere - The lower atmosphere, from the earth's surface to approximately 12 km. This portion of the earth's atmosphere contains about 95 percent of the atmospheric gases. The temperature gradually declines through this region as elevation increases.
U
Upper explosive limit (UEL) - The maximum concentration of a gas or vapor that will burn in air. Above this level, the mixture is too “rich” to burn.
Understory burn - Prescribed burning under a forest canopy.
Unplanned ignition - The initiation of a wildfire that was unplanned.
V
Vaporization - The process in which a substance changes from a solid or liquid into a gas.
Ventilation - an intentional introduction of ambient air into an enclosed space in order to control air quality by diluting and displacing pollutants.
Viscosity - S measure of a fluid's resistance to flow. In the SI system, the viscosity units are Ns/m2, Pa s or kg/(m s) – where 1 Pa s = 1 N s/m2 = 1 kg/(m s)
Volatility - describes how easily a substance will vaporize (turn into a gas or vapor).
Volt (V) - The unit of electrical pressure (electromotive force) represented by the symbol "E"; the difference in potential required to make a current of one ampere flow through a resistance of one ohm. (NFPA 3.3.163).
V-pattern - A characteristic fire cone shaped pattern left by a fire on the wall, near the point of origin.
W
Watershed – The geographical land area from which water drains to a given point.
Watt (W) - Unit of power, or rate of work, equal to one joule per second, or the rate of work represented by a current of one ampere under the potential of one volt. (NFPA 3.3.164).
Weak acid - An acid that does not ionize completely in solutions. An example is acetic acid.
Weight percent or Percent by mass - Defined as the mass of the solute divided by the total mass of the solution and multiplied by 100%.
Wet bulb temperature - The lowest temperature that air can be cooled by evaporation.
Wetland – An area of land that is either inundated or saturated by water for varying periods of time during each year, and that supports aquatic vegetation which is specifically adapted for saturated soil conditions.
White ash – In a wildland fire, windblown white ash that is deposited on the exposed side of objects and white ash exposure which is created by the more complete combustion of materials on the exposed side of fuels. This is one of the categories of fire pattern indicators.
Wildland fire - An unplanned and uncontrolled fire spreading through vegetative fuels, including any structures or other improvements thereon.
X
Y
Yield strength - The stress at which a material exhibits a specified permanent deformation or set.
Z