The definitions below are included to help provide context to current articles and discussions on fire dynamics and fire attack. It should be understood the fire service across the United States often has slightly different meanings for the same word.
Additionally, some areas have completely different meanings for the same word or phrase, thus several definitions may be included for a single word or phrase.
The pressure of the weight of air on the surface of the earth, approximately 14.7 pounds per square inch
(psia) (101 kPa absolute) at sea level.
A building opening that serves as both an intake and exhaust vent of a flow path at the same time.
A stream of water that has been broken into coarsely divided drops; usually created by the rapid movement of a nozzle.
See Heat Release Rate (HRR).
The amount of heat necessary to raise 1 gram of water 1 C at the pressure of 1 atmosphere and temperature of 15 C; a calorie is 4.184 joules, and there are 252.15 calories in a British thermal unit (Btu).
A 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.
The heat, gases, volatilized liquids and solids, particulate matter, and ash generated by combustion.
A room or area that is subdivided from other areas of the structure.
Heat transfer to another body or within a body by direct contact.
Heat transfer by circulation within a medium such as a gas or a liquid.
Attack method that involves the discharge of water or a foam stream directly onto the burning fuel.
Firefighting operations involving the application of extinguishing agents directly onto the burning fuel.
The difference between pressures at different points along a flow path. The pressure difference creates the flow of gases or fluids from an area of higher pressure to an area of lower pressure.
A state of non-fire growth. To completely stop the combustion process.
A rapid oxidation process, which is a gas-phase chemical reaction resulting in the evolution of light and heat in varying intensities.
See Fire Suppression
Limiting the size of the fire so as to decrease the heat release rate and prevent fire spread to adjacent combustibles, while reducing fire gas temperatures.
The detailed study of how chemistry, fire science, and the engineering disciplines of fluid mechanics and heat transfer interact to influence fire behavior.
Smoke, products of combustion and pyrolyzates, and gaseous fuels that are present and could ignite and increase the size and intensity of the fire.
The body of knowledge concerning the study of fire and related subjects (such as combustion, flame, products of combustion, heat release, heat transfer, fire and explosion chemistry, fire and explosion dynamics, thermodynamics, kinetics, fluid mechanics, fire safety) and their interaction with people, structures, and the environment.
The movement of fire from one place to another.
The activities involved in controlling and extinguishing fire.
A body or stream of gaseous material involved in the combustion process and emitting radiant energy at specific wavelength bands determined by the combustion chemistry of the fuel. In most cases, some portion of the emitted radiant energy is visible to the human eye.
The condition where unburned fuel from a fire has accumulated in the ceiling layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns; can occur without ignition of, or prior to, the ignition of other fuels separate from the origin.
Capable of burning with a flame.
A rapid transition from the growth stage to the fully developed stage.
A transition stage in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space, resulting in full room involvement or total involvement of the compartment or enclosed space.
A transition phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space, resulting in near full room involvement.
Composed of at least one inlet opening, one exhaust opening, and the connecting volume between the openings. The direction of the flow is determined by difference in pressure.
Heat and smoke in a high-pressure area will flow toward areas of lower pressure.
The volume in a structure between an inlet and an outlet that allows the movement of heat and smoke from the higher pressure within the fire area toward the lower pressure areas accessible via doorways, halls, stairs, and window openings.
The area(s) within a structure where heat, smoke and air flows from an area of higher pressure to lower pressure. It is composed of at least one intake vent, one exhaust vent and the connecting volume between the vents.
A material that will maintain combustion under specified environmental conditions.
(Fuel-Controlled) A fire with adequate oxygen in which the heat release rate and growth rate are determined by the characteristics of the fuel, such as quantity and geometry.
A fire that has sufficient oxygen for fire growth but has a limited amount of fuel available for burning.
A fire that has a heat release rate that is controlled by the material burning.
A fire in which the heat release rate and growth rate are controlled by the characteristics of the fuel, such as combustibility, quantity and geometry, and in which adequate air for combustion is available.
The total quantity of combustible contents of a building, space, or fire area, including interior finish and trim, prior to ignition.
The physical state of a substance that has no shape or volume of its own and will expand to take the shape and volume of the container or enclosure it occupies.
Using the broken stream of the nozzle to get water into the fire room above grade level.
This is a secondary water application method for the exterior portion of transitional attack.
A form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state.
The measure of the rate of heat transfer to a surface, expressed in kilowatts/m2, kilojoules/m2*sec, or Btu/ft2*sec.
Heat Release Rate (HRR)
The rate at which heat energy is generated by burning.
Form of fire attack that involves directing fire streams toward the ceiling of a compartment in order to generate a large amount of steam in order to cool the compartment. Converting the water to steam displaces oxygen, absorbs the heat of the fire, and cools the hot gas layer sufficiently for firefighters to safely enter and make a direct attack on the fire.
Firefighting operations involving the application of extinguishing agents to reduce the buildup of heat released from a fire without applying the agent directly onto the burning fuel.
A fire attack where the application of water occurs on the interior utilizing a hoseline to cool adjoining spaces and extinguish the fire.
The process of initiating self-sustained combustion.
Immediately Dangerous to Life and Health (IDLH)
Any condition that would pose an immediate or delayed threat to life or irreversible adverse health effects.
The specialized or technical language of a trade, profession, or similar group.
The preferred SI unit of heat, energy, or work. A joule is the heat produced when one ampere is passed through a resistance of one ohm for one second, or it is the work required to move a distance of one meter against a force of one newton. There are 4.184 joules in a calorie, and 1055 joules in a British thermal unit (Btu). A watt is a joule/second.
A measurement of energy release rate. A kilowatt is 1000 watts. A watt is a joule/second.
A state of partial fire extinguishment which will allow for fire regrow in a short period of time without additional intervention.
A state of partial fire extinguishment that is close to full extinguishment and where regrowth is unlikely.
The interface or level of zero differential pressure at a compartment vent, such as a door or window, between the higher pressure hot gas flowing out of a fire compartment and the lower pressure cooler air flowing into the compartment.
Insufficiency of oxygen to support combustion.
Positive Pressure Ventilation
The utilization of powered blowers or fans, post-fire control, to exhaust heat and smoke from the fire area.
Pressure is a measure of force per unit area exerted on a surface at 90 degrees to that surface.
Values for pressure may be given in pounds per square inch (psi) or Pascals (Pa) The earth is surrounded by an atmosphere made up of approximately 78% nitrogen, 21% oxygen and 1% of other gases. The weight of these gases on the earth creates a force of 14.7 pounds per square inch (psi) at sea level. This is referred to as Atmospheric pressure. Pressure in the fire service is typically referenced in the units of pounds per square inch or PSI, as this is the standard pressure unit for many of the pump panel gauges on an engine. The pressure shown on the pump panel gauge is actually measured relative to the atmospheric pressure.
In other words, 50 psi is really 50 psi over the atmospheric pressure. This type of pressure measurement is referred to as psi gauge or psig. The pressure developed by the fire or by a fan is the measured pressure over and above the atmospheric pressure. Fires create pressure that push smoke and gases throughout a room or structure. The pressures are very small, on the order of one thousandth of a psi. Therefore it is best to use a different unit for measuring pressure. This unit is called a Pascal. When it is written, it is abbreviated as Pa. 101,325 Pa equals 14.7 psi. Or 1 Pa equals 0.00015 psi.
Products of Combustion
See Combustion Products.
A process in which material is decomposed, or broken down, into simpler molecular compounds by the effects of heat alone; pyrolysis often precedes combustion.
Heat energy carried by electromagnetic waves that are longer than light waves and shorter than radio waves; radiant heat (electromagnetic radiation) increases the sensible temperature of any substance capable of absorbing the radiation, especially solid and opaque objects.
Heat transfer by way of electromagnetic energy.
Rate of Heat Release
See Heat Release Rate (HRR).
The degree of peril; the possible harm that might occur that is represented by the statistical probability or quantitative estimate of the frequency or severity of injury or loss.
Ongoing evaluation of influential factors at the scene of an incident.
The observation and evaluation of existing factors that are used to develop objectives, strategy, and tactics for fire suppression.
The observation and evaluation of existing factors in order to develop objectives, strategies, and tactics for fire suppression.
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.
Black particles of carbon produced in a flame.
The physical event where water is delivered to the heat of a fire and the water is converted from a liquid to a vapor in the form of steam.
The degree of sensible heat of a body as measured by a thermometer or similar instrument.
A fire attack where the application of water starts on the exterior to cool the fire area for a period and then repositioned to the interior for final suppression.
A term used to describe when visible and audible signs of combustion are absent from the environment.
A building opening that serves as either an intake or an exhaust vent of a flow path at a given point in time.
An opening for the passage of, or dissipation of, fluids, such as smoke, gases, and heat.
Circulation of air in any space by natural wind or convection or by fans blowing air into or exhausting air out of a building; a fire-fighting operation of removing smoke, gases and heat from the structure by natural or mechanical methods.
A fire in which the heat release rate or growth is controlled by the amount of air (oxygen) available to the fire.
(Ventilation-Controlled) A fire with limited ventilation in which the heat-release rate or growth is limited by the amount of oxygen available to the fire.
A fire in an enclosed building that is restricted because there is insufficient oxygen available for the fire to burn as rapidly as it would with an unlimited supply of oxygen.
A fire where every object in the fire compartment is fully involved in fire and the heat release rate depends on the airflow through the openings to the fire compartment.
NICK J. SALAMEH is a 36 year veteran of the fire service. He was a Fire/Emergency Medical Services Captain II and previous Training Program Manager for the Arlington County (VA) Fire Department, with which he served 31 years. He is a former Chair of the Northern Virginia Fire Departments Training Committee. Nick is a contributor to Fire Engineering Magazine www.fireengineering.com and Stop Believing Start Knowing (SBSK), https://www.facebook.com/StopBelievingStartKnowing/.