Firefighter Dictionary: I

The following is common terminology to structural fire firefighters. There are additional definitions for emergency medical terminology, building construction, arson investigation and hazardous materials and more. Please note that some definitions have more than one meaning but are spelled the same. Click on a letter to take you to that index.

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 

I

I-beam

A steel beam with a cross section resembling the letter I. It is used for long spans as basement beams or over wide wall openings, such as a double garage door, when wall and roof loads bear down on the opening.

ICC   

Interstate Commerce Commission; now the U.S. Department of Transportation.

IDLH (Immediately Dangerous to Life or Health)

Concentrations immediately dangerous to life and health. An atmospheric concentration of any toxic, corrosive or asphyxiant that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere. (29 CFR 1910.120)

IFSTA 

 International Fire Service Training Association.

Ignitable Liquid

Any liquid or the liquid phase of any material that is capable of fueling a fire, including a flammable liquid, combustible liquid, or any other material that can be liquefied and burn.

Ignition 

The beginning of flame propagation or burning; the start of a fire.

Ignition Energy 

The quantity of heat energy that must be absorbed by a substance to ignite and burn.

Ignition sources 

Energy activators that allow chemical reactions (fire or explosion) to take place. Examples are light, heat, friction, or spark.

Ignition temperatures

The lowest temperature at which a fuel when heated will ignite in air and continue to burn; the temperature required to cause ignition of a substance. Minimum temperature a substance must attain in order to ignite under specific test conditions. Reported values are obtained under specific test conditions and may not reflect a measurement at the substance's surface. Ignition by application of a pilot flame above the heated surface is referred to as pilot ignition temperature. Ignition without a pilot energy source has been referred to as auto-ignition temperature, self-ignition temperature, or spontaneous ignition temperature. See fire point

I-joist 

Manufactured structural building component resembling the letter "I". Used as floor joists and rafters. I-joists include two key parts: flanges and webs. The flange of the I joist may be made of laminated veneer lumber or dimensional lumber, usually formed into a 1 ½" width. The web or center of the I-joist is commonly made of plywood or oriented strand board (OSB). Large holes can be cut in the web to accommodate duct work and plumbing waste lines. I-joists are available in lengths up to 60 feet long

Immiscible

That which cannot be mixed. For example, water and gasoline are immiscible.

Impeller 

A rotating disc on a shaft at the center of a centrifugal pump housing. The slanted vanes of a rotating impeller impart the centrifugal force that expels water from the pump.

Impeller eye 

The opening through which water flows into the center of an impeller.

Impermeable 

Cannot be penetrated by liquid or vapor. The state of a material that does not allow another substance to penetrate or pass through it.

Impinging stream nozzle

Nozzle that drives several jets of water together at a set angle in order to breakwater into finely divided particles.

In line eductor

Eductor that is placed along the length of a hose line.

In line relay valve

Valve placed along the length of a supply hose that permits a pumper to connect to the valve to boost pressure in the hose.

In service  

 When an apparatus is available to respond to an alarm.

Incendiaries

Substances or mixtures of substances consisting of a fuel and an oxidizer used to initiate a fire

Incendiary 

A fire believed to have been deliberately set; an incendiary agent like a bomb.

Incendiary fires 

Fires set by human hands.

Inches of mercury

A scale used in measuring negative pressure; used to measure barometric pressure.

Incident 

An occurrence or event, natural or human-caused, that requires an emergency response to protect life or property. Incidents can, for example, include major disasters, emergencies, terrorist attacks, terrorist threats, wildland and urban fires, floods, hazardous materials spills, nuclear accidents, aircraft accidents, earthquakes, hurricanes, tornadoes, tropical storms, war-related disasters, public health and medical emergencies, and other occurrences requiring an emergency response.

Incident Action Plan (IAP) 

An oral or written plan containing general objectives reflecting the overall strategy for managing an incident. It may include the identification of operational resources and assignments. It may also include attachments that provide direction and important information for management of the incident during one or more operational periods.

Incident Base 

Location at the incident where the primary Logistics functions are coordinated and administered. (Incident name or other designator will be added to the term Base.) The Incident Command Post may be collocated with the Base. There is only one Base per incident.

Incident characterization  

The process of identifying the substance(s) involved in an incident, determining exposure pathways and projecting the effect it will have on people, property, wildlife and plants, and the disruption of services.

Click here to return to top of this page

Incident Command Post (ICP)

The field location at which the primary tactical-level, on-scene incident command functions are performed. The ICP may be collocated with the incident base or other incident facilities and is normally identified by a green rotating or flashing light.

Incident Command System (ICS)  

A management system of procedures for controlling personnel, facilities, equipment and communications from different agencies to work together towards a common goal in an effective and efficient manner. Is the chain of leadership and command at the scene of an emergency. A standardized on-scene emergency management construct specifically designed to provide for the adoption of an integrated organizational structure that reflects the complexity and demands of single or multiple incidents, without being hindered by jurisdictional boundaries. ICS is the combination of facilities, equipment, personnel, procedures, and communications operating within a common organizational structure, designed to aid in the management of resources during incidents. It is used for all kinds of emergencies and is applicable to small as well as large and complex incidents. ICS is used by various jurisdictions and functional agencies, both public and private, to organize field-level incident management operations.

Incident Commander (IC)

The individual responsible for all incident activities, including the development of strategies and tactics and the ordering and the release of resources. The IC has overall authority and responsibility for conducting incident operations. In smaller events he may be responsible for the management of all incident operations at the incident site. The IC delegates responsibility to other officers by assigning them into pre-defined roles that are understood by everyone operating in the incident.

Incident Communications Center 

The location of the Communications Unit and the Message Center.

Incident Complex  

See Complex.

Incident Management System (IMS)  

The flexible on scene incident management system that identifies key roles and tasks that must be filled to safely manage an emergency incident. It stipulates that one person (Incident Command) is responsible for overall operations during the incident.

Incident Management Team (IMT)

The Incident Commander and appropriate Command and General Staff personnel assigned to an incident.

Incident Objectives 

Statements of guidance and direction necessary for the selection of appropriate strategy (ies), and the tactical direction of resources. Incident objectives are based on realistic expectations of what can be accomplished when all allocated resources have been effectively deployed. Incident objectives must be achievable and measurable, yet flexible enough to allow for strategic and tactical alternatives.

Incident of National Significance (IONS)

An actual or potential high-impact event that requires a coordinated and effective response by and appropriate combination of Federal, State, local, tribal, nongovernmental, and/or private-sector entities in order to save lives and minimize damage, and provide the basis for long-term community recovery and mitigation activities. (Source: National Response Plan)

Incident Support Organization     

Includes any off-incident support provided to an incident. Examples would be Agency Dispatch centers, Airports, Mobilization Centers, etc.

Incident Types 

Incidents are categorized by five types based on complexity. Type 5 incidents are the least complex and Type 1 the most complex.

Incidental accelerants 

Flammable or combustible liquids which are usual and incidental to an area where they are detected.

Incipient fire stage

The first phase of the burning process where the substance being oxidized is producing some heat, but the heat has not spread to other substances nearby. During this phase, the oxygen content of the air has not been significantly reduced. A fire that is in the initial or beginning stage and that can be controlled or extinguished by portable fire extinguishers, Class D-type standpipe, or small hose systems without the need for protective clothing or breathing apparatus.

Incombustible

Incapable of burning.

Incompatibility 

The inability to function or exist in the presence of something else such as when a chemical will destroy the container or a particular level or class of personal protective clothing. See incompatible material

Incompatible material

Material that, if mixed with another specified material or chemical, could result in an undesirable or dangerous reaction.

Increaser 

Adapter used to attach a larger hose line to a smaller one. The increaser has female threads on the smaller side and male threads on the larger side.

Incrustation 

A deposit on the inner wall of a water pipe creating additional friction and loss of pressure.

Indicating valve

Water main valve that visually shows the open or closed status of the valve.

Indicator tube

A tube containing a chemisorbent material that provides an indication, typically by color change, of the concentration of a specific substance in air drawn through the tube. Also referred as a detector tube.

Indirect application

A method of extinguishing fire by putting water fog into a closed superheated atmosphere to obtain the maximum heat absorption and steam generation for smothering and cooling the fire area.

Click here to return to top of this page

Inert gas 

A nonreactive gas, such as argon, helium, and neon. Also called noble gases.

Inertia

The tendency of a body to remain at rest or of a body in motion to stay in a straight line unless disturbed by an external force.

Information officer 

The individual responsible interface with the media or other appropriate agencies requiring information direct from the incident scene. Member of the Command Staff. Known as PIO or public information officer

Ingestion

The taking in of toxic materials through the mouth.

Inhalation 

The taking in of toxic materials by breathing through the nose and mouth.

Inhalator

A mechanical device for administering breathing oxygen to an individual who is breathing. See also aspirator and resuscitator.

Inhibitors   

Chemicals added to unstable substances to prevent violent reaction. (Also called stabilizers.)

Initial Action

The actions taken by resources that are the first to arrive at an incident site.

Initial attack

The first attack when hose lines are employed to prevent further extension of fire and to safeguard life and property while additional lines are being laid and other forces put in motion.

Initial attack apparatus 

Fire apparatus whose primary purpose is to initiate a fire attack on structural and wildland fires and support associated fire department actions. Also called mini-pumpers or midi-pumpers.

Initial Response

Resources initially committed to an incident.

Initiators 

Cylinder-shaped explosive or gas pressure devices used to create gas or mechanical pressure to activate another device; usually found in the seat and canopy ejection mechanism of jet military fighter aircraft.

Injury

Physical damage to body tissue caused by an accident or by exposure to environmental stressors.

Insulation

Materials for obstructing the passage of sound, heat, or cold from one surface to another. Aluminum or copper wire is covered by an insulating material. The insulating material may be rubber (R), thermoplastic (T), or asbestos (A). Thickness of insulation varies with wire size and type of material, application or other code limitations.

Insurance Services Office (ISO)  

Formed January 1971, a national insurance organization licensed as a fire rating organization; an advisory organization to other property-liability insurance companies. Private agency that rates fire department for setting insurance rates.

Intake

Inlet for water into the fire pump.

Intake hose 

Non-collapsible hose used to draft water into pumpers from static sources lower than the pump; formerly called hard suction hose. Flexible intake hose is a short length of large-diameter hose used to connect pumpers to hydrants.

Intake pressure 

Pressure coming into the fire pump.

Intake relief valve 

Valve designed to prevent damage to a pump from water hammer or any sudden pressure surge.

Intake screen  

Screen used to prevent foreign objects from entering a pump.

Intelligence

Information obtained from existing records or documentation, placards, labels, signs, special configuration of containers, visual observations, technical records, eyewitnesses, and others.

Intelligence Officer

The intelligence officer is responsible for managing internal information, intelligence, and operational security requirements supporting incident management activities. These may include information security and operational security activities, as well as the complex task of ensuring that sensitive information of all types (e.g., classified information, law enforcement sensitive information, proprietary information, or export-controlled information) is handled in a way that not only safeguards the information, but also ensures that it gets to those who need access to it to perform their missions effectively and safely.

Interior Attack

An interior attack is a firefighting technique in which the fire is fought from within a structure. The personnel arriving first on the scene will determine how the fire is to be attacked by taking into account the location and volume of fire. If the structure is heavily involved or if there is no threat to life the decision may be made to attack the fire from outside.

Intermodal container

Freight container designed and constructed to permit it to be used interchangeably in two or more modes of transport. (i.e., highway and rail or water and rail).

Intrinsically safe construction

Equipment or wiring is incapable of releasing sufficient electrical energy under both normal and abnormal conditions to cause the ignition of a flammable mixture. Commonly used in portable direct-reading instruments for operations in Class I, Division 2 hazardous locations and portable radios used in atmospheres that may contain flammable gases.

Inversion     

 Horizontal layers of air through which the temperature increases with increasing altitude.

Click here to return to top of this page

Inverter 

 Auxiliary electrical power generating device. The inverter is a step-up transformer that converts the vehicle's 12 or 24-volt DC current into 110 or 220-volt AC current.

Investigative mode

When the first-arriving companies go on standby because the cause of the alarm is not readily ascertainable.

Involved 

The actual room, portion, area, or building involved in or affected by fire.

Ion                               

An unbalanced atom; any atom that has an electrical charge, either positive or negative.

Irritant 

A material with an anesthetic, irritating, noxious, toxic or other similar property that can cause extreme annoyance or discomfort. A noncorrosive material that causes a reversible inflammatory effect on living tissue by chemical action at the site of contact as a function of concentration or duration of exposure.

Isolation  

The first operational priority of a hazardous material emergency responder. This will set apart a spilled or released material limiting the harm to lives, environment, and property.