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Ultra High Frequency (UHF-FM)

1. Radio frequencies from 300 Megahertz (MHz) to 3,000 MHz with a normal range of less than 50 miles. Radio frequency common to military aircraft and used in the logistics radio system. The most common frequencies used by fire and public safety are from 406 MHz to 512 MHz.

Unacceptable Risk

1. Level of risk as determined by the risk management process which cannot be mitigated to an acceptable safe level.

Uncontrolled Airport

1. Airport not having an approved agency with radio communications to direct aircraft take-offs and landings.

Uncontrolled Fire

1. Any fire which threatens to destroy life, property, or natural resources, and (a) is not burning within the confines of firebreaks, or (b) is burning with such intensity that it could not be readily extinguished with ordinary tools commonly available.

see also: Wildfire

Underburn

1. A fire that consume surface fuels but not the overstory canopy.

see also: Understory Burning

Undercut Line

1. A fireline below a fire on a slope. Should be trenched to catch rolling material. Also called underslung line.

see also: Cup Trench

Understory Burning

1. Prescribed burning under a forest canopy.

see also: Underburn

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Unicom

1. VHF/AM aircraft radio frequencies assigned by the FAA for use in air-to-ground communications at uncontrolled airfields. The frequencies most commonly used are 122.8 MHz and 122.85 MHz.

Unified Area Command

1. A unified area command is established when incidents under an area command are multijurisdictional.

Unified Command

1. In ICS, unified command is a unified team effort which allows all agencies with jurisdictional responsibility for the incident, either geographical or functional, to manage an incident by establishing a common set of incident objectives and strategies. This is accomplished without losing or abdicating authority, responsibility, or accountability.

Unit

1. The organizational element of an incident having functional responsibility for a specific activity in the planning, logistics, or finance/administration activity.

Unity of Command

1. The concept by which each person within an organization reports to one and only one designated person.

Unlined Fire Hose

1. Hose commonly of cotton, linen, or synthetic fiber construction without rubber tube or lining, often used for wildfires because of its light weight and self protecting (weeping) characteristics; such hose is attached to first-aid standpipes in buildings. At a specified flow, friction loss in unlined hose of a stated diameter is about twice that of lined fire hose.

Upper Level (Cold) Low

1. (Upper Level Disturbance, Cold Low Aloft) A circulation feature of the upper atmosphere where pressure, at a constant altitude, is lowest. Winds blow counter-clockwise around the center in an approximately circular pattern. Upper level lows are usually quite small. The mechanics of these upper lows is such that a pool of cool moist air always accompanies their development. There is often no evidence of low pressure at the earth's surface. An upper low may exist above a surface high pressure system.

Upper Level (Cold) Trough

1. (Trough, Trough Aloft, Upper Level [Cold] Low) An elongated area of relatively low pressure, at constant altitude, in the atmosphere. The opposite of an upper level ridge. Upper level troughs are usually oriented north-south with the north end open. That is, air currents moving from west to east around the earth flow around three sides of the trough then turn eastward rather than toward the west, as in the case of a closed circulation. A large upper level trough may have one or more small upper level closed low circulation systems within it.

Upper Level High

1. (Upper High, High Aloft, Upper Level Ridge) A circulation feature of the upper atmosphere where pressure, at a constant altitude, is higher than in the surrounding region. Winds blow clockwise around an upper level high. Air in an upper level high is usually subsiding. This results in comparatively warm dry air with light winds over a large area. An upper level high may exist without there being high pressure at the earth's surface.

Upper Level Ridge

1. (Upper Level High, Ridge Aloft) An elongated area of relatively high pressure, at a constant altitude, in the atmosphere. The opposite of an upper level trough. Upper level ridges are often oriented north-south, alternating between upper level troughs, however, during summer they may assume random orientations and vast dimensions.

Urban Interface

see: Wildland Urban Interface

Use Level

1. The appropriate ratio of liquid foam concentrate to water recommended by the chemical manufacturer for each class of fire, usually expressed as a percent (such as 0.5%).

Useful Load

1. Maximum computed gross weight minus equipped weight of a helicopter.

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V Pattern

1. Characteristics fire cone-shaped pattern left by a fire on a wall, at or near its point of origin.

see also: V Pattern Indicators

V Pattern Indicators

1. The overall "V" or "U" shape of the exterior perimeter of a fire.

Values To Be Protected

1. Include property, structures, physical improvements, natural and culture resources, community infrastructure, and economic, environmental, and social values.

Values-At-Risk

see: Values To Be Protected

Vapor Suppression

1. Creating a seal with foam which prevents a release of flammable vapors from fuels.

Variable

1. Any changing characteristic; in statistics, a measurable characteristic of an experimental unit.

Variable Ceiling

1. A ceiling of less than 3,000 feet (900 m) which rapidly increases or decreases in height by one or more reportable values during the period of observation.

Variable Danger

1. Resultant of all fire danger factors that vary from day to day, month to month, or year to year (e.g., fire weather, fuel moisture content, condition of vegetation, variable risk)

Variable Sky Condition

1. A sky condition that varies between reportable values of sky cover amounts during the period of observation.

Variable Visibility

1. A condition when the prevailing visibility is less than 3 miles (5 km) and rapidly increases and decreases by one or more reportable values during the period of observation.

Variable Wind Direction

1. Wind direction which varies by 60 degrees or more during the period of time the wind direction is being determined.

Vectors

1. Directions of fire spread as related to rate of spread calculations (in degrees from upslope).

Vegetative Regeneration

1. Development of new aboveground plants from surviving plant parts, such as by sprouting from a root crown or rhizomes. Even if plants form their own root system, they are still genetically the same as the parent plant.

Vegetative Reproduction

1. Establishment of a new plant from a seed that is a genetically distinct individual.

Vehicle Fire

1. Fire originating in or on a vehicle or mobile equipment.

Vent

1. The release of enclosed smoke and heat from a structure by creating openings in it, as by hacking a hole in the roof, to allow free passage of air.

Ventilation Factor

1. A numerical value relating the potential of the atmosphere to disperse airborne pollutants from a stationary source, calculated by multiplying the mixing height by the transport wind speed.

see also: Mixing Layer ; Transport Wind Speed

Ventilation Index

1. A measure of the volume rate of horizontal transport of air within the mixing layer, per unit distance, normal to the wind. Units are measured in square meters per second or knot-feet.

Vertical Fuel Arrangement

1. Fuels above ground and their vertical continuity, which influences fire reaching various levels or vegetation strata.

Vertical Temperature Profile

1. Plot of the actual dry-bulb temperature against height above the earth's surface, most commonly determined by a RAWINSONDE observation.

Very High Frequency (VHF-AM)

1. Radio frequency range from 30 MHz to 299 MHz. The sub-bands most commonly used by fire are: VHF-FM Lo band: Frequency Modulation 30 MHz - 80 MHz, of which fire frequencies are between 30 MHz and 50 MHz. VHF-FM Hi band: Frequency Modulation 150 MHz - 174 MHz. This is the most widely used band by fire agencies. VHF-AM: Amplitude Modulation. This band is commonly referred to as the "Victor or VHF" band. The frequency range is from 118 MHz to 136 MHz. The only authorized use of this band is for aviation. The FAA controls and assigns all frequencies within this sub-band.

VHF Omnidirectional Radio Range (VOR)

1. System of radio navigation in which any magnetic bearing relative to a special radio transmitter on the ground may be chosen and flown by an aircraft pilot.

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Vigor

1. A subjective assessment of the health of individual plants in similar site and growing conditions; or a more specific measure based upon a specific facet of growth, such as seed stalk or tiller production per plant or per unit area.

Virga

1. Precipitation falling out of a cloud but evaporating before reaching the ground.

Viscosity

1. Thickness of a liquid, the degree to which it resists flow.

Viscous Water

1. Water that contains a thickening agent to reduce surface runoff; tends to cling to burning fuels and spread in layers that are several times thicker than plain water, thereby having an increased capacity to absorb heat, cool fuel, and exclude oxygen. Also called thickened water.

Visibility

1. The greatest horizontal distance at which selected objects can be seen and identified, or its equivalent derived from instrumental measurements.

Visible Area Map

1. Map showing the different classes of visible area covered by a lookout point or points; may differentiate between seen areas, indirectly visible areas, and blind areas, or only between seen areas and blind areas. Also called seen area map.

see also: Seen Area

Visual Flight Rules Conditions (VFR)

1. Basic weather conditions prescribed for flight under Visual Flight Rules: ceiling above 1,000 feet (300 m) and flight visibility in excess of 3 miles (5 km).

see also: Instrument Flight Rules Conditions

Visual Greenness (VG)

1. An NDVI-derived image of vegetation greenness compared to a very green reference such as a golf course.

see also: Greenness Factor

Visual Range

1. Maximum distance at which a given object can just be seen by an observer with normal vision.

Visual Resource Management (VRM)

1. The inventory and planning actions taken to identify visual values and to establish objectives for managing those values; and the management actions taken to achieve the visual management objectives.

Visual Resources

1. The visible physical features on a landscape (e.g., land, water, vegetation, animals, structures and other features).

Volatile

1. Readily changeable into vapor at low temperatures.

Volatiles

1. Readily vaporized organic materials which, when mixed with oxygen, are easily ignited.

Volunteer Fire Company

1. A fire department company or a response unit, the members of which are not paid.

Volunteer Fire Department (VFD)

1. A fire department of which some or all members are unpaid.

Volunteer Firefighter

1. Legally enrolled firefighter under the fire department organization laws who devotes time and energy to community fire service without compensation other than Worker's Compensation or other similar death and injury benefits.

Vortex Turbulence

1. Miniature whirlwinds trailing from the wingtips of any aircraft in flight. Vortex will be in the form of a horizontal whirlwind with velocities up to 25 mph (40 km) per hour or more. Also created by action of rotor blades on helicopters; these whirlwinds tend to move downward toward the ground. If an aircraft flies low over a fire, vortices may reach the ground and suddenly cause violent and erratic fire behavior.

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