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Objective
(1) A description of a desired condition; quantified and measured, and where possible, with established time frames for achievement.
(2) Specific, achievable, measurable, time-limited results to be achieved through land management practices, either through a description of a desired condition or the degree of desired change in an attribute.

Observation Time
Time of day required to record meteorological data at a fire danger station.

Obstruction to Vision
Condition in which obscuring phenomenon restricts horizontal visibility to six statute miles (10 km.) or less.

Occluded Front or Occlusion
The front that is formed when and where a cold front overtakes a warm front or a stationary front.

Occurrence Index (OI)
A number in the National Fire Danger Rating System related to potential fire incidence within a protection unit.

Officer
The ICS title for personnel responsible for the Command Staff positions of Safety, Liaison, and Information.

Off-road Vehicle (ORV)
Any motorized vehicle designed for, or capable of, cross-country travel on or immediately over land, water, sand, snow, ice, marsh, swampland, or other terrain.
synonym: All Terrain Vehicle

Offshore Flow
Wind blowing from land to water.

On-Call
Status of a federal casual or federal regular government employee used for timekeeping purposes. An employee is considered to be in on-call status (off shift-federal casuals and federal regular government employees) when he or she is allowed to leave a telephone number or to carry an electronic device for the purpose of being contacted, even though the employee is required to remain within a reasonable call-back radius and may include restrictions on alcohol consumption or use of certain medications. 5 CFR 551.431(b)(1)

One Lick Method
A progressive system of building a fireline on a wildfire without changing relative positions in the line. Each worker does one to several “licks”, or strokes, with a given tool and then moves forward a specified distance to make room for the worker behind.

One-hour Timelag Fuel Moisture (1-h TL FM)
Moisture content of one-hour timelag fuels.

One-hour Timelag Fuels
Fuels consisting of dead herbaceous plants and roundwood less than about one-fourth inch (6.4 mm) in diameter. Also included is the uppermost layer of needles or leaves on the forest floor.
see also: One-hour Timelag Fuel Moisture

One-hundred Hour Timelag Fuel Moisture (100-h TL FM)
The moisture content of the 100-hour timelag fuels.

One-hundred Hour Timelag Fuels
Dead fuels consisting of roundwood in the size range of 1 to 3 inches (2.5 to 7.6 cm) in diameter and very roughly the layer of litter extending from approximately three-fourths of an inch (1.9 cm) to 4 inches (10 cm) below the surface.
see also: One-hour Timelag Fuel Moisture

One-thousand Hour Timelag Fuel Moisture (1,000-h TL FM)
The moisture content of the 1,000-hour timelag fuels.

One-thousand Hour Timelag Fuels
Dead fuels consisting of roundwood 3-8 inches in diameter and the layer of the forest floor more than about 4 inches below the surface.
see also: One-hour Timelag Fuel Moisture

Onshore Flow
Wind blowing from water to land.

Open Burning
Burning of any fuel outdoors without the use of mechanical combustion enhancements.

Open Line
Refers to open fire front where no line has been constructed.

Operating Weight
For helicopters, the equipped weight plus weight of the crew and fuel.
see also: Allowable Payload

Operational Control
The exercise of authority over initiating, conducting, or terminating any operation. Often associated with aviation operations.

Operational Period
The period of time scheduled for execution of a given set of tactical actions as specified in the Incident Action Plan. Operational Periods can be of various lengths, although usually not over 24 hours.

Operational Tempo
The speed and intensity of actions relative to the speed and intensity of the unfolding events in the operational environment.

Operations Branch Director (OPBD)
This ICS position is responsible for implementing that portion of an incident action plan (IAP) appropriate to a designated operational branch and reports to the Operations Section Chief.
see also: Operations Section

Operations Coordination Center (OCC)
Primary facility of the Multi-agency Coordination System (MACS); houses staff and equipment necessary to perform the MACS function.

Operations Section Chief (OSC1 or OSC2)
This ICS position is responsible for supervising the Operations Section. Reports to the Incident Commander and is a member of the General Staff. This position may have one or more deputies assigned.
see also: Operations Section

Operations Section
The section responsible for all tactical operations at the incident. Includes branches, divisions and/or groups, task forces, strike teams, single resources and staging areas.

Orbit
A circular holding pattern of an aircraft around a fixed location often related to a wildland fire. For example, the circular pattern of an air tanker in the vicinity of a wildland fire, waiting to make a retardant drop.

Ordering Manager (ORDM)
This ICS position is responsible for ordering personnel, equipment, and supplies for the incident and reports to the Supply Unit Leader.
see also: Supply Unit

Organic Matter
That fraction of the soil that includes plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by the soil population.

Organic Soil
Any soil or soil horizon containing at least 30% organic matter (e.g., muck, peat).

Orographic
Pertaining to, or caused by mountains.

Orthophoto Maps
Aerial photographs corrected to scale such that geographic measurements may be taken directly from prints. They may contain graphically emphasized geographic features and may be provided with overlays of such features as: water systems, facility location, etc.

Orthophoto
Photograph obtained from the orthogonal (i.e., horizontal) projection of a correctly oriented stereoscopic model formed by two overlapping aerial photographs; an orthophoto is free of tilt and relief displacements.

Osborne Firefinder
A sighting device used by lookouts to determine the horizontal bearing and sometimes the vertical angle of a fire from a lookout.
synonym: Alidade
see also: Firefinder Map

Out-of-Service Resources
Resources assigned to an incident but unable to respond for mechanical, rest, or personal reasons.

Outside Aid
Firefighting assistance given to adjacent areas and nearby communities by contract or other agreement that covers conditions and payment for assistance rendered and services performed. Contrasted to mutual aid, in which neighboring firefighting organizations assist each other without charge.

Outside Diameter (OD)
External diameter of a cylinder or tube, conductor, or coupling as distinguished from the internal diameter.

Overhaul
Fire department procedure of inspecting premises after extinguishment of fire, to insure that fire is completely out and unable to rekindle before returning control to owner or occupants.

Overhead
Personnel assigned to supervisory positions, including incident commander, command staff, general staff, branch directors, supervisors, unit leaders, managers and staff.

Overload
(1) Gross vehicle weight (GVW) in excess of the gross vehicle weight rating (GVWR) specified by the chassis manufacturer. Also an excess of weight over the gross vehicle axle weight rating (GAWR) specified by the chassis manufacture.
(2) A situation that taxes an operational system to the limit of its functional capabilities. Such as too many fires for an individual unit to handle (fire overload), or too many orders for an individual dispatch center to process (dispatch overload).

Overwintering Fire
A fire that persists through the winter months until the beginning of fire season.

Oxidation
Process during which oxygen combines with another substance.

Oxidizer
The portion of a chemical mixture or compound which furnishes oxygen for burning a fuel or propellant, creating an oxide.

Source: National Wildfire Coordinating Group