Prepared and Approved by the U. S. Forest Service

Absolute Humidity. See Humidity, absolute.

Actionable Fire. A fire started or allowed to spread in violation of any law or regulation.

Alidade. A straightedge equipped with sights; an essential part of a device for locating fires.

Anemometer. An instrument for measuring wind velocity in miles per hour or other units.

Aneroid Barometer. An instrument which indicates atmospheric pressure and usually the elevation above sea level. The actuating element consists of partially exhausted, thin, corrugated metallic cells.

Appalachian Scale. See Scale, Appalachian.

Area Needing Protection. In general any acreage needing systematic fire control to avoid serious damage to watersheds or other damage to the land or the growth thereon or to safeguard adjacent lands or other values. For estimate and allotment purposes on national forests, the term includes all acreage inside the legal boundaries of national forests and approved purchase areas, less the following deductions:

(a)   Portions of approved purchase areas on which organized fire control has not been established.

(b)   Blocks of barren lands, noninflammable grass or water surface even if lying in two adjacent forests, if larger than 9 square miles, on which fires will not start or will not run far enough to cause concern. The high Sierra in California, Mt. Hood, and areas in Colorado above timber line are the most perfect examples.

(c)   Solid blocks of more than 9 square miles of private or State land which are protected by the owners, directly or through agencies other than the Forest Service.

Atmospheric Visibility. See Visibility, atmospheric.

Attack Time. See Elapsed time.

Azimuth. The angle measured from the north in a clockwise direction, which any line makes with the true north and south reference line.

Azimuth, Back. Azimuth plus 180° when Azimuth is 180° or less. Azimuth minus 180° when Azimuth is more than 180°.

Azimuth Circle. A circle graduated in degrees in a clockwise direction.

Back Azimuth. See Azimuth, back.

Backfire. A fire intentionally set on the fire side of a control line as a part of the process of controlling a fire. (Using such a fire when the control line is close to the fire edge is sometimes called "burning out" or "clean burn-ing"-)

Base Camp. See Camp, base.

Beaufort Scale. See Scale, Beaufort.

Blind Area. Area where the ground or the vegetation growing thereon can not be seen directly from any established lookout station or point, or by any lookout cooperator, when atmospheric visibility is normal. See Seen area.

Boss. A man responsible for certain definite activities on a fire. The following terms should not be confused with payroll titles:

Fire Boss. The man in charge of all operations on a fire.

Division Boss. The man who on a large fire has charge of two or more sectors. See Sector.

Sector Boss. The man in charge of a defined section of the perimeter of a fire and supervising two or more crews.

Crew Boss. The man in charge of a group of men composing a crew unit larger than a straw-boss unit. (Sometimes called "foreman". When necessary, has straw bosses working under his supervision.)

Straw Boss. The man directly supervising the work of a small group of men under the direction of a "crew" or other boss.

Patrol Boss. The man in charge of patrol and mop-up after control-line construction.

Camp Boss. The man in charge of camp activities in the fire camp. (Sometimes called "camp manager".)

Brush. A standing woody growth of species that do not form forests, e. g., chaparral, scrub oak, etc. (Not to be confused with Slash, Debris, or Reproduction. )

Burning, Controlled. The use of fire as a tool in forest protection and management; burning that is confined, according to a plan, to specific areas and intensities of heat.

Burning, Light. The use of fire at intervals in broadcast burning on the theory that such repeated fires will consume much of the forest fuels and so reduce the volume of these materials that accidental fires would cause less damage and would be controlled more easily.

Burning Period. That part of the day when a fire spreads more rapidly than at any other time. (Usually thought of as the "heat of the day" but may also occur during the night under adverse fire-weather conditions.)

Camera, Photo-Transit. See Photo-transit camera.

Camp, Base. The central base, usually only on larger fires, for the assembly and distribution of men, equipment, and supplies. See Camp, side.

Camp Boss. See Boss.

Camp Manager. See Boss, camp.

Camp, Side. A fire camp, usually small, for accommodating a crew working on an isolated section of a fire. (Sometimes called "spike camp".) See Camp, base.

Cat Face. See Fire scar.

Causative Agencies. The causes or agencies responsible for the origin of forest fires. See Causes of fires.

Causes of Fires. The eight standard major causes of forest fires recognized in national forest practice are:

Camp Fire. Fires resulting from fires started for the purposes of cooking, warming, or providing light by persons camping or traveling on or near wild land, except those started by railroad or lumbering employees in connection with their duties.

Debris Burning. Fires resulting from any fires originally set for clearing land for any purpose, or for rubbish, garbage, range, stubble, or meadow burning without intent on the part of the burner to have such fires spread to lands not intended to be burned. (This does not include lumbering fires or hazard reduction on right-of-ways of common-carrier railroads.)

Incendiary. Fires that in the judgment of the reporting officer are deliberately set by anyone with the intention of burning over land or damaging property not owned or controlled by him.

Lightning. Fires caused directly or indirectly by lightning.

Lumbering. Fires, except those caused by smokers, resulting from lumbering operations. (Lumbering operations include all activities connected with the harvesting or processing of wood for use or sale. Lumbering fires will include those caused by logging railroads which are not common carriers. )

Railroad. Fires resulting from maintenance of right-of-ways or construction or operation of common-carrier railroads.

Smoker. Fires caused by smokers' matches, or by burning tobacco in any - form.

Miscellaneous. Fires that cannot be properly classified under any of the seven standard causes just listed. (Fires of unknown causes should be classified under the most probable cause and not under "Miscellaneous".)

Character of Fires.

Smoldering. A fire making no appreciable spread and burning without flame.

Creeping. A fire spreading slowly, usually with low flame.

Running. A fire spreading rapidly and with a well-defined head but without spotting or crowning.

Spotting. A fire spreading as a result of sparks or embers falling ahead and starting new fires.

Crowning. A fire advancing primarily from crown to crown rather than from ground to crown. See Types of fires.

Checking Station. A contact point on main routes of travel, usually at or near the boundary of the forest, where traffic is checked and travelers contacted as a fire-prevention measure. Sometimes called "registration station".

Class A Fire. A fire of one-fourth acre or less.

Class B Fire. A fire of more than one-fourth acre but less than 10 acres.

Class C Fire. A fire of 10 acres or more but less than 100 acres.

Class D Fire. A fire of 100 acres or more but less than 300 acres.

Class E Fire. A fire of 3 00 acres or more.

Classification, Control-Line. See Control-line classification.

Climate. The long-time average, or generally prevailing weather conditions of any locality. See Weather.

Cloudiness. The fraction of the sky covered by clouds. It is estimated in tenths and expressed as follows:

Clear__________________ 0 to . 3 covered

Partly Cloudy___________ .4 to .7 "

Cloudy________________ .8 to completely overcast.

Closed Area. An area in which because of the fire danger travel is prohibited or restricted for temporary periods.

Cold Trailing. Very careful inspection of a partly dead fire edge, digging out any live spots or trenching short pieces of live edge, and feeling with hands where there is any doubt as to whether any fire remains.

Constant Danger. See Danger, constant.

Control a Fire. To surround a fire and any spot fires therefrom, with control lines and complete the backfiring of any unburned surface adjacent to the inner edge of the control lines.

Controlled Burning. See Burning, controlled.

Control Line. An inclusive term for all the constructed or natural barrier used in controlling a fire. Includes (1) clearing when that is necessary, (2) the fire line when that is needed, (3) removal of immediate threats to line constructed, (4) the edge of a grass or other fire which has been worked by direct method, (5) roads, lakes, bare rock, or other natural barriers used in controlling a fire.

Control-Line Classification. The principal classes of control-line construction methods with respect to distance from the fire edge are:

Direct Method. A method of suppression that applies work immediately at the edge of the fire. (Includes building a control line there, beating out, extinguishing with water or earth, digging out and shoveling in burning material, etc.)

Two-Foot Method. A method of suppression in which a fire line is constructed not over 2 feet from edge of fire. (It contemplates no backfiring, and aims to leave a minimum strip of unburned material. The distance from the edge permits safer use of hand tools than the direct method.)

Parallel Method. The method used in suppression when a continuous fire line is constructed parallel to but within 100 feet from the edge of the fire and the intervening strip is immediately burned out. (The object is to keep just far enough away from the fire to enable men to work most efficiently.)

Indirect Method. Under this method the control line is located along favor-able breaks in topography or natural firebreaks, and the intervening strip is backfired. (By implication any control line more than 100 feet from the edge represents application of the indirect method, even if the line is not located along a break in the topography.)

Control Time. See Elapsed time.

Controlled. See Control a fire.

Cooperator, Fire. A local person or resident with whom arrangements have been made in advance (1) to furnish incidental detection service at no charge or (2) to fight or to direct the action on fires in his vicinity with or without compensation, or (3) to be available for full-time service with pay. Limited authority to hire crews and to incur other expenses in fighting fires is often delegated to cooperators in advance. Called by various local terms, such as "fire agent", "key man", "warden", "per diem guard".

Coverage. The extent to which some standard such as travel time or detection has been met by an existing or a planned system.

Crew Boss. See Boss.

Crown Fire. See Types of fires.

Cumulative Relative Humidity. See Humidity, cumulative relative.

Damage, Fire. See Fire damage.

Danger Board. A danger meter especially designed for display purposes. See Danger meter.

Danger Class. A numerical or percentage rating of the variable fire danger existing at a given time.

Danger, Constant. A term used to include all phases of fire danger which are, for a given area, relatively unchanging, e. g., normal risk, topography, all fuels, exposure to prevailing wind, etc. See Danger, variable.

Danger, Fire. A general term expressing the sum total of both the constant and the variable factors which determine whether fires will start, spread, and do damage and that determine their difficulty of control. (Constant factors include values at stake, normal occurrence, fuel type, slope, aspect, soil type, etc. Variable factors include lightning, incendiary epidemics, illegal burning, inflammability, wind velocity, etc.)

Danger Meter. A device which by integrating the combined effect of the more significant variable fire-danger elements, rates current fire danger into specific classes. (For each class, the specific fire-control measures which should be taken are indicated in some appropriate way.) See Danger board.

Danger, Variable. A term used to include all phases of fire danger of a given area which vary from day to day and result in producing variations of danger within the season and from year to year, e. g., all weather elements, fuel moisture content, variable man-caused hazards, etc. See Danger, constant.

Debris Burning. See Causes of fires.

Detection. The act or system of discovering and locating fires.

Direct Method. See Control line classification.

Direction, Wind. See Wind direction.

Discovery. The act of determining the existence of a fire. Differs from detection in that location is not required. See Detection.

Discovery Time. See Elapsed time.

Dispatcher. A member of the fire-control organization who receives reports of discovery and status of fires, determines the locations of fires, and sends men, supplies, and equipment to suppress fires. (A central dispatcher functions over an entire forest or several ranger districts; a ranger district dispatcher, within a ranger district only.)

Division. A group of two or more sectors on a large fire. (Size of division should be no larger than the division boss can supervise and inspect adequately each shift.)

Division Boss. See Boss.

Drift. The term used by lookout men to give the direction taken by smoke from a fire, particularly in describing fires the bases of which are partially or wholly unseen, but are evidenced by smoke rising above the obstruction.

Drift Smoke. Smoke from fires or industrial activities which is moved by air currents into other areas.

Dry Storm. A lightning storm with less than 0.10 inch of precipitation measured or estimated as reaching the ground.

Duff. The dead organic material making up a part of the forest floor.

Duff Hygrometer. An instrument for measuring the moisture content of the litter or duff.

Economic Theory. A theory of forest fire control which postulates that the object of control is to keep total cost (prevention plus presuppression plus suppression plus damage) to a minimum. (Abbreviated as minimum P+P+S+S+D or, least cost, or least cost and damage. See Minimum-damage theory.)

Edge, Fire. See Fire edge.

Effects, Fire. Any consequence—neutral, detrimental or beneficial—result-ing from fire.

Effects, Net Fire. The sum of all effects, both detrimental and beneficial, resulting from burning.

Elapsed Time. The difference in time between the beginning of any fire control action and its actual accomplishment:

Discovery Time. Elapsed time from start of fire (known or estimated) until the time of the first discovery which results directly in subsequent suppression action.

Report Time. Elapsed time from discovery of a fire as defined above until the first man who goes to the fire is notified of the existence and location of the fire.

Attack Time. Elapsed time beginning when the man to perform first effective work on a fire learns that there is a fire and ending when he begins first control work.

Control Time. Elapsed time from first effective work until fire is controlled. See Control a fire, and Control line.

Mop-Up Time. Elapsed time from completion of controlling process until enough mop-up has been done to insure that the fire will not break out.

Elapsed Time Standards. Definite maximum allowable periods of time set for various steps of the suppression job.

Emergency Rations. See Rations, emergency. Equipment, Fire. See Fire control equipment.

Extra-Period Fire. A fire not controlled by 10 a. m. of the day following discovery.

Fag Station. An area fire proofed and signed to allow smoking in a restricted area in forests closed to smoking.

False Alarm. (1) A smoke or fire reported but requiring no actual suppression, e. g., donkey engine, brush burning under control, and (2) any phenomenon reported as a fire but upon investigation found not to be a fire, e. g., dust from a band of sheep. See Smoke, false.

False Smoke. See Smoke, false.

Fan Psychrometer. See Psychrometer, fan.

Feeling for Fire. Act of following an edge of a burn after fire is apparently out, and feeling with bare hands the burned edge to determine if ground fire still exists.

Fingers of a Fire. See Parts of a fire.

Fire Assistant. A man specially qualified in fire control, who, acting under the general direction of the forest supervisor, specializes in the study of fire problems and in the execution of fire-control activities.

Fire Behavior. A general term used to describe the action of fire as a result of the complex of variable factors that influence it.

Fire Boss. See Boss.

Firebreak. A partially or wholly cleaned barrier constructed before a fire occurs and designed to stop or check fires that may occur, or to be used as a line from which to work.

Fire Chief. The man in charge of fire control activities of a region, State, or association. (Not to be confused with "fire assistant" or "fire boss".)

Fire Control. Protection of wild land and the growth thereon from fire. (Includes prevention, presuppression, and suppression.)

Fire-Control Equipment. All the tools, conveyances, machinery, and special instruments or devices purchased for or allocated to fire-control purposes, but not including structures.

Fire-Control Improvements. The structures used in fire control, e. g., lookout towers, guard cabins, telephone lines, roads, trails, etc.

Fire-Control Planning. A technological and administrative management process used in preparing for action in protecting wild land from fire.

Fire Damage. (1) The value expressed in money or otherwise, of the loss, tangible or intangible, caused by fire; (2) a general term applying to the destructive effects of forest fires either (a) direct, e. g., killing or burning of trees, forage, and crops; destruction of fish and game, scenery or facilities for recreation; destruction of improvements; and loss of human life; or (b) indirect, e. g., reduction in rate of growth resulting from site deterioration; physical injury such as wounding; subsequent attack by fungi and insects; reduction in watershed values resulting from the destruction of the infiltration capacity of the soil; destruction of favorable conditions for wildlife; and depreciation in property or social values.

Fire Danger. See Danger, fire.

Fire-Danger Board. See Danger board.

Fire-Danger Class. See Danger class.

Fire-Danger Meter. See Danger meter.

Fire-Danger Station. See Station, fire-danger.

Fire Dispatcher. See Dispatcher.

Fire Edge. The line, usually irregular, to which a fire has burned at a given moment.

Fire Effects. See Effects, fire.

Fire Foam. A term applied to the product of various chemicals which when mixed with water, cause a great increase of volume by forming froth or bubbles, which may or may not be filled with noninflammable gas. (The bubbles adhere to the burning fuel and reduce combustion by excluding oxygen as well as by cooling and moistening.)

Fire Guard. See Guard, fire.

Fire Hazard. See Hazard.

Fire Line. The strip which, when necessary, is scraped or dug to mineral soil in a control line; a part of a control line. (Fire line exists only when it has been necessary to remove inflammable material from a narrow ribbon of mineral soil. The edge of a grass fire which has been beaten out is a control line but not a fire line.)

Fire-Line Patrol. See Patrol.

Fireman. A guard whose dominant function is suppression. (He generally stays at a fixed point awaiting an order to go to and suppress a fire.) See Lookout fireman, Smoke chaser.

Fire Pack. A unit of tools, supplies, and equipment prepared in advance for immediate and convenient transportation to a fire.

Fire, Parts of. See Parts of a fire.

Fire Patrol. See Patrol.

Fire Prevention. See Prevention.

Fireproof. To treat an area, hazard, road, etc., so as to reduce the danger that fires will start or spread, e. g., to fireproof a roadside or campground.

Fire Protection. Synonymous with "fire control" which is the preferred term.

Fire Scar. The physical evidence in the form of a superficially healed fire wound or cavity.

Fires, Causes of. See Causes of fires.

Fires, Character of. See Character of fires.

Fires, Class of. See Class A to E fire.

Fire Season. The period or periods of the year during which fires are likely to occur, spread, and do sufficient damage to warrant organized fire control.

Fire Suppression. See Suppression.

Fire Trap. An accumulation of highly inflammable material or any situation in which it is dangerous to fight fire on a bad day.

Fires, Types of. See Types of fires.

Fire Warden. See Cooperator, fire.

Fire-Weather Forecast. A weather prediction specially prepared by the U. S. Weather Bureau for use by forest fire control agencies. (Three types are issued: (1) a "general outlook" for 2 to 3 days; (2) a "daily forecast" for the ensuing 36 to 48 hours; and (3) "special localized forecasts" for short periods (3 to 12 hours) when requested.)

Fire-Weather Station. See Station, fire-weather.

First Work Period. Time between discovery of fire and 10 a. m. of following calendar day. (Second and succeeding work periods are 24 hours long beginning at 10 a. m.)

Flanks of a Fire. See Parts of a fire.

Flanking. A method of attacking a fire by working around either edge, usually from the point of origin, and endeavoring eventually to pinch it out by connecting the two flank lines at the head of the fire.

Flash Fuels. See Fuels, flash.

Foam. See Fire foam.

Follow Up. The act of supporting the first man or men who go to a fire by sending additional manpower to facilitate either suppression or mop-up work.

Foreman. See Boss, crew.

Forest Fire. A fire burning on wild land in peat, duff, litter, ground cover, or crowns and not being used as a tool in forest protection or management in accordance with an authorized plan.

Forest Protection. The activities connected with the control of damage to forests from fire, insects, disease, and other harm-producing agencies.

Forest Pyrology. The science of protecting forests from fire.

Freeburning. Used to describe a fire or portion of the perimeter of a fire on which no work has been done to hinder or stop its spread.

Front of a Fire. See Parts of a fire.

Fuel-Moisture-Indicator Sticks. Specially prepared wooden sticks of known dry weight, which are exposed and weighed periodically to determine their change in moisture content which indicates the change in moisture content of lightweight forest fuels.

Fuel Reduction. Any action taken to reduce the volume of fuel as by burning. See Hazard reduction.

Fuels, Flash. Light fuels such as grasses, ferns, tree moss, etc., which ignite readily and are consumed very rapidly and thus contribute to very rapid rate of spread.

Fuels, Heavy. Fuels such as snags, windfalls, branchwood, etc., which, while they usually burn more slowly than flash fuels, liberate a greater amount of heat and burn more fiercely, thus materially increasing the difficulty of suppression.

Fuel-Type Classification. The division of forest areas into units according to both the normal rate of spread of fire on an average bad day, and the resistance to control line construction offered by the fuels, topography, and soil.

Gravity Chance. Physical conditions that offer an opportunity to put water on a fire by the force of gravity alone.

Gridiron Method. A method of finding a small fire. (The fireman paces a certain distance at right angles to the line of sight from lookout station, then runs a compass line parallel to the line of sight, repeating the process if necessary, to cover a considerable area on each side of the line of sight.)

Ground Fire. See Types of fires.

Guard, Fire. A general term applied to patrolmen, firemen, lookout men, and others, who, working under direct supervision of a district ranger, are employed during the fire season for the prevention, and suppression of fires, and presuppression activities.

Guard, Per Diem. See Cooperator, fire.

Guard Unit. A natural unit, usually part of a ranger district, assigned to a fire guard.

Gutter Trench. A ditch dug on a slope below a fire; designed to catch rolling cones, small chunks, and other rolling burning material. See Control line, Fire line.

Hang-Over Fire. A fire started by lightning which remains dormant until a later period when it becomes active. (Includes a lightning fire when the lookout man sees the strike or smoke but which subsides before ground forces are able to locate it until subsequent rediscovery. Does not include fires merely difficult to find.)

Hazard. A term applied to materials which form a threat of special suppression difficulties if ignited, and which it is practicable to treat in ways which will remove or diminish the threat. (For example: Snags; jungles of windfalls; fuels immediately adjacent to roads or railroads; fuels around village dumps, ash dumps, or buildings; such dumps and buildings themselves as distinct from the fuels surrounding them; the burnable materials collected at small sawmills; old sawdust piles; meadows covered at certain times with inflammable grass; and man-made debris around homes.)

Hazard Reduction. The removal, destruction, or treatment of inflammable physical materials, at any time other than on a going forest fire, for the purpose of diminishing the chances of fires starting or spreading. "Physical materials" may or may not include those included in the terms "flash" or "heavy" fuels.

Haze. A condition of the atmosphere due to the presence of light vapor, fine dust or smoke, which impedes vision and decreases the transparency of the atmosphere; also produced at times by optical irregularities in the atmosphere.

Haze Meter. See Visibility meter.

Head of a Fire. See Parts of a fire.

Held Line. All worked line which has not been abandoned for a line on a new location when control and mop-up are completed. (Lost line, unbackfired natural barriers, and unused safety lines are excluded.)

Herbaceous Stage. A term applied to the current inflammable condition of herbaceous vegetation. (Three stages are generally recognized—green, curing, and cured.)

Hold-Over Fire. See Hang-over fire.

Hot Spotting. Checking the spread of the fire on main leads or at salient points as an emergency measure employed in advance of control line construction.

Hour Control. A term used to describe the elapsed time, from origin of a fire to arrival of the first man or men of a given suppression force, required to hold acreage burned to a predetermined area for a given unit or cover type.

Humidity, Absolute. (1) The mass of water vapor per unit volume of space, (2) the gaseous pressure exerted by water vapor present in a space.

Humidity, Cumulative Relative. The algebraic sum of the departures from or differences between daily relative humidity readings and a fixed base.

Humidity, Relative. (1) The ratio of actual mass of water vapor per unit of volume to mass of water vapor that would saturate that volume at the same temperature and pressure; (2) the ratio of actual vapor pressure to saturated vapor pressure at the same temperature. In the forest fire weather forecasts issued by the U. S. Weather Bureau relative humidity forecasts are modified by the following terms, the changes indicated referring to the previous corresponding 24-hour period:

Higher Humidity. Modified by the following terms to indicate magnitude of expected change:

Slightly—Change of 5 per cent or less.

Somewhat—Change of 6 to 15 per cent.

Materially—Change of 16 to 3 0 per cent.

Decidedly—Change of 31 per cent or more.

Lower Humidity. Modified by the terms given under "Higher" to indicate magnitude of expected change.

Little Change. Change of less than 5 per cent expected.

Maximum or Minimum. The maximum or minimum humidity expected during the period is indicated by specific figures.

Rising or Falling. Progressive change in the direction indicated. The approximate level of relative humidity expected during the next 24-hour forecast period is indicated by these terms:

Very High—More than 80 per cent.

High—61 to 8 0 per cent.

Moderate—41 to 60 per cent.

Low—21 to 40 per cent.

Very Low—11 to 20 per cent.

Acutely Low—10 per cent or less.

Becoming. Used to indicate a change from either a higher or lower humidity level and used in connection with the foregoing terms.

Humidity: Relative-Humidity Tables. Psychrometric tables giving only the relative humidities prevailing at different combinations of wet- and dry-bulb temperatures for specific barometric pressures or elevations above sea level.

Hygrograph. A self-recording instrument for measuring relative humidity.

Hygrometer, Duff. See Duff hygrometer.

Hygrothermograph. An instrument which measures and automatically records both relative humidity and temperature on a single chart.