A glossary of terms associated with bushfire science and management
Prepared by the Bushfire Front Inc. [Updated July 2013]
The Bushfire Front Inc is an organisation of professional bushfire scientists and managers, operating from Perth, Western Australia, and with links to all Australian states and overseas. Our objective is to promote best practice in bushfire management, so as to minimise the damage caused by bushfires to human life, community assets and the environment.
We have prepared this simple glossary to assist with public understanding about bushfires, and the underlying fire science. To this end, the glossary is written in everyday language and goes beyond definition to explanation and example. The list of terms explained is not exhaustive, and it is intended that it will be updated. Input is welcomed. We have deliberately not included terms in everyday use, which do not need explanation, such as “arson”.
In preparing the glossary we used a number of published sources, existing glossaries and input from bushfire specialists, and fire scientists around Australia.
Terms explained in this Glossary
Adaptive management
Back burn
Best practice bushfire management
Biodiversity
Bioregion
Blow up
Burning program
Bush
Bushfire
Bushfire management
Bushfire Proneness
Bushfire risk
Bushfire threat
Bushfire threat analysis
Climate Change
Controlled burn
Convection winds and column
Crown fires
Department of Conservation and Land Management (CALM)
Drought index
Ecology
Ecosystem
Enforcement and compliance management
Environmental care
Escape
Extreme (bushfire) conditions
Fire and Emergency Services Authority (FESA)
Fire attack
Fire Benchmark Area
Fire break
Fire danger
Fire detection system
Fire Exclusion Area
Fire hazard
Fire impact
Fire Information System
Fire intensity
Fire line
Fire Operations Manual
Fire Preparedness and Response Plan
Fire regime
Fire season
Fire sensitive community
Fire storm
Fire suppression
Fire triangle
Fire vulnerable community
Flame height
Forest
Fuel
Fuel load
Fuel moisture content
Fuel quantity
Fuel reduction burn
Head fire, flank fire, tail fire
High risk areas
High value areas
Hop over
Interagency Agreement
Junction zone
Land management scale fire protection plans
Land tenure
Landscape scale fire protection plans
Lightning fire
Master Burn Plan
Mild conditions
Adaptive management
Mopping up
No Planned Burn Area
Old growth forest
Plantation
Post-logging burn
Prescribed burn Prescribed Burning Plan
Pre-suppression activities
Rate of spread
Regeneration burn
Regrowth forest
Retardant
Scientific Reference Area
Scorch height
Scrub
Severe conditions
Smoke management
Spot fire
Surface moisture content
Traditional owners
Water bombing
Wilderness
Wildfire
Woodland
Working arrangements
Adaptive Management
Management, in this case bushfire prevention and control, that is continuously modified according to field observations, experience and new facts.
“Active” adaptive management employs management programs that are designed to experimentally compare selected policies or practices, by evaluating alternative hypotheses about the system being managed.
Back burn (sometimes written ‘backburn’)
A fire deliberately lit to remove the fuel in front of an advancing bushfire so that the advancing fire will have reduced levels of fuel and will therefore be more easily controlled. A back burn is generally lit into the wind and thus can be a dangerous manoeuvre. It should only be carried out by experienced fire fighters who understand the risks and the weather. Not to be confused with ‘prescribed burn’.
Best practice bushfire management
Best Practice in bushfire management is defined as a system which:
* Delivers protection of community assets and human values from destructive bushfires;
* Minimises undesirable impacts on the environment (including biodiversity) from both destructive wildfires and fire management activities.
* Ensures, as far as is possible, the safety of fire fighters;
* Is based on credible science, and employs protocols and prescriptions continually updated in the light of research and field experience;
* Provides for independent monitoring of outcomes, and public reporting;
* Has community and media support, stemming from strong political leadership
and a high level of public understanding of the issues.
Biodiversity
Short for “biological diversity”. Biological diversity is the variety of all life forms – the plants, animals and micro-organisms – their genes, and the ecosystems they inhabit.
The interaction between biodiversity and the various fire regimes (see below) is a subject of particular interest to ecologists and land managers. Fire is a necessary factor in sustaining the biodiversity of most Australian ecosystems.
Bioregion
A large area with broadly similar groups of plants, animals and landscapes. There are about 80 bioregions throughout Australia including two largely forested bioregions – Jarrah Forest and Warren – in the south west of Western Australia. The Jarrah Forest bioregion is dominated by jarrah forest. The Warren bioregion is dominated by karri forest.
Blow up
A bushfire is said to “blow up” when there is a sudden and massive increase in the intensity of the fire. This can occur when a fire ignites an area of much heavier fuel, encounters a steep upslope, or if there is a sudden indraft of fresh air into the fire as a result of a wind change or convection. A blow up can also occur when two or more fires coalesce. “Blow up conditions” result from a combination of all the factors which optimise fire intensity. They usually result in a “fire storm”. Under these conditions, serious damage is inevitable.
Burning program
A program that sets out and schedules a number of prescribed burns for a designated area over a nominated time, normally looking ahead over one fire season (for the coming spring to the following autumn), but can also look ahead 5 years or more.
Bush
General term for all types of forest, woodland and scrub areas. Under the WA Bush Fires Act 1954 the term ‘bush’ is defined to include “trees, bushes, plants, stubble, scrub, and undergrowth of all kind whatsoever whether alive or dead and whether standing or not standing”. Land carrying bush is often referred to as “bushland”, or just bush. In addition, common Australian usage refers to all land outside the city as “the bush” irrespective of whether it is native forest, woodland or cleared paddocks.
Bushfire (sometimes written ‘bush fire’)
An unplanned fire in bush. This is a general term, uniquely used by Australians, and includes grass fires, forest fires and scrub fires, i.e. any fire outside the built-up urban environment. Also sometimes known as a wildfire. In the United States always called a wildfire and sometimes a “wildland fire”; in Europe, and Asia usually called a “forest fire”.
Bushfire management
All those activities directed to prevention, detection, damage mitigation and suppression of bushfires. Includes bushfire legislation, policy, administration, law enforcement, community education, training of fire fighters, planning, communications systems, equipment, research, and the multitude of field operations (including fuel reduction) undertaken by land managers and emergency services personnel relating to fire prevention and control.
A “bushfire management system” is a calculated, determined and holistic approach to preventing and controlling bushfires. As a minimum a bushfire management system should comprise:
* a stated set of objectives;
* a clear statement of who is responsible for system implementation and who is
accountable for outcomes;
* the strategies to be adopted to achieve the objectives (often set out in a stand-alone
document called a “Fire Management Plan”);
* funding arrangements;
* monitoring protocols, to allow actual and planned outcomes to be compared;
* arrangements for reporting the results of monitoring system implementation and
outcomes;
* a research program directed at unknowns and problems; and
* a communications strategy directed at informing stakeholders about the system and
its implementation.
Bushfire Proneness
The extent to which an area may be prone to bushfires. The degree of proneness will depend on the condition and quantity of the fuel present and the likelihood of a fire starting. Local Governments may declare an area “Bushfire Prone” and any new residential development within such areas must comply with the requirements of Australian Standard AS 3959.
Bushfire risk (also known as wildfire risk)
The chance of a bushfire occurring that will have harmful consequences to human communities and the environment. Bushfire risk is usually assessed through consideration of (i) likelihood of ignition; and (ii) threats and consequences. See also Bushfire Threat Analysis.
Bushfire threat
A term used to describe and analyse the danger that a bushfire poses in a particular place, or to specified values. There are four main aspects:
1. the likelihood of a fire starting and of it becoming uncontrollable;
2. the values that will be lost or damaged if a bushfire starts and gets out of control;
3. the extent of the damage that could be caused;
4. the resources that can be brought to bear on a fire and their effectiveness.
Bushfire Threat Analysis (BTA) (also known as Wildfire Threat Analysis)
This is a structured approach used to analyse the bushfire threat for a particular area or a nominated set of values, to calculate a response and to determine priorities for funding or action. It is usually the first step in producing a Fire Management Plan, which sets out the actions to be taken to minimise a threat and to mitigate possible damage. It also ranks actions, allocates responsibility for actions, and establishes protocols for action in the event of a fire and for post-fire monitoring. The Fire Management plan should also set up cooperative and command arrangements, and put in place mechanisms for review and updating of the action plan.
Climate Change
Refers to changes in global climate. Current emphasis is usually on changes caused by an increase in greenhouse gases in the earth’s atmosphere believed by some people to be a cause of global warming, but climate changes can be due to other factors. Any change in the climate of an area may result in the need for a change in the approach to fire management in that area. The consequences of global warming are not necessarily more difficult bushfires, as temperature per se is a far less significant factor in bushfire behaviour than, for example fuel levels and wind strengths.
Controlled burn
Obsolete term, these days replaced by ‘prescribed burn’ or in some cases ‘fuel reduction burn’.
Convection winds, convection column
A bushfire releases energy which heats the surrounding air, causing it to rise. This process is referred to as convection, and the column of hot air rising above an intense fire is referred to as the convection column. Winds are drawn in at ground level to replace the rising air. These ‘convection winds’ can flow against the prevailing wind, causing extreme difficulty and danger for firefighters. The interaction of the prevailing winds with convection winds and the convection column can result in a tornado-like phenomenon with swirling and twisting flames reaching hundreds of metres into the sky. The tornado-like phenomenon is also sometimes referred to as a ‘fire storm’.
Crown fires
Occur when a ground fire is so intense that whole trees catch fire and all or parts of the upper branches and crown are consumed. In a crown fire, the probability of spot fires is greatly increased. Spot fires originate from burning embers sucked up into the convection column and carried down-wind to start new fires.
The term Crown Fire is usually only applied to vegetation with both an upper and a lower canopy – as in a forest with trees and a shrub understorey.
Department of Conservation and Land Management/Department of Environment and Conservation)
In Western Australia the government department responsible for managing land classified as nature reserve, national park, conservation reserve, regional park and State forest as well as marine parks and several less common land classifications. CALM was formed in 1985 and in 2006 was incorporated into a new Department of Environment and Conservation (DEC). In July 2013 the section of the department concerned with land management and conservation was established as a new stand-alone agency called the Department of Parks and Wildlife.
Drought index
A numerical value reflecting the dryness of soils, deep forest litter, logs and living vegetation. Typically in South-western WA the drought index is nil or very low at the end of winter, but progressively increases across the spring/summer months, until a maximum is reached before the onset of the next autumn/winter.
In times of extended drought (consecutive years of well-below-average rainfall), the drought index may not “bottom out” during winter. Drought years greatly increase bushfire problems, as the whole ecosystem becomes drier and more flammable.
Ecology
Ecology is the branch of the natural sciences devoted to the study of the interactions between plants, animals, micro-organisms and their environment. Scientists who study ecology are referred to as ecologists. “Fire ecology” refers to the study of the response of and interactions between plants, animals, micro-organisms and the environment and various fire regimes.
Ecosystem
An assemblage of plants, animals and micro-organisms interacting with one another and the environment in which they live.
Enforcement and compliance management
System of ensuring adherence to legislation that applies to land management, fire prevention and control. This ranges from awareness raising; responding to complaints; gathering evidence and fire investigation; warnings; penalties and prosecution. Often involves the Police Service, who have an “Arson Squad” trained to investigate fires and follow through on prosecution of offenders.
Escape (see also hop over)
A bushfire or a prescribed burn is said to “escape” when it breaks away from control lines. Usually caused by a change in wind direction catching firefighters unawares.
Environmental care
Refers to the approach to planning and implementation of the operations that will ensure that these are done with care and take into consideration the impact of the operations on the environment.
Extreme (bushfire) weather
Extreme bushfire weather occurs when the temperature is high, the wind strength is high, the drought index is high, the relative humidity is low, and the fuel moisture is low. These conditions can occur every summer in southern Australia. A bushfire occurring under extreme conditions moves rapidly and generates intense heat and is very difficult or impossible to suppress.
It is usual for fire scientists to make a distinction between severity of burning conditions (weather, fuel moisture, drought index, terrain) and condition of the fuels. For example weather conditions may be mild, but fire behaviour intense if fuels are long unburnt. A good example was the fire that burnt the karri-tingle forest in the Nuyts Wilderness Area during March 2001. Much of the fire run took place at night, and even during light coastal drizzle, but due to long-unburnt heavy fuels the fire was still very intense and damaging.
Note that in 2010 Australian fire authorities introduced a new category of bushfire weather which is termed ‘catastrophic’. The Bushfire Front argued against this terminology, on the basis that a fire can be catastrophic, but not weather.
Department of Fire and Emergency Services (DFES)
In Western Australia the agency with the responsibility for dealing with emergencies and with fires in cities, towns and suburbs. DFES also controls urban fire brigades and has administrative control of volunteer bush fire brigades.
Formerly known as the Fire and Emergency Services Authority (FESA).
Fire attack
Fire attack can take two forms: (i) direct attack, where fire fighters work on the very edge of the fire, knocking down the flames with water, hand tools or earthmoving machinery, or perhaps by dropping water or retardant from the air; and (ii) indirect attack, where firefighters drop back to a prepared fire line some distance from the fire edge and light a back burn. Direct attack is only successful on fires of mild intensity.
Fire Benchmark Area / Fire Reference Area
Refers to the designated areas where fire has been excluded, or treated under a specified fire regime so that any changes in ecosystem components or fuel/vegetation structure that result from these treatments can be studied and compared with other areas.
Fire break (sometimes “firebreak’ see also see fire line.)
A fire break is a strip of land where bushfire fuels are removed in advance of a fire occurring, usually trafficable by a firefighting vehicle, and formed by grading, cultivation or spraying with herbicide. Often Local Government Authorities require property owners to install fire breaks around their property boundaries before each fire season under a Firebreak Order. Firebreaks rarely stop a fire, especially under windy conditions, but they provide access and a prepared line from which to conduct a backburn or make a stand against an approaching fire.
By comparison, a fire line is a control line constructed around a bushfire.
Fire danger
An index which combines all the factors that determine the likelihood of a bushfire starting, spreading and causing damage to identified values, and the difficulty of control. Used for daily preparedness planning by land managers and on signs warning the public of the daily fire danger on a six level scale of low, moderate, high, very high, extreme and catastrophic.
Fire danger ratings are provided daily during the fire season by the Bureau of Meteorology for newspapers, TV and radio.
The fire danger scale used throughout Australia was devised by the pioneering bushfire scientist and forester Alan McArthur. The scale ranges from an index of one where fires will not burn or if they do they are very easy to suppress, to more than 100 where suppression is impossible. The benchmark weather that computes an index of 100 was the weather in Melbourne during Black Friday January 13 1939 when bushfires ravaged large areas of Victoria and Southern New South Wales and killed 71 people and vast areas of Mountain Ash forest.
The McArthur scale combines measures of seasonal drought, the moisture content of dead fuel and the average speed of the wind into an index of fire danger. The original five fire danger classes are familiar to most Australians from roadside warning signs. The message on the signs is a simple one. They tell you how difficult it will be to extinguish a bushfire should one break out under the present or forecast weather for the day. The Extreme category is reached when the fire danger index exceeds 50 on the 1-100 scale. A sixth category Catastrophic applies when the predicted index exceeds 100. This situation is also referred to (usually in the media) as ‘Code Red’.
When fires burn during extreme weather the speed of their development is staggering. Above a fire danger index of 100 (for example a day when the temperature is 38 degrees, the fuels are dry and the average wind is 50 gusting to 90 km/hour) grassfires can travel at an average of 20 kilometers per hour. Forest fires are slower, burning at around 10 – 12 kilometers per hour but they can throw spot fires 10 – 15 kilometers ahead. From a single ignition on a day of extreme or catastrophic fire danger, both forest and grass fires can burn out more than 100 000 ha in 8 hours. That’s an area 50 by 20 kilometres wide.
Fire detection system
The system devised to detect the position and, where possible, the condition of any wildfire. It consists of spotter planes, lookout towers, a communication network and trained fire management officers.
Fire Exclusion Area
An area for which a management aim is to exclude all fire, including prescribed burns and wildfires.
Fire hazard
The term “fire hazard” can be used to describe a fuel which, if ignited, may be difficult to extinguish. There is also a scale of fire hazard from “nil” to “dangerous” which expresses the dryness of a fuel, and thus the likelihood of it catching alight. This is rarely used these days being replaced by the Fire Danger Scale.
Fire impact
The effect that fire has on an area and its assets or values. Sometimes also referred to as ‘fire damage’.
Fire Information System
Refers to a database system that records information related to all aspects of fire management. This includes spatial and non spatial data, maps, remote sensing images. This system provides a vital input into decision making for fire management.
Fire intensity
The ferocity of a bushfire. Fire intensity is a function of the fuel consumed and the rate of spread of the fire. It is expressed as the rate of energy release per unit length of fire front.
Fire intensity is defined by the equation: I = H x W x R where: Prepared by the Bushfire Front Incorporated
Annotated glossary of terms associated with bushfire management
I = fire intensity measured in kilowatts /metre.
H = heat yield of fuel measured in kilojoules/kg of fuel.
W = dry weight of fuel consumed measured in kilograms /square metre. R = rate of spread in metres /hour.
A mild fire produces up to 350 kilowatts /metre. An intense fire produces 2000 or more kilowatts /metre.
Fire Intensity can also be described in terms of rate of spread and flame height.
Mild fires (or low intensity fires) used for most prescribed burning have rates of spread generally below 40 metres/hour and flame height less than 2 metres. In a forest, a mild fire will usually cause little or no scorch to tree crowns. Mild fires are easily controlled except in peatland.
Intense fires (or high intensity fires) can exceed a rate of spread of 3000 metres/hour and flame heights in heavy forest can exceed 70 metres. The following table demonstrates the relationship between fire intensity, fire damage and suppression difficulty.
|
Fireline intensity (KW /m) |
|
|
| 20-500 | Low intensity, patchy burn (the intensity prescribed for most fuel reduction burns). Rapid recovery of ecosystems. | Direct attack on the headfire is relatively easy |
| 500-1700 | Moderate intensity, little damage to ecosystems | Direct attack usually succeeds, but headfire must be “pinched in” from the flanks |
| 1700-3500 | Medium intensity, trees are killed, no or few unburnt patches. Very slow recovery of ecosystems | Direct attack not likely to be successful on head or flank fires |
| 3500-7000+ | High intensity, extensive and long-lasting damage to ecosystems | Crown fires occur – suppression impossible |
| 20,000-60,000+ | Extreme fire behaviour, ecosystems wiped out | Mass fires, firestorms – suppression impossible |
Impact
Suppression Difficulty
Fire Intensity is affected by
* The quantity of flammable fuel, its moisture content and fuel type eg. Jarrah litter profiles are more flammable than karri because karri litter usually contains more decomposing moister material. Flammable fuel includes litter on the forest floor [litter increases annually with leaf, twig and bark fall], understorey, shrubs [scrub], and rough bark. Heavy ground-wood such as dry logs which burn behind the main fire front, do not contribute significantly to the fire line intensity.
* Weather conditions especially high temperatures and strong winds, and predisposing climatic factors such as drought.
* Topography. Fires burn more intensely uphill than downhill.
* Events such as two or more fires coming together, producing a “junction zone” where the two fires feed each other, and draw in additional fresh
oxygen from the surrounding atmosphere.
Fire line (also known as a firebreak or fire control line)
A natural or constructed barrier such as a graded track or cultivated soil, or fire edge free from flammable vegetation, used both to limit the spread of fire and to provide access for fire fighters.
Fire Operations Manual
In Western Australia, the Department of Environment and Conservation’s reference document used to plan and conduct all fire management activities. It lays down the statewide standards and instructions for fire management by DEC/PAW staff.
Fire Preparedness and Response Plan
PAW’s District or Regional plan that sets out the instructions to be followed regarding fire prevention, fire preparedness, fire response and recovery operations. This plan includes information on fire resources available to the District or Region to conduct these fire operations.
Fire regime
Fires can be viewed both as “a single event” of which the most important characteristics are size, intensity and season of occurrence, or as part of a “fire regime” which describes a series of fires at the same locality. A regime has many variables, for example the fire frequency (or interval between fires), intensity, season and distribution across the landscape or patchiness.
Variation in fire regime is regarded as a critical factor in ecological studies, i.e. research into the effects and the interrelationship of fire, plants, animals and ecosystems. The reconstruction of past fire regimes, e.g. before European settlement, or before occupation of Australia by Aboriginal people, is a subject of controversy between some scientists.
Fire season
The time of the year when a bushfire can start and will spread. In southern Western Australia generally confined to the spring, summer and autumn months (October to April), and lasting about 5-7 months depending on latitude; in northern Western Australia confined to the dry season (April to October). In general a fire season will extend as rainless months go by. The peak fire season in southern Australia usually coincides with the hottest months at the end of summer (i.e. February and March).
In southern Western Australia, fire seasons become more dangerous if there is a run of dry winters. Dry winters, leading to “drought”, dry out logs, creeks and wetlands, and cause trees and shrubs to shed their leaves, adding to the amount of fuel on the forest floor.
Fire sensitive community
A plant community that is known to be adversely affected by a given fire regime. The community might be sensitive to fires that occur too frequently or are too hot or to a regime in which fire is deliberately excluded.
Fire storm (see Blow up)
Fire suppression
Suppression of a bushfire consists of the many activities connected with restricting the spread of the fire, extinguishing it and making it “safe” so it will not flare up and escape later. The principal activities in fire suppression are locating the fire, arranging rapid movement of fire fighters to the fire, attacking and extinguishing the fire edge, then mopping up the edge to ensure it cannot later escape.
Fire triangle
Diagrammatic expression of the three elements that are necessary for a fire to continue to burn: FUEL – HEAT – OXYGEN. The removal of any one of these will extinguish a fire.
Fire vulnerable community
A residential area where the inhabitants and their assets are ill-prepared in the face of a bushfire and consequently an area in which extensive bushfire damage is likely.
Flame height
The average height of the flames, disregarding any occasional flare up, measured vertically from the ground. Flames are commonly 1 to 2 metres in height in a prescribed burn under mild conditions and can be over 70 metres in an intense forest fire.
There is a strong relationship between flame height and fire intensity, and for a given fuel type one variable can be inferred from the other.
Fire scientists also measure “flame length”. The greater the flame length, the greater is the horizontal reach of a tongue of flame as it is bent over by the wind. In a grassfire, flame length can be a significant factor, affecting the usefulness of a firebreak, and in other situations will determine how close to a fire that fire fighters can work.
Forest
Simply put – a large area of land covered with trees.
Two kinds of forest frequently referred to in bushfire management are:
* Old growth forest: Old forests, comprising mainly trees which are physiologically mature or over-mature, often (but not necessarily) also “virgin” forest, i.e., forests never previously subjected to agricultural clearing, timber cutting, grazing, mining or other human-induced disturbance, other than activities of Aboriginal people in pre- settlement times.
* Regrowth forest: Forests regrown after disturbance, including disturbance by high intensity stand-replacement bushfires. Can contain mature and over-mature trees, depending on the time since regeneration, but generally the term ‘regrowth forest’ is used to refer to forest that has not reached maturity.
Fuel
Any material such as grass, leaf litter, twigs, bark, logs, even live vegetation, that can be ignited and sustain a fire. Measured in tonnes per hectare.
Fuel type. An association of fuel characteristics such as species, form, size, and arrangement that will cause a predictable rate of spread, or difficulty of suppression, under a particular set of weather conditions. The following fuel terms relate mainly to forests:
* Litter fuel. The top layer of the forest floor composed of loose dead sticks, branches, twigs and recently fallen leaves that are little altered by decomposition.
* Surface fuel. The loose surface litter on the forest floor. Can consist of fallen leaves, twigs, bark, small branches, grasses, shrubs, tree saplings less than a metre high, heavier branches, fallen logs, stumps, seedlings and small plants.
* Trash. The component of surface fuel above the leaf litter layer made up of dead twigs, branches and scrub debris of at least 10mm diameter.
* Fine fuel. Dead leaves, twigs and bark in the litter layer less than 6 mm thick as well as the green leaves and twigs of shrubs and grasses less than 2mm in diameter, and all less than 1 metre above the ground.
* Heavy fuel. Dead woody material in contact with the soil surface, greater than 25mm in diameter. Also called ‘coarse fuel’.
* Elevated fuel. Fuels that are suspended above the ground, such as shrubs, bark, seedlings.
* Available fuel. The amount or weight of fuel that will be consumed under prevailing weather conditions during a prescribed burn or a bushfire. Available fuel can be less than total fuel, where part of the fuel profile is still damp from previous rain. Measured in tonnes per hectare.
* Total fuel. The sum of the fuel quantity of litter, trash, scrub and fuels that are available to burn under extreme wildfire conditions. Measured in tonnes per hectare.
* Organic fuel. This term is sometimes used to describe subterranean fuels such as peat, or coal seams.
Fuel age. The length of time elapsed since fuel was last burnt, usually expressed in years. As fuels accumulate over time, fuel age gives an approximate guide to the fuel load.
Fuel load. The oven-dry weight of fuel per unit area. Also known as fuel quantity. Expressed as tonnes per hectare.
Fuel moisture content. The water content of an amount of fuel expressed as a percent of oven dry weight (ODW) of that fuel.
Fuel quantity. See fuel load.
Fuel reduction burn (see also ‘Prescribed burn’)
A prescribed burn carried out with the intention of reducing the fine fuel load so as to minimise the intensity of any subsequent bushfire and to ensure that it is easier and safer to suppress. Always carried out under mild weather conditions.
Head fire; Flank fire; Tail fire (see also Rate of Spread)
The head fire is that part of the fire where the rate of spread, flame height and fire intensity are greatest. This is usually at the downwind part of the fire or, in hilly country, at the upslope part of the fire.
The flank fires are those parts of a fire that are roughly parallel to the main direction of spread.
The tail fire is that part of a fire that is burning back into the wind, where the flame height and rate of spread are low. Also known as a backing fire.
High Risk areas
An area that is considered to have a high risk of being adversely affected (i.e., damaged) by wildfire.
High Value areas
An area that has valuable community or private assets, rare or endangered species, is scenically attractive, has recreational facilities or has other high value qualities, such as forming part of a water catchment area.
Hop over (sometimes written ‘hopover’, and sometimes called an” escape” or a ‘jump over’)
A fire that has escaped from the main fire and started in the unburnt area immediately across an existing track or a fire line constructed around the perimeter of the main fire. Usually started by sparks or burning embers, carried on gusts of wind. Most hop overs start within a few metres of the fire edge.
By comparison ‘spot fires’ are thrown far ahead of a fire front for distances of up to several kilometres. A hopover can become a big fire, but in this case the term “escape” is more likely to be used.
Interagency Agreements
Where more than one government agency is responsible for managing an area, or some component of the objectives of management for an area, an interagency agreement sets out the responsibilities of each agency. Interagency Agreements dealing with bushfire management generally spell out who is responsible for what, who funds what, and who is accountable at the end of the day. The IAA is signed off by both parties and reviewed annually.
Junction zone
The point or area where two separate fires meet up and become one fire. Also known as the area of coalescence. Fire intensity generally increases at a junction zone, due to combined convection forces.
Landscape scale fire protection plans
A fire protection plan covering a large area such as a bioregion.
Land tenure
The legal status of an area of land – whether it is National Park, Nature Reserve, Private Property, State Forest or some other classification. Because the objectives for different tenures often differ, fire management for each tenure may have different objectives.
Landscape scale fire protection plans
Refers to burning and suppression plans that cover large areas that are defined by landscapes with common attributes such as soil types, topography, and assemblages of native plants and fauna habitats. Landscape scale is smaller than bioregion scale.
Lightning fire
Fire started by lightning. Lightning strikes are a major cause of bushfires in Western Australia every summer. One thunderstorm can generate dozens of lightning strikes over a wide area. A lightning strike into damp fuels may smoulder for several days before commencing a run. These small smouldering fires are sometimes referred to as “sleeper fires”. Fire spotters and lookouts are trained to keep a good watch for sleeper fires over the week following a thunderstorm.
Master Burn Plan
All the prescribed burns scheduled for a designated area over a nominated period of time, usually 20 years or more.
Mild bushfire conditions
Conditions of weather and fuel such that if a fire starts it can be easily suppressed. For example, a bushfire burning under the following conditions will be a mild fire:
Wind: less than 15km/hour
Temperature: less than 25 degrees
Relative humidity: greater than 50%
Moisture content of fuel: 12% to 20%
Fuel load: up to 8 tonnes per hectare.
Mopping up (or mop up)
The operation carried out by firefighters after the run of a fire has been stopped. The aim is to make the fire edge safe so the fire will not later flare up and escape. Mopping up in forest country requires extinguishing all smouldering logs and trees adjacent to the fire line and sometimes felling trees which are alight in the crown and are throwing embers across the fire line that could cause hop overs. Mopping up should always be accompanied by “patrol”, where a fire edge is closely monitored by fire fighters for a period (sometimes weeks) after a fire was first extinguished.
No Planned Burn Area
An area that is planned to be kept free of fire, whether prescribed burn or wildfire. This is generally because the area is set aside for scientific study, or because it contains regeneration that needs to be protected from fire, or because it has an ecosystem that is sensitive to fire.
Old growth forest (See under forest)
Plantation
A stand of trees established by the planting of seeds or seedlings of trees of either native or exotic species. Can also consist of dense plantings of commercial shrub species, for example oil mallees or titree plantations, or horticultural crops such as sugar cane.
Post-logging burn.
A prescribed burn carried out under mild weather conditions but when the fuel is dry, to remove the crowns and other debris left in the forest after a logging operation. Generally the purpose is fuel reduction, but can be associated with a regeneration burn.
Prescribed burn
A general term indicating the planned application of fire to achieve specific land management objectives. ‘Prescribed burn’ replaces the old term ‘controlled burn’
A prescribed burn is carried out under predetermined (or “prescribed”) environmental conditions within defined geographical boundaries, and at the time, intensity and rate of spread required to achieve specific objectives. Before a prescribed burn is commenced a “burn prescription” is prepared. The burn prescription details the objectives of the burn, the conditions under which it will be carried out, the precise location, and deals with any specific considerations for the particular burn. It is desirable that burn prescriptions are drawn up a year or more in advance, to ensure all key factors are checked and put in place.
The following terms are sometimes used interchangeably with prescribed burn: community protection burn; environment protection burn; forest protection burn; hazard reduction burn; pre-emptive burn; fuel reduction burn. These terms relate to the purpose of the prescribed burn. The term “pre-emptive burn” applies to both a prescribed burn and a back burn – which is not prescribed, as back burns are normally lit under conditions selected by nature, not by humans. Bushfire managers prefer not to use the term ‘pre-emptive burn’ to avoid this confusion.
Prescribed burning can be undertaken to achieve any of the following land management objectives:
Fuel reduction. A fuel reduction burn is carried out under mild conditions to reduce any risks associated with the fire.
Regeneration. A ‘regeneration burn’ is lit under prescribed conditions for the purpose of achieving regeneration of a particular vegetation type. In forestry the aim is usually to regenerate seedlings of adjacent trees with viable seed in their crowns, but the same burn will also regenerate understorey species present in the forest. In wildlife management, a regeneration burn may be used to create a particular habitat for some selected animal species, or to favour a particular plant, or to regenerate species with seed stored in the soil.
Site preparation. A burn conducted to clean up a site before undertaking some other activity or converting to a different land use. Examples are stubble burning by cereal growers before sowing the next crop, or burning debris on a mine site before the area is mined. Site preparation burns are not usually undertaken with a prescription, and are more properly regarded as “burning off” rather than “prescribed burning.”
In agricultural areas burns are sometime lit to germinate clover or to rid a paddock of insect pests.
Prescribed Burning Plan
A map showing, for a region, the areas to be prescribed burnt over the next several years.
Pre-suppression activities
Those activities carried out before the fire season to minimise the risk of a fire starting, or to ensure that if a fire does start there is the best possible chance of suppressing it and preventing it seriously damaging people, the environment and property.
Pre-suppression includes prescribed (fuel reduction) burning, ensuring an effective detection and communication system is in place, that access tracks are trafficable, that fire fighting vehicles, machinery and equipment are in sufficient supply and in good working condition and that sufficient personnel are well-trained in command roles, suppression, mop up, safety and other fire management techniques.
Rate of spread (ROS)
The rate at which a fire advances and enlarges. For forests, is generally expressed as metres/hour. In grassland fuels, rate of spread is often measured in kilometres/hour. Mild fires used for prescribed burning in forests have a headfire rate of spread generally below 40 metres/hour.
A bushfire spreads in four directions: down wind (the head fire which burns with the wind behind it); sideways (the flank fires) and into the wind (the tail fire where the ‘back’ of the fire burns slowly into the wind). A fire is usually elliptical in shape, since the head fire rate of spread is normally much greater than the flank fire rate of spread. In the unusual event of completely windless conditions, the shape of a fire will be circular.
Intense bushfires can have a head fire rate of spread which exceeds 3000 metres/hour. The rate of spread depends mainly on wind strength, vegetation type, fuel quantity, fuel condition, and slope.
Under the same weather conditions the rate of fire spread is generally greater in grassland and crops than in forest because the wind strength is reduced under forest canopy. Above a threshold of intensity (in the vicinity of 1500 Kw/m), rate of spread of forest fires is also influenced by spot fire development. In dry, heavy fuels, spot fires will be carried downwind ahead of the main head fire, starting new fires, which in turn start new fires. This effect can quadruple the rate at which a fire moves, resulting in vegetation being engulfed by fire.
Intense fire spotting (also sometimes referred to as an “ember attack”) often catches inexperienced firefighters by surprise and can result in loss of life, or of fires burning into suburbia from the forest.
Regeneration burn (See under prescribed burn)
Regrowth forest (See under forest)
Retardant
A fire retardant is a chemical applied to a fire to reduce combustion rates. Retardant is sometimes delivered by fixed wing aircraft or helicopter, or is applied in from a fire truck. Aerial retardant dropping is usually regarded by fire fighters as a “holding action” that is, it helps to keep fire intensity and fire spread down until fire fighters on the ground can reach the fire and control and mop up the fire edge. Most land managers prefer to drop water rather than fire retardant chemicals into native bushland because of uncertainty about possible side effects.
Scientific Reference Area
An area available for study in which the factors causing its condition are known.
Scorch height
The maximum height above the ground to which the leaves of trees or shrubs are browned (“scorched”) by a fire. In Australia, eucalyptus tree crowns that are merely scorched by a fire tend to recover, whereas trees that are defoliated can take several years to recover or may never recover. Most European, North American and many tropical tree species are not resilient to fire, and even a mild scorching of the crown results in tree death.
Research has shown that scorch height in jarrah forest is generally 5 times flame height in a spring burn, and 9 times flame height in an autumn burn. The difference is due to the greater combustion of bark and woody fuels in the drier conditions of an autumn burn.
Scrub
Vegetation, such as heath and shrubs, that grows either as an understorey or by itself in the absence of a tree canopy. The components of scrub are usually called shrubs. In coastal areas, scrub is often referred to as heath or heathland.
Severe conditions
The condition of the fuel, weather, drought index and topography at a bushfire that makes it difficult or impossible to suppress the fire. See also extreme bushfire conditions.
Smoke management
Used by land managers and meteorologists planning a prescribed burn, in an attempt to ensure that smoke does not cause problems as a result of the burn. Bushfire smoke can reduce visibility, and is believed to interact with air pollutants such as vehicle exhausts, and this can irritate some people. Smoke management involves prediction of surface and upper wind direction and strength for the time of the burn and on subsequent days until a smoke plume has dissipated.
Smoke is also produced by wildfires, but in this situation, smoke management is not usually the priority concern of firefighters. Nevertheless smoke from wildfires can cause serious problems, e.g. closure of airports, accumulation in valleys, or pollution if the wildfire burns through areas where toxic chemicals have been stored.
Spot fire
A new fire occurring downwind of a head fire (up to 10 kilometres has been observed), usually started by a piece of burning bark. Contrast with hop over which is a new fire that has jumped directly immediately across a fire line and not necessarily at the head fire.
Surface moisture content
The moisture content of the fine fuels in the top 5 – 10 mm of the litter. It is expressed as a percentage of oven dry weight of those fine fuels. See also fuel moisture content.
Traditional owners
The Aboriginal people who are acknowledged as being responsible for Aboriginal culture in an area.
Water bombing
The dropping of water onto a bushfire from an aeroplane or helicopter. The water is usually admixed with an anti-dispersant to maximise the volume reaching the drop point. Water bombing is most useful in helping protect houses threatened by a bushfire. In forest situations it is usually regarded as a holding action, giving time for firefighters on the ground to get to the fire. Water-bombers can also be very effective in containing the development of spot fires ahead of the main fire front. Water bombers are generally ineffective in high winds or conditions of poor visibility, and usually do not operate on fires at night.
Wilderness
A remote area where the hand of modern humans is currently absent or not obvious. In Australia all such areas have been influenced by Aboriginal people for millenia. Originally considered as areas without roads or tracks and suitable only for self reliant recreation activities such as walking, canoeing or climbing, wilderness is more commonly today mainly allied with remoteness from towns or farms. In heavy forest, the lack of vehicle access in a wilderness area can make prescribed burning for fuel reduction, and the suppression of wildfires dangerous, difficult or impossible, especially if water bombing is also not permitted.
Wildfire
An American term used to describe an unplanned fire, started by lightning strike, arson or accident, now also used throughout the world. It is a generic term that may include forest fires, scrub fires and grass fires. The uniquely Australian term is “bushfire”.
Woodland
Large tract of land covered by trees but more open than a forest and often with a grassy understorey.
Working arrangements (See also ‘Interagency agreement’)
Those arrangements necessary to implement the objectives of management for an area, usually where there are overlapping or intersecting responsibilities or interests between parties. Working arrangements are sometimes spelled out in a Memorandum of Understanding (MOU) between two or more parties.
Prepared by the Bushfire Front Incorporated 2013