Reference Material
This section of our website provides a selection of reference material on fire management issues. It begins with a glossary of bushfire terms and continues with the following items. To see any of these sections, click on the appropriate bar on the menu at right.
- Links to Relevant Websites
- Useful Scientific References
- Examples of The Value of Prescribed Burning
- Canberra Day Oration by Phil Cheney
- Fires Around Sydney by David Ryan 2004
- Four Fire Management Scenarios by David Ward 2005
- Presentations from the 2005 Eaton Seminar
- Text of BFF Submissions to Various Inquiries
Glossary of Bushfire Terms
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.
Prepared by the Bush Fire Front Incorporated June 2007
Back burn (sometimes written ‘backburn’)
A deliberately lit fire to remove the fuel in front of an advancing bushfire or grass fire 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;
* Avoids or minimises undesirable environmental impacts;
* Ensures, as far as is possible, the safety of firefighters;
* 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”. The variety of nature, including the number of species and the amount of genetic variation present in an area of interest; the range of native plants and animals found at a particular site. One measure of diversity is the number of different species at a site. This number increases, is sustained or can be reduced by various events or processes, including the passage of time. Examples of natural processes in Australia include fire, frost, flood and drought; in general, native ecosystems recover from such events. Examples of imposed processes include feral predators (e.g. the fox) or herbivores (e.g. rabbits), weeds, clearing of bushland for agriculture or urban development, chemical pollution and salinity. These can lead to “local extinction” of a species, and loss of biodiversity at a site. The interaction between biodiversity and the wide range of fire regimes (see below) is a subject of interest to ecologists and land managers.
Burning program
A program that sets out a number of prescribed burns and schedules these 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, many city dwellers refer 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 firefighters, planning, communications systems, equipment, research, and the multitude of field operations undertaken by land managers and emergency services personnel relating to bushfire 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 objectives;
* a clear statement of who is responsible for system implementation and accountable for outcomes;
* the strategies to be adopted to achieve the objectives (often set out in a stand-alone document called a “Bushfire Management Plan - see below);
* funding arrangements;
* monitoring protocols, to allow actual and planned outcomes to be compared;
* reporting of the results of monitoring;
* a research program directed at unknowns and problems; and
* a communications strategy directed at informing stakeholders about the system and its implementation.
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 aspects: (i) the risk of a fire starting, and of it becoming uncontrollable; (ii) the values which will be lost or damaged if a bushfire starts and gets away; (iii) the extent of damage which could be caused; and (iv) the resources which can be brought to bear on a fire and their efficiency and effectiveness.
Bushfire Threat Analysis (BTA) is a structured approach used to analyse the bushfire threat for a particular area or a nominated set of values and calculate a response or determine priorities for funding or action. It is usually the first step in producing a Bushfire Management Plan, which sets out the actions to be taken to minimise a threat, mitigate possible damage, ranks actions, allocates responsibility for action, establishes protocols for action in the event of a fire and post-fire monitoring. The Bushfire Management plan should also set up cooperative and command arrangements, and put in place mechanisms for review and updating of the action plan.
Containment line
A boundary within which the suppression team aims to contain a bushfire. A bushfire within a containment line is not necessarily considered to be under control. Formerly called a firebreak, containment line came into use by the media during the Canberra fires of 2003. It has been in regular use by the media since. See also fire line.
Controlled burn
Obsolete term, these days replaced by ‘prescribed burn’.
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, burning embers are sucked up into the convection column and can be carried down-wind to start new fires called spot-fires. The term Crown Fires is usually only applied in vegetation with both an upper and a lower canopy, as in a forest with trees and a shrub understorey.
Ecology
Ecology is the branch of the natural sciences devoted to the study of the interactions between plants, animals 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 and the environment and various fire regimes.
Ecosystem
An assemblage of plants and animals in a particular environment A terrestrial ecosystem encompasses a particular biota, the soil, rock outcrops, wetlands and waterways and the atmosphere. Different ecosystems may respond differently to external pressures, for example, a bushfire, a frost, a flood or prolonged drought. The principal focus of the science of ecology is to understand different responses to imposed or natural events, and the many interactions between species and the environment.
Ember attack
The sparks and burning material blown by the strong wind associated with a bushfire under severe weather conditions. Can cause spot fires and can also set fire to houses
Extreme (bushfire) conditions
Extreme bushfire conditions occur when the fuel load is high, 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.
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 scale from low to extreme.
Fire intensity (Also known as fire line 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.
This is defined by the equation: I = H x W x R where:
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 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. 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.
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| 20-500 | Low intensity, patchy burn (the intensity prescribed for most fuel reduction burns). Rapid recovery of ecosystems. | 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 |
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 material. Flammable fuel includes litter on the forest floor [litter increases annually with leaf, twig and bark fall], understorey, shrubs[scrub], rough bark and heavy ground-wood such as dry logs which burn behind the main fire front.
* Weather conditions and predisposing climatic factors such as drought.
* Topography. Fires burn more intensely uphill than downhill.
Fire line (Also known as a fire control line or a firebreak)
A natural or constructed barrier such as a graded track or ploughed soil, or treated fire edge free from flammable vegetation, used in both fire suppression and prescribed burning to limit the spread of fire or to provide access for firefighters.
Fire regime
To ecologists, fires can be viewed 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 interactions of fire on flora, fauna 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 lasts 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 intensify 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 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 tonnage of fuel on the forest floor.
Fire suppression
Suppression of a bushfire consists of the many activities connected with restricting the spread of the bushfire, extinguishing it and making it “safe” so it will not flare up later. The principal activities in fire suppression are locating the fire, arranging rapid movement of firefighters to the fire, attacking and extinguishing the fire edge, and then mopping up the edge to ensure it cannot later escape.
Fire attack can take two forms: (i) direct attack, where firefighters 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 fireline some distance from the fire edge and light a backburn. Direct attack is only successful on fires of mild or moderate intensity.
Fire triangle
Diagrammatic expression of the three elements that are necessary for a fire to occur: FUEL - HEAT - OXYGEN. The removal of any one of these will extinguish a fire.
Flame height
The average height of the flames, disregarding any occasional high flashes, measured vertically from the ground. Flames are commonly 1 to 2 metres in height in a prescribed burn under mild conditions and over 5 metres in a bushfire. Flame height can be over 100 metres in an intense forest fire.
Fire scientists also measure “flame length”, which 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 value of a firebreak, and in other situations will determine how close to a fire firefighters can work.
Forest
Large area of land covered with trees.
Fuel
Fire Fuel. Any material such as grass, leaf litter, twigs, bark, logs and live vegetation that can be ignited and sustain a fire. Measured in tonnes per hectare.
Fuel age. The period of time elapsed since fuel was last burnt, usually expressed in years.
Fuel load. The oven-dry weight of fuel per unit area. Also known as fuel quantity. Expressed as tonnes per hectare.
Fuel quantity. - See fuel load.
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 specified weather conditions.
* Heavy fuel. Dead woody material in contact with the soil surface, greater than 25mm in diameter. Also called ‘coarse fuel’.
* Litter fuel. The top layer of the forest floor composed of loose dead sticks, branches, twigs and recently fallen leaves 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.
* 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.
Fuel reduction burn
A prescribed burn carried out with the intention of reducing the fire fuel so as to minimise the intensity of any subsequent bushfire and to ensure the bushfire is easier and safer to suppress.
Green burn
That type of prescribed burn carried out under mild conditions to reduce fuel in the forest as part of the pre-suppression activities of a best practice bushfire management program. See also prescribed burn, and best practice bushfire management.
Hop over (sometimes written ‘hopover’)
A fire that has started in the unburnt area immediately across 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.
Lightning fire
Fire started by lightning striking into dry vegetation. Lightning strikes are a major cause of bushfires in Western Australia each summer. One thunderstorm can generate dozens of lightning strikes over a wide area.
Mild conditions
Conditions of weather and fuel such that if a fire starts it will behave mildly, and can be easily suppressed. For example:
Wind less than 15km/hour
Temperature less than 25 degrees
Relative humidity greater than 50%
Moisture content of fuel 2% to 20%
Tonnes per hectare of fuel - up to 8 tonnes per hectare.
Mopping up (or Mop up)
The operation carried out by firefighters after a running fire has been stopped. The aim is 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 hopovers across the fire line. Mop up work should always be accompanied by “patrol”, where a fire edge is closely monitored by firefighters for a period (sometimes weeks) after a fire is out.
Plantation
A forest established by the planting of trees of either native or exotic species. Can also comprise dense plantings of commercial shrub species, for example oil mallees or titree plantations, or horticultural crops such as sugar cane.
Pre-emptive burn
Misleading term used by media commentators when they can’t remember that, depending on the circumstances, prescribed burn or backburn is the word they were looking for.
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’ and is preferred to ‘pre-emptive burn’, because it more accurately describes the process and the objectives.
The 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 the specific land management objectives. Before a prescribed burn is commenced a “burn prescription” is prepared. The 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 burning prescriptions are drawn up a year or more in advance, to ensure all key factors are checked and put in place.
Prescribed burning can be undertaken to achieve any of the following land management objectives:
Fuel reduction. A fuel reduction burn is nearly always carried out under mild conditions to ensure that no, or minimal, damage is done to the vegetation and associated environment. The following terms are used interchangeably with fuel reduction burn and mean the same thing: Community protection burn; Environment protection burn; Forest protection burn; Green burn; Hazard reduction burn.
Regeneration. A regeneration burn is lit under prescribed conditions for the purpose of achieving regeneration of a particular vegetation type, in forestry usually seedlings of adjacent trees with viable seed in their crowns.
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 minesite before mining and rehabilitation. Site preparation burns are not usually undertaken with a prescription, and are more properly regarded as “burning off” rather than “prescribed burning.”
Pre-suppression activities
Those activities carried out before the fire season to minimise the risk of a bushfire starting, or to ensure that if a bushfire 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 burning, ensuring an effective detection and communication system is in place, that access tracks are trafficable, that firefighting vehicles, machinery and equipment are in sufficient supply and 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. It is measured in metres/hour. Mild fires used for prescribed burning in forests have rates of spread generally below 40 metres/hour.
A bushfire spreads in four directions: the headfire (which burns downwind, or with the wind behind it), the flank fires (which spread sideways) and the tailfire (where the back of the fire burns slowly into the wind). A fire is usually elliptical in shape, since headfire rate of spread is always at least double flankfire rate of spread. Intense bushfires can have a headfire rate of spread which exceeds 3000 metres/hour or more. The rate of spread depends mainly on wind strength, vegetation type, fuel quantity 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, but 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 headfire, starting new fires, which in turn start new fires. This effect can quadruple the rate at which a fire moves, resulting in bush being “engulfed” by fire. These conditions have lead in the past to loss of life of inexperienced firefighters operating in heavy fuel conditions.
Regeneration burn
A burn 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 species of fauna, or to favour a particular plant.
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 the form of foam from a fire truck. Aerial retardant dropping is usually regarded by firefighters as a “holding action” that is, it helps to keep fire intensity and fire spread down until ground firefighters can reach the fire. Most land managers prefer to drop water rather than fire retardant chemicals into native forests and conservation reserves because of uncertainty about after-effects.
Scorch height
The maximum height above the ground to which the leaves of trees or shrubs are browned by a fire. Generally about four times the flame height. 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 and many tropical tree species are not resilient to fire, and even a mild scorching of the crown results in tree death.
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”.
Spot fire
A new fire occurring downwind of a headfire (up to 10 kilometres has been observed), usually started by a piece of burning bark. Compare with ‘hop over’ which is a new fire that has started immediately across a fireline and not necessarily at the headfire.
Smoke management
Used by land managers and meteorologists planning a prescribed burn, to ensure that smoke does not cause problems downwind 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 humans. Smoke management involves prediction of surface and upper wind direction and strength for the day of the burn and subsequent days until a smoke plume has dissipated.
Smoke is also produced by wildfires, but in this situation, smoke management is not generally possible.
Surface moisture content
The moisture content of the fine fuels in the top 5 - 10 mm of the litter bed. It is expressed as a percentage of oven dry weight of those fine fuels.
Water bombing
The dropping of water onto a bushfire from an aeroplane or helicopter. Waterbombing is most useful to help protect houses threatened by a bushfire. In forest situations it is usually regarded as a holding action, giving time for ground firefighters to get to a fire.
Wilderness
A remote area where the hand of humans is absent or not obvious. Therefore without roads or tracks and so suitable for self reliant recreation activities such as walking, canoeing or climbing. 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 not permitted.
Wildfire
An American term used to describe an unplanned fire, started by lightning strike, arson or accident. A generic term that may include forest fires, scrub fires and grass fires. Usually referred to in Australia as a bushfire.
Woodland
Large tract of land covered by trees but more open than a forest and often with a grassy understorey.