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Wildfires are spectacular. They are dangerous. If a wildfire threatens you, what do you do? |
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There is a good chance you can save your life and your house if you have a basic understanding of wildfire behaviour and take actions to protect yourself. |
Wildfire Behaviour
Caution
A number of the comments made below are specific to south-eastern Australia. Make appropriate modifications if you live in other areas. In addition, although the science of fire behaviour is well researched, new findings are continually refining the state of our knowledge. The comments are generalisations and must be treated with caution. Fire behaviour is unique to each situation and the comments must be considered as introductory rather than final. Although these qualifications are made, it is believed that the description of fire behaviour outlined below will assist individuals in preparing for the event of wildfire in a general sense. If you need advice about your specific situation, consult a fire expert in your area. Your local fire brigade is a good place to start.
Vulnerability
The vulnerability of people and property is directly related to the intensity of wildfire. The variables that determine the intensity of wildfires include a number of factors such as climate, weather conditions (wind speed and direction, temperature, humidity), slope and aspect, fuel characteristics (amount, distribution, moisture content, chemical composition). The landowner or manager of a facility cannot control most of these characteristics. However, much can be achieved by selecting appropriate sites for activities and developments, by safe design and by controlling fuel type and distribution. Ongoing management of the facility and of the behaviour of residents and patrons can also lessen risks.
The very young, the very old, the sick, the disabled and those affected by alcohol or drugs are at particular risk.
Protect your life
The major threat to life occurs with radiant heat and the release of radiant heat is greatest at the fire front. Radiant heat travels in straight lines and rapidly debilitates any person not shielded from its effects. It decreases with the square of the distance from the source. A barrier placed between a person and the fire (such as appropriate clothing) will provide some protection, but the safest option is to provide a refuge (even if temporary) so that people are not exposed to the fire front. A dwelling may act as a suitable refuge while the fire-front passes. Even if the dwelling catches fire there is generally sufficient time for the fire-front to move past the dwelling enabling those sheltering to exit in relative safety onto blacked ground. They may then be in a position to extinguish small fires, thus saving the dwelling as well as their lives.
If you intend to evacuate, do it early. Don't wait till you see a fire front approaching and risk getting trapped in the open without adequate protection from radiant heat.
Protect your house
Structures are ignited by radiation, direct flame contact and ember attack. To lower the risk to structures, the levels of fuels near buildings must be reduced so that the chance of the structure catching fire is lessened. Even if the building is maintained in a state where fuels in the vicinity of the building are eliminated, they may still be vulnerable. Research has shown that embers ignite most buildings in wildfires. These may be lighted brands or glowing embers blown onto the structures before the fire front arrives, as it passes or after the fire front has passed.
Research has shown that most dwellings are ignited by embers. These can enter any open spaces. It is necessary to enclose any gaps. For example, flywire screens over window openings and sealing up under-house and under-eave spaces are good construction practices. As a fire approaches close all windows and doors.
Safety may also be increased if the pattern of wildfire behaviour for a locality is recognised and anticipated before the event. The pattern of weather that is typical of intense wildfires is this area is as follows. The worst days typically are hot days with low humidity and with strong winds, usually from the north. Wildfires move in the direction of the winds and the shape of the fire in these conditions is long and thin with a compact fire front and long flanks. Man in these extreme conditions cannot contain the more severe fires.
Due to the passage of high and low pressure systems across southern Australia, the hot dry northerly winds are typically replaced by strong turbulent southwesterly winds that precede a change. The long easterly flank of the fire then becomes a very wide fire front that is often a major threat to life and property. These general patterns can be affected by local circumstances such as topography and locations near major water bodies such as the ocean. Sea breezes are typical of coastal locations and will affect the direction of fire movement. Gully breezes may also occur in directions different to the prevailing winds.
Fuel
Typically, wildfires burn liberating vast amounts of energy at the fire front. The fire front consumes fine fuels such as leaves and sticks less that 6mm in diameter. Following the passage of the fire front, heavier fuels burn but the vast energy release which is the source of most damage to life and property is the critical issue that needs to be considered in the planning of a new tourist facility on this site. The moisture content of the forest fuel is important but is normally beyond the control of the manager with the exception of the immediate environs of the facility where green lawns and dampened surfaces in the near vicinity of a development may assist. The distribution of the fine fuels is vital. Fine fuels that are distributed in continuous layers either horizontally or vertically assist in the development of a fire which proceeds fastest in the direction of the current winds in a horizontal direction and vertically to the crowns of trees leading to crown fires.
Many of the forest communities in the south-eastern Australia are conducive to the production of high quantities of fine fuels that typically carry a fire front. While some are generally wet and burn in wildfire situations only in more exceptional conditions, others are drier and regularly support wildfires. All the grazing properties regularly face conditions where wildfire is possible. Apart from some of the deep gullies, most of the forest communities in the vicinity of the subject land are of the dryer type and each year could carry a fire front.
The chemical composition of the fuel can also affect the intensity of a fire. Fine fuels containing volatile oils (such as eucalypt leaves) can intensity a fire. Conversely, the high moisture contents of the leaves of some species can lower the intensity. Some species have other chemicals that lead to higher intensities of fire and some to lower intensities. The fire history of a site may also be significant, because forest communities may accumulate fine fuels over time and a wildfire can eliminate this reservoir. The amount that is stored in this reservoir of fine fuel is dependant on the forest composition and the ecological processes that occur there. In some seasons the conditions suit the natural decaying organisms and the amount of fine fuel may decline. In other seasons, the decay rate may decline leading to an accelerated build-up.
The implications for the proposed development are that the fuel distribution, type and amount will be important, both within a site and external to it. While the ability to affect the area external to it is limited, the design and management of the site is critical and is within the control of the landowner. This means that the landscaping, the design of the facility and the way it is managed are vital elements of the fire management program.
Slope and Aspect
Fire travels faster up steeper slopes and slower going down slope. A general rule of thumb is that a wildfire will double its rate of spread for every ten-degree increase in slope and the intensity of the fire will quadruple. The converse applies to down-slopes. Aspect is important from two major aspects.
The aspect of a site will affect the amount of insolation received from the sun that affects local temperatures and drying of fuels. In forest situations, different communities of plants become adapted to different aspects and they are generally moister on southeastern aspects than those on northwestern aspects. Aspect is also important when considered with slope because wildfires are more likely to approach from some directions than others. Weather characteristics of days on which wildfires may be of particular concerns typically have high temperatures and strong gusty winds from the north or northwest. On such days the hot northerlies typically change to south westerlies as a cold front approaches and the change is accompanied by unstable atmospheric conditions that make fire behaviour unpredictable. This change may be abrupt leading to dramatic changes in fire behaviour.
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