What you will find on this page: Brown Hill community risk; what is it like when fire meets urban fringe (Canberra fires 2003 – video); radiant heat versus embers (video); How mentally prepared are you? (video); Victorian bushfire outlook update; Check your level of risk; Myth Busters – common myths about bushfire; how a bushfire behaves; learn about embers and their role in house fires
FireAware Network – Understanding risk of a bushfire event
27 September 2016: Recently **Assoc Professor Kevin Tolhurst spoke to a small group of residents at the information session for the Finlay St Bradbury St Cluster and provided an insight into the potential risk of a bushfire event impacting on our community. The following come from notes taken at the session:
Brown Hill Bushfire Prone Area
Brown Hill Risk Level
- The highest risk areas of Ballarat to a bushfire threat are Nerrina, Invermay and Brown Hill;
- The direction of the threat coming from the forested areas north-west of the city – Creswick and Clunes – depending on ignition point a fairly large fire could develop;
- Intensity of any fire depends on the fire rating and weather conditions at the time of ignition;
- wind direction on high fire danger days usually comes from the north west – the fire front could change dramatically if a south westerly wind change comes through – which causes significant changes to the configuration of the fire front
- However the terrain is not significantly steep as the more mountainous areas of eastern Victoria.
- With a relative narrow range of vegetation and therefore a lower fuel load; a fire travelling at about 10 km/h on flat ground would have a flame depth of about 110 m in forest and 14 m in grassland.
- If the width of the vegetation (fuel) is less than these dimensions, such as alongside a road or creek or narrow windbreak, then the heat from the fire will be less than if it was coming from a deep area of fuel such as a forested area.
- Due to the lower fuel load and relatively smaller forested area, than other forested mountainous areas of Victoria, it is less likely that a fire would have the ability to develop into a catastrophic event. This however, does not mean that a fire hasn’t the potential to infiltrate the urban fringe of the city
To view the Bushfire Prone Area of Brown Hill access the link here. Source: Visualising Ballarat. What are Bushfire Prone Areas? Bushfire Prone Areas are areas that are subject to or likely to be subject to bushfires. Access property detail reports and Bushfire Prone Area status here
Main risk for Brown Hill Clusters south of the freeway (Finlay & Russell Sq)
- Houses adjacent to the Yarrowee River and nature reserve are at a higher risk of direct fire contact;
- The greatest threat to the majority of the suburb is from ember attack; to defend against an ember attack can take hours of vigilance both outside and inside a house;
- Houses can burn down hours after a fire has past due to a slow build up of embers;
- Investigation into the Canberra fires in 2003 and the Wye River fires in 2015 revealed that the majority of houses lost were from ember attack and not the direct fire front;
- Spot fires can start in multiple backyards as embers can travel long distances before a fire arrives, during and long after the initial threat has past;
- If embers have time to build up and are not extinguished quickly they can enter unsealed areas/weak points and ignite houses;
- Once houses have ignited, house to house fires then become a high risk;
- If high winds are created by the fire they have the potential to lift tiles, even momentarily, which allow entry of embers in roofing area;
- Having metal fencing, protecting windows with metal (aluminium flywire) screens and ember proofing a house can assist to lower the risk of ignition;
- As environmental moisture is also key to the intensity of a fire it is easier for a fire to take hold when moisture content is low e.g. during drought conditions. This also applies to houses as they also dry out.
- Due to the high moisture content build up during our wet winter it could lessen the intensity of this coming fire season (2016/17) but fine fuels such as undergrowth and grasses can dry out quickly with a run of hot days
- To access the full notes on this session about risk of a bushfire event go here
- ** To access background on Assoc Professor Kevin Tolhurst go here
Risk notes for Janson Rd/Stringybark Drive Cluster and Coorabin Estate Cluster will be added here shortly
The time of day that the fires came through the suburbs was mid afternoon. Video showing the bushfire emergency in Canberra on 18 January 2003 – During that time all urban & rural fire units across the city set up defensive positions around the suburbs – The fires were impacting both the northern and southern districts of the city…Footage was taken by Channel Nine cameraman, Richard Moran during a ride through the fires with ACT Fire Brigade District Officer Darrell Thornthwaite and the crew of Bravo 3. There is also previously unseen footage of ACT Police evacuating suburbs and firefighters arriving from interstate to help…
Source: Interview with Jack Cohen, Fire Sciences Researcher, Fire Sciences Lab, Missoula, Mt.
No one has done more to define the wildland-urban interface problem and empower homeowners to reduce their risk of wildfire than Jack Cohen. His post-fire field examinations and laboratory-based research on fire dynamics led to the concept of the home ignition zone, a phrase he coined. Cohen also co-developed the U.S. National Fire Danger Rating System and contributed to the U.S. fire behavior prediction systems. Access what Jack believes is our role in home protection here
Bushfire & Natural Hazards CRC November update: Following on from a wet winter across large parts of southern Australia (the second wettest winter on record for the country), September saw further rainfall, with more records broken in parts of central and western New South Wales, western Victoria, eastern South Australia and western Queensland. With this in mind, the bushfire seasonal outlook has been re-examined.
Further rainfall is expected to be average to below average in most areas, and when this is coupled with summer temperatures that are forecast to be average to above average, more areas are now expected to experience above normal fire conditions. This increase in fire potential is predominantly in grassland areas of Victoria and New South Wales, with above average rainfall leading to ideal growing conditions. As temperatures warm, this grass will dry, increasing the risk.
For those in our community that live, work or recreate beside, or close to open spaces, reserves and nature parks, you are classified as living on the urban-rural interface. You will need to take action each and every fire season to prepare you, your family and your home.
Even if you live several streets back from these interface areas you are not necessarily safe from bushfire as the Canberra 2003 bushfires demonstrated how powerful a bushfire can be and how it can reach well inside a suburb to destroy lives and homes.
There are some basic questions you can ask yourself to check your level of risk
- Do you live within a couple of streets of bushland?
- Does your local area have a history of bush fires?
- Do you have many trees and shrubs around your home?
- If you need to leave your home, do you need to travel through bushland?
- Is your Bush Fire Survival Plan more than one year old?
If you answered ‘Yes’ to one or more of these questions, then you and your family may be at risk in the event of a fire. Knowing your level of risk means you will be able to make the safest decision for you and your family
If your home may be at risk of a bush fire you need to have a Bush Fire Survival Plan.
Your Bush Fire Survival Plan will help you make decisions that will give you and your family the best chance of surviving a bush fire. These decisions include:
- How will you PREPARE. ACT. SURVIVE?
- Will you Leave Early or will you Stay and Defend?
- What will your triggers be to act?
- What will your back-up plan be?
Source & for more information on how to prepare a bushfire plan go here
If your home is not directly at risk from a bush fire, there are still some general actions you should take to protect you and your family:
- Make sure your family has a general understanding about bush fires and bush fire safety. If they are in an area that is affected by a bush fire, such as at work or on holiday, they will be able to make the safest choices.
- Make basic preparations to your home. Embers can travel many kilometres ahead of a fire, so even if you are not directly threatened by a bush fire, you may be impacted by embers. Preparing your home can reduce the risk of embers starting spot fires around your home.
- Keep yourself informed on days of increased fire danger. You should get into the habit of paying attention to your local radio and TV stations on hot, dry, windy days. This will help you plan your day and make sure you avoid areas where there is an increased risk of a bush fire.
Source: ACT Bushfire Survival Plan 2013
Here are some of the common myths about bush fires and bush fire safety. Not knowing the facts can be life threatening for you and your family
MYTH There will always be a fire truck available to fight a bush fire threatening my home FACT There will never be as many fire trucks as there are houses. Do not depend on a fire truck being available at your home.
MYTH I’ll be fine; the bush is a few streets away FACT Most houses are burnt in bush fires because of ember attack. Embers can cause fires many kilometres in front of the main fire and can start falling hours before the fire arrives at your home. You need to make sure that your home is properly prepared to withstand an ember attack.
MYTH Filling the bath tub when a fire is approaching is to sit in FACT The ESA recommends that you fill your bath and sinks with water so that you will have water in case water supply to your home is cut off. This water can then be used to put out small spot fires that may start in and around the home.
MYTH It won’t happen to me FACT No one can guarantee that it won’t happen to you. When you think of recent large bush fire events in Australia, do you think that the people that were impacted by those fires thought that a bush fire would happen to them? If you prepare and nothing ever happens then you have lost nothing. If you do not prepare your family and home in order to best protect them from a bush fire you may regret it when a bush fire does occur!
MYTH Standing on my roof and hosing it down with water will help FACT During a bush fire more injuries normally occur from people falling off roofs than from burns! Filling your gutters with water and hosing down your roof will help with spot fires due to ember attack, but any hosing should be done from the ground or off a ladder.
MYTH If I know the back streets in my suburb or town really well, it will be okay for me to leave at the very last minute FACT Smoke from a fire can make it very hard to see and make it dark during the day. Objects like power lines and fallen trees on roads may be hard to see, making driving dangerous. It is always better to leave long before the fire arrives.
MYTH Fire travels slower up hill FACT Fires will move faster up a hill and slower down a hill. The speed of a fire will double with every 10 degree increase in slope. For example on a 20 degree slope, bush fire speed is four times faster than on flat ground!
MYTH A house can explode if it catches on fire FACT That depends on what is stored in the house. You should consider what flammable and explosive objects you have in your home and where you can move them to reduce the risk to your home.
Source: ACT Bushfire Plan 2013
Source and further details go here: SA Country Fire Service
The combustion process
Before discussing fire behaviour we need to know how fires ignite. There are three basic components that are required for a fire to ignite, burn and continue to burn. These are oxygen, heat and fuel and are described in the fire triangle. The fuel can be any material that can be burnt, oxygen (O2) is an essential part of the chemical reaction needed to create fire, and heat is needed for ignition.
Fire behaviour is how fast a fire spreads and how intensely a fire burns and is determined by fuel,topography and weather (predominantly wind and temperature). Fire spreads by a process called heat transfer. This is when the material immediately next to a fire is preheated to point where it gets hot enough to ignite.
The process of heat transfer is influenced by topography (slope and aspect). Because heat rises (convection) fuel above the fire is preheated more than fuel bellow a fire. Heat transfer therefore occurs more rapidly through fuels up a slope causing a fire to travel more quickly up slope than down slope. Aspect will influence the type of vegetation and fuel moisture. West facing slopes are usually hotter and dryer and support more fire tolerant (therefore more flammable) vegetation. South facing slopes however, are usually cooler and wetter and support more fire intolerant (less flammable) vegetation. Image source: CFS website
The amount of fuel available to burn is defined in terms of low, moderate, high, very high or extreme overall fuel hazard. Not all vegetation is fuel that burns. The important fuel is dead vegetation that is thinner than a pencil called fine fuels and the type of bark on trees. Fine fuels comprise surface fine fuels (leaves, fallen bark etc.. in the litter layer on the ground) and elevated fine fuels (twigs, leaves and grasses just above the ground surface). How much fuel builds up in a given area depends upon how much the local vegetation ‘sheds’ dead fine fuel litter and how quickly it rots. The overall fuel hazard is measured by assessing the influences or hazard of the type of bark on trees, the amount of elevated fuel such as grasses, ferns and shrubs and the amount of fine fuel on the surface of the ground.
Overall Fuel Hazard = Bark Hazard + Elevated Fuel Hazard + Surface Fine Fuel Hazard
This approach is current best practice developed by the then Victorian Department of Natural Resources and Environment (now Department of Environment and Primary Industries), and represents a significant change in the philosophy of assessing fuel factors affecting fire behaviour. Rather than simply considering surface fine fuel loads (in tonnes per hectare) as in the past, it shifts the emphasis to considering the whole fuel complex, and particularly the bark and elevated fuels (fuel arrangement). Research into the fuel accumulation and rotting rates of different vegetation communities have been used to develop fuel accumulation models. Office of Environment and Heritage uses fuel accumulation models as one of the indicators for prescribed burning.
Weather influences fire behaviour by creating conditions suitable for burning. Obviously it is harder for a fire to burn in high humidity or rain however, wind and temperature are the predominant drivers of fire behaviour. Hot temperatures will speed up the process of preheating and heat transfer and allow a fire to spread more quickly. Wind also speeds up the process of heat transfer by pushing flames and heat sideways to preheat unburnt areas. Wind can also change the direction of a fire and turn a fire flank (the side of a fire – lower intensity) into a fire front (the head of the fire – highest intensity). More information on how weather can affect fire behaviour can be found on the ‘Bushfire Weather’ web page maintained by the Bureau of Meteorology. This site describes how weather systems like highs, lows and cold fronts affect fire behaviour.
Types of bushfires
Fire behaviour will determine what type of bushfire occurs. There are three types of bushfire; ground fire, surface fire and crown fire and one, two or all of these types of fire may make up a fire event.
A ground fire can occur in any conditions and is where peat, coal, tree roots or other materials ignite and burn under the ground. Ground fires can burn through to the surface and become surface fires.
Surface fires are low to high intensity fires that burn on the surface of the ground. The tree canopy may be scorched but does not burn to the extent that it will carry a fire.
A crown fire occurs during fires of extreme intensity. A crown fire is when fire burns and spreads through the crown or canopy of trees. The influence of wind is greater in the tree canopy and where this canopy is interconnected or continuous, fires can spread incredibly quickly.
Image source: Bushfire CRC & DSE
Text Source: NSW Office of Environment & Heritage
This program is based on the research of Jack Cohen, U. S. Forest Service, Research Physical Scientist, at the Fire Sciences Laboratory of the USDA Forest Service in Missoula, MT. The program discusses how the combustion process effects forest fires, what you can do to create survivable space, why some homes are destroyed while others survive, how to identify your home’s Ignition Zone — the area that includes the home and its immediate surroundings, which, if properly conditioned, can save the home during a wildfire. Source NFPA Firewise Community
Dr. Jack Cohen, Fire Science Researcher with the USDA Forest Service, explains current research about how homes ignite during wildfires, and the actions that homeowners can take to help their home survive the impacts of flames and embers. Featuring footage from the IBHS Research Center showing ember experiments on full-scale structures, this primer helps explain the basic steps to protect homes, and shows where to find more information. Source: NFPA (USA)