Southern Rural Fire. How To Safety Burn Piles and Windrows.

Transcription

1 Southern Rural Fire How To Safety Burn Piles and Windrows.

2 Contents 1 Understanding the Risks Fire Environment and Fire Behaviour Topography Fuel Weather Fire Environment Hazards Understand How Fires Spreads Understand The Parts Of The Fire And How They Behave Planning Your Burn Plan for the Worst Weather Window Firebreaks Insurance Carrying Out Your Burn Clothing Factors That Affect Ignition and Fire Spread Burning Windrows Before Burning During Burning After Burning Burning Piles Before you burn: During Burning After Burning... 21

3 1 Understanding the Risks Fire is a valuable land management tool for large scale land clearance. However fire use comes with an inherent set of risks, knowledge of these hazards will help reduce the risks associated with fire use. 2 Fire Environment and Fire Behaviour Fire is created by fuel, oxygen and heat, if we take one of these away the fire goes out. Similarly the fire environment is made up of fuel, topography and weather. Although we can t take away of these elements in order to put the fire out, the Fire Environment helps us understand how the fire will behave and manage it accordingly. If we understand the Fire Environment we understand the Fire Behaviour and can put things in place to reduce the risk.

4 2.1 Topography Is the shape of the land and Topography Description Slope Will affect the speed that a fire travels up hill. A fire doubles it speed for every 10 degrees of uphill slope. Aspect Terrain Elevation North/West facing slopes are usually sunny and dry and have lighter more flammable vegetation, allowing fire to spread faster and fire to be more volatile. The valleys, gullies, slopes, ridges and flat areas can all affect the direction and speed that a fire travels. Rough, uneven or steep terrain can make traveling difficult and slow for vehicles, machinery and people. Terrain may not affect the rate at which a fire spreads but can affect how people move around. Generally temperature decreases with elevation and relative humidity increases. Wind strength can increase as airflow is forced over or around hills. Rainfall will be greater on the side of a hill or mountain range that faces the prevailing wind.

5 2.2 Fuel Understanding the vegetation ( fuel) you intended to burn off is important to achieving the result you want. There are a number of fuel factors which will determine how hot and long your fire will burn and how far and fast it will travel. Fuel Density Fuel Fine Fuels Description Such as grasses, fallen leave, pine needles and small twigs, loose moisture easily and dry out quickly. Dry fine fuels ignite easily and can carry a fire rapidly. In most cases fires start in light fuel and spread to other fuel types. Medium Fuels Such as scrub, branches and young trees require more time to dry out and are too large to start a fire. Medium Fuels will produce a hot fire. Heavy Fuels Such as stumps, logging slash mature trees, native forest and peat are usually difficult to ignite. Once on fire heavy fuels will produce high intensity fires and are difficult to put out. Fine Medium Heavy

6 Three-Dimensional Fuel Fuel is also described spatially across the land scape Fuel Ground Fuels Surface Fuels Ladder Fuels Contiguous Fuels Crown Fuels Description Ground fuels are the rotted materials under the surface of the ground (duff, roots, peat, buried wood etc.). These fuels can burn from centimetres deep to a metre or more Surface fuels are on the ground. Examples are litter, low and medium sized shrubs, seedlings, grasses, fallen dead matter Fuels that link together vertically. They may include dead fuels hung up in lower branches of scrub or un-pruned trees, tall shrubs, small size trees, bark flakes, draped needles, tree lichens This is the distribution of all the different fuel types across the land scape. It includes how far the fire might spreads and how dense or scattered the fuel is. Crown fuels are the tops of the trees. They are more affected by wind. Crown fires may be hotter and faster than surface fires. Figure 1 - Fuel Types

7 The final two factors to consider are: The quantity of fuel the more fuel there is the greater the intensity of your fire Fuel moisture The greater the moisture content of your fuel (especially green vegetation) the harder it will be to light and sustain a fire.

8 2.3 Weather Weather the most variable factor in the Fire Environment changing the fastest and catch people out. It is the element of the fire environment that can. Element Air Temperature Description Fuels in a warm environment are pre-heated by the air temperature and the sunlight, drying it out and making ignition easier. Relative Humidity The amount of moisture in the air. When relative humidity is low, fuels dry and ignite easier. Wet fuels lose moisture to dry air (sunny days). Green vegetation does not lose or gain moisture as quickly as dead fuels. Wind Speed Wind helps dry out fuels, it directly affects the speed at which a fire spreads and direction the fire will travel. Wind is the biggest element that catches people out when they are using fire. Rainfall Fuels absorb moisture in continuous rain or high relative humidity. In short periods of heavy rain, water tends to run off and not be absorbed by fuels.

9 Change between day and night You need to be familiar with your local and regional weather patterns. Fire generally burns quickly during mid-afternoon when relative humidity is low and the temperature is higher. In coastal areas, look out for the onshore coastal breeze that arrives most afternoons In hilly/mountainous areas, cool wind displaces warm air down valley systems in the afternoon.

10 2.4 Fire Environment Hazards Each Fire Environment element can has its own set of hazards. When Fire Environment hazards overlap increases the chances of a disaster occurring. Fire Environment Topographic Fuel Weather Sample of Hazard Being uphill of a fire (if moves faster up hill) Obstacles, loose ground and slips Rough country Unfamiliar area Not being able to see the fire Un-burnt vegetation Fire spreading across fine fuels more quickly than you can escape A spar is unstable and can break and fall. Spot fires Change of wind speed or direction Being downwind of a fire Weather hotter and drier after midday. Be aware of the combined effects of topography, fuel and weather

11 3 Understand How Fires Spreads Heat can be transferred from burning vegetation to un-burnt vegetation through: Radiation Conduction Convention Ember Transport The rays of heat from a fire travel in a straight line in all direction and heat unburned vegetation near it. Different substances carry heat at different rates. If burnt logs are left in a pile or buried underground they continue to burn slowly. Hot air from the fire rises up. These columns of hot air can carry ash, embers and small pieces of burning fuel. Embers can be transported by wind, in convection column or by rolling down hill, they can be caught in gutters on houses, piles of vegetation or trees spreading the fire Figure 2 - How heat from fie spreads

12 4 Understand The Parts Of The Fire And How They Behave Parts of the Fire Area of origin Description Where the fire starts Base This is the least intense part of the fire s outer edges, and has the lowest flames and slowest rate of spread Bays Indents between forward moving fingers of the fire Fingers Narrow slivers of the advancing vegetation fire that extend beyond the head or flanks. Embers & Firebrands Loose particles of burning fuel in the air Flanks The left and right outside edges of the fire The fire intensity is lower along the flanks Head The head is the part of a fire where the rate of spread, flame length and intensity are greatest, usually when burning downwind or upslope. The position of the head of the fire depends on wind direction, fuel and topography. It is dangerous to work in this area. Islands Areas of un-burnt fuels within the fire Perimeter The whole outer edge, or boundary of the fire Spot fires New fires ignited by embers ahead of the main fire Figure 3 - Parts of a fire

13 5 Planning Your Burn Before undertaking any kind of burning activity, it pays to spend some time thinking about how to keep you, your property and your fire safe. If you would like some advice contact Southern Rural Fire, they provide free advice and guidance on how to safely undertake a burn off while achieving the result you want. Southern Rural Fire does not charge for this service; however their advice does not take away your responsibility for the fire but makes use of their expertise to minimise your risk. Think about the time of year you want to burn. During March-April and September- October strong equinoctial winds make burning potentially dangerous and during the summer month s fire bans maybe in force. Give your vegetation plenty of time to dry out. The majority of sap is water. Windrowing or spraying vegetation and leaving for up to six months will allow it to dry out and give you a much better burn. If possible prepare the burn site in the spring and burn in the autumn. This gives the vegetation plenty of time to dry over the summer months and will produce a good clean burn, reducing the likelihood of fire escaping. Once vegetation is dry it takes longer to regain the moister making autumn a good time to burn. Good planning creates good burning results Figure 4 - Controlled Burn Off

14 5.1 Plan for the Worst Think about where your risk areas our and how a fire might break away then plan for how to deal with it. When preparing the site ensure there is no debris piled on the outside of the fire break. Heaping debris away from fire edge can create a nest of material for embers to catch in and spread the fire outside of the burn area. Within the burn-off area, ensure there are no large piles of slash on the edge of the fire as this will create high intensity fire near your boundary. Place large material in the centre of the burn area to ensure the boundary of the fire isn t compromised.

15 5.2 Weather Window Determine how many favourable days with the right weather conditions you need to burn. Compare this with previous year s weather information to determine the likelihood of achieving this. NIWA provides climatic information, but there are lots of websites available. Give yourself a good window of opportunity to ensure you don t miss out when seasons change. Understand the effects of weather on your local area. What effect will an approaching front have? What does the topography effect wind change? How will this affect the way your fire behaves?

16 5.3 Firebreaks What is the purpose of a firebreak? Generally firebreaks will not, stop a fire. This is because embers can be transferred on the wind and start spot fires on the opposite side to firebreaks. A firebreaks main function is to break the continuity of the fuel and provide: A place to light up from Access for crew and equipment to deal with spot fires across the break A safety zone and escape route for the fighters. A firebreak will not guarantee a fire will stop where you want it to How Wide Should My Firebreak Be? The required width of a firebreak is relative to many fixed and variable factors including fuel type, fuel dryness, topography and the weather on the day of the fire. Nevertheless, it needs to be wide enough to prevent flames, flying embers or falling or rolling burning material from crossing it A firebreak must not have any fuel present in it. Firebreaks may consist of a dozed mineral earth track, green grassy paddock, river, road or other similar noncombustible features. How do I Form a Firebreak? Figure 5 - Firebreak breached due to steepness of slope Cut firebreaks to mineral earth Push debris to the outer edge (away from the fire) Choose natural barriers where a fire will naturally slow down, e.g. ridge tops, area of sparse fuels

17 5.4 surance Although not a hazard when you are burning it pays to check with your insurance company exactly what you re rural fire insurance covers. Here are the types of insurance you should have for rural fire. Insurance of property for loss and replacement from fire: For your house, household effects, other buildings, vehicles, plant and machinery, forests and crops. Public Liability Insurance: To cover the cost of damage and loss to a third party from any fire that escapes from your property and damages other parties property. Forest and Rural Fires Act fire suppression Insurance: To cover the costs of fire suppression from a fire caused by you or started on your property. Cover is required under Section 43, 46 and 46A of the Forest and Rural Fires Act 1977

18 6 Carrying Out Your Burn 6.1 Clothing To prevent injury and harm to yourself and others, wear the right clothing when working around fire. Wear natural fibre clothing, such as cotton or wool. Synthetic materials can melt and cause severe injuries. Ensure your legs and arms are covered Do not tuck clothing in; instead create layers so hot material you come into contact with doesn t catch in your clothing. E.g. don t tuck the bottom of trousers into socks, let the trouser leg fall over the outside of your boot. Wear sturdy laced up leather boots, ideally with a steal cap. When working close to the fire use heavy leather gloves to protect your hands from radiant head and hot material. When working around heavy machinery and large piles wear a safety helmet. 6.2 Factors That Affect Ignition and Fire Spread Wind Strength Will have a significant influence on the direction the fire will travel, the rate spread, and fire intensity. Slope The shape of the land will influence direction the fire will travel, the rate spread, and fire intensity Light up pace Will determine if you have a low or high intensity fire. Low Intensity fire Created by lighting a series of spot fires spaced along the edge of the area to be burnt. A low intensity fire is characterised by a flame length less than 1.5 meters and a low rate of spread, less than 100m per hour. NOTE: - If the spot fires are lit too close together along the line then a junction zone develops resulting in a faster, more intense fire with extreme fire behaviour, including spot fires and fire whirls High Intensity Fire Created by a solid strip of fire. The fire will accelerate and spread fast (high rate of spread) and build up intensity quickly. A high intensity fire is characterised by a flame of more than 2 meters high.

19 What happens when two fires come together? This is called the junction zone effect, it occurs where separate areas of fire come together. Flame height typically doubles. This creates twice the intensity and often twice the rate of spread. Fire intensity increases abruptly, and may cause spot fires through ember transport, fire swirls and other unstable fire behaviour. The increase is greater when fires converge along a line rather than at a point The result may lead to an intensity that exceeds your objectives or ability to control the fire. Figure 6 - High intensity fire created through applying a continual strip to dense fuel on a uphill slope

20 7 Burning Windrows 7.1 Before Burning If you are considering burning windrows, then your fire planning will start prior to machinery arriving to windrow the vegetation. With windrowing vegetation you have a chance to control the fuel element of the Fire Environment triangle. The right placement, spacing and composition of your windrows will go a long way to ensuring a safe burn. Placement Windrows should be at least 50 meters away from any other combustible material. Windrows tend to have a large quantity of medium to heavy fuels, so the distance required to reduce the effects of radiant heat on surrounding combustible fuels, and ensure embers aren t transferred outside the burn area. Spacing Similarly windrows should be widely spaced so the fire can t transfer to other windrows which allows you to retain control of the fire. Composition Making sure your windrows are free of soil will assist in the vegetation drying and the burning of the rows to. Windrows with lots of soil will cause the fire to smoulder, creating a low intensity burn with lots of smoke and a lot of left over material. The soil assists in holding the heat creating problems for managing the fire and possible flair up issues later down the track. 7.2 During Burning What is the best way to light a windrow? Light each windrow along its length. Only light the first third and see how it goes. When windrows are on a slope, light from the top (upslope) and work down. Where windrows are on flat ground start at the downwind end. Once started, windrows are difficult to extinguish. By burning into the wind or down slop you can retain control of the burning better. Burning only a few windrows at a time you will be able to keep control of the fire. 7.3 After Burning When strong winds occur it can fan the fire back into life and transfer embers, creating unwanted fires. Piles of burnt vegetation can hold heat for months after burning, Check your windrows in the days and weeks following burning to ensure it is cold in the centre. Turn the windrows to ensure complete burning of the material. Figure 7 - Controlled burning using windrows

21 8 Burning Piles 8.1 Before you burn: If you are using a contractor for tree trimming or stacking your piles discuss with them prior to trimming the best location of the tree trimmings to be piled. Ensure trimmings are at least metres away and on the downwind side of any shelter belt, trees, fences, buildings or other combustible material. Ensure smoke does not create a nuisance to neighbouring properties and public roads. Check you have adequate insurance to cover for property loss, public liability, or fire suppression costs (See section 5.4). Check the fire season status; you may need a permit to burn. This can be done through the Southern Rural Fire website Click Here During Restricted Fire Season permits are required for burning activities. During a Total Fire Ban no open fires can be lit. Contact the appropriate authority if power and telephone lines are nearby. Check the long range weather forecast for the following 48 hours and make sure no strong winds are forecast Consider lighting your fire after 1pm as weather patterns for the day are generally more stable in the afternoon The fire should only be lit with wind blowing away from any shelter belt, trees, fences, buildings or other combustible material. Have a plan encase things don t go as planned 8.2 During Burning Have a plan (see section 5, Planning Your Burn). Be ready to put the fire out at the first indication of any adverse change in weather or other conditions which could move the fire out of your control. In the event of fire moving outside the area, dial 111 and ask for the Fire Service 8.3 After Burning When strong winds occur it can fan the fire back into life and transfer embers, creating unwanted fires. Piles of burnt vegetation can hold heat for months after burning, Check your pile in the days and weeks following burning to ensure it is cold in the centre. Turn the pile to ensure complete burning of the material.