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australia:bushfires

bushfire safety

Introduction

  • south-east Australia is prone to major bushfires in the summer months - see history of bushfires
  • in Australia, we call wildfires “bushfires”
  • bushfires can be grouped as:
    • grass fires:
      • relatively short-lived and lower intensity but fast moving fires which may reach 18km/hour and catch people by surprise
    • scrub fires:
      • bushes and small multi-stemmed trees.
      • the more litter there is on the ground to pre-heat the scrub above, the more readily it will ignite.
      • trunks of bushes and small trees will sustain an intense fire.
    • forests:
      • tree trunks, logs and densely compacted litter sustain an intense fire.
      • fire can be carried through surface and elevated fuels like bark.
      • severe fires may “crown” - spreading via tree tops.
      • forest fires produce burning debris and embers.
      • large fires make a sound like the roar of a passing train or jet engine as they approach and generate their own wind (often sucking in air creating reverse wind directions in the front of the fire), weather and potential fire tornadoes strong enough to tip at 14 ton firetruck over
  • fires need 3 main components, remove any one of them and the fire will go out:
    • fuel - this can be limited by controlled burn offs, by separating fuel (eg. use of rakes to spread burning fuel), etc.
    • oxygen - this can be limited by covering the fire
    • heat - this can be reduced by adding water
  • bush fires spread by 3 main modes:
    • ember attack - wind blowing burning embers and debris ahead of a fire - this is the usual mode of houses being burned, while spot fires can form several kilometers ahead of the main fire.
    • heat radiation - as the fire front approaches - heat radiation decreases by the square of the distance to the fire.
    • direct flame contact - a fire front usually takes about 10-20min to pass
  • bush fires kill people mainly via:
    • direct exposure to heat radiation
      • exposed skin at the approach of a fire front
      • survivability from radiant heat is said to be under threat at distances within 4x the height of the fire
        • ie. a 35m high forest fire blaze on an Australian bushfire day may threaten life to those within 140m without protection. 
    • heat stroke (hyperthermia)
    • dehydration
    • asphyxiation from smoke
    • car accidents - poor visibility, stress, falling trees, pedestrians all combine to increase the danger.
    • NB. other than fire fighters, most people who die in bushfires die from the above causes before direct flames contact them.
  • the smoke may be so dense that even in daytime, the sun is blocked out so much it appears as dark as night
  • remember a fire destroys infrastructure as well - no power (hence no credit cards can be used), no phones (except perhaps a Telstra pay phone), no internet, no roads out and perhaps no fuel, water or food
    • a radio becomes essential along with water supplies and local power options such as power banks and generators
    • rainwater tanks can be contaminated by debris, ash, dead animals, aerial fire retardants and water-bombing
    • smoke is likely to remain for a long time and this may cause respiratory issues in those at risk - face masks have very limited utility, and to be of use must be a N95 or P2 mask with a good seal (men need to be shaven) and replaced when moist or after about 4 hours.

Prescribed cool burns to prevent bushfires

  • burning off the undergrowth in forests during the cooler months of the year in order to prevent major bushfires has limited effectiveness for the following reasons1):
    • the most important reason is that once the Forest Fire Danger Index (FFDI - a scale of 1 to 100) is over 50, major bushfires will burn even in areas of prior burns as they become dependent upon the extremely hot dry winds over over 40degC which will cause EVERYTHING organic to burn and will become INDEPENDENT of fuel load and the winds will allow the fires to skip firebreaks through ember attack and spot fires
      • in these situations, a prior cool burn will not affect the fire behaviour
      • as our temperatures increase above 42degC, fires in dry forests will be weather-dependent and not fuel dependent
    • wet rainforests cannot have a cool burn as they won't burn - its like putting green leaves to start a camp fire
    • cool burns are often not possible due to smoke pollution effects or local protests 2)

Protecting yourself in a bushfire:

  • avoid going to a region exposed to a bushfire or indeed to ANY forest region on extreme hot, windy bushfire-prone days.
  • avoid late evacuations from the region - it will probably be safer to stay in a defendable house.
  • whilst well prepared homes can usually be defended against most bush fires, as Feb 2009 showed, in extreme conditions when bushfires develop in conditions of ambient temperatures above 40degC in tinder-dry drought conditions in forests and fanned by 100kph winds, the ferocity and speed of the resultant fires are unlikely to allow homes in direct line of the fire to be defendable reliably. Unfortunately in these extreme conditions, these fires kill due to their rapid progression with limited warning (not even the authorities may be aware) and houses and cars are not reliable refuges as its no longer just a matter of fighting embers but the full brunt of fire balls in a fire storm. The main survivors in the Marysville fire in 2009 survived by taking refuge in the middle of a sports oval, covering themselves with woolen blankets to shield themselves from the radiant heat. It would seem the best way to survive such extreme fires may be to have concrete fire bunkers or cellars given early evacuation is unlikely to be a feasible option, late evacuation likely to be fatal  and defending the house is certainly not a guarantee. Although many survived by being in cars on cleared gravel areas or driving onto just burnt fields, many also died in their cars in the panic of trying to get to safety at the last minute when there is no visibility.
  • if you are caught in a car during a bushfire:
    • consider doing a U-turn to avoid the fire
    • listen to radio ABC for news bulletins
    • if you cannot get out of its way:
      • pull off into a clearing so that there is minimal scrub/forest fuel around you and you will be less likely to be hit by another car - put your hazard lights on
      • if possible find refuge in a solid building rather than being in a car BUT once the fire is close DO NOT get out of the car and try to make a run for it, the radiant heat will get you.
      • close all doors, windows and vents
      • cover up with wool/cotton clothing and rugs to protect yourself from radiant heat
      • get down low to minimise exposure to radiant heat via the windows.
      • drink water to prevent dehydration and keep you cooler.
      • remember, the fire front will usually pass within 10-20min.

Protecting your house in a bushfire:

  • decide well before the bushfire season if your house is defendable or not and develop a bushfire survival plan
    • minimise risk to your house:
      • clean up regularly to reduce fuel around the house - remove bush litter, hazards and rubbish, keep bush, trees and grass away from house
      • keep roof gutters clear of leaves and debris
      • don't use woodchip mulch around the house
      • remove combustible items such as door mats, building materials, wood heaps, fuel and paint cans, gas bottles.
      • ensure chimneys can be closed
      • ensure roof tiles and corrugated roofing are well fitting to minimise ember entry into roof space.
      • design house for fire-proofing and minimising risk to ember attack:
        • avoid exposed skylights
        • breaks in roofline or complicated roof lines
        • avoid dormer windows
        • avoid exposed wood such as pergolas, timber decking, unprotected windows and unpainted window sills
        • avoid timber contacting the ground where embers may collect eg. timber posts to ground level, timber stairs.
        • avoid external recesses that promote collection of embers
  • if it is not defendable then decide on EARLY evacuation, well before the bushfire is a threat.
    • late evacuation can be deadly.
    • don't expect the fire brigade to be able to assist during the fire.
  • if it is defendable and you decide to stay:
    • remember most homes burn down long after the fire front has passed - use the home to protect yourself during the fire front and at the same time defend it.
    • be alert, watch and listen if it is a Total Fire Ban in your area or a bushfire is known to be nearby
      • listen for weather forecasts and sirens and be on the lookout for smoke.
      • you may receive little warning.
    • ensure you have a good water supply and equipment to fight ember attack:
      • do not rely on mains water or mains power but use water from a swimming pool or dam with a diesel or petrol fire fighting pump.
      • buckets - preferably metal but plastic will do
      • mops - especially old mops that hold a lot of water are great for extinguishing embers
      • hoses will need to reach all extremities of your home
      • use metal tap fittings and put a hose fitting onto your washing machine tap
      • 44 gallon (200L) drums, rubbish bins (eg. wheelie bins), wheelbarrows, troughs or garden ponds filled with water placed strategically around the home
      • garden sprinkler systems can be used before the arrival of the front
      • consider roof-mounted sprinklers as long as you can get water to them.
      • knapsack firefighting backpack that holds about 9L water and uses a spray.
      • wet blankets to seal gaps under doors to prevent ember and smoke entering.
      • shovels and rakes to break up piles of burning material.
      • downpipe or gutter plugs - buy them or use tennis balls, stockings, sand and PVC pipes.
      • ladders inside and outside to allow entry into roof space via man hole.
    • ensure you have adequate personal protective clothing:
      • each person needs long trousers or overalls in natural fibre (eg. jeans or cotton overalls), a long-sleeved shirt or jumper (cotton or wool), broad-rimmed hat, sturdy leather boots, goggles, gloves, and face mask.
      • cover all skin with a woollen blanket
    • battery operated torches including one in the roof space.
    • battery operated radio tuned to radio ABC.
    • during the fire front:
      • shelter from radiant heat inside the house away from windows and regularly patrol the house looking for embers to put out.
    • after the fire front has passed:
      • go outside wearing your protective clothing and extinguish any spot fires.

CSIRO 2012 recommendations to be safe in a bushfire

WHEN THE BUSHFIRE EMERGENCY MESSAGE IS “It Is too Late to Leave, You Should Take Shelter and Stay Indoors” - WHAT SHOULD YOU ACTUALLY DO?

IF YOU CANNOT SHELTER IN A BUILDING

  • Shelter behind a wall; beside a large fire resistant tree (that has no flammable undergrowth); in nor beside a car; in a dam (if no vegetation is near either), in a ditch, (cover yourself with earth or blanket); crouch beneath a blankets (must be PURE WOOL) on bare ground or an already burnt area.

IF YOU CAN SHELTER IN A BUILDING

Before you go inside:

  • Shut off gas and electricity at the mains.
  • Put pets inside: dogs on leash, cats in covered cages.
  • Take in outdoor furniture, doormats, hanging baskets, plastic pot plants.

When you are inside:

  • Make sure all doors and windows are securely shut.
  • Turn off air conditioners; cover their internal vents.
  • If windows are unshuttered, cover with blankets (must be PURE WOOL), heavy quality quilts, foil or wet towels.
  • Move flammable furniture away from windows.
  • Close internal doors to limit fire spread if embers enter and ignite inside.
  • Put on protective clothing and nose mask and drink often.
  • Keep blankets (must be PURE WOOL) handy.
  • Cool off when possible.
  • Watch the conditions outside if possible through a small window or peephole. Do not open a door or window to look outside.
  • When you are sure flaring shrubs have blackened, it’s safe to go out again. (Burning tree trunks do not generally emit killing radiant heat.)
  • PASSIVE SHELTERERS
    • DO NOT SHELTER IN AN INNER ROOM. Not in the hallway. Not in the bath. If you shelter in ANY kind of inner room – no matter how many doors it has – you could be trapped. Embers may have ignited sub-floor or wall cavities or rafters in the ceiling space,. Flaming walls or ceiling could collapse on you. Toxic fumes from smouldering furnishings, synthetic furniture or wall linings could overcome you.
    • STAY BY A DOOR THAT EXITS TO OUTSIDE in protective clothing and with blankets (must be PURE WOOL).
    • It is vital for passive shelterers to exit as soon as the potentially killing radiant heat from fames has died down.
  • ACTIVE SHELTERERS
    • Take hose, sprayers and ladder inside with you.
    • Fill bath & troughs with water, immerse towels, roll up and place at door gaps and window ledges. Plug keyholes with play dough, blue-tack or soap.
    • Fill containers (e.g. garden sprayers) with water; put these, with dippers, mops etc, in each room.
    • Watch for invading embers. Particularly in the ceiling space, through windows, gaps under doors. Spray or hit with wet mop any sparks, embers or smouldering furnishings.
    • If any ignition cannot be extinguished, close the door of that room.
    • Maintain easy access to an exit door.
    • Never go outside during a flame front to douse an outside ignition.
  • EXITING
    • Exit with great care, preferably from a door that is sheltered from the wind.
    • Wear protective clothing & nose cover, cover yourself with your blanket (must be PURE WOOL), crouch, lower your eyelids and open the door gradually.
  • The quintessential bushfire survival resource is a HEAVY DUTY PURE WOOL BLANKET
    • Covered with their blanket and with a flask of water people have withstood the most catastrophic conditions.

 

australia/bushfires.txt · Last modified: 2020/01/05 12:05 by gary1