Bush fire building safety advice

1. Bush fire building safety advice Ralph Smith Fire & Emergency Services Authority

3. People and Bush Fires • Greatest threat to people is radiant heat • Critical to protect people and buildings from radiant heat and direct flame contact • Most bush fires are started by people

4. Buildings and Bush Fires Buildings are affected by three main factors: • Burning debris – embers • Radiant heat • Direct flame contact • Most homes are lost to ember attack

5. Limiting Vulnerability FESA and local governments publish information on fire risk Limiting the fuel quantity around communities and buildings Limiting extremes in fire behaviour by the appropriate placement of building – slope Limiting ember attack through materials and building design Water supplies

7. Limiting Vulnerability • Ember attack – Jarrah forest type fuels • Spotting distances associated with the Jarrah forest • Fibrous bark main source of firebrand • More embers are generated from the older fuels – around double the number of embers between the 5 year old fuel and the 22 year old fuel

9. Limiting Vulnerability - Slope • Fire rates of spread (RoS) increase upslope

10. Radiant heat and flame contact • By maintaining the building protection zone (BPZ) and hazard separation zone (HSZ) will reduce the potential for radiant heat and direct flame contact • As a general guide when planting shrubs determine the height they will grow and then double it to get the planting distance from the house

11. Radiant heat and flame contact • Try and maintain a gap of between 10 – 15 metres between trees • Be careful not to place plants that may compromise the integrity of the building – windows can be a weak point and allow embers to enter

13. BPZ & HSZ

14. Low Bush Fire Hazard Include • Areas devoid of scrub vegetation & thinned overstorey • Areas due to climatic conditions do not experience bush fires

17. Reducing the Hazard • Choose a method that you know you can apply for the long term • It may be: • Burning • Slashing • Parkland clearing

18. Hazard Separation Zone • To achieve a fire of intensity of around 2000 kW/m requires a fuel load of less than 5 t/ha when the FFDI - 80 • This equates to a parkland type of vegetative cover

19. Hazard Separation Zone • Research undertaken by McArthur from the CSIRO indicates that a fuel load of less than 8 t/ha will not support a crown fire

20. Building Protection Zone • To achieve a fire of intensity less than 800 kW/m requires a fuel load of around 2 t/ha when the FFDI - 80 • This does not equate to a cleared area, but a managed area with appropriate vegetative cover

21. Building Protection Zone • Have a 2 m gap between trees and houses – no overhanging limbs • Prune the low limbs of trees to 2 m • Cut the long grass and dense scrub • Rake up the leaves and twigs • Plant shrubs singularly • Prune the dead material from the shrubs

23. Scorch in the crown Low intensity fire near to the house

24. Tree crowns Burnt shed

26. House damage – low intensity fire ember attack

28. How to Assess your Hazard • Determine the vegetation type and class • Determine the slope • Determine the distance between predominant vegetation class and the site

30. Hazard & AS 3959

31. Hazard Separation Zone • The distance between the predominant vegetation and the building is critical in determining the level of protection required from the: • Potential ember attack • Flame contact • Radiant heat

32. HSZ – AS 3959 • As the distance between the predominant vegetation reduces the construction standard increases (+ BPZ) • Forest >100m – no increased construction • Forest 60 – 100m (medium) – level 1 • Forest 35 – 60m (high) – level 2 • Forest < 35m (extreme) – do not build

33. Fuel levels • At an FFDI of 80 • HSZ – To achieve a fire of intensity of around 2000 kW/m requires a fuel load of less than 5 t/ha • BPZ - To achieve a fire of intensity less than 800 kW/m requires a fuel load of around 2 t/ha

34. Thank you