Bushfires (Wildfires) IRCC Workshop Australia, 2011 Jon S. Traw PE Traw Associates Consulting

Transcription

1 Bushfires (Wildfires) IRCC Workshop Australia, 2011 Jon S. Traw PE Traw Associates Consulting

2 Topics Covered Status of Global Approaches to Bushfires Bushfire Threat Area Risk Bushfire Attack Mechanisms Conclusions of Workshop

3 Almost all countries have management plans for fire but with variations as to actual activities Objectives Reduce number of human-induced fire ignitions Manage fuel Reduce vulnerability by improving preparedness Effective means to contain fires

4 Only Two Countries Have Building Regulations Intended To Mitigate The Impact of Bushfires Australia United States

5 Bushfire Threat Area In 1976 Pres Butler coined the term Urban Wildland Interface (UWI) Within distances of a few feet, two distinct and noncompatible environments can be recognized the building, where fire must be controlled at all times, and the bush where fire is a perfectly natural part of the ecology. The boundary between these two environments is called the interface.

6 RISK What is Risk? The possibility of an unwanted outcome in an uncertain situation, where the possibility of the unwanted outcome is a function of three factors: loss or harm to something that is valued, the event or hazard that may occasion the loss or harm, and a judgment about the likelihood that the loss or harm will occur. NAP 1996, Meacham 2004

7 RISK to What? What Are the Desired Outcomes Property Protection People Protection Both Likelihood (Probability) Consequences X (Damage and/or Life = Loss) Risk

8 Bushfire Exposure Australia AS Set by Bushfire Attack Level (BAL) United States Set by Mapping

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10 Fundamental Question Property Protection? United States Ready Set Go People Protection? (or) Both? Australia

11 Principal Factors Presence of significant vegetation within or adjacent to populated areas Societal desire to be in remote areas Nature of risk probability of fire and anticipate consequences Acceptance of risk as a matter of public policy Acceptance of risk by individuals or general public Economic implications of enacting building regulations for bushfire threats

12 Bushfire attack mechanisms Three primary mechanisms embers, radiation and flame contact, either individually, or in combination Vince Dowling, CSIRO

13 The role of radiation More difficult to ignite materials by radiation in the absence of a pilot [Drysdale; Poon] Radiation from the flame front accounts for a maximum of 10% of the house losses in bushfires each year [Leonard et al, CSIRO] In 2003 Canberra fires, it was 0% [Blanchi and Leonard] Vince Dowling, CSIRO

14 Impact of radiation - calculated Annual average house loss due to bushfires Region Exposed Number Value proportion radiation embers radiation embers NSW $564,400 $5,079,600 Victoria $415,000 $3,735,000 Queensland $315,400 $2,838,600 SA $132,800 $1,195,200 WA $166,000 $1,494,000 Tasmania $33,200 $298,800 NT $16,600 $149,400 ACT $33,200 $298,800 Australia $1,660,000 $14,940,000 Vince Dowling, CSIRO

15 Victorian Royal Commission Report Report references 60 years of research most houses ignited by wind-borne embers, rather than by direct flame contact or radiant heat presence of people to control spot fires greatly increases the likelihood of a building surviving

16 When is a house destroyed? Research has shown: Always more destroyed houses than damaged houses Very few badly damaged houses Damaged is usually light damage Vince Dowling, CSIRO

17 Why no badly damaged? Research has shown Houses do not explode Houses do not burn down from the outside If the fire does not gain ingress to the house, only minor damage If the fire does gain ingress to the house, but no flashover, only minor damage If the fire does gain ingress to the house, and flashover does occur, house is destroyed Vince Dowling, CSIRO

18 Duration of ember attack Duration of ember attack varies from fire to fire Ember showers: commence long before a fire front arrives continue for many hours after the fire front has passed [Ramsay et al; Leonard; Blanchi and Leonard] Vince Dowling, CSIRO

19 Distance of ember travel spot fires Fire location and year Distance Reference (m) Wandilo, SA, Luke and McArthur Los Angeles, USA, NBTC Hobart, Tasmania, Wettenhall Sakata City, Japan, Babrauskas, p 501 Glengower-Creswick, Victoria, McArthur et al Melton, Victoria, Maynes and Garvey Avoca/Maryborough, Victoria, Maynes and Garvey Oakland Hills, Cal., USA, Pagni Cedar, Cal., USA, Mitchell Vince Dowling, CSIRO

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21 What impact do embers have? Factors that make ember attack so dangerous include: their ability to ignite both vegetation and structures the prolonged duration of the ember attack the enormous quantity of embers produced the long distances they can travel Vince Dowling, CSIRO

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33 Researching ember attack Questions about embers that need to be addressed : their nature; their mode of transport; and their ability to ignite materials used in structures. Vince Dowling, CSIRO

34 Bushfire attack research Data needed: ignition source ignition scenario material first ignited how fire progressed Vince Dowling, CSIRO

35 Wood fence impact on houses

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37 Australian Activities ABCB agreed to develop a performance standard for design and construction of private use bushfire bunkers Standards Australia directed to develop appropriate methods of testing external building elements exposed to bushfire Standards Australia amend AS and AS so that the "methods provide a reliable predictor of the performance of construction elements under bushfire conditions."

38 SUMMARY OF MAJOR CONCLUSIONS 1. Must decide on goal Property Protection People Protection Both 2. Mechanism of failure not well understood Field data collection needs significant improvement Laboratory validation necessary 3. Primary research focus on embers

39 SUMMARY OF MAJOR CONCLUSIONS 4. Characterization of vegetation 5. Representation of exposures 6. Understanding relationship between structure ignition mechanisms and structure loss mechanisms 7. Availability of existing data 8. Coordination of research efforts

40 Observations 1. Research dedicated directly to the quantification of exterior fire exposures has not been well coordinated. 2. The complexity of factor influencing the impact of exterior fire exposures is not yet well understood. 3.Research that has been conducted has not been aggregated and research gaps have not been sufficiently identified.

41 THANKS FOR YOUR ATTENTION!

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