MOVING FORWARD ON A VERIFICATION METHOD FOR BUSHFIRE

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MOVING FORWARD ON A VERIFICATION METHOD FOR BUSHFIRE PROTECTION UNDER THE NATIONAL CONSTRUCTION CODE.

Grahame Douglas Yaping HeSenior Lecturer Senior LecturerWestern Sydney UniversitySchool of Computing, Engineering and Mathematics


INTRODUCTION

• VM for bushfire protection has been advocated for some time (Douglas et al., 2006)

• ABCB is introducing risk based verification methods (VM) in support of qualitative performance requirements of NCC

• Draft GV5.1 released in 2014 for Bushfire Protection triggered technical discussion

• After some deliberation ABCB agreed further research warranted.• England (2016) undertook useful review and significant contribution

to the debate on acceptance criteria, notably on probability of fire initiation and weather considerations


HOUSE LOSSES AND FATALITIES ARISING FROM BUSHFIRES IN AUSTRALIA (BLANCHI ET AL, 2012)

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y = 4E-05x2 - 0.0062x + 1.8915R² = 0.9263

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Correlation between life safety and house loss.Cumulative fatality with increasing FFDI


HOUSE LOSSES AND FIRE WEATHER ASSOCIATED WITH 54 BUSHFIRE EVENTS

Data sourced from Blanchii et al, 2012)


HOUSE LOSS CONTEXT

Highest losses are associated with closer proximity to RUI.

Approx. 70% of houses are lost within first 25 metres without controls

House losses within 100-150 metres is approx. 10%

As seen, fire weather conditions are critical.


BUSHFIRE PERFORMANCE REQUIREMENT


DRAFT VM FOR BUSHFIRE PROTECTION (GVM5.1)

“Compliance with GP5.1 is verified if the probability of risk of ignition of a building is not greater than 20% when the building is exposed to a 1:25 year bushfire conditions event ………” (Draft NCC 2014)

Bushfire conditions expressed through FFDI. Is this appropriate?

Does not allow for human intervention.

Applied to Classes 1, 2 and 3 buildings. What about Class 4 and 9s?


TOWARDS A VERIFICATION METHOD

VM can include:• Calculations using analytical techniques or models, and• Tests of technical operation to measure performance.

No universally adopted method, however…

Method 2 of AS3959-2009 is used by bushfire practitioners and fire engineers (see also Douglas, Tan and Midgley; 2005).


DETERMINING RETURN PERIOD

Policy neutrality? What does this mean?

What is meant by fire weather – can FFDI (or GFDI) be used?

Some fire behaviour models use combinations of factors – e.g. wind speed and fuel moisture content.

Annual probability of exceedance is appropriate for rarer events.


DATA AND METHODOLOGY

Challenges are associated with:• Data availability• Model availability and validity; and• Methodology for determining extreme values.

Up to date BoM data utilised (Lucas, 2010; Douglas, 2016)

GEV method used and compared to existing AS3959-2009 values


COMPARATIVE ASSESSMENT OF FFDI VALUES


FIRE INITIATION INSIDE A BUILDING

Not many fires involving use of AS3959-2009 (or 1999).

Two Case studies – Wye River and Winmalee but limited data

Uncertainties in the data• Incorrect BAL assessment (Wye River)• Landscaping post approval• Intervention• Fire weather may be different on-site to that measured.


WYE RIVER (VICTORIA COAST) ASSESSMENT

Wye River (2015)• 80 approvals from May 2003.• 7 house losses AS 3959 compliant (?) representing 8.75% of total.• Higher losses from AS 3959-2009 than AS 3959-1999 but that does

not mean less effective.• Intervention (water bombing) may have assisted by sub-floors a

major source of ignition.• Fire weather conditions (FFDI=49) not excessive and often burning

downhill.


WINMALEE (NSW BLUE MOUNTAINS) ASSESSMENT

Winmalee (Oct, 2013)Fire behaviour extreme due to slopes and FFDI (80 at Richmond but lower at Springwood).

374 records of building approvals.

22 destroyed and 8 damaged represent 8% of houses lost.

Minimum level of intervention.


OTHER CLASSES OF BUILDINGS

England (2016) proposed to include Importance Levels (IL) for Bushfire Protection concept.


CONCLUSION

Development of risk based approaches and methods to bushfire performance is supported. IL’s supported for design variation .

Recurrence of 1:25 is too low (IL 2 buildings) and should be 1:50 for design bushfire (not bushfire conditions event). Queensland to increase to FFDI 80.

Design weather is regionally dependent.

Probability of ignition of 20% is too high and should be <10% based on limited data and case studies.


THANK YOU AND QUESTIONS

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MOVING FORWARD ON A VERIFICATION METHOD FOR BUSHFIRE