short fire run - fpa australiashort fire run › calculated where the fire is running perpendicular...

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SHORT FIRE RUNASSESSING BUSH FIRE RISK FROM SMALL AREAS OF VEGETATION

John Delany and Stuart MatthewsCommunity Resilience

New South Wales Rural Fire Service


SHORT FIRE RUN

To provide a robust methodology that identifies

the bush fire impact of lower risk bush fires

burning on the bushland interface.

Intent …


SHORT FIRE RUN

1. the difference between a Short Fire Run (SFR) and a Fully Developed Fire (FDF)?

2. a deterministic model to ‘factor down’ APZ’s based on thelower risk provided by a partially developed bush fire.

To address the intent we need to identify …


SHORT FIRE RUN

SFR’s are currently assessed as if they are;• large scale hazards;• have the existing vegetation downgraded to rain forest (lower fuel

load); or• by ‘expert’ judgement.

‘These practices can result in onerous bush fire protection measures and lead to inconsistent treatments’’.

Issues …


SHORT FIRE RUNWhat is a SFR …

Aerial picture not to scale and indicative only


SHORT FIRE RUNA SFR is …



SHORT FIRE RUNA SFR is not …


Has connectivity to vegetation that will support a FDF.


SHORT FIRE RUN

For the purposes of modelling, a SFR is …› a small low risk fire not expected to crown (usually taken as not

exceeding a fire run of 150 metres and burning perpendicular to contours and directly at an asset).

› a small low risk fire having a calculated maximum head width not exceeding 100 metres;

› on downslope not exceeding 30 degrees;› on site slope not exceeding 20 degrees;› on up slope not exceeding 15 degrees;

How is SFR assessed …


SHORT FIRE RUN

For development application purposes a SFR is considered to be a performance evaluation and as such site specifics need to be identified to model the design fire …

1. Assess site as per requirements of AS3959 Method 2 steps 1 > 5;

2. Calculate SFR flame height using Project Vesta methodology;

3. Calculate the SFR head width;

4. Calculate SFR radiation (kWm2);

How is SFR assessed … cont’d


SHORT FIRE RUN

5. Calculate Bush Fire Attack Level (BAL).6. Apply appropriate construction requirements to mitigate the

calculated bush fire impact.

Note:2 models have been developed;

• Forest / Woodland developed using MacArthur 1973 and Noble et al. 1980 and Project Vesta.

• Heath – developed using Byram’s equation (Heath and Shrub Model).

How is SFR assessed … cont’d


SHORT FIRE RUNSFR fire growth …

Point of origin

Wind direction

Downslope



Wind direction

Downslope



Wind direction

Measuredfire run

Site slope

CalculatedHead Width


SHORT FIRE RUN

The SFR model has the following limitations and assumptions.

› wind direction and speed is constant in the direction of fire spread;› slope is considered uniform throughout the length of the fire run;› flaming is restricted to surface, near surface and elevated fuels only

for forest & woodland vegetation;› Heath, Shrub, Mallee & Tussock Moorland formations. Average

height is determined on site and by vegetation classification;

SFR limitations and assumptions …


SHORT FIRE RUN

› fuel load is distributed equally and is continuous for the entire fire run length;

› The fire develops from a single ignition point and does not include ignition time, fire growth or fuel moisture;

› The fire is not expected to crown;

SFR limitations and assumptions … cont’d


SHORT FIRE RUN

› calculated where the fire is running perpendicular to contours and directly at an asset whilst also not having direct connectivity.

› limited to 150 metre fire run length (measured on the effective slope);

› limited to maximum input of 2 metres for elevated fuel (Project Vesta) in forest formations only.

SFR limitations and assumptions … cont’d


SHORT FIRE RUNSFR development …

The size and shape of a bush fire hazard influences the behaviour of bush fire and the associated risk to the built environment.


SHORT FIRE RUNFire shape development…

Simple elliptical fire growth model (Van Wagner 1969).



RFS has adopted a wind speed of 30 kph for assessing SFR design fires



Speculative Head Width= 2/3rd of ellipse breadth


SHORT FIRE RUNBushfire fuel structure (Forest) … is presented in 3 tiers

Drawing courtesy ‘DSE Overall fuel Hazard guide’ 4th edition.

High

Medium

Low

2 metresmax. for Project Vesta


SHORT FIRE RUNSurface, near surface & elevated fuel loads (Project Vesta) …

An additional input is required for fuel height. Those inputs represent the height value for the three fuel structure forms, surface, near surface & elevated fuels with a further sub classification of tall, medium and low being identified for each tier.

That is:Three defined fuel tiers;

• Surface (Low) = 0 - <0.9 metres;• Near surface (Medium ) = >0.9 - <1.4 metres• Elevated (Tall) = >1.4 – 2.0 metres


SHORT FIRE RUN

• The SFR Methodology provides a more appropriate determination of the bush fire impact of lower risk vegetation located on the bushland interface.

• The SFR Methodology represents a combination of existing science and new data.

• This results in a more appropriate fire protection based on hazard.

Conclusion …


SHORT FIRE RUN

Thank you …

QUESTIONS?

short fire run - fpa australiashort fire run › calculated where the fire is running perpendicular...

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