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Building in Bushfire-Prone Areas After Black Saturday
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Building in Bushfire-Prone Areas After Black Saturday
Requirements and limitations of the new Australian Standard on Construction of Buildings in Bushfire-Prone Areas

By Simon Carroll | Fire Protection Engineering

Australia is a land of contrasts, and the occurrence of natural disasters such as bushfires and floods at the same time in different parts of the country emphasize that this is a nation that is at the mercy of its environment. It is somewhat ironic that, in the last days of 2009, while floodwaters inundated vast areas of land in New South Wales on the east coast, severe bushfires destroyed approximately 40 homes in Western Australia.


It was during the early part of 2009 that the impact of perhaps the most significant natural disaster in Australia's history affected the way that Australians live within their environment. On Feb. 7, 2009, 173 people perished in Victoria as a result of bushfires - the "Black Saturday" bushfires - that swept across the State.1

 

ROYAL COMMISSION
It is a tragic fact that a disaster such as the Black Saturday bushfires becomes the catalyst for change. In the case of the State of Victoria, the circumstances surrounding the bushfires are the subject of examination by the 2009 Victorian Bushfires Royal Commission.

The Royal Commission (the Commission) is an administrative inquiry established by the Victorian Government on Feb. 16, 2009, to independently and publicly examine and provide recommendations for the involvement of the government or its agencies in an event such as the Black Saturday bushfires.1

 

Fifty-one recommendations were made by the Commission in its first interim report, which was published in August 2009. Those recommendations dealt mainly with actions to be implemented prior to the commencement of the 2009-10 bushfire season and included:1

  • The manner in which bushfire warnings are issued and the development of a new fire severity scale to identify the risk posed by bushfires;
  • The provision of information during bushfire events and arrangements for multi-agency sharing and use of bushfire information;
  • Arrangements to facilitate the ability for households or communities to relocate during bushfires, including amendments to operational policies of fire authorities to assess and recommend early relocation when warranted;
  • The provision of advice by fire authorities - via a "stay or go" policy - that not all homes are defendable in all circumstances and that the safest option is to leave early rather than to stay or defend;
  • The progressive identification, establishment and advertisement of designated community refuges, with priority given to areas where bushfire risk is identified as high;
  • In order to avoid confusion in relation to incident management, the development of procedures by agreement between the fire authorities to ensure that the most experienced, qualified and competent person is appointed as Incident Controller for each fire;
  • The requirement for the State to settle the higher level emergency management and coordination arrangements that are to apply during the bushfire season;
  • The encouragement of coordination between the Commonwealth and States/ Territories to ensure the rapid and effective use of Commonwealth resources during bushfire events, including the potential for resources to be used to detect, track and suppress bushfires.

A NEW STANDARD FOR CONSTRUCTION OF BUILDINGS IN BUSHFIRE-PRONE AREAS
One important regulatory change that pre-empted the interim recommendations of the Royal Commission concerned the construction of buildings in bushfire-prone areas.

 

Australian Standard 3959, "Construction of Buildings in Bushfire-prone Areas,"2 was published in 2009, approximately one month following the devastating Black Saturday bushfires. The new standard was adopted by the Victorian Government, via amendments to the Building Regulations 2006,3 on March 11, 2009.

 

The March 2009 amendments to the regulations related to residential buildings (or residential parts of buildings) including single dwellings, duplexes, boarding houses, guest houses, hostels (or the like), residential flat buildings and residential parts of buildings such as hotels, motels, schools, healthcare buildings and detention centers. The amendments also relate to non-habitable buildings associated with residential buildings, for example, private garages and sheds.4

 

 

From a legislative point of view, the buildings covered by the amendments to the Building Regulations are those identified as Class 1, 2, 3 and 10a buildings for the purposes of the Building Code of Australia (BCA).

 

The BCA details provisions for the design and construction of buildings and other structures in Australia. Australian Standard 3959-2009 is referenced in the 2010 edition of the BCA, which came into force as of May 1, 2010.4

 

AS3959 contains cautionary notes to advise that compliance with the requirements of the standard do not guarantee survival of a building. In Section 11 (Scope), the following is noted:2

 

Although this Standard is designed to improve the performance of buildings when subjected to bushfire attack in designated bushfire-prone areas, there can be no guarantee that a building will survive a bushfire event on every occasion. This is substantially due to the unpredictable nature and behaviour of fire and extreme weather conditions.
 

The objective of AS3959 is to prescribe particular construction details for buildings to reduce the risk of ignition from a bushfire while the fire front passes.

 

AS3959 identifies a "bushfire-prone area" as "an area that is subject to, or likely to be subject to, bushfire attack."

 

Importantly, AS3959 only applies if the site and building are located in a designated bushfire-prone area as defined by the BCA. The BCA defines "designated bushfire-prone area" as:4

 

land which has been designated under a power of legislation as being subject, or likely to be subject, to bushfires.
 

What is, or is not, land within a "designated" bushfire-prone area varies between virtually every state and territory within Australia. In Victoria, the March 2009 amendments to the Building Regulations apply to the effect that a reference in the standard to a bushfire-prone area or a designated bushfire-prone area is a reference to the whole of Victoria. AS3959, therefore, applies to the entire State of Victoria and a site-specific assessment should be undertaken.

 

The process of determining construction requirements for the purposes of AS3959 requires an initial determination to be made as to the Bushfire Attack Level (BAL) for the particular building. This determination is made via an assessment of the site (of the building) and the vegetation impacting the site.

 

There are six BALs identified by AS3959, based upon heat flux exposure thresholds. An abridged version of Table 31 from AS3959 is reproduced in Table 1,2 which describes the predicted bushfire attack and levels of exposure for each BAL.

 

While not discussed in more detail here, AS3959 provides two methods for the determination of the BAL: a simplified procedure or a detailed procedure.

 

One of the key features of AS3959 is that the standard seeks to prescribe a deemed-to-satisfy solution for any building built within 100 meters of vegetation that is identified as a bushfire hazard. This has also been one of the main criticisms of the new standard.

 

The adoption of AS3959 was opposed by two significant stakeholders on the FP-020 committee, Australasian Fire and Emergency Service Authorities Council (AFAC) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The main reason for the opposition of AFAC, in particular, was that organisation's belief that there are serious flaws in the new standard. The clear message from the opposition to the adoption of the standard is that construction standards in bushfire-prone areas need to be much tougher.5

 

The reasons for AFAC's opposition included: 6

  • Provisions for construction in the flame zone (highest level of risk) - any home/building that is being constructed in these areas (flame zone) needs an individual assessment and needs to be individually designed to the specific fire risks the property faces.
  • Gaps - the new standard specifies gaps to be up to 3 mm (or of an unspecified size if sarking is used behind the gap), allowing for a much greater likelihood of ember ignition of roof cavity, wall cavity and the occupied spaces within the house. Sarking (or, more specifically, sarking-type material) is defined by the BCA as "a material such as a reflective insulation or other flexible membrane of a type normally used for a purpose such as water proofing, vapor proofing or thermal reflectance".4
  • Test methods - there are reservations about test methods identified by the standard for determining the performance of components under bushfire conditions.
  • Subfloor requirements for BAL 12.5 and BAL 19 - the new standard has no requirements for subfloors or to prevent the spread of fire from adjacent decks into the subfloor of the building.
  • Grasslands - the new standard provides no requirements for this fuel type.
  • Issues relating to doors, windows, shutters and wall barriers.
  • Egress - no consideration of requirements for the egress path or destination.
  • No provisions for ongoing maintenance - to ensure compliance to the standard for the life of the building.

The issues relating to construction in the flame zone, gaps (aperture size of window mesh and perforated sheeting), test methods, subfloors, grasslands, doors, sarking-type material and glazed elements are identified in the Preface to AS3959 as being issues that are likely to be reconsidered by the FP-020 committee for inclusion in a future edition of the standard or as amendments to the standard. The preface to AS3959 also notes that the committee will review the standard, including construction in the flame zone, following the outcomes of the 2009 Victorian Bushfires Royal Commission.2

 

PRIORITIES FOR BUILDING IN BUSHFIRE-PRONE AREAS
The second interim report of the 2009 Victorian Bushfires Royal Commission - Priorities for Building in Bushfire-Prone Areas - was published in November 2009.

 

The commission's second interim report contained seven additional recommendations, with specific reference to the commission's terms of reference, which require it to "consider and make recommendations on the fireproofing of houses and other buildings, including the materials used in construction".7

 

In relation to AS3959, the commission heard evidence in relation to several issues relating to the standard, including:7

  • The apparent weakening of the intent of the standards via a combination of no requirements for subfloor materials and the allowance of grassland fuels right up to the structures;
  • Key concerns regarding the use of sarking-type material behind wall cladding, effectively as a secondary ember-protection measure, in the absence of any definitive testing of such material to determine its performance as an ember barrier;
  • Concerns that AS3959 provides for a lesser level of ember-protection measures for BAL 12.5 and BAL 19 in the areas of subfloors and material prescriptions for doors, windows and wall barriers (than the 1999 version of the standard).

The recommendations made by the commission in its second interim report7 included amendments to AS3959 to:

  • address the inclusion of unmanaged grassland in the vegetation types and classifications, and use of sarking as a secondary ember-protection measure; and
  • increase ember-protection measures at lower Bushfire Attack Levels, in particular in relation to subfloor requirements and materials prescribed for doors, windows and wall barriers.

REBUILDING
In the meantime, recovery and rebuilding efforts are well under way.

 

The first interim report of the Royal Commission noted that in excess of 2,200 homes were lost during the Black Saturday bushfires on February 7, 2009.1

 

The rebuilding process is a key part of the recovery of individuals, families and communities affected by any natural disaster, especially one of the scale and intensity of the Black Saturday bushfires.

 

It is apparent that the publication of AS3959, and its subsequent adoption in Victoria via amendments to the Victorian Building Regulations, was intended to clear the way for the rebuilding process to commence as soon as possible after the devastation of Black Saturday.8

 

The process has not been without its problems, however.

 

The issues identified by stakeholders in relation to the standard, particularly those in relation to provisions for construction in the flame zone (that is, those buildings assessed as being subject to BAL-FZ) have translated to delays for rebuilding.

 

A significant criticism of authorities has been that rebuilding efforts are being hampered by bureaucratic delays and an obsession with process.9 The criticisms have seized upon the perception that there does not appear to be any defined policy from regulators as to how to deal with issues with building in the flame zone. As a result, rebuilding has been slow due to the continued disagreement of how to deal with houses identified as being subject to BAL-FZ under AS3959.

 

The challenges facing those wishing to rebuild have been acknowledged by the Victorian Bushfire Reconstruction and Recovery Authority (VBRRA). A key contributing factor to delays in plans for rebuilding has been identified as a lag in terms of the availability of building materials that are approved as being suitable for use in BAL-FZ situations.5

 

The issues relating to the unavailability of building materials have been most prevalent in terms of requirements to install bushfire (proof) shutters or fire-rated window systems10 in BAL-FZ situations.

 

The VBRRA identified the availability of an increased range of BAL-FZ-compliant materials as helping to reduce delays in rebuilding efforts.5

 

Cost is another significant issue for those people seeking to rebuild their homes. Anecdotal evidence suggests that the costs associated with achieving the construction requirements for buildings proposed to be rebuilt in the most extreme bushfire areas could amount to an additional $22,000 (AUD) for fire safety measures on top of the usual construction costs.8

 

While the State Government has indicated that the Victorian Bushfire Appeal Fund was likely to make some funds available to help compensate for rebuilding costs, there has been no decision to commit the fund to meeting all of the extra expenses for the bushfire victims relating to the achievement of the additional construction requirements of AS3959-2009.8

 

The Royal Commission plans to deliver its final report by July 31, 2010, on its investigations of the causes and responses to the bushfires that swept through parts of Victoria in late January and February 2009.

 

The recommendations made in the commission's final report will be intended to minimize the likelihood of a recurrence of the tragedy of February 7, 2009.1

 

A review of AS3959 following the release of the commission's final report will have the benefit of the commission's findings and recommendations to assist in shaping future editions of the standard.

 

Simon Carroll is with Australian Bushfire Assessment Consultants.

 

References:

  1. Interim Report, Victorian Bushfires Royal Commission, Melbourne, Australia, 2009.
  2. Australian Standard 3959, "Construction of buildings in bushfire-prone areas," Standards Australia, Sydney, 2009.
  3. (Victorian) Building Regulations, Building Commission, Melbourne, Australia, 2006.
  4. Building Code of Australia, Australian Building Codes Board, Canberra, Australia 2010.
  5. Blundell, L. "Rebuilding After the Bushfires," The Fifth Estate, 17 December 2009.
  6. Llewellyn, R. "New AS:3959 Building in Bushfire-Prone Areas," kw news, Australian Fire and Emergency Service Authorities Council, East Melbourne, Australia, March 2009.
  7. Interim Report 2, Victorian Bushfires Royal Commission, Melbourne, Australia, 2009.
  8. Rood, D. & Dowling, J. "Bushfire Rebuilding to Cost Victims $22,000 Extra," Stock & Land, March 8, 2009.
  9. Bachelard, M. & Beck. M. "Bushfire Rebuilding a Failure," Stock & Land, May 2, 2010.
  10. Draper, M., "Bushfire Rebuilding Is a Pain: Resident," Sydney Morning Herald, August 24, 2009.

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