Assessing the bushfire risks for different classes of buildings

Most of the design standards and recommendations for buildings subject to bushfires have been developed for detached, low-rise residential buildings as they have been the largest class of buildings destroyed in bushfires. However, there is a need for guidelines for the design of other classes of buildings such as public buildings, schools, offices, apartment buildings, hotels, motels, hospitals and aged care facilities which may be built in designated bushfire areas. These buildings are generally larger than detached houses and are occupied by many more people of different physical and mental capability. In addition, some of these buildings have post disaster functions. Traditionally these buildings are evacuated when the bushfire path is predicted to impact on the buildings to minimize the risk to the occupants' lives. This is a very disruptive and time-consuming exercise. However, more disruptive is the loss of the facility in a bushfire and the economic and social cost that results. The risk factors are defined for failure of the buildings under bushfire attack for the various classes of buildings. These risk factors include number of occupants, capability of occupants, bushfire attack level (BAL) of site, external cladding materials, building height and footprint, fire-fighting support, site accessibility, asset protection zones, maintenance of building, landscaping and evacuation procedures. The most significant hazard is that of ember attack which is a function of the nature of adjacent vegetation and distance from the dwelling. Resistance to ember attack is profoundly influenced by the building construction details as well as local landscaping. The risks from bushfire attack are assessed for each class of building. The requirements of the NASH Standard - Steel Framed Construction in Bushfire Areas are reviewed in the light of these risks and recommendations made for modifications to the NASH Standard for different building classes.