2.12 Design scenario (SS)
Design scenario in brief
The fire design is used to demonstrate that the structural response of a building in a credible worst case design scenario does not present an unacceptable risk to other property.
Demonstrate that the building does not present an unacceptable risk to other property due to collapse or barrier failure resulting from a fire; and
Demonstrate that the level of safety be at least equivalent to the Deemed-to-Satisfy Provisions.
2.12.1 Design scenario description
A fundamental requirement of CP1 and CP2 is that a building should not present a risk to other property in a fire event. The purpose of this design scenariois to demonstrate that a building does not present a risk to other property during a fire event that has the potential to impact on the building’s structure.
Unlike the CF design scenario, the worst credible case fire for this design scenario must be located within any space of the building rather than only within an occupied space. It is likely that several different fire design locations will be required to be tested to determine the location of the worst credible case fire.
The designer must—
for each location of the design fire, use a single fire source to evaluate the building’s protection measures; and
consider the impact on occupants who may be using evacuation routes external to the building as well as internal routes.
Both CF and SS design scenarios refer to credible worst case design fires. These may not necessarily be the same design fire, as they relate to different safety systems of the building.
2.12.2 Typical method or solution
The impact of a fully developed fire in the worst-case location on the structural stability of a building must be assessed.
Simultaneous and individual failures of active fire suppression systems (if provided), delayed fire brigade intervention and premature failure of structural fire protection should be considered and probabilities assigned to the occurrence of each of the events and the outcomes predicted.
If a simplistic approach is adopted the outcomes and probabilities of each combination of outcomes should be predicted and compared with a deemed-to-satisfy benchmark building.
Typically the fire safety engineer, with the assistance of a structural engineer, would demonstrate that appropriate features have been incorporated into the building which either—
- ensure the risk of collapse is equivalent or less than a similar deemed-to-satisfy structure; and
- there is no increased risk from outward structural collapse compared to a similar deemed-to-satisfy structure; and
- the risk to life for the subject building is no greater than that for a similar deemed-to-satisfy structure.