2.11 Design scenario (RC)
Design scenario in brief
Demonstrate that if a single fire safety system fails, the design is sufficiently robust that disproportionate spread of the fire does not occur (e.g. ASET / RSET for the remaining floors or fire compartments is satisfied); and
Demonstrate that the level of safety be at least equivalent to the Deemed-to-Satisfy Provisions.
2.11.1 Design scenario description
The key fire safety systems to be considered must be agreed as part of the PBDB.
Where the probability of failure of a single system failure is low and it is impractical to provide additional redundancies it may be acceptable to accept some exposure of occupants to untenable conditions. An appropriate deemed-to-satisfy building should be used to provide a benchmark.
Ideally, a comprehensive quantitative probabilistic risk assessment would be used to assess the safety of a design. However, the risk assessment tools and supporting data have not been included in this Verification Method. The framework currently permits a simple deterministic ASET / RSET approach with additional checks and balances.
As a general rule, when calculating ASET times, fire safety systems may be assumed to operate as designed, provided they are manufactured and installed in accordance with recognised national or international standards. However, in the situations designed above, additional fire safety systems provide the redundancy and robustness to fire safety designs.
2.11.2 Typical method or solution
In the circumstances described in the design scenario, assume the failure of each key fire safety system in turn as determined by the PBDB. If ASET cannot be shown to be greater than RSET for the building, apart from the room of fire origin, then the design must be altered until the requirements for ASET and RSET are achieved.