NCC 2019 Volume Three
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2.11 Design scenario (RC)

2.11 Design scenario (RC)

Robustness check

Design scenario in brief

The fire design will be checked to ensure that the failure of a critical part of the fire safety system will not result in the design not meeting the Performance Requirements.

Required outcome

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

This design scenario applies where failure of a key fire safety system could expose occupants to untenable conditions. The key fire safety systems must be agreed as part of the PBDB.

Comment:

Comment:

The key fire safety systems to be considered must be agreed as part of the PBDB.

This particular design scenario focuses on the ASET / RSET life safety calculations performed as part of the design scenario CF challenging fire (2.10).

The robustness of the design must be tested by considering the design fire with each key fire safety system rendered ineffective in turn.

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.

Explanatory information:

Explanatory information:

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.