NCC 2019 Volume Two
2.9 Design scenario (UF)

2.9 Design scenario (UF)

Unexpected catastrophic failure

Design scenario in brief

The design will be suitably robust to prevent catastrophic structural failure in a fire.

Required outcome

Demonstrate that disproportionate failure does not occur for the duration of the fire event; and

Demonstrate that the level of safety be at least equivalent to the Deemed-to-Satisfy Provisions.

2.9.1 Design scenario description

The fundamental principles of the UF design scenario are that the building structure and/or critical elements should not suffer unexpected disproportionate failure during a fire event. This design scenario for the prevention of unexpected catastrophic failure aligns with the principles of structural robustness.

The unexpected catastrophic failure design scenario is intended to prevent unexpected catastrophic failure of a building component as a result of a fire event.

This design scenario assessment must be undertaken in conjunction with the structural engineer, to ensure that unexpected catastrophic failure should not occur for all critical elements. Ductility of the structure must also be considered so that visual cues that act as a warning occur prior to collapse.



This design scenario is intended to be used in conjunction with the fire brigade intervention (FI) design scenario. These two design scenarios will ensure that facilities for fire brigade intervention are appropriately incorporated.

2.9.2 Typical method or solution

Compliance with this design scenario is achieved by demonstrating that the building structure and components have considered the following elements during a fire event:


Assessment of the building structure and critical components such that upon the notional removal, in isolation, due to the fire event the probability of unexpected catastrophic failure of the entire element, or a significant proportion, is unlikely to occur.


Demonstrating that if a component of the building is relied upon to carry a significant portion of the total structure, a systematic risk assessment of the building is undertaken and critical high risk components are identified. High risk components are designed to cope with the identified hazard or protective measures chosen to minimise the risk during a fire event. The proportion of the structure that triggers this analysis will have a range that the designer will have to identify and justify.