NCC 2019 Volume Two
2.10 Design scenario (CF)

2.10 Design scenario (CF)

Challenging fire

Design scenario in brief

A fire starts in a normally occupied space and presents a challenge to the building’s fire safety systems, threatening the safety of occupants.

Required outcome

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

2.10.1 Design scenario description

The challenging fires are intended to represent the credible worst case design scenario in normally occupied spaces that will challenge the fire protection features of the building.

This design scenario requires the use of design fires in various locations within the building.

The design fires must be characterised with a steady state fire, or a power law HRR, peak HRR and FLED. Design values for yields are specified for soot/smoke.

The design fires must be modified during an analysis (depending on the methodology used) to account for building ventilation and the effects of automatic fire suppression systems (if any) on the fire. The design scenario RC (2.11) will require the overall robustness of the design to be examined separately.

The designer must—


for each location of the challenging fire, use a single fire source to evaluate the building’s protection measures; and


consider the impact on occupants who may be using escape routes external to the building as well as internal routes; and


assume that active and passive fire safety systems in the building will perform as intended by the design.

Explanatory information:

Explanatory information:

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.

2.10.2 Typical method or solution

This design scenario requires the ASET/ RSET analysis of the impact on all building occupants with design fires located in various locations within the building, except for those rooms or spaces excluded in the design scenario described above.

The designer must calculate the fire environment in the evacuation routes over the period of time the occupants require to escape. Assess the fire environment based on the FED and visibility at the location of the occupants.

The designer must select a fire calculation model appropriate to the complexity and size of the building/space that allows the FED and visibility to be determined.