Assess the prospect of external fire spread to neighbouring buildings, through either of:
Mitigating Internal (Vertical) and External Fire Spread
– Applying the principles of BR187 (but capturing the increased fire load due to the combustible structure and increased external flaming). – Undertaking full first principles external fire spread assessment, where the external flaming is characterised.
4(B)
In all cases it should be explicitly demonstrated that the fire will not spread to neighbouring buildings.
Mitigating Internal (Horizontal) Fire Spread
Similar procedure to 4(a) (internal), but applied horizontally:
Compartmentation should be such that all occupants have an adequate opportunity to remain safe. This includes all occupants with limitations that might complicate or limit their capacity to reach a place of safety. If a Personal Emergency Evacuation Plan (PEEP) is required, this will have to be constructed in a manner that suitably accounts for the use of structural timber.
– Retain
appropriate
levels
of
horizontal
compartmentation. – Decide appropriately challenging design fire scenarios. – Characterise internal fire. – Assess capacity of compartmentation to mitigate internal fire spread during the required safe egress time (RSET). – Define expected mechanical functionality. – Define performance threshold. – Decide appropriately challenging design fire scenarios. – Carry out analysis to quantify mechanical behaviour under those scenarios. – Assess performance relative to threshold. – For encapsulated structure see Principle 7, for exposed mass timber see Principle 8.
5
Expected Performance of Structure and Compartmentation
The construction should deliver its expected mechanical functionality as regards compartmentation and structural performance until the combustion of the contents and combustible structure has stopped (and accounting for the decay and cooling phases of the fire, where necessary).
6
Survival of Burnout with Encapsulated Mass Timber
Within the process of qualifying principle 6, the following would apply:
For cases where the structure is intended to survive burnout and the structural protection strategy used is encapsulation, it should be explicitly demonstrated that the encapsulation will prevent the ignition of the timber structural elements being encapsulated for the duration of the expected fire scenarios. Given the natural performance uncertainties of encapsulation, explicit safety factors and redundancies will need to be included.
– Decide appropriately challenging design fire scenarios. – Define performance threshold for ignition. – Carry out analysis for the identified scenarios. – Assess criteria relative to the threshold.
7
F I R E
7 3
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