Assumed Redundancies for Life Safety Design
Fire brigades are to be treated as a redundancy in the fire safety strategy, and therefore should not be included in the assessment of adequacy of a fire safety strategy. The fire safety strategy has to provide an adequate level of safety independent of presumed fire brigade intervention.
– Quantify consequences of no fire brigade intervention, by undertaking an analysis that doesn’t include this. – Make design decisions based on the outcomes of the analysis and the acceptable risk.
2(B)
Demonstrate that structural timber doesn’t affect the available safe egress time (ASET) by either:
Impact on Escape from Area of Fire Origin
The contribution of the combustible structure to fire growth should be demonstrated to be negligible in the enclosure of fire origin during the escape of occupants from within. Alternatively, provisions will have to be included that consider such contribution in a manner that does not adversely affect the available safe escape time from the enclosure of fire origin.
– Applying ADB/BS 9999 recommendations, ie. reaction to fire of exposed surfaces, or – Ensure there is no ignition of the surface linings (including the timber) prior to the last person leaving the compartment of fire origin, or – Demonstrate through a full assessment that flame spread over the surface linings (including the timber) will not happen at a stage that adversely affects evacuation from the compartment of fire origin.
3
Addressing internal spread:
– Retain appropriate levels of compartmentation. – Decide appropriately challenging design fire scenarios. – Characterise internal fire. – Assess capacity of compartmentation to mitigate internal fire spread.
Mitigating Internal (Vertical) and External Fire Spread
In all but the lowest consequence class, if the structure is allowed to contribute as a source of fuel, it should be explicitly demonstrated that the fire will not spread beyond the storey of origin. This should include an explicit demonstration that internal and external detailing is sufficient to achieve this outcome.
Addressing external spread:
4(A)
– Decide appropriately challenging design fire scenarios. – Characterise external flame. – Determine heat flux from characterisation of external flame. – Identify threshold to evaluate against. – Include appropriate design provisions to mitigate circumvention of compartmentation.
7 2
F I R E
Made with FlippingBook - professional solution for displaying marketing and sales documents online