Departures from the Acceptable Solutions can be minor, major or multiple. A departure from Verification Method C/VM2 would need to be undertaken by a suitably qualified fire engineer.
Minor departure from the Acceptable Solutions
A minor departure from the Acceptable Solutions may require a simple qualitative, or perhaps quantitative analysis. This will typically require a good level of understanding of fire engineering design principles and of the Acceptable Solutions.
The most common justification for a minor departure from the Acceptable Solutions is some kind of compensatory or mitigating feature or features (refer example below). Alternative solutions can be justified using a comparative approach (eg International Fire Engineering Guidelines), where the proposed building design is demonstrated to provide a level of life safety at least equal to the Acceptable Solution.
By understanding the holistic nature of fire design and the construct of the relevant Acceptable Solution a fire engineer/designer should be able to propose various features that achieve the required performance criteria of the Building Code.
Justification for the departure from Acceptable Solutions may be provided, in some instances, with a qualitative reason (based on judgement). A demonstrated knowledge of the Acceptable Solutions for Protection from Fire is required to undertake a single minor departure from the Acceptable Solutions.
Example: Extended travel distance
A building complies with the relevant Acceptable Solution apart from a minor extension to the travel distance.
In this case, compliance with Code clauses C4.3 and C4.5 (which relate to the toxicity of smoke and reliability of systems) needs to be addressed. The design solution could involve proposing a smoke detection system to provide early warning where one is not otherwise required to compensate for longer travel time. Alternatively the building might have a very high ceiling, which would allow for longer escape times.
In either of these cases a quantitative comparative approach could be used to demonstrate compliance with the Building Code. In the first instance the Required Safe Egress Time (RSET) in the proposed building could be demonstrated to be less than in the reference Acceptable Solution compliant design by calculating the increase in travel time compared to the decrease in detection time. In the second justification case the Available Safe Egress Time (ASET) could be calculated in the design building and, due to the smoke filling volume of the building, shown to provide a greater improvement in the ASET-RSET determination than the delay resultant from the extra travel time.
Major or multiple departures from the Acceptable Solutions
For more complex alternative solutions involving a significant departure or a number of departures from the Acceptable Solutions, quantitative fire engineering analysis will almost certainly be required.
This requires a higher level of understanding of fire safety design, the Acceptable Solutions and Verification Method, and the inter-relationship between various aspects of these.
This type of alternative solution is similar to the one described above (a single minor departure). However, it is scaled up in terms of complexity as the fire engineer needs to carry out analyses and consider the effect of each proposed departure on the others.
One approach to demonstrate Building Code compliance would be to use the appropriate design scenarios from Verification Method C/VM2 as a quantitative assessment.
It should be noted that the level of complexity of the proposed design is expected to be reflected in the complexity of the design review and approval process agreed with the building consent authority (BCA). The fire engineer should bear this in mind when proposing a certain compliance methodology.
Example: Multiple departures from the Acceptable Solutions
An office building complies with the Acceptable Solutions apart from longer travel distances and a reduced exit width.
In this case, an appropriate method of analysis could be a fire engineering ASET v RSET analysis using the relevant Design Scenarios of Unforseen threat (UT), Challenging fire (CF) and Robustness check (RC) from Verification Method C/VM2. Where this analysis shows that there is sufficient escape time to meet the relevant performance, and is supported by the appropriate stakeholder consultation and review documentation to the satisfaction of the BCA, compliance is shown to the Building Code.
Example: Vertical fire spread
A building has an issue with vertical fire spread. This can affect life safety as well as protection of other property. In this case, clauses C3.2, C3.3, C3.5 and C4.3 all need to be addressed. This is to deal with fire spread via openings and cladding to neighbouring property and to make sure occupants on upper levels can escape in time. Design Scenario Vertical spread of fire (VS) from the Verification Method can be used to show compliance provided the objective of life safety or protection of other property is established.
The proposed solution to use the VS scenario directly from C/VM2 in its entirety is more straightforward than the example above as VS is a prescriptive clause. The extent of external review and stakeholder consultation accepted by the BCA could therefore be reduced also.
Departure from Verification Method C/VM2 or specific fire engineering design
A fire safety design that departs from the Verification Method C/VM2 would need to be undertaken by a suitably qualified and experienced fire engineer with understanding of C/VM2 and the process of performance-based design. Any departure from the C/VM2 design scenarios needs to be carefully considered for any unintended consequences for other design scenarios within the Verification Method.
This type of alternative solution will need to include an appropriate safety margin.
Specific fire engineering design requires a high level of understanding of the Building Code and the inter-relationship between the Building Code clauses.
This type of design can be from first principles or using the Acceptable Solutions or Verification Method as the basis for compliance. The fire safety design should use a range of international fire engineering guidelines, research and methodology such as:
- International Fire Engineering Guidelines, Australian Government, 2005
- BS 7974 -0:2002 Part 0 Application of fire safety engineering principles to the design of buildings
- SFPE Engineering Guide to Performance-Based Fire Protection.
BCAs should be satisfied that the fire engineers and reviewers involved have the relevant qualifications and experience for the proposed type of alternative solution and building design and use.
Specific fire engineering design may be necessary for unique and specialised buildings, such as stadia, tunnels and for complex projects.
Fire alternative solutions resources has more information.
Safety margin in fire safety design has further details.