Apparent Level of Safety of Buildings Meeting the New Zealand Building Code Approved Document C/AS1 – Fire Safety (2007)
AuthorsMcGhie, Craigshow all
The key objective of the project was to develop a risk ranking model to assess the apparent level of safety of buildings designed to the Approved Document for New Zealand Building Code, Fire Safety Clauses C1, C2, C3, C4 (C/AS1)(1). This is a prescriptive fire safety code. The study included a literature review of fire risk analysis methods. This found that there are numerous methods from simple risk ranking techniques such as that used in this project to detailed probabilistic risk analysis (PRA) techniques. It was generally found that more sophisticated analysis, such as PRA and Reliability Index methods are most suited to specific engineering problems while the risk ranking schemes are better suited to “broad-brush analyses” across a large range of buildings. The risk ranking model developed is based on a simple weighted points system where the building geometry, use and fire safety features are graded according to the likely impact they will have on safety. The model output is a single numerical index value, termed the Fire Safety Index (FSI). A high index indicates a safer building. The model is best used for a comparative analysis as the results are not an absolute measure of risk. The results of the analysis of buildings designed to C/AS1 indicate that the level of safety increases predominantly with increasing building escape height and/or increasing occupant numbers. The report raises questions over the level of safety afforded by sprinkler systems and whether or not the sprinkler tradeoff provisions of C/AS1 are appropriate. The model proposed in this study could be developed further and used to determine whether or not a specific fire engineering design (alternative solution) provides an “equivalent” level of safety to that achieved by the prescriptive solution C/AS1. The model requires further testing and validation before it would be suitable for this task or any other practical uses.