Prescribing the Input for the ASET versus RSET Analysis: Is This the Way Forward for Performance Based Design?
The popularity of Performance Based Design (PBD) has continued to increase over the last two decades and many consider PBD provides for cost effective and innovative solutions to fire safety challenges. Fundamental to PBD for life safety, is the principle that the occupants have enough time to exit the building before being overcome by the fire. In fire engineering terms the Available Safe Egress Time (ASET) must exceeding the Required Safe Egress Time (RSET) with an appropriate margin of safety. Currently the necessary input and acceptance criteria are left up to the fire engineer with the approval from the authority having jurisdiction. Unfortunately the conventional guidance is more qualitative rather than quantitative which can lead to varying levels of safety in buildings depending on the values chosen for use in the analysis. This paper describes the necessary input parameters and the appropriate acceptance criteria for ASET versus RSET analysis and discusses some of the available guidance for determining these values. The paper ends with a brief description of the framework that the Department of Building and Housing is proposing for PBD in New Zealand. The framework outlines the design fire scenarios, design fires, premovement times and acceptance criteria that is currently being field tested.