Is Prescription the Future of Performance Based Design?

Abstract

The popularity of performance-based design (PBD) has continued to increase over the last two decades and many consider PBD provides 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 exceed the required safe egress time (RSET) with an appropriate margin of safety. Currently the necessary input and acceptance criteria are left up to the designer to decide with the approval from the authority having jurisdiction (AHJ). Unfortunately the conventional guidance on design scenarios, design fires and acceptance criteria are typically more qualitative than quantitative in nature which often leads to widely varying interpretation and significant differences in the safety levels for buildings that are substantially similar. This paper reviews the current guidance on design scenarios, design fires and acceptance criteria necessary for an ASET versus RSET analysis as well as highlighting areas where additional research is needed. The paper ends with a brief description of the new verification method that the Department of Building and Housing is proposing for PBD in New Zealand. The Verification Method (VM2) outlines the design fire scenarios, design fires, pre-movement times and acceptance criteria that are currently being reviewed after the public comment period.