Simulating pre-evacuation times using hazard-based duration models: Is waiting strategy more efficient than instant response?

Abstract

In an indoor evacuation scenario, an early decision to be made by each occupant is when to initiate the (decisive) evacuation movement, a decision that determines the pre-evacuation (or pre-movement) time. We employ a class of econometric models, proportional hazard duration models, to simulate the probabilistic relation between the pre-movement times and the occupant’s proximity to exits at the onset of evacuations. This is based on the empirically-supported assumption that occupants that are relatively further from exit locations when the evacuation cue is perceived, take relatively longer times to initiate their evacuation movement. Implementing these parametric models and using extensive numerical simulations, we investigate the effects of (various degrees and forms of) pre-movement-time heterogeneity on the evacuation efficiency. This is to revisit and test the anecdotal idea that occupants’ collective instant rush hinders evacuation processes. In testing this assumption, we examined whether heterogeneity (i.e. variation) in pre-movement times can lead to better outcomes (i.e. shorter evacuation times). Our analyses included both purely-random heterogeneity as well as strategized heterogeneity, one in which occupants nearer to exits are prioritised, as a (probabilistic) waiting strategy. We observed that the instant movement of occupants led to bigger crowd jams at bottlenecks and created greater degrees of congestion which sustained for longer amounts of time. However, from a time-minimisation perspective, collective instant movement was invariably the best strategy. Neither the random nor the strategized forms of pre-movement-time heterogeneity resulted in any shorter evacuation time than when all occupants initiated their movement instantly. In fact, increasing the degree of pre-movement-time heterogeneity led monotonically to longer evacuation times, despite making the evacuation more orderly. This finding suggests that advising occupants to avoid instant rush may not be a time-optimal strategy, even though it mitigates congestion. The finding has not been tested in relation to high-rise buildings and needs further investigation in that context.