The use of confidence intervals to determine convergence of the total evacuation time for stochastic evacuation models. (1st December 2017) - Grandison, Angus
Abstract: International guidelines (IMO MSC.Circ 1533) specify that evacuation models used to certify evacuation performance of passenger ships must demonstrate that the calculated representative evacuation time, the sample 95th percentile time τ S, is lower than a prescribed Pass/Fail Criterion Time (PFCT). In this paper a Confidence Interval Convergence Test (CICT) method is presented that minimises the computational burden required to demonstrate that a model design has passed/failed by calculating a CI for the population 95th percentile time, τ P, rather than simply relying on τ S determined from an arbitrary sample of 500 simulations as specified in the current guidelines. The CICT has comparable pass/fail accuracy to using 500 simulations whilst significantly reducing the number of simulations required when the PFCT is far from the τ P . In addition, the proposed method has superior accuracy to the convergent method described in the IMO guidelines. Furthermore, the methodology described in the guidelines fails to identify situations where there may be uncertainty in the pass/fail status due to proximity of τ P to PFCT. The CICT identifies these situations and provides a means of resolving the uncertainty. The CICT can be applied to any stochastic evacuation model to determine parameter convergence. Highlights: Total Evacuation Time convergence using Confidence Intervals has been developed. Method is particularly suited to maritime evacuation modelling (IMO MSC.1/1533). Reduces computational burden when design clearly passes or fails. Unlike other methods, identifies and resolves uncertainty in pass/fail status. Can be applied to other stochastic egress model to establish convergence criteria.