Principles for Monte Carlo agent-based evacuation simulations including occupants who need assistance. From RSET to RiSET

Abstract

A few modelling approaches are available to assess the egress of people who need assistance to evacuate, since both physical and cognitive aspects should be considered. In this study, an agent-based approach has been adopted with a focus on the behavioural rules assigned to the agents depending on their characteristics and goals. In emergency, while the majority of the occupants recognise the risk and start their evacuation autonomously, the people who need assistance do not necessarily act in that way. Trained and skilled staff are required to contact and assist those needing help that could otherwise remain inside. In this study, “meta-communication” defines the different ways that “link” the rescuers and the people who need assistance during the evacuation. A unified framework is proposed to establish a standard codification of the occupant profiles, both autonomous and those who need assistance, in order to evaluate their evacuation capabilities for use in agent-based models. Based on their mobility and way-finding abilities, occupants are classified into a basic set of five categories. For each occupant category, the mobility device and the staff assistance eventually required are specified. This codification may originate a variety of design occupant profiles which are applied to specific groups of building occupants. Apart from occupant characteristics, it is necessary to define the service discipline, consisting of three components: the staffskills and consistency, the scheduling policy, and the mobility device eventually required to relocate the assisted occupant. The movement of people as groups should also be considered to establish a link between the occupants, including those who need assistance. The inclusive approach proposed in this study has been implemented using Pathfinder software and applied to the analysis of the assisted horizontal evacuation scenario of a hospital ward. The stochastics variables representing the occupant characteristics and the service discipline have been described by probability distributions, including both autonomous and assisted profiles. The Monte Carlo methods provide the means to address the parameter uncertainty in probabilistic risk analysis. The general relationship between the number of iterations executed and the accuracy of the results of interest (mean, variance, proportion of population of the output stochastic variable of interest) is discussed. Based on the Central Limit Theorem, a general a priori estimate of the number of trials required for a specified accuracy in the evacuation time modelling is obtained and a predictor-corrector scheme for conducting and terminating a single loop Monte Carlo evacuation modelling analysis is proposed and applied to the worked case. Model validation is then required to establish whether the results of the simulations are accurate and correctly predict the relevant evacuation scenario. The principles of performance-based inclusive design are thus established, introducing the occupants who need assistance, the assisting staff role, and the service discipline, in a generalization of the conventional Required Safe Escape Time (RSET): the Required Safe and inclusive Escape Time (RiSET).