Design of fire safety equivalence of building open arcades to exterior spaces

摘要

An arcade is a succession of arches, each counter-thrusting the next, supported by columns, piers, or a covered walkway enclosed by a line of such arches on one or both sides. In warm or wet climates regions, exterior arcades provide shelter for pedestrians. A building open arcade is sometimes called a porch. Arcades usually border a covered section of a building and sometimes they support roofs. They are very old architectural elements that date back thousands of years. Building open arcades ("Portici") are traditionally employed in cities to provide shelter for pedestrians along public and private streets. Along the closed side of the arcades, commercial activities of all sort often offer their main entrance and exhibition spaces. Other activities as private dwellings or any other kind of civil activity may communicate directly through doors or other openings towards the covered space under the arcade. According to current prescriptive fire safety regulations, open arcades cannot be considered equivalent to exterior open spaces, and all the activities that have openings towards these covered spaces should be presumed in mutual communication from a fire safety design point of view. In fact, it is hypothesized that closed enclosures allow for the faster spread of fire effluents between the communicating spaces. Nevertheless, according to experiences and engineering judgments, under certain conditions and constraints, the open arcades allow for evacuation of smoke and heat towards the exterior spaces through the open side. When these conditions are met, all the activities that have openings towards these covered spaces could be assumed mutually independent from a fire safety design perspective, because, in case of fire, the fire effluents do not spread easily towards the adjoining activities. In this paper a fire safety engineering calculation is performed to assess in which circumstances an open arcade can be considered as equivalent to an exterior space for deemed-to-satisfy solutions of the Italian Fire Code (IFC 2015). The study proposes an arcade parametric fire model, whose pre-processor has been developed in Python, for assessing conditions, safety measures and geometric constraints that allow to recognize building open arcades as exterior safety places. The open arcade can be considered equivalent to exterior space for deemed-to-satisfy solutions when occupants can safely escape from the open arcade towards a safe place, occupants of other activities abutting in the same open arcade are not harmed by the fire effluents coming from the activity involved in the fire, and when fire and its effluents do not spread to other abutting activities. Furthermore, the paper assumes a simplified equivalent model structure of the building arcade where the parametric study conducted with FDS is aimed at setting some basic rules for the fire safety design of building open arcades. The results of the parametric study show that under certain conditions and constraints, the open arcades allow for evacuation of smoke and heat towards the exterior spaces through the open side. Therefore, when these conditions are met, all the activities that have openings towards these covered spaces could be assumed mutually independent from a fire safety design perspective, since in case of an outbreak of a fire the fire effluents do not spread easily towards the adjoining activities.