Novel smoke control for tall buildings

Abstract

Buildings are evolving in height, construction materials, use, and compartmental composition at staggering pace. The tall buildings of today are a completely different entity to that of a decade ago with the propensity for change even greater in the immediate future. The advancements in structural engineering have arisen to make possible the increase in height, size and complexity. Forensic analyses of tall building fires have indicated that the needs of modern tall buildings are beyond the scope of applicability of current fire safety codes and engineering practices. The ever increasing heights combined with the limited number of vertical escape routes results in these two components becoming coupled. The considerable time that occupants spend within the stairwells means that for any fire strategy to be successful stairwells must remain smoke and heat free and the entire building structurally sound. Without adequate protection the number and width of stairwells is irrelevant, as smoke-logged stairwells are unusable and the Fire Safety Strategy is therefore void. Reported failure rates for stairwell smoke control systems are extremely high, this implies that safe stairwell tenability levels are currently not guaranteed, thus the cornerstone of contemporary tall building fire safety design may not be valid. This research project investigates current smoke control methods used for the protection of stairs in tall buildings through the review of literature and theory for the methodologies. In understanding the design assumption and actual stresses smoke control systems are subjected to, a novel concept for smoke control will be presented, investigated and developed. It is intended that this work will become a proof of concept, or otherwise for the novel smoke control system. Several conceptual smoke control systems were developed around the following principles; localised solution to minimise under or over pressurisation of the stairwell, performance be independent of fire size, perform under extreme environmental conditions and be effective when protecting a fully open door. Three concepts were investigated using CFD modelling, these being: - Concept 1- vertical perimeter vents to the opening resulting in converging flow field - Concept 2 - concept 1 with the additional horizontal vent - Concept 3 – concept 2 with baffle chamber The preliminary modelling predicted that Concept 3 would provide the most robust solution. The provision of baffles provided stability to the vent flow which contained an area of high pressure within the baffle chamber, relatively to areas adjacent to the baffle chamber, this encouraged smoke flow away from the chamber. It appeared that the effectiveness of the system was a function of baffle flow and pressure load caused by wind and fire characteristics, the larger the pressure load across the door the greater the vent velocity required to limit or prevent smoke flow through the opening. Full-scale experiments were undertaken to prove in principle that the proposed baffle smoke control system can limit the passage of smoke through an opening under generated pressure loads. The experiments did demonstrate in principle the baffle smoke control system could be effective in limiting smoke flow through an open door under the pressure loads tested.