Project Overview & System Type
This case study examines a proposed smoke control strategy for a six-storey residential development arranged around protected stair cores and corridor-based smoke ventilation. The scheme supports a stay-put evacuation strategy and uses two different smoke control philosophies across the building: Levels 1 to 4 employ enhanced mechanical smoke extract with a natural replacement air shaft, while Level 5 adopts an intelligent reversible push-pull arrangement in which one shaft extracts and the opposite shaft supplies replacement air.
The Engineering Challenge & Regulatory Framework
The engineering challenge was to demonstrate that both corridor tenability and firefighting access conditions could be maintained without allowing smoke to contaminate the protected stairs. The study was developed against Approved Document B, BS 9991:2024, BS EN 12101, Smoke Control Association guidance, and a Qualitative Design Review that defined the fire scenarios, tenability criteria, and expected system response.
CFD Modelling & Analysis Methodology
Transient CFD simulations were carried out in NIST Fire Dynamics Simulator. Three worst-case apartment fire scenarios were tested: a Level 1 flat close to a stair core, a Level 5 flat furthest from the escape stair to stress corridor tenability, and a Level 5 flat closest to the stair to create the most onerous stair-protection condition. Each scenario used a medium-growth t-squared design fire with a 1 MW peak heat release rate, polyurethane fuel properties, and a soot yield of 0.1 so that smoke movement, heat, visibility, airspeed, and pressure conditions could all be assessed together.
Performance Criteria & Design Checks
The performance objectives focused on maintaining usable escape and firefighting routes while limiting pressure effects that could impede door operation. Acceptance criteria included temperatures below 60°C for means of escape, visibility above 10 metres, airflow velocities below 5 m/s, and pressure differentials below 50 Pa. Particular attention was given to the transition period immediately after apartment door opening, because that interval controls whether smoke reaches the adjacent stair before the ventilation system ramps up.
Results & Performance Outcomes
The simulations showed that corridor conditions remained within the target tenability limits in all assessed scenarios. Visibility, temperature, airflow velocity, and pressure criteria were satisfied, and the prescribed heat release rate profiles were achieved as intended. The modelling therefore confirmed that the proposed systems provide effective corridor smoke management and acceptable firefighting-route conditions for the building layouts studied.
The critical finding concerned stair protection where the fire apartment sits immediately beside the protected core. In two of the assessed scenarios, a degree of smoke ingress into the stair occurred during the early stages of operation. The report attributes this to the short separation distance between the apartment entrance and the stair door combined with the finite activation and ramp-up time of the smoke control system. The strategy reduced smoke migration but did not fully eliminate stair contamination under those worst-case arrangements.
Value Delivered & Design Implications
The CFD study provided a clear performance-based basis for decision-making: the corridor smoke control concept is robust, but stair-adjacent apartment layouts demand further refinement before the full strategy can be considered complete. That outcome gives the design team a targeted route forward, whether through revised layouts, faster-operating controls, or an alternative stair protection approach, while preserving the validated corridor ventilation performance already demonstrated by the analysis.