Using Probabilistic Zone Model Simulations to Investigate the Deterministic Assumptions of UK Residential Corridor Smoke Control Design

Abstract

The modelling of common corridor smoke control systems in residential buildings is one of the most frequently undertaken performance-based assessments by fire engineers in the UK. However, there is limited understanding of how the deterministic assumptions provided in modelling guidance are derived, and to what extent these are representative of a range of possible outcomes. To place these assumptions into context, the Monte Carlo method is applied using the zone modelling software B-RISK for an exemplar residential arrangement. Distribution functions are adopted to inform inputs for fire parameters, sprinkler performance, and occupant behavioural characteristics. An output distribution for the corridor smoke clearance time is determined and compared to the clearance time of an equivalent set of deterministic simulations applying the assumptions of modelling guidance. The probabilistic study indicates that modelling guidance assumptions typically result in a scenario severity greater than the 99th percentile of possible outcomes. The work also considers the sensitivity of individual input parameters, ranking these based on their impact. These sensitivity analyses highlight the importance of occupant behavioural assumptions around the pre-evacuation time and door open time, and the significance of fire parameters including the elevation of the fuel bed, soot yield, and fire growth rate. Sprinkler parameters are shown to have a lesser impact on the corridor clearance time. The work therefore provides practitioners with an indication of which parameters are worth considering in greater detail when assessing scenario sensitivity.

A Compressed Timeline Approach to Residential Corridor Smoke Control Modelling Using Initial Apartment Conditions

“…Inlet was provided at the opposite end of the corridor by an automatically openable vent (AOV) to external air, with a geometric free area of 0.96 m 2 (0.8 m wide by 1.2 m high). The adopted exemplar and ventilation provisions were consistent with previous studies by Hopkin et al [4].…”

“…Where neither of these documents provided a specific recommendation, previous revisions of SCA guidance were considered [15][16][17]. In cases where recommendations are provided in neither the existing nor previous SCA guidance, parameters were adopted from the work of Hopkin et al [4] on deterministic assumptions of residential corridor smoke control design, or from elsewhere in the published literature.…”

“…Q is the heat release rate per unit area (HRRPUA) (kW/m 2 ), r is the radius of the fire (m), and s is the spread rate (m/s). Note: Parameters taken from SCA guidance [11,[14][15][16][17], or from Hopkin et al [4] where not specified in SCA guidance.…”

“…In instances where the travel distances within the corridor are greater than the maximum bounds recommended in these guidance documents, a mechanical (or combined mechanical and natural) smoke control system is often adopted. The purpose of this system is to return the extended corridor and associated stair enclosure to tenable conditions, as well as to protect the stair from smoke ingress during fire service operations [4]. Further discussion on the role of residential smoke control in UK design can be found elsewhere [4,5].…”

“…The purpose of this system is to return the extended corridor and associated stair enclosure to tenable conditions, as well as to protect the stair from smoke ingress during fire service operations [4]. Further discussion on the role of residential smoke control in UK design can be found elsewhere [4,5]. To determine whether the proposed smoke control system can adequately support a design incorporating extended corridors, a performance-based fire and smoke modelling assessment is usually undertaken [6], with the computational fluid dynamics (CFD) based Fire Dynamics Simulator (FDS) [7][8][9] software being the de facto tool applied by most engineers within the UK consultancy environment [10].…”