Theoretical Analysis and Numerical Investigation of Atrium Fire Engineering Design Principles

Abstract

In the project described in this thesis, computational fluid dynamics (CFD) was used comparatively with the traditional calculation approach to predict smoke behaviour in tall and long atrium geometries in order to review the empirical correlations used to this day. It is demonstrated that the empirical correlations specified in the regulations, design guides, and handbook for the industry, which were based on theory and experiments done for more than 30 to 45 years before, may not be applicable nowadays to large volumes and high atriums.
A number of correlations exist, related to cross-sectional area and height. Particular focus is made in one of the most widely used correlations for smoke mass flow rate and height defined in the National Fire Protection Association (NFPA). The constant, 0.28 used in NFPA 92: 2021 for smoke layer height applied in atrium design based on cross-sectional area is evaluated. A parametric study and the limits of applicability of the correlation are investigated by numerical analysis. A wide range of geometric characteristics, i.e., height, width, Sectional Aspect Ratio (SAR) and Plan Aspect Ratio (PAR) are investigated.
Based on the results of the current investigation, new constants are proposed to be used, namely 0.25 and 0.24 for 20-30 m and 40 m tall atrium respectively.
For long atriums, results from empirical equations for rectangular-base long atriums with different PAR have also been compared with a series of numerical simulations.
New constants 0.25 and 0.27 seem to better fit the numerical results for 10-20 m and 30-40 m long atriums. A simple table is presented for use by practitioner designers.
Current thesis results indicate that the constant is not universally applicable to atriums that are particularly high or long, and new correlations are applied with the aim of being used by fire safety engineers.
Some new results are also presented on the development of stratification in taller atria. There is an existing formula for this, valid for small atria, based upon the oxymoron of a temperature gradient. It was found that velocity profiles can identify where stratification will occur, and this influences the design strategy, such as not extracting gas above this height because it is not smoke.