A brief review on applying computational fluid dynamics in building fire hazard assessment

Most of the construction development projects with new architectural features are found in the Far East including Hong Kong, China Mainland, Taiwan, Japan, Korea and Singapore. There are difficulties for those construction projects to comply with the prescriptive fire safety codes. Performance-based design has to be applied with fire models and accepted by the authorities. With the rapid development of computer hardware, Computational Fluid Dynamics (CFD) is widely used for hazard assessment. CFD has been used in different areas for over 30 years, but with little progress in developing research software for building applications. More efforts were spent on applying CFD in those big projects. Most applications are in smoke management systems. There were very few verification and validation works, leading to numerous debates and queries on the technique. Normally, consultants are required to justify the results while testing and commissioning the sytems. Hot smoke tests in the site are required to evaluate the performance of smoke exhaust systems. A brief review on the updated use of CFD in building fire studies will be presented in this paper. Several key points to note in the simulations will be discussed. On the physics behind, key issues are turbulence models, combustion process with intermediate chemistry and thermal radiation. Mathematical aspects to concern are the discretization of partial differential equations, algorithms for solving the velocity-pressure linked equations and treatment of the free boundary conditions. There are also key issues on carrying out numerical experiments such as selecting relaxation factors, convergencees criteria, avoiding false diffusion, and dealing with sudden changes in flow parameters across the heat source. Most of the practical CFD tools were based on Reynolds Averaging Navier-Stokes (RANS) equations with a k-e based turbulence model for predicting velocity, pressure and temperature distributions. This technique is mainly used in designing smoke management systems. The fire is taken as a volumetric heat source and buoyancy effects are included in the equations for the vertical momentum and turbulent parameters. The Fire Dynamics Simulator (FDS) developed at the Building and Fire Research Laboratory, National Institute of Standards and Technology in the USA is now a popular design tool accessible to the general public. Predicted results by FDS were challenged in performance-based design projects. Many sub-models such as combustion of solid materials have not been realistically modeled. This would lead to future arguments for those using FDS.