Numerical analysis of the effect of external opening on fire safety of refuge floors in tall buildings

Refuge floors are fire safety requirements for tall buildings in many Asia-Oceania cities. However, there are concerns on the adequate provision of cross-ventilation and drencher system to openings on refuge floors. To review the existing situation, a survey of 44 building developments involving 51 blocks of both residential and non-residential tall buildings was conducted. A new fire safety parameter, i.e. the ratio of external wall openings areas to the nominal total wall areas of refuge floors (wall opening area ratio, or WOAR), was introduced to provide a quantitative measure in analysing fire safety level of tall buildings. To study how the ventilation provision is affected by WOAR, numerical simulations for the effect of natural ventilation on fire growth on the refuge floor were conducted by incorporating the wind data collected from the tallest building in Hong Kong. In the simulations, an office layout was adopted on both upper and lower floors for the sake of illustrating the possible smoke and heat spread from lower floor to upper floor (refuge floor). Finally, fire safety issues in relation to natural ventilation on fire in tall buildings were discussed. Suggestions in improving the fire safety design of tall buildings are proposed.