Smoke control in tunnels with various water-based fire suppression systems

Medium scale tunnel fire tests (1:3) were carried out to investigate smoke control in tunnels with various water-based fire suppression systems. The critical velocity decreases as the water density and water pressure increase, and it also approximately follows the 1/3 power of the heat release rate for small fires but becomes independent for large fires. The momentum of the water sprays is found to play a key role in the critical velocity. A calculation model for critical velocity is proposed to cover all tunnel scenarios, i.e., with and without water-based fire suppression systems. The smoke backlayering behaves differently within and beyond the water spray region. Within the water spray region, the backlayering length is less sensitive to the longitudinal ventilation velocity, i.e., a large reduction in velocity results in only a slight increase in the backlayering length. Beyond the water spray zone, the variation of the backlayering length with velocity approximately follows the same trend as for the tunnel without water-based fire suppression systems. Calculation models for the backlayering length both within and beyond the water spray region are proposed. Comparisons of the calculation models with data from various large scale tunnel fire tests and medium scale tests show reasonably good agreement for both models.