Full-scale experimental study on the smoke and thermal insulation of a water mist fire extinguishing system in a short road tunnel with natural ventilation

Abstract

Tunnel fires have become a huge threat to human life and property, and the large amount of smoke and thermal produced by the fire is the principal cause of human casualties. The water mist system is considered a highly promising fire extinguishing technology. However, the research on the water mist system which could simultaneously extinguish fire and block smoke is rare. The objective of this study is to propose a new water mist fire extinguishing system, which can achieve effects of fire suppression, smoke suppression and thermal insulation concurrently. Two full-scale fire tests were conducted: one involving free combustion without the activation of the water mist system and another where the water mist was activated after ignition. The fire extinction mechanism of the proposed water mist system was discussed via the analysis of heat release rate and flame characteristics. Moreover, the smoke and thermal insulation capabilities were qualitatively investigated by observing the longitudinal temperature variation below the tunnel ceiling and the temperature distribution within the tunnel. Additionally, the smoke insulation performance was quantitatively analyzed based on the concentration of particulate matter and the concentration of carbon monoxide. The results revealed that with the activation of water mist system, the fire source was continuously suppressed until it was extinguished. The water mist fire extinguishing system proposed in this research can effectively block the heat and smoke generated by combustion. Notably, the system exhibited an excellent barrier effect on smoke particles, ensuring that the tunnel space beyond the mist spray segment remained visibly clear during the fire. Thanks to the inhibitory effect of water mist onto the fire source, the concentration of carbon monoxide inside the tunnel was reduced by over 30%, and the presence time of carbon monoxide inside the tunnel was shortened by over 58%. However, the water mist fire extinguishing system failed to effectively block the spread of carbon monoxide.