Water Mist Suppression in Conjunction with Displacement Ventilation
Degree GrantorUniversity of Canterbury
This study proposes and investigates a new type of water mist system where by air and water mist are blown into a fire compartment at low level using a displacement ventilation system. The air/water mist mixture enters the compartment and due to thermal stratification spreads out across the floor forming a protective lake. As the lake increases in depth, it creates a protective cool clean environment that protects the occupants and electrical equipment. The water mist has a very fine diameter in the order of 20µm that allows it to remain suspended within the air for long periods, providing cooling and radiant protection while not causing significant damage to electrical equipment. The density of the water mist is controlled to create a level where flame suppression occurs. Theoretically occupants and electrical equipment can remain safely within the compartment protected by the air/water mist lake, until the fire is extinguished. To investigate the feasibility of this concept a test compartment and associated displacement water mist system were designed based in the standard ISO room. A full-scale test compartment was built and tests run for a number of 20 kW fires of different types and in different positions. The proposed displacement water mist system was tested along with comparison tests using a conventional sprinkler. Within the live test compartment, lights and a computer we installed and monitored to determine the effect of the water mist on electrical equipment. The basic setup and a selection of fires were also simulated using the computational fluid dynamics program Fire Dynamics Simulator (FDS). FDS simulations were run as they provided more information on the species concentrations within the compartment, while allowing a comparison of how FDS simulated the situation compared to the live tests. With the use of computer programs become more wide spread, this comparison provided valuable information on the limits of computer modeling in this situation.