Experimental studies on the effect of mechanical ventilation on performance of water mist spray

Water mist fire suppression system is one of the alternatives to the gas protection system based on halon. However, it is observed that performance of the system might be affected by indoor aerodynamics. Water mist discharged might not be able to reach the burning object when there is a strong upward air movement induced by the fire. Understanding this phenomenon is very important for integrating the design of a water mist system with the mechanical ventilation and air-conditioning system. This article will report on the experiments on water mist system, with and without a fire, carried out in a laboratory of size typical to an office with mechanical ventilation. Under different ventilation conditions, the water discharged pattern, fire extinguishing time, and air temperature profile were measured. It is concluded that a water mist system should be designed carefully in a mechanical-ventilated compartment. But for ill-designs, an immediate action is to shut down the ventilation system before discharging water mist. Full-scale burning tests should be carried out to demonstrate that the design would work in a fire when necessary.