1992

Mangs, Johan; Keski-Rahkonen, Olavi

In this study a new method for the determination of the opening time and the discharge coefficient of smoke vents is proposed based on a series of experiments. A roof was constructed of steel beams and plates of mineral wool. The walls made of thin steel plates left a gap above the floor and the system was heated with commercial heptane. The opening time was measured with a stopwatch and the discharge coefficient determined by equating the mass flow from the fire plume into the hot gas layer and the mass flow through the smoke vent. The mass flow into the hot gas layer was calculated from the measured thickness of the hot gas layer and the rate of heat release obtained by following the mass loss of heptane. The mass flow through the vent was calculated from the pressure difference over the vent determined by measuring the temperatures in the hot gas. A series of tests was performed with a mockup vent of adjustable size and operating temperature and two smoke vents of different size and construction. The results show that the opening time of smoke vents can be measured under pre-flashover conditions and that a hot gas layer of stable thickness is attained which enables the calculation of the discharge coefficient. The method is quick, cheap and does not require special methods or materials. It can be carried out in most fire laboratories where full scale testing is possible.