The number of huge oil storage tanks is increasing in the world. If a fire occurs in one of these tanks, it is very difficult to suppress. Additionally, if a fire whirl occurs in an oil tank fire, it is extremely dangerous for firefighters to extinguish the fire. The authors have numerically studied huge fire whirls in a large oil tank depot and predicted the generation of those fire whirls. Here, another study is attempted to clarify the details of huge fire whirl in a large oil tank, using two kinds of fire whirl generation channels in CFD simulations using the software, FDS by NIST. Details of burning rates, velocities of whirling flames, radiative heat flux, heat release rates and whirling cycles are examined, using oil tanks with the diameters of 0.2 to 80 m. In oil tanks with a diameter of 80 m, a tall fire whirl is generated. The height is about 1000 m. In this study of oil tanks fires with small to large diameters, it has been found that fire whirl lengths are about 8 to 11 times of the oil tank diameter. The maximum radiative heat flux due to a fire whirl in 80 m diameter oil tanks exceeds 100 kW/m~2. Since the maximum radiation is found at twice the distance of oil tank diameters from the tank centers, adjacent oil tanks may be ignited. This study has also examined a method used to prevent fire whirl generation in huge oil tanks.
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