PURPOSE: To perform fire fighting at close range, to cool an oil layer and to contribute to the extinguishment of a fire at an early stage by generated steam, by injecting noncombustible gas to the bottom part of a tank and providing a noncombustible gas emitting hole on the bottom part of a tank for a combustible substance.

CONSTITUTION: The bottom part of tank is equipped with a large number of noncombustible gas emitting holes having a small diameters. These emitting holes are desirably provided to the bottom surface of the tank over the almost entire surface thereof from such a point that the bubbles of the gas are uniformly dispersed to the whole of the tank. By emitting the noncombustible gas in water, a large amount of water droplets are contained in the gas bubbles and, when said gas bubbles rise through an oil layer 7, the heat of evaporation of water droplets cools the oil layer 7. As the noncombustible gas to be used, any noncombustible gas stable to heat such as nitrogen or argon can be used. This gas is emitted in separated water as gas bubbles and the oil layer is cooled by the latent heat of evaporation of water while the gas bubbles rise through the oil layer 7 accompanied by the circumferential water 6 and a large amount of steam is discharged to the surface of the oil layer on fire. Therefore, the supply of oxygen to the surface of the oil layer on fire is prevented to also achieve the action supporting fire fighting action.