A correlation of flame heights is presented for recent experiments of merging group fires produced from arrays of gaseous burners. The correlation is based on two considerations: a) the air entrainment up to the flame height is proportional to the stoichiometric requirements for combustion of the fuel and b)the air entrained is equal to the side area of the plume multiplied by an entrainment velocity proportional to the square root of the vertical distance from the source. This correlation is applicable for an array of merging fires as recent results verify. Justification for merging of the investigated group fires is given together with comparison with older work.
For underground station buildings, a passive safety system is proposed for energy conservation under daily use and for evacuation safety in case of a fire. The stack effect by a solar chimney and the ambient air cooling effect by dry mist, which have been examined in recent years, are used in the proposed system. During any period of the year, the proposed system controls the air current in the direction of "outside air → staircase → concourse and platform → solar chimney → outside air ". If a fire occurs under this status, the safety of staircases will be secured because smoke will be discharged through chimneys. When adopting this system for an underground station building, it is necessary to check the boundary conditions in the building for effective system operation. Therefore, in the present study, a model as small as 1/20 the size of an actual station building was fabricated, and experiments were conducted using scaling laws.