Regarding the issues of sealing gas and isolation gas,

It is recommended to look for such diagrams on Baidu Images; it will be clear at a glance. Strictly speaking, they all belong to the category of sealing functions.

There is a 10-centimeter gap between the isolation air and the gas seal in the turbine. I think the isolation air is there to prevent oil from leaking out and causing a fire

This is a simple schematic diagram of a dry gas seal structure. In a centrifugal compressor, the atmosphere on the left side represents the bearing housing; inside this housing there are bearing shells along with lubricating oil. The isolation gas serves to separate the lubricating oil and its vapor from the seal area (the part between the leaking gas and the buffer gas). The pressure is slightly positive, around 0.05 MPa. In the diagram, the yellow color indicates the path of the isolation gas. Above the oil tank that supplies lubricating oil to the bearings, there is an oil mist fan which draws the oil vapor from within the tank outside, thereby maintaining a slight negative pressure in the oil system – that is, a slight negative pressure exists inside the bearing housing. The pressure of the sealing gas and the buffer gas shown in the diagram is around 0.5 MPa. The end face of the moving ring 1 features a sealing groove; when the moving ring 1 rotates, a thin, rigid air film is formed between the end face of the moving ring 1 and that of the stationary ring 2, thereby keeping the two rings separated. After passing through these end faces, part of the sealing gas leaks into the bearing housing via the air seal marked in red, while most of it leaks into the atmosphere through the leakage air pipe. (The blue path in the diagram represents the path taken by the sealing gas.) Due to the pressure difference, as well as the air seal marked in red, the isolation gas does not leak into the sealing gas.