Is a 300mA RCD main switch a requirement or recommendation on a 3phase DB with 30mA RCBO protection on the outgoing ways except for the fire panel feed and SPD?

Unless the building is part of an agricultural installation, or maybe a fuel depot or ammo dump, or in some other way an unusual fire risk, probably not a requirement to have the TD RCD at the incomer at all. But what makes you think there might be ? is there some other documentation or requirement you have been given ?
Customer and insurance requirements often have requirements that exceed minimal regs level ;-)

In terms of the SPDs, when they eventually reach end of life, the elements will go dead short circuit so something will need to clear that LN fault, but given the solid earth, a suitable fuse or MCB maybe just fine.

Is there anything special about the fire panel supply?

Mike.

Thanks for the reply. 

The building contains two separate sauna/steam rooms with wood fired boilers.  The DB is located in a third mechanicals room, so should be fairly well protected from the moisture in the rest of the building.  

There is ventilation makeup air ducts connecting the mechanicals room to the changing rooms, and since the changing rooms are adjacent to the steam rooms, when the sauna users go back and forth, the changing rooms get some steam in them.

The fire panel is a Morley Zx1se, connected to a campus wide fire panel network, so faults are monitored and if it lost power that would be noticed within a few hours even if the building was unoccupied.  The supply to the fire panel is all surface run, nothing special.

The project is in the design phase and the customer initially requested 300mA RCD main switch, but in discussions about pricing they couldn't point to a reg that made it mandatory to have that.

Regards 

Thanks for the reply. 

The building contains two separate sauna/steam rooms with wood fired boilers.  The DB is located in a third mechanicals room, so should be fairly well protected from the moisture in the rest of the building.  

There is ventilation makeup air ducts connecting the mechanicals room to the changing rooms, and since the changing rooms are adjacent to the steam rooms, when the sauna users go back and forth, the changing rooms get some steam in them.

The fire panel is a Morley Zx1se, connected to a campus wide fire panel network, so faults are monitored and if it lost power that would be noticed within a few hours even if the building was unoccupied.  The supply to the fire panel is all surface run, nothing special.

The project is in the design phase and the customer initially requested 300mA RCD main switch, but in discussions about pricing they couldn't point to a reg that made it mandatory to have that.

Regards