I have the following situation:
In an underground metro station,
one horizontal standpipe is installed in the lower level serving an office/hall areas (feeding three 2.5 inches hose valves).
And two horizontal standpipes are installed in the upper level serving the two platforms (feeding three 2.5 inches hose valves each).
As per NFPA 14 item 18.104.22.168.2, the minimum flow rate for horizontal standpipe is 750 gpm, while item 22.214.171.124.3 is requiring an additional 250 gpm for each additional standpipe.
The question is :
Does additional standpipe mean vertical standpipes or it applies also to the additional horizontal standpipes (noting that as described above, no vertical standpipes are installed) .