Can someone urgently advise on aggregate/total capacity for tanks in a dyked area?

I have come across information in the internet recommending the following :


Aggregate capacity in one dyke enclosure:

Group of Fixed roof tanks: Upto 60*000 m3
Group of Floating roof tanks: Upto 120*000 m3
Fixed cum floating roof tanks shall be treated as fixed roof tanks.
Group containing both Fixed roof tanks & Floating roof tanks* shall be treated as fixed roof tanks.

However* I have not come across the same being referred to in any standard. NFPA 30 mentions much lower capacities not practical.

Could someone advise me regarding the above.