Hi,
You need to talk to your fire brigade , they should be helping you . A call to your insurance broker is advisable .
You need to consider how far is your facility from the fire brigade and availability of water ( flow and pressure) .
I'm aware of projects in Asia where the water storage capacity is about 4 hours , let say 2000 m3 with fire fighting pumps pumps operating @ 500 m3/h .
Good luck
Pierre