Backup Foam Concentrate PD Pump Requirement

[az5333]

Hi fellow members. I have recently been working on a project where we are engineering a new foam system to be incorporated into the client's existing firewater system. This is to have a foam-water solution for effective firefighting application. We are going with an atmospheric storage tank with a motor-driven foam concentrate PD pump for pumping the foam to the water line. As per feedback from the client, the electrical power at site is not reliable and they do not have a back-up power system. Any filling / offloading operations (for a jetty)of inflammable / combustible liquids are suspended during this outage. My question is: do we need to consider an auxiliary / backup diesel-driven foam concentrate pump in addition to the motor driven foam concentrate PD pump to ensure this system is 100% available? Even if they have suspended the operations at the jetty during the power outage time? As per my research so far from NFPA 20, the system has to be available at all times and it does not explicitly state anything about power outage scenario for the foam concentrate PD pump. Appreciate the insight from your experiences.