NFPA 22, 2018 Edition regarding filling requirement and duration - 

Section 4.2.1.4. states "The water supply shall be capable of filling the minimum required fire protection volume within the tank in a maximum of 8 hours" and at the same time Section 14.4.3 states "The tank shall be kept filled, and the water level shall never be more than 4 in. (102 mm) below the designated fire service level."

If I understand correctly, as soon as the water goes below 4-inches from the normal filled level in the tank (HHL), the makeup water supply should be starting to replenish and the pipe sizes should be provided in such a way that the tank can be filled within 8-hours.

In a fire, as the water is going down, the tank will always start full.

What is the case where the tank would be emptied out (except maintenance) and need to be refilled within 8-hours?

What if we store water in two tanks to allow maintenance - would we not need to meet this 8-hour requirement?

I'm unsure of how these two requirements work together. Appreciate any feedback.

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I’m working in the construction of 4-star hotel. The water storage tank is underground made from concrete and the pump room is located above the water tank. The designer specified the fire pumps to be vertical split-case type! In order to follow code, I proposed to install vertical turbine pumps instead of the specified vertical-split case.

The supervisor Engineer is insisting to follow the specification of the fire pump and pushing me to create an underground pump room in order to install the specified pump set.

Any recommendations to avoid this directive?

I have a bad flooding experiences with this this type of subgrade pump rooms.

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