Fire Water Distribution Systems
Fire water systems should be designed to supply sufficient quantities of water to all areas of a facility. The fire water distribution system should be sized to limit the friction loss from the supply to the greatest hazard and to meet the maximum fire water demand including expected fire hose and monitor nozzle requirements. Future plans should be included in any design. NFPA 24, “Standard for the Installation of Private Fire Service Mains and Their Appurtenances” should be consulted for minimum installation requirements.
When laying out the fire water distribution system the following are usually considered:
• Sizing distribution mains to take advantage of the water supplies available. Large pumping capacities can be wasted if the water distribution system cannot deliver the water to the desired areas at effective pressures. This usually means a looped or gridded distribution system.
• Sizing the distribution piping to meet anticipated demands with any part of the distribution system out of service.
• Providing adequate backflow prevention where public or other potable supplies connect to the system.
• Providing a separate connection to the distribution system for each source of supply.
• Burying distribution piping even in climates where freezing is not a problem to prevent an explosion within the facility from impairing the system.
• Providing adequate valving to isolate damaged sections of the system. Water supply mains generally should have indicating-type sectional valves located at appropriate locations on the grid. The sectional valves should be installed at other appropriate points in order to minimize the extent of impairments. The isolating valves should be placed so that hydrants, monitors, deluge systems, sprinkler systems or other fire protection systems could still operate by isolating the problem using the valves. Sectional valves should be arranged so that no more than four to seven pieces of equipment (hydrant, deluge valve, monitor, etc.) will be impaired at any one time. Multiple impairment scenarios may be considered, and the possible need of large diameter temporary water transmission hose should be considered for supplemental fire water supply in extreme emergencies.