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Chapter 9

Chapter 9 . Water Supply. Introduction. Water supply is one of the most critical elements of firefighting Water supply dictates the fire flow capacity Pressure is the force of water Measured over an area Fire flow requirement is the amount of water required for putting out the fire

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Chapter 9

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  1. Chapter 9 Water Supply

  2. Introduction • Water supply is one of the most critical elements of firefighting • Water supply dictates the fire flow capacity • Pressure is the force of water • Measured over an area • Fire flow requirement is the amount of water required for putting out the fire • Water’s ability to absorb large quantity of heat makes it effective in fighting fire • Water cools the fuel below its ignition temperature

  3. Sources of Water Supply • A wide range of natural and man-made factors affects water sources • Water in a constant cycle of change • Sun evaporates water into atmosphere • Condenses into clouds • Eventually falls as rain • Some areas alternate between rainy and dry seasons • Some areas have plenty of water, but it is frozen

  4. Groundwater • Most of Earth’s freshwater supply is groundwater • Seeps into the ground from rain and other sources • Collects in aquifers • Permeates into layers of water-bearing soil • Water table: level of water under Earth’s surface • Springs are groundwater sources that flow to the surface • Shallow wells prone to changes in water table • Deep wells more predictable • Less chance of contamination

  5. Surface Water • Almost 75 percent of the Earth covered with water • Most found in oceans and seas • Man-made surface sources include lakes, ponds, reservoirs, swimming pools, water tanks • Tidal changes are rising and falling of surface water levels • Due to gravitational effects between Earth and moon • May be as much as 40-foot difference between high and low

  6. Mobile Water Supply Apparatus • Water tank on fire apparatus supplies the water • Small fires and fires in areas without water distribution system • Water tender: mobile water supply apparatus • Tenders combined with portable water tanks provide large volumes of water to fireground • Tenders may have small booster pump of at least 250 gpm • Fire pump of at least 750 gpm • Transfer pump of at least 250 gpm

  7. Tanks, Ponds, and Cisterns • Water tanks may be: • Underground • Ground level • Elevated • May have a dry hydrant or other connection, or just a drafting point • Ponds may be developed for fire protection • Lined or unlined, with or without dry hydrants • Cistern: underground tank made from rock or concrete

  8. Water Distribution Systems • Components of water distribution system: • Method of getting the water • Filtration, treatment processes • Storage, supply, and distribution • Small groundwater systems require a well with pumping station • Large well systems: multiple supply, processing, storage units with massive feeder lines • Water supplied in three ways: gravity fed, pumped, combination

  9. (A) (B) (C) Figure 9-4 (A) Gravity-fed water distribution system. (B) A direct pump water distribution system. (C) A combination gravity-pumped water distribution system.

  10. Fire Hydrants • Fire hydrants allow access to water supply systems • Two major hydrant types: • Wet and dry barrel hydrants • Dry hydrant: pipe system for drafting from static water source

  11. Wet Barrel • Water in the barrel up to valves of each outlet • Used in areas not subject to freezing • Allows each outlet to be controlled by separate valve • Additional lines taken off or supplied if outlet available • Additional connection does not require flow through other outlets to be stopped • Main control valve controls flow to all outlets

  12. Figure 9-7 Typical schematic of wet barrel hydrant.

  13. Dry Barrel • Used in areas where freezing temperatures could damage the hydrant • Valve at base controls water flow to all outlets • Base and valve below ground at water main • Entire hydrant shut down to connect additional lines • Operation in partially open position undermines the hydrant and ground • Imminent damage to roads and buildings

  14. Figure 9-8 Dry barrel hydrant.

  15. Figure 9-9 Typical schematic of dry barrel hydrant.

  16. Dry Hydrant • Not really a fire hydrant • Connection point for drafting from a static water source such as a pond or stream • Pipe system with pumper suction connection at one end and strainer at other • Primarily used in rural areas with no water distribution system • May be found in urban or suburban areas as backup water supply

  17. Figure 9-11 Schematic of dry hydrant installation.

  18. Specialty Hydrants • Wall hydrants mounted on wall of a building • Be sure to connect to wall hydrant and not the fire pump test connection outlet • Direct connection to water supply system • Flush-type hydrant mounted below grade level • Found in a pit, vault, or valve box • Allows access to water source where above-grade hydrant interferes with operations • High-pressure hydrants connected to separate high-pressure water system

  19. Figure 9-12 Wall fire hydrant.

  20. Hydrant Protective Devices • Devices or valves designed to protect the water system • Most hydrants connected directly to domestic water supply • Many water suppliers added measures to protect water supply • Interior valves, exterior protective devices • Exterior systems require lock and key • Mostly found on privately owned property

  21. Figure 9-13 External hydrant protective device.

  22. Valves Associated withWater Distribution Systems • Gate valves (butterfly valves) opened and closed to control water flow • Non-indicating gate valves installed at: • Interconnections of water mains • Intermediate points of long sections of water mains • Before each hydrant and major building connection • Check valves control water flow in one direction • Backflow preventers: check valves that prevent backflow of water from one system into another

  23. Figure 9-14 Hydrant with plumbing. Note the location of a gate valve between the water main and hydrant.

  24. Rural Water Supply • Rural water supply can occur anywhere • Urban and suburban areas often have places where hydrants are too far away • Limited access highways, large bridges • Require careful coordination and control • Water supply group supervisor part of incident command system • Full authority over water apparatus operations • Firefighters assigned to water supply are vital

  25. Portable Water Tanks • Mobile water supply apparatuses must quickly offload water and return to fill site • Each mobile apparatus should have a portable water tank • Capacity equal or greater than its tank size • Collapsible or inflatable tanks set up next to engine • Jet dump speeds unloading of tanks • Multiple tanks using a jet siphon set up together

  26. Figure 9-17 Tender at dump site dropping water directly into portable tank. Figure 9-15 Portable water tanks are an essential piece of equipment for shuttle operations.

  27. Mobile Water ApparatusOperation • Shuttle operation involves moving water between dump site and fill site • Dump site: where water delivered for quick unloading • Set up first • Fill site: location of water source • Optimum fill site allows vehicles to drive through • Shuttle operations time cannot be decreased by increased vehicle speed

  28. Pressure Associated withWater Distribution Systems • All Earth’s water under pressure • Atmospheric pressure: 14.7 pounds per square inch • Atmospheric pressure reduces 0.5 psi per 1,000 feet of elevation • Pressure in non-flowing closed system equal at all points • While flowing, reduced by friction and loss of pressure at opening

  29. Pressure Associated with Water Distribution Systems (cont’d.) • Distribution systems supplied under pressure • System pressure never as high as firefighters prefer • Pressures below recommended low residual pressure create a vacuum in part of the supply • High-flow and/or high-pressure areas are an advantage • Low-flow and/or low-pressure areas should be avoided

  30. Figure 9-21 Atmospheric pressure being exerted on container of water.

  31. Figure 9-22 Pressure is expressed in pounds per unit area (psi).

  32. Testing Operability andFlow of Hydrants • Regular testing identifies inadequate hydrants • Coordinated between fire and water departments • Operability testing: • Wet and dry hydrants: • Visual inspection for damage • Ensuring hydrant valve closed • Remove all caps, check threads and gaskets • Check that all valves allow water to flow

  33. Testing Operability andFlow of Hydrants (cont’d.) • Operability testing (cont’d.): • Dry barrel hydrant: • Ensure drain valve working • Determine water level dropping after hydrant shut off • Visual inspection of piping, caps, gaskets • Flow test followed by backflushing of the hydrant • Replace caps, oil moving parts, and paint the hydrant • Fireground method for flow tests

  34. Determining Static, Residual,and Flow Pressures • Connect a pumper to a hydrant and turn it on • Static pressure: pressure in the system with no hydrants or water flowing • Charge the first line with desired volume • Check compound gauge for residual pressure • Compare percentage of pressure drop from static to residual • Second test involves multiple hydrants • Not conducted during fire operations

  35. Table 9-1 Percentage Drop Measurements

  36. Obstructions and Damageto Fire Hydrants and Mains • Obstructions and damage can occur to fire hydrants and water mains • Small leaks develop as water system matures • Vandals damage by opening or closing valves • Opening valve in freezing weather without allowing water to flow may cause hydrant to freeze and crack • Accidents can crack pipes or break off a hydrant • Firefighters should ensure hydrant is opened or closed fully

  37. Lessons Learned • Water is the most common fire extinguishing agent • Must be supplied in sufficient quantity • Supplying water requires understanding of the water source and the valves and hydrants • In areas with no distribution system, create one • Difficult to sustain adequate fire flow with mobile apparatus

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