Returning to the foundations: Water supply


CarolinaFireJournal - By Mike Coffey
By Mike Coffey
01/10/2013 -

In order to fight the majority of fires we encounter today, water is the main ammunition we use in battle due to its availability, affordability and its effectiveness in absorbing heat from combustion. Securing a water source is highly important for fire suppression efforts. That water source can be static — meaning natural or fabricated lakes, ponds, rivers or other spots of water availability — or pressurized by the local water system providing water for drinking and sanitary reasons. Understanding where the water comes from aids us in fire extinguishment and ultimately in life safety and property conservation.

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Static water supply consists of the earth’s available surface water. Access to these may not be simple or extremely well kept due to efforts of the property owner and the fire department using the water source. If source is close enough — the water is used to fight fire directly; if not close enough — water has to be transported by hose, engine relays or mobile water supply apparatus also known as a tanker or tender. Using these sites requires the engine or portable pump to draft or pull the water up into the pump and be distributed through the pump and out the hose. Dry hydrants are polyvinyl chloride (PVC) pipes with a strainer attached placed in some agricultural ponds that allow the fire department to access the local water by drafting and use it for firefighting purposes designed to supply at least 1000 gallons per minute (GPM). Dry hydrants are also installed to access water during cold weather as water levels may recede below certain levels. The installation of dry hydrants and more on what is required for departments having rural water issues can be found in NFPA 1142 – Standard on Water Supplies for Suburban and Rural Firefighting.

Once the water point is located, moving that water from Point A to the fire attack point falls upon hose evolutions using relay pumping operations — apparatus, equipment and staff-intensive — or mobile water shuttles using tankers/tenders and portable water tanks — locally known as drop tanks. These rolling water ponds can be from 500 gallons in tank capacity to over 8000 gallons. Some have pumps for nothing more than off-loading the apparatus tank to pumps capable of pumping 2000 gallons per minute for structural firefighting. These apparatus also have the ability to dump their tank water into the portable water tanks from valves at the rear or the sides of the unit by using gravity or using the on-board pump known as jet-assist dumping. The National Fire Service Incident Management System Consortium, the International Association of Firefighters (IAFF), International Association of Fire Chiefs (IAFC), National Wildfire Coordinating Group (NWCG) and FIRESCOPE (Fire Resources of Southern California Organized for Potential Emergencies) endorses the term “tenders” for land-based water supply apparatus. The term “tanker” refers to aircraft capable of carrying and dropping water for firefighting operations. Some alternative definitions are tankers being land-based mobile water supply apparatus and tenders being hose-carrying apparatus. Keep in mind that true tenders may or may not have pumps.

Shuttle apparatus drop their payloads into portable tanks having capacities typically between 600 and 5000 gallons. These tanks should be set up for access from multiple directions. Higher fire flows require more tanks to be deployed. Multiple tanks can be linked together to maintain the higher flows by connecting through the drain fittings or jet siphon devices that moves water between tanks. The siphon devices use a one and one-half inch discharge line connected to the siphon that is connected to a hard suction hose extended between tanks. One alternative method uses four inch PVC or aluminum piping has been used with six-inch units are more common. Another alternative uses a one-half inch nozzle with one and one-half inch hose allowing a possibility to transfer 500 GPM and added to a hard suction hose as well. Fill and dump sites are preferred to be arranged so a minimum of backing/maneuvering is required. Efficiency is preferred at both these sites to improve fill times, dump times and keep the tenders/tankers moving.

Relay operations begin at the water point. Ideally, the largest pump should set up at the supply point with the smaller capacity pumps working back to the fire area. The next ideal point is large diameter hose — usually four inch or five inch — laid between the pumpers. Two more factors to consider: the water supply must be able to maintain the desired volume required for the duration of the incident and the relay established quickly enough to be worthwhile. This is a time-consuming operation. Once established, the supply pumper should alert the next pumper in line that the supply line is ready for water and fill that line slowly. This continues for all the pumpers in the relay up to the attack pumper. The attack pumper establishes base flows and notifies the supply pumper if more water or pressure is needed. Pressure is added in increments until fire flow is established. The relay begins shutting down at the fire attack pumper back to the supply pumper. Communications in this operation is critical as to not create a lull in water being supplied that can compromise pump safety or firefighter safety.

Municipal or local water supply systems are comprised of piping, larger volume pumps to supply the system and some kind of storage. Some systems are designed to be in a grid-like pattern — the more efficient style of system — or in a tree-branch-like pattern. These systems draw their water from larger static sources — lakes or rivers — retain that water in retention ponds to allow the sentiment to settle then bring the water in for treatment before pumping it out into the system for use or storage. Water supply and distribution systems should be designed to meet community needs — domestic, industrial and fire protection at peak periods. These systems use three methods to move water through the system: direct pumping systems involving pumps that move water, gravity systems that rely on the reservoir or tanks being higher than the distribution system using gravity to pressurize the system and combination systems that use both pumps and gravity tanks to pressurize and fill the system. Underground mains supply water to end user and come in several sizes. Primary feeders involve large mains with relatively widespread spacing that conveys large quantities of water to various points in system for distribution by secondary feeders and smaller mains. Secondary feeders are a network of intermediate-sized mains that subdivide a grid with various loops of primary feeders and supplies distributors. The distributors are an arrangement of smaller mains serving the individual hydrants and blocks of consumers. To ensure a sufficient water supply two or more primary feeders should run from supply source to the high-risk and industrial districts by separate routes. Secondary feeders connect the primary feeders and supplies water from two directions to any point within a grid system.

Fire hydrants attach to the water main systems at certain points on the water system possibly every 500 feet in residential areas and every 300 feet in high-value commercial and industrial areas. Hydrants come to be in two forms — dry-barrel or wet-barrel. Dry-barrel hydrants are valves that allow water from the system to be used through two or three outlets — usually two and one-half inch for dual outlet hydrants or (two) two and one-half inch outlets and a four and one-half inch outlet for larger diameter hose connections. When opened, water floods the barrel and is available at all the outlets at once. If all outlets are used, extra gate valves on the smaller outlets attach to control flow from them. Dry barrel hydrants are found where freezing is a problem with above ground water supplies and has a drain opening at the base of the hydrant valve for water to escape the barrel when the barrel is closed to flows. Wet barrel hydrants have water on them at all times. Individual valves control flow from each outlet. These hydrants are found in areas where freezing is not a problem. All hydrants should be opened and closed slowly to prevent water hammer. Water hammer is pressure recourse when a valve is shut off quickly that stops water flow quickly and creates a backpressure enough to break piping or valves.

Several pressures relate to firefighters. These pressures are important to developing fire flows, fire streams and amount of water available. Static pressure is water standing still under pressure. With most water systems, water really does not stay still as water is constantly moving in the system. Residual pressure is pressure left over after water is flowing in the system. It is part of the total available pressure that is NOT used to overcome friction or gravity with water flowing through pipes, valves, hydrants or hose. Twenty psi is the minimum useable residual pressure needed to reduce any damage risk to underground pipes and valves. Flow pressure is forward velocity pressure at the discharge opening while water is flowing.

This brief look at our main weapon against “old man fire” gives us the ability to understand how and where the “bullets” we use come from. Water availability varies agency to agency. Whether you use tankers/tenders or utilize a municipal-type water system, understand what you have to work with and use it as efficiently as possible.

I sincerely hope all your holiday activities went off as expected and did well in giving and receiving. Stay well and keep safe in the streets.

Captain Coffey currently serves as one of the training officers of the High Point Fire Department. He has been an instructor with the NC Community College system and the Office of the State Fire Marshal since 1990. He can be reached at [email protected].
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