It’s 3 a.m. and you hear the tones: It’s a structure fire. As you roll out of bed and head for the door, more details come over the radio. It’s a 2-story, mixed-occupancy, mixed-construction building and it’s fully involved. The trucks roll out of the station, and as your head starts to clear, you think to yourself, OK, plenty of equipment, plenty of firefighters, things look good. Then you ask yourself, are there hydrants nearby? If so, are they up to the task? And then it hits you — I should know this.

Unfortunately, this is a common issue in the fire service. Departments know their fire apparatus and equipment, their people and their capabilities, but often they are not entirely familiar with the water system they use. While equipment and staffing are critical to effective firefighting, most would agree that an adequate water supply is equally important.

So where do you start to learn about your community’s water supply? The critical first step is to determine what is needed for fire-protection purposes. To make such a determination, you must identify the needed fire flows (NFFs) for various buildings, which sets a good benchmark for assessing the water system’s capabilities. NFFs consider the construction type, square footage and occupancy of the subject building. That information then is converted into a necessary flow of water for fire extinguishment expressed in gallons per minute (gpm). With such information in hand, you can conduct an analysis to determine how your community’s water system measures up.

The next step is to schedule a meeting involving your staff and the manager and/or operator of the water system. Generally, the manager can advise you about ongoing projects, timelines, and future improvements, while the operator will be familiar with information on the pumps, tanks, treatment facilities, and water lines — all of which are important to understanding system operations and capabilities. You’ll want to know the following:

• The system’s production capacity (generally stated in millions of gallons per day, or mgd)
• Storage tank capacity and type
• Average minimum tank levels
• Storage tank locations
• Pump station locations, their capacity, and how they work in the system
• Maximum consumption figures for a given day

In addition, you’ll need to know about emergency interconnects with other water systems, if they exist, and how to get them flowing. Now, armed with all that information, it’s time to consider water main capacity.

Test, Test, Test

Fire flow testing provides a great deal of information about the condition of a water system at a specific point within the system. It also provides the water-carrying capacity of the water mains in the system. With additional information such as line sizes and/or previous flow results, the flow volumes quickly can point to problems, including closed or partially closed valves and heavily scaled mains.

The testing process also provides valuable information on the operability and integrity of fire hydrants. While single-hydrant testing can provide helpful data, ideally, two hydrants will be used in order to obtain the most accurate results. The two-hydrant approach provides enough data to calculate expected flow volumes at a given residual pressure; generally, 20 pounds per square inch (psi) is acceptable. In other words, there may be more water available in the water mains for firefighting than the hydrant discharge indicates if the water main pressures during flow testing are above 20 psi. Using standard flow-test calculations, you can then determine the available flows and compare the results with the NFFs of the buildings in the area. Deficiencies should be discussed with the water department.

With fire flows calculated, you will know what the water mains in the area will produce. But will you know whether that volume is sustainable? The information gathered during the meeting with the water department system operator will help you answer that question. Let’s start with water plant production capacity, which often is expressed in mgd. To simplify things, you’ll need to convert the rated capacity from mgd to gpm. To do so, take the mgd number and divide by .00144 to get the gpm rating. You’ll need to do the same calculation for the maximum daily consumption if it is provided in mgd.

Next, calculate the capacity of each tank at its average level and divide that number by 120 minutes to get a gpm rating for a two-hour period. Then, add the treatment capacity to the tank capacities and deduct the maximum consumption number to determine the expected available volume that the water main system will provide. (If emergency interconnects are available, add the expected volumes for each one into the calculation.) Generally, this number will be a constant for each NFF location. Compare this number to the NFFs to determine whether deficiencies exist.

Finally, are there enough fire hydrants near the NFF locations to get the water out of the mains and onto the building if it were on fire? After all, having plenty of water in the water mains but having no ability to access it is not helpful. So, depending on the size of the supply hose used, consider a value for each hydrant within 1,000 feet of each NFF location. If you’re carrying 2.5-inch supply hose, hydrants within 300 feet are credited at 1,000 gpm; hydrants between 301 and 600 feet are credited at 670 gpm; and hydrants between 601 and 1,000 feet are credited at 250 gpm. Larger supply hose will increase the values for the hydrants over 300 feet. The increased values will depend on hose size and operational methods. For example, with a 1,000 gpm pumper, 1,000 feet of 5-inch pumped supply line could produce 1,000 gpm at 1,000 feet. For each NFF, add the hydrant credits to determine whether there are any deficiencies.

What if you’re evaluating areas that don’t have fire hydrants? Alternative water sources can be very beneficial. They might include ponds, lakes, rivers or other sources from which an apparatus can draft water safely. To determine the capacity available to the fire department in dry weather conditions, a 50-year drought study is helpful. Establishing a water supply in such areas might involve long hose lays or water shuttles, or a combination of the two. Regardless of the method or source, evaluations should be run to determine expected flow rates.

Fire Protection Systems

Reliable water supplies are essential not only for structural firefighting activities, they also are critical for the effective operation of water-based fire-protection systems, such as automatic sprinklers. While many components make up an automatic sprinkler system, the single most important component is the water supply.

Every sprinkler system must have at least one automatic water supply capable of providing the needed flow and pressure for the required duration. Systems that are designed inadequately, have areas lacking sprinkler protection or contain questionable components — such as obsolete valves or recalled sprinkler heads — may still have some ability to control a potential fire. However, sprinkler systems with poor water supplies may have little or no value for fire-protection purposes.

The remainder of this article will focus on sound risk-management and preventive-maintenance measures for ensuring reliability of the most common water supply sources for automatic sprinkler systems:

• Public and private water mains
• Elevated storage tanks
• Ground-level suction tanks
• Static water sources
• Pressure tanks

Public and private water mains. These are the most common and usually the most reliable water sources for fire protection systems. In addition, they’re often the least expensive to install and can provide a virtually unlimited water supply.

Both public and private water supply mains require regular inspection, testing and maintenance. The American Water Works Association and the National Fire Protection Association recommend that water distribution systems be maintained at least annually, including flushing and testing of fire hydrants. This helps to ensure that the system is in good working order, removes foreign materials from the water main, and identifies obstructions and closed valves in the underground piping that could impair the sprinkler system. Regular testing of the sprinkler system by fully opening the main drain and documenting the static and residual pressures also can uncover similar problems in the water supply main.

For high-rise buildings and large-scale storage warehouses that require high pressures or large volumes of water for the fire sprinkler system, the municipal supply may not be capable of meeting the system demand. In such cases, a fire booster pump usually is provided to supplement the pressure available from the water supply main. This can lead to additional problems because fire pumps are subject to mechanical failure and require frequent testing to ensure that they’ll operate when needed. According to NFPA 25, Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, requirements for testing of fire pumps include a weekly churn test without flowing water and an annual discharge test under the pump’s minimum, rated and peak capacities.

Elevated storage tanks. Rooftop and tower-supported gravity tanks usually are constructed of wood or steel and range in capacity from 5,000 to 500,000 gallons. They can be the primary or supplemental water supply for the fire sprinkler system and may supply a single building or a large complex of buildings. Such tanks leverage gravity and therefore do not require a mechanical means to provide pressure to the fire system.
Some of the main concerns with elevated storage tanks are their limited capacity; the potential for freezing; and the need for a comprehensive inspection, testing and maintenance program.

Because storage tanks are limited in their capacity, they eventually can run out of water. This is especially problematic if the sprinkler system supplied by the tank is not properly designed for the building occupancy. For example, a 12,000-gallon rooftop gravity tank would be sufficient for a light-hazard occupancy requiring a flow of 400 gpm for 30 minutes. However, if the building occupancy changes to ordinary hazard with a demand of 750 gpm for 60 minutes, the minimum tank capacity would need to increase to 45,000 gallons.

Elevated storage tanks subject to freezing must be heated in accordance with NFPA 22, Water Tanks for Private Fire Protection. Failure to maintain adequate heat could lead to catastrophic failure of the tank. During the cold season, tanks also must be checked daily for proper temperature or outfitted with low-temperature alarms.

Inspection, testing and maintenance are required for the actual tank structure and all of its components, including: weekly inspection of the water supply control valves; monthly inspection of the water level; quarterly inspection of exterior supporting structures, vents, foundations, catwalks and ladders; annual inspection of hoops, grillage, and painted, coated, and insulated surfaces; and an internal inspection every three to five years.

Ground-level suction tanks. Such tanks serve as the supply source for an adjacent fire pump that may provide protection to a single building or an entire complex, including the water supply for yard mains and fire hydrants. They usually are of steel construction and can range in size from 50,000 to 1 million gallons.

Potential problems with suction tank systems are similar to those of elevated storage tanks — specifically, they’re of limited capacity; are subject to freezing; and require regular inspection, testing and maintenance. Since suction tanks are dependent on fire pumps, mechanical failure also is a possibility. Another concern is that the tank and pump house could be exposed to the same fire they’re intended to control.

Static water sources. Water for sprinkler systems can come from natural or manmade sources, such as lakes, ponds, reservoirs and wells. These usually are found in areas where there is no municipal water system. To be an acceptable water supply for fire protection, the static source must be capable of delivering the volume and duration required by the system, and available 24/7/365.

When designing these types of systems, detailed engineering studies are required to determine whether the volume and capacity will be available under 50-year drought conditions. For instance, an engineer must ensure that a well’s water supply can keep up with the demand and draw of the fire pump. An additional concern with fire pumps is the possibility that they can become clogged with debris, fish and silt from lakes and ponds.

Pressure tanks. They usually are found in rural locations where city water is unavailable or used as supplemental water supplies in high-rise buildings. They typically range in size from 3,000 to 9,000 gallons and are filled two-thirds with water and one-third with air to maintain a minimum pressure of 75 psi.

Pressure tanks as a primary water supply have minimal value for fire protection. Because of their very limited capacity, they are designed only to suppress room fires in light-hazard occupancies. Once the water is gone, no more water is available to the sprinkler system.

“Be prepared” is a core philosophy for all firefighters. Learning in advance about your community’s water system capabilities will ensure that your department will be better equipped to handle all contingencies. So, the next time you hear that bell and ask yourself about the needed fire flows at a structure fire location, you’ll already know the answer.

Brad Bain, CFPS, is manager of community hazard mitigation services at Insurance Services Office. Eli Stern, CPCU, CFPS, is ISO’s manager of survey services.

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