From Hoselines to Hydrants: Understanding Water Supply

Effective supply hoseline operations are essential to engine company operations. While some operations will be performed through drafting, water shuttles or relay pumping, the most common and basic water supply operation is through a fire hydrant. For hydrant operations, firefighters must understand the capabilities and limitations of the supply hoselines as well as the water main system that is supplying the hydrants, not to mention the hydrants themselves.

Hoseline operation basics

The three most common supply hoseline setups are two 2½-inch, two 3-inch and a single 5-inch supply hoseline. Both 2½- and 3-inch hoselines are considered medium-diameter, while the 5-inch hoseline is considered large-diameter. Many firefighters will say that two 2½-inch hoselines equal one 5-inch hoseline, but this is not the case.

When evaluating the effectiveness of a supply line setup, firefighters must evaluate each factor that affects the operation—water quantity, friction loss and distance. Water quantity refers to the amount of water that a supply line contains when charged. Friction loss refers to the amount of pressure that is lost due to friction within the hoseline. Distance refers to the distance that the water must be transported from the water supply source to the fire scene.

Medium-diameter hoseline comparisons

The two 2 ½-inch hoselines is a common setup. Departments often use 2½-inch instead of 3-inch hoselines so that they can order a single size hoseline for multiple purposes, such as supply attack hoselines. The problem with using 2 ½-inch lines as supplylines is that they are not as effective as other size hoselines.

The two 2½-inch supply hoseline setup will contain approximately 26 gallons of water per 100 feet once charged. The friction loss is as follows¹:

500 gpm – 15.5 psi per 100 feet
600 gpm – 23 psi per 100 feet
700 gpm – 29.5 psi per 100 feet
800 gpm – 38 psi per 100 feet
900 gpm - 48 psi per 100 feet

The increased amount of pressure that is lost from friction in the two 2½-inch supply hoseline setup greatly reduces the distance in which this supply hoseline setup can effectively transport water from the supply source to the scene. The distances for which the two 2½-inch line setup can effectively transport water is as follows²:

750 gpm – 640 feet
1,000 gpm – 360 feet
1,250 gpm – 200 feet

The two 3-inch supply hoseline setup is identical to the two 2½-inch setup in both the manner in which the supply hoselines are loaded in the hosebed of the apparatus as well as the manner in which the supply hoselines are placed into operation. Due to the larger size of each hoseline used in this setup, the quantity of water that the hoselines contain is increased while the friction loss in the hoselines is decreased. This allows for the two 3-inch line setup to effectively transport water for a greater distance than the two 2½-inch line setup.

The two 3-inch supply hoseline setup contains approximately 36 gallons of water per 100 feet when the hoselines are charged. The friction loss is as follows¹:

500 gpm – 6 psi per 100 feet
600 gpm – 8.5 psi per 100 feet
700 gpm – 11.5 psi per 100 feet
800 gpm – 14.5 psi per 100 feet
900 gpm – 18.5 psi per 100 feet
1,000 gpm – 22.5 psi per 100 feet
1,100 gpm – 27 psi per 100 feet
1,200 gpm – 32 psi per 100 feet
1,300 gpm – 38 psi per 100 feet
1,400 gpm – 44 psi per 100 feet
1,500 gpm – 50 psi per 100 feet

The decrease in friction loss between the two 3-inch and the two 2½-inch setup allows for a much greater fire flow to be produced. While the two 2½-inch setup must account for nearly 50 psi per 100 feet of the supply line with a fire flow of 900 gpm, the two 3-inch setup will allow for a fire flow of 1,500 gpm to be produced with the same amount of friction loss in the supply hoselines.

The two 3-inch setup also allows for the effective transportation of water over a greater distance than the two 2½-inch setup. The distances in which the two 3-inch supply hoseline setup can effectively transport water is as follows²:

750 gpm - 1,600 feet
1,000 gpm - 900 feet
1,250 gpm - 500 feet

With this in mind, when selecting from medium-diameter supply hoselines, the 3-inch hoseline option is preferable over the 2½-inch option.

The large-diameter hoseline option

While medium-diameter supply hoseline setups are effective, they do not compare to the effectiveness of large-diameter hoselines (LDH), which allow for an increased quantity of water to be transported while losing minimal pressure to friction loss. This produces greater fire flows and allows LDH to transport water a much greater distance than medium-diameter lines. Whenever possible, the use of LDH is recommended, particularly when large fire flows will be needed or when water must be transported a great distance.

The most commonly used LDH is the 5-inch hoseline. When charged, a single 5-inch line contains approximately 100 gallons per 100 feet of hoseline. This is approximately 74 gallons more than the two 2½-inch supply lines sand approximately 64 gallons more than the two 3-inch supply lines.

The difference in friction loss between the large-diameter and the medium-diameter supply setups is also significant. The friction loss in a single 5-inch LDH is as follows¹:

500 gpm – 2 psi per 100 feet
600 gpm – 2.5 psi per 100 feet
700 gpm – 3.5 psi per 100 feet
800 gpm – 4.5 psi per 100 feet
900 gpm – 5.5 psi per 100 feet
1,000 gpm – 6.5 psi per 100 feet
1,100 gpm – 8 psi per 100 feet
1,200 gpm – 9.5 psi per 100 feet
1,300 gpm – 11 psi per 100 feet
1,400 gpm – 13 psi per 100 feet
1,500 gpm – 15 psi per 100 feet

The amount of pressure lost in LDH is minimal, allowing for great fire flows. A 900-gpm fire flow will create 48 psi of pressure loss per 100 feet with the two 2½-inch lines setup and has 18.5 psi of pressure loss per 100 feet of supply hoseline when the two 3-inch setup is used. The same 900-gpm fire flow only creates 5.5 psi of pressure loss per 100 feet of supply hoseline in a 5-inch LDH. The minimal pressure loss allows for a single 5-inch large-diameter supply hoseline to transport water over a much greater distance than both the two 2½-inch and the two 3-inch supply hoseline setups.

The distances in which a single 5-inch large diameter supply hoseline can effectively transport water is as follows²:

750 gpm – 3,670 feet
1,000 gpm – 2,050 feet
1,250 gpm – 1,320 feet

The use of a single LDH is much more effective than the use of multiple medium-diameter supply hoselines during identical supply hoseline operations. LDH allows for greater fire flows to be produced and at greater distances. In some environments—such as urban environments where there is an established water supply source through the use of a fire hydrant system that utilizes adequately sized water mains to supply the hydrants and the distance between hydrants is minimal—medium-diameter supply hoselines are effective. In these environments, the use of LDH becomes more optional than mandatory, whereas in suburban and rural environments, the use of LDH is many times mandatory if the operation is to be successful.

Whenever a LDH is not available and a medium-diameter setup will be used, 3-inch lines should be used rather than 2½-inch lines. Even in the environments where medium-diameter supply hoseline setups are oftentimes successful, a LDH supply should be used in place of the medium-diameter options.

Hydrant capabilities and locations

Firefighters must also understand water supply sources. The most common is a fire hydrant that is supplied by a municipal water main system.

At the most basic level, the municipal water main system supplies water to the individual hydrants, which supply water to the supply hoselines, which supply water to the engine apparatus, which supplies water to the hoselines that are being used for fire attack.

Most firefighters understand that there are three types of water mains: primary feeders, secondary feeders and distributors.

Primary feeders are large pipes that transport large quantities of water from the pumping station to the distribution system.
Secondary feeders transport water from the primary feeders to the distributors.
Distributors are the smaller mains that create the grid system that serve individual hydrants.

Firefighters should pay closest attention to the distributors, as this is the type of water main that supplies the individual hydrants. The supply of water to a hydrant from a municipal water main system depends on multiple factors, including the location of the hydrant on the main and the size of the main itself.

The location dictates the number of directions from which the hydrant can receive its water supply. While some receive their water supply from multiple directions, others can only receive their supply from one direction. Such hydrants are known as being located on a dead-end main. Hydrants that receive their water supply from multiple directions are supplied with a greater quantity of water than their dead-end main counterparts and should be used whenever possible, especially when the required fire flow will be great.

The minimum size of distributor mains that supply individual hydrants is 6 inches and most modern systems are 8 inches or larger. Sometimes they can be up to 72 inches.

The quantities and flow rates of water in different size water mains are as follows³:

6-inch water main: 150 gallons of water per 100 feet – flow rate up to 800 gpm
8-inch water main: 260 gallons of water per 100 feet – flow rate up to 1,600 gpm
12-inch water main: 590 gallons of water per 100 feet – flow rate up to 4,700 gpm
24-inch water main: 2,350 gallons of water per 100 feet – flow rate up to 18,000 gpm

Hydrants that are supplied by larger water mains produce greater flow rates than hydrants supplied by smaller ones. Due to the larger volume of water and the decreased loss of pressure due to friction loss in the main, individual hydrants can be separated by greater distances when they are located on larger mains. For example, fire hydrants can be separated by the following distances based on the size of the water main that supplies them:

6-inch water main – hydrants can be up to 600 feet apart
8-inch water main – 900 feet apart
12-inch water main – 1,200 feet apart
16-inch water main – 1,600 feet apart

The distance between individual hydrants is extremely important, as larger water mains will allow for hydrants to be separated by distances that exceed the capabilities of some supply hoselines. Just because the larger size of a main allows for greater separation between individual hydrants along that water main does not mean that the individual fire hydrants will actually be separated by such distances. This separation may occur in rural areas but will not occur in urban areas. It is common practice to position fire hydrants as follows:

Residential – 400 to 500 feet apart
Townhouses and garden apartments – 250 to 300 feet apart
Commercial/industrial/high-rise areas – 250 to 300 feet apart

Flow rates & supply source

It is important for firefighters to understand the flow rate capabilities of the hydrant being selected for fireground operations.

In many communities, there is a color-coded system to assist firefighters with identifying the flow rate capability. Each paint color, found on the top bonnet of the hydrant, indicates a fire hydrant classification, which identities the flow rate capability of the hydrant. The system is as follows⁴:

Blue: Class AA – flow rate of 1,500 gpm or greater
Green: Class A – flow rate of 1,000 - 1,499 gpm
Orange: Class B – flow rate of 500 - 999 gpm
Red: Class C – flow rate of less than 500 gpm

The flow capacity rating of a hydrant is determined while water is flowing from all of the hydrant's discharge outlets. Therefore, unless all of the hydrants’ discharge outlets are being used, the flow from the hydrant will be less than the rated flow capacity. Whenever possible, firefighters should select either a Class AA or Class A hydrant for interior firefighting operations.

The company officer of the initial-arriving company must also understand the water main system that supplies the fire hydrant as well as other hydrants in the area. At fires that require the use of multiple engine company apparatus to achieve the needed fire flow, multiple fire hydrants will need to be used to supply those apparatus with water.

While the paint color on the top bonnets may indicate that they are capable of providing a specific flow rate, if all of the fire hydrants being used to supply the operation are located on the same water main, their ability to provide their identified flow rate will be compromised. The company officer should know the water main system in the area and advise other responding companies of which fire hydrants should be selected. At large fires, it is beneficial to use multiple fire hydrants that are located on different water. If possible, firefighters should use fire hydrants that are located on the larger water mains in the area.

The supply source can sometimes be identified by a paint color on the fire hydrant, usually on the body. Typically, the color codes vary from department to department. One common color code is to paint the body of hydrants supplied by a municipal water main system yellow, while the bodies of hydrants supplied by privately owned systems are painted red. If no color code system is used, pre-fire planning will be the only method for firefighters to learn where each fire hydrant in their response area receives its water supply from.

Issues of pressure

Pressure affects the operational capabilities of a hydrant as well. Like other fire service pressure calculations, both static pressure and residual pressure affect hydrant operations.

Static pressure is the pressure at the individual hydrant before water is flowing, and residual pressure is the pressure while water is flowing. The available flow rate from a hydrant is determined using residual pressure, but static pressure also factors into the equation. The flow rate of a hydrant is typically identified by determining the available flow rate when the residual pressure drops to 20 psi. While a residual pressure of 20 psi is the general rule of thumb, NFPA allows for the available flow rate from a hydrant to be determined at residual pressures less than 20 psi in low-pressure areas. In these areas, instead of calculating the flow rate that the hydrant is capable of producing at a residual pressure of 20 psi, the flow rate should be determined at a residual pressure that is half of the static pressure of the hydrant. The reasoning is to place a demand on the fire hydrant that is typical of a firefighting operation and then determine the amount of water that the hydrant is capable of supplying under those conditions.

Some hydrants contain two 2½-inch discharge outlets while others also contain a 4½-inch steamer connection. If the hydrant that has been selected possesses a 4½-inch steamer connection, the steamer connection should be used with a LDH. This will provide the greatest initial flow rate with the least amount of pressure loss due to friction.

Firefighters should understand the flow rate that a hydrant discharge outlet can produce. Fire hydrants are flow-tested at a residual pressure of 20 psi; therefore, firefighters should understand the typical flow rates of fire hydrants at that pressure. They should not expect that the fire hydrant will be supplied at an increased pressure, resulting in a greater flow rate. Instead, they should understand the typical flow rate for each fire hydrant discharge outlet as well as understand the effect of under-pressurization of the fire hydrant.

Typical flow rate for fire hydrant discharge outlets are as follows⁵:

2½-inch discharge outlet:

10 psi – 500 gpm
15 psi – 610 gpm
20 psi – 700 gpm

4½-inch discharge outlet:

10 psi – 1,730 gpm
15 psi – 2,110 gpm
20 psi – 2,430 gpm

Understanding static and residual pressures will also assist firefighters with determining the number of hoselines that a hydrant can supply. A reading of the static pressure should be taken prior to charging any hoselines. This is performed by reading the pressure indicated on the apparatus’ intake compound gauge. Once the first hoseline is charged, another reading of the apparatus’ intake compound gauge should be taken. The difference between the static pressure reading and the residual pressure reading will indicate the amount of pressure that will be lost for each additional hoseline of the same size and flow rate as the first hoseline. This information can then be used to determine how many hoselines that fire hydrant can supply.

There are multiple ways to calculate how many hoselines a fire hydrant can supply. One of the easiest is the percentage method. For example, the static pressure reading of the apparatus’ intake compound gauge is 80 psi. After charging the first handline, the residual pressure reading is 75 psi. Charging the initial hoseline resulted in a pressure loss of 5 psi. Using the percentage method, the fire hydrant can supply three times the amount of water that is currently being supplied. The percentage method is used as follows:

0–10 percent drop in pressure = 3 times the amount of water currently being delivered remains available
11–15 percent drop in pressure = 2 times the amount of water currently being delivered remains available
16–25 percent drop in pressure = the same amount of water being delivered remains available
Greater than 25 percent drop in pressure = less water than is currently being delivered remains available

Once the number of hoselines that an individual hydrant can supply has been determined, the number of hydrants needed can also be determined. Anytime that a large fire flow is expected, such as a high-rise or commercial structure, additional fire hydrants should be utilized to establish additional water supply sources. In these situations, at a minimum, the first two arriving engine companies should utilize a fire hydrant located on separate water mains to establish multiple water supplies for the firefighting operation.

Elevation issues

Elevation differences between the individual hydrant and the water supply source also affect pressure. When the hydrant is located at a greater elevation than the source, it will have a decreased static pressure. When it is located at a lower elevation, the hydrant will have an increased static pressure. This is why reduced residual pressures are used for determining the flow rate capacity of fire hydrants located in low-pressure areas.

Firefighters should know which areas of their response area are located at increased elevations from the water supply source and which are located at lower elevations. This information will also factor into the decision-making regarding the type of supply line that will be utilized during operatios. Individual fire hydrants that are at an equal elevation to the water supply source or a lower will typically produce an adequate fire flow through the use of a forward supply hoseline lay or a reverse supply hoseline lay. Hydrants located at a greater elevation will typically require the use of a relay pumping operation to pump water to the fire scene.

When making the connection to the fire hydrant, firefighters must again remember that the identified flow rate capability of the fire hydrant is when water is flowing from all of the hydrant’s discharge outlets. Therefore, in order to receive the total flow capacity all of the hydrant’s discharge outlets must be used. In some instances, this may occur when the initial-arriving engine company connects supply hoselines to all of the hydrant’s discharge outlets. This type of operation typically only occurs when the fire hydrant is located at the same location as the fire building. In most cases, using all of the fire hydrant’s discharge outlets requires the use of hydrant valves.

The types of valves used for hydrant operations vary by department and and allow later-arriving companies to connect their supply lines to the same hydrant without having to shut down the hydrant. For example, if the initial-arriving engine company performs a forward supply hose lay operation using a 5-inch LDH line, two ball valves can be placed on the other discharge outlets of the hydrant. The second-arriving engine company can then connect its supply hoselines to the hydrant valves. Once in position, the hydrant valves can be opened, allowing for the second-arriving engine company’s supply hoselines to be charged with water.

In sum

There is a lot more that goes into a supply hoseline operation than simply laying a supply hoseline on the ground and charging it with water. Firefighters must understand the capabilities and limitations of their equipment as well as the water supply systems that they will use during a firefighting operation. Unlike the common belief of many firefighters, two 2½-inch lines do not equal a 5-inch line. The 5-inch LDH possesses a water flow capability that is unparalleled by other supply hoselines. Further, the capabilities of the lines are not the only factor that affects the effectiveness of the supply line operations. The water main system and the hydrants that are used also have a great impact. If a hydrant with a limited water flow capability on a small dead-end water main is selected, it will not matter that the supply hoseline can transport a great amount of water over a great distance, as the fire may not be able to produce that same water flow rate.

References

Elkhart Brass Manufacturing Company. Fire Hose Friction Loss. Retrieved from www.elkhartbrass.com/files/aa/downloads/performance/Fire%20Hose%20Friction%20Loss.pdf.
International Fire Service Training Association. Pumping and aerial apparatus driver/operator handbook (3rd ed.). 2015. Stillwater, OK: Fire Protection Publications Oklahoma State University.
The reference for the gallons of water per 100 feet is Torrent Engineering and Equipment. Pipeline Volume Capacities. Retrieved from www.torrentee.com/pdf/Pipe_Volume_Capacity_Table_Jun-02.pdf.
The Engineering Tool Box. Still Pipes and Maximum Water Flow Capacity. Retrieved from www.engineeringtoolbox.com/steel-pipes-flow-capacities-d_640.html.
Akron Brass Company. Flow Test Procedures. 2002. Retrieved from www.akronbrass.com/media/pdf/HK_Instructions.pdf.