Managing the Urban Water Supply

The end result of any fireground water delivery operation is to provide the required volume of water in the form of effective firefighting streams to reach and overwhelm the British thermal units of the fire, achieving a knockdown as quickly and as safely as possible. This holds true for the smallest and the largest fires to which firefighters respond.

 

When dealing with a hydrant water supply, the operations need to be based on a proactive process. Proactive means being able to act in anticipation of a need or situation, which, in this case, means an insufficient water supply. It’s real simple: don’t wait until the water supply problem occurs. Have a plan for developing additional water in anticipation of its need. Too often we do the opposite and don’t address a water supply problem until it happens. By then, it can be too late. It can take as long as 15 minutes to set up a water supply operation. In 15 minutes, a fire can easily grow out of control, making the operation a catch-up disaster.

 

The following information will enable the decision makers on the fireground to maintain an adequate uninterrupted water supply throughout the duration of the incident. First, let’s discuss the low-flow fire of 500 gallons per minute (gpm) or less. 

SMALL-GPM WATER SUPPLY

The small- gpm fires statistically do fine with a basic supply line evolution from the hydrant. However, in the rare situation that the initial supply line can’t produce the required flow, you must have a plan to get more water. This type of operation is called “supplemental pumping,” a term used for operations that bring in an additional water supply to an engine that has its initial water supply and is running out. It is important to delegate this task to a unit from the start before a problem arises, not after. It can be as simple as having one operator with an engine set in staging ready to lay that second supply line to the pumping engine. 

Many departments use a hydrant assist valve to increase the flow to an existing water supply. This appliance is preconnected to the end of the supply line on the unit and is attached to the hydrant when a line is laid. When the hydrant is turned on, the water flows through the valve and into the supply line directly to the receiving pump as in a normal operation. If more water is needed from the hydrant, a second pumper can connect into the valve, divert the water through its pump, and boost the flow through the supply line without shutting the hydrant down.

.(1) This Los Angeles City (CA) Fire Department engine is pumping from

 

Because of the rare chance that a problem can occur, I don’t think a secondary line should be laid automatically, although if a commander chooses to do this, I would not fault him.

 

The secondary water supply should be based on a maximum effort within reason. Obviously, dual large-diameter hose (LDH) supply lines are not called for in a low-volume operation; however, a single LDH line, and even a pump on the hydrant, is acceptable. It will most likely be overkill, but why not? It takes little effort, and it is better to have more than enough water rather than too little. You never know when a fire could escalate rapidly. 

LARGE-FLOW WATER SUPPLY

During the initial size-up of a large-volume fire, one of the tasks that needs to be addressed is setting up secondary water supplies to the initial attacking units. Again, as with the small-fire operations, assign operators and their units to develop the evolutions needed. The only difference between the large- and small-water supplies is that the units should immediately deploy the secondary water supply evolutions. There’s that proactive word again. Don’t wait for a water supply problem to arise; set up that backup system in anticipation of having issues, because on the big one, there is a good chance it will. Now is the time to make a maximum effort to get as much water as possible to the fireground.

(2) If you run out of water, do you want to wait 15 minutes with streams like this?  

Supplemental pumping is the key ingredient for a large-flow water delivery operation, especially when distant hydrants are needed to supply engines already operating and in need of more water. Often at large fires, the first few units will lay from hydrants close to the fire and spot in the area needed. This is when a water supply problem usually starts. These units have everything they need to attack the fire. They have the personnel, correct apparatus placement, and proper deployment of the discharge evolutions. Since these units brought in hydrants close to the fireground, the hydrant grid system in that area is becoming depleted of water or pressure.

 

This is when distant hydrants come into play. The goal is to pick a hydrant that is on another grid. Choosing hydrants on another grid means there is a good chance that they will be far away. The long supply lines needed for these hydrants will create high friction loss, which, in turn, will result in a significant loss from the hydrant being used.

 

To rectify this problem on these long lays, a relay pump operation should be set up to overcome the friction loss. A relay pump operation involves placing an engine at the water source to increase the pressure in the supply line by pumping into it. Now, for the receiving end of the relay pump operation. Remember, we already have units connected to depleted water supplies delivering water onto the fire. One of the goals for a relay is to supplement the existing operations with more water. For the most part, these individual units do not need a lot of water to fulfill their water requirements. There is a good chance that a relay pump operation will be able to move from 1,500 to 2,000 gpm. With this being the case, one relay can supplement two to three units already working on the fireground.

 

 

Water main maps are very helpful in locating grids, but they are not always available to the fire departments. If in doubt as to where another grid is located, take the overkill approach. Lay extra hose to get far away from the fireground. This may require the unit’s laying the line to pass up several hydrants to get far enough away. It would not be uncommon to see a 1,000-foot or more lay to accomplish this.

 

A dual-pump operation can be set up between the units on the receiving end of the relay, allowing them to share the extra water being brought in. Dual pumping is an evolution that allows engines to share the same water supply by connecting the supply hose from the intake of one pump to the other. The residual pressure from the pump receiving the water supply from the relay will push the water from that pump to the other.

 

 

Dual pumping can also be set up between engines before the water need arises. Establishing this link will open a line between the engines that will automatically share the water as needed. The unit in the dual-pump operation that has the lowest residual pressure will receive water from the unit with the higher residual pressure. Water flow takes the path of least resistance. Placing engines together with dual pumping and relay pumping, especially when more than one hydrant is used, can be referred to as a “looped supply line operation.” It works on the same principle as a looped water main system does, which is getting water from more than one direction or source. 

(6) An alternative to the dual-pump operation uses a large gated manifold at the receiving end of the relay to distribute the water to multiple engines on the fireground.

 

Figure 1. This illustration shows a looped supply line evolution. Several engines are connected to five hydrants, sharing water using dual-pump operations.

Providing an adequate water supply to a fireground incident, big or small, is crucial for a successful operation. This article has given the information needed to move the water efficiently. Don’t wait until the water supply problem shows its face to rectify it. A proactive approach ensures that the water supply is never in jeopardy.

 

Paul Shapiro is director of Fire Flow Technology. He is a nationally recognized instructor on large-flow water delivery. He is also a retired engineer from the City of Las Vegas (NV) Fire Department. He has authored numerous articles for fire trade magazines. He has been in the fire service since 1981 and is author of Layin’ the Big Lines and produced the first in a series of videos on large-flow water delivery. He is available to answer questions; he can be reached at (702) 293-5150 or Layinline @aol.com.