By Chris Mc Loone
FireEngineering.com
Hose relays can be as simple as an attack truck in front of a dwelling with a supply line connected to it from a hydrant and an engine connected to the hydrant to boost the pressure in the supply line, or as complex as a mile’s worth of hose in the street with engines connected to relay valves throughout the line. Simple or complex, the critical factors that can make or break a successful relay are the individual chosen to establish the water supply as water supply officer and the engine operators throughout the relay.
You’ll see large-scale hose relays employed at large-scale fires where defensive operations have been initiated and a substantial amount of water is required to extinguish the fire.
When setting up to deliver a high volume of water, we are often establishing a large-diameter hose (LDH) operation of some sort. There are several things to consider when establishing an operation of this type:
- The total amount of water (gpm) you are trying to flow;
- Procedures for establishing an LDH relay;
- Friction loss involved in delivering the gpm;
- Location from which you are supplying the water; and
- What resources are available to move the amount of water required.
These are only a few items. The water supply officer chosen should be knowledgeable enough to make the decisions necessary to get the IC the water needed for extiguishment.
The Water Supply Officer
If you’ve been put in charge of establishing a water supply, you should know a few things before you go about setting up a major water supply operation. You’ll be coordinating numerous incoming units, determining the pressures each should pump, and directing them to lay a specified amount of hose, to name just a few things. You need to know what media will be used to transport the water. If you’re establishing a hose relay operation with LDH, you’ll be able to easily move 1,000 gallons per minute (gpm). Is that overkill? Is it not enough? Prior to the IC putting you in charge of getting the operation up and running, what decisions were already made? How much setup has been accomplished? What units are already committed? Was this a defensive attack from the start? Are we talking a mill burning to the ground or a Cape Cod dwelling with fire on the second floor? Many of these things you’ll already know–type of structure, occupancy, offensive/defensive-via the dispatch and radio traffic. Some of it you might not, depending on when you were recruited to establish the water supply. Once you have the answers to these questions, you can begin to implement a plan, beginning with your water source.
Where’s the Water?
When you’re setting up a hose relay, you want the biggest, fattest hydrant(s) you can find to deliver the amount of water you need. For more rural response areas, drafting operations might be the norm. For tanker shuttles or tanker task force operations, know where you intend to get the water to fill the tanker.
It helps to have a few different hydrants built into your preplan, in case one is out of service, it’s a cold night and your hydrant of choice freezes, or a hydrant has been moved since the preplan was written. There are also cases where two hydrants operating from different mains might be required. Regardless, as soon as you determine where you are getting your water, it’s time to figure out the logistics of transporting it.
How is it going to get here?
Deciding how you’re going to get the water to the scene is the easy part-via LDH, tankers, etc. The more appropriate question is, “How long will it take to get here?” LDH operations take a long time to set up. They are methodical. If the site of the fire has been preplanned, then incoming units already know how much hose they are going to lay; how much water they expect to flow; and, with any luck, the apparatus operator has a good feel for what the water supply commander is trying to accomplish and is competent enough to set things up. These factors ease the pain of figuring out how the water will get to the fireground.
If the operation becomes an LDH operation, the water is going to travel from a hydrant with an engine connected to it, through the hose, through a relay valve with another engine connected to the valve, and again through the relay valve/engine combination until the water reaches the main attack truck. Circumstances might exist where you have an attack engine with several lines stretched and operating with master streams, and another attack apparatus like a ladder or quint flowing water. In this case, you’ll probably need to get water from two separate hydrants on different mains unless your first choice is a monster. Otherwise you’ll be stealing from one attack truck or the other and your pressures won’t be as great.
A tanker shuttle operation will require tankers to travel to the source of the water to be refilled, transporting water back to the scene. At times, multiple tankers will be required at the water source
Physically, we’ve determined how the water will get to the scene. Now it’s time for Water Supply to consider the equipment involved with the task.
Apparatus Involved
The potential exists that you’ll have engines coming from different municipalities that may not have standardized pump setups. Some might have 15-year-old engines with 1,250-gpm pumps; others might have new engines with 2,000-gpm pumps on them. Either variation can handle a hose relay moving 1,000 gpm. It is important to know the largest diameter hose these engines carry. Some municipalities have moved to 6-inch hose, others still use 5-inch, and some never made the switch from 4- to 5-inch. The IC must know what engines are in the relay and what their capabilities are. Remind the 1,250-gpm engine operators if they have two-stage pumps to set the pump in the volume position. Try to ensure that the engines you direct to the relay operation are equipped with an extra length of hose just in case a length should blow in the line. And know what different types of relay valves these companies use. The officer chosen will more than likely have a good feel for all these things.
Preplan, preplan, preplan
All the topics covered so far involve items that can be preplanned. Drive around your first due, determine various hydrant pressures, and select the best ones for a particular occupancy. Make a list of the hydrants the water supply commander can easily consult when establishing the water supply. Create a task force (call it whatever you want) made up of units preselected for the equipment they carry to do the job. Only put the highest gpm pumpers on the list, for instance, or only put engines that carry a certain amount of LDH on the list.
Preselect a gpm you want to operate at any time a hose relay is called for. For instance, if you decide that a hose relay operation calls for 1,000 gpm, you can figure out the friction loss per 100 feet of hose (for 5-inch, this is approximately 7 psi). Once you decide how many lengths each truck will lay, you multiply that number times 7 and add whatever you want the residual pressure (pressure on the compound gauge) of each truck to be.
If you know what’s coming, you can more easily determine how the water will get from its source to its destination; and, as units call on location, you can put them to work quickly, reducing (hopefully) the time it takes to establish the supply.
Hose down, now for the water
Different departments have different SOPs for hose relays. Use your department’s obviously, and communicate the procedures to all units in the relay. If your SOP calls for all trucks to be in pump gear but their transmissions in neutral as the hydrant is charged, make sure the units in the relay know that. Communication is the key. As water supply officer, you are going direct the whole evolution. Remember that no one shuts down before the attack truck at the end of the relay shuts down. Make sure there is no freelancing. Multi-thousand-dollar pieces of equipment could face serious repair if anyone decides to freelance.
And don’t forget to call the IC and announce a water supply has been established. That’s one item he can check off his list.
Next week we’ll cover engine operations during a relay.
Chris Mc Loone is FireEngineering.com’s Web Editor. An 11-year veteran of the fire service, he holds the position of First Assistant Engineer for Weldon Fire Company in Glenside, PA. He can be reached at chrism@pennwell.com.
