The Interior Attack Line: Getting the Most Bang for Your Buck

By Paul Shapiro


Did you know that National Fire Protection Association (NFPA) 1710, Standard for the Organization and Deployment of Fire Suppression Operations, Emergency Medical Operations, and Special Operations to the Public by Career Fire Departments, requires a minimum of two handlines for an interior attack with a combined total of 300 gallons per minute (gpm)?


Dividing this flow by the two handlines means that each line should be able to flow 150 gpm. Is your department currently meeting this standard? What would you say if I told you that it is possible for that initial 1¾-inch attack line to flow up to 240 gpm with two firefighters and is no harder to use than a 150-gpm attack line with a 100-pound-per-square-inch (psi) nozzle pressure (NP)?

Over the past several years there has been a push to lower the NP on handlines to make them more user-friendly for firefighters. The main focus has been on 100-psi combination nozzles and their nozzle reaction, especially with higher flows. Some departments that use 100-psi nozzles actually keep the flows as low as 100 gpm to make the handlines more manageable. Doing this corrects the handling issues. However, it comes at a cost by creating inferior flows. Remember-the minimum flow is 150 gpm. This article is going to show how a low-pressure nozzle in conjunction with proper hose-handling techniques can allow for an increased flow of 240 gpm using a 1¾-inch handline with an increase in nozzle reaction by no more than five pounds over nozzles flowing 150 gpm with 100-psi NP.

Before I cover how to accomplish this feat, consider the four main characteristics an interior attack line must possess: hose performance, nozzle performance, kink resistance, maneuverability.

Hose Performance

two types of 1¾-inch hose
1 There are basically two types of 1¾-inch hose: that which specs out to exactly 1¾ inches and one that is slightly larger at 17⁄8 inches. Shown here, with 1¾-inch on the left and 17⁄8-inch on the right, they look almost identical. However, the 17⁄8-inch hoseline’s friction loss is 20 psi less than 1¾-inch hose. (Photos by author.)

When 1¾-inch hose was first introduced back in the 1970s, its claim to fame by the hose peddlers was that it could take the place of 2½-inch hose in terms of handline flow capabilities. In those days, most 2½-inch handlines were only flowing 250 gpm, and folks were told that the 1¾-inch hose would also flow 250 gpm. What they neglected to tell firefighters was that the pump discharge pressure had to be high to move the 250 gpm with the smaller hose.

Here’s an example of what firefighters saw when they tried to flow 250 gpm through the 1¾-inch hose. With their 2½-inch lines, the average pump pressures were between 80 and 150 psi, depending on the length of the line and the type of nozzle they used. When they tried to pump 250 gpm through their 1¾-inch lines, they were developing pressures easily greater than 200 psi and sometimes pushing 250 psi. This was the trade-off for using the smaller-diameter hose.

Fire hose manufacturing has come a long way since the 1970s in improving hose quality, which in turn has lowered the friction loss (FL) numbers. So, what is the FL now?

There are two basic types of 1¾-inch hose in the industry. The first specs out to a true 1¾-inch-diameter dimension. Based on a 240-gpm flow, FL in this hose is between 60 and 70 psi per 100 feet. Keep in mind that these numbers are only approximate. To come up with exact numbers, it is important to do flow tests on the hose your department uses. Based on a 200-foot hand-line flowing 240 gpm, its FL, and the NP for the nozzle being used, approximate pump discharge pressures are as follows:

  • 160 psi for 40-psi NP and 60-psi FL per 100 feet.
  • 190 psi for 70-psi NP and 60-psi FL per 100 feet.
  • 220 psi for 100-psi NP and 60-psi FL loss per 100 feet.

The second type of 1¾-inch hose is actually slightly wider than 1¾ inches. The actual diameter is 17⁄8 inches. The hose weighs 20 pounds and looks no different than the standard 1¾-inch hose. The 1⁄8-inch increase in diameter provides a dramatic FL reduction. At a flow of 240 gpm, the FL for 100 feet of hose is approximately 40 psi.

The pump discharge pressure for 200 feet of this type of hose flowing 240 gpm is as follows:

  • 120 psi for 40-psi NP and 40-psi FL per 100 feet.
  • 150 psi for 70-psi NP and 40-psi FL per 100 feet.
  • 180 psi for 100-psi NP and 40-psi FL per 100 feet.

Out of the six handline examples, only one had a pump discharge pressure of greater than 200 psi. Additionally the 17⁄8-inch hose was able to lower the FL by 20 psi per 100 feet. With that being said, it is clear how 1¾-inch hose is very capable of higher flows. However, remember that this only addresses beefing up interior attack handlines, nothing else.

Nozzle Performance

Shown here are various nozzles. All will allow high flows on interior attack lines
2 Shown here are various nozzles. All will allow high flows on interior attack lines. From left to right are the Vindicator Heavy Attack, a 11⁄8-inch smooth bore, and a 250-gpm at 50 psi NP fixed-gallonage combination nozzle.

When choosing a nozzle for the high-flow interior attack line, make sure the nozzle can accomplish everything the department wants it to do. First, choose a smooth bore nozzle, combination nozzle, or Vindicator nozzle. This article does not cover the pros and cons of these nozzles. However, all three of them will achieve high flows for the interior attack line.

NP is probably the most important thing to address when choosing the correct nozzle for this operation. Remember the goal is to flow 240 gpm while keeping as close as possible to the 75-pound nozzle reaction of a 150-gpm/100-psi nozzle. It is possible to get really close to this number. To do this and get a good working stream, the NP is in the range of 40 and 45 psi. What about the reach of the fire stream? If the stream is reaching its target and delivering the required flow, then a lower NP is acceptable. The streams listed below have more than enough reach for an interior attack:

  • Automatic nozzle flowing 150 gpm with 100-psi NP and 75-pound nozzle reaction yields a 90-foot reach.
  • 11⁄8-inch smooth bore nozzle flowing 240 gpm with 40-psi NP and 79-pound nozzle reaction yields an 84-foot reach.
  • Fixed-gallonage nozzle flowing 237 gpm with 45-psi NP and 80-pound nozzle reaction yields an 86-foot reach.
  • Vindicator nozzle flowing 240 gpm with 40-psi nozzle base pressure and 60-pound nozzle reaction yields a 90-foot reach.

Kink Resistance

Kinks in handlines
3 Kinks in handlines, like the one shown here, are often blamed on low pressures. However, tests have shown that departments can achieve high flows with low pressure. The higher the volume of water flowing through the line, the harder it will be to kink it.

When I was a pump operator, one of my jobs, besides getting water to the troops, was to chase kinks in the handlines coming from my rig. It seems like every fire was good for at least a couple of kinks. A lot of firefighters associate the kinking problem with low pressures in the handlines-the big contributing factor being a low-pressure nozzle.

Kirk Allen, from First Strike Technologies, has proven through flow tests that low pressure is really not a main contributor to the kinking issue. He has proven that it is the volume of water being delivered. The higher the volume, the less kinking will occur-even under low pressure. The current flow range of interior attack lines (the 150-gpm range) is a low enough volume to allow for kinking. Keep the physics here in mind-150 gpm is within the standard for fire flows. Allen performed the following test to prove this.

Using two-inch hose, he first flowed 140 gpm using an automatic nozzle with a 100-psi NP. His pump discharge pressure was 130 psi. Personnel placed a severe kink in the line, which reduced the flow to 65 gpm. Again the NP was 100 psi, which is not considered a low-pressure issue. He then used a Vindicator nozzle with a nozzle base pressure of 30 psi and flowed 260 gpm with the same 130-psi pump discharge pressure. Personnel tried to put a severe kink in the line, but it was extremely hard to do. A flow reading revealed no loss in gpm. The 30-psi base pressure is considered extremely low, but there was no loss in flow.

The following series of flow tests using 1¾-inch hose are designed to prove this concept.


  • An automatic nozzles flowing 150 gpm with a 100-psi NP flowed 105 gpm when kinked.
  • A smooth bore nozzle with a one-inch tip flowing 200 gpm with a 45-psi NP flowed 170 gpm when kinked.
  • A smooth bore nozzle with a 11⁄8-inch tip flowing 240 gpm with a 45-psi NP flowed 220 gpm when kinked.
  • A Vindicator nozzle flowing 250 gpm with a 30-psi base pressure flowed 225 gpm when kinked.


Based on the increased flow of 240 gpm, if you are expecting to learn new hose handling techniques to handle the increased flow, you are going to be disappointed. Even though the flow has increased significantly, the nozzle reaction has not.

There are two easy ways to handle the 240-gpm 1¾-inch handline. Remember, it is the same as a 150-gpm/100-psi-NP line. If the two firefighters on the line are both at the nozzle, simply have the backup firefighter support the nozzle firefighter by grabbing the back of the line and laying his body into the firefighter on the nozzle if needed. The other technique is also very simple. If the firefighter at the nozzle needs to flow the nozzle and is having a difficult time, and the backup firefighter is not next to him for whatever reason, all the firefighter has to do is put his weight on the hose by kneeling on it and the nozzle reaction will be basically put into the ground at the point where the firefighter’s body contacts the hose.

Increased Flows Possible

Higher flows do not mean higher pressures
4 Higher flows do not mean higher pressures; there doesn’t have to be a high nozzle reaction when using high-flow interior lines. Shown here is an example of a firefighter down low, applying his weight on the hose for control. Personnel using high-flow interior lines do not need to master any new hose-handling techniques.

Low-pressure interior attack nozzles have been around for years and are designed for standard interior attack line flows of 150 to 185 gpm. The main purpose for low-pressure nozzles is to reduce nozzle reaction for firefighters. The high-flow interior attack line works on the same principle with one exception-the nozzles are rated for 250 gpm with low NPs. Additionally, many departments are using 100-psi combination nozzles with flows of 150 gpm-sometimes higher-and have adapted to their use successfully. For these folks, making a change to the high-flow interior attack line will be a piece of cake. At the most, they will only see a five-pound increase in nozzle reaction. With proper training, all departments can use the high-flow interior attack line, even the ones that are currently using low-pressure nozzles.

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 Las Vegas (NV) Fire Department. He has authored numerous articles for fire trade magazines. He has been in the fire service since 1981, is author of Layin’ the Big Lines, and produced the first in a series of videos on large-flow water delivery.

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