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Nozzles 101: Smooth-bore vs. combination/fog nozzle

Master the operating pressures, flow rates and features associated with each nozzle type


You may think of nozzles as simple tools designed to deliver water via a standard stream, but are you really being as efficient as possible in the fire attack process?

No matter what side of the table you sit on in the smooth-bore vs. fog nozzle debate, there is no other tool that is as iconic, nor more important for the engine company, than the nozzle. These priceless instruments of extinguishment are too often taken for granted, incorrectly used or simply misunderstood.

You may think of nozzles as simple tools designed to deliver water via a standard stream, but are you really being as efficient as possible in the fire attack process? Or are you using old pump operation methods that have been passed down through generations or written in policy even though the nozzles may have changed or been updated?

Here we’ll explore the various types of nozzles – pros, cons, use cases and more – but first, a reminder to review the relevant NFPA standard.

NFPA 1964

All nozzles in the fire service are manufactured in accordance with and classified by NFPA 1964: Standard for Spray Nozzles and Appliances, which was last updated in 2018. NFPA 1964 covers everything from operational design, construction materials, testing methods and compliance testing. The content is highly technical, essentially fire service encyclopedias that contain all the pertinent information to help you understand how to use your nozzles. Take time to review this standard to expand your knowledge of fire service nozzles.

Key question: Smooth-bore vs. fog/combination?

The first point in any discussion of nozzles comes back to nozzle type – smooth bore vs. fog or combination. We throw around these terms, but do you know the differences between them?

  • Smooth-bore nozzles have a cylindrical metal fixed-size orifice. They produce one type of fire stream – solid.
  • Fog or combination nozzles are synonymous. A combination fog nozzle can produce different fog streams by rotating the stream pattern’s bumper. These nozzles do not produce a true “solid” stream like a smooth-bore nozzle but rather a straight or narrow fog stream. Although similar in appearance, a fog nozzle’s straight stream is not the same as the solid column of water produced by a smooth-bore nozzle.

The fog nozzle is intended to create a higher heat absorption rate due to the smaller water particles produced, while the smooth-bore has some advantages in stream reach and penetration. While the two will likely continue to be debated, each nozzle has its place in the fire service, so we’ll focus on both, exploring the different nozzle types and design characteristics.


Nozzle components

Fire service spray nozzles can be produced as a single piece or in two pieces, often referred to as breakaways. Regardless, both contain core components that create the complete nozzle.

All nozzles are produced with either a 2.5- or 1.5-inch threaded connection. These are to attach to the male coupling of the fire hose. The water is then funneled into the shut-off portion of the nozzle. This contains the internal valve that is controlled by a lever called the bale.

Nozzles can be produced with several different types of valves, each one designed for a specific function when paired with the appropriate nozzle tip. These valves are commonly ball or slide valves. Furthermore, the ball valve can be either “whole” or “split,” again, each bringing its own functionality to the nozzle design and intended use.

Specifically, a whole ball valve maintains a smooth internal waterway that helps maintain a solid, undisturbed stream through the shut-off. These pair great with smooth-bore nozzles and their solid streams. However, these valves required more force to open and close in comparison to the split ball valve, which is assisted into an open or shut position via the pressure of the water flow. The split ball valve creates an indentation inside the waterway that generates turbulence as water passes through the shut-off and into the nozzle. Although not as impactful on a combination nozzle, this will have an immediate impact on the solid stream of a smooth-bore nozzle.

Once water flows past the valve, it then enters the true nozzle tip. Here the fire stream is produced through a combination of designed hydraulics and pump operations specific to the nozzle type and intended flow rate. We will dive more into that as we get into the four different nozzle types – one being smooth-bore and the other three variations of fog/combination nozzles.

1. Smooth-bore nozzles

Smooth-bore nozzles are the true trailblazer in this tool category – the OG of the fire service nozzles. These nozzles are simple to produce, have no internal parts (only the valve assembly inside the shut off) and are relatively cheaper in comparison to other nozzle types.

As noted, smooth-bore nozzles have a tapered metal fixed-size orifice that produces a solid fire stream. They can be produced in either a long- or short-barrel variety (similar to rifles and ballistics), with the longer barrel intended to produce a longer stream reach.

Smooth-bore nozzles for handlines are designed for an operating pressure of 50 psi, although I have seen functional fire streams produced with as low as 35 psi – obviously not ideal. The internal orifice size then determines the intended flow rate (gpm) of the nozzle tip at 50 psi. For example, the following are common smooth-bore orifice sizes and their flow rate at 50 psi:

  • 7/8-inch = 161 gpm
  • 15/16-inch = 185 gpm
  • 1-inch = 210 gpm
  • 1 1/8-inch = 266 gpm
  • 1 1/4-inch = 328 gpm

It is easy to find smooth-bore nozzle charts from nozzle manufacturers. Although 50 psi is the rated pressure, these charts often reference 40 psi and 60 psi flow rates. We refer this to the -10/+10 rule. Due to the fixed orifice size, the nozzle will still produce an anticipated flow rate at these other pressures. Using a 15/16-inch orifice as an example, which at 40 PSI will reach flow capabilities similar to a 7/8-inch (161 gpm) at 40 PSI, while achieving 1-inch nozzle diameter flows of (210 gpm) at 60 PSI.
There are some benefits and disadvantages of under-pumping (-10) or over-pumping (+10) these nozzles. Some include decreased nozzle reaction. Nozzle reaction is the opposite reactive force - measured in pounds - created from both the water volume and operating nozzle pressure that the firefighter experiences when water is flowing. By decreasing the nozzle pressure to 40 psi, it creates both a lower flow volume and nozzle pressure, which reduces the nozzle reaction. This could be helpful when lower water volume (gpm) are sufficient enough for extinguishment in certain situations, like overhaul, trash fires etc. But the reduced nozzle pressure can potentially lead to increased hose-kinking and different handling characteristics. Conversely, the higher the nozzle pressure of 60 psi will increase both the flow rate (gpm) and overall nozzle reaction. This may be beneficial when fire conditions are advanced and extinguishment would be better achieved with higher gpm.

When to use: Smooth bores are an open-shut case in my humble opinion. They are a must for high-rise/standpipe operations and municipalities seeking to have low-pressure attack packages. There is no risk of the pattern being unintentionally changed during advancement to the seat of the fire, and are good for single point ventilation compartment fires due to their reduced air entrainment properties. They are also very effective in large-open floor plan fire scenes where nozzle stream reach and penetration is favorable.

2. Fixed-gallonage combination fog nozzles

Fixed-gallonage combination nozzles are similar to smooth-bore nozzles in that they have a single intended operating pressure and flow rate. These two factors are determined by a rated stem that is inside the fog nozzle tip, which works like a fixed-orifice size for smooth bores.

The rated nozzle pressures for these nozzle types are 50, 75 and 100 psi, and correlate closely to smooth-bore flow rates. This creates a pressure interface on the internal stem, and as the pattern selector is rotated by the operator, it keeps a “fixed” flow rate regardless of the fog pattern utilized.

Because of the stem, the fire stream is actually hollow in the center, as the nozzle stream is forced around the head of the stem into the selected pattern. Many fixed-gallonage nozzles can have the stems changed in order to replace damaged or worn stems or to match the intended hose and operational capability of the fire department.

Some commonly used fixed-gallonage stem ratings are:

  • 150 gpm at 100 psi
  • 160 gpm at 50 psi
  • 185 gpm at 50 psi
  • 200 gpm at 75 psi
  • 250 gpm at 50 psi
  • 275 gpm at 75 psi

When to use: Fixed-gallonage nozzles can closely match certain smooth-bore counterparts depending on the stem chosen by the user. This is good for the overall pump-operations side of things, especially if the municipality uses a mix of both types of nozzles. The known flow rate is optimal. These nozzles are more effective in hydraulic ventilation tactics, vapor suppression, and specialized water delivery tactics, like compartmentalized attic fires due to their ability to deliver water in a fog pattern that increases heat absorption.

3. The selectable-gallonage nozzle

A selectable-gallonage nozzle is a combination fog nozzle that has a gallonage-selectable ring between the valve and the internal nozzle stem. This ring can be rotated and set to a specific flow rate but at a fixed nozzle pressure. The ring changes the internal diameter of the nozzle which has a corresponding flow rate at that setting.

Typically, these nozzles have a 75 or 100 psi operating pressure and can commonly have selectable flow rates of 60/90/125/150/200 gpm.

There is the risk of user error with these nozzles, as the nozzle firefighter must ensure that the proper flow rate is selected to achieve the target flow rate needed for the incident, as flows of 60/90/and 125 are too low for interior firefighting operations.

When to Use: Selectable-gallon nozzles are good for foam operations, as they can be adjusted to match the foam eductor’s settings for optimal foam production.

4. Automatic fog nozzles

Automatic fog nozzles have a different functionality and purpose in comparison to the other two types of combination fog nozzle. Automatic fog nozzles do not operate in a set flow rate; instead, they operate in a variable flow rate, or flow range, throughout a rated operating pressure.

The internal component of these nozzles is to create a constant nozzle stream and constant steam reach regardless of the flow or pressure. This is achieved by the internal baffle, which is loaded under tension by a coiled spring.

The flow ranges for these nozzles are 90-200 gpm with 75-100 PSI operating pressures. These nozzles will have labeling on the exterior of the nozzle for the operator to reference. Below is an example of a chart from a nozzle manufacture.


As the operating pressure of the nozzle is increased or decreased, the spring assists with maintaining the baffle in a fixed position, which in turn provides a steady stream reach, regardless of the gpm flowing. The weakness with this design is that a fire attack team may be grossly under-supplied but have a visually effective looking fire stream because of the internal baffle design.

When to use: I don’t have a whole lot of personal experience with these nozzles, other than some field testing, so those of you who do feel free to add some feedback into the comments section of this article. With that said, I think a department who has a good understanding of the flow variables these nozzles can produce on the fire ground, and teach solid pump operations, as the water delivery is essentially controlled by the pump operator may do OK with these as primary attack nozzles. Otherwise, I say these nozzles have a place in master-stream delivery methods where stream reach is imperative.

Fullest potential

As you can see, each of the four spray nozzles commonly used in the fire service brings its own operability and designs indications. They also have their benefits and opportunities for improvement in some applications. Whatever nozzles you have in your arsenal, make sure you are using these potent weapons to their fullest potential on the fireground.

Bonus: Why do combination fog nozzles have teeth?

Fog nozzles have either fixed or spinning teeth. The purpose of the teeth is to create a continuous water curtain. As the pattern selector is moved into a fog pattern, the stream engages with the teeth. Fixed teeth are usually rubber and are placed toward the outer edge of the nozzle’s bumper. Fixed teeth do not operate in very wide patterns and create more of “fingers” look in wide fog settings. These teeth are more durable, resistant to impacts, and function when dirty.

In comparison, rotating teeth are placed in a moving track close to the center of the nozzle. They can be plastic or metal, and spin when the fog pattern is moved to wide. These teeth create a wider, more consistent looking fog pattern when compared to fixed; however, they are suspectable to damage and debris (like sand) that can impact the functionality of the teeth.

Bonus: Alternative attack

Spray nozzles will always be the nuts and bolts of fire suppression, but as technology advances and we learn more about fire behavior, alternative fire attack tools will be introduced to the fire service on a more frequent basis.

In high-rise firefighting, there has been good success with flow-below nozzle systems, designed to attack the fire from the floor below. Large fire departments like FDNY and Toronto carry these attack options.

Further, as the fire service has adopted drones, it’s easy to start considering upper-floor firefighting. Testing has begun with drones that are large enough to deliver a substantial fire attack through the use of water and foam. As this technology advances into something that is feasible to deploy in the field, it will no doubt be a game-changing alternative.

Another alternative fire attack tool is the use of firebombs or grenades. These little devices are capable of delivering an aerosol of dry chemical or other compounds that can quickly suppress compartment fires within their early stages of growth. This is a good concept in theory, and it could be an option for some early first responders to deploy in certain situations.

But will anything ever replace the fire nozzle? Doubt it.

Vince Bettinazzi joined the Myrtle Beach (S.C.) Fire Department in 2007. He currently holds the rank of battalion chief and is assigned as a shift commander on C-Shift. Bettinazzi is a member of the department’s Ocean Rescue Team as a certified USLA lifeguard. He completed the NFA’s Managing Officer Program in 2016, and recently obtained his Chief Fire Officer Designation from CPSE. Bettinazzi is a co-host on the “Beyond the Stretch” podcast.