Visualize the difference by looking at a straw
One of the longest lasting debates in the American fire service is the smooth bore vs. fog debate. One of the greatest problems with this debate is that in many areas of today’s fire service, it has resulted in firefighters’ knowledge of nozzles being limited to smooth bore or fog. Some firefighters lack the knowledge of the different types of nozzles that fall into the fog nozzle category as well as knowledge of the operational capability of each nozzle. In all trades, professionals know and understand their equipment, how it works, and its operational capabilities. As professionals, firefighters must also understand their equipment, how it works, and its operational capabilities and this includes nozzles.
The first issue with some firefighters’ knowledge of nozzles is that they can only differentiate between smooth bore nozzles and fog nozzles. The fact that there are multiple types of fog nozzles is a foreign concept to some firefighters as they have simply been taught the difference between the smooth bore nozzle and the fog nozzle. The problem that this creates is that these firefighters cannot identify which type of fog nozzle is being used. Each type of fog nozzle operates differently. Understanding how each type of nozzle operates allows firefighters to overcome problems that are encountered during the hoseline operation. The first step in a firefighter’s path to gaining knowledge of the nozzle is to be able to identify which type of nozzle is being used. All firefighters MUST be capable of identifying the type of nozzle being used. This includes smooth bore nozzles, fixed-gallonage fog nozzles, selectable-gallonage fog nozzles, and automatic fog nozzles.
Smooth bore nozzles are the oldest and most basic design of the modern-day nozzles. They are also the cheapest to purchase. These nozzles also contain the least amount of moving parts. The smooth bore nozzle provides a clear and unobstructed path of water flow through the nozzle. It is because of this unobstructed path that smooth bore nozzles are the least susceptible to clogging from debris of all nozzles. Smooth bore nozzles are operated at a nozzle pressure of 50 pounds per square inch (psi) when they are being used on handlines. Solid streams are produced by smooth bore nozzles. These nozzles come in two designs: the shutoff design and the play pipe design. The play pipe design is a larger nozzle and has a set of handles to assist in the handling of the nozzle. These handles add to the weight and size of the nozzle, making it bulky, and should be removed to allow for a better nozzle during interior fire attack operations, as these handles will not be used during interior fire attack operations, they are to assist with the handling of the nozzle during defensive fire attack operations. Smooth bore nozzles offer multiple operational benefits over their fog nozzle counterpart. These benefits include greater reach and penetration, less nozzle reaction (except when compared to a 50-psi fog nozzle), reduced susceptibility to clogging by debris, and an increased capability to produce an adequate flow rate during low-pressure situations. Below are some of the most commonly used smooth bore nozzle tip sizes and their associated flow rates:
7/8 inch – 161 gallons per minute (gpm)
15/16 inch – 185 gpm
1 inch – 210 gpm
1 1/16 inch – 237 gpm
1 1/8 inch – 265 gpm
1 3/16 inch – 296 gpm
1 1/4 inch – 327 gpm
The fixed-gallonage fog nozzle is the fog nozzle design that operates in the most similar manner to a smooth bore nozzle. This nozzle provides a constant flow rate at a set nozzle pressure. Like the smooth bore nozzle, if the pump operator provides the proper nozzle pressure, the fixed-gallonage fog nozzle will provide a known constant flow rate. Like all fog nozzles, the fixed-gallonage nozzle allows the nozzle firefighter to select the stream pattern ranging from straight stream to wide fog stream. Nozzle pressures for fixed gallonage nozzles range from 50 psi to 100 psi. Some of the common fixed gallonage nozzles are as follows:
150 gpm @ 50 psi
150 gpm @ 75 psi
150 gpm @ 100 psi
160 gpm @ 50 psi
175 gpm @ 50 psi
175 gpm @ 75 psi
175 gpm @ 100 psi
185 gpm @ 75 psi
200 gpm @ 75 psi
250 gpm @ 50 psi
250 gpm @ 75 psi
275 gpm @ 75 psi
300 gpm @ 75 psi
325 gpm @ 100 psi
350 gpm @ 100 psi
The selectable-gallonage fog nozzle is similar to the fixed-gallonage fog nozzle in that if the pump operator provides the proper nozzle pressure, the nozzle will provide a known flow rate. The difference between this nozzle and the fixed-gallonage nozzle is that while the nozzle will provide a known flow rate, the flow rate is adjustable. This nozzle contains an adjustable ring that allows the nozzle firefighter to adjust the flow rate by twisting the gallonage selector. This is an additional variable over the fixed-gallonage and smooth bore nozzles as the nozzle firefighter must ensure the proper gallonage selection to achieve the target flow rate.
Another variable associated with this nozzle is the direction of the gallonage selector. If the stream pattern is accidentally rotated to a fog stream and the firefighter adjusts the stream back to a straight stream, he must make sure to grasp only the stream selection of the nozzle and not the gallonage selection because the direction that the nozzle tip will be rotated to achieve a straight stream (right) will also decrease the flow rate if the gallonage selection is also grasped and rotated while attempting to correct the stream pattern.
Nozzle pressures for selectable-gallonage fog nozzles are typically either 75 psi or 100 psi. Like all other fog nozzles, the selectable-gallonage fog nozzle allows for stream pattern adjustment by the nozzle firefighter ranging from straight stream to wide fog stream. Some examples of common selectable gallonage nozzles include the following:
30/60/90/125/150/200 gpm @ 75 psi
30/60/90/125/150/200 gpm @ 100 psi
95/125/150/200/250 gpm @ 100 psi
The automatic fog nozzle has the most variables of all nozzles. Unlike the smooth bore nozzle, the fixed-gallonage fog nozzle, and the selectable-gallonage fog nozzle, the automatic fog nozzle does not provide a known flow rate at a specific nozzle pressure. Instead, the automatic nozzle provides a known flow rate range at a specific nozzle pressure. This is a major variable in the hoseline operation. With all other nozzle types, firefighters know what the flow rate will be if the pump operator provides the proper nozzle pressure, but with the automatic nozzle they only know what the flow rate range will be. Another issue with the variable of providing a flow rate range rather than a constant flow rate is that the flow rate range is not minimal. Instead, the flow rate range typically spans more than 100 gpm. There are many firefighters who have a misunderstanding of the automatic nozzles. This misunderstanding is that the automatic nozzle will automatically adjust to provide a constant flow rate at different nozzle pressures. This is not how the automatic nozzle works–it works to automatically adjust to provide a content stream appearance (reach) at different nozzle pressures, not to provide a constant flow rate.
One of the most common analogies used to describe the operation of automatic nozzles is the garden hose. If a garden hose with no nozzle is turned on and water is allowed to run freely out of the tip of the hose, the stream of water will have minimal reach, as it will only extend slightly past the tip of the hose. If you then place your thumb partially over the tip of the hose, the reach of the stream will greatly increase. The important thing to note here is that while the stream appearance (reach) improved, the flow rate remained the same. This is similar to how the automatic nozzle works: It ensures a constant stream appearance (reach) regardless of flow. Nozzle pressures for automatic nozzles vary from 75 psi to 100 psi.
Another important aspect of understanding nozzles is the difference between the streams produced by different nozzles. As you have probably noticed throughout this article, only the term fog has been used to describe today’s modern fog nozzles even though today they are termed combination fog nozzles. The issue with the term combination fog nozzle is not the term itself but that there is a misunderstanding by many firefighters of the operation of today’s fog nozzles and the streams produced because they have taken the term combination fog nozzle to mean that today’s fog nozzles are a combination of smooth bore nozzles and fog nozzles and that the straight stream of today’s fog nozzles is the same as the solid stream produced by a smooth bore nozzle while also having the ability to produce a fog stream. The solid stream (smooth bore nozzle) and the straight stream (fog nozzle) are similar but different. The solid stream is exactly as the term describes, solid. Due to the unobstructed path through the smooth bore nozzle, the stream produced is a solid tube of water. The straight stream is similar in appearance to the solid stream but rather than being a solid stream of water it is a hollow stream of water.
Visualize the difference between these streams by looking at a straw. If the straw is filled with fluid, it is similar to a solid stream in that the inside of the straw is filled with water but with a straight stream the straw itself would be the water and the inside of the straw would remain a hollow tube of air. You will see this if you view a solid stream and a straight stream side by side. As the two streams leave their respective nozzles, the straight stream produced by the fog nozzle will begin to converge on itself and the stream will decrease in width as it travels away from the nozzle. This does not happen with the solid stream produced by the smooth bore nozzle because this stream is not hollow like the straight stream as it leaves the nozzle.
The difference between the solid stream and the straight stream goes beyond the solid vs. hollow stream. The water droplets produced by the straight stream of the fog nozzle are smaller than those produced by the solid stream of the smooth bore nozzle. This decreases the penetration capability of the straight stream in comparison to the solid stream as the smaller water droplets are more easily vaporized en route to the seat of the fire than the larger droplets produced by the solid stream.
Another nozzle design characteristic is whether the nozzle is of the one-piece or two-piece (breakaway) design. The one-piece nozzle is exactly how it sounds: The entire nozzle is one piece from the inlet coupling to the tip of the nozzle. The nozzle tip of the one-piece nozzle cannot be removed. The two-piece (breakaway) nozzle consists of the shutoff and the nozzle tip. The ability to remove the nozzle tip from the shutoff provides additional operational capability to overcome two obstacles that can arise during the hoseline operation: debris clogging the nozzle and a short stretch. If debris enters the nozzle, specifically a fog nozzle, it is likely to clog the nozzle and reduce the flow rate. If a one-piece fog nozzle is being used, the only option to overcome this obstacle is the flush option on the fog tip. When a two-piece nozzle is being used, the removable nozzle tip can be removed. The debris clogging the nozzle will be inside the nozzle. The nozzle can then be opened again, passing any remaining debris in the nozzle. Some two-piece nozzles have an integrated smooth bore tip so that when the tip is removed, the nozzle can still produce a quality stream without the tip.
The second benefit of the two-piece nozzle is the ability to extend a hoseline off the nozzle. If a short stretch occurs and you are using a one-piece nozzle, you cannot extend the hoseline off the nozzle because you cannot remove the tip. The only option is to shut down the water supply to the nozzle and remove the nozzle from the hoseline to add additional lengths of hose or to stretch another line. If a short stretch occurs when using a two-piece nozzle, the hoseline can be extended off the nozzle. When the tip of a two-piece nozzle is removed, 1.5-inch hose threads become exposed with which you can connect additional lengths of hose with an additional nozzle to the tip of the original nozzle. This is true of both the 1.5-inch nozzle and the 2.5-inch nozzle.
Not all nozzles have the same ball valve design inside the nozzle. This is especially important when smooth bore nozzles are used. There are three ball valves used in nozzles: full round, single cut, and double cut. The full round provides a smooth surface through the nozzle while the single cut and double cut have cutouts on the bottom of the ball valves to assist with the opening and closing of the nozzle. However, the cutouts create turbulence in the water as it passes though the nozzle. This turbulence decreases the quality of the solid stream produced. When using smooth bore nozzles, I recommend the full round ball valve design.
Nozzle reaction determines the manageability of the hoseline. This also dictates the staffing needs of the hoseline. The late Lieutenant Andrew Fredericks of the Fire Department of New York identified the safe nozzle reaction force for a single firefighter to be 69 lbs. of force. Paul Grimwood of the London Fire Bridage identified safe nozzle reaction forces for one, two, and three firefighters to be 60 lbs., 75 lbs., and 95 lbs., respectively. You can use these rules of thumb to determine the staffing needs of the nozzle team.
A common theme today is to reduce nozzle reaction forces to produce more manageable hoselines. There are only two ways to do this: reduce the flow rate or reduce the nozzle pressure. Reducing the flow rate is not always advisable to achieve extinguishment. The minimum flow rate for interior structural firefighting has been established to be 150 gpm. Therefore, if the common 150-gpm nozzle is being used, reducing the flow rate is not an option. Reducing the nozzle pressure is an option and is being applied as U.S. fire departments are switching from high-pressure fog nozzles (100 psi) to smooth bore nozzles or low-pressure fog nozzle (50-75 psi). The nozzle reaction forces of some common nozzles are as follows:
150 gpm @ 50 psi = 54 lbs.
7/8-inch tip (161 gpm) = 60 lbs.
150 gpm @ 75 psi = 66 lbs.
15/16-inch tip (185 gpm) = 69 lbs.
150 gpm @ 100 psi = 76 lbs.
1 1/8-inch tip (265 gpm) = 99 lbs.
250 gpm @ 75 psi = 109 lbs.
1 3/16-inch tip (296 gpm) = 111 lbs.
1 ¼-inch tip (327 gpm) = 123 lbs.
250 gpm @ 100 psi = 126 lbs.
All firefighter, especially those assigned to engine companies, must have knowledge of their nozzles. This knowledge must extend beyond simply being able to identify if the nozzle is a smooth bore nozzle or a fog nozzle to include the ability to identify the nozzle type, understand how the nozzle operates, and understand the operational capabilities of the nozzle.
Anthony Rowett Jr. is a captain with the Mobile (AL) Fire Rescue Department. He was previously a firefighter with the Ogdensburg (NJ) Fire Department. He has an A.A.S in fire science technology, a B.S. in fire science, and an M.S. in emergency services management. He is a graduate of the Alabama Smoke Diver course. He is the founder of Port City Fire Training. He is a contributing author for multiple fire service publications. He has instructed at multiple fire service conferences as well as for individual fire departments. He has served as a lead H.O.T engine company operations instructor. He is also a co-host of the “Generation Engine” podcast on Fire Engineering Blog Talk Radio.