The concept behind having a preconnected handline is to facilitate quick deployment for a quick attack.Most pumpers are set up with two types of preconnects: one for what I like to call medium flows of 100 to 185 gallons per minute (gpm) and the other for large flows ranging from 250 to 500 gpm. The high end of the large-flow handline is normally 325 gpm. However, there are a few exceptions. Flows will sometimes reach 500 gpm, but that is more the exception than the rule. The main reason for having a large-flow preconnect is to make a quick large-flow attack on a significant fire to achieve a quick knockdown. This is usually done by the first-in unit. When it comes to large-flow handlines, the 2½-inch hose has always been the weapon of choice, because its lower friction loss capabilities allow for more flow. The drawback to using 2½-inch line is that it is heavy, making it tough to deploy, especially in a quick-attack mode. It is also pretty difficult to move around after it is charged. Because of these negative traits, firefighters will tend to not choose the 2½-inch line. The end result is that firefighters will pull smaller lines, delivering lower than required flows.
This article focuses on the large-flow preconnected handline with a different twist to it: using two-inch hose for the preconnected high-flow handline to make this big-hit line easier to deploy.
Why Two-Inch?Two-inch hose has been around for several years. The advantages have been for slightly elevated flow and reduced pump discharge pressure (PDP), which reduces engine rpm, reducing wear and tear on the equipment.
The question that comes to mind is whether a two-inch attack line will provide the flows that a 2½-inch line can produce. In the majority of the cases, I would say yes. Take a look at the 2½-inch nozzles in use today. You will find that the majority have flows that top out at 300 to 325 gpm.
The reason for going to two-inch hose is to make hose deployment easier-especially for one firefighter. Whether the staffing on your engine company is four firefighters, three firefighters, or even two firefighters, when a first-in engine company is faced with enough fire to warrant the initial line being a 2½-inch, let's face it-you don't have enough people. This is where the two-inch line comes into play.
|The flow tests comparing two-inch and 2½-inch hoselines used |
smooth bore nozzles. Because the two-inch will have a higher
friction loss at high flows, a nozzle with a low nozzle pressure
keeps the overall discharge pressure as low as possible. (Photos
Flow StudyCharts 1 and 2 show 2½-inch and two-inch lines at 200 feet with corresponding flows and PDPs. The two-inch hose is manufactured by Key Fire Hose and is the ECO-10 line. We tested the standard two-inch with 1½-inch couplings weighing 20 pounds per 50-foot section as well as two-inch hose with 2½-inch couplings, which is a new concept. The reason for the 2½-inch couplings is to reduce the friction loss. The tradeoff is two more pounds for the larger couplings (22 pounds total).
The nozzles used for this test are smooth bore tips for a 50-psi nozzle pressure. Because the two-inch will have a higher friction loss at the high flows we tried to achieve, a nozzle with a low nozzle pressure kept the overall discharge pressure as low as possible. The flows for the 2½-inch started at 265 gpm because it is considered a high-flow handline. The flows for the two-inch start at 185 gpm because this line can be used for both low- and high-flow operations-185, 210, 265, 325, and 400 gpm.
Referring to charts 1 and 2, the two-inch hose matched 2½-inch hose in every flow category. The tradeoff for the lighter and easier-to-deploy hose was a higher PDP because two-inch hose has a higher friction loss than 2½-inch hose. Should the higher PDP be a big concern? I say no. First, it's important to understand that the higher pressure used on the hose itself is well within the pressure capabilities for which the two-inch hose is designed. The most common hose pressure ratings for attack line hose include a 1,200-pound-per-square-inch (psi) burst pressure and a 400-psi annual test pressure. According to that National Fire Protection Association (NFPA), this means the hose can be used at up to 360 psi on the fireground. We did not get anywhere close to 360 psi on any of the lines we tested. The stopping point was 220 psi. The average rpm range for the two-inch line was 1,700 to about 1,800 rpm.
|The two-inch hose was able to match the 2½-inch hose in every |
flow category. The tradeoff for the lighter and easier-to-deploy
hose is that a two-inch hose requires a higher pump discharge
pressure because it has a higher friction loss than 2½-inch hose.
One thing to add about the flow tests is that the nozzle reaction for flows above 250 gpm with the two-inch hose was severe enough to cause the hose to buckle right at the nozzle. Because the two-inch hose is smaller than the 2½-inch line, it does not handle the nozzle reaction as well. The 2½-inch hose did not have a problem with nozzle reaction at all. Keeping that in mind, we decided to use a short piece of 2½-inch five feet long at the end of the two-inch handline for the sole purpose of absorbing nozzle reaction to assist the firefighter with handling the high flows. It worked great.
When using two-inch hose in conjunction with 1½-inch couplings, it's important to remember that the standard for the small handline preconnect plumbing is two inches, which will not be able to support the flows needed for a high-flow handline, at least efficiently. Therefore, it is crucial to connect the two-inch line to a to a 2½-inch discharge-whether it be a standard 2½-inch or one that is designed for a 2½-inch preconnect.
|Because the two-inch hose is smaller than the 2½-inch line, it |
does not handle nozzle reaction as well. The 2½-inch hose did not
have a problem with nozzle reaction at all. Keeping that in mind,
crews used a short piece of 2½-inch line five feet long at the end
of the two-inch handline for the sole purpose of absorbing nozzle
reaction to handle the high flows.
Strive for ImprovementStriving to do a better job means being able to constantly review and change things as needed. The 2½-inch preconnect has been a great tool for initial attack on a large volume of fire. In reviewing the big line, one area of improvement identified was deploying and delivering the 2½-inch line's big water capability. Two-inch hose is a fix for this problem. As firefighters, we need to always look to improve our work environment. Just because it has worked in the past doesn't mean it can't be done better.
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.