Big Knockdown Using the Little Guy With the Big Punch

Big Knockdowns Using The

Little Guy With the Big Punch

 

I think we are all aware of what the 2-1/2” handline can do for us in regards to big flow however we also understand the difficulties that might be encountered in its deploying. This is not to say that the 2-1/2” handline should be discouraged from its use because of the difficulties. Probably the most difficult part of using the big line is moving it while charged even when water is not being flowed. It’s a heavy line. When the 2 ½’s are used on large fires there is normally plenty of firefighters available to maneuver it. But what about the first-in company faced with a large volume of fire that needs to be suppressed with a large volume of water especially with the first line out? Most engines are set up with a pre-connected 2-1/2” handline for this reason. The pre-connected line makes deployment with minimum manpower (more than likely the crew of the first engine) much easier. But again, the one thing that pre-connected 2-1/2” line does not offer is maneuverability of the line after it has been charged and with the first-in scenario with minimum manpower it becomes even more difficult.

This article is going to offer an alternative to the pre-connected 2 ½“ handline that will make it really easy for one firefighter to maneuver after it has been charged. The handline I am talking about is the 1-3/4”.

When 1-3/4” was introduced to the fire service many years ago one of the big sales pitches that was presented to the firefighters was that it was going to be able to produce flows equal to the 2 ½ inch lines and be much easier to handle. Believe it or not a lot of departments believed this pitch and actually got rid of their 2 ½“ hose. They soon realized that achieving 250 GPM from the 1-3/4” handline was not possible the big majority of the time. There were several reasons for this. The required pump discharge pressures were easily over 200 psi and sometimes reaching 250 PSI which made firefighters hesitant to use. Since they already had nozzles on their 1-3/4” handlines that had the ability to flow 250 GPM, it was automatically assumed that they could use the same nozzle. The problem they wound up having was for the most part these were rated at a 100 psi nozzle pressure. This basically made the 250 GPM flow not obtainable. One other thing that was realized was that the nozzle reaction flowing 250 GPM with the small diameter 1-3/4” hose created severe kinking at the nozzle because of the nozzle reaction. With all this being said basically the 1-3/4” hose was not used in the high flow 2-1/2” mode.

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      High flows using 1-3/4” hose can cause kinking at the nozzle due to the nozzle reaction.

Well that was then and this is now. Let’s see how the 1-3/4” hose can be used for that initial pre-connected big hit line by the first-in engine company safely and efficiently. It’s important to understand the intention of this article is not to persuade fire departments to get rid of their   2- ½ “ hose. This is only meant as an alternative for the pre-connected 2-1/2.

This article is going to talk about two different types of 1-3/4” hose that can be used for this scenario. The first is the standard 1-3/4” that actually measures out to be 1-3/4”in diameter. The second one is a 1-3/4” line that is sold by several manufacturers with the claim of being able to get higher flows. This 1-3/4” is actually oversized and measures out to approximately   1-7/8 Why it’s not sold as 1- 7/8″ hose I do not know. However I can tell you that the difference in flows between the standard 1-3/4” and the 1-7/8” hose is tremendous.

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On the left is standard 1-3/4” and on the right is the oversized 1-3/4”

Standard 1-3/4”Hose

The goal for a maximum flow on standard 1-3/4” hose is going to be 250 GPM. This is going to be based on a 200’ line. Let’s address the issues that firefighters were faced with years ago when they originally tried to flow 250 GPM through their 1-3/4” hose and make improvements.

The first thing I’d like to address is the pump discharge pressure. There are ways to lower the required pump discharge pressure but we are still going to be looking at pressures close to  200 psi. Is this something to be concerned about? I say no and here’s the reason why. It’s important to understand what today’s fire hose is rated at in regards to maximum pressures. Most attack hose used in the fire service today has high pressure ratings. For example the burst pressure is 1200 psi. The annual service test pressure can be tested up to 400 psi. By the way I do recommend testing it at 400 psi because this will give us a wide safety margin from the test pressure to the operating pressure of no higher than 250 psi NFPA used to say that the maximum operating pressure shall be 10% less than the annual service test pressure which would make the standard 1-3/4” hose have an operating pressure of 360 psi. They have since changed their wording to state that the attack hose should be able to have at least a 275 psi operating pressure is still higher than what we will pump our lines for this operation.

The 250 GPM flow on the 1-3/4”line is going to require the use of a 2 ½“ discharge to be an efficient line. The plumbing in the traditional crossways for pre-connected 1-3/4” lines is just too small.

Now let’s address the nozzle itself. We need to get away from the 100 PSI nozzles in order to keep the pump discharge pressure as low as possible. A 50 psi smooth bore nozzle or a combination nozzle rated at 50 psi works well for this operation. If you’re using a smoothbore nozzle the inch and 1/8 tip is the standard for the 250 GPM flow (it’s actually 265 GPM but we’ve always rounded it off to 250). Combination nozzles can be rated at 250 GPM also with a 50 psi nozzle pressure rating.

There’s a real simple fix for addressing the severe nozzle reaction kinking in the hose just behind the nozzle. A short section 2 ½ inch hose connected to the end of the 1-3/4” and then to the nozzle totally eliminates all nozzle reaction kinking simply because it’s a larger hose. A 5 foot section works well for this however it is possible to go to 10 feet and still have the lightweight capabilities of the small diameter hose. Remember this line is set up to be a big hit line so the short section of 2-1/2” should be an issue. If we chose to take this line interior I still don’t think the 2 ½ would hinder hose advancement.

A short section of 2-1/2” at the end of the line takes away the kinking caused by nozzle reaction.

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As far as nozzle handling techniques are concerned the only thing that has really changed, and it has changed for the better, is that advancing a charged line has become a lot easier. Take a look at a scenario where a one person evolution is used for deploying a pre-connected big flow line. There’s a real good chance that a first-in unit would actually use just one person to deploy even a 2-1/2” line. Pulling the line from the hose bed has become easier simply because of the weight of hose. Nozzle handling with one firefighter will most likely be done from a stationary position simply because if you’re attacking a large volume of fire you’re going to have to knock it down first before advancing in. With this being said using some type of technique where the firefighter’s bodyweight is on top of the hose pushing to the ground makes it very easy to handle the nozzle reaction that a 250 GPM flow will produce.

The following chart is going to show flow tests that were done with a 200 foot 1-3/4” line using a 1 1/8 “ smooth bore tip at 50 pounds nozzle pressure and the combination nozzle rated at 250 GPM with a 50 pound nozzle pressure.

GPM              NOZZLE         NP      FL        PDP

250                  1-1/8”             45        70        185

250                FIXED GAL.        50        70        190

There is another way to bring down the pump discharge pressure if 190 psi is a little high for you. Theoretically on the 200 foot line most if not all the maneuvering after it has been charged will be done at the last 100 feet. With this being the case if you wanted to build this line with 100 feet of 2 ½” from the discharge out and have 100 feet of 1-3/4” line at the working end, this will lower the pump discharge pressure to 135 psi.

 

1-3/4” Oversized Hose

The 1-3/4” hose with the oversized diameter, 1-7/8”, has the ability to flow up to 325 GPM on a 200 foot line. Yes you heard it right. 325 GPM is at the high end of most 2-1/2” handlines. This particular hose has a burst pressure of 1500 psi with an annual service test pressure of 500 psi. According to the previous NFPA standard the maximum operating pressure for this hose can be as high as 450 PSI. Based on the 325 GPM flow on a 200 foot line the pump discharge pressure is 205 psi. This type of hose is very kink resistant however it still requires the short piece of 2 ½ at the end of the line to negate the kinking from the nozzle reaction of these high flows. If you want a lower pump discharge pressure by replacing the first hundred feet of 1-3/4” with 100 feet of 2 ½, pressure will be lowered to 140 PSI. The chart below shows the specs on the 200 foot line using this hose.

 

 

GPM              TIP SIZE         NP      NR      FL        PDP

250                 1-1/8″           45       99       50       145

275                 1-1/8″           55       109     56       180

300                 1-1/8″           65       129     62       200

328                 1-1/4″           50       123     76       205

 

I know the basis for this article calls for the replacement of the 2 ½ “ pre-connect however there’s nothing that says you can have both lines especially with flow capabilities of the 2 ½” line reaching 500 GPM using the single inlet mini monitors that have proven themselves over the last few years. In fact there’s even some that have been getting 500 GPM flows on specific types of handline nozzles with a lot of success.

In closing

This article has been based on being progressive, keeping an open mind and continuous evaluation of equipment and techniques.  Most of what you have read will not be found in the standard fire stream books in circulation today.  Does that mean that this is not an acceptable way to deliver high flows through 1-3/4” handlines?  In my opinion, it does not.  At no time do any of the above mentioned flows, nozzle combinations, and nozzle pressures go against what the manufacturers say their equipment can or cannot do.  If you like what you have read, don’t implement it tomorrow – train, train, train,.  Feeling comfortable and confident is the key to success.