There are many things to consider when drilling on the stretching, advancing and operation of attack hoselines. Here are a few pointers to aid in achieving realistic results with regard to the length of the hose being used during drills.

Hose length is often not even considered in drills, and often the length of the hoses used is relative to the amount of anticipated cleanup. In many instances, 1 or 2 lengths is considered sufficient for drills in the parking lot when reviewing hose handling techniques and such. In reality, you can actually suffer negative consequences running shorter lines for training. Fire departments need to be realistic in training by using the hose lengths that would commonly be used at a fire. If you drill with only 1 or 2 lengths of hose to avoid having to clean up more equipment, etc, you could end up suffering from complications. The example below will use true diameter 1 3/4" hose with a standard coefficient of 15.5.

EXAMPLE 1: 200 foot attack line with a 7/8" smooth bore nozzle. Pump pressure (PDP) of around 130 PSI - using theoretical numbers. Reduce the hose length to 100 feet and the PDP drops to 90 PSI

You can see how much the pump pressure drops by subtracting 100 feet of hose in the above example, but why is that a problem? Some would say keeping pump pressures low is a good idea. Is it though?

We have a dirty little secret in the industry that fire hose is no longer being sold as true diameter, in fact much of it has "creeped" up in internal diameter over the last decade or so as a result of competition among manufacturers. The resultant effect are hoses with drastic differences in internal diameter and coefficients, causing havoc on our normal PDP and FL formulas. This can negatively impact hose training.

Do you know the true diameter and coefficient of your hose?

Lets look at the example from before and apply a coefficient for "fat hose" to see how it impacts the equation. We will use the coefficient 10.22, for a hose that is considered 1 3/4" but sizes in at closer to 1.81" inside diameter.

EXAMPLE 2: 200 foot attack line with 7/8" smooth bore nozzle. Pump pressure (PDP) of 102 PSI. Reduce the length of the hose to 100 feet and the PDP drops to 75 PSI

The lower pump pressure brings two factors into play, one is the back pressure at the nozzle inlet and the second is the ability of the pump governor or relief valve to function properly.

Lets look at the nozzle back pressure issue. The back pressure is created by the pressure within the hose as its restricted by the nozzle orifice. If you follow the old rule that the nozzle shall not be larger than 1/2 the diameter of the hoseline, you will have addressed one issue that contributes to acceptable back pressure and reduced the propensity of the hose to suffer from what we call "whip," a condition often influenced by low back pressure and a soft hose at the nozzle inlet.

Line gauges at the nozzle inlet will always read low, as they show sidewall pressure, not nozzle flow pressure (stream velocity). They can give some information, but flowmeters and pitot gauges are the best way to assure accurate flow. The line gauge will also not decipher a mismatched nozzle to hose, but may show even lower readings as the tip size increases past the 1/2 diameter rule.

In example 1 there was 80 PSI of pressure loss in the hose. This helps stiffen the hose up a bit, can aid in reducing kinks and helps to build some backpressure at the nozzle inlet. When the length was dropped to 100 feet in example 1, the pressure loss was dropped to 40 PSI. You would start to see that the hose might be a bit softer, slightly more kink prone and may start to experience unfavorable handling at the nozzle.

In example 2, things get worse. The "fat hose" drops the pressure loss significantly, making it notably less. in a 200 foot length the pressure loss is 52PSI. By reducing the hose line to 100 feet, the pressure loss drops to 26 PSI. These drastic differences will translate to handling issues, and to low pump pressures.

The issue of low PDP can complicate the pump operators job as well. Most single stage pumps will produce around 30-50 PSI at idle, and will amplify that when a pressurized source is introduced (hydrant). The "net pump pressure" can end up being 125-150 PSI if your fire hydrants are good performers. This means that the pump pressure control device (electronic governor -aka EPG or relief valve) will be unable to operate as designed. The unusually low pressures required to supply effective streams to unusually short handlines means that the operator must become the pressure governor, by gating the discharges, essentially eliminating discharge pressure protection until such a time as the discharge flow increases enough for the engine to require additional throttle. Remember that if your discharge pressure is lower than intake pressure, that the relief or pressure control device will be unable to operate properly. It is generally desirable to have a cushion of pressure between intake and discharge pressure to allow the pressure relief/control device to function. If the net pressure is at 125 PSI with the motor idling and the required PDP for the attack like is only 75 PSI, the discharge will require gating to control the flow/pressure and the pressure control device will be incapable of operating properly.

Lets look at example 2, because it uses numbers that are in line with modern hose. With a short length line (100 feet) and a pump pressure of 75 PSI to support the 160 GPM stream, we know that we need the engine to throttle up a bit when operating from booster tank water. With the pump engaged, and a static pressure of around 50 PSI, we still need an additional 25 PSI or so. The EPG will throttle up in the pressure mode, or the operator would throttle up if the pump was equipped with a manual throttle and discharge relief valve. This works out perfectly well when we are supporting the line from tank water, but things change a bit when we introduce pressure from an external source.

With the pump operating at 75 PSI discharge pressure, we know we are a bit above idle. Now we would prepare for the changeover to pressurized source. This is often in the form of opening the intake line from a hydrant, but could also be from a nurse tanker/engine etc. If we knew that the pump was producing around 50 PSI at idle, and we introduce an additional 50 PSI from an external source, the EPG will automatically see that spike in discharge pressure and lower the throttle. If operating with discharge relief valve, it would open as the pressure rose over 75 PSI. In both instances, though, the pressure being discharged to the handline will end up being higher than the pressure coming in, rendering either style pressure control device useless, and requiring intervention by the operator.

To support a 160 GPM 1 3/4" stream, this pump is operating at near idle (900 RPM) and discharging approx 110 PSI. Fat hose contributes to the low pump pressure. There is virtually no discharge protection available in this situation.

With the operation of the discharge relief valve and EPG in mind, its fair to say that you actually want some friction loss. You need some throttle to get the pump up above idle for these devices to work. Without throttle, you sit at idle, and all pressure changes must be regulated by the operator by gating the lines manually. It is worth noting that in some locations, water systems are so strong that you're left without the options suggested in this article. In such instances, diligence to maintain pressures must be exercised by the pump operator.

When you are conducting pump operator training, this issue can come into play as well. In order to simulate the restriction imposed by pressure loss in hose, it may be necessary to gate the pump discharge valve back and use the throttle to overcome the restriction to ultimately achieve the proper nozzle pressure. This action may result in broken streams, which can be rectified by attaching stream shapers to the nozzles for training purposes.

You would never pump a hoseline thats supplying a stream at its tip pressure, but when attaching nozzles to the pump thats exactly what happens in most instances. This can result in the creation of poor habits by pump operator candidates and unrealistic pump pressures that lead the issues discussed in the previous section.

Lastly, its important to understand just how much of a consequence that extra pressure has on the nozzle. If we stick to the 7/8" tip in the previous examples, the reaction force at 50 PSI is 60Lbs. This is easy for one ff to manage; an additional 10 PSI on the nozzle will raise that reaction to 72Lbs (at 60 PSi tip pressure), If the nozzle is pumped 20 PSI "hot" (70 PSI tip) the reaction jumps to 84 Lbs. That extra pressure the pressure control device cannot handle during the changeover will translate to extra nozzle reaction, and may cause loss of control or force the nozzleman to gate back. If using automatic nozzles, additional flow will result, but at the cost of additional reaction forces also.

Here are a few tips to aid in better handline drills.

• Use the attack hose and nozzles you'd be deploying for actual fire attack
• Use the length of hose that you'd be stretching and operating. This could vary greatly, but you should regularly train on these lengths. Generally less than 150 feet may lead to issues.
• Try to maintain the 1/2 nozzle orifice to hose diameter rule, but remember that the rule changes with fat hose. Knowing the true ID of your hose means that you can usually increase one tip size for certain models of "1 3/4" hose, as their internal diameter may creep up to nearly 2" ID.
• If you use line gauges, understand that they read sidewall pressure and will have an error margin of anywhere from 5-10 PSI on average (lower than stream pressure)
• If you are using nozzles attached to pump outlets to train pump operators, gate the discharge valves back to simularte the restriction imposed by the absent pressure loss in the hose.
• Note the pressure your pumps produce at idle and know what that pressure will increase to (net pump pressure) when connected to a hydrant
• If you can use pitot gauges and/or calibrated flowmeters, they will often be the best measuring tools.

Like all training, its important to train as you'd work in the real world. Hopefully this article illustrates some points which will help prevent problems in your future drills.

-MG