By Paul Shapiro
There are two key ingredients involved with any pump operation: water and pressure. Both are absolutely mandatory for producing the finished product, an adequate firefighting stream. To appreciate the importance of each, firefighters must first have an understanding of what an adequate firefighting stream is.
An adequate firefighting stream must be able to produce enough water to suppress the fire in a reasonable amount of time (to be determined by each agency) and deliver it onto the fire with enough velocity to achieve a knockdown as quickly as possible.
The first part of this combination, the water, comes into play as soon as the company officer begins making the size-up. A decision needs to be made on where the water will come from and how much will be needed. Whether the water comes from the booster tank, a fire hydrant, a draft sight, or a water shuttle, a water source needs to be established.
Once the fire attack begins, the water needs to be moved through the delivery vessel to the fire. As you well know this needs to be done under pressure–that is, unless the method of delivery is going to be a water drop.
This is where the water pump in the fire apparatus comes into play. It is the pump operator’s job to establish pump pressures high enough to move the water through the hose and/or appliances to produce an adequate stream. The only limitation that governs how high the pump pressure can be (providing there is a sufficient water supply) is the maximum operating pressure established by the manufacturer of the equipment delivering the water and the equipment handling capabilities of the firefighters.
There are several pressure specifications that the manufacturers must build into their products to assure that the equipment we use in the field is as safe as can possibly be. The National Fire Protection Association (NFPA) sets the minimum standard that the manufacturers shall follow.
The NFPA rule for the maximum operating pressure on any type of fire hose is based on the service test pressure. It states that the purchaser shall specify a service test pressure of at least 10 percent greater than the normal highest operating pressure at which the hose is expected to be used. Put more simply, the hose is tested to at least 10 percent higher than it will ever be used on the fireground.
Currently, the NFPA has no specifications for master stream appliances. All manufacturers have set up their own specifications, which are high in the respect that they have created a wide margin of safety from maximum test pressures in the factory to what we are allowed in the field. The only statistics found on master stream appliances in literature provided by manufacturers has to do with maximum allowed inlet operating pressures, which is a good rule to operate from.
The following chart shows some examples of specifications on hose and appliances from various manufacturers.
As you can see, the difference in the burst pressure and the service pressure (maximum operating pressure) of the hose is just about a 3:1 ratio. That tells me that there is a big safety factor built in to the equipment that we use. Yet there is still a big concern in the fire service about operating in the higher pressure range.
In my travels across the country presenting seminars, I have listened to a lot of concerns from firefighters about why they choose not to perform high pressure operations both for safety and performance reasons. Let’s analyze some of these concerns to see whether they are valid or not.
There is a concern that a handline pumped at the top end of the pressure range will become stiff like a pipe, thus making the line too difficult to maneuver, especially in the interior attack mode where it might be required to advance through tight areas.
The hose does get stiff, but only at the last couple of feet at the nozzle. Advancing the line should not be a problem. Try a couple of experiments. First, charge a handline to 250 psi and advance it through an interior setting not flowing water. Your neighborhood burn tower works well for this one. Next, take the same line at a 250 psi static pressure again. Go back about 10 feet from the nozzle and place a loop in it as tight as you can make it. I think you will agree that the hose bends quite easily.
The higher handline pressures create a higher nozzle reaction, thus making the line more difficult to handle.
This is true. The higher the nozzle pressure and flow from a nozzle is, the higher the nozzle reaction will be. The following chart is a good reference to show what the nozzle reaction can be at various nozzle pressures and flows using smooth bore tips and combination nozzles.
Too often, firefighters tend to judge how much pressure/flow they can handle in the standing position. I like to call this the parking lot training mode. This is the way we train with our hose drills–standing up. Well, guess what? What stance do we usually use when fighting fire? More often than not we are down low to the ground, trying to stay out of the heat and smoke as much as possible. Keeping this in mind, let’s see how to make nozzle handling a lot easier.
The key to handling a high-pressure/high-nozzle reaction handline is to give the nozzle reaction a place to be absorbed. Whether the handline is being used for an offensive interior attack or a stationary blitz attack blast, allow as much hose as possible to be on the ground with the weight of the firefighters directly on top of it. If possible, no more than about the first two feet of the hose at the nozzle should be off the ground. You will be surprised to see how much one or two firefighters can handle. In fact two medium size firefighters can handle a 500 GPM handline in the blitz attack mode with no problem at all.
There is a concern that overpumping a smooth bore tip (whether it be on a master stream or a handline) will create a hard-to-handle and/or unstable stream delivery and a poor quality stream.
The previous concern addressed the hard-to-handle handline, which dispels the fears of what an over-pressurized smooth bore tip handline will do. As far as master streams are concerned, a portable monitor should never be pumped higher than what the manufacturer recommends. That includes the inlet pressure to the appliance as well as the nozzle pressure, nozzle reaction, and maximum flow. The same holds true for an elevated stream. Follow all factory specifications for the ladder or boom that is supporting the elevated device including the tip load, maximum flow, elevation and angle requirements, and all other rules that apply to water flow.
A fixed master stream (a.k.a. deck gun, wagon battery, stang gun, etc.) can withstand much more than the elevated and portable master streams. Again, follow the manufacturer’s recommendations for maximum inlet pressures allowed to the appliance and the maximum flows while in the fixed mode of operation. Additionally, consult the fire apparatus manufacturer to determine the maximum nozzle reaction force that the discharge plumbing to the gun can withstand.
A master stream used in the fixed mode allows us to operate a high-pressure smooth bore tip operation. A high-pressure smooth bore tip operation creates a higher velocity stream, which in turn develops a farther reaching, harder hitting stream. This application works well in a windy situation, which tends to destroy streams. It also works well when the stream is needed for deep penetration or for hydraulic overhaul. Again the rules to follow for this application are the maximum allowed inlet pressure for the appliance and the maximum allowed flow. All plumbing and brackets for the fixed master stream should be inspected to assure that there are no flaws that could cause failure. This holds true for both standard and high-pressure operations. Additionally, you should always check with the apparatus manufacturer to ascertain what the maximum nozzle reaction can be for the plumbing supplying the fixed master stream.
The fire stream textbooks in the fire service state that a smooth bore tip on a handline shall have a standard nozzle pressure of 50 psi and not exceed 60 to 65 psi. Furthermore, a smooth bore tip on a master stream shall have nozzle pressure of between 80 and 100 psi. Nozzle pressures higher than these maximum recommendations will produce poor quality streams. The books state that the streams will start to break up.
It seems that the most popular belief of what the ultimate solid stream should look like is that of a rope-like appearance from the end of the nozzle to the target it is attempting to hit. It is further believed that the peel-off of water from the stream is a sign of a poor quality stream.
This is where I disagree. I have developed master stream nozzle pressures up to 180 psi within the operating range of the appliance with fantastic results. The performance of a solid stream should be based on its water-delivery capabilities which include putting a high percentage of the water onto the fire with as much velocity as safely as possible. The small amount of water that may not reach the fire in a high-pressure operation because of water peel-off is insignificant in relation to the positive effects of a high-pressure stream. This isn’t to say that all streams should be high pressure; however, if the need should arise, you can bet that a properly produced high-pressure stream will be the stream best suited to get the job done.
Finally, 100 percent of this article discussed high-pressure operations in both handline and master stream operations. If you decide any of this can work in your department, I think you will find that high-pressure operations are rarely needed. High-pressure operations are mostly designed to work when standard operations are not enough.
Remember, before deciding to adopt any type of high-pressure operations, please refer to all manufactures specifications of the equipment. Make sure that in fact the operations in question can be safely performed. Additionally, all personnel should be thoroughly trained in the operations before implementing these into your department’s standard operating procedures so that firefighters to completely understand what is involved in the operation and that they have the confidence to be able to use it under fireground conditions safely.
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 City of Las Vegas (NV) Fire Department. He has authored numerous articles for fire trade magazines. He has been in the fire service since 1981 and is author of Layin’ the Big Lines and produced the first in a series of videos on large-flow water delivery. He is available to answer questions; he can be reached at (702) 293-5150 or Layinline @aol.com.