Benefits of Conducting a Nozzle Study - From Aug 2011 Fire Apparatus & Emergency Equipment Magazine

Following the completion of the nozzle study, our standpipe operations and equipment also underwent complete revision, bringing higher volume flows at lower pressures to these incidents. (Photos by author.)

Company involvement in the evaluation process placed a concept physically in the hands of those operating the nozzles on incidents. This improved both understanding and resultant trainings.

Inline pressure gauges and properly calibrated flow meters were key components in testing to provide solid data sets. This was a foundation for equipment selection and improving accuracy of department pump charts.

Past pump charts were a full-page spreadsheet with a slide rule-style chart for the automatic nozzle. The revised pump chart is more accurate, based on newly calculated coefficients from actual department-specific flow testing. The physical design is also more user-friendly in a pocket guide, waterproof, and writable format.

Fire streams and nozzle selection have become increasingly popular topics of discussion and research in the American fire service. It was this renewed interest in one of the most basic and traditional elements of fire suppression that prompted a review of West Metro (CO) Fire Rescue’s equipment and procedures in 2005 after a nozzle study. Our department, like many, had readily accepted the use of low-pressure, fixed-gallonage nozzles for standpipe operations because of their many benefits in high-rise settings. Unfortunately, prior to our study, low-pressure fog and smooth bore nozzles remained a component of high-rise packs but had not been revisited for our more common preconnect operations. The application of these nozzles is nearly undisputed for high-rise operations, yet the task of applying this same logic to the “routine” fireground occasionally meets resistance. Operationally, with the water system, the apparatus, and the equipment working at higher pressures, few take the time to question why.

Two things led us to fire streams and nozzles. First, the fire service has been greatly influenced by a small group of instructors and educators who have dedicated their careers to helping firefighters across the country become better at what they do. One such individual is the late Andrew Fredericks of the Fire Department of New York (FDNY). Fredericks is best known for his unparalleled commitment to engine company operations, his writing for Fire Engineering, and his involvement with the Fire Department Instructors Conference (FDIC). Next, Captain David Fornell of the Danbury (CT) Fire Department has become known as a fireground hydraulics guru with the publication of his Fire Stream Management Handbook. His book is regarded as the foremost text on the subject of nozzles and fireground hydraulics. Last, Paul Grimwood, of the London Fire Brigade, and his extensive research and testing of nozzle reaction and its effects have been a catalyst for change in equipment for fire attack on an international level.

Second, department-initiated studies and equipment reviews have also prompted changes. Following nozzle and hose studies, departments in Boise, Idaho, St. Petersburg, Florida, and Oakland, California, changed their equipment and operations to increase fireground flows for modern fuels and decrease the nozzle reaction encountered by firefighters. The studies and changes that resulted in Boise and St. Petersburg were acts of forward thinking and efforts to be progressive in firefighter safety and equipment. The Oakland Fire Department made its changes based on the recommendations of a study following a firefighter fatality in which inadequate fire flows were cited as a key contributing factor leading to the firefighter’s death.

In September 2004, West Metro initiated a nozzle study to see how our 1¾-inch equipment and operations compared to these current trends. Our department’s nozzle of choice at the time was an automatic fog nozzle. It met the current 1¾-inch flow rate trend of 150 gpm. We found, however, that most of our pump operators had developed a habit of “underpumping” initial attack handlines, gradually increasing pressure for greater flow as the interior crews indicated. Their reasoning was to provide a more manageable line during the stretch. In doing so, our pump operators, on average, only supplied our firefighters 128 gpm. By planning to increase pressures with demand, we are playing catch-up with the fire and compromising safety by putting firefighters behind the ball. This type of pumping will also add to the nozzle firefighter’s workload, in terms of nozzle reaction, with every increase in pump discharge pressure.

Armed with these initial findings, we decided to outline specific objectives for our study to move forward. The first was to meet National Fire Protection Association (NFPA) 1710, Standard for the Organization and Deployment of Fire Suppression Operations, Emergency Medical Operations, and Special Operations to the Public by Career Fire Departments (2004 ed.) by setting a standard fireground flow of 150 gpm from our 1¾-inch handlines. The second was to improve the effectiveness of fire stream application and hoseline management by decreasing nozzle reaction. The third was to simplify fireground hydraulics to ensure we were getting consistent fire flows with every handline deployment.

Why 150 gpm? Nationally, 150 gpm has become the target flow for 1¾-inch handlines. This number comes from NFPA 1710. The standard outlines that the first two handlines in operation at any initial alarm structure fire flow a minimum of 300 gpm combined. Following discussion with other departments and a review of recent publications, it was determined that 150 gpm per 1¾-inch handline was the most common way to meet the 300 gpm minimum. The West Metro Operations Division also felt that 150 gpm minimum from all 1¾-inch deployments would be the most appropriate operation. As we mentioned before, our current nozzle choice was capable of supporting this flow rate.

Controlling the Nozzle

Because of the high nozzle reaction of [our automatic fog nozzle], we wanted to evaluate other nozzles that could meet 150 gpm or greater at lower operating pressures to decrease our associated reaction forces. Smooth bore nozzles provide a high gpm flow with a nozzle pressure of 50 psi. We chose to test two smooth bore tips, the 7⁄8-inch tip with a flow of 161 gpm at 50 psi and the 15⁄16-inch tip with a flow of 185 gpm at 50 psi. Another low-pressure option was 50- and 75-psi low-pressure, fixed-gallonage fog nozzles that provide low-pressure qualities and an adjustable stream. We chose to add a 150-gpm at 50 psi low-pressure, fixed-gallonage fog tip to the study to meet the 150 gpm minimum and simplify hydraulics by having a target nozzle pressure that was the same as the smooth bore tips.

A Little About Nozzle Reaction

Why is nozzle reaction now an issue? Nozzle reaction forces are based on Newton’s first law of motion that says for every action there is an equal and opposite reaction. In fire streams, this equal-and-opposite reaction is dictated by the volume of water leaving the nozzle and the pressure at which it leaves the nozzle. To change the reaction force, we must either change our gpm output, the nozzle pressure, or both. The reason this has recently become such a popular consideration is, in part, thanks to the work by Fornell and Grimwood. Through extensive research, they have outlined working limits for firefighters with respect to managing nozzle reaction. This is a simple theory: Firefighters are not safely fighting fire when their efforts are focused on fighting nozzle reaction. Some of the most common side effects of high nozzle reaction are improper stream selection (the change from a straight stream to a fog pattern), gating down the bale to lessen nozzle reaction forces, and excess water damage from difficulties in stream direction. Grimwood’s study outlines the number of firefighters required to safely counter nozzle reaction: one firefighter for 60 lbs. force, two firefighters for 75 lbs. force, and three firefighters for 95 lbs. force. Keep in mind that these working limits are for safely managing the nozzle reaction. This is not how many firefighters should be on the handline for hose advancement or management, but how many firefighters should be directly behind the nozzle to support the reaction.

During our flow testing, we found nozzle reaction of 75 lbs. force for our automatic nozzle at 150 gpm—the upper limit of two firefighters (our typical staffing for handlines). This presented us with a potential safety issue, because it does not free up one of those firefighters to properly advance and manage the hoseline. The second firefighter would be committed to supporting the nozzle firefighter while flowing water. The flow testing found that, at the same 150-gpm flow rate, the low-pressure, fixed-gallonage fog had a nozzle reaction of 54 lbs. force. This is 21 lbs. force less than the automatic fog at the same flow. The smooth bores provided even higher flow rates with reaction forces that were well below that of the automatic fog nozzle. The 7⁄8-inch tip provides a flow of 161 gpm and a nozzle reaction 57 lbs. force; the 15⁄16-inch tip with 185 gpm flow has a nozzle reaction of 66 lbs. force.

Hydraulics Made Easy

How are we simplifying hydraulics? It is a rule of thumb to provide a fog nozzle with 100-psi nozzle pressure. Automatic nozzles, because of their compensatory spring and working parts, vary flow to maintain a constant nozzle pressure. With a 100-psi nozzle pressure, you may be supplying anywhere from 100 to 200 gpm. The gpm output of automatic nozzles is actually determined by pump discharge pressure, not nozzle pressure. The fact that this nozzle is so versatile in its flow range is an attractive option for departments seeking a nozzle with a wide operating range. This same characteristic may also be viewed as a hazard because the stream changes very little with the flow rate. This can lead to poor gpm output without recognition by firefighters at the nozzle. Also, knowledge of the wide operating ranges can lead to misconceptions of hydraulics and underpumping.

By changing to a nozzle with a single-target nozzle pressure for a single-target gpm output, we can make our pump discharge pressure a single setting dictated by our hose length. This would make a departmentwide fire flow standard easier to implement and eliminate the need for sliding pump charts to assist with varying flow calculations. When we choose a fog nozzle with a 50-psi operating pressure, the target nozzle pressure now becomes standard for both smooth bores and fogs, simplifying training and department pump charts. Additionally, all those involved know exactly what the flow rate is, from the nozzle firefighter to the incident commander, making operational decisions such as adding lines or changing to bigger lines easy to calculate.

Following a presentation of the aforementioned studies, research, and the results of our flow testing, we began a six-month trial period with three engine companies. The operational phase of the study served to evaluate the potential benefits of lower operating pressures on the fireground and the performance of these low-pressure, fixed-gallonage nozzles. At the conclusion of the study, a final presentation was made on both subjective data and crew reviews. The department leadership decided that the benefits of the low-pressure fixed-gallonage nozzles were worth the equipment change, associated costs, and training.

When I look back at the nozzle study, my opinion of the process has changed. At the time, I felt as if we were unnecessarily reinventing the wheel because of the amount of supportive documentation and similar changes sweeping the American fire service. I now realize that the study did not just serve to change nozzles. The accessory findings and unintended changes that resulted from this complete review brought us training, better equipment, and improved operations and has made us a better department overall. Without conducting this study with our equipment and our members, we would not have the greater understanding of one of our most basic functions that we enjoy today. Our pump charts were completely redone as a result of the data collected from flow testing and engineer feedback. This resulted in an extremely accurate and user-friendly pump chart. The information collected and training used for the study have been the base for change in our 2½-inch operations, high-rise equipment and policy change, recruit training, and especially our equipment specifications for new apparatus down to the ball valve selection in our 1½-inch shutoffs.

Our department stands behind the research and resultant changes. Our 128-page document is fully available for distribution to anyone interested by contacting me through West Metro Fire Rescue or the Fire Engineering Training Community Web page. The study has been used by other departments across the country to initiate change or to provide a guide for a process. With that said, I encourage any department considering making an equipment change to take on the process for itself and not rely entirely on the work of others. You might just be surprised how much a nozzle study will improve your organization.

Complete Study PDF Link

WMFRNozzleStudy.pdf

BRIAN BRUSH is a lieutenant assigned to Company 10 at West Metro Fire Rescue in Lakewood, Colorado. He began his fire service career in 1996 in Northern California as a volunteer. He has a bachelor’s degree in fire and emergency services administration and an associate degree in paramedicine.