Nozzle tests
I read with interest the series of articles “Nozzle Tests Prove Fireground Realities.” I was pleased to see that the authors, Jerry Knapp, Tim Pillsworth, and Sean White, were attempting to use scientific methods to resolve misunderstood issues with stream selection for proper interior fire attack. However, I was very disappointed with the results.
In Part 1 (February 2003), the authors tried to prove how much air would be drawn through a building during fire attack. At one point, where their airflow-measuring instrument could not register high enough, they simply guessed at the result. This is enough to destroy any credibility their tests might have. A good researcher gathers facts, not guesstimates. Also, one of the hallmarks of a good scientific inquest is that it is begun by a thorough literature search. Had a credible literature search been done, they may have found that the University of Maryland (U of Md) conducted similar research and reported it in the March 1971 issue of Fire Engineering. The research at the U of Md found that the pattern of the nozzle and how close it is to the opening are critical. They were also able to demonstrate that how much water is flowing makes a significant difference in how much air is moved. This means that just because you use a fog nozzle doesn’t mean you get maximum airflow. To get the maximum airflow using a fog nozzle, it must be on a 55º to 60º pattern positioned so that the fog cone fills 85º to 90º of the opening.
The authors also mention that William E. Clark, in Firefighting Principles and Practices, points out that a fog nozzle flowing 60 gpm will move 12,000 cubic feet of air per minute. The U of Md found that at 60 gpm, the airflow was only 5,406 cubic feet of air per minute. This is not an insignificant difference. I wonder how Clark did his airflow measurements. I know that the U of Md had the assistance of the Mechanical Engineering Department. My money is on the U of Md figure.
Also in Part 1, the authors mention that a photograph they placed in the article shows a “dangerous ricochet of superheated air and steam onto the nozzle team.” Could this be related to an excessive flow of water for the room size, not poor stream selection or application method?
In Part 2 (September 2003), they use flows of 180 gpm with both the solid-bore nozzle and the fog nozzle. I wonder how much air would be moved with a more reasonable flow. If we apply the Iowa State Rate-of-Flow Formula to their scenario, a room 12′ 2 10′ 2 8′ (the size room used in their live fire tests) requires a flow of only 9.6 gpm for extinguishment. This means that a rate of flow of 180 gpm is 19 times what is needed. And, since the Iowa Formula further states that the water must be applied within the first 30 seconds, only 4.8 gallons of water is necessary to extinguish this fire. At 180 gpm, it will take only 1.6 seconds to deliver the proper amount of water for extinguishment.
There is actually quite a bit of credible scientific information concerning fire attack. The research began in the early ’40s with Lloyd Layman and his “Theory of Indirect Application and Atmospheric Displacement.” Then, in 1951, the National Board of Fire Underwriters impaneled a committee, the Exploratory Committee on the Application of Water, to determine if Layman’s theory was accurate. But the single most significant event to fire research in this country occurred in 1952 when Iowa State University hired Keith Royer and Floyd W. (Bill) Nelson. They conducted research on fire and fire attack for more than 20 years and developed the indirect method of fire attack. When properly done, a combination attack is still a valid and safe interior attack option.
Briefly stated, applying Royer and Nelson’s research, we find that there is a critical amount of water that has to be applied to a fire. Too much water, according to their research, has undesirable side effects, while it is obvious that too little water won’t work either. But they proved that with a near ideal rate of flow a combination attack is safe and efficient. Also, they explain the importance of the clockwise direction of nozzle rotation and how to properly do an indirect attack. Another fact that was researched at Iowa State is that when done properly and with a near-ideal rate of flow, the combination attack doesn’t disturb the thermal balance in a room. This is a matter of scientific fact from years of experimentation at Iowa State University.
The U.S. Navy also conducted a series of tests in the 1990s. By 1994 it was conducting full-scale tests to evaluate the difference between what it called “traditional straight stream” (actually anything between straight stream and 30º fog) used for direct fire attack and “aggressive fog attack” (3D fog attack). As a result of the full-scale tests, the test committee recommended the adoption of the aggressive fog attack for fires that could not be easily controlled with a direct fire attack. The Navy also found that the “traditional straight stream” attack produced a great deal of agitation of the thermal layer, while the “aggressive fog attack” did not.
It is very evident from this series of articles just how little is understood today about the proper application of fog streams. For example, in these articles the authors are measuring the flow of air with the stream aimed at the vent opening. This is an ideal flow condition. Under most fire situations, this will never happen by chance, which will mean that any airflow will be significantly less than the maximum possible. Also, in these experiments they have an extremely high rate of flow—far more than is necessary for the fire scenario they have set up.
The authors state in Part 3 (February 2004) that they were taught to “set the nozzle for 30º fog, whip the nozzle around, and the fire goes out.” Notice no mention was made about how long to keep the nozzle open or how critical it was to have the outside of the fog cone actually touch the ceiling, walls, and floor as the pipe is worked around in the room. Also there is no mention that properly done, the nozzle (not the firefighter) should actually be in the fire room.
In short, firefighters today are not being taught proper use of the fog nozzle. I do not say this as a criticism of the ability or knowledge of these three authors but as an indictment of the dumbing down of the fire service over the past 20 to 30 years.
Finally, as I am writing this, the National Institute of Standards and Technology (NIST) is doing research on the effectiveness of fire streams. Results may be available to us by this summer. It will be interesting to see if their research uncovers any major new issues or just confirms the work that has already been done.
William F. Crapo
Assistant Chief
Harrisonburg, Virginia
The authors respond: Our testing/research and the articles that reported the data and conclusions were very successful in advancing the practical knowledge of the effect of hose streams on the fire environment. We resolved a number of myths that have been around the fire service for eons. Our research and tests for the first time put hard numbers against what we have known intuitively for years but now we can prove. Additionally, we provided a way for all firefighters to be able to test and judge for themselves the effectiveness of their own nozzles.
Our tests were designed to simulate with a nozzle and a handline and a fire flow consistent with today’s fire attack doctrine what effect the stream would have on the airflow. The Maryland study is now 33 years old; even the fire service has changed a little since then.
Notably, our tests were not conducted under laboratory conditions, but efforts were made to reduce the variables in the results. As far as our test methods, some of the values were estimated because of the limitations of the instrument. Estimates were reported as such.
Our literature research found that many departments have target flows for handlines of 125, 150, or 180 gpm. We have determined that the Iowa Formula developed in the ’50s must have been based on fuel loads of ordinary combustibles of the era. With the amount of plastics used in today’s furnishings and the number of items in a home today (more stuff, more fire), we feel that the Iowa Formula will leave you dangerously short of gpm for the Btus. Yes, 180 gpm may be overkill, but whoever said we wanted an aggressive interior fire attack to be a fair fight? By the way, how many gpm did the nozzleman not get because of each kink or severe bend in the line?
For the indirect or combination fire attack method, we believe that any fire attack method that incorporates steam as an extinguishing agent has determined that a successful rescue is not possible. As Crapo points out “that properly done the nozzle (not the firefighters) should actually be in the fire room,” the occupants of the fire room will be scalded. Search operations now become body recoveries.
Lloyd Layman tried to apply his shipboard firefighting experience to structural fires, which is where this debate began. Crapo also spoke of tests conducted by the Navy in the ’90s. Were they also trying to apply shipboard techniques to structural fires? And were they factoring an “acceptable” loss of life into that calculation?
The comment about the “30° fog and whip it around” came from the fertile minds of our earliest instructors—guys who based all their fire attack methods on their limited experience with one-room fires. It was to confirm the naivete of some members of the fire service and their (mis) understanding of the fire environment and their total lack of understanding of the effect of a fog stream used inside a building. That was what we were told 30 years ago, and it is from that misunderstanding that we have worked to explain proper techniques of stream application.
We do take exception to the statement that this is “an indictment of the dumbing down of the fire service.” But why does each generation have to answer the same questions?
Our research was not perfect, but it was solidly grounded in the tactics we use today. We did advance our common goal at least a few important steps.
The issue of how best to extinguish the fire is still unresolved by the American fire service. Chief Crapo has lots to contribute to this effort. We need to work together.
Insane staffing
Regarding Bill Manning’s “From Inane to Insane, Coast to Coast” (Editor’s Opinion, June 2004), within our own department, the City Administration is fond of stating there have been no layoffs. Yet our authorized strength is 1,655, and our current strength is 1,540, including a 25-person recruit class graduating soon. Dayton, Ohio, has closed several fire stations, and its mutual-aid companies are starting to complain about the volume of runs they take into Dayton. Chillecothe, Ohio (population 55,000), has three to four firefighters on duty per shift. An asthmatic child there waited 30 minutes one weekend for a medic because the engine was on a fire run. Her parents transported her to the hospital by other means. Circleville, Ohio (population 18,000), had four firefighters on duty last winter (18°F at the time) in two stations. When two homes across (literally) from fire headquaters burned to the ground, the mayor chastised the department for allowing it to happen. My question is, headquarters of what?
I get beat up all the time because I say we are two stations behind where we ought to be. The last fire station we added in anticipation of the need was Station 26 in 1975! All since have been reactive, which means political.
Thanks to Bill Manning for the terrific editorials; keep up the good work!
Karry L. Ellis
Assistant Chief
Support Services Bureau
Columbus (OH) Division of Fire
Safety problem
Congratulations to Michael S. Terwilliger for the great article “Why Is Safety Such a Problem?”(Fire Commentary, June 2004). I have been reading Fire Engineering for many years. I often make copies of articles for my fire science students.
I am retired from a small department near Chicago, and I have served as a safety officer for a fire protection district for about five years. I have witnessed firsthand all the reasons Terwillger mentions that have caused problems with safety in the fire service. Recently, one firefighter was killed and several other firefighters seriously injured when two engines collided in my area while responding to a garage fire. Both vehicles were obviously traveling at an excessive speed. The accident was totally unacceptable, possibly the result of “throwing caution to the wind.”
I hope that all subscribers read the article and do some hard, objective thinking about it. With individuals such as Terwilliger “telling it like it is,” there might be real progress made in the area of fire service safety.
Joe Martinek
College of Du Page
Harper College
Crest Hill, Illinois
Flashover risk management
After reading “Flashover Risk Management” (June 2004), I would concur with author Scott Burnette’s assertion that flashover poses a great risk to the fire service. However, based on 30 years of operational experience and research into fire behavior and fire control methods, I disagree strongly with his assertion that straight or solid streams are the most effective method for preventing or controlling flashover.
The greatest misconception in the use of water fog for interior fire attack is that massive production of steam will always result. This is similar to the argument that high flow rates from interior handlines result in excessive water damage. The answer to both of these potential problems lies in a well-trained nozzle operator. Use of a wide fog pattern as described in the article (continuous application) would result in the consequences the author described, production of a large quantity of steam and untenable conditions. However, application of an appropriate volume of water fog into the hot gas layer would result in production of a limited quantity of steam, reducing potential for flashover or controlling preflashover rollover conditions.
Burnette correctly identifies the heat absorption capability of a fog pattern as being related to the latent heat of vaporization (conversion of water in liquid form to steam). Introduction of water in droplet form into the hot gas layer will absorb more heat because of the increased surface area of the water, thus increasing the total heat absorbed. Use of an appropriate volume of water can cool the hot gas layer, causing it to contract and raising the neutral plane. In this manner, use of water fog can actually reduce the heat firefighters and victims are subjected to while limiting potential for flashover. The effectiveness of this method for flashover control has been demonstrated through both operational experience and scientific research in many countries including Sweden, England, Australia, Canada, and the United States.
Use of a solid stream can control fire conditions most effectively when water can be placed on burning fuel. However, when the source of the fire is shielded, this type of stream is less effective. Flashover does not directly involve burning solid fuel but flammable products of combustion (such as unburned pyrolyzed materials and carbon monoxide) located in the hot gas layer above the neutral plane. Flashover control requires that these materials be cooled to prevent ignition—a task most effectively accomplished by skilled application of water fog.
Ed Hartin
Battalion Chief
Gresham (OR) Fire and Emergency
Services Department
Rural tours
Having served in a rural volunteer fire department, I cannot say how much I enjoyed “Rural Fire Department Tours” by Stanford E. Davis (Volunteers Corner, June 2004).
Often it makes sense to “downsize” fire apparatus. Davis mentioned the use of a mini pumper as well as a 6 2 6 forestry engine. If you use a “downsized” truck for structure fires, make sure it has the necessary forcible entry tools, SCBA, pike poles, axes, and extinguisher—all necessary to begin an initial attack.
Private roads and 600-foot driveways are dilemmas in many fire districts. One Connecticut town even “downsized” a tanker. After using three tandem-axle tankers that were each too big for some residents’ driveways, the town cut back to a commercial chassis 4 2 2 with an 1,800-gallon tank and a 500-gpm pump. The department ended up with a mobile water supply fire apparatus tanker of which it is extremely proud. A well-planned and well-thought-out “downsized” fire apparatus does have a place in today’s fire service.
David Titus
Firefighter (Retired)
North Haven, Connecticut
Apparatus supplement on target
Wow! What an outstanding Apparatus Supplement included with the June 2004 issue. This supplement should be in the library of every driver training/certifying member of the fire service. The information is concise, on target, and current. Apparatus today are significantly more complex than those of days gone by, and the supplement provides good information on these issues. Thanks to Chief William C. Peters for producing the material for the supplement.
John M. Buckman III
Chief
German Township (IN)
Volunteer Fire Department
Keep up “tradition”!
I have just received my first issue of Fire Engineering, and if this is what I have to look forward to, it is the professional magazine I have been seeking! In the July issue, in the article “Pride and Ownership: the Love for the Job: The Company Officer,” author Rick Lasky gives the origins of some fire department traditions. I want more! This article is a timely wake-up call to us “aging veterans.”
Ron Boyd
Captain
Chattanooga, Tennessee
