As we start the New Year it is a good time to reaffirm our commitment to mastering our craft. Developing and maintaining proficiency in reading the Fire using the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme for fire behavior indicators, requires practice. This post provides an opportunity to exercise your skills using a video segment shot during a residential fire.

Residential Fire

Early on the morning of December 23, 2009, the Cheektowaga Police department was dispatched to 305 Highland Drive in Cheektowaga to investigate a 911 call for an unknown type problem. The female caller was screaming, but the dispatcher was unable to determine the nature of the emergency. The first arriving police unit discovered a residential fire with persons trapped, and requested fire response. The police officers rescued a male victim from just inside the door, but fire and smoke conditions prevented them from assisting the other occupants.

The Hy-View Volunteer Fire Company responded with a first alarm assignment and observed flames showing on Side C.

Download and the B-SAHF Worksheet.

Watch the first 1 minute 10 seconds (1:10) of the video. This segment was shot from Side B at the B/C Corner.  First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions?

1. What additional information would you like to have? How could you obtain it?
2. What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
3. What burning regime is the fire in (fuel controlled or ventilation controlled)?
4. What conditions would you expect to find inside this building? If presented with persons reported (as the first arriving companies were) how would you assess potential for victim survival?
5. How would you expect the fire to develop over the next two to three minutes

Now watch the remainder of the video clip and answer the following questions:

1. Did fire conditions progress as you anticipated?
2. A voice heard in the video states that this was a backdraft. Do you agree? Why or why not?

Hy-View Volunteer Fire Company personnel recovered two female civilian victims from the residents. However, all three victims died as a result of smoke inhalation.

Ed Hartin, MS, EFO, MIFIreE, CFO

The first two posts in this series, Effective and Efficient Fire Streams, and Effective and Efficient Fire Streams: Part 2, discussed theoretical cooling capacity, fire stream efficiency, flow rate, nozzle design characteristics and methods of use. This post drills down with a look at the relationships between the pump, hose, and nozzle in developing effective and efficient fire streams.

Where to Start?

It is likely that the most common system for developing effective and efficient fire streams involves use of combination nozzles having a designed operating pressure of approximately 100 psi (690 kPa) and what my British and Australian colleagues would refer to as “layflat” hose with a diameter between 1-1/2” (38 mm) and 2” (52 mm). As this type of system seems to be common to most fire services (with a few variations), this is a good place to start.

Hydraulics

Developing effective and efficient fire streams requires an understanding of basic principles of fireground hydraulics. As discussed in earlier posts, each nozzle has a designed operating pressure. In order to provide this pressure at the nozzle, it is necessary to overcome loss of pressure in hoselines due to friction loss and increases in elevation.. Add To keep this discussion simple, the pump and nozzle will be at the same elevation.

Figure 1. Basic Handline Hydraulics

The major factors influencing friction loss in a hoseline are flow rate and diameter of the hoseline. The Pumping Apparatus Driver/Operator Handbook (IFSTA, 2006) identifies four friction loss principles:

First Principle: All other conditions being equal, friction loss varies directly with the length of the hoseline.

Second Principle: When hoseline diameter remains constant, friction loss varies approximately with the square of the increase in flow rate. Doubling the flow increases friction loss by a factor four.

Third Principle: At the same flow rate, friction loss varies inversely as the fifth power of the diameter of the hoseline (increasing hose diameter, even a small amount has a dramatic effect on friction loss. Increasing hose diameter from 1-1/2” (38 mm) to 1-3/4” (45 mm) reduces friction loss by 46% (1.50⁵/1.75⁵=0.46).

Fourth Principle: If hose diameter and flow rate are held constant, friction loss is independent of pressure.

Apparatus operators must understand these basic concepts and be proficient at determining the line pressure required to develop adequate nozzle pressure to produce the necessary reach and droplet size for effective and efficient fire control operations.

Scalability

Critical and optimal flow rate are dependent on the heat release rate from the fire. The higher the heat release rate, the higher the flow rate necessary to achieve fire control. However, the flow rate required for gas cooling (unignited gas phase fuel) is not so dependent on HRR! Cooling unignited gases is most effective at a considerably lower flow rate. 30 gal/min (115 l/min) to 60 gal/min (230 l/min) is often sufficient for gas cooling (unless compartment size is extremely large).

Single flow nozzles are simple to operate as control is limited to the angle of the fog pattern and the shutoff valve. The term single flow is a bit misleading in that flow can be varied using the shutoff valve. Partially opening the shutoff valve will provide a reduced flow rate. However, partially opening the valve also provides considerably lower nozzle pressure (at the orifice), resulting in poor stream performance (limited reach and large droplet size). If a nozzle is designed to develop the low flow rate and small droplet size that is typically optimal for gas cooling, it may not have sufficient flow for direct attack on larger fires or fires in larger compartments. On the other hand, nozzle designed for higher flow rates may be ideal for direct attack on larger fires or large compartments, but are inefficient and in some cases ineffective when used for gas cooling.

Ideally, the hose and nozzle system should be scalable to provide effective and efficient operation over a fairly wide range of flow rates. At the low end, the nozzle should be capable of gas cooling at 30 gpm (115 lpm). The upper end of flow capability for direct attack has room for considerable debate.

Some agencies such as the New South Wales Fire Brigades in Australia uses the Akron Turbojet with flow settings of 30, 60, 95, & 125 gal/min (115, 230, 360, 475 l/min). On the other hand, many fire departments in the United States use nozzles having upper end flow rates of 150-200 gal/min (568-757 l/min). Having a higher flow capability provides the ability to deal with higher HRR and larger size compartments typical in contemporary residential structures and commercial buildings.

Variable flow and automatic nozzles provide the capability to vary flow rate as needed to deal with varied tactical applications and fire conditions. However, each accomplishes this task in a different manner.

Variable Flow Nozzles

When using a variable flow nozzle, the size of the nozzle orifice can be changed manually to provide several specific flow rates at the designed nozzle pressure. This requires that the apparatus operator know the flow setting of the nozzle as well as the length of line in order to determine the line pressure required to develop the correct nozzle pressure. At first glance, it appears that changing flow rates on the fly would require a great deal of radio communication between the nozzle team and apparatus operator (communication of flow setting each time it is changed). However, this challenge can easily be overcome!

Consider what happens when the nozzle operator changes flow setting and the apparatus operator maintains the same line pressure. If the flow setting is reduced (decreasing the orifice size), flow rate will be decreased, reducing friction loss in the hoseline. As the line pressure remains the same, the pressure that is not used to overcome friction loss increases nozzle pressure. For example, if a 200’ (60 m) long 1-3/4” (45 mm) hoseline equipped with a variable flow nozzle such as an Akron Turbojet is flowing 125 gal/min (475 l/min) at a nozzle pressure of 100 psi (690 kPa) and the nozzle operator changes the flow setting to 30 gal/min (115 l/min) and discharge pressure remains constant, the flow rate will be reduced to 40 gal/min (150 l/min) at a nozzle pressure of 140 psi (965 kPa) (see Figure 2).

Figure 2. Changes in Flow Rate and Nozzle Pressure

Note: The preceding example is based on tests conducted with an Akron Turbojet variable flow nozzle.

How does the reduced flow rate and increased nozzle pressure impact on fire stream effectiveness and efficiency? Increased velocity of discharge (resulting from the higher nozzle pressure) results in reduced droplet size, increasing the effectiveness and efficiency of the stream when used for gas cooling. The reduced flow rate may be insufficient for direct attack on larger fires, but the nozzle operator can quickly return to a higher flow rate by adjusting the nozzle flow control. Pumping to deliver maximum flow allows the nozzle operator to select the flow rate and nozzle pressure that is appropriate based on conditions.

Automatic Nozzles

Automatic nozzles maintain a relatively constant nozzle pressure through a given flow range. The nozzle operator controls flow using the shutoff (opening the nozzle partially provides a lower flow rate than when the nozzle is opened fully).

The shutoff valve controls both water application and flow rate, automatic nozzles are a bit simpler to use, but unlike the example provided on how to maximize the capability with the variable flow nozzle, nozzle pressure remains constant (e.g., 100 psi (690 kPa).

System Design

The starting point for designing an effective system to develop effective and efficient fire streams needs to consider the desired flow rate, typical length of hoselines required, and tactical applications. Remember there is no universal, one size fits all, answer to this question. Fire services around the world successfully use a variety of different systems. Consider the following as a starting point:

• Both variable flow and automatic nozzles can be used effectively to apply water at varied flow rates. Automatic nozzles are simpler to operate (as they have fewer controls), but at lower flow rates are likely to develop larger droplets than variable flow nozzles operated at over 100 psi (690 kPa).
• Hoseline diameter should be sufficient to develop the desired flow rate given the likely attack line length. Remember that as hoseline diameter increases, friction loss decreases (but so may mobility).
• Pumping for maximum flow from the nozzle provides the nozzle operator with maximum flexibility as flow rate can be selected based on conditions. If other than maximum flow is selected as the standard flow rate it is important to train nozzle operators to request that the apparatus operator increase discharge pressure to provide maximum flow if needed.

The next post in this series will examine applications of high pressure and ultra-high pressure systems for developing effective and efficient fire streams. While considerably different than the system described in this post, this technology shows promise in expanding the range of tools available for fire control operations.

Ed Hartin, MS, EFO, MIFireE, CFO

References

International Fire Service Training Association (IFSTA). (2006). Pumping apparatus driver/operator handbook (2^nd ed). Stillwater, OK: Fire Protection Publications.

The ability to read the fire and predict likely fire behavior is a critical skill for both firefighters and fire officers. Previous posts have examined how to use the B-SAHF scheme to recognize critical fire behavior indicators and identify the stage of fire development, burning regime, and potential for extreme fire behavior such as flashover or backdraft. However, there is something missing!

Experience is critical to adapting standard procedures and practices to a complex and dynamic operational environment. However, learning about fire behavior and changes in fire conditions based on fireground observations are a bit like a black box test. Black box testing is a technique for testing computer software in which the internal workings of the item being tested are not known by the tester. This is not entirely true in the case of fire behavior, but there is much that we don’t know when assessing conditions on the fireground. How long has the fire been burning? What are the specific characteristics of the fuel? What sort of internal compartmentation is present? What exactly is the ventilation profile? Some of these factors can be determined during fire investigation and it is also possible to determine (with some degree of uncertainty) what influence these factors had on the outcome of the incident. Did you ever wonder how fire behavior would have changed if you had used different tactics? Unfortunately, in real life there are no “do overs”!

UL Tactical Ventilation Research Project

One of the people who has asked himself the question of what would have changed if different tactics were used is Underwriters Laboratories Fire Protection Engineer Steve Kerber.

Underwriters Laboratories (UL) has received a Firefighter Safety Research and Development Grant from the Department of Homeland Security (DHS). This research project will investigate and analyze the impact of natural horizontal ventilation on fire development and conditions in legacy (older, more highly compartmented) and contemporary (multi-level, open floor plan) residential structures.

Preliminary work has included review of literature related to horizontal ventilation and incidents in which ventilation had a significant influence on firefighter injuries and fatalities. In addition, UL has done preliminary work on the performance of various structural components such as single and multi-pane windows as preliminary input for design of full scale residential fire experiments.

In mid-December 2009, Steve Kerber met with the project advisory panel comprised of Captain Charles Bailey, Montgomery County (MD) Fire Department; Lieutenant John Ceriello New York City Fire Department, Firefighter James Dalton and Director of Training Richard Edgeworth, Chicago Fire Department, Chief Ed Hartin, Central Whidbey Island (WA) Fire & Rescue, Chief Otto Huber Loveland-Symmes (OH) Fire Department, and Chief Mark Nolan, Northbrook (IL) Fire Department. In addition, the advisory panel includes Fire Protection Engineers Dan Madrzykowski from the National Institute of Standards and Technology (NIST) and Dr. Stefan Svensson, a research and development engineer from the Swedish Civil Contingencies Agency.

Figure 1. Defining Experiment Parameters for the Contemporary Structure

The main task presented to the advisory panel at the first meeting was to aid in defining the parameters for the experiment; including fire location, changes in ventilation profile, timing of these changes, and instrumentation to measure effects on fire development and conditions.

UL Large Fire Research Facility

The ventilation experiments will be conducted at the UL Large Fire Research Facility in Northbrook, IL. From the exterior, this facility simply looks like a large industrial building (see Figure 2). However, the interior of the structure includes a unique facility for fire research.

Figure 2. UL Large Fire Research Facility

One of the facilities inside this building is a 100’ x 120’ (30.48 m x 36.58 m) with a ceiling height that is adjustable up to 50’ (15.24 m) (see Figure 3). All of the smoke resulting from tests in this facility is exhausted through a system designed to oxidize unburned fuel and scrub hazardous products from the effluent prior to discharge to the atmosphere. Tests are monitored from a control room that overlooks the large burn room.

Figure 3. Large Burn Room

Over the next month, the two residential structures to be used for the ventilation experiments will be constructed inside the large burn room at the UL Large Fire Test Facility. After construction is complete, a series of 16 full scale fire experiments is planned to evaluate a range of different horizontal ventilation scenarios.

Research with the Fire Service

Steve Kerber has often stated that it is essential that scientists and engineers conduct research with, not for, the fire service. Engagement between researchers and firefighters on the street is essential in advancement of our profession. With this ventilation research project, Underwriters Laboratories is actively engaged in this process.

The outcome of this project will not simply be an academic paper (but there might be one or more of those as well). As part of the DHS grant, UL will be developing an on-line course to present the results of the experiments and their practical application on the fireground.

Happy Holidays,

Ed Hartin, MS, EFO, MIFireE, CFO

The first post in this series, Effective and Efficient Fire Streams, discussed theoretical cooling capacity, fire stream efficiency, and flow rate. This post extends the discussion, by examining how nozzle design characteristics and methods of use influence efficiency.

Think!

I do not ask that anyone believe anything that I say (or write in this blog) simply because I said so. Firefighters� opinions about nozzles are as strong as their opinions about what color fire apparatus should be painted and what type of helmet should be used to protect our heads. Each kind and type of nozzle discussed in this post is being used by firefighters all over the world to extinguish fires in buildings. This does not mean that they are all equally effective, or appropriate in all circumstances. I challenge you to think about the physics of fire control and examine your assumptions about nozzles, fire stream characteristics, and how to develop effective and efficient fire streams.

Nozzle Classification

There are several different ways to approach classification of nozzles used in structural firefighting. One simple approach is to consider the pattern or patterns in which water can be applied:

Solid Stream/Smooth Bore: This type of nozzle provides a single pattern consisting of a jet of water that maintains coherence throughout its effective reach (breaking up into extremely large droplets beyond that point)

Combination: This type of nozzle can produce a variety of patterns from a straight stream to a fog cone. Both the straight stream and fog cone are comprised of small droplets of varying diameters. Droplet diameter and consistency of droplet size is dependent on nozzle design and operating pressure (higher pressure results in smaller droplets).

Special Purpose Nozzles: In addition to solid stream and combination nozzles, there are a variety of other specialized nozzles such as piercing nozzles (fog nails), cellar nozzles (of various types), and ultra high pressure solid stream nozzles that can be used for cutting through a variety of materials as well as to produce a fog pattern with extremely small droplets. Specialized nozzles and in particular high pressure and ultra-high pressure systems will be examined in detail in a subsequent post in this series.

Nozzle Characteristics

Beyond simple classification of structural firefighting nozzles as solid stream, combination, or special purpose, nozzles may be further classified based on a number of other characteristics such as the flow rate(s) or flow range and designed operating pressure.

Single Flow: Some nozzles are designed to provide a specific, fixed flow rate at their designed operating pressure. This includes solid stream nozzles with a single sized tip and fixed flow rate combination nozzles. While these nozzles are considered to provide a single flow rate, this is not exactly true. The nozzle orifice is of fixed size, providing a given flow rate at a specified nozzle pressure. As discussed in Under Pressure, flow rate from an opening is based on the area of the opening and the velocity of the water being discharged. Increased or decreased nozzle pressure influences flow rate. For example, increasing the nozzle pressure on a solid stream nozzle from 50 psi (345 kPa) to 80 psi (352 kPa) increases flow rate by approximately 22%.

Variable Flow: Nozzles may also be designed to allow orifice size to be changed, providing variable flow rates at a given nozzle pressure. With solid stream nozzles, this is accomplished by changing the tip size. With some combination nozzles, flow and pattern vary together (e.g., the fog pattern has a lower flow rate than the straight stream setting). However, most modern combination nozzles used for structural firefighting allow adjustment of the spray pattern while maintaining flow rate. Variable flow combination nozzles may be manually adjustable with several different flow rate settings at a specified nozzle pressure.

Automatic Nozzles: Another type of nozzle that allows variation of flow rate is the automatic nozzle. With this design the nozzle adjusts flow rate by varying orifice size automatically to maintain a relatively constant nozzle pressure. With automatic nozzles the flow range specifies the lowest and highest flow rate at the designed nozzle pressure. Some automatic nozzles allow adjustment of the nozzle pressure setting to allow operation at two different nozzle pressures such as 100 psi (690 kPa) and 50 psi (345 kPa).

Nozzle Pressure: At one time the question of nozzle pressure was fairly simple, combination nozzles generally were designed to operate at 100 psi (690 kPa) nozzle pressure. However, today it is not that simple. For a variety of reasons ranging from limited pressure available from high-rise standpipe systems to the desire for lower nozzle reaction force, nozzle manufacturers are producing combination nozzles with varied designed operating pressures (commonly 50 psi (345 kPa), 75 psi (517 kPa), and 100 psi (690 kPa).

Nozzle Performance

Floyd Nelson (1989) captured the essence of nozzle performance in the following statement: �In principle, firefighting is very simple. All one needs to do is put the right amount of water in the right place and the fire is controlled� (p. 102).

Nozzles used for gas cooling must produce small droplets, be capable of varying the angle of the fog cone to have sufficient reach to cover varied sizes of compartments. Droplets with a diameter of 0.3 mm are small enough to vaporize readily in the hot gas layer, but also have sufficient mass to travel a reasonable distance (Herterich, 1960). Droplets larger than 1 mm are likely to penetrate some distance through hot gases and flames without completely vaporizing (S�rdqvist, 2001). In reality, while we know a fair bit about droplet size and performance. We don�t know much at all about the droplet sizes produced by the nozzles we are using.

What we do know is that lower pressure nozzles develop larger droplets than higher pressure nozzles of the same general design. Specific design characteristics such as the angle that the water must take as it exits the orifice and forms the fog cone also impact on droplet size. This can be illustrated using a nozzle such as the Akron Turbojet. When set on 30 gal/min (115 l/m) or 60 gal/min and operated at a nozzle pressure of 100 psi, droplet size is extremely small, providing excellent gas cooling performance. However, when flow rate is increased to 95 gal/min (360 l/min) or 125 gal/min (473 l/min) droplet size increases dramatically. While still effective for gas cooling, water application at these flow rates is less efficient.

There is no standardized test used for nozzles that determines the range of droplet sizes produced under different flow rates, nozzle pressures, cone angles, etc. However, there is light at the end of the tunnel. The technology exists to answer this interesting (and I believe important) question. Figures 1 and 2 illustrate a system comprised of lasers and a high speed camera that is used to determine droplet size from sprinkler heads. This system could also be used to assess droplet size developed by handline nozzles (if funding was available).

Figure 1. UL Sprinkler Droplet Size Test Facility

Note: Underwriters Laboratories, Northbrook, IL

Figure 2. Laser and Camera Used for Measuring Droplet Size

Note: Underwriters Laboratories, Northbrook, IL

One factor that complicates things when considering droplet size and nozzle performance is that the nozzle is only one part of the equation. The nozzle operator has a significant influence on performance. For example, in a short pulse, if the nozzle is opened quickly, more of the droplets are formed with the nozzle operating at full nozzle pressure than if it is opened slowly (providing a lower pressure at the start of the pulse). The same is true if the nozzle is closed slowly rather than quickly. This is less significant with long pulses as the opening and closing phase of the pulse comprises a small percentage of the total operating time.

In direct and indirect attack, water must pass through the hot gas layer and reach burning fuel (direct attack) and/or hot surfaces (indirect attack) before significantly evaporating. If distances are not great or the temperature of the hot gas layer is not extremely high, a straight stream or narrow fog cone comprised of small droplets may be effective in accomplishing this task. When gas cooling precedes direct attack, this is often the case. However, if the distance between the nozzle and intended target is large and/or the temperature of the hot gases is high, larger droplets (or a solid stream) may be much more effective.

Selection

Many factors can (and should) be considered when selecting a system to develop effective and efficient fire streams. I used the word system intentionally as a nozzle is useless without hose, a pump, source of water, and most importantly knowledgeable and skilled firefighters to operate it.

The ideal system to develop effective and efficient fire streams for offensive firefighting would have the following capabilities (but not necessarily at the same time).

• Can produce small droplets for gas cooling
• Can produce larger droplets to penetrate hot gases and reach burning fuel or hot surfaces
• Adjustable fog cone angle (allows effective reach in varied size compartments)
• Adequate reach and stream cohesion when adjusted to straight stream
• Ability to vary flow rate depending on fire conditions and tactical application
• Light weight and high level of maneuverability
• Ease of operation to simplify training requirements

At present, it is unlikely that any single system meets all of these requirements (but that is open to debate). Future posts will examine a variety of systems including those that use low, medium, high, and ultra-high nozzle pressure as well as a range of flow rates.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Nelson, F. (1991). Qualitative fire behavior. Ashland, MA: International Society of Fire Service Instructors.

Herterich, O. (1960). Wasser als loschmittel [in German]. Heidelberg, Germany: Alfred Huthig

S�rdqvist, S. (2001). Water and other extinguishing agents. Karlstad, Sweden: R�ddnings Verket.

The previous posts in this series, examined the importance of proficiency in use of the firefighters’ primary weapon in offensive firefighting operations, and outlined several drills that can be used to develop proficiency in basic nozzle operation and hose handling.

• My Nozzle
• Basic Nozzle Techniques & Hose Handling
• Nozzle Techniques & Hose Handling: Part 2
• Nozzle Techniques & Hose Handling: Part 3

This post extends this examination of how to develop proficiency in nozzle operation and hose handling, presenting method or developing skill in working under conditions with poor visibility and application of indirect attack as an offensive firefighting tactic.

This is my nozzle, there are many like it but this one is mine. My nozzle is my best friend. It is my life. I must master it as I master my life. Without me it is useless, without my nozzle I am useless.

I will use my nozzle effectively and efficiently to put water where it is needed. I will learn its weaknesses, its strengths, its parts, and its care. I will guard it against damage, keep it clean and ready. This I swear [adapted from the Rifleman’s Creed, United States Marine Corps].

Operating Without Visual Reference

Drills to this point have been under conditions of good visibility where firefighters can observe nozzle pattern and fire stream effects. However, on the fireground it is critical that these skills can be used effectively under conditions of low or no visibility.

Sometimes it is necessary to go backward in order to move forward. One way to begin the process of developing the ability to work effectively with limited visibility is to go back to Nozzle Technique and Hose Handling Drills 1 & 2 and repeat these exercises with the firefighter’s breathing apparatus facepieces covered (unlike working in the dark, this makes it much easier for the instructors to observe and provide feedback). While this seems like an extremely slow and incremental process, it is likely to build a higher level of skill and require less time to develop proficiency than simply fumbling about in the dark!

Door Entry and Gas Cooling

In Nozzle Technique and Hose Handling: Part 3, door entry was illustrated at an exterior door. However, this method should be used anytime that firefighters encounter a closed door that may have hot gases or fire behind it. This becomes even more important when operating in a smoke (fuel) filled environment.

Smoke is fuel! The upper (hot gas) layer may contain a substantial mass of fuel that is ready to ignite. Flames exiting from a compartment door can ignite this fuel, resulting in rapid fire progression through the upper layer and into adjacent compartments. This phenomenon is demonstrated by CFBT-US Senior Instructor Trainer Matt Leech (LT Tualatin Valley Fire & Rescue) in Figures 1 through 3. While this demonstration involves use of a single compartment doll’s house and “porch roof”, the same phenomena can occur on a larger scale in any type of structure.

Figure 1. Accumulation of Fuel Overhead

Figure 2. Extension of Flames and Ignition of Fuel Overhead

Figure 3. Transition to Flaming Combustion Overhead

This simple demonstration illustrates the hazards presented by smoke overhead, the importance of gas cooling, and good door entry technique. While often overlooked, recognition of this hazard is not new. “Smoke contains unburned fuel and when mixed with air in the proper proportion becomes a flammable mixture” (Layman, 1955).

When working under conditions of limited visibility, other sensory feedback becomes even more important to the nozzle operator. It is essential that firefighters become familiar with audible indicators of stream performance. Think about the sound of a straight stream hitting the ceiling or a wall versus the sound of a fog pattern applied into the hot gas layer (without significant contact with compartment linings). Would you be attuned to the difference in sound? This is important when you can’t see the pattern being discharged. Changes in temperature can also be an important indicator. However, it is important to remember that perceived temperature is also influenced by moisture. Excess steam production (from water hitting hot compartment linings) may make it seem like the temperature is rising, when this is due to increased moisture content in the smoke and air. If it seems like it is getting hotter, it is important to recognize if this is due to worsening fire conditions, or inappropriate water application.

Drill 6-Operating Without Visual Reference: This drill integrates door entry, hose handling, and nozzle techniques (pulsing and painting) under conditions with limited visibility. The drill can be conducted with the facepiece covered, in darkness, or using cold smoke (e.g., from a smoke machine). Learners should begin by using good door entry technique on an exterior door and then move through several compartments (preferably of different sizes), encountering several doors (some of which should be closed) along the way to the seat of the “fire”. Alternately, this drill can be used to practice hose handling and nozzle technique in the context of primary search with a hoseline (or in support of crews performing search).

Hose Handling & Nozzle Technique Drill 6 Instructional Plan

Indirect Attack

Indirect attack is a commonly misunderstood firefighting tactic. Common misconceptions include:

• Indirect attack is only performed from the exterior of the building.
• Indirect attack will push fire throughout the building.
• Indirect attack involves banking water off the ceiling to reach burning fuel that is inaccessible to direct application of water (see Figure 4).
• Indirect attack and gas cooling is the same thing.

These statements are absolutely incorrect!

Figure 4. What Indirect Attack is NOT.

Several years ago I had a company officer that I worked with tell me that he had learned about a “new” fire control technique called the indirect attack at strategies and tactics class. I loaned him a small blue book titled Attacking and Extinguishing Interior Fires (Layman, 1955) and observed that this was not exactly a “new” idea.

The concept of the indirect attack was an outgrowth of extensive study of fuel oil fires within confined spaces conducted by the instructor staff of the US Coast Guard Firefighting School at Fort McHenry in Baltimore, Maryland during World War II (Layman, 1955). The term indirect, referred to application of water into a hot compartment, but not directly onto the burning fuel. Conversion of water to steam absorbed a tremendous amount of energy and the expansion of steam filled the compartment (and potentially adjacent compartments which may also have been involved in fire).

In 1947, Lloyd Layman completed his service with the US Coast Guard and returned to duty as Fire Chief with the Parkersburg West Virginia Fire Department. Over the next two years, Layman and the members of his department worked to implement the concept of indirect attack for structural firefighting. In 1950 Chief Layman delivered a presentation titled Little Drops of Water (Layman, 1950) which outlined the adaptation of indirect attack for structural firefighting. In 1952 he completed Attacking and Extinguishing Interior Fires (Layman, 1955), a textbook that provided a more comprehensive look at indirect attack including several case studies based on incidents in Parkersburg where this approach had been used successfully in dealing with both residential and commercial fires.

As presented by Layman, the indirect attack was generally performed from the exterior of the building. However, it is important to recognize historical context. In the late 1940’s respiratory protection (when it was used) was often limited to All Service Masks, which used a filter mechanism to remove toxic products of combustion (to some extent), but could not be used in significantly oxygen deficient atmospheres.

Layman’s Error: Chief Layman made a number of extremely important and astute observations, particularly with regards to the tremendous cooling capacity of water when it is not only heated to its boiling point, but also converted to steam. However, one of the major assumptions related to indirect attack was in error. Layman states: “The injection of water into a highly heated atmosphere results in rapid generation of steam…[increasing] the atmospheric pressure within the space (p. 36-37). This points to the Chief’s assumption that steam produced as water was evaporated in the hot gas layer added to the total volume of gas and vapor within the space (i.e., the volume of steam was added to the volume of smoke and hot gases in the compartment). As discussed in Estimating Required Fire Flow: The Iowa Formula [LINK]; this is incorrect, water vaporized as it passes through the hot gas layer actually reduces total volume (due to cooling of the hot gases). On the other hand, water that is vaporized in contact with hot surfaces (that did not significantly cool the gases as it passed through the hot gas layer) adds to total volume as expanding steam is added to the volume of hot gases within the compartment. The difference between indirect attack and gas cooling will be explored in detail in my next post on Fire Stream Effectiveness and Efficiency.

Figure 5. Indirect Attack

Drill 7-Indirect Attack from the Door: When faced with a fully developed fire in an enclosed area or a severely ventilation controlled fire (decay phase) that presents potential for a ventilation induced flashover or backdraft. Indirect attack may be an effective option for fire control. However, this tactic is not limited to exterior operations. Indirect attack can be initiated as part of the door entry procedure (exterior or interior doorway). If dynamic risk assessment indicates that entry is not viable due to fire conditions, the nozzle operator can use long pulses from the doorway (while the other member of the hose team controls the door) to apply water to hot surfaces, producing steam to gain control of conditions within the compartment prior to entry. This fire control method should be integrated with effective tactical ventilation (think planned, systematic, and coordinated).

Hose Handling & Nozzle Technique Drill 7 Instructional Plan

This approach can be extremely useful when the door to the fire compartment can be controlled and the hose team is presented with multiple priorities (persons reported and the need to control the fire to maintain the safety of interior operations). Figure 6 illustrates an example of how an indirect attack may be used when operating from the interior. In this scenario, the first arriving engine observes a fully developed fire in the bedroom on the A/D corner of a single family dwelling and receives information that an occupant is in the bedroom on the C/D corner. Rapidly developing fire conditions require immediate fire control. The crew makes entry from Side A, cools the hot gases overhead as they proceed to the fire compartment. As it is necessary to control the fire before proceeding past the involved compartment, they control the door, implement an indirect attack, and then extend an oriented search to locate the occupant while the nozzle operator protects the means of egress and maintains orientation for the firefighter performing the search in the adjacent compartments.

Figure 6. Application of Interior Indirect Attack.

While there are other tactical approaches that could be taken in this situation, use of an indirect attack allows the hose team to address both life safety (firefighters and occupants) and fire control tactical priorities.

Ed Hartin, MS, EFO, MIFIreE, CFO

References

Layman, L. (1955). Attacking and extinguishing interior fires. Boston, MA: National Fire Protection Association.

Layman, L. (1950). Little drops of water. Unpublished paper, presented at the Fire Department Instructors Conference (FDIC), Memphis, TN.

As discussed in prior Reading the Fire posts and the ongoing series examining fire behavior indicators (FBI), using the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme, developing proficiency requires practice. This post provides an opportunity to exercise your skills using three video segments shot during an apartment fire.

Apartment Fire

At 2235 hours on November 19^th the Bethlehem, PA fire department dispatched Engines 6, 9, 7, Ladder 2 & Chief 205 for an apartment fire with persons reported at 1992 Gatewood Lane. On arrival Engine 6 reported a working fire in an end-of-row unit. Tower Ladder (TL) 2 made two vertical ventilation (exhaust( openings in the roof above the fire. Chief 205 requested a second and then third alarm as the fire extended rapidly into the trussloft.

Download and the B-SAHF Worksheet.

The video segment was shot after TL 2 opened the roof.  First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions?

1. What additional information would you like to have? How could you obtain it?
2. What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
3. What burning regime is the fire in (fuel controlled or ventilation controlled)?
4. What conditions would you expect to find inside this building (on floor 2 and in the attic)?
5. How would you expect the fire to develop over the next two to three minutes

Crews use a combination of exterior attack (from the tower ladder and the roof) and interior attack from the second floor to control the fire.

1. Did fire conditions progress as you anticipated?
2. What concerns would you have about working on the top floor or roof in the involved area?
3. How did vertical ventilation influence the fire in the trussloft (think about positives and negatives)?
4. What alternatives to vertical ventilation of this lightweight roof system could be used to control the fire and prevent extension over uninvolved units?

While this incident had a positive outcome, it is important to recognize the potential for collapse of lightweight, engineered structural systems such as truss roof assemblies. Tactical success in one incident is not necessarily a predictor of future success should conditions be different (e.g., duration of fire impingement on structural members prior to arrival, burning regime, changes to the ventilation profile, etc.).

Remember the Past

Line of duty deaths involving extreme fire behavior has a significant impact on the family of the firefighter or firefighters involved as well as their department. Department investigative reports and NIOSH Death in the Line of Duty reports point out lessons learned from these tragic events. However, as time passes, these events fade from the memory of those not intimately connected with the individuals involved. It is important that we remember the lessons of the past as we continue our study of fire behavior and work to improve firefighter safety and effectiveness on the fireground.

November 23, 2006
Firefighter Steven Mitchell Solomon
Atlanta Fire Department, Georgia

Firefighter Solomon was working a 24-hour shift on Thanksgiving Day. Shortly after 2000hrs, Atlanta Fire-Rescue dispatched a full first-alarm assignment for a reported fire in an abandoned house. On arrival, companies encountered heavy smoke showing from a boarded-up single-story brick structure. As other crews removed plywood window coverings and forced entry through the front door, the crew of Engine 16 prepared to advance a 1-3/4inch attack line into the house. Firefighter Solomon was on the nozzle as the line was advanced inside. The attack team immediately encountered high temperature and zero-visibility conditions. Within seconds after they entered, the battalion chief arrived, assumed command, and ordered the companies to operate in a defensive strategy. Before the line could be backed out, the interior became enveloped in flames and the 3 firefighters from Engine 16 lost track of each other. Two of the firefighters managed to escape through the front door. Firefighters who were outside saw the silhouette of a firefighter, enveloped in flames, running past the front door and moving toward the rear of the house. The fire was quickly knocked down and crews made entry from both the front and rear to conduct a search. Firefighter Solomon was located almost immediately by a member who was using a thermal imaging camera and several firefighters quickly removed him from the dwelling. He was unconscious and critically burned. When he was found, Firefighter Solomon had removed his helmet, hood, and SCBA facepiece. One boot was also missing. Although he received immediate treatment from firefighter/paramedics on the scene and was transported within minutes to a level-one trauma center and regional burn unit, Firefighter Solomon died 6 days later without regaining consciousness.

Ed Hartin, MS, EFO, MIFIreE, CFO

It is often stated and commonly believed that it takes gpm to overcome Btu. While I suspect that firefighters understand the underlying intent of this statement, it is actually incorrect as it is comparing apples and oranges. Flow rate is expressed in terms of volume and time (gal/m or l/m). However, Btu (or Joules) is a measure of quantity (more like volume than flow rate).

You can say that it takes gallons (or liters) to overcome Btu (or Joules), But the rate at which energy is absorbed by a fire stream must overcome heat release rate (energy released/unit of time). This concept points to the need for a higher flow rate when the heat release rate from a fire is larger. This leads to another common fire service saying: “Big Fire, Big Water”. While this is not completely incorrect, it is a bit misleading as it does not account for the efficiency of the fire stream in absorbing energy. Not all of the water that leaves the nozzle absorbs the same amount of energy.

Theoretical Cooling Capacity

Water is an excellent extinguishing agent because it has a high specific heat (energy required to raise its temperature) and high latent heat of vaporization (energy required to change it from water to steam). As illustrated in Figure 1, conversion of water to steam is most significant as it absorbs 7.5 times more energy than heating water from 20^o C (68^o F) to its boiling point.

Figure 1. Theoretical Cooling Capacity

However, this only tells us the theoretical cooling capacity of a single kilogram of water at 20^o C (68^o F) if it is raised to 100^o C (212^o F) and completely vaporized. Examining theoretical cooling capacity in terms of flow rate requires a bit more work.

Flow is defined in terms of gallons per minute (gal/m) or liters per minute (l/m) and theoretical cooling capacity of water was defined in terms of energy absorbed per second per unit mass (MJ/kg) we need to work through conversion to common units of measure.

While SI units are simpler to work with, I have worked cooling capacity out in both liters per minute (LPM) and gallons per minute (GPM). However, in that specific heat and latent heat of vaporization are applied to mass rather than volume and Watts are joules per second, it is first necessary to covert flow rate into kg/s

Figure 2. Flow Rate and Theoretical Cooling Capacity

This example assumes instantaneous heat transfer and 100% efficiency in conversion of water to the gas phase. Neither of which is possible in the real world!

Factors influencing effectiveness and efficiency of heat transfer (Svennson, 2002) include:

• Diameter (in the gas layer and on surfaces)
• Temperature (in the gas layer and on surfaces)
• Velocity (in the gas layer)
• Film formation (on surfaces)
• Temperature of the gas layer
• Surface temperature

Fire Stream Efficiency

The firefighter’s power is not simply related to flow rate, but flow rate effectively applied to transfer heat from hot gases and surfaces by changing its phase from liquid (water) to gas (steam). Extinguishing a compartment fire generally involves converting a sufficient flow (gal/m or l/m) of water to steam. So while the “steam” itself does not generally extinguish the fire, the energy absorbed in turning the water to steam has the greatest impact on fire extinguishment.

Experimental data (Hadjisophocleous & Richardson, 2005; Särdqvist, S., 1996) has shown that the cooling efficiency of water in both laboratory experiments and actual firefighting operations ranges from 0.2 to 0.6. Särdqvist (1996) suggests that an efficiency factor of 0.2 be used for interior fog nozzles. Based on my personal observations (but no experimental data), I think that Särdqvist’s efficiency factor of 0.2 might be just a bit on the low side. Barnett (as cited in Grimwood,2005) suggests that an efficiency factor of 0.5 be used for solid or straight stream application and 0.75 for fog application. The following table takes a slightly more conservative approach, using 0.6 as an average efficiency factor.

Figure 3. Flow Rate and Adjusted Cooling Capacity

Figure 3 is provided to illustrate the impact of efficiency (or lack thereof) on fire stream cooling capability. The key point is that actual cooling capability is considerably less than the theoretical cooling capacity. Another complication is that in addition to nozzle performance characteristics, nozzle efficiency is also dependent on the skill of the nozzle operator, the manner in which water is applied (straight stream, narrow fog pattern, wide fog pattern), the configuration of the space, and fire conditions. Unfortunately, there is no standardized test with specified conditions that permits comparison of different nozzles and/or methods.

However, the concept of efficiency gives rise to an interesting question. Does a nozzle flowing 100 gpm with an efficiency factor of 0.6 have the same extinguishing capability as 200 gpm nozzle with an efficiency factor of 0.3. This is simple math! The cooling capacity would be identical. While the practical application is more complex (as we do not really know the efficiency factors for the two nozzles and manner in which they are being used), this is worth thinking about.

Flow Rate or Heat Absorption Capacity

CFBT-US Senior Instructor Trainer Matt Leech (LT Tualatin Valley Fire & Rescue) proposed (half in jest) that nozzles should be labeled with their potential cooling capacity rather than flow rate. While this idea did not get significant traction, it is important for firefighters to recognize that flow rate and fire stream characteristics have a significant impact on potential cooling capacity.

Fire Stream Effectiveness

Safe, effective and efficient fire control requires:

• Water application to control the fire environment as well as direct attack on the fire
• Appropriate flow rate for the tactical application (cooling hot, but unignited gases may be accomplished at a lower flow rate than direct attack on the fire)
• Direct attack to exceed the critical flow rate based on the fire’s heat release rate
• Sufficient reserve (flow rate) be available to control potential increases in heat release rate that may result from changes in ventilation
• Water application in a form appropriate to cool its intended target (i.e., small droplets to cool hot gases or to cover hot surfaces with a thin film of water)
• Water to reach its intended target (fog stream to place water into the hot gas layer and a straight or solid stream to pass through hot gases and flames and reach hot surfaces)
• Control of the fire without excessive use of water

Accomplishing this requires different stream characteristics at different times. The characteristics that are optimal for gas cooling are likely quite different than for cooling hot surfaces, particularly when dealing with fully developed fire conditions in a large compartment.

Priorities

As regular readers have likely noted my posting schedule has been a bit off of late. My responsibilities as the new Fire Chief with Central Whidbey Island Fire & Rescue preclude the necessary research and writing necessary to constantly post twice weekly. I will be scaling back to a single post on Thursday for the next few months while I get a handle on my new job and get my family moved to Whidbey Island.

Ed Hartin, MS, EFO, MIFIreE, CFO

References

Grimwood, P. (2005) Firefighting Flow Rate: Barnett (NZ) – Grimwood (UK) Formulae. Retrieved January 26, 2008 from http://www.fire-flows.com/FLOW-RATE%20202004.pdf

Hadjisophocleous, G.V. & Richardson, J.K. (2005). Water flow demands for firefighting. Fire Technology 41, p. 173-191.

Särdqvist, S. (1996) An Engineering Approach To Fire-Fighting Tactics Sweden, Lund University, Department of Fire Safety Engineering

Svennson, S. (2002). The operational problem of fire control (Report LUTVDG/TVBB-1025-SE). Sweden, Lund University, Department of Fire Safety Engineering.

The previous posts in this series, examined the importance of proficiency in use of the firefighters’ primary weapon in offensive firefighting operations, and outlined several drills that can be used to develop proficiency in basic nozzle operation and hose handling.

• My Nozzle
• Basic Nozzle Techniques & Hose Handling
• Nozzle Techniques & Hose Handling: Part 2

Developing proficiency in nozzle use is somewhat like building skill with a rifle. Understanding what end of the rifle the bullet comes out of and that the rifle is fired by pulling the trigger is the easy part, learning to consistently hit what you are aiming at over varied distances requires considerably more effort.

This is my nozzle, there are many like it but this one is mine. My nozzle is my best friend. It is my life. I must master it as I master my life. Without me it is useless, without my nozzle I am useless.

I will use my nozzle effectively and efficiently to put water where it is needed. I will learn its weaknesses, its strengths, its parts, and its care. I will guard it against damage, keep it clean and ready. This I swear [adapted from the Rifleman’s Creed, United States Marine Corps].

In the first three nozzle drills learners develop basic proficiency in basic nozzle use (fixed position), integrating nozzle use while moving a hoseline forward and back, and use of the nozzle while moving the hoseline through varied size compartments. This post will provide an overview of door entry procedures.

Door Entry Concepts

For many firefighters, door entry is simply a process of remembering to “try before you pry” and then figuring out how to force the door if it is locked. For others it is simply kicking the door in! Often overlooked is the fact that the entry point is a ventilation opening; sometimes an inlet, sometimes an outlet, and often both. When the fire is ventilation controlled, opening the door and increasing air flow to the fire will result in increased heat release rate. Depending on the stage of fire development and conditions within the compartment or structure, this may result in extreme fire behavior such as a ventilation induced flashover or backdraft (see Fuel & Ventilation).

As illustrated in Figure 1, firefighters often encounter rapidly changing conditions after making entry. In this incident, flashover occurred less than 60 seconds after firefighters opened the door and made entry (see Situational Awareness is Critical for additional information on this incident)

Figure 1. Rapidly Changing Conditions

Note: Photos by Probationary Firefighter Tony George, Prince Georges County Fire Department.

Safe and effective firefighting operations depend on effectively reading the fire and recognizing potential stages of fire development and burning regime (see previous posts on Reading the Fire) and effective tactical operations to take control of the fire environment. Door entry is an important element in this process.

Door Entry Procedure

As you review this door entry procedure, you may find that it makes sense to you exactly as presented. On the other hand, you may find that some elements (e.g., size-up and dynamic risk assessment) make sense, but other components (e.g., cooling overhead prior to opening the door) require a bit more of a leap. The elements of the door entry process reinforce one another, adopt the elements that make sense to you, but consider the value of the procedure as an integrated process. The process outlined is not followed in a lock-step manner, it is important for the hose team to take action based on observed conditions.

Size-Up: Door entry begins with a focused size-up as you approach the building. Assessment of conditions is not only the incident commander or officer’s job. Each member entering the building should perform a personal size-up and predict likely conditions. When making entry, size-up becomes more closely focused on conditions observed at or near the door and includes an assessment of potential forcible entry requirements as well as B-SAHF (Building-Smoke, Air Track, Heat, and Flame) indicators. If available, a thermal imaging camera (TIC) can be useful, but remember that temperature conditions may be masked by the thermal characteristics of the building. If a thermal imaging camera is not available, application of a small amount of water to the door may indicate temperature and the level of the hot gas layer (water will vaporize on contact with a hot door).

Size-up begins as you exit the apparatus and approach the building, but continues at the door and after you make entry!

At the door, pay close attention to air track and heat (door temperature) indicators as these can provide important clues to conditions immediately inside the building!

Control the Door: If the door is open, close it. If it is closed, don’t open it until you are ready. Heat release requires oxygen, controlling the air supply to the fire controls heat release rate. If you force the door in preparation for making entry, make sure you maintain control of it.

Gas Cool Above the Door and Assess, and Control Interior Conditions: When you open the door to assess conditions inside, hot smoke will likely exit at the top of the door. If it is hot enough it may auto-ignite. The hazard presented by the exiting smoke can be reduced by applying two short pulses above the door just as it is opened (the firefighter controlling the door should crack the door as the first pulse is applied).

The door should be opened sufficiently to allow the nozzle operator to visualize interior conditions, but not so much that a large amount of air is introduced (no magic number on how far to open, “it depends”). If hot smoke is present, the nozzle operator should cool the gases inside the compartment from the doorway. This may involve a short pulse or two or it may involve a longer pulse, depending on the size of the compartment and conditions (again, this requires the nozzle operator to think!).

Close the Door: While there is often a sense of urgency to make entry (due to developing fire conditions, persons reported, etc.), this step is important as it provides an opportunity for a focused risk assessment.

Risk Assessment: Is it safe to make entry (or to make entry through this opening)? Fully developed fire conditions inside the door or a pulsing air track (indicating potential for vent induced flashover or backdraft) may indicate a need to consider alternative tactics).

Entry: If it is safe to make entry, the process of cooling above the door as it is opened is repeated and hot gases inside the compartment are cooled as the hose team makes entry.

Figure 2. Door Entry Procedure

Note: Adapted from video clip 00000010 on the 3D Firefighting: Training, Techniques and Tactics Resource DVD.

Remember: The purpose of door entry procedures is to reduce risk of extreme fire behavior during and immediately after entry! Door entry procedures should be used any time that hot smoke or flames may be on the other side of the door. These procedures are used at exterior doors when making entry and on closed doors encountered inside the building.

Drill 4-Door Entry-Inward Opening Doors: Many doors (particularly interior and exterior residential) open inward (away from the nozzle team), door entry requires that the hose team integrate forcible entry, door control, and nozzle operation. Practicing door entry procedures with a variety of inward opening door configurations (location of the door in relation to walls and with varied size compartments) is critical in developing proficiency.

Drill 5-Door Entry-Outward Opening Doors: Commercial doors (and some interior doors) will open outward (towards the hose team). Outward opening doors require a somewhat different position when performing door entry. Firefighters must develop skill in performing door entry with both inward and outward opening doors.

Hose Handling & Nozzle Technique Drill 4 & 5 Instructional Plan

These two drills can be conducted using any door where water can be applied. However, a free-standing door entry prop (see Figure 3) provides a simple and effective aid to developing door entry proficiency.

Figure 3. Door Entry Prop

Note: Photo by Inspector John McDonough, ASFM, New South Wales Fire Brigades.

Alternately, a forcible entry prop could be used to integrate the forcible entry component of the door entry process.

Drills

As discussed in Nozzle Techniques and Hose Handling: Part 2 [LINK], it is essential for firefighters to have the ability to react immediately to deteriorating conditions. While battle drills will be discussed in depth in a subsequent post, consider how this concept might apply during door entry. What action should the hose team take if they encounter strong indicators of backdraft conditions at the doorway (e.g. pulsing air track, thick (optically dense) smoke)? How should the hose team react if, despite following good practice, conditions worsen immediately after entry?

Ed Hartin, MS, EFO, MIFireE, CFO

References

Grimwood, P., Hartin, E. McDonough, J. & Raffel, S. (2005). 3D firefighting: Training, techniques, and tactics. Stillwater, OK: Fire Protection Publications.

Understanding how to develop fire streams has been critical since firefighters began to use hose and nozzles (Figure 1) to increase the effectiveness and efficiency of firefighting operations.

Figure 1. In the Beginning!

When selecting handline nozzles, firefighters and fire officers generally consider four nozzle characteristics: 1) type of nozzle (combination or solid stream/smoothbore), 2) fixed or variable flow, 3) flow rate, and 4) designed operating pressure. Saving the big debate regarding combination and solid stream/smoothbore nozzles for another post, this post will focus primarily on nozzle pressure and flow rate.

Nozzle Function

A little over 20 years ago I was asked an interesting question by a newly hired recruit firefighter. She had no prior fire service experience and was puzzled by the hose evolutions being taught during her academy. As I attempted to help her make sense of these alien concepts, she finally asked “What’s the pump for? Why don’t we just put the nozzle on the end of the hose from the hydrant?” Her instructors may have assumed that hydraulics was a topic for apparatus operators or that everyone understood the basic concepts involved in developing an effective fire stream.

The primary function of a nozzle is to increase the velocity of water flowing from the hoseline. A fire stream must have sufficient velocity for water to reach from the nozzle to the intended target. The simple equation illustrated in Figure 2 is essential to understanding nozzle design and performance. Flow rate (the quantity of water) from a nozzle is dependent on the area of the opening and the velocity of the water being discharged (for a given size opening, the greater the velocity the higher the flow rate).

Figure 2. Important Equation

As indicated in the equation Q=AV, flow rate is related to velocity and the size (area) of the nozzle orifice. This relationship is simple to understand when looking at solid stream/smoothbore nozzles. Nozzle pressure translates to velocity at the tip. For a given size tip, increasing nozzle pressure increases velocity and thus the flow rate from the tip. For example, a 1-1/4” (32 mm) tip will flow 317 gpm (1200 lpm) at 50 psi (345 kPa). Increasing the nozzle pressure to 80 psi (552 kPa) increases the flow rate to 401 gpm (1518 lpm). Flow rate can be varied by changing the size of the tip, the nozzle pressure, or both.

Visualizing nozzle orifice size is a bit more difficult with combination nozzles. Most combination nozzles use a deflection stem (see Figure 3) to form the fog pattern. The nozzle orifice is an annular (ring shaped) space between the deflector and the body of the nozzle tip.

Figure 3. Combination Nozzle Orifice

The change in direction at the deflection plate results in formation of small droplets of water. Nozzles may also have fixed teeth or a spinning, toothed turbine to aid in the production of appropriate sized droplets as water leaves the nozzle.

Nozzle Pressure and Droplet Size

Water is an excellent extinguishing agent because it has a high specific heat (energy required to raise its temperature) and high latent heat of vaporization (energy required to change it from water to steam). Of these two factors, conversion of water to steam is most significant as it absorbs 7.5 times more energy than heating water from 20^o C (68^o) to its boiling point. The firefighters’ power is not simply related to flow rate, but flow rate effectively applied to transfer heat from hot gases and surfaces by changing its phase from liquid (water) to gas (steam). Extinguishing a compartment fire generally involves converting a sufficient flow (gpm or lpm) of water to steam. So while the “steam” itself does not generally extinguish the fire, the energy absorbed in turning the water to steam has the greatest impact on fire extinguishment

Where the water is vaporized into steam depends on the method of fire control being used (direct attack, indirect attack, or 3D gas cooling). In direct attack water is vaporized on burning and pyrolyzing fuel surfaces to slow and stop the process of pyrolysis. Water is also vaporized on contact with hot surfaces in an indirect attack, but in this case the purpose is to produce a sufficient volume of steam to fill the compartment, achieving fire control or mitigating potential for extreme fire behavior such as a backdraft. Gas cooling on the other hand requires that the majority of the water be vaporized in the hot gas layer. This cools the hot gases (fuel) overhead, providing buffer zone and safer work environment for firefighters. It is important to remember that gas cooling is not an extinguishing technique, but merely one tool in controlling the fire environment.

Heat moves from objects of higher temperature to objects of lower temperature until temperature equalizes. Key factors in the speed of heat transfer are the difference in temperature and surface area of the materials. In the fire environment, burning fuel, nearby surfaces, and hot gases are considerably higher temperature than the water used for fire control and extinguishment. Surface area of the water in contact with the material being cooled is extremely significant in determining the speed of heat transfer. A larger surface area in relation to the amount of water will result in faster heat transfer and more rapid cooling.

If the volume of water remains the same, reducing droplet size increases surface area substantially. For example if droplet size is reduced by half, surface area increases by a factor of four (see Figure 4).

Figure 4. Droplet Diameter and Surface Area

Note. Adapted from Water and Other Extinguishing Agents (p. 194) by Stefan Särdqvist, 2002, Karlstad, Sweden: Raddningsverket. Copyright 2002 by Stefan Särdqvist and the Swedish Rescue Services Agency

Increased surface area increases heat transfer as droplets travel through the hot gas layer, rapidly reducing temperature. However, the down side of smaller droplets is that they do not travel as far and may not be able to penetrate a large distance in an extremely hot environment, making a fog pattern with small droplets potentially less effective in direct attack or when working in an extremely large compartment. Fortunately, when a fog pattern is adjusted to a straight stream much (but not necessarily all) of this problem is overcome.

What does nozzle pressure have to do with droplet size? Nozzles do not produce uniform droplet sizes. The fog pattern developed by a typical combination nozzle produces a mix of small and larger droplets. However, average droplet size and the percentage of droplets that are 0.3 mm (0.012”) in diameter is dependent on both nozzle design and pressure. However, for any nozzle design, increased nozzle pressure will result in smaller droplets.

Gresham Fire & Emergency Services conducted a series of qualitative tests on droplet size produced by the Task Force Tips Dual-Pressure Mid-Force Nozzle operating at 50 psi (345 kPa) and 100 psi (689 kPa). Droplet size was assessed by examining hang time, the time which droplets remained suspended in the air after a short pulse of water fog (smaller droplets remain suspended for a longer time while large droplets fall to the ground more quickly). Results of this test were captured on video and synched to ensure that the visual comparison was at the same time after the nozzle was closed. As illustrated in Figure 5, with the same flow rate, the nozzle pressure of 50 psi (345 kPa) resulted in larger droplets than a nozzle pressure of 100 psi (689 kPa).

Figure 5.

Nozzles operating at a lower pressure will have larger droplet size. This does not impact substantially on direct attack, but can have a significant impact on the effectiveness and efficiency of these nozzles when used for gas cooling. This does not mean that they cannot be used! It simply means that they will be less effective and are likely to result in less efficient vaporization of water (more water will end up on the floor).

Impact on Operations

While it is important to understand the underlying principles related to nozzle design and performance, it is even more important to understand the impact of these concepts on firefighting operations. The next post in this series will examine the concepts of efficiency and effectiveness in greater depth and why effective cooling capacity may be more important than simply looking at flow rate.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Särdqvist, S. (2002). Water and other extinguishing agents. Karlstad, Sweden: Raddningsverket (Swedish Rescue Services Agency).

Prior posts in this series, My Nozzle and Basic Nozzle Techniques & Hose Handling, examined the importance of proficiency in use of the firefighters’ primary weapon in offensive firefighting operations.

This is my nozzle, there are many like it but this one is mine. My nozzle is my best friend. It is my life. I must master it as I master my life. Without me it is useless, without my nozzle I am useless.

I will use my nozzle effectively and efficiently to put water where it is needed. I will learn its weaknesses, its strengths, its parts, and its care. I will guard it against damage, keep it clean and ready. This I swear [adapted from the Riflemans Creed, United States Marine Corps].

It is critical that firefighters have both a sound understanding of nozzle performance and skill in the use of their primary weapon. In Figure 1, Assistant Superintendent Mohamed Roslan Bin Zakaria, Bomba dan Penylamat, Malaysia examines stream characteristics from an Akron Turbojet. Note the change in droplet size as the nozzle is closed (droplet size increases as pressure drops). In a short pulse opening and closing the nozzle quickly minimizes production of large droplets that are unlikely to vaporize in the hot gas layer. In long pulses, closing the nozzle slowly increases the percentage of large droplets, but this is a necessary tradeoff to prevent excessive water hammer.

Figure 1. Determining Stream Characteristics

Note: Photo by Shan Raffel, ASFM, CMIFireE, EngTech.

This post continues with a discussion of training methods that can be used to develop proficiency in nozzle techniques and hose handling while deploying hoselines and in compartments having varied configurations. Continuing with our military metaphor, we will be practicing fire and maneuver.

Instructional Concepts

As discussed in Basic Nozzle Techniques and Hose Handling this sequence of drills is designed using the Simplifying Conditions Method (Reigeluth, 1999). This approach moves from simple to complex, beginning with the simplest version of the task that represents the whole and moves to progressively more complex versions until the desired level of complexity is reached. In the case of nozzle technique and hose handling, this involves moving from basic, individual skills, to team skills, and on to integration of physical skills and decision-making.

While modeling a specific technique (such as the short pulse) can be helpful in aiding the learners in developing basic skill, there is a danger. Technique is often mimicked without thought to why it is performed in a particular manner under specific circumstances. Demonstration of a short pulse with a 40o fog pattern (which might be appropriate in a small room) becomes “that is how all short pulses must be performed”. As the learners complete Hose and Nozzle Technique Drills 2 and 3, it is critical to provide changing conditions and encourage the learners to adapt their technique based on conditions.

Drill 2-Hose Handling and Nozzle Operation: Firefighters often lose focus on nozzle technique and operation when they are moving. This drill provides an opportunity for the firefighter with the nozzle and backup firefighter to develop a coordinated approach to movement and operation.

Hose Handling & Nozzle Technique Drill 2 Instructional Plan

Drill 3-Nozzle Operation Inside Compartments: Deployment of hoselines inside a building requires a somewhat different set of skills than simply moving forward and backward. Movement of hoselines around corners and adjustment of nozzle pattern to cool gases in hallways and varied size compartments are important additions to the firefighters’ skill set and provide the next step in developing proficiency in nozzle use.

Hose Handling & Nozzle Technique Drill 3 Instructional Plan

Battle Drills

Analysis of firefighter line-of-duty deaths (LODD) during structural firefighting operations points to the need for highly disciplined, immediate, and appropriate response to rapidly deteriorating conditions. In terms of military small unit tactics, battle drills provide a standardized, collective action rapidly executed without application of a deliberate decision making process (US Army, 1992).

Adapted to firefighting operations, Battle Drills:

• Require minimal leader orders to accomplish and are standard throughout the department
• Are sequential actions vital to success in firefighting operations or critical to preserving life
• Apply to individual companies or teams
• Are trained responses to changing conditions or leader’s orders
• Represent mental steps followed for actions followed in training and firefighting operations

As a starting point for discussing this concept, give some thought to what situations might require a pre-planned and trained set of actions during offensive firefighting operations. For example, this might apply to locating a victim while deploying a hoseline for fire attack, rapidly deteriorating conditions, breathing apparatus malfunction, etc. Also consider how hose handling and nozzle techniques might apply in each of these situations.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Reigeluth, C. (1999). Elaboration theory: Guidance for scope and sequence decisions. In C.M. Reigeluth (Ed.) Instructional-design theories and models: A new paradigm of instructional theory volume II. Mawah, NH: Lawrence Erlbaum Associates.

United States (US) Army. (1992). FM 7-8 Infantry rifle platoon and squad. Washington, DC: Headquarters, Department of the Army