The Problem

NIOSH has investigated a number of incidents in which firefighters trapped by rapid fire progress did not take appropriate survival action. Last September, I was reading NIOSH Report F2007-02, which outlined the circumstances surrounding the death of Firefighter Steven Solomon in Atlanta, Georgia. Firefighter Solomon was severely burned after being caught by rapid fire development while advancing an attack line in a vacant structure (see Figure 1).

Figure 1. Rapid Fire Development

Note: Atlanta Fire Department photo from NIOSH Report F2007-02

Firefighter Solomon was on the nozzle as the first arriving truck removed the plywood covering the front door and thick, black smoke came rolling out the top of the doorway. Firefighter Solomon and the crew of Engine 16 advanced the line into the building as the truck continued horizontal ventilation. After advancing a short distance, fire conditions quickly worsened and the crew attempted to back out, but collided with another company who was advancing a backup line. After exiting the building the crew of Engine 16 realized that Firefighter Solomon was still inside. Crews outside the door on Side A observed the silhouette of a firefighter running through the flames inside the building.

As I read the report, I asked myself how a firefighter on a hoseline that was just a short distance could have been killed by rapid fire development. The NIOSH report identified four contributing factors:

• Initial size-up not conducted.
• Failure to recognize the signs of an impending flashover/flameover.
• Inadequate communication on the fireground.
• Possibility of ventilation induced rapid fire progression.

While these factors likely contributed to Firefighter Solomon’s death, I still did not have a solid answer to my question of how a firefighter on a hoseline just a short distance inside the doorway could have died in this type of event.

Predictability

The best way to avoid being injured or killed in an extreme fire behavior event is to read the fire, anticipate likely fire behavior, and control your operating environment. A majority of our effort should be spent on mastering these skills.

There is no unpredictable fire behavior. Under the same conditions, a compartment fire will develop and behave consistently. However, conditions are not always the same! In addition, firefighters operate with limited information, imperfect skill in anticipating likely fire behavior, and often under pressure to take rapid action. When making decisions under pressure, in a complex and dynamic environment, and with limited information, potential for error increases.

Improved understanding of fire dynamics and development of a high level of skill reduces, but does not eliminate your risk of encountering extreme fire behavior. When this occurs it is essential that firefighters understand the fire behavior, their own reactions to stress, and have well practiced (to automaticity) responses to increase the chance of survival.

Training for Survival

What exactly are firefighter survival skills? Firefighters may encounter a number of life threatening problems while operating in the hazardous environment of as structure fire. Threats include breathing apparatus emergencies (e.g., malfunctions, running out of air), becoming disoriented, and being trapped by collapse or rapid fire progress.

A quick survey of survival skills training programs from around the United States shows a fair degree of consistency in curriculum content:

• Emergency Communications Procedures (Mayday, Radio Emergency Distress Button)
• Personal Alert Safety System (PASS) Activation
• Reorientation, Searching for an Exit & Following a Hoseline to Safety
• Air Conservation Techniques
• Assuming a Horizontal Position to Enhance Thermal Protection and Audibility of the PASS
• Escape to a Place of Refuge
• Use of Visual and Audible Signals (Flashlight, Tapping with a Tool)
• Reduced Profile Maneuvers to Escape Through Small Openings
• Emergency Window Egress (Ladder Bail, Rope Systems)

These techniques may provide useful in dealing with a number of the threats that may be encountered in a structure fire. Taking refuge in an uninvolved compartment (with the door closed) may buy time for firefighters to escape through a window. However, the other elements will have little impact on increasing survival potential when encountering extreme fire behavior phenomena.

What is the missing element in the typical survival skills curriculum? In some cases, firefighters are taught breathing techniques to control their respiratory rate and conserve air, but little emphasis is provided on the psychological and physiological effects of the stress encountered in life threatening situations. This is critical to survival regardless of the nature of the threat. When faced with extreme fire behavior, particularly wind driven flames, flashover, and flash fire, appropriate nozzle technique and immediate tactical withdrawal to a safer area is absolutely critical. However, most survival skills curriculums do not address these critical skills.

When was the last time you practiced withdrawing a hoseline while operating the nozzle in the context of offensive, interior firefighting operations?

Performance Under Stress

There has been little if any research has been done to identify factors influencing firefighters’ performance under the extreme stress of a life threatening situation. However, there has been considerable investigation in other domains, particularly in the military and law enforcement

Increased psychological and physiological arousal prepare the human body for action. As this occurs, the sympathetic nervous system increases heart rate and blood pressure to maximize the body’s physical capacity. However, extreme levels of stress can result in significant deterioration in performance.

In On-Combat: The Psychology and Physiology of Deadly Conflict in War and Peace, LT COL Dave Grossman (2008) identifies five levels of arousal designated Conditions White, Yellow, Red, Grey, and Black. While cautioning against fixing specific heart rate numbers (or other precise physiological measures) to these levels of arousal, heart rate can be used as an indicator (see Figure 2).

Figure 2. Effects of Hormonal or Fear Induced Increases in Heart Rate

Note. Adapted from On-Combat: The Psychology and Physiology of Deadly Conflict in War and Peace (p. 31), by Dave Grossman, 2008, Millstadt, IL: Warrior Science Publications Copyright 2008 by David A. Grossman.

When face with an immediately life threatening situation, the resulting stress can significantly impact an individual’s ability to respond appropriately. In addition to the physiological responses (e.g. increased heart rate, visual and auditory distortion) decreased cognitive processing may delay appropriate response or result in freezing, with the inability to act (Wallenius, Johansson, & Larsson, 2002).

Recently a colleague related the experience of a firefighter who had been trapped by a wind driven fire. The firefighter dropped to the floor, went into the fetal position, said goodby to his wife and children and thought he was dead. Fortunately, the firefighter was rescued, but this illustrates the potentially incapacitating effects of stress in life threatening situations.

What is the answer? Military research points to the need for a highly trained (to automaticity) response. Battle drills integrate these immediate individual actions in the context of small unit operations.

Battle Drill

In a military context, battle drills are an immediate response to enemy contact that requires fire and maneuver in order to succeed. Battle drills are initiated with minimal commands from the unit leader. Soldiers or marines execute preplanned, sequential actions in response to enemy contact.

The battle drill concept has direct applicability to training firefighters to react appropriately on contact with our enemy (the fire) which requires fire (application of water) and maneuver (movement to a safer location) in order to succeed.

Unless a barrier (such as a door) is available to block the flow of flames and hot gases towards the firefighters position, attempts to escape without protection from a hoseline are likely to fail as fire can spread far more quickly than you can move.

Remember: The key elements of a battle drill are fire and maneuver! This requires the ability to operate and maintain control of the hoseline while moving backward.

The next post in this series will return to hose and nozzle drills with development of a battle drill for response to rapid fire progression.

Ed Hartin, MS, EFO, MIFireE, CFO.

References

Grossman, D. (2008). On-combat: The psychology and physiology of deadly conflict in war and peace. Millstadt, IL: Warrior Science Publications.

Wallenius, C. Johansson, C. & Larsson, G. (2002). Reactions and performance of Swedish peacekeepers in life-threatening situations. International Peacekeeping, 9(1), 133-152.

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At a formal dinner on 23 January 2010, Chief Ed Hartin was recognized as an honorary member of Company 1 “Germania” of the Valdivia, Chile Fire Department. In addition, he was awarded a commendation for supporting the ongoing professional development of the members of Company 1 “Germania” of the Valdivia, Chile Fire Department and encouraging them in their efforts to share their knowledge with Chile’s fire service.

Commendation for Support of Company 1 “Germania”

Left to Right: Teniente Juan Esteban Kunstmann, Chief Ed Hartin, Capitán Francisco Silva V.

On 24-27 January 2007, the Company 1 “Germania” of the Valdivia, Chile Fire Department hosted the first international fire service congress to be held in South America. Participants included over 150 firefighters and officers from Chile, Peru, Argentina, and the United States. The congress provided an opportunity to participate in both classroom and hands-on workshops on a wide range of fire service topics including fire behavior, ventilation, search, rapid intervention, technical rescue, and extrication. While topical areas were diverse, the congress had a substantive emphasis on compartment fire behavior with lectures presented by CFBT-US Chief Instructor Ed Hartin and Geraldo Crespo of Contraincendio in Buenos Aires, Argentina and practical training sessions conducted by Ed Hartin and Juan Esteban Kunstmann of the Valdivia Company 1 “Germania”.

Lecture Presentation

Lecture presentations by CFBT-US Chief Instructor Ed Hartin included (click on the links for a copies of the presentations):

• Fire Development and Flashover: Foundational Knowledge
• Extreme Fire Behavior: Understanding the Hazard
• 3D Firefighting: Controlling the Fire Environment
• Reading the Fire: B-SAHF
• Modern Buildings: Fires in the Built Environment
• Large Area Fires: Tactical Implications
• Fire and Smoke in Void Spaces: Hidden Hazards
• Live Fire Training as Simulation: The Role of Fidelity

CFBT practical skills sessions were held at the Valdivia Fire Department’s training center and focused on developing basic skill in nozzle technique and understanding fire development in a compartment.

This is My Nozzle! There are many like it, but this one is mine…

Center: Ed Hartin

Practicing Nozzle Techniques

Right: Teniente Juan Esteban Kunstmann

International Collaboration

Left to Right: Battalion Chief Danny Sheridan, FDNY and Capitán Giancarlo Passalacqua Cognoro, Lima, Pe?u Cuerpo General de Bomberos Voluntarios

Congratulations to the members of Company 1 “Germania” for their success with the first Congreso Internacional Fuego y Rescate! I look forward to working with these outstanding fire service professionals in their ongoing efforts to learn and share knowledge with the fire service throughout Chile, Latin America, and the World.

Ed Hartin, MS, EFO, MIFireE, CFO

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Two recent events in Baltimore, Maryland and Gary, Indiana point to the criticality of recognizing key fire behavior indicators and understanding practical fire dynamics.

Five Firefighters Injured in Baltimore

Early on the morning of Friday, January 15, 2010, the Baltimore City Fire Department was dispatched to a residential fire Southeast Baltimore. First arriving companies observed a row house of ordinary construction with a large volume of smoke and flames issuing from the basement and extending to the first floor.

According to a department spokesperson, the first engine took a line through the front door to the rear kitchen area where crew had some trouble finding the basement stairs. Another engine company went to the rear with a line to the outside stairwell leading to the basement and was just starting down the stairs. The first truck vented some skylights on the roof as well as the front basement windows. As crews were attempting to access the fire, some type of transient extreme fire behavior resulted in flames blowing through the unit and out the front door, rear stairwell, second floor windows, and skylights. The firefighter from the first arriving truck assigned to the roof described the sound of a freight train coming through.

Five firefighters injured as a result of this explosive fire behavior phenomenon were transported to area hospitals. The officer of the first in engine company was admitted to the Bayview Burn Center, where he is listed in stable condition

Find more videos like this on firevideo.net

What Happened?

As always when a video of an incident involving extreme fire behavior is posted to the web, there is ongoing debate about what happened. Was it a backdraft? Was it a flashover? An interesting debate, but the value is not so much in being “right”, but in understanding how these phenomena occur, what might have happened in this incident, key indicators that may (or may not) be visible in the video, and most importantly how to prevent this from happening to us and the firefighters that we work with!

Flashover: sudden transition to fully developed fire. This phenomenon involves a rapid transition to a state of total surface involvement of all combustible material within the compartment.

Given adequate fuel and ventilation, a compartment fire may reach flashover as it develops from the growth to fully developed stage. However, when fire development is limited by the ventilation profile of the compartment, changes in ventilation will directly influence fire behavior.

For many years firefighters have been taught that ventilation reduces the potential for flashover. However, when a fire is ventilation controlled, heat release rate is limited by the available oxygen. Under these conditions; increasing air supply by creating opening results in increased heat release rate. This increased heat release rate may result in flashover.

If a fire is sufficiently ventilation controlled and a high concentration of excess pyrolizate and unburned flammable products of combustion accumulate in a compartment, the outcome of increased ventilation may be different.

Backdraft: Deflagration of unburned pyrolyzate and combustion products following introduction of air to a ventilation controlled compartment fire and ignition of the fuel/air mixture. This deflagration results in a rapid increase in pressure within the compartment and extension of flaming combustion through compartment openings. Occurrence of this phenomenon requires an atmosphere in which the fuel concentration is too high to deflagrate without introduction of additional oxygen.

As introduced in Extreme Fire Behavior: An Organizational Scheme, extreme fire behavior phenomena can be classified on the basis of outcome and conditions (see Figure 1)

Figure 1. Extreme Fire Behavior Classification.

Use of this approach may aid in making sense of what may have occurred in the Baltimore incident. But, it is often difficult to classify extreme fire behavior phenomena into discrete, black and white categories. What is the dividing line between a ventilation induced flashover and a backdraft. One key difference may be the speed with which heat release rate increases, but where is the dividing line (see Figure 2)?

Figure 2. The Gray Area.

Keep in mind that while being right is great, it is more important to work through the process of figuring things out to improve your understanding.

Near Miss in Gary

Monday morning January 18, 2010 firefighters in Gary, Indiana were operating at a residential fire at 24^th and Massachusetts when they experienced a near miss involving rapid fire progression. Have a look at video of this incident and give some thought to what influenced fire behavior. Also look at the similarities and differences between the extreme fire behavior that occurred in the Baltimore and Gary incidents.

Back on Task!

I have been extremely busy working on a project for the National Institute for Occupational Safety and Health and preparing for the International Fire & Rescue Congress in Valdivia, Chile. Next week’s post will provide a quick update on training conducted at the Congress.

After returning from Chile, I will be back on task with examination of the concept of battle drills to develop effective reaction to worsening fire conditions while operating in an offensive mode.

Ed Hartin, MS, EFO, MIFireE, CFO

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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

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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.

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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

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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 (Särdqvist, 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

Särdqvist, S. (2001). Water and other extinguishing agents. Karlstad, Sweden: Räddnings Verket.

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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.

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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

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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.

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