Archive for October, 2009

As discussed in Flashover and Fully Developed Fires: Key Fire Behavior Indicators, providing additional oxygen to a ventilation controlled fire will result in a corresponding increase in heat release rate (HRR). This occurs because oxygen is required to release the chemical potential energy in fuel. The energy released per unit of mass of oxygen is remarkably consistent for both natural and synthetic organic (carbon containing) fuels.

Thornton’s Rule specifies that one kilogram (1 kg) of oxygen is required to release 13.1 mega joules (MJ) of energy. Multiplying 13.1 MJ/kg of oxygen by 21% (the concentration of oxygen in air) provides a value of 2.751 MJ/kg of air. The Society of Fire Protection Engineering (SFPE) Handbook of Fire Protection Engineering (SFPE, 2002) rounds this value to 3.0 MJ/kg of air. For a more detailed discussion of Thornton’s Rule and the relationship between fuel, oxygen, and energy release, see Fuel and Ventilation.

Decay Stage

A compartment fire may enter the decay stage as the available fuel is consumed or due to limited oxygen. As discussed in relation to flashover, a fuel package that does not contain sufficient energy or does not have a sufficient heat release rate to bring a compartment to flashover, will pass through each of the stages of fire development (but may not extend to other fuel packages). On a larger scale, without intervention an entire structure may reach full involvement and as fuel is consumed move into the decay stage. However, there is another, more problematic way for the fire to move into the decay stage. When the ventilation profile of the compartment or building does not provide sufficient oxygen, the fire may move into the decay stage. Heat release rate decreases as oxygen concentration drops. While temperature follows heat release rate, the temperature in decay stage fire may remain high for some time (particularly in well insulated, energy efficient buildings). This presents a significant threat as solid fuel packages continue to pyrolize and the involved compartment(s) may contain a high concentration of hot, pyrolized fuel, and flammable gaseous products of incomplete combustion.

Ventilation Controlled Fires

Under ventilation controlled conditions excess pyrolizate and flammable products of combustion present in smoke are a significant hazard to firefighters. Let’s go back to the fire triangle to examine the nature of this threat. While fuel, heat, and oxygen are present in proportion to support combustion where the fire is burning, the heat of the fire is pyrolyzing more fuel vapor than the fire can consume. In addition, incomplete combustion results in production of flammable gases such as carbon monoxide. The speed of fire development is limited by the availability of atmospheric oxygen provided by the current ventilation profile of the compartment or building.

In his presentation, Fire Dynamics for the Fire Service, Dan Madrzykowski of the National Institute of Standards and Technology (NIST) discussed the increased potential for ventilation controlled, decay stage fires in today’s modern, energy efficient structures. Dan presented the time temperature curve illustrated in Figure 1 to describe modern fire development and the potential influence of firefighting tactics.

Figure 1. Fire Development in the Modern Environment

Note: Adapted from National Institute of Standards and Technology (NIST) Fire Dynamics for the Fire Service, D. Madryzkowski.

The data in Figure 1 could be presented as HRR over time as well, but as HRR cannot be measured outside the lab, temperature is often used to describe fire development in full-scale tests. When the fire is burning in a ventilation controlled state, any increase in the supply of oxygen to the fire will result in an increase in heat release rate. Increase in ventilation may result from firefighters making entry into the building (the access point is a ventilation opening), tactical ventilation (performed by firefighters), or unplanned ventilation (e.g., failure of window glazing due to elevated temperature).

It is essential to recognize when the fire is, or may be ventilation controlled and the influence of planned and unplanned changes in ventilation profile. Most compartment fires that progress into the growth stage are ventilation controlled when the fire department arrives. A bi-directional air track (smoke out the top and air in the bottom) is often a significant indicator of a ventilation controlled fire, but what about before the door is open?

Figure 2. Assessment of Conditions at the Door

As combustion becomes more incomplete, smoke production increases, color darkens, and optical density increases. However, these indicators may be subtle when observing fire conditions from the exterior. Assessment of conditions must continue after making entry. Smoke and air track indicators can be particularly useful in addressing the stage of fire development and burning regime when working inside. In addition, flames moving through the hot gas layer are a strong indicator of a ventilation controlled fire (as well as a threat to your safety which should be dealt with immediately).

Ventilation Induced Extreme Fire Behavior

When the fire is ventilation controlled, increased air supply to the fire will result in increased heat release rate and depending on conditions may result in extreme fire behavior such as flashover or backdraft. While both phenomena result from an increase in ventilation, vent induced flashover and backdraft are different phenomena. The conditions required for a ventilation induced flashover are 1) a compartment fire which has an insufficient HRR to reach flashover due to ventilation controlled combustion, and 2) insufficient concentration of excess pyrolizate and unburned products of incomplete combustion to result in a backdraft. While complex, the key determinant in the occurrence of a backdraft is likely to be the concentration of gas phase fuel within the compartment.

While these phenomena are different, both present a significant threat to firefighters. Rapid fire progress due to ventilation induced flashover or backdraft is not an instantaneous process. Depending on a number of variables such as the location of the fire, current level of involvement, temperature of the smoke (hot gas) layer, and extent of the increase in ventilation these rapid fire progress phenomenon may take some time to occur. However, when it does, fire development will be extremely rapid! Firefighters entering a compartment or building containing an under ventilated fire must be aware of and manage the hazards presented by the potential for rapid fire progress. Remember, many if not most fires that have progressed beyond the incipient stage before firefighters arrival are ventilation controlled and present the potential for rapid fire progress with increased ventilation (see Situational Awareness is Critical).

Figure 3 lists the fire behavior indicators related to ventilation controlled decay stage conditions and the potential for ventilation induced extreme fire behavior. It is important to note that there are not always clear distinctions in the visual indicators for vent induced flashover and backdraft.

Figure 3.  FBI: Decay Stage

Be Wary

Decay stage indicators can sometimes be subtle and conditions may not look too bad (maybe like an incipient or early growth stage fire if you are not paying close attention and consider the possibilities).

It is often assumed (incorrectly) that ventilation induced extreme fire behavior (flashover or backdraft) will occur immediately after an increase in ventilation. Depending on fire conditions and building configuration there may be a significant time lag between ventilation and resulting changes in fire behavior. When ventilation controlled decay conditions are indicated (or suspected), firefighters should move cautiously and take action to change conditions inside the building or compartment (e.g., gas cooling, ventilation).

You have responded to a fire in a one-story single family dwelling of wood frame construction. A fire which started in a bedroom on the Alpha Bravo corner of the structure has gone from fully developed to the decay stage due to a lack of oxygen as building openings (doors and windows) remain closed and intact.

• What conditions would you expect to see from the exterior of the structure?
• What indicators may be visible from the front door as you make entry?

A fire in the decay stage (particularly when this is due to limited oxygen) still presents a significant threat as conditions can change rapidly.

• If the door at your entry point remains fully open, how will this influence fire behavior (assuming no other ventilation has been performed)?
• How would fire behavior be influenced if a window (or windows) in the fire compartment are opened along with the door at your entry point?
• What indicators would you anticipate observing as you traveled through the living room to the hallway leading to the bedroom?

• What conditions would you find in the hallway outside the fire compartment?

After making entry, consider if conditions are different than you anticipated?

• Why might this be the case?
• What differences in conditions would be cause for concern?

Late Breaking News

I have been selected to serve as Fire Chief with the Central Whidbey Island Fire District in Washington and anticipate starting in my new position by mid November.

Over the next year I will also be serving on an advisory panel to assist Underwriters Laboratory with a research project on to examine the impact of ventilation on fire behavior in legacy and contemporary construction. Output from this project will include a formal technical report, articles in fire service publications, presentation to the fire service community, and a stand-alone web-based training module.

References

Society of Fire Protection Engineers (SFPE). (2002). The SFPE handbook of fire protection engineering (3^rd ed.). Quincy, MA: National Fire Protection Association.

Madrzykowski, D. Fire dynamics for the fire service [PowerPoint Presentation], Gaithersburg, MD: National Institute of Standards and Technology.

Warfare is often used as a metaphor for firefighting with fire being the enemy and the building the ground on which we fight. Extending warfare as a metaphor, handline nozzles are firefighters’ principle weapon in offensive firefighting operations.

In the early 1940s Major General William H. Rupertus, United States Marine Corps (USMC), wrote the Rifleman’s Creed (also known as My Rifle). The creed is part of Marine doctrine that emphasizes that regardless of specialty or assignment, all Marines are riflemen. The Rifleman’s creed emphasizes the criticality of caring for and mastering the use of the Marine’s individual weapon. How many firefighters have the same commitment to care and mastery of their nozzle?

All too often, firefighters consider the nozzle to be a simple device requiring little practice to master and seldom thought of until needed. Take a minute and think about the nozzle(s) that you use!

Nozzle Knowledge

These 20 questions focus on some of the fundamental knowledge that firefighters must have if they are truly going to master their primary weapon in offensive firefighting operations.

1. What kind of nozzle(s) are on your preconnected hoseline (combination or solid stream)?
2. What type of nozzles are they (i.e., fixed flow, variable flow, automatic, or single tip, stacked tips)?
3. What flow rate, rates, or range do they have?
4. If flow rate can be varied, how is this accomplished? Does the mechanism used to change flow operate freely?
5. If you change the flow without a corresponding change in line pressure at the pump, what happens to the nozzle pressure?
6. What is their designed operating pressure or pressures (for dual pressure nozzles)?
7. For combination nozzles, what is the impact of nozzle pressure on droplet size? Can you operate the nozzle at more than one nozzle pressure?
8. If a variable flow or automatic combination nozzle, does droplet size change with flow rate? Why might this be significant?
9. What is the maximum effective reach of the nozzle?
10. Can you flush debris from the nozzle? If so, how?
11. What type of coupling is the nozzle equipped with (e.g., if threaded, is it National Standard Hose, Iron Pipe, or some other thread)?
12. What type of valve is the nozzle equipped with (ball or slide valve) and what difference does it make?
13. If it is a combination nozzle, does it have fixed or spinning teeth? Why would this matter?
14. If the nozzle is equipped with spinning teeth, does the turbine spin freely?
15. Do your nozzles open and close easily when under pressure?
16. Are your nozzles clean (inside and out)? How should they be cleaned?
17. Do your nozzles require lubrication to ensure free movement of their operating mechanism? If so, when was the last time that they were lubricated?
18. If a combination nozzle, how to you adjust the nozzle to a wide angle fog pattern?
19. For combination nozzles, what is the maximum angle of the wide fog pattern?
20. If a combination nozzle, how far from straight stream or wide angle fog does the pattern control need to be turned to produced a 40^o (medium) fog pattern?

While knowing the answers to these questions, is necessary, it alone is not sufficient. In addition to knowledge of operating characteristics and maintenance procedures, firefighters must be skilled in nozzle operation in order to be able to accurately put water where it is needed.

Nozzle Skills

In some respects a nozzle is a fairly simple device designed to increase the velocity of water and provide a useful stream for firefighting operations. However, can you consistently:

1. Adjust a fog pattern to the desired angle without visual reference, before opening the nozzle to check the pattern?
2. Apply a short or long pulse of water fog so that the droplets evaporate in the hot gas layer, minimizing water contact with compartment linings (i.e. walls and ceiling)?
3. Apply a fog pattern to fill the maximum volume of a compartment without excessive water hitting the compartment linings?
4. Apply water gently in the form of a straight stream so that it flows onto a hot surface, maximizing cooling and minimizing runoff?
5. Recognize audible indicators of fire stream impact on compartment linings?
6. Adjust flow rate based on conditions and tactical application (i.e. gas cooling, indirect attack, direct attack)?
7. Maximize both effectiveness (in controlling the fire) and efficiency (by minimizing water use)?

These questions are obviously focused on combination nozzles. If you more commonly use solid stream nozzles, ability to cool hot gases is limited by the form in which water is applied. While limited in gas cooling effectiveness, what techniques can you use to have some impact on the threat presented by the hot gas layer?

As with knowledge of your nozzle, these skills are necessary, but not sufficient. Firefighters must be able to integrate physical skill with situational awareness and team based tactical skill.

My Nozzle

With due credit to General Rupertus and the USMC; I have adapted The Rifleman’s Creed:

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.

Developing Skill

During structural firefighting operations firefighters are faced with dynamic and rapidly changing conditions in which situational awareness is critical. Basic skills in the use of personal protective equipment and the tools of the firefighters’ craft must have reached the autonomous stage of performance to allow focus on critical decisions and tasks.

Habit hardens the body for great exertions, strengthens the heart in great peril, and fortifies the judgment against first impressions. Habit breeds that priceless quality, calm, which passing from hussar and rifleman up to the general himself, will lighten the commanders task. (Von Clausewitz, p. 122)

Colonel B.P. McCoy, USMC (2007) drew on Clausewitz’s wisdom in identifying combat marksmanship as a critical habit. “Anybody, even in the middle of a phobic response to the violence of combat can yank on a trigger and spray rounds in the general direction of the enemy, ‘spray and pray'” (p. 25). How many firefighters have the same response in the fire environment? “Combat marksmanship is the hallmark of the infantryman. Nothing nurtures confidence like the knowledge that one can hit what one is shooting at” (McCoy, 2007, p. 25). Firefighters require the same skill in nozzle use as Colonel McCoy’s Marines required in the use of their rifles.

During offensive firefighting operations firefighters apply water for one of two purposes. 1) to cool hot gases or 2) to cool hot surfaces (Grimwood, Hartin, McDonough, & Raffel, 2005). Each of these tasks requires a different method to put water where it is needed in a form that will accomplish the intended outcome.

Gas Cooling: In general water application to cool hot gases should be based on the following requirements:

• Most of the water applied must vaporize in the hot gas layer (not on surfaces)
• Nozzle pattern should maximize the volume of hot gases cooled.

The challenge to the nozzle operator is that there is not one single approach to meeting these requirements. In general, smaller droplets work better than large droplets, but nozzle pattern (wide, medium, or narrow fog) is dependent on the size of the space and temperature of the flames and/or hot, unignited gases.

Surface Cooling: The requirement for cooling hot surfaces is different than those required for gas cooling, but is equally simple.

Most of the water applied must vaporize on contact with hot surfaces (not in the hot gas layer)

As with gas cooling there is not a single approach to meeting these requirements. In general, effective surface cooling requires a thin layer of water on the hot surface. If the surface is extremely hot, water application must be continued until the temperature is reduced sufficiently to slow and stop pyrolysis.

Important! Water on the floor after extinguishment is completed did not do significant work. Far more energy is required for water to change phase into steam than to simply raise its temperature. Water application must be effective (in achieving fire control), but should also be efficient (in minimizing the water used and limiting fire control damage).

Effective and efficient fire control requires that firefighters be skilled at putting water in the right form where it is needed (in the hot gases or on hot surfaces). Development of autonomous (habitual) skill in nozzle use requires deliberate practice. This is not simply repetition of our current skills, but continuing to stretch just beyond our current abilities. Deliberate practice is designed specifically to improve sharply defined elements of performance.

The next several posts in this series will examine how research in sport psychology regarding motor learning and performance can be used to enhance our ability to develop proficiency in nozzle use (as well as other physical firefighting skills).

Ed Hartin, MS, EFO, MIFireE, CFO

References

US Army (1992). Field manual 7-8 infantry Rifle platoon and squad. Washington, DC: Headquarters, Dept. of the Army.

Clausewitz, C. (1984) On war. (M. Howard & P. Paret, Trans.). Princeton, NJ: Princeton University Press

McCoy, B. (2007). The passion of command. Quantico, VA: The Marine Corps Association.

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

This post continues examination of key indicators used to recognize stages of fire development (i.e., incipient, growth, fully developed, and decay), burning regimes (i.e., fuel and ventilation controlled) with a look at indicators of the fully developed stage of fire development. Most buildings are comprised of multiple, interconnected compartments and fire conditions can vary widely from compartment to compartment. Fire in the compartment of origin may have reached the fully developed stage, while adjacent compartments may have just entered the growth stage.

Figure 1. Fully Developed Fire

National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Report F2007-02 (2009) recommends that fire service agencies: “Train fire fighters to recognize the conditions that forewarn of a flashover/flameover [rollover] and communicate fire conditions to the incident commander as soon as possible” (p. 2). Note: flameover and Rollover are synonyms.

Flameover (Rollover): The condition where unburned fuel (pyrolyzate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns; can occur without ignition of, or prior to, the ignition of other fuels separate from the origin. (NFPA 921, 2008, 3.3.67 and 3.3.137)

Recognition of key fire behavior indicators is critical. However, communication of this information to the incident commander (as it may impact on strategies) alone is not sufficient. Companies working in the fire environment must proactively mitigate this threat through effective fire control and ventilation strategies and tactics.

Flashover

Flashover is the sudden transition from a growth stage to fully developed fire. When flashover occurs, there is a rapid transition to a state of total surface involvement of all combustible material within the compartment. Conditions for flashover are defined in a variety of different ways. In general, ceiling temperature in the compartment must reach 500^o-600^o C (932^o-1112^o F) or the heat flux (a measure of heat transfer) to the floor of the compartment must reach 15-20 kW/m² (1.32 Btu/s/ft²)-1.76 Btu/s/ft²). When flashover occurs, burning gases will push out openings in the compartment (such as a door leading to another room) at a substantial velocity (Karlsson & Quintiere, 2000).

It is important to remember that flashover does not always occur. There must be sufficient fuel and oxygen for the fire to reach flashover. If the initial object that is ignited does not contain sufficient energy (heat of combustion) and does not release it quickly enough (heat release rate), flashover will not occur (e.g., small trash can burning in the middle of a large room). Likewise, if the fire sufficiently depletes the available oxygen, heat release rate will drop and the fire in the compartment will not reach flashover (e.g., small room with sealed windows and the door closed). A fire that fails to reach a sufficient heat release rate for flashover to occur due to limited ventilation presents a significant hazard as increased ventilation may result in a ventilation induced flashover (see Understanding Flashover: Myths & Misconceptions Part 2 and The Ventilation Paradox).

Indicators of Flashover Potential

Recognizing flashover and understanding the mechanisms that cause this extreme fire behavior phenomenon is important. However, the ability to recognize key indicators and predict the probability of flashover is even more important. Indicators of potential or impending flashover are listed in Figure 2.

Figure 2. Indicators of Potential Flashover

If the fire in our residential scenario is nearing flashover (in the compartment of origin) what fire behavior indicators might be observed? Use the B-SAHF model to help you frame your answers.

You have responded to a fire in a one-story single family dwelling of wood frame construction. A fire which started in a bedroom on the Alpha Bravo corner of the structure is nearing flashover. A thick hot gas layer has developed in the bedroom and is flowing out the open door into the hallway. The fire has extended to the bed and flames in the plume have reached the ceiling and have begun to extend horizontally in the ceiling jet. Fuel packages below the level of the hot gas layer (e.g., furniture, carpet, and contents) are beginning to pyrolize.

• What conditions would you expect to see from the exterior of the structure?
• What indicators may be visible from the front door as you make entry?

Remember that fire conditions will vary throughout the building. While the fire is in the growth stage and nearing flashover in the bedroom, conditions may be different in other compartments within the building.

• What indicators would you anticipate observing as you traveled through the living room to the hallway leading to the bedroom?
• What conditions would you find in the hallway outside the fire compartment?
• After making entry, consider if conditions are different than you anticipated?
• Why might this be the case?
• What differences in conditions would be cause for concern?
• How might your answers to the preceding questions have differed if the bedroom door was closed and fire growth limited by ventilation?

Fully Developed Fire

At this post-flashover stage, energy release is at its greatest, but is generally limited by ventilation (more on this in a bit). Unburned gases accumulate at the ceiling level and frequently burn as they leave the compartment, resulting in flames showing from doors or windows. The average gas temperature within a compartment during a fully developed fire ranges from 700^o-1200^o C (1292^o-2192^o F)

Remember that the compartment where the fire started may reach the fully developed stage while other compartments have not yet become involved. Hot gases and flames extending from the involved compartment transfer heat to other fuel packages (e.g., contents, compartment linings, and structural materials) resulting in fire spread. Conditions can vary widely with a fully developed fire in one compartment, a growth stage fire in another, and an incipient fire in yet another. It is important to note that while a fire in an adjacent compartment may be incipient, conditions within the structure are immediately dangerous to life and health (IDLH).

Indicators of a Fully Developed Fire

Remember that a fully developed fire refers to conditions within a given compartment or compartments. It does not necessarily mean that the entire building is fully involved. Figure 3 lists indicators of fully developed fire conditions.

Figure 3. FBI-Fully Developed Stage

If the fire in our residential scenario has progressed to the fully developed stage (in the compartment of origin) what fire behavior indicators might be observed? Use the B-SAHF model to help you frame your answers.

You have responded to a fire in a one-story single family dwelling of wood frame construction. A fire which started in a bedroom on the Alpha Bravo corner of the structure has reached the fully developed stage and now involves the contents of the room and interior finish of this compartment.

• What conditions would you expect to see from the exterior of the structure?
• What indicators may be visible from the front door as you make entry?

Remember that fire conditions will vary throughout the building. While the fire is fully developed in the bedroom, conditions may be different in other compartments within the building.

• What indicators would you anticipate observing as you traveled through the living room to the hallway leading to the bedroom?
• What conditions would you find in the hallway outside the fire compartment?
• After making entry, consider if conditions are different than you anticipated?
• Why might this be the case?
• What differences in conditions would be cause for concern?

Ventilation Controlled Fires

When the fire is burning in a ventilation controlled state, any increase in the supply of oxygen to the fire will result in an increase in heat release rate. Increase in ventilation may result from firefighters making entry into the building (the access point is a ventilation opening), tactical ventilation (performed by firefighters), or unplanned ventilation (e.g., failure of window glazing due to elevated temperature).

It is essential to recognize when the fire is, or may be ventilation controlled, and the influence of planned and unplanned changes in ventilation profile on fire behavior. Most compartment fires in the late growth stage or which are fully developed are ventilation controlled when the fire department arrives. Even if the fire has not entered the decay stage due to limited ventilation, the increased oxygen provided by increases in ventilation (such as that caused by opening the door to make entry) will increase heat release rate. This is not to say that increased ventilation is a bad thing, but firefighters should be prepared to deal with this change in fire behavior.

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.

October 29, 2008
Firefighter Adam Cody Renfroe
Crossville Fire Department, Alabama

The Crossville Fire Department was dispatched to a fire in a single-family residence. was on the first engine to arrive on the scene to find thick, black smoke from the roof and a report that all occupants were out of the house.

Firefighter Renfroe and another firefighter advanced a hoseline to the front door of the residence. He sent the other firefighter back to the fire truck for a tool. When the firefighter returned, Firefighter Renfroe was gone and the nozzle remained by the doorway. At about the same time, the fire inside of the structure intensified. Firefighter Renfroe transmitted a distress message from the interior. Firefighters were not immediately able to enter the structure due to fire conditions.

Firefighters discovered Firefighter Renfroe about 4 feet from the home’s back door, but By the time firefighters reached him, he was deceased. The cause of death was smoke inhalation and thermal burns.

For more information on this incident, see NIOSH Death in the Line of Duty Report F2008-34.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Karlson, B. & Quintiere, J. (2000) Enclosure fire dynamics. Boca Raton, FL: CRC Press.

National Institute for Occupational Safety and Health (NIOSH). (2009). Death in the Line of Duty Report F2007-02. Retrieved October 22, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200702.pdf .

On 12-16 October 2009 a group of compartment fire behavior training (CFBT) instructors representing six nations gathered for a seminar at the Myndigheten för Samhällsskydd och Beredskap (MSB) (Swedish Civil Contingencies Agency) College in Sandö, Sweden. This was a unique event in that the group had the opportunity to learn the history of Swedish fire behavior training from Mats Rosander, Marcos Dominquez, and Nils Bergström, three pioneers in fire control methods and training.

Figure 1. Mats Rosander and Nils Bergström

(Left to Right) Mats Rosander, Ed Hartin, & Nils Bergström

In addition to presentations on the history and evolution of Swedish fire behavior training and fire control methods, workshop participants participated in representative examples of fire behavior classroom instruction laboratory exercises and practical evolutions conducted at Sandö.

Figure 2. Practical Exercises

The MSB College at Sandö has extensive live fire training facilities with demonstration, attack, window, and large volume cells as well as a variety of multi-compartment live fire training props.

Figure 3. Mats, Marcos, & Nisse Preparing the Aquarium

Figure 3. Backdraft Demonstration in the Classroom

Seminar Presentations

On Thursday morning, Shan Raffel, Peter McBride, John McDonough, and Ed Hartin delivered short presentations on Reading the Fire, Role of the Incident Safety Officer, Firefighter Behavior (transfer of training to incident operations), and Live Fire Training as Simulation: The Role of Fidelity in Effective Training. This segment of the workshop was open to college staff, students attending courses at the college, and local fire service personnel.

Figure 4. Seminar Presentation

Download Live Fire Training as Simulation: The Role of Fidelity in Effective Training.

So What?

Seminar participants all recognized this seminar as an extremely significant event. On the surface, it appears to be an ordinary seminar, but in reality it was really quite different. Great strides have been made in developing relationships between compartment fire behavior training practitioners around the world through the Institution of Fire Engineers (IFE) Compartment Firefighting Special Interest Group (SIG) International Fire Instructors Workshops held in Revenge, Sweden (2008) and Sydney, Australia (2009). However, this event was unique in that it provided a bridge back into history. Unfortunately, leaders and pioneers in many fields are not recognized during their lifetime, limiting researchers and students to often meager written records of their contributions. This workshop provided the participants with the opportunity to make a direct connection to the origins of many innovative concepts and developments in fire behavior and fire control theory.

Fire Behavior Pioneers Honored

Yesterday morning, Acting Inspector Shan Raffel, ASFM, CMIFireE, EngTec, presented certificates of recognition to Mats Rosander, Nils Bergström, Marcos Dominguez, and Krister Giselsson (posthumously) on behalf of the Institution IFE and fire services around the world for their pioneering work in fire behavior training and firefighting operations.

Special Thanks

I would like to acknowledge the efforts of Roy Reyes, his colleague David Flatebö, and the staff of the MSB College at Sandö in facilitating this important seminar. This was an important step in forging a stronger network of fire service leaders committed to ensuring that firefighters have the knowledge and skills necessary to operate safely and effectively in an ever changing built environment.

What’s Next?

It will take some time to digest the tremendous amount of information from the Sandö Workshop. However, I look forward to sharing what I have learned and providing a bit of historical context for much of what we are doing in fire behavior training today.

My next post will return to examination of fire behavior indicators related to fires in the fully developed stage along with variations in conditions when fire conditions impact on multiple compartments (as is usually the case).

Ed Hartin, MS, EFO, MIFireE, CFO

Open Enrollment CFBT Level I & Instructor Courses

CFBT-US, LLC and the Northwest Association of Fire Trainers (NAFT) will be offering CFBT Level I and Instructor Courses at the Clackamas County (OR) Fire District I CFBT facility.

CFBT Level I
7-9 November 2009
Course Fee: $335

CFBT Instructor
9-13 November 2009
Course Fee: $915

Instructor course participants receive a copy of 3D Firefighting: Training, Techniques, & Tactics and an extensive 2-DVD library of CFBT resources including the CFBT Level I curriculum. For information on these courses download a NAFT CFBT Brochure and the CFBT Level I and CFBT Instructor Course Information Sheets.

CFBT Workshop in Sandö, Sweden

From 12-16 October 2009, I will be participating in a CFBT workshop in Sandö, Sweden along with a small group of instructors from around the world. We will be studying the compartment fire behavior curriculum at the Swedish Civil Contingencies Agency (Myndigheten för samhällsskydd och beredskap (MSB)) College in Sandö.

Figure 1. Fire Behavior Training in Sandö

In January of 2009 MSB replaced the Swedish Rescue Services Agency, the Swedish Emergency Management Agency, and the Swedish National Board of Psychological Defense. The MSB maintains two fire service colleges, one in Sandö (see Figure 2) and the other in Revinge.

Figure 2. MSB College in Sandö

The International Conference of Fire and Rescue, Valdivia – Chile 2010 CIFR

My brothers with Company 1 “Germania” of the Valdivia, Chile Fire Department have taken on a tremendous task with delivery of the first International Conference of Fire & Rescue in Valdivia. The conference will be held 23-27 January 2010.

Conference presenters include a diverse cadre of instructors from around the world. I will be presenting a series of seminars on fire behavior as well as a hands-on CFBT workshop. Presentations will be simultaneously translated into English and Spanish (as applicable). Have a look at the Conference Web Site for more information on this tremendous learning opportunity.

NIOSH Death in the Line of Duty F2007-02

On November 23, 2006, Firefighter Steven Solomon, a 33-year-old career fire fighter was seriously injured during a ventilation induced flashover or related fire behavior event in an abandoned single story duplex in Atlanta, GA; he died as a result of these injuries 6 days later.

NOSH Report F2007-02 provides an excellent description of fire behavior indicators observed prior to the occurrence of extreme fire behavior and correctly identifies that increased ventilation without coordinated fire attack resulted in worsening fire conditions.

Several conclusions in the report were based on computational fluid dynamics (CFD) modeling using the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator software. As discussed in a previous post computer modeling is an excellent tool, but it is important to understand both its capabilities and limitations (see Townhouse Fire-Washington, DC: Computer Modeling)

It is crucial to bear in mind that fire models do not provide a reconstruction of the reality of an event. They are simplified representation of reality that will always suffer from a certain lack of accuracy and precision. Under the condition that the user is fully aware of this status and has an extensive knowledge of the principles of the models, their functioning, their limitations and the significance attributed to their results, fire modeling becomes a very powerful tool (Dele´mont & Martin, J., 2007, p. 134).

Review NIOSH Report F2007-02 and see if you agree or disagree with the conclusions regarding the type of extreme fire behavior phenomena involved in this incident.

Ed Hartin, MS, EFO, MIFireE, CFO

Chicago Dollar Store Fire

On the morning of October 1, 2009 the Chicago Fire Department (CFD) responded to a fire in the Super Dollar and Up store at 3952 West Cermak Road. CFD Senior Fire Alarm Operator and Fire Photographer Steve Redick captured early incident operations on video.

The first segment of the video was shot in the alley on Side C from the B/C Corner. The next several minutes of video are shot from positions on Side A as indicated in Figure 1.

Figure 1. Plot Plan and Approximate Video Camera Locations

Download the B-SAHF Worksheet.

Watch the first 60 seconds of Video Segment 1. Consider the information provided in this segment of the video clip. First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators and 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?
5. How would you expect the fire to develop over the next two to three minutes?

After completing the B-SAHF worksheet and answering the five standard questions, watch the next minute and twenty seconds of the video.

1. Did you anticipate this change?
2. What factors may have influenced this change in conditions?

Visit Steve Redick’s Web Site for additional video and excellent photos of this incident.

Memphis Dollar Store LODD

The rapidly changing conditions in the Chicago incident reminded me of the fire in Memphis, Tennessee that took the lives of Lieutenant Trent Kirk and Private Charles Zachary. Similar to the fire in Chicago, this incident involved a fire in a one-story, non-combustible building containing multiple commercial occupancies. As companies arrived they observed a small volume of smoke from the roof and little smoke inside the building. Approximately nine minutes after arrival conditions worsened with a large volume of smoke pushing from the doorway on Side A. Crews became disoriented as a result of rapid fire progression, and Lieutenant Kirk and Private Zachary were trapped.

For additional information on this incident see NIOSH Death in the Line of Duty Report F2003-18 and Memphis Fire Department Director’s Review Board Family Dollar Store Fire report.

Dollar Stores as a Target Hazard

Dollar stores and similar types of commercial occupancies should be considered as a target hazard that presents a significant threat to firefighters. These types of stores are generally in an enclosed building (good access from the front, but not generally from the other sides of the building) with high ceilings and a cockloft or other ceiling void space. In addition, this type of store contains a large fuel load comprised predominantly of synthetic fuel with a high heat of combustion (think high energy) and potential for extremely rapid fire development.

Fires in this type of occupancy are not uncommon! A quick search uncovered 15 similar incidents across the United States in the last three years (and 11 in 2009). There were likely more (as the scope of this search looked for fires in “dollar stores” and stopped after the first several hundred hits with the Google search engine).

• Broadview, IL (June 9, 2009)
• Flint, MI (August 24, 2009)
• Lubbock, TX (September 15, 2009)
• Terre Haute, IN (June 29, 2009)
• New York, NY (June 9, 2009)
• Midlothian, IL (February 6, 2008)
• Highland Park, MI (October 7, 2007)
• Denver, CO (June 29, 2009)
• Sanford, FL (March 23, 2009)
• Chattanooga, TN (April 14, 2009)
• Conklin, NY (August 27, 2009)
• Muncie, IN (September 16, 2009)
• Lake Worth, TX (November 25, 2006)
• Omaha, NE (April 8, 2008)
• Bells Corner, PA (June 3, 2009)

Building Factors and Fire Behavior

Building factors include the construction, configuration, and contents of a structure. These factors are critical fire behavior indicators that must be assessed during pre-planning and in the course of size-up and incident operations. Consider how building size (particularly volume, ceiling height, and presence of ceiling, attic, or cockloft void spaces) impacts on both fire behavior and how the other B-SAHF indicators present.

Reporting on the Dollar Store fire in Chattanooga, TN in April 2009, a Chattanooga Fire Department spokesperson said:

At first, it appeared that the firefighters would be able to get the fire under control fairly quickly, but the fire got into the attic and was difficult to locate in the thick, black smoke… The firefighters made an interior attack and tried to use thermal imaging cameras to locate the fire. However, other firefighters noticed that the roof was beginning to sag, so the order was given to evacuate the building for the safety of the firefighters.

It is essential to recognize potential for worsening conditions and extreme fire behavior. This is particularly important when faced with an incident outside the norm of fires in residential structures such as one and two-family dwellings and apartments.

Posts from Sandö, Sweden

Next week I will be posting from Sandö, Sweden as 12-16 October I will be participating in a Compartment Fire Behavior Training Workshop at the Swedish Civil Contingencies Agency College. Along with representitives from Australia, Canada, Germany, and Spain, I will be studying contemporary approaches to fire behavior training as well as the evolution of Swedish fire behavior training since the 1980s. This workshop provides a tremendous opportunity to learn along with Mats Rosander, Nils Bergström, and Marcos Dominguez, poneers in the evolution of fire behavior training in Sweden and around the world.

Ed Hartin, MS, EFO, MIFIreE, CFO

This post continues study of an incident in a townhouse style apartment building in Washington, DC with examination of the extreme fire behavior that took the lives of Firefighters Anthony Phillips and Louis Mathews. As discussed in Townhouse Fire: Washington, DC-Computer Modeling Part I, this was one of the first cases where the NIST Fire Dynamics Simulator (FDS) software was used in forensic fire scene reconstruction (Madrzykowski and Vettori, 2000).

Quick Review

As discussed in prior posts, crews working on Floor 1 to locate the fire and secure the door to the stairwell were trapped and burned as a result of rapid progression of a fire in the basement up the open interior stairway after an exterior sliding glass door was opened to provide access to the basement. For detailed examination of incident operations and fire behavior, see:

• Fire Behavior Case Study Townhouse Fire: Washington, DC
• Townhouse Fire: Washington DC-What Happened
• Townhouse Fire: Washington DC-Extreme Fire Behavior
• Townhouse Fire: Washington DC-Computer Modeling

Figure 1. Conditions at Approximately 00:28

Note: From Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 29 & 32. District of Columbia Fire & EMS, 2000.

Smokeview

Smokeview is a visualization program used to provide a graphical display of a FDS model simulation in the form of an animation or snapshot. Snapshots illustrate conditions in a specific plane or slice within the building. Three vertical slices are important to understanding the fire dynamics involved in the Cherry Road incident: 1) midline of the door on Floor 1, Side A, 2) midline of the Basement Door, Side C, and midline of the Basement Stairwell (see Figure 2). Imagine that the building is cut open along the slice and that you can observe the temperature, oxygen concentration, or velocity of gas movement within that plane.

Figure 2. Perspective View of 3146 Cherry Road and Location of Slices

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 15) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

In addition to having an influence on heat release rate, the location and configuration of exhaust and inlet openings determines air track (movement of smoke and air) and the path of fire spread. In this incident, the patio door providing access to the basement at the rear acted as an inlet, providing additional air to the fire. The front door and windows on the first floor opened for ventilation served as exhaust openings and provided a path for fire travel when the conditions in the basement rapidly transitioned to a fully developed fire.

Figures 3-10 illustrate conditions at 200 seconds into the simulation, which relates to approximately 00:27 during the incident, the time at which the fire in the basement transitioned to a fully developed stage and rapidly extended up the basement stairway to Floor 1. Data is presented as a snapshot within a specific slice. Temperature and velocity data are provide for each slice (S1, S2, & S3 as illustrated in Figure 2).

Figure 3. Temperature Along Centerline of Basement Door Side C (S1) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 17) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 4. Vector Representation of Velocity Along Centerline of Basement Door Side C (S1) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 18) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 5. Oxygen Concentration Along Centerline of Basement Door Side C (S1) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 23) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 6. Temperature Slice Along Centerline of Basement Stairwell (S2) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 21) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 7. Vector Representation of Velocity Along Centerline of Basement Stairwell (S2) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 22) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 8. Oxygen Concentration Along Centerline of Basement Stairwell (S2) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 24) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 9. Temperature Slice Along Centerline of Floor 1 Door Side A (S3) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 19) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 10. Vector Representation of Velocity Along Centerline of Floor 1 Door Side A (S3) at 200 s

Note: From Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 20) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

Figure 11. Perspective Cutaway, Flow/Temperature, Velocity, and O₂ Concentration

Figure 12. Thermal Exposure Limits in the Firefighting Environment

Note: Adapted from Measurements of the firefighting environment. Central Fire Brigades Advisory Council Research Report 61/1994 by J.A. Foster & G.V. Roberts, 1995. London: Department for Communities and Local Government and Thermal Environment for Electronic Equipment Used by First Responders by M.K. Donnelly, W.D. Davis, J.R. Lawson, & M.J. Selepak, 2006, Gaithersburg, MD: National Institute of Standards and Technology.

Compartment Fire Thermal Hazards

The temperature of the atmosphere (i.e., smoke and air) is a significant concern in the fire environment, and firefighters often wonder or speculate about how hot it was in a particular fire situation. However, gas temperature in the fire environment is a bit more complex than it might appear on the surface and is only part of the thermal hazard presented by compartment fire.

Tissue temperature and depth of penetration determine the severity of a thermal burn. Temperature and penetration are dependent on the amount of energy absorbed and the duration of the thermal insult as well as the properties of human tissue. In a compartment fire, firefighters absorb energy from any substance that has a temperature above 37^o C (98.6^o F), including hot compartment linings, contents, the hot gas layer, and flames. The dominant mechanisms of heat transfer involved in this process are convection and radiation (although conduction through personal protective equipment is also a factor to be considered).

The total thermal energy received is described in joules per unit area. However, the speed or rate of energy is transferred may be more important when assessing thermal hazard. Heat (thermal) flux is used to define the rate of heat transfer and is expressed in kW/m² (Btu/hr/ft²).

One way to understand the interrelated influence of radiant and convective heat transfer is to consider the following scenario. Imagine that you are standing outside in the shade on a hot, sunny day when the temperature is 38^o C (100^o F). As the ambient temperature is higher than that of your body, energy will be transferred to you from the air. If you move out of the shade, your body will receive additional energy as a result of radiant heat transfer from the sun.

Convective heat transfer is influenced by gas temperature and velocity. When hot gases are not moving or the flow of gases across a surface (such as your body or personal protective equipment) is slow, energy is transferred from the gases to the surface (lowering the temperature of the gases, while raising surface temperature). These lower temperature gases act as an insulating layer, slowing heat transfer from higher temperature gases further away from the surface. When velocity increases, cooler gases (which have already transferred energy to the surface) move away and are replaced by higher temperature gases. When velocity increases sufficiently to result in turbulent flow, hot gases remain in contact with the surface on a relatively constant basis, increasing convective heat flux.

Radiant heat transfer is influenced by proximity and temperature of the radiating body. Radiation increases by a factor of four when distance to the hot material is reduced by half. In addition, radiation increases exponentially (as a function of the fourth power) as absolute temperature increases.

Thermal hazard may be classified based on hot gas temperature and radiant heat flux (Foster & Roberts, 1995; Donnelly, Davis, Lawson, & Selpak, 2006) with temperatures above 260^o C (500^o F) and/or radiant heat flux of 10 kW/m² (3172 Btu/hr/ft²) being immediately life threatening to a firefighter wearing a structural firefighting ensemble (including breathing apparatus). National Institute of Standards and Technology (NIST) experiments in a single compartment show post flashover gas temperatures in excess of 1000^o C (1832^o F) and heat flux at the floor may exceed 170 kW/m² (Donnelly, Davis, Lawson, & Selpak, 2006). Post flashover conditions in larger buildings with more substantial fuel load may be more severe!

Figure 11 integrates temperature, velocity, and oxygen concentration data from the simulation (Figures 3-10). Detail and accuracy is sacrificed to some extent in order to provide a (somewhat) simpler view of conditions at 200 seconds into the simulation (approximately 00:27 incident time). Note that as in individual slices, data is presented as a range due to uncertainty in the computer model.

Alternative Model

In addition to modeling fire dynamics based on incident conditions and tactical operations as they occurred, NIST also modeled the incident with a slightly different ventilation profile.

The basic input for the alternate simulation was the same as the simulation of actual incident conditions. Ventilation openings and timing was the same, with one exception; the sliding glass door on Floor 1, Side C was opened at 120 s into the simulation. Conditions in the basement during the alternative simulation were similar to the first. However, on Floor 1, the increase in ventilation provided by the sliding glass door on Side C resulted in a shallower hot gas layer and cooler conditions at floor level. A side-by-side comparison of the temperature gradients in these two simulations is provided in Figure 13.

Figure 13. Comparison of Temperature Gradients Along Centerline of Basement Stairwell (S2) at 200 s

Note: Adapted from Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510 (p. 21 & 27) by Dan Madrzykowski and Robert Vettori, 2000, Gaithersburg, MD: National Institute for Standards and Technology.

The NIST Report (Madrzykowski & Vettori, 2000) identified that the significant difference between these two simulations is in the region close to the floor. In the alternative simulation (Floor 1, Side C Sliding Glass Door Open) between the doorway to the basement and the sofa, the temperatures from approximately 0.6 m (2 ft) above the floor, to floor level are in the range of 20 °C to 100 °C (68°F to 212 °F), providing at least an 80 °C (176 °F) temperature reduction.

While this is a considerable reduction in gas temperature, it is essential to also consider radiant heat flux from the hot gas layer. Given the temperature of the hot gases from the ceiling level to a depth of approximately 3′ (0.9 m), the heat flux at the floor would likely have been in the range of 15-20 kW/m² (or greater).

Questions

1. Temperatures vary widely at a given elevation above the floor. Consider the slices illustrated in Figures 3, 6, and 9, and identify factors that may have influenced these major differences in temperature.
2. How might the variations in temperature illustrated in Figures 3, 6, and9 and location of Firefighters Phillips (basement doorway), Mathews (living room, C/D corner), and Morgan (between Phillips & Mathews) have influenced their injuries?
3. Examine the velocity of gas movement illustrated in Figures 4, 7, and 10 and integrated illustration conditions in Figure 11. How does this correlate to the photos in Figure 1 illustrating incident conditions at approximately 00:28?
4. Explain how the size and configuration of ventilation openings resulted in a bi-directional air track at the basement door on Side C.
5. How did the velocity of hot gases in the stairwell and living room influence the thermal insult to Firefighters Phillips, Mathews, and Morgan? What factors caused the high velocity flow of gases from the basement stairwell doorway into the living room?
6. Rescue 1B noted that the floor in the living room was soft while conducting primary search at approximately 00:30. Why didn’t the parallel chord trusses in the basement fail sooner? Is there a potential relationship between fire behavior and performance of the engineered floor support system in this incident?
7. How might stability of the engineered floor support system have differed if the sliding glass door in the basement had failed prior to the fire departments arrival? Why?
8. How might the double pane glazing on the windows and sliding glass doors have influenced fire development in the basement? How might fire development differed if these building openings had been fitted with single pane glazing?
9. What was the likely influence of turbulence in the flow of hot gases and cooler air on combustion in the basement? What factors influenced this turbulence (examine Figures 4, 7, and 10) illustrating velocity of flow and floor plan illustrated in conjunction with the second question)?
10. How did conditions in the area in which Firefighters Phillips, Mathews, and Morgan were located correlate to the thermal exposure limits defined in Figure 12? How did this change in the alternate scenario? Remember to consider both temperature and heat flux.

Extended Learning Activity

The Cherry Road case study provides an excellent opportunity to develop an understanding of the influence of building factors, burning regime, ventilation, and tactical operations on fire behavior. These lessons can be extended by comparing and contrasting this case with other cases such as the 1999 residential fire in Keokuk, Iowa that took the lives Assistant Chief Dave McNally, Firefighter Jason Bitting, and Firefighter Nathan Tuck along with three young children. For information on this incident see NIOSH Death in the Line of Duty Report F2000-4, NIST report Simulation of the Dynamics of a Fire in a Two Story Duplex, NIST IR 6923.and video animation of Smokeview output from modeling of this incident

Ed Hartin, MS, EFO, MIFireE, CFO

References

District of Columbia (DC) Fire & EMS. (2000). Report from the reconstruction committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999. Washington, DC: Author.

Madrzykowski, D. & Vettori, R. (2000). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510. August 31, 2009 from http://fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf

National Institute for Occupational Safety and Health (NIOSH). (1999). Death in the line of duty, Report 99-21. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

The last post in this series, Incipient Fires: Key Fire Behavior Indicators reviewed stages of fire development (i.e., incipient, growth, fully developed, and decay), burning regimes (i.e., fuel and ventilation controlled) and identified key indicators used to recognize incipient stage fires. This post examines key indicators to identify growth stage fires and their burning regime.

Growth Stage & Burning Regime

Like many concepts in fire dynamics there is a bit of ambiguity between where the incipient stage ends and the growth stage begins. For firefighters, this distinction is important as growth stage fires are deemed to present an Immediately Dangerous to Life and Health (IDLH) threat based on the increasing speed of fire development, toxicity and thermal environment. This triggers Occupational Safety and Health Administration (OSHA) respiratory protection regulations requirements for “two-in/two-out”. Key characteristics of a growth stage fire include increasing heat release rate (HRR), significantly increasing temperature within the compartment.

The speed of fire development in the growth stage may be limited by fuel characteristics and configuration or ventilation. Typically compartment fires in the early growth stage are fuel controlled. However, if the compartment is small and/or has limited ventilation, continued combustion will result in slowing fire development as the fire enters the ventilation controlled burning regime. Recognizing the ventilation controlled burning regime is critical as increases in ventilation will result in increased HRR. This is not necessarily a major problem unless it is unanticipated or firefighters do not have the capacity to control this additional HRR.

A Single Compartment

While most buildings have multiple, interconnected rooms, providing a complex environment for fire development, it is useful to begin by examining fire development in a single compartment (see Figure 1)

Figure 1. Fire Development in a Single Compartment.

Note: Photos adapted from National Institute of Standards and Technology (NIST) ISO-Room/Living Room Flashover [Digital Video Disk].

As a compartment fire develops hot products of combustion and entrained air rise in a plume from the burning fuel package. When the plume reaches the ceiling, hot gases begin to move horizontally, forming a ceiling jet. As the fire progresses through the incipient stage and into growth, additional fuel will become involved and the heat release rate from the fire will increase. While thermal conditions can be considerably more complex, gas temperatures within the compartment may be described as existing in two layers: A hot layer extending down from the ceiling and a cooler layer down towards the floor. Convection resulting from plume and ceiling jet along with radiant heat from the fire and hot particulates in the smoke increases the temperature of the compartment linings and other items in the compartment.

The fire can continue to grow through flame spread or by ignition of other fuel within the compartment. As flames in the plume reach the ceiling they will bend and begin to extend horizontally. Pyrolysis products and flammable byproducts of incomplete combustion in the hot gas layer will ignite and continue this horizontal extension across the ceiling. As the fire moves further into the growth stage, the dominant heat transfer mechanism within the fire compartment shifts from convection to radiation. Radiant heat transfer increases heat flux (transfer of thermal energy) at floor level.

As gases within the compartment are heated they expand and when confined by the compartment increase in pressure. Higher pressure in this layer causes it to push down within the compartment and out through openings. The pressure of the cool gas layer is lower, resulting in inward movement of air from outside the compartment. At the point where these two layers meet, as the hot gases exit through an opening, the pressure is neutral. The interface of the hot and cool gas layers at an opening is commonly referred to as the neutral plane.

If the compartment is sealed (e.g., door closed and windows intact), the fire may become ventilation controlled, slowing the increase in HRR and temperature, and eventually moving the fire into the decay stage (defined by decreasing HRR). However, if the compartment is not sealed (e.g., open door), the fire may become ventilation controlled, but HRR can continue to increase as smoke flows out of the involved compartment and air from the remainder of the building flows in at floor level, providing the oxygen necessary for continued combustion.

In growth stage fires, fire behavior indicators are often visible from the exterior of the building. However, depending on fire location and building factors (e.g., energy efficiency, ventilation profile) these indicators may be fairly obvious or quite subtle. Growth stage indicators are listed in Figure 2

Figure 2. FBI: Growth Stage

In Incipient Fires: Key Fire Behavior Indicators you were presented with a residential fire scenario as an opportunity to give some thought to how key fire behavior indicators may present. Consider

Use the B-SAHF model to help you frame your answers.

You have responded to a fire in a one-story single family dwelling of wood frame construction. A growth stage fire is burning a bedroom on the Alpha Bravo corner of the structure. The fire involves a plastic trash can, the bed, and night stand.

• What conditions would you expect to see from the exterior of the structure?
• What indicators may be visible from the front door as you make entry?
• What indicators would you anticipate observing as you traveled through the living room and down the hallway to the bedroom where the fire is located?
• What conditions would you find in the bedroom?

As the fire moves through the growth stage, the speed at which conditions change increases rapidly. After making entry, consider if conditions are different than you anticipated?

• Why might this be the case?
• What differences in conditions would be cause for concern?

More to Follow

The next post in this series will continue examination of the relationship between the B-SAHF indicators, fire development, and burning regime by connecting to the parallel series of posts on flashover and examining fully developed fires.

Ed Hartin, MS, EFO, MIFireE, CFO

References

National Institute of Standards and Technology. (2005). ISO-room/living room flashover [digital video disk]. Gaithersburg, MD: Author.