Posts Tagged ‘fire behavior’

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

Building Factors, Smoke, Air Track, Heat, and Flame (B-SAHF) are critical fire behavior indicators. Understanding the indicators is important, but more important is the ability to integrate these factors in the process of reading the fire as part of size-up and dynamic risk assessment.

This post reviews application of the B-SAHF organizing scheme to recognizing and identifying stages of fire development and burning regime.

Compartment Fire Development

Part of the process of reading the fire involves recognizing the stages of fire development and burning regime (e.g., fuel or ventilation controlled). Remember that fire conditions can vary considerably throughout the building with one compartment containing a fully developed fire, an adjacent compartment in the growth stage, and still other compartments yet uninvolved. Similarly, burning regime may vary from compartment to compartment. Recognizing the stages of fire development and burning regime allows firefighters to predict what is likely to happen next (if action is not taken), potential changes due to unplanned ventilation (such as failure of a window), and the likely effect of tactical action.

Compartment fire development can be described as being comprised of four stages: incipient, growth, fully developed and decay (see Figure 1). Flashover is not a stage of development, but simply a rapid transition between the growth and fully developed stages.

Figure 1. Heat Release Rate (HRR) and Fire Development

Compartment fires do not always follow the simple, idealized fire development curve illustrated in Figure 1. The speed with which the fire develops, peak heat release rate, and duration of burning are dependent on both the characteristics of the fuel involved and ventilation profile (available oxygen).

Hazard of Ventilation Controlled Fires

Many if not most fires that have progressed beyond the incipient stage when the fire department arrives are ventilation controlled. This means that the heat release rate (the fire’s power) is limited by the ventilation profile, in particular, the existing openings.

If ventilation is increased, either through tactical action or unplanned ventilation resulting from effects of the fire (e.g., failure of a window) or human action (e.g., exiting civilians leaving a door open), heat release rate will increase, potentially resulting in a ventilation induced flashover as illustrated in Figure 2.

Figure 2. Ventilation Induced Flashover

Incipient Stage

Going back to the basics of fire behavior, ignition requires heat, fuel, and oxygen. Once combustion begins, development of an incipient fire is largely dependent on the characteristics and configuration of the fuel involved (fuel controlled fire). Air in the compartment provides adequate oxygen to continue fire development. During this initial phase of fire development, radiant heat warms adjacent fuel and continues the process of pyrolysis. A plume of hot gases and flame rises from the fire and mixes with the cooler air within the room. This transfer of energy begins to increase the overall temperature in the room. As this plume reaches the ceiling, hot gases begin to spread horizontally across the ceiling. Transition beyond the incipient stage is difficult to define in precise terms. However, as flames near the ceiling, the layer of hot gases becomes more clearly defined and increase in volume, the fire has moved beyond its incipient phase and (given adequate oxygen) will continue to grow more quickly.

Depending on the size of the compartment and ventilation profile, there may only be a limited indication (or no indication at all) from the exterior of the building that an incipient stage fire is burning within. Incipient stage indicators are listed in Figure 3

Figure 3. B-SAHF Indicators of an Incipient Stage Fire

Application Exercise

Consider the following situation and how critical fire behavior indicators would present. 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. An incipient fire is burning in a bedroom on the Alpha Bravo corner of the structure. The fire is limited to a plastic trash can containing waste paper which is located next to the bed.

• 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 might you observe traveling through the living room and down the hallway?
• What conditions would you find in the bedroom?

It is essential to think about what you are likely to find inside when observing fire behavior indicators from the exterior and performing a risk assessment. 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 with a look at growth stage fires in both fuel and ventilation controlled burning regimes.

Ed Hartin, MS, EFO, MIFireE, CFO

The first post in this series, Reading the Fire: How to Improve Your Skills, I discussed building a concept map of fire behavior indicators as a method to increase competence in reading the fire. In the 12 posts that followed, we have explored each of the categories of the B-SHAF organizing scheme by developing a concept map for each type of indicator.

• How to Improve Your Skills
• Building Factors
• Building Factors Part 2
• Building Factors Part 3
• Smoke Indicators
• Smoke Indicators Part 2
• Air Track Indicators
• Air Track Indicators Part 2
• Heat Indicators
• Heat Indicators Part 2
• Heat Indicators Part 3
• Flame Indicators
• Flame Indicators Part 2

I have been working through this process as well in an effort to expand and refine my personal B-SAHF concept map. This post will review the work accomplished so far and lay the foundation for moving to the next step in the process; applying B-SAHF to recognize key indicators and predict likely fire behavior.

This review will be graphic, using the current version (5.2.2.1) of each of the concept maps developed in this series of posts.

Building Factors

Unlike the other elements of the B-SAHF organizing scheme for fire behavior indicators, Building Factors are present before the fire. Frank Brannigan was fond of saying “the building is the enemy” (Brannigan & Corbett, 2008, p. 81). The term enemy (2009) can be used to describe one who is antagonistic or seeking to injure or harm another. In this sense the building is not our enemy as it has no intent. However, it may also be used to describe something that is potentially harmful (Enemy, 2009). From this perspective Frank could be correct. However, I find that in the use of warfare as a metaphor for firefighting, I find it more useful to consider the building as the terrain that we fight on, rather than the enemy.

Building factors (such as use of lightweight or engineered wood support systems) present a significant hazard, but only under fire conditions. Fire dynamics and building performance under fire conditions are interrelated and should be key considerations in the pre-planning process.

In many respects, Building Factors is the most complex category of the fire behavior indicators. Figure 1 illustrates my current concept map capturing many (but likely not all) of the key building factors that influence fire behavior.

Figure 1. Building Factors

Consider what other building factors might be of interest or concern as well as how these factors may be interrelated with the other elements of the B-SAHF scheme.

Smoke Indicators

There are a significant number of interrelationships between smoke indicators and the other elements of the B-SAHF model, particularly Building Factors, Air Track, and Heat. These relationships reinforce the importance of looking at fire behavior indicators holistically, rather than simply as individual elements.

Figure 2. Smoke Indicators

Are there other indicators related to smoke that may be useful in identifying or assessing the stage of fire development, burning regime, or other important aspects of fire behavior? What additional interrelationships exist with the other elements of B-SAHF?

Air Track Indicators

Air track is the movement of both smoke (generally out from the fire area) and air (generally in towards the fire area). Air track is caused by pressure differentials inside and outside the compartment and by gravity current (differences in density between the hot smoke and cooler air). Air track indicators include velocity, turbulence, direction, and movement of the hot gas layer. As in the case of smoke, air track is closely interrelated with Building Factors, Smoke, and Heat Indicators.

Figure 3. Air Track Indicators

Are there other air track indicators that might be useful in assessing conditions and making predictions about likely fire behavior? What other interrelationships exist between air track and the other elements of B-SAHF?

Heat Indicators

In considering heat indicators, it is important to distinguish between energy, temperature, and heat. While this category is titled heat indicators, much of what we observe and feel is based on increased temperature due to transfer of energy (energy in transit is heat). To review the discussion of energy, temperature and heat, see Reading the Fire: Heat Indicators.

Figure 4. Heat Indicators

What other heat indicators may be useful in assessing conditions, the risk to firefighters, and impact of tactical operations on fire behavior? Are there additional interrelationships with other elements of B-SAHF?

Flame Indicators

Flames are the visible, light emitting product of combustion. In compartment fires, flames are the result of glowing particulate material (predominantly carbon). While extremely useful, information from flame indicators must be considered in conjunction with the other elements of B-SAHF.

Figure 5. Flame Indicators

Are there other flame related indicators that might be useful? Are there additional interrelationships with other elements of B-SAHF?

Applying B-SAHF

Developing your skill in reading the fire requires ongoing deliberate practice. What does this look like? In the following video clip, Tiger Woods is described as “just a pro who wants his game to get better, every day”

Are we professionals who want our skill at reading the fire to get better, every day? What does will it take for us to accomplish this task? It takes more than just talking about it or attending a class. Developing this level of skill requires ongoing, deliberate practice. Building a concept map of the B-SAHF indicators is an early step in this process as it gives you a way to think about information provided by the building and fire that will allow you to recognize important conditions and what is likely to happen next. Developing this understanding is necessary, but not sufficient. You also need to work on your skill at recognition and developing the ability to interpret this information in the context of the situation.

Using video is a great way to practice your skill in recognizing key indicators. On the fireground, you may only see a particular indicator for a few seconds. There is no instant replay. However, with video you can watch a particular clip again and again to practice your skill and develop the ability to separate critical indicators from the noise of extraneous information.

Practice Your Craft!

Reading the fire and recognizing likely and potential fire development is a critical part of initial size-up and action planning. However, this process needs to continue throughout incident operations as you evaluate the impact of tactical operations (the responsibility of everyone on the fireground, not just officers or the incident commander). Use the following two video clips of tactical operations to practice your skill (and maybe discover a few additional indicators to add to your B-SAHF concept maps).

Video Clip1-Roof Operations: Watch this video clip of vertical ventilation operations and identify the key B-SAHF Indicators. What information do the building, smoke, air track, heat, and flame indicators provide about current conditions? How is fire behavior likely to change?

Video Clip 2-Fire Attack: Watch this video clip of initial attack operations at a commercial fire. What building, smoke, air track, heat, and flame indicators can you observe in this clip? What information do these indicators provide? How do the indicators change based on application of water? What can you determine based these changes?

More to Follow

The next post in this series will begin to examine application of the B-SAHF scheme to recognizing stages of fire development and burning regime as part of initial and ongoing size-up and situation assessment.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Brannigan, F. & Corbett, G. (2008). Building construction for the fire service. Sudbury, MA: Jones & Bartlett.

Enemy. (2009). In Merriam-Webster Online Dictionary. Retrieved September 17, 2009, from http://www.merriam-webster.com/dictionary/enemy

The previous post in this series, Reading the Fire: Flame Indicators briefly looked at flames, the visible, light-emitting product of combustion and identified several basic categories of flame related fire behavior indicators as illustrated in Figure 1.

Figure 1. Basic Flame Indicators

As with each of the B-SAHF (building, smoke, air track, heat, and flame) indicators, it is essential that assessment of flame related indicators is integrated with other elements of the B-SAHF scheme to gain a clearer sense of fire conditions and likely fire behavior.

Size and Location

Location of the flames may provide important information. If flames are visible from outside the structure, where are they coming from? It is important to connect this information with building factors such as compartmentation. Is fire showing from a single window due to compartmentation or simply because that is the only window that has failed? Are the flames pushing from inside a compartment or is smoke igniting and burning outside?

Given the conditions depicted in Figure 2, the size and location of flames make it obvious that the fire involves multiple compartments of this single family dwelling. However, it is important not to be distracted or deceived by conditions observed from one location!

Figure 2. Fire Showing from a Single Family Dwelling

Note: Photo by Marc Caron, Gatineau, Québec Canada

Early on the morning of July 21, 2007; Contra Costa County Engine 70 responded to a residential fire with persons reported at 149 Michelle Drive. On arrival, Engine 70 observed fire showing from the door and large picture window on Side A. From this limited view of the building, the fire appeared to be in the living room with potential for trapped occupants in the bedrooms. Engine 70 went to work knocking down the fire from the doorway and initiating a primary search of the bedrooms. However, conditions were not as simple as they seemed. The fire, which had originated in one of the bedrooms on Side B was burning in a ventilation controlled state with a substantial accumulation of gas phase fuel in the bedrooms and hallway. As Engine 70 conducted their search, increased ventilation returned the fire to flaming combustion, igniting the gas phase fuel (smoke) in a flash fire that killed Captain Matthew Burton and Engineer Scott Desmond (for more information on this incident see: Contra Costa LODD, Contra Costa LODD: Part 2, Contra Costa LODD: What Happened?).

It is absolutely critical that observation of flames be integrated with all of the B-SAHF indicators from more than one perspective. The first arriving officer should conduct a 360^o reconnaissance whenever possible. However, this is not always possible. If the first arriving company cannot accomplish this task, it does not diminish the importance of determining conditions on other sides of the building and another company should be assigned to complete this task as soon as possible.

While working inside the building, what is the flame height? Are the flames impinging on the ceiling and bending to travel horizontally? Do you observe flames in the hot gas layer (i.e., ghosting, rollover)? Fire development speeds considerably after flames in the plume of hot gases reach the ceiling and begin to travel horizontally in the ceiling jet. Isolated flames in the hot gas layer are a strong indicator of a ventilation controlled fire. Flames in the hot gas layer or development of rollover are an important indicator of imminent flashover.

With flame indicators, it is not just what you see that is important. What you do not see is equally important. Remember that the low oxygen concentration in backdraft conditions may preclude flaming combustion (at least in that compartment). However, conditions can vary widely from compartment to compartment (void spaces are compartments too!) and you may have visible flames from the exterior, but quite different conditions inside the building.

As with other fire behavior indicators, change over time is an important indication of fire development or progress towards control. This is particularly true with flaming combustion. Once fire control operations have started, firefighters and fire officers must evaluate the effect of fire streams. Failure of water application to reduce the size of the fire indicates that either the flow rate is inadequate, the application point is ineffective, or both.

Flame Color

Flame color is largely dependent on the type of fuel involved and the extent to which the fuel and oxygen are mixed (see the previous post Reading the Fire: Flame Indicators, Figure 2-Diffusion and Premixed Flames). Because there are several influences on flame color, it is important to interpret this information in context with other fire behavior indicators. Organic materials (natural or synthetic) will tend to burn with light yellow to reddish orange color depending on oxygen concentration as illustrated in Figure 3.

Figure 3. Fire Showing

Note: Photo courtesy of Mercer County Fire Protection District

While flame color can often be observed from the exterior as illustrated in Figure 3, it is also important while working inside as observed by Captain James Mendoza of the San Jose Fire Department.

The coloration of diffusion flames commonly encountered in structure fires runs from red to orange to yellow to almost white. This scale tells you something about the energy of the fire, with the redder the flame, the less temperature and radiant heat it is releasing. Often the lower energy red flames are due to combustion occurring with limited air, and if ventilation is increased, the energy released increases, temperature increases, and color changes from red to orange to yellow to white. So, if you are feeling extreme heat as you move towards dark orange flames, realize the air you just let in by opening the door can make the conditions worse, and you may be able to see that visually by a lighter flame color.

If organic fuel gas or vapor is premixed with air, flame color will be bluish. In compartment fires, a lazy bluish flame moving through the hot gas layer is an indication of a substantially ventilation controlled fire. However, it is important to remember that flame contact with other materials may influence color. For example, flame impinging on copper will have a blue green color.

Less commonly encountered in compartment fires, a bright white flame is usually indicative of high temperature such as that generated by burning metal (i.e., magnesium).

Duration

Given adequate fuel and oxygen, flaming combustion is likely to be continuous. However, when a compartment fire is burning in a ventilation controlled regime, flames may be intermittent as fuel and oxygen concentration varies. Watch the following video and observe the difference in flaming combustion from the window on Side B in the first 45 seconds (0:00 to 0:45) and from the window on Side A the next 30 seconds (00:46 to 1:16). How are the flames different? Why do you think that this is the case?

Work in Progress

Hopefully we have been working on this project together and you have been developing or refining the flame segment of your fire behavior indicators concept map. My current map is illustrated in Figure 4.

Figure 4. Flame Indicators Concept Map v5.2.2.1

You can also download a printer friendly version of the Flame Indicators Concept Map v5.2.2.1 As always, should you have any suggestions or feedback, please post a comment!

Ed Hartin, MS, EFO, MIFireE, CFO

I had intended to continue discussion of flame indicators in this post, but was motivated to address a common fire service myth based on information presented in an article in the New Canaan (Connecticut) Advertiser’s on-line newspaper titled Real ‘Backdraft’.

Figure 1. Backdraft Demonstration

Note: Photos of backdraft demonstration at the Swedish Civil Contingencies Agency College in Revinge, Sweden by Ed Hartin

The Question

The article was written by a fire officer in response to the question” “is there really such a thing as a backdraft as depicted in the 1991 Ron Howard movie by the same name?” His response to the question:

I found the movie very entertaining; however, I was completely distracted by the unrealistic depiction of fire and how it behaved compared to real life. . . . A backdraft occurs when a fire, in a confined space (room or building), has used up the available air and begins to starve for oxygen. When this occurs, great quantities of carbon monoxide (CO) are produced.

We all know that CO is the odorless, colorless and tasteless gas that can kill us. Another lesser known fact is that it is also highly flammable – like propane or natural gas.

This last characteristic is the catalyst for a backdraft. If a door or window is opened and a fresh supply of oxygen is introduced at the right (wrong) time, all of the built up CO will explode with devastating results.

Most action adventure films fail to depict fires and firefighting accurately, fueling (no pun intended) the public’s misperception of the hazards presented in the fire environment. While not likely the result of watching Backdraft and Ladder 49, many fire behavior myths and misperceptions persist in the fire service as well.

Fire Service Myth

The response to the question about backdraft is partially correct, this phenomenon involves introduction of air to a ventilation controlled fire. However, presumption that carbon monoxide is the predominant fuel in backdraft is a common fire service myth that is not supported by scientific research.

As observed by Gorbett and Hopkins (2007), there is considerable misunderstanding about extreme fire behavior such as flashover and backdraft. For example, many fire service texts and standards (e.g., National Fire Protection Association (NFPA) 402 Guide for Aircraft Rescue and Fire-Fighting Operations) continue to perpetuate the misconception that carbon monoxide concentration is a major determinant in the occurrence of backdraft.

Scientific Evidence

A substantial number of scientific studies have demonstrated that the major component of gas phase fuel involved in backdraft phenomenon is unburned, excess pyrolizate from solid fuel (Gottuk, 1999; Gojkovic, 2000; Sutherland, 1999; Fleischmann, 1993; Fleischmann & Pagni, 1993; and Weng & Fan, 2003). While backdraft conditions develop under ventilation controlled conditions with lower than normal (21%) oxygen concentration, the concentration of total hydrocarbons is the primary determinant of backdraft potential (Fleischmann, 1992 Weng & Fan, 2003).

As illustrated in Figure 2, smoke from incomplete combustion of organic materials includes a substantial concentration of unburned pyrolysis products. containing considerable potential (chemical) energy. If this gas phase fuel accumulates in sufficient concentration while the fire is in decay due to limited oxygen, an increase in ventilation may result in a backdraft.

Figure 2. Multi-Compartment Doll’s House Demonstration, Klana Croatia

Note: Photo by Nikola Tramontana, Vatrogasci Opatija, Croatia.

As actor and author Will Rogers said “It’s not what we don’t know that hurts, it’s what we know that ain’t so.” What I learned about fire behavior as a recruit firefighter was incomplete and in some cases inaccurate. I don’t fault the instructors or the textbook that was used as both were the best available at the time. However, it is important that we continue to push at the edges of our understanding of fire behavior and recognize that what we recognize as fact today may not be so tomorrow.

For more information on the backdraft phenomenon, see:

• Hazard of Ventilation Controlled Fires
• Smoke Explosion or Backdraft?
• Language & Understanding: Extreme Fire Behavior
• 15 Years Ago: Backdraft at 62 Watts Street
• 62 Watts Street: Modeling the Backdraft
• Extreme Fire Behavior: An Organizational Scheme (Ontology)
• Gas Explosions
• Gas Explosions Part 2

Barring another target of opportunity, my next post will return to Reading the Fire and revision and extension of the Flame Indicators concept map.

Ed Hartin, MS,EFO, MIFireE, CFO

References

Fleischmann, C. & Pagni, P. (1993) Exploratory backdraft experiments.” Fire Technology, 29(4), 298-316

Fleischmann, C. (1993) Backdraft phenomena, National Institute for Standards and Technology NIST-CGR-94-646). Retrieved March 26, 2009 from http://fire.nist.gov/bfrlpubs/fire94/PDF/f94008.pdf

Gojkovic, D. (2000) Initial backdraft experiments, Lund University. Sweden

Gorbett, G. & Hopkins, R. (2007). The Current Knowledge and Training Regarding Flashover, Backdraft, and Other Rapid Fire Progression Phenomenon. Retrieved March 19, 2009 from http://www.kennedy-fire.com/backdraft%20paper.pdfGottuk, D., Peatross, M., Farley, J. Williams, F. (1999) The development and mitigation of backdraft: A real-scale shipboard study. Fire Technology 33(4), 261-282.

Sutherland, B. (1999) Smoke sxplosions. University of Canterbury: Department of Engineering. Christchurch, New Zealand

Weng, W. & Fan, W. (2003). Critical condition of backdraft in compartment fires: A reduced scale experimental study. Journal of Loss Prevention in the Process Industries, 16, 19-26.

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 a commercial fire. In addition to practicing your skill in reading the fire, use these video clips to help develop or refine your smoke indicators concept map (see Reading the Fire: Smoke Indicators).

Commercial Fire

The Lake Station (IN) Fire Department was dispatched to a reported structure fire in the vicinity of the American Legion Hall on Central Avenue. Responding companies found a commercial building with fire and smoke showing at the intersection of Central Avenue and Howard Street.

Download and the B-SAHF Worksheet.

While the video clip of this incident does not allow you to walk around the building and observe fire conditions, Google maps street view allows you to view all sides of the building. If you haven’t used street view, have a look at the following Google Street View Tutorial.

Perform a “walkaround” by clicking on the following link to view the building involved at this incident: 1691 Central Ave, Lake Station, IN. Note: Radio communication in the video clip identifies the Incident Commander as “Howard Command”. However, for this activity, I have identified Central Avenue as the A Side of the involved building. Click on the arrows to move east on Central Avenue and move and adjust the compass rose to look at Side D. Move back along Central Avenue and then go down Howard Street, again adjusting the compass rose to look at Sides B and C. After your “walk around”, complete the Building Factors segment of the B-SAHF Worksheet.

The video clip of this incident begins with the view of Side B from the A/B Corner prior to the arrival of the first engine company. 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 (add to what you have done so far), 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?

Watch the next three minutes of the video and identify if, and how conditions change from the beginning of the clip until the first line is placed in operation (at approximately 04:00).

Watch the next 2 minutes 30 seconds until the firefighters make entry through the door on Side A (at approximately 06:30).

1. What conditions would you expect to find inside this part of the building?
2. How would you expect the fire to develop over the next two to three minutes?

Watch the remainder of the video clip.

Important: While not related to Reading the Fire, you likely heard the Personal Alert Safety System (PASS) device sounding through much of the incident. While PASS devices can (and often are) accidentally activated, continuous sounding of a PASS indicates a firefighter in distress. While this was not the case in this incident, failure to silence PASS devices that are accidentally activated desensitizes firefighters to this important audible signal.

Remember the Past

August 1994 saw the loss of two company officers and a firefighter in three separate incidents involving extreme fire behavior. Rapidly changing fire conditions are a threat to firefighters working in career staffed, urban fire departments and volunteer departments serving small communities.

August 7, 1994
Captain Wayne Smith
Fire Department of the City of New York, New York

On August 7, Captain Wayne Smith of the New York City Fire Department was critically injured while conducting search and rescue operations on an upper floor of a building when he was trapped by high heat and heavy smoke conditions. Captain Smith was burned over 40 percent of his body and received severe smoke inhalation injuries to his lungs. He died on October 4 from his injuries. Fourteen other firefighters were injured in the blaze. Initial operations were hampered by a faulty fire hydrant across the street from the building.

August 8, 1994
Sergeant Craig Drury
Highview Fire District, Kentucky

On August 8, Sergeant Craig Drury of the Highview (KY) Fire District was caught in a flashover while making entry into a single story house. Sgt. Drury suffered severe burns to his lungs that eventually caused his death. The fire was started by an arsonist.

August 27, 1994
Firefighter Paul MacMurray
Hudson Falls Volunteer Fire Department, New York

On August 27, Firefighter Paul MacMurray of the Hudson Falls (NY) Volunteer Fire Department responded as part of an engine company to a fire on the first floor of in a three story hotel. Assigned to search for and rescue occupants on the second floor, MacMurray and another firefighter successfully evacuated several victims while attempts to extinguish the fire were initiated below them. Upon their return to continue the search, conditions quickly changed from a light haze of smoke to black smoke with high heat conditions. MacMurray and his partner became separated in their attempt to locate the stairwell and get out of the building. The other firefighter made several efforts to locate MacMurray, but was forced to retreat due to untenable conditions. Several rescue efforts were made but heavy fire conditions eventually forced the evacuation of all fire personnel to defensive positions as the entire structure burned. MacMurray’s body was recovered the following day. The fire was of incendiary origin.

Ed Hartin, MS, EFO, MIFIreE, CFO

I originally intended to write this post about the influence of air track on flashover in multiple compartments. However, after several conversations in the last week about the bathtub analogy and ventilation induced flashover, I had a change in plans.

The Bathtub Analogy

In Understanding Flashover: Myths and Misconceptions, I presented the bathtub analogy (Kennedy & Kennedy , 2003)as a simplified way of understanding how flashover occurs when a compartment fire is burning in a fuel controlled regime.

Flashover has been analogously compared to the filling of a bathtub with the drain open. In this practical, though not perfect, analogy water represents the heat energy. The quantity of water available is the total heat of combustion of the available fuels (fuel load). The size of the spigot and the water pressure control the amount of water flow that is the heat release rate. The volume of the bathtub is analogous to the volume of the compartment and its ability to contain the heat energy. The size and location of the bathtub drain controlling the rate of water loss is the loss of heat energy through venting and conductance. In this analogy, if the bathtub becomes full and overflows, flashover occurs. (Kennedy & Kennedy, 2003, p. 7)

Figure 1. The Bathtub Analogy-Fuel Controlled Burning Regime

Note: Adapted from Flashover and fire analysis: A discussion of the practical use of flashover in fire investigation, p. 7, by Patrick Kennedy & Kathryn Kennedy, 2003. Sarasota, FL: Kennedy and Associates, Inc.

All Models are Wrong

While the bathtub model provides a simple explanation and makes it easy to understand how flashover might occur, it is inaccurate. However, as Box and Draper (1987) stated: “Essentially, all models are wrong, but some are useful” p. 424).

Models or analogies provide a way of understanding based on simplification. This is useful, but this simplification, while providing a starting point for understanding can overlook important concepts or elements of a complex system. In the case of the bathtub analogy, simplification overlooks the criticality of oxygen to the combustion process.

Ventilation is the exchange of the atmosphere inside a compartment with that which is outside. This process is necessary and ongoing in any space designed for human habitation. In a compartment fire, ventilation involves the exhaust of smoke and intake of air from outside the compartment.  Note that this is different than tactical ventilation, which is the planned and systematic removal of hot smoke and fire gases and their replacement with fresh air. However, both normal and tactical ventilation involve exhaust of the compartment atmosphere and replacement with fresh air.

While the bathtub analogy is simple, and provides a useful starting point, it fails to address the air side of the ventilation equation. As ventilation is increased, the compartment looses energy through convection. However, if the fire is ventilation controlled (heat release rate (HRR)is limited by the available oxygen), increased ventilation will also increase HRR.

Revised Bathtub Analogy

For many years, firefighters have been taught tactical ventilation prevents or slows progression to flashover. Somewhat less commonly, firefighters have been taught to close the door to the fire compartment, limiting inward air flow and slowing fire growth (tactical anti-ventilation). My friend and colleague Inspector John McDonough of the New South Wales (AU) Fire Brigades refers to this as the Ventilation Paradox. Increased ventilation increases the HRR required for flashover to occur and may prevent or slow progression to flashover or it may (and often does) result in flashover. Reduction in ventilation may prevent or slow progress to flashover, but also reduces the HRR required for flashover to occur and (less commonly) may result in flashover. It depends! Not the answer that firefighters want to hear.

Making the bathtub analogy a bit more complex may provide a starting point for understanding the ventilation paradox. At the root of this apparent paradox is the impact of ventilation on the thermodynamic system and the relationship between oxygen and release of energy from fuel (Thornton’s Rule). See Fuel and Ventilation [LINK) for more information on Thornton’s Rule and the relationship between oxygen, fuel, and energy.

As illustrated in Figure 2, the revised bathtub analogy incorporates several changes. The inlet pipe has been enlarged (making it larger than the drain) and valves have been added to both the inlet and drain pipes. Most importantly, control of the valves is interconnected (but this is not shown visually as it makes the drawing even more complicated). Changing the position of either the inlet or drain, results in a corresponding change in the other valve.

Figure 2. Revised Bathtub Analogy-Ventilation Controlled Burning Regime

This analogy provides a reasonable (but still overly simplified and thus somewhat inaccurate) representation of a ventilation controlled compartment fire when normal building openings (e.g., doors, windows) serve as ventilation openings.

As illustrated in Figure 2, opening the drain also results in an increase in flow from the (larger) inlet, which without intervention is likely to result in the tub overflowing. In a compartment fire, increasing ventilation to a when the fire is burning in a ventilation controlled regime, increases convective heat loss, but HRR will also increase, potentially resulting in flashover.

Resolving the Paradox

Resolution of the problems presented by the paradox involve recognition of what burning regime the fire is in (fuel or ventilation controlled), understanding the influence of the location and size of ventilation openings on convective heat loss, understanding the influence of increased air intake on HRR, and coordination of ventilation and fire control tactics. On the surface, this all sounds quite simple, but is considerably more complex in practice.

Feedback

I would like to thank my friend and colleague Lieutenant Chris Baird, Gresham Fire & Emergency Services and my wife Sue for serving as my sounding board as I worked through the process of revising the bathtub analogy. As always your feedback and suggestions will be greatly appreciated.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Box, G.& Draper, N. (1987). Empirical Model-Building and Response Surfaces, San Francisco: Wiley & Sons.

Kennedy, P. & Kennedy, K. (2003). Flashover and fire analysis: A discussion of the practical use of flashover in fire investigation. Retrieved July 30, 2009 from http://www.kennedy-fire.com/Flashover.pdf

A Quick Review

The first post in this series, Understanding Flashover: Myths & Misconceptions provided a definition of flashover and examined this extreme fire behavior phenomenon in the context of fire development in a compartment.

Flashover is the 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….Flashover may occur as the fire develops in a compartment or additional air is provided to a ventilation-controlled fire (that has insufficient fuel in the gas phase and/or temperature to backdraft).

Burning Regime

In the incipient and early growth stages of a compartment fire, the speed of fire growth is fuel controlled as fire development substantially influenced by the chemical and physical characteristics of the fuel. However, oxygen is required for the fuel to burn and release thermal energy. As a compartment fire develops, the available air supply for combustion becomes a more important factor. Increased combustion requires more oxygen and as smoke fills the compartment while the lowering neutral plane at compartment openings restricts the introduction of air into the compartment (see Figure 1).

The neutral plane is the level at a compartment opening where the difference in pressure exerted by expansion and buoyancy of hot smoke flowing out of the opening and the inward pressure of cooler, ambient temperature air flowing in through the opening is equal (Karlsson & Quintiere, 2000).

Figure 1. Lowering Neutral Plane

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

The distinction between fuel controlled and ventilation controlled is critical to understanding compartment fire behavior. Compartment fires are generally fuel controlled while in the incipient and early growth stage and again as the fire decays and the demand for oxygen is reduced (see Figure 2).

Figure 3. Fire Development with Limited Ventilation

While a fire is fuel controlled, the rate of heat release and speed of development is limited by fuel characteristics as air within the compartment and the existing ventilation profile provide sufficient oxygen for fire development. However, as the fire grows the demand for oxygen increases, and at some point (based on the vent profile) will exceed what is available. At this point the fire transitions to ventilation control. As illustrated in Figure 1, a ventilation controlled fire may reach flashover, all that is necessary is that sufficient oxygen be available for the fire to achieve a sufficient heat release rate for flashover to occur.

Heat Release and Oxygen

Combustion, as an oxidation reaction requires sufficient oxygen to react with the available fuel. Heat of combustion (energy released) and oxygen required for complete combustion are directly related (Thornton, 1917).The energy released per gram of oxygen consumed during complete combustion of natural and synthetic organic fuels is fairly consistent, averaging 13.1 kJ/g (±0.5%) (Huggett, 1980).

Release of chemical potential energy from fuel is dependent on availability of adequate oxygen for the combustion reaction to occur. Interestingly, while the heat of combustion of various types of organic (carbon based) fuel varies widely, the amount of oxygen required for release of a given amount of energy remains remarkably consistent.

In the early 1900s, British scientist W.M. Thornton (1917) discovered that the amount of oxygen required per unit of energy released from many common hydrocarbons and hydrocarbon derivatives is fairly constant. In the 1970’s, researchers at the National Bureau of Standards independently discovered the same thing and extended this work to include many other types of organic materials and examined both complete and incomplete combustion (Huggett, 1980; Parker, 1977).

Each kilogram of oxygen used in the combustion of common organic materials results in release of 13.1 MJ of energy. This is referred to as Thornton’s Rule. See Fuel and Ventilation for a more detailed discussion of the application of Thornton’s Rule to compartment fires and ventilation.

Failure to Reach Flashover

Ventilation controlled compartment fires may reach flashover and fully developed compartment fires are generally ventilation controlled (IAAI, 2009). However, lack of ventilation may prevent a compartment fire from generating sufficient heat release rate to reach flashover. In some cases, ventilation controlled fires to not become fully developed, but decay and self-extinguish due to lack of oxygen.

In late 2007 an engine and truck company responded to a report of an odor of smoke in a three-story, wood-frame, apartment building. They discovered a ground floor apartment was smoke logged. They requested a first alarm assignment, forced entry, and initiated fire attack and primary search. Smoke was cool and to the floor, the fire was confined to an upholstered chair and miscellaneous items in the living room and at the time of entry was simply smoldering (see Figure 3). A rapid search discovered a deceased occupant in a bedroom remote from the fire.

Figure 3. Self-Extinguished Compartment Fire

Note: Gresham Fire & Emergency Services Photo

While a fire involving an upholstered chair typically results in sufficient heat release rate for the fire to extend to other nearby fuel packages and ultimately reach flashover, this fire did not as evidenced by the condition of the Christmas tree on the opposite side of the living room from the point of origin (see Figure 4). The Christmas tree, like many other fuel packages in the apartment showed evidence of pyrolysis, but did not ignite.

Figure 4. Condition of Other Fuel Packages

Note: Gresham Fire & Emergency Services Photo

Why didn’t this fire reach flashover? The fire occurred in early winter and the apartment’s energy efficient windows and doors were tightly closed. The developing fire consumed the oxygen available within the apartment and absent significant ventilation, decayed, and the temperature inside the apartment which had been increasing as the fire developed, dropped to a temperature slightly higher than would normally be expected inside an occupied apartment.

How might the development of this fire been different if it had been discovered earlier? What if a neighbor had opened a door or window in an effort to rescue the occupant? What if the fire department had opened the door without recognizing that the fire was significantly ventilation controlled?

When fire development is limited by the ventilation profile of the compartment, changes in ventilation will directly influence fire behavior. Reducing ventilation (i.e. by closing a door) will reduce the rate of heat release and slow fire development. Increasing ventilation (i.e. by opening a door or window) will increase the rate of heat release and speed fire development. Changes in ventilation profile may be fire caused (failure of glass in a window), occupants (leaving a door open), or tactical action by firefighters; but all will have an influence on fire behavior!

Figure 5. Ventilation Induced Flashover

For many years firefighters have been taught that ventilation reduces the potential for flashover. While this is sometimes true, it is only part of the story. Increasing ventilation to a fuel controlled fire will allow hot gases to exit, transferring thermal energy out of the compartment and replacing the hot gases with cooler air (which increases heat release rate). The combined influence of these two factors slows progression towards flashover and increases the heat release rate required to reach flashover. The bathtub analogy presented in Understanding Flashover: Myths and Misconceptions [LINK], does not apply in this case, because when a fire is ventilation controlled, heat release rate is limited by the available oxygen. Under ventilation controlled conditions; increasing air supply by creating opening results in increased heat release rate. This increased heat release rate may result in flashover (see Figure 5). For more information see Hazards of Ventilation Controlled Fires.

Two Paths to Flashover

With adequate fuel and oxygen, a growth stage compartment fire may flashover and rapidly transition to the fully developed stage. Given adequate fuel, but lacking adequate oxygen (due to limited ventilation), a growth stage compartment fire may begin to decay before becoming fully developed. However, this can quickly change if ventilation is increased, potentially resulting in ventilation induced flashover.

Understanding these two paths to flashover is essential, but still does not provide a complete picture of the flashover phenomena. The next post in this series will will use several case studies to examine the influence of air track on flashover in multiple compartments the threat that rapid fire progression presents to firefighters.

Ed Hartin, MS, EFO, MIFIreE, CFO

References

Karlsson, B. & Quintiere, J. (2000). Enclosure fire dynamics. New York: CRC Press.

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

Thornton, W. (1917). The relation of oxygen to the heat of combustion of organic compounds. The Philosophical Magazine,33(6), 196-203.

Parker, W. (1977). An investigation of the Fire Environment in the ASTM E 84 Tunnel Test, NBS Technical Note945. Gaithersburg, MD: U.S. Department of Commerce/National Bureau of Standards.

International Association of Arson Investigators (IAAI). (2009). Post flashover fires. On-Line Training Program, Downloaded August 6, 2009 from http://www.cfitrainer.net.

In Reading the Fire: How to Improve Your Skills, I discussed building a concept map of fire behavior indicators as a method to increase competence in reading the fire. Construction of a concept map increases awareness of key indicators and understanding their interrelationships. I am working through this process along with you, with the latest revision to my concept map. Thus far, I have examined Building Factors, the first category of indicators in the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme. For review of the discussion of building factors and revision of this segment of my concept map see the following three posts:

Reading the Fire: Building Factors

Reading the Fire: Building Factors Part 2

Reading the Fire: Building Factors Part 3

Focus Question

As pointed out at the start of this project, a concept map starts with a focus question that specifies the problem or issue that the map is intended to help resolve. The fire behavior indicators (FBI) concept map starts with the following focus question:

What building, smoke, air track, heat, and flame indicators
provide clues to current and potential fire behavior?

It is important to remember that a concept map is never finished. After you develop the first draft, it is always necessary to revise the map to increase clarity or add important concepts that you discover as work continues.

In the next few posts in the series, we will apply this focus question to smoke indicators.

Smoke Versus Air Track

There are a number of interrelationships between Smoke and Air Track. However, in the B-SAHF organizing scheme they are considered separately. As we begin to develop or refine the map of Smoke Indicators it is useful to revisit the difference between these two categories in the B-SAHF scheme as outlined in Reading the Fire: Building Factors

Smoke: What does the smoke look like and where is it coming from? This indicator can be extremely useful in determining the location and extent of the fire. Smoke indicators may be visible on the exterior as well as inside the building. Don’t forget that size-up and dynamic risk assessment must continue after you have made entry!

Air Track: Related to smoke, air track is the movement of both smoke (generally out from the fire area) and air (generally in towards the fire area). Observation of air track starts from the exterior but becomes more critical when making entry. What does the air track look like at the door? Air track continues to be significant when you are working on the interior.

Getting Started

When reading the fire it is important not to focus on a single indicator or category of indicators. However, Smoke Indicators often provide critical information about stages of fire development, burning regime, and differences in conditions throughout the building.

As always in developing a concept map it is important to move from general concepts to those that are more specific. Basic smoke indicators may include location, optical density (thickness), color, physical density (buoyancy), and volume as illustrated in Figure 1. However, you may choose to approach this somewhat differently.

Figure 1. Basic Smoke Indicators

Developing the Detail

Expanding the map requires identification of additional detail for each of the fundamental concepts. If an idea appears to be obviously related to one of the concepts already on the map, go ahead and add it. If you are unsure of where it might go, but it seems important, list it off to the side in a staging area for possible additions. Download a printer friendly version of Smoke Indicators to use as a starting point for this process.

Next Steps

Remember that the process of contracting your own map is likely as important as the (never quite) finished product. The following steps may help you expand and refine the Smoke Indicators segment of the map:

• Look at each of the subcategories individually and brainstorm additional detail. This works best if you collaborate with others.
• Have a look at the following video clip using your partially completed map and notes as a guide to identifying important smoke indicators. Think about what the smoke indicators mean and visualize developing fire conditions inside the building.

The following video has some excellent smoke indicators towards the middle of the clip that may aid in developing and refining your Smoke Indicators concept map.

Step Back and Look at the Entire Picture

I would not want to waste the opportunity to engage with the rest of the B-SAHF indicators. Download and print the B-SAHF Worksheet. Consider the information provided in each of the short video clips and complete the worksheet for each. 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

Twitter

While I did not get any response from the questions I posted on Twitter related to Building Factors, I will continue this practice as we explore smoke indicators. Have a look [http://twitter.com/edhartin] and join in by responding to the questions. End your comments related to Fire Behavior Indicators on Twitter with #B-SAHF (this hashtag simplifies searching for FBI related posts). In addition to B-SAHF questions, I also post links to video clips and fire behavior related new items on Twitter.

Ed Hartin, MS, EFO, MIFireE, CFO

While I have not had much input (via Twitter or post comments), I have been working on the Building Factors map to include factors related to the surrounding environment and to revise fire protection systems, construction, fuel, size, and ventilation profile.

Surrounding Environment

Previous versions of the fire behavior indicators (FBI) concept map considered wind effects as a component of air track (which it influences significantly), but did not consider other environmental influences on fire behavior. After considerable thought, I recognized that building factors (and to some extent all of the FBI) can be viewed like Matryoshka Dolls (nested Russian dolls) when used to think about a single compartment, the building, or the building in its surrounding environment.

Environmental factors include exposures (which fire can extend from or to), ambient weather conditions, and terrain. Weather and terrain likely deserve a bit of explanation. While these factors are recognized as major players in wildland fire behavior, their influence is often not as quickly recognized in the built environment. Wind is likely the greatest meteorological concern when dealing with compartment fires. As discussed in prior posts (Wind Driven Fires, NIST Wind Driven Fire Experiments: Establishing a Baseline, Evaluating Firefighting Tactics Under Wind Driven Conditions), wind driven fires present a significant threat to firefighters. However, while buildings are generally designed to minimize the impact of temperature, humidity, and precipitation on their occupants, these factors can influence fire behavior directly or indirectly. For example, combustible exterior surfaces (e.g., wood shingle or shake roofs) present an increased hazard if humidity is low and ambient temperature is high. The influence of terrain may not be quite as obvious. In some cases, terrain may influence wind effects and in others slope may result in differences in elevation on each side of the building. When unrecognized, this has been a factor in a number of firefighter fatalities due to the resulting air track and path of fire spread from lower, to upper floors. For example see NIOSH (1999) Death in the Line of Duty Report F99-21 and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C. (NIST, 2000).

Fire Protection Systems

Fire suppression systems such as automatic sprinklers can obviously have a direct influence on fire development in a protected compartment. Similarly, fire detection may reduce the time between ignition and intervention by the fire department. However, prior versions of the FBI concept map did not include passive fire protection such as fire rated separations (other than generically as compartmentation).

Construction & Fuel

Prior versions of the FBI map linked Building to Contents and Construction. I have changed this to consider both contents and construction as fuel, while maintaining a link between building factors and construction as there are other facets of construction that can influence fire behavior. However, this area of the map remains a bit tentative (with more work to be done). Other changes to this part of the map include the addition of fire load density (kJ/m2) and increasing clarity of the concepts related to flow rate requirements for fire control.

Size

The concept of size can be a bit confusing as it applies to individual compartments (habitable or void spaces), interconnected compartments, and the entire building. Refinements include the addition of void spaces and normal door position to the concept of compartmentation.

Ventilation Profile

Thermal performance of potential openings has been added to ventilation profile, recognizing that single pane windows perform considerably different than multi-pane, energy efficient windows under fire conditions. In addition, a note was added to clarify that ventilation may be from compartment to compartment or from the building to the external environment.

Figure 1. Building Factors Concept Map v5.2.2.1

You can also download a larger, printer friendly version of the Building Factors Concept Map v5.2.2.1 (including notes made during development). Several colleagues who have had a look at this map observed that it is extremely complicated. While this is true, if you take the time to examine each of the factors and give some thought to the interrelated influences on fire behavior, it becomes a bit clearer. Remember that this is my representation of the concepts, yours will likely be a bit different! As always, feedback is greatly appreciated.

Subsequent posts will examine the rest of the B-SAHF (Building, Smoke, Air Track, Heat, & Flame) organizing scheme for fire behavior indicators.

Ed Hartin, MS, EFO, MIFireE, CFO

References

National Institute for Occupational Safety and Health (NIOSH) (1999) Death in the line of duty report F99-21. Retrieved July 2, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face9921.pdf

National Insitute for Standards and Technology (NIST). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C. Retrieved July 2, 2009 from http://www.fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf