Archive for the ‘Extreme Fire Behavior’ Category

This post continues study of an incident that resulted in two line-of-duty deaths as a result of extreme fire behavior in a townhouse style apartment building in Washington, DC.

A Quick Review

The previous post in this series, Fire Behavior Case Study of a Townhouse Fire: Washington, DC examined building construction and configuration that had a significant impact on the outcome of this incident. The fire occurred in the basement of a two-story, middle of building, townhouse style apartment with a daylight basement. This configuration provided an at grade entrance to the Floor 1 on Side A and an at grade entrance to the Basement on Side C.

The fire originated in an electrical junction box attached to a fluorescent light fixture in the basement ceiling (see Figures 1 and 2). The occupants of the unit were awakened by a smoke detector. The female occupant noticed smoke coming from the floor vents on Floor 2. She proceeded downstairs and opened the front door and then proceeded down the first floor hallway towards Side C, but encountered thick smoke and high temperature. The female and male occupants exited the structure, leaving the front door open, and made contact with the occupant of an adjacent unit who notified the DC Fire & EMS Department at 0017 hours.

Dispatch Information

At 00:17, DC Fire & EMS Communications Division dispatched a first alarm assignment consisting of Engines 26, 17, 10, 12, Trucks 15, 4, Rescue Squad 1, and Battalion 1 to 3150 Cherry Road NE. At 0019 Communications received a second call, reporting a fire in the basement of 3146 Cherry Road NE. Communications transmitted the update with the change of address and report of smoke coming from the basement. However, only one of the responding companies (Engine 26) acknowledged the updated information.

Weather Conditions

Temperature was approximately 66^o F (19^o C) with south to southwest winds at 5-10 mi/hr (8-16 km/h), mostly clear with no precipitation.

Conditions on Arrival

Approaching the incident, Engine 26 observed smoke blowing across Bladensburg Road. Engine 26 arrived at a hydrant at the corner of Banneker Drive and Cherry Road at 00:22 hours and reported smoke showing. A short time later, Engine 26 provided an updated size-up with heavy smoke showing from Side A of a two story row house. Based on this report, Battalion 1 ordered a working fire dispatch and a special call for the Hazmat Unit at 00:23. This added Engine 14, Battalion 2, Medic 17 and EMS Supervisor, Air Unit, Duty Safety Officer, and Hazmat Unit.

Firefighting Operations

DC Fire and EMS Department standard operating procedures (SOP) specify apparatus placement and company assignments based on dispatch (anticipated arrival) order. Note that dispatch order (i.e., first due, second due) may de different than order of arrival if companies are delayed by traffic or are out of quarters.

Standard Operating Procedures

Operations from Side A

The first due engine lays a supply line to Side A, and in the case of basement fires, the first line is positioned to protect companies performing primary search on upper floors by placing a line to cover the interior stairway to the basement. The first due engine is backed up by the third due engine. The apparatus operator of the third due engine takes over the hydrant and pumps supply line(s) laid by the first due engine, while the crew advances a backup line to support protection of interior exposures and fire attack from Side A.

The first due truck takes a position on Side A and is responsible for utility control and placement of ladders for access, egress, and rescue on Side A. If not needed for rescue, the aerial is raised to the roof to provide access for ventilation.

The rescue squad positions on Side A (unless otherwise ordered by Command) and is assigned to primary search using two teams of two. One team searches the fire floor, the other searches above the fire floor. The apparatus operator assists by performing forcible entry, exterior ventilation, monitoring search progress, and providing emergency medical care as necessary.

Operations from Side C

The second due engine lays a supply line to the rear of the building (Side C), and in the case of basement fires, is assigned to fire attack if exterior access to the basement is available and if it is determined that the first and third due engines are in a tenable position on Floor 1. The second due engine is responsible for checking conditions in the basement, control of utilities (on Side C), and notifying Command of conditions on Side C. Command must verify that the first and third due engines can maintain tenable positions before directing the second due engine to attack basement fires from the exterior access on Side C.

The second due truck takes a position on Side C and is responsible for placement of ladders for access, egress, and rescue on Side C. The aerial is raised to the roof to provide secondary access for ventilation (unless other tasks take priority).

Command and Control

The battalion chief positions to have an unobstructed view of the incident (if possible) and uses his vehicle as the command post. On greater alarms, the command post is moved to the field command unit.

Notes: This summary of DC Fire & EMS standard operating procedures for structure fires is based on information provided in the reconstruction report and reflects procedures in place at the time of the incident. DC Fire & EMS did not use alpha designations for the sides of a building at the time of this incident. However, this approach is used here (and throughout the case) to provide consistency in terminology.

First due, Engine 26 laid a 3″ (76 mm) supply line from a hydrant at the intersection of Banneker Drive and Cherry Road NE, positioned in the parking lot on Side A, and advanced a 200′ 1-1/2″ ( 61 m 38 mm) pre-connected hoseline to the first floor doorway of the fire unit on Side A (see Figures 1 and 2). A bi-directional air track was evident at the door on Floor 1, Side A , with thick (optically dense) black smoke from the upper area of the open doorway. Engine 26’s entry was delayed due to a breathing apparatus facepiece malfunction. The crew of Engine 26 (Firefighters Mathews and Morgan and the Engine 26 Officer) made at approximately 00:24.

Figure 1. Plot and Floor Plan-3146 Cherry Road NE

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 18 & 20. District of Columbia Fire & EMS, 2000; Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 12-13, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology, and NIOSH Death in the Line of Duty Report 99 F-21, 1999, p. 19.

Engine 10, the third due engine arrived shortly after Engine 26, took the hydrant at the intersection of Banneker Drive and Cherry Road, NE, and pumped Engine 26’s supply line. After Engine 10 arrived at the hydrant, the firefighter from Engine 26 who had remained at the hydrant proceeded to the fire unit and rejoined his crew. Engine 10, advanced a 400′ 1-1/2″ (122 m 38 mm) line from their own apparatus as a backup line. Firefighter Phillips and the Engine 10 officer entered through the door on Floor 1, Side A (see Figure 2) while the other member of their crew remained at the door to assist in advancing the line.

Truck 15, the first due truck arrived at 00:23 and positioned on Side A in the parking lot behind Engine 26. The crew of Truck 15 began laddering Floor 2, Side A, and removed kitchen window on Floor 1, Side A (see Figure 2). Due to security bars on the window, one member of Truck 15 entered the building and removed glass from the window from the interior. After establishing horizontal ventilation, Truck 15 accessed the roof via a portable ladder and began vertical ventilation operations.

Engine 17, the second due engine, arrived at 00:24, laid a 3″ (76 mm) supply line from the intersection of Banneker Drive and Cherry Road NE, to a position on Cherry Road NE just past the parking lot, and in accordance with department procedure, stretched a 350′ 1-1/2″ (107 m 38 mm) line to Side C (see Figure 2).

Approaching Cherry Road from Banneker Drive, Battalion 1 observed a small amount of fire showing in the basement and assigned Truck 4 to Side C. Battalion 1 parked on Cherry Road at the entrance to the parking lot, but was unable to see the building, and proceeded to Side A and assumed a mobile command position.

Second due, Truck 4 proceeded to Side C and observed what appeared to be a number of small fires in the basement at floor level (this was actually flaming pieces of ceiling tile which had dropped to the floor). The officer of Truck 4 did not provide a size-up report to Command regarding conditions on Side C. Truck 4, removed the security bars from the basement sliding glass door using a gasoline powered rotary saw and sledgehammer. After clearing the security grate Truck 4, broke the right side of the sliding glass door to ventilate and access the basement (at approximately 00:27) and then removed the left side of the sliding glass door. The basement door on Side C was opened prior to Engine 17 getting a hoseline in place and charged. After opening the sliding glass door in the basement, Truck 4 attempted to ventilate windows on Floor 2 Side C using the tip of a ladder. They did not hear the glass break and believing that they had been unsuccessful; they left the ladder in place at one of the second floor windows and continued with other tasks.

Figure 2. Location of First Alarm Companies and Hoselines

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 27. District of Columbia Fire & EMS, 2000.

Unknown to Truck 4, these windows had been left open by the exiting occupants. Truck 4B (two person team from Truck 4) returned to their apparatus for a ladder to access the roof from Side C. Rescue 1 arrived at 00:26 and reported to Side C after being advised by the male occupant that everyone was out of the involved unit (this information was not reported to Command). Rescue 1 and Truck 4 observed inward air track (smoke and air) at the exterior basement doorway on Side C and an increase in the size of the flames from burning material on the floor.

Engines 26 and 10 encountered thick smoke and moderate temperature as they advanced their charged 1-1/2″ (38 mm) hoselines from the door on Side A towards Side C in an attempt to locate the fire. As they extended their hoselines into the living room, the temperature was high, but tolerable and the floor felt solid. It is important to note that engineered, lightweight floor support systems such as parallel chord wood trusses do not provide reliable warning of impending failure (e.g., sponginess, sagging), failure is often sudden and catastrophic (NIOSH, 2005; UL, 2009).

Prior to reaching Side C of the involved unit, Engine 17 found that their 350′ 1-1/2″ (107 m 38 mm) hoseline was of insufficient length and needed to extend the line with additional hose.

Engine 12, the fourth arriving engine, picked up Engine 17’s line, completed the hoselay to a hydrant on Banneker Drive (see Figure 2). The crew of Engine 12 then advanced a 200′ 1-1/2″ (61 m 38 mm) hoseline from Engine 26 through the front door of the involved unit on Side A and held in position approximately 3′ (1 m) inside the doorway. This tactical action was contrary to department procedure, as the fourth due engine has a standing assignment to stretch a backup line to Side C.

Rescue 1’s B Team (Rescue 1B) and a firefighter from Truck 4 entered the basement without a hoseline in an effort to conduct primary search and access the upper floors via the interior stairway. Engine 17 reported that the fire was small and requested that Engine 17 apparatus charge their line.

Questions

Consider the following questions related to the interrelationship between strategies, tactics, and fire behavior:

1. Based on the information provided to this point, what was the stage of fire development and burning regime in the basement when Engine 26 entered through the door on Floor 1, Side A? What leads you to this conclusion?
2. What impact do you believe Truck 4’s actions to open the Basement door on Side C will have on the fire burning in the basement? Why?
3. What is indicated by the strong inward flow of air after the Basement door on Side C is opened? How will this change in ventilation profile impact on air track within the structure?
4. Did the companies at this incident operate consistently with DC Fire & EMS SOP? If not, how might this have influenced the effectiveness of operations?
5. Committing companies with hoselines to the first floor when a fire is located in the basement may be able to protect crews conducting search (as outlined in the DC Fire & EMS SOP). However, what building factors increased the level of risk of this practice in this incident?

More to Follow

My next post will examine the extreme fire behavior phenomena that trapped Firefighters Phillips, Mathews, and Morgan and efforts to rescue them.

Remember the Past

This week marked the anniversary of the largest loss of life in a line-of-duty death incident in the history of the American fire service. Each September, we stop and remember the sacrifice made by those 343 firefighters. However, it is also important to remember and learn from events that take the lives of individual firefighters. In an effort to encourage us to remember the lessons of the past and continue our study of fire behavior, each month I include brief narratives and links to NIOSH Death in the Line of Duty reports and other documentation in my posts.

September 9, 2006
Acting CAPT Vincent R. Neglia
North Hudson Regional Fire & Rescue Department, NJ

Captain Neglia and other firefighters were dispatched to a report of fire in a three-story apartment building in Union City. Upon their arrival at the scene, firefighters found light smoke and no visible fire. Based on reports that the structure had not been evacuated, Captain Neglia and other firefighters entered the building to perform a search. Due to the light smoke conditions, Captain Neglia was not wearing his facepiece.

Captain Neglia was the first firefighter to enter an apartment. Conditions deteriorated rapidly as fire in the cockloft broke through a ceiling . Captain Neglia was trapped by rapid fire progress and subsequent collapse. Other firefighters came to his aid and removed him from the building. Captain Neglia was transported to the hospital but later died of a combination of smoke inhalation and burns.

NIOSH did not investigate and prepare a report on the incident that took the life of Captain Neglia.

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

National Institute for Occupational Safety and Health (NIOSH). (2005). NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters Due to Truss System Failures. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

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.

This series of posts focused on Understanding Flashover has provided a definition of flashover; examined flashover in the context of fire development in both fuel and ventilation controlled fires; and looked at the importance of air track on rapid fire progression through multiple compartments. To review prior posts see:

• Myths and Misconceptions
• Myths and Misconceptions: Part 2
• The Ventilation Paradox
• The Importance of Air Track

This post begins study of an incident that resulted in two line-of-duty deaths as a result of extreme fire behavior in a townhouse style apartment building in Washington, DC. This case study provides an excellent learning opportunity as it was one of the first times that the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator (FDS) and Smokeview were used in forensic fire scene reconstruction to investigate fire dynamics involved in a line-of-duty death. Data development of this case study was obtained from Death in the line of duty, Report 99-21 (NIOSH, 1999), Report from the reconstruction committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999 (District of Columbia (DC Fire & EMS, 2000), and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999 (Madrzykowski & Vettori, 2000).

The Case

In 1999, two firefighters in Washington, DC died and two others were severely injured as a result of being trapped and injured by rapid fire progress. The fire occurred in the basement of a two-story, middle of building, townhouse apartment with a daylight basement (two stories on Side A, three stories on Side C).

Figure 1. Cross Section of 3146 Cherry Road NE

The first arriving crews entered Floor 1 from Side A to search for the location of the fire. Another crew approached from the rear and made entry to the basement through a patio door on Side C. Due to some confusion about the configuration of the building and Command’s belief that the crews were operating on the same level, the crew at the rear was directed not to attack the fire. During fireground operations, the fire in the basement intensified and rapidly extended to the first floor via the open, interior stairway.

Building Information

The unit involved in this incident was a middle of row 18′ x 33′ (5.6 m x 10.1 m) two-story townhouse with a daylight basement (see Figures 1 and 3). The building was of wood frame construction with brick veneer exterior and non-combustible masonry firewalls separating six individual dwelling units. Floors were supported by lightweight, parallel chord wood trusses. This type of engineered floor support system provides substantial strength, but has been demonstrated to fail quickly under fire conditions (NIOSH, 2005). In addition, the design of this type of engineered system results in a substantial interstitial void space between the ceiling and floor as illustrated in Figure 2.

Figure 2. Parallel Chord Truss Construction

Note: This is not an illustration of the floor assembly in the Cherry Road Townhouse. It is provided to illustrate the characteristics of wood, parallel chord truss construction.

The trusses ran from the walls on Sides A and C and were supported by steel beams and columns at the center of the unit (See Figure 3). The basement ceiling consisted of wood fiber ceiling tiles on wood furring strips which were attached to the bottom chord of the floor trusses. Basement walls were covered with gypsum board (sheetrock) and the floor was carpeted. A double glazed sliding glass door protected by metal security bars was located on Side C of the basement, providing access from the exterior. Side C of the structure (see Figure 3) was enclosed by a six-foot wood and masonry fence. The finished basement was used as a family room and was furnished with a mix of upholstered and wood furniture.

The first floor of the townhouse was divided into the living room, dining room, and kitchen. The basement was accessed from the interior via a stairway leading from the living room to the basement. The door to this stairway was open at the time of the fire (see Figures 1 and 3). The walls and ceilings on the first floor were covered with gypsum board (sheetrock) and the floor was carpeted. Contents of the first floor were typical of a residential living room and kitchen. A double glazed sliding glass door protected by metal security bars similar to that in the basement was located on Side C of the first floor. An entry door and double glazed kitchen window were located on Side A (see Figure 3). A stairway led to the second floor from the front entry. The second floor contained bedrooms (but was not substantively involved in this incident). There were double glazed windows on Sides A and C of Floor 2.

Figure 3. Plot and Floor Plan-3146 Cherry Road NE

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 18 & 20. District of Columbia Fire & EMS, 2000; Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 12-13, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology, and NIOSH Death in the Line of Duty Report 99 F-21, 1999, p. 19.

Figure 4. Side A 3146 Cherry Road NE

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 17. District of Columbia Fire & EMS, 2000 and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 5, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology.

Figure5. Side C 3146 Cherry Road NE

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 19. District of Columbia Fire & EMS, 2000 and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 5, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology.

The Fire

The fire originated in an electrical junction box attached to a fluorescent light fixture in the basement ceiling (see Figures 1 and 3). The occupants of the unit were awakened by a smoke detector. The female occupant noticed smoke coming from the floor vents on Floor 2. She proceeded downstairs and opened the front door and then proceeded down the first floor hallway towards Side C, but encountered thick smoke and high temperature. The female and male occupants exited the structure, leaving the front door open, and made contact with the occupant of an adjacent unit who notified the DC Fire & EMS Department at 0017 hours.

Questions

It is important to remember that consideration of how a fire may develop and the relationship between fire behavior and your strategies and tactical operations must begin prior to the time of alarm. Assessment of building factors and fire behavior prediction should be integrated with pre-planning.

1. Based on the information provided about the fire and building conditions, how would you anticipate that this fire would develop?
2. What concerns would you have if you were the first arriving company at this incident?

More to Follow

My next post will examine dispatch information and initial tactical operations by first alarm companies.

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

National Institute for Occupational Safety and Health (NIOSH). (2005). NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters Due to Truss System Failures. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

This is the fourth in a series of posts dealing with flashover, to review prior posts see:

• Understanding Flashover: Myths and Misconceptions
• Understanding Flashover: Myths and Misconceptions: Part 2
• The Ventilation Paradox

As previously discussed flashover requires sufficient heat release rate for the temperature of fuel packages within a compartment to increase sufficiently to ignite and the fire to rapidly transition to the fully developed stage. However, during fire development in a compartment the fire often becomes ventilation controlled, with fire growth and heat release rate limited by the available air supply. In some cases, the fire generates sufficient heat release rate despite being ventilation controlled. In others, there is insufficient oxygen in the air supplied for the fire to reach flashover (unless ventilation is increased). All of this is fairly simple and straightforward if we are examining fire in a single compartment. This simple explanation of flashover is based on fire development in a single compartment, such as that described in the ISO 9705 Fire Tests-Full Scale Room Fire Tests for Surface Products6American Society for Testing and Materials (ASTM) Standard E 603-6 (Figure 1)

Figure 1. Full Scale (Six Sided) Room Fire Test Compartment

Note: Underwriters Laboratory (UL) fire test photo adapted from Fire Behavior in Single Family Dwellings, [PowerPoint Presentation], National Fire Academy.

Things get a bit more complex when a fire occurs in a multi-compartment building as individual compartments are interconnected smoke and flames may extend from compartment to compartment throughout the building.

Ventilation and Air Track

Contrary to the common fire service definition of ventilation as “[planned and] systematic removal of heated air, smoke, and fire gases and replacing them with cooler air (IFSTA, 2008), ventilation is simply the exchange of the atmosphere inside the building with that which is outside. This process is ongoing under normal, non-fire conditions. However, under fire conditions, ventilation also involves movement of smoke and air between compartments as well as discharge of smoke from the building and intake of air from outside the structure.

Remember! If you can see smoke coming from the building, ventilation is occurring (but not necessarily the type or amount of ventilation that you need to effectively control the fire environment and the fire).

The term air track is used to describe the characteristics of air and smoke movement (e.g., direction, velocity). The movement of both air and smoke are important, but the direction and path of smoke movement is particularly significant for several reasons:

• Smoke is fuel
• Hot smoke has energy

Through convection, smoke carries energy away from the fire compartment and transfers this energy to objects having lower temperature (such as other fuel packages or firefighters working inside the building). The rate of heat transfer is substantially dependent on temperature difference and in the case of convection on the velocity of the hot gases. Higher velocity and turbulence results in a higher rate of convective heat transfer (much the same as the increase in wind chill as wind speed increases in a cold environment).

Air Track on a Single Level

Examination of air track on a single level provides a simple way to illustrate the influence of air track on the movement of smoke (think fuel and energy) from compartment to compartment, fire extension, and multi-compartment flashover.

With no significant ventilation (with the exception of slight building leakage) smoke will fill the fire compartment and extend through openings such as doorways to adjacent compartments (see Figure 2). If insufficient oxygen is available from the air within the compartments the fire will become ventilation controlled and growth may slow and the fire may decay (heat release rate lessens)

Figure 2. Limited Ventilation

Note: Unless the building is tightly sealed, there is likely to be some leakage resulting in smoke discharge and inward movement of air.

If an opening is made in the presently uninvolved compartment, smoke will move from the fire to the opening, exiting out the upper area of the opening while cool air moves inward through the bottom of the opening and towards the fire (see Figure 3). This is a bi-directional air track.

Figure 3: Single Opening with Bi-Directional Air Track

As pointed out in The Myth of the Self-Vented Fire and The Ventilation Paradox, providing additional oxygen to a ventilation controlled fire results in increased heat release rate and may result in ventilation induced flashover. However, it is important to consider how this impacts adjacent compartments as well.

Increased heat release rate in a still ventilation controlled fire results in higher hot gas layer temperatures and increased smoke production. Increasing temperature and volume of the hot gas layer will cause it to lower and velocity to increase as the smoke moves through adjacent compartments and out ventilation openings. This increases both radiant and convective heat transfer and potentially speeds progression to flashover in adjacent compartments.

Horizontal tactical ventilation can be accomplished rapidly and may, under some conditions, be a useful approach to improving interior conditions. Increasing the number and size of horizontal openings can raise the level of the hot gas layer (by providing additional exhaust). However, when dealing with a ventilation controlled fire the increased oxygen supplied to the fire will increase heat release rate. In addition, in the absence of wind or application of positive pressure at the entry point, two openings at the same level will result in a bi-directional air track at both openings as illustrated in Figure 4.

Figure 4. Two Openings with a Bi-Directional Air Track

If heat release rate is sufficient, this may result in vent induced flashover in the compartments between the fire and the exhaust openings as illustrated in the following video clip.

Important! Horizontal ventilation is not a bad tactic. However, it is essential to recognize and manage the air track as well as ensuring that ventilation is coordinated with fire attack.

More to Follow

Examination of the flashover phenomenon will continue with a case study involving a 1999 fire in a Washington, DC townhouse that resulted in the line of duty deaths of two firefighters. This incident is particularly important as it is one of the first times that the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator (FDS) and Smokeview were used for forensic fire scene reconstruction. This data, in conjunction with the District of Columbia Fire and EMS Reconstruction Report and National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Report provides a solid basis for understanding the impact of burning regime and air track in multi-compartment, ventilation induced flashover.

Ed Hartin, MS, EFO, MIFireE, CFO

References

International Fire Service Training Association (IFSTA). (2008). Essentials of firefighting (5^th ed.). Stillwater, OK: Fire Protection Publications.

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.

Flashover is likely the most common type of extreme fire behavior encountered in structural firefighting. As my friends and colleagues from Sweden frequently observe, this is not really extreme fire behavior, its normal fire behavior. I think it is both. The term extreme “is framed within the context of our perception with ‘extreme’ defining our limited ability to control it and its potential impact on firefighter safety” (Close, 2005). However, occurrence of flashover is not abnormal or random; it is a simple matter of the chemistry and physics involved in a compartment fire.

Misconceptions

For some time, I have been collecting comments and statements related to extreme fire behavior phenomena in the press, fire service publications, and training materials. While it is quite possible to find accurate information on the phenomena of flashover, misconceptions and erroneous information are also common.

• There may have been a flashover at the home when gas in the air ignited
• Firefighters who responded to the blaze nearly got caught inside when an explosion or dangerous condition called a “flashover” occurred
• A flashover occurs when the air temperature reaches between 900 and 1,000, which is hot enough to ignite any gases that are in the air… The result is potentially deadly explosive conditions
• It’s what we call a flashover, were you have a combustible gas or even dust in the area and then all of a sudden, almost explosive-like, that vapour cloud will ignite
• Firefighters were caught in a rare “flashover,” an instance in which superheated gases and combustible materials simultaneously ignite
• When the room bursts into flame, flashover has occurred

Each of the preceding statements was made (or at least reported to have been made) by experienced fire officers. Failure to recognize and mitigate conditions that may result in flashover during firefighting operations results in significant risk to firefighters. At the core of recognition and mitigation is understanding what flashover is, what causes it, and the conditions necessary for it to occur.

What is Flashover?

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. If flashover occurs, the rate of heat release in the compartment as well as the temperature in the compartment increases rapidly. 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).

Indicators of flashover include a radiant heat flux at the floor of 15-20 kW/m² (radiant heat transfer sufficient to quickly raise ordinary combustibles to their ignition temperature) and average upper layer temperature of 500^o-600^o C (932^o-1112^o F) (Drysdale, 1998). More observable indicators include rapid flame spread and extension of flames out of compartment openings. Compartment windows may also fail due to rapid temperature increases on the inner surface of window glazing (Gorbett & Hopkins (2007).

Figure 1.Flashover

Note: Photo by William Cobb, Cornelius – Lemley Fire Rescue

Flashover and Fire Development

There are a number of definitions or ways to describe flashover, but most importantly, it is a rapid transition to a fully developed fire.

A fuel package such as a couch or upholstered chair burning in open air progresses through four phases. In the incipient stage the fire involves only a small amount of fuel, as the fire moves into the growth stage, more fuel becomes involved and the speed of the combustion reaction increases. Eventually the entire object becomes involved and the fire is fully developed. As the fuel is consumed the fire begins to decay. Throughout this process, fire development is fuel controlled; the speed of fire development and energy released is dependent on the characteristics and configuration of the fuel. As combustion is taking place in the open, there is adequate oxygen to support combustion as the fire progresses through each of the four stages.

Heat of combustion is the energy released when a specific mass of fuel is completely burned. The total energy released when an object burns is dependent on the heat of combustion and the amount (mass) of fuel burned. Heat of combustion is measured in Joules (J). However, this only provides part of the picture. Heat release rate (HRR) is the amount energy released per unit of time. HRR is measured in Watts (W). A Watt is a Joule (unit of energy) per second (unit of time).  The fire service in the United States has traditionally used the British thermal unit (Btu) as a unit of energy. Using this unit of measure, HRR could be expressed in Btu/s. All of this is very interesting, but what does this have to do with flashover? As it turns out, heat release rate has everything to do with flashover!

When a fire is unconfined, much of the heat produced by the burning fuel escapes through radiation and convection. What changes when the fire occurs in a compartment? Fire development becomes influenced by the characteristics of the compartment. Other materials in the compartment as well as the walls, ceiling and floor absorb some of the energy released by the fire.  Some of the energy is not absorbed, but radiates back to the burning fuel continuing and accelerating the combustion process.

Hot smoke and air heated by the fire become more buoyant and rise, on contact with cooler materials such as the ceiling and walls of the compartment; heat is transferred to the cooler materials, raising their temperature. This heat transfer process raises the temperature of all materials in the compartment. As nearby fuel is heated, it begins to pyrolize. Eventually the rate of pyrolysis may reach a point where flaming combustion can be supported and the fire extends to other fuel packages.

However, the most significant difference with fire in a compartment is the compartment’s ventilation profile. The size, location, and configuration of openings in the compartment influence both the oxygen available for combustion and the retention or escape of thermal energy contained in the hot gases and smoke produced by the fire.

While the “stages of fire” have been described differently in fire service textbooks the phenomenon of fire development is the same. For our purposes, the stages of fire development in a compartment will be described as incipient, growth, fully developed and decay (see Figure 2). Despite dividing fire development into four “stages” the actual process is continuous with “stages” flowing from one to the next. While it may be possible to clearly define these transitions in the laboratory, in the field it is often difficult to tell when one ends and the next begins.

Figure 2. Stages of Fire Development

If the fire releases energy faster than it can escape from the compartment, temperature will increase and if sufficient energy is released, flashover will occur and the fire will transition rapidly from the growth to fully developed stage (see Figure 2). As this occurs, the fire will spread across all combustible surfaces in the compartment and flames will exit through compartment openings.

The bathtub analogy (see Figure 3) provides a simple way to explain the relationship between ventilation and flashover in a fuel controlled compartment fire.

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 3. The Bathtub Analogy

More to Follow

Posts over the next few weeks will continue to examine the process of reading the fire with further exploration of air track, heat, and flame indicators. In addition, I will be continuing this look at the flashover phenomena with a particular emphasis on the relationship between heat release rate, ventilation, and flashover.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Close, K. (2005) Fire behavior vs. human behavior: Why the lessons from Cramer matter. Paper presented at the Eighth International Wildland Fir e Safety Summit, Missoula,MT. Retrieved May 13, 2008 from http://www.myfirecommunity.net/documents/Close.pdf

Drysdale, D. (1998). An introduction to fire dynamics. New York: John Wiley & Sons.

Gorbet, G & Hopkins, R. (2007) The current knowledge & training regarding backdraft, flashover, and other rapid fire progression phenomena. Paper presented at the annual meeting of the National Fire Protection Association, Boston, MA.

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

Unanticipated smoke explosion and building collapse nearly kills three firefighters.

Portsmouth, VA Near-Miss Incident

Firefighter Eric Kirk gives a firsthand account of a near-miss incident involving a smoke explosion in the June 2009 issue of FireRescue magazine. On a December morning in 2007, firefighters in Portsmouth, Virginia responded to a fire in a church. On arrival, the building was well involved and defensive operations were initiated to protect exposures and confine the fire. Over the course of the fire, smoke extended into an attached, three-story, brick building and formed a flammable fuel/air mixture. Subsequent extension of flames from the church to the interior of the exposure resulted in ignition and explosive combustion of this fuel (smoke)/air mixture.

Incident Photos from PilotOnline.com

Smoke Explosion

This post expands on Smoke is Fuel (Hartin, 2009), a sidebar that I wrote for FireRescue that accompanies Eric’s article examining the Portsmouth, VA smoke explosion incident.

Smoke explosions have resulted in three firefighter fatalities in the United States since 2005, two in Wyoming (see NIOSH Report F2005-13) and one last year in Los Angeles California (NIOSH report pending). In addition, there have been a number of near miss incidents including this one in Virginia and another in Durango, Colorado (see NIOSH Report F2008-02)However, many firefighters have not heard of or misunderstand this fire behavior phenomenon.

The terms backdraft and smoke explosion have typically been used to describe explosions resulting results from confined and rapid combustion of pyrolysis and unburnt products of incomplete combustion. Describing a backdraft incident at a Chatham, England Mattress Store in 1975, Croft (1980) states “this is not an entirely new phenomenon, the first formal description of what have been called ‘smoke explosions’ having been given in 1914” (p. 3).

As an explanation of many contradictory statements in reference to explosions that are reported to have occurred in burning buildings, where it is also testified that explosives were non-existent, we may cite so-called “smoke explosions.”

Distinct from, yet closely allied with explosions of inflammable dust, are explosions caused by the ignition of mixtures of air with the minute particles of unconsumed carbon and invisible gaseous matter in smoke from the imperfect combustion of organic substances…

These “smoke explosions” frequently occur in burning buildings and are commonly termed “back draughts” or “hot air explosions” (Steward, 1914).

As discussed in my earlier post, Fires and Explosions, the term Smoke Explosion was a synonym for Backdraft. In fact, if you look up the definition of smoke explosion in the National Fire Protection Association (NFPA) 921 (2008) Guide for Fire and Explosion Investigation, it says “see backdraft” (p. 921-15). However, today it identifies a different, and in many respects more dangerous extreme fire behavior phenomenon. Smoke (or Fire Gas) Explosion is described in fire dynamics textbooks such as Enclosure Fire Dynamics (Karlsson and Quintiere) and An Introduction to Fire Dynamics (Drysdale) and Enclosure Fires (Bengtsson). Of these, the text Enclosure Fires by Swedish Fire Protection Engineer Lars-Göran Bengtsson provides the best explanation of how conditions for a smoke explosion develop. However, this phenomenon is less well known among firefighters and fire officers. In fact many well known fire service authors continue to use backdraft and smoke explosion interchangeably.

A smoke or fire gas explosion occurs when unburned pyrolysis products accumulate and mix with air, forming a flammable mixture and introduction of a source of ignition results in a violent explosion of the pre-mixed fuel gases and air. This phenomenon generally occurs remote from the fire (as in an attached exposure) or after fire control.

Conditions Required for a Smoke Explosion

The risk of a smoke explosion is greatest in compartments or void spaces adjacent to, but not yet involved in fire. Infiltration of smoke through void spaces or other conduits can result in a well mixed volume of smoke (fuel) and air within its flammable range, requiring only a source of ignition.

Smoke explosions create a significant overpressure as the fuel and air are premixed. Several factors influence the violence of this type of explosion:

• The degree of confinement (more confinement results in increased overpressure)
• Mass of premixed fuel and air in the compartment (more premixed fuel results in a larger energy release)
• How close the mixture is to a stoichiometric concentration (the closer to an ideal mixture the faster the deflagration)

For additional information on transient, explosive, fire phenomena see earlier posts: Gas Explosions and Gas Explosions Part 2.

Indicators Smoke Explosion Potential

It is very difficult to predict a smoke explosion. However, the following indicators point to the potential for this phenomenon to occur.

• Ventilation controlled fire (inefficient combustion producing substantial amounts of unburned pyrolysis products and flammable products of incomplete combustion)
• Relatively cool (generally less than 600^o C or 1112^o F) smoke
• Presence of void spaces, particularly if they are interconnected
• Combustible structural elements
• Infiltration of significant amounts of smoke into uninvolved exposures

Mitigating the Hazard

As with recognizing the potential for a smoke explosion, mitigation can also be difficult. The gases are relatively cool, so application of water into the gas layer may have limited effect. Tactical ventilation to remove the smoke is the only way to fully mitigate the hazard and establish a safe zone. However, use care not to create a source of ignition (such as the sparks created when using an abrasive blade on a rotary saw).

The best course of action is to prevent infiltration of smoke into uninvolved spaces using anti-ventilation (confinement) tactics. Anti-ventilation is the planned and systematic confinement of heat, smoke, and fire gases, and exclusion of fresh air (from the fire). In this case, anti-ventilation may involve pressurizing the uninvolved are to prevent the spread and accumulation of smoke.

Ed Hartin, MS, EFO, MIFIreE, CFO

References

Bengtsson, L. (2001). Enclosure fires. Karlstad, Sweden: Räddnings Verket.

Croft, W. (1980) Fires involving explosions-a literature review. Fire Safety Journal, 3(1), 3-24.

Drysdale, D. (1998). An introduction to fire dynamics (2^nd ed.). New York: John Wiley & Sons.

Hartin, E. (2009, June). Smoke is fuel. FireRescue, 27(6), 54.

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

Kirk, E. (2009, June). Sudden blast: Unanticipated smoke explosion & building collapse nearly kills 3 firefighters. FireRescue, 27(6), 52-54.

National Fire Protection Association. (2008). NFPA 921 Guide for fire and explosion investigations. Quincy, MA: Author.

National Institute for Occupational Safety and Health (NIOSH). (2006) Death in the Line of Duty Report F2005-13. Retrieved June 22, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200513.pdf

National Institute for Occupational Safety and Health (NIOSH). (2009) Death in the Line of Duty Report F2008-02. Retrieved June 22, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200803.pdf

Steward, P. (1914). Dust and smoke explosions, NFPA Quarterly 7, 424-428.

Fire Behavior Indicators – A Quick Review

The B-SAHF (Building, Smoke, Air Track, Heat, & Flame) organizing scheme for fire behavior indicators provides a sound method for assessment of current and potential fire behavior in compartment fires. The following provides a quick review of each of these indicator types.

Figure 1. B-SAHF

Building: Many aspects of the building (and its contents) are of interest to firefighters. Building construction influences both fire development and potential for collapse. The occupancy and related contents are likely to have a major impact on fire dynamics as well.

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.

Heat: This includes a number of indirect indicators. Heat cannot be observed directly, but you can feel changes in temperature and may observe the effects of heat on the building and its contents. Remember that you are insulated from the fire environment, pay attention to temperature changes, but recognize the time lag between increased temperature and when you notice the difference. Visual clues such as crazing of glass and visible pyrolysis from fuel that has not yet ignited are also useful heat related indicators.

Flame: While one of the most obvious indicators, flame is listed last to reinforce that the other fire behavior indicators can often tell you more about conditions than being drawn to the flames like a moth. However, that said, location and appearance of visible flames can provide useful information which needs to be integrated with the other fire behavior indicators to get a good picture of conditions.

It is important not to focus in on a single indicator, but to look at all of the indicators together. Some will be more important than others under given circumstances.

Getting Started

Considering the wide range of different building types and occupancies, developing a concept map of the factors and interrelationships that influence fire behavior is no simple task. As you begin this process, keep in mind that it is important to move from general concepts to more specific details. For example, you might select construction type, contents, size, ventilation profile, and fire protection systems as the fundamental factors as illustrated in Figure 2. (However, you also might choose to approach this differently!).

Figure 2. Basic Building Factors

Remember that this is simply a draft (as will each successive version of your map)! Don’t get hung up on getting it “right”. The key is to get started and give some thought to what might be important. After adding some detail, you may come back and reorganize the map, identifying another basic element. For example, early versions of this map listed Fire Suppression Systems (e.g., automatic sprinklers) as one of the core concepts. However, after adding some detail, this concept was broadened to Fire Protection Systems (e.g., automatic sprinklers, fire detection, and other types of inbuilt fire protection).

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. For example, area and height are important concepts related to size. However, compartmentation may be related to size or it may be a construction factor. If you are unsure of where this should appear on the map, place it in the Staging Area for now.

Figure 3. Expanding the Map

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 building factors segment of the map:

• Look at each of the subcategories individually and brainstorm additional detail. This works best if you collaborate with others.
• Take your partially completed map and notes and visit several different types of buildings. Visualize how a fire might develop and what building features would influence this process.
• Examine the incident profiled in the Remember the Past segment of this post and give some thought to how building factors may have influenced fire behavior and the outcome of this incident.

In addition, I am still posing questions related to B-SAHF using Twitter. Have a look [http://twitter.com/edhartin] and join in by responding to the questions. While this is not a familiar tool to most firefighters, I think that it has great potential.

Thanks

I would also like to thank Senior Instructor Jason Collits of the New South Wales (Australia) Fire Brigades and Lieutenant Matt Leech of Tualatin Valley Fire and Rescue (also an Instructor Trainer with CFBT-US, LLC) for their collaborative efforts on extending and refining our collective understanding of the B-SAHF indicators. Jason and Matt have been using Bubbl.us to develop and share their respective maps and I will be integrating their work into future posts on Fire Behavior Indicators.

Figure 4 Jason Collits and Matt Leech

Remember the Past

Yesterday was the eighth anniversary of a tragic fire in New York City that claimed the lives of three members of FDNY as a result of a backdraft in the basement of a hardware store.

June 17, 2001
Firefighter First Grade John J. Downing, Ladder 163
Firefighter First Grade Brian D. Fahey, Rescue 4
Firefighter First Grade Harry S. Ford, Rescue 3
Fire Department City of New York

Fire companies were dispatched to a report of a fire in a hardware store. The first- arriving engine company, which had been flagged down by civilians in the area prior to the dispatch, reported a working fire with smoke venting from a second-story window.

A bystander brought the company officer from the first-arriving engine company to the rear of the building where smoke was observed venting from around a steel basement door. The first-arriving command officer was also shown the door and ordered an engine company to stretch a line to the rear of the building. A ladder company was ordered to the rear to assist in opening the door; Firefighter Downing was a member of this company. The first-due rescue company, including Firefighters Fahey and Ford, searched the first floor of the hardware store and assisted with forcible entry on the exterior.

The incident commander directed firefighters at the rear of the building to open the rear door and attack the basement fire. Firefighters on the first floor were directed to keep the interior basement stairwell door closed and prevent the fire from extending. The rear basement door was reinforced, and a hydraulic rescue tool was employed to open it. Once the first door was opened, a steel gate was found inside, further delaying fire attack.

Firefighters Downing and Ford were attempting to open basement windows on the side of the building, and Firefighter Fahey was inside of the structure on the first floor.

An explosion occurred and caused major structural damage to the hardware store. Three fire-fighters were trapped under debris from a wall that collapsed on the side of the hardware store; several firefighters were trapped on the second floor; firefighters who were on the roof prior to the explosion were blown upwards with several firefighters riding debris to the street below; and fire-fighters on the street were knocked over by the force of the explosion.

The explosion trapped and killed Firefighters Downing and Ford under the collapsed wall; their deaths were immediate. Firefighter Fahey was blown into the basement of the structure. He called for help on his radio, but firefighters were unable to reach him in time.

The cause of death for Firefighters Downing and Ford was internal trauma, and the cause of death for Firefighter Fahey was listed as asphyxiation. Firefighter Fahey’s carboxyhemoglobin level was found to be 63%.

In addition to the three fatalities, 99 firefighters were injured at this incident. The fire was caused when children – two boys, ages 13 and 15 – knocked over a gasoline can at the rear of the hard-ware store. The gasoline flowed under the rear doorway and was eventually ignited by the pilot flame on a hot water heater.

For additional information on this incident, see the following:

NIOSH Death in the Line of Duty Report F2001-23,

Simulation of the Dynamics of a Fire in the Basement of a Hardware Store

Incident Photos by Steve Spak

Ed Hartin, MS, EFO, MIFireE, CFO

References

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

Hartin, E. (2007) Fire behavior indicators: Building expertise. Retrieved June 17, 2009 from www.firehouse.com.

Hartin, E. (2007) Reading the fire: Building factors. Retrieved June 17, 2009 from www.firehouse.com.

National Institute for Occupational Safety and Health (NIOSH). (2003) Death in the line of duty report F2001-23. Retrieved June 18, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200123.pdf

Bryner, N. & Kerber, S (2004) Simulation of the dynamics of a fire in the basement of a hardware store – New York, June 17, 2001 NISTR 7137. Retrieved June 18, 2009 from http://www.fire.nist.gov/bfrlpubs/fire06/PDF/f06006.pdf

United States Fire Administration (USFA) Firefighter fatalities in 2001. Retrieved June 18, 2009 from http://www.usfa.dhs.gov/downloads/pdf/publications/fa-237.pdf

Art and Science of Firefighting

NIST has performed a wide range of research that can have a positive impact on the safety and effectiveness of firefighting operations. However, all too often, this information has not made it to front line firefighters. Dan Madrzykowski and Steve Kerber have made a concerted effort to address this issue and increase the day to day impact of NIST fire research. In the video overview of the wind driven fire research, Battalion Chief Jerry Tracy of the FDNY stated that this project was an effort to bridge the gap between the science and art of firefighting and get science to the street.

Research on Wind Driven Fires= Governors Island, New York City

Note: John Freeman Photo from NIST Report TN 1629

Understanding, Surviving, & Fighting Wind Driven Fires

This two DVD training package is based on NIST research conducted at the Building Fire Research Lab (BFRL) in Gaithersburg, MD and on Governors Island in New York city. The package contains:

• Written reports on the laboratory and field experiments
• Multiple videos of the experiments (from standard and thermal imaging video cameras)
• PowerPoint presentation on experimental procedures and results
• Video overview of the research and implications for fireground operations

While the reports and detailed video are tremendous resources, I believe that every firefighter in the United States would benefit from taking 86 minutes to watch the introductory video overview narrated by Battalion Chiefs Peter Van Dorpe (Chicago Fire Department), Jerry Tracy (Fire Department of New York), Dan Madrzykowski (NIST), and Steve Kerber (NIST). The overview presentation is divided into four segments:

1. Introduction and the Chicago Fire Department Experience (BC Peter Van Dorpe)
2. The FDNY Experience (BC Jerry Tracy)
3. Laboratory Experiments (Dan Madrzykowski, PE)
4. Governors Island Experiments (Steve Kerber)
5. Conclusion (BCs Peter Van Dorpe and Jerry Tracy)

This video provides a powerful explanation of the potential danger of wind driven fires (in both high and low-rise structures) and illustrates how scientific research can have a positive impact on the safety and effectiveness of fireground operations. While some may discount the information presented because the research focused (to a large extent) on high-rise buildings, many of the lessons learned have applicability to a much wider range of buildings.

In the summary section of the overview video, BC Peter Van Dorpe made several interesting observations regarding the lessons he learned from this research:

In a high-rise building, you don’t ventilate until you have water on the fire based on potential for a wind driven fire and dramatic influence of wind and ventilation on fire behavior.

Consideration of the concept that the first water on a high-rise fire [in a non-sprinklered building] should be from the exterior based on the dramatic effect of relatively low flow application from the exterior in changing conditions from severe to controllable.

BC Jerry Tracy emphasized the importance of integrating the art and science of firefighting and the need for change. Credibility is critical, both from a scientific and operational perspective. He pointed to the importance of understanding impact of changes in ventilation profile on fire behavior in all types of fires and the potential benefits of alternative strategies and tactics.

How to Order

This two DVD set can be ordered from the United States Fire Administration (USFA) Web Site. However, orders are limited to a single set per organization.

Order Evaluating Firefighting Tactics Under Wind Driven Conditions

Information on this research is also available on the NIST Wind Driven Fire Research web page.

Action Steps

Get a copy of this training package and have a look at the overview video. Ask yourself how this information can be put to work in your environment? What application does this research have beyond high-rise buildings? How can we use this information to increase the safety and effectiveness of firefighting operations in single and multi-family dwellings and in commercial buildings?

CFBT-US on Twitter

In an effort to expand our network, CFBT-US is now on Twitter! Follow Chief Instructor Ed Hartin for information on fire behavior, incident information, photos and video for B-SAHF exercises. Check out the Twitter Portal for an overview video on Twitter and additional information on this social networking tool.

CFBT-US is exploring how to integrate Twitter with the CFBT Blog (and the blog with Twitter). Please share your feedback on the effectiveness and utility of this approach to information sharing.

Ed Hartin, MS, EFO, MIFireE, CFO