Posts Tagged ‘flash fire’

My last post, Hazards Above, provided a brief overview of three incidents involving extreme fire behavior in the attic or truss loft void spaces of wood frame dwellings. This post will examine the similarities and differences between these lessons and identify several important considerations when dealing with fires occurring in or extending to void spaces. At the conclusion of Hazards Above, I posed five questions:

1. What is similar about these incidents and what is different?
2. Based on the limited information currently available, what phenomena do you think occurred in each of the cases? What leads you to this conclusion?
3. What indicators might have pointed to the potential for extreme fire behavior in each of these incidents?
4. How might building construction have influenced fire dynamics and potential for extreme fire behavior in these incidents?
5. What hazards are presented by fires in attics/truss lofts and what tactics may be safe and effective to mitigate those hazards?

Similarities and Differences

The most obvious similarities between these incidents was that the buildings were of wood frame construction, the fire involved or extended to an attic or truss loft void space, and that some type of extreme fire behavior occurred. In two of the incidents firefighters were seriously injured, while in the other firefighters escaped unharmed.

Given the limited information available from news reports and photos taken after the occurrence of the extreme fire behavior events, it is not possible to definitively identify what types of phenomena were involved in these three incidents. However, it is interesting to speculate and consider what conditions and phenomena could have been involved. It might be useful to examine each of these incidents individually and then to return to examine fire behavior indicators, construction, and hazards presented by these types of incidents.

Minneapolis, MN

In the Minneapolis incident the fire occurred in an older home with legacy construction and relatively small void spaces behind the knee walls and above the ceiling on Floor 3. The triggering event for the occurrence of extreme fire behavior is reported to be opening one of the knee walls on Floor 3. As illustrated in Figure 1, the fire appeared to transition quickly to a growth stage fire (evidenced by the dark smoke and bi-directional air track from the windows on Floor 3 Side A. However blast effects on the structure are not visible in the photo and were not reported.

Figure 1. Minneapolis MN Incident: Conditions on Side A

Note: Photo by Steve Skar

Potential Influencing Factors: While detail on this specific incident is limited, it is likely that the fire burning behind the knee wall was ventilation controlled and increased ventilation resulting from opening the void space resulted in an increase in heat release rate (HRR). Potential exists for any compartment fire that progresses beyond the incipient stage to become ventilation controlled. This is particularly true when the fire is burning in a void space.

Extreme Fire Behavior: While statements by the fire department indicate that opening the knee wall resulted in occurrence of flashover, this is only one possibility. As discussed in The Hazard of Ventilation Controlled Fires and Fuel and Ventilation, increasing ventilation to a ventilation controlled fire will result in increased HRR. Increased HRR can result in a backdraft (if sufficient concentration of gas phase fuel is present), a vent induced flashover, or simply fire gas ignition (such as rollover or a flash fire) without transition to a fully developed fire.

Harrisonburg, VA

The Harrisonburg incident involved extreme fire behavior in Exposure D (not the original fire unit). The extreme fire behavior occurred after members had opened the ceiling to check for extension. However, this may or may not have been the precipitating event. As illustrated in Figure 2, as members prepare to exit from the windows on Floor 3 , Side C, flames are visible on the exterior at the gable, but it appears that combustion is limited to the vinyl siding and soffit covering. There are no indicators of a significant fire in Exposure D at the time that the photo was taken. However, it is important to remember that this is a snapshot of conditions at one point in time from a single perspective.

Figure 2. Harrisonburg, VA Incident: Conditions on Side C

Note: Photo by Allen Litten

Potential Influencing Factors: The truss loft was likely divided between units by a 1 hour fire separation (generally constructed of gypsum board over the wood trusses). While providing a limited barrier to fire and smoke spread, it does not generally provide a complete barrier and smoke infiltration is likely. Sufficient smoke accumulation remote from the original fire location can present risk of a smoke explosion (see NIOSH Report 98-03 regarding a smoke explosion in Durango, Colorado restaurant). Alternately, fire extension into the truss loft above an exposure unit can result in ventilation controlled fire conditions, resulting in increased HRR if the void is opened (from above or below).

Extreme Fire Behavior: Smoke, air track, and flame indicators on Side C indicate that the fire in the truss loft may not have continued to develop past the initial ignition of accumulated smoke (fuel). It is possible that smoke accumulated in the truss loft above Exposure B and was ignited by subsequent extension from the fire unit. Depending on the fuel (smoke)/air mixture when flames extended into the space above Exposure B ignition could have resulted in a smoke explosion or a less violent fire gas ignition such as a flash fire.

Sandwich, MA

In the Sandwich incident, the extreme fire behavior occurred shortly after the hose team applied water to the soffit. However, this may or may not have been the precipitating event. As illustrated in Figure 3, the fire transitioned to a fully developed fire (likely due to the delay in suppression as the injured members were cared for). Blast effects on the structure are obvious.

Figure 3: Sandwich, MA: Conditions on Sides C and D

Note: Photos by Britt Crosby (http://www.capecodfd.com)

Potential Influencing Factors: The roof support system in this home appears to have been constructed of larger dimensional lumber (rather than lightweight truss construction). In addition, it is likely that the attic void spaces involved in this incident were large and complex (given the size of the dwelling and complex roof line). It appears that at least part of the home had a cathedral ceiling. Fire burning in the wood framing around the metal chimney would have allowed smoke (fuel) and hot gases to collect in the attic void in advance of fire extension.

Extreme Fire Behavior: The violence of the explosion (see blast damage to the roof on Side D in Figure 3) points to the potential for ignition of pre-mixed fuel (smoke) and air, resulting in a smoke explosion. However, it is also possible that failure of an interior ceiling (due to water or steam production from water applied through the soffit) could have increased ventilation to a ventilation controlled fire burning in the attic, resulting in a backdraft).

Fire Behavior Indicators

The information provided in news reports points to limited indication of potential for extreme fire behavior. One important question for each of us is how we can recognize this potential, even when indicators are subtle or even absent.

Important! A growth stage fire can present significant smoke and air track indicators, with increasing thickness (optical density), darkening color, and increasing velocity of smoke discharge. However, as discussed in The Hazard of Ventilation Controlled Fires, when the fire becomes ventilation controlled, indicators can diminish to the point where the fire appears to be in the incipient stage. This change in smoke and air track indicators was consistently observed during the full-scale fire tests of the influence of ventilation on fires in single-family homes conducted by UL earlier this year.

Even with an opening into another compartment or to the exterior of the building, a compartment fire can become ventilation controlled. Consider building factors including potential for fire and smoke extension into void spaces in assessing fire conditions and potential for extreme fire behavior. A ventilation controlled fire or flammable mixture of smoke and air may be present in a void space with limited indication from the exterior or even when working inside the structure.

Building Construction

Each of these incidents occurred in a wood frame structure. However, the construction in each case was somewhat different.

In Minneapolis, the house was likely balloon frame construction with full dimension lumber. As with many other structures with a “half-story”, the space under the pitched roof is framed out with knee walls to provide finished space. This design is not unique to legacy construction and may also be found with room-in-attic trusses. The void space behind the knee wall provides a significant avenue for fire spread. When involved in fire, opening this void space can quickly change fire conditions on the top floor as air reaches the (likely ventilation controlled) fire.

The incident in Harrisonburg involved a fire in a townhouse with the extreme fire behavior phenomena occurring in an exposure. While not reported, it is extremely likely that the roof support system was comprised of lightweight wood trusses. In addition, there was a reverse gable (possibly on Sides A and C) that provided an additional void. As previously indicated, the truss loft between dwelling units is typically separated by a one-hour rated draft stop. Unlike a fire wall, draft stops do not penetrate the roof and may be compromised by penetrations (after final, pre-occupancy inspection). Installed to code, draft stops slow fire spread, but may not fully stop the spread of smoke (fuel) into the truss lofts above exposures.

Firefighters in Sandwich were faced with a fire in an extremely large, wood frame dwelling. While the roof appeared to be supported by large dimensional lumber, it is likely that there were large void spaces as a result of the complex roofline. In addition, the framed out space around the metal chimney provided an avenue for fire and smoke spread from the lower level of the home to the attic void space.

Hazards and Tactics

Forewarned is forearmed! Awareness of the potential for rapid fire development when opening void spaces is critical. Given this threat, do not open the void unless you have a hoseline in hand (not just nearby).

Indirect attack can be an effective tactic for fires in void spaces. This can be accomplished by making a limited opening and applying water from a combination nozzle or using a piercing nozzle (which further limits introduction of air into the void).

If there are hot gases overhead, cool them before pulling the ceiling or opening walls when fire may be in void spaces. Pulses of water fog not only cool the hot gases, but also act as thermal ballast; reducing the potential for ignition should flames extend from the void when it is opened.

Lastly, react immediately and appropriately when faced with worsening fire conditions. Review my previous posts on Battle Drill (Part 1, Part 2, and Part 3). An immediate tactical withdrawal under the protection of a hoseline is generally safer than emergency window egress (particularly when ladders have not yet been placed to the window).

Ed Hartin, MS, EFO, MIFireE, CFO

My last two posts (Contra Costa County Line of Duty Deaths (LODD) Part 1 & Part 2) examined the conditions and circumstances involved in the incident that took the lives of Captain Matthew Burton and Engineer Scott Desmond while conducting primary search in a small residential structure in San Pablo, California early on the morning of July 21, 2007.

As identified in the Contra Costa County Investigation and NIOSH Death in the Line of Duty Report F2007-28, these line of duty deaths were the result of a complex web of events, circumstances, and actions.

These two reports identify the rapid fire progression that trapped Captain Burton and Engineer Desmond as a fire gas ignition (county and NIOSH reports) or ventilation induced flashover (NIOSH report). Both reports also point to ineffective or inappropriate use of positive pressure ventilation as a contributing factor in the occurrence of extreme fire behavior. However, neither report provides a substantive explanation of how and why this extreme fire behavior occurred.

Investigative Approach

Developing a reasonable explanation of the extreme fire behavior that occurred in this incident involved application of the scientific method as outlined in NFPA 921 Standard on Fire and Explosion Investigations (2008).

The following analysis is based on narrative data and photographic evidence provided in the Contra Costa County Fire Protection District Investigation Report: Michele Drive Line of Duty Deaths and the video taken by the Q76 Firefighter.

In that the district and NIOSH had already collected data, this effort focused on 1) analysis of the data contained in the incident reports, photographs, and video; 2) development of a hypothesis that provided an explanation for what occurred (deductive reasoning), 3) testing this hypothesis (inductive reasoning); 4) revising the hypothesis as necessary; and 5) selecting a final hypothesis.

Figure 1. Fire Development in Bedroom 2

Hypothesis

The fire originated in Bedroom 2, likely on or near the bed. In the growth stage, the fire extended through the hallway into the living room (see Figure 1). The fuel load in the living room and ventilation provided by the open front door permitted the fire to progress through flashover and become fully developed (see Figure 2).

Figure 2. Extension and Fire Development in the Living Room

The extent of fire in the living room consumed the oxygen supplied through the front door, resulting in an extremely ventilation controlled fire in the hallway and bedroom. Unburned flammable products of combustion and pyrolysis products from contents and structural materials accumulated in the upper layer in the bedrooms and hallway.

Figure 3. Fire Control and Development of a Gravity Current

Extinguishment of the fire in the living room allowed development of a gravity current and movement of oxygen through the living room to the hallway and bedrooms allowing flaming combustion in these areas to resume.

Figure 4. Positive Pressure Ventilation

Flaming combustion in the hallway or bedroom resulted in piloted ignition of a substantive accumulation of pyrolysis products and flammable products of incomplete combustion in the upper layer within the hallway and bedrooms. Application of positive pressure at the door on Side A influenced (or speeded up) this phenomena and may have increased the violence of this ignition (due to increased pressure and confinement) but likely aided in limiting the spread of flaming combustion from the hallway into the living room.

Figure 5. Fire Gas Ignition

Supporting Information

Information supporting the preceding hypothesis is divided into three categories: Known, suspected, and assumptions.

Known

The cause and origin� and line of duty death investigation conducted by the Contra Costa Fire Protection District and line of duty death investigation conducted by NIOSH identified and documented a range of data supporting this hypothesis. These data elements include physical evidence, and narrative data obtained from interviews with individuals involved in the incident.

• The fuel load in the bedroom included a bed, dresser, and other contents, exposed wood ceiling, carpet, and carpet pad.
• Fire originated in Bedroom 2 (on or near the bed)
• The female occupant exited the structure prior to making a 911 call to report the fire (via cell phone).
• The female occupant then reentered the building prior to the arrival of the first fire unit in an effort to rescue her husband. [Observations by bystanders included in the report]
• The fire in Bedroom 2 entered the growth stage and extended into the hallway and subsequently the living room. This fire spread was in part due to the combustible wood ceiling. [Information on the cause and origin investigation provided in the report]
• Windows other than the living room window on Side A were substantively intact until the occurrence of the extreme fire behavior event. [Observation by firefighters included in the report]
• E70 knocked down the fire in the living room prior to initiating primary search (without a hoseline). E70 used a left hand search pattern in which they would have moved into the hallway and bedrooms located on Side B of the residence.
• A blower was placed at the front door while E70 and E73 were conducting primary search. Due to the placement of the blower close to the door, it is possible that the air cone did not fully cover the door opening. There is no mention in the report regarding the air track at the door or living room window following placement of the blower. However, E73 reported increased visibility and temperature in the kitchen a short time after the blower was placed, and observed rollover from the hallway leading to the bedrooms.]
• The large window in the living room (if fully cleared of glass) would provide approximately equal area as the door on Side A used as an inlet. Given an equal sized inlet and outlet, efficiency of PPV is likely to be approximately 70%. However, given the location of the exhaust opening next to the inlet, the effectiveness of this ventilation at clearing smoke from compartments beyond the living room and kitchen would have been limited.
• Vertical ventilation was not completed until after the occurrence of the extreme fire behavior phenomena that trapped and killed Captain Burton and Engineer Desmond. The exhaust opening created in the roof had limited impact on interior conditions when it was completed due to the presence of the original roof.
• Fuel load in this compartment was more than sufficient to provide the heat release rate necessary to allow fire development to flashover. [This assessment is based on post-fire photos, room dimensions, and ventilation openings at the time of the ignition].
• Other bedrooms contained a similar fuel load.

Deductions

Several factors supporting the stated hypothesis are not directly supported by physical evidence or narrative data. These elements are deduced based on the design, construction, and configuration of the building and principles of fire dynamics in conjunction with known information.

• The front door remained open after the female occupant reentered. [E70 reported fire and smoke showing from the door and living room window on arrival, but no information provided in the report regarding the position of the door or extent to which the window had failed (fully or partially)]
• Use of the blower is likely to have increased mixing of air and hot, fuel rich fire gases in the hallway, particularly near the opening between the hallway and the living room. Ventilation of smoke from the living room and kitchen through the window on Side A, likely reduced the potential for flaming combustion to have extended from the hallway into the living room.
• Heat conducted through the tongue and groove wood roof/ceiling may have resulted in melting and gasification of asphalt roofing which may have been forced through gaps between the planks to add to the gas phase fuel resulting from pyrolysis and incomplete combustion of contents and structural surfaces within the involved compartments.
• The primary source of air for the fire was through the front door and the living room window. The bottom of the doorway was the lowest opening in the building, likely resulting in a bi-directional air track with smoke exiting out the top of the door and air entering at the bottom. While the sill of the living room window was higher than the door, a bi-directional air track likely developed at this opening as well, with the extreme lower portion of the window opening serving as an inlet while the top of the window functioned as an outlet for flames and smoke [No information about air track at the front door was provided in the report.]
• The fire in the living room reached the fully developed stage after the civilian occupant reentered and prior to the arrival of E70 [This deduction is based on the ability of the female occupant to enter and make her way to the kitchen and the presence of flames exiting the door and living room window on Side A when E70 arrived]

Assumptions

In addition to known and deduced information, the hypothesis is based on the following assumptions.

• The fully developed, ventilation controlled fire in the living room substantively utilized the atmospheric oxygen provided by the air entering through the front door, causing the fire in Bedroom 2 and the hallway to enter ventilation controlled decay. The decay stage fire and heat from the hot gas layer present in the hallway and adjacent rooms continued pyrolysis of fuel packages in this area, resulting in accumulation of a substantial concentration of gas phase fuel in the smoke.
• Control of the fully developed fire in the living room reduced oxygen demand from the fire. The bi-directional air track would have continued and gravity current would have increased air supply to the ventilation controlled decay stage fire in the hallway and bedroom(s).
• Establishment of positive pressure ventilation with the door on Side A serving as the inlet (or inlet and outlet) and the living room window serving as an outlet would have cleared smoke from the living room, but would not have influenced smoke movement from the hallway and bedrooms (as quickly).

Validation

Special thanks to Dr. Stefan Svensson of the Swedish Civil Contingencies Agency and Assistant Professor Greg Gorbett of Eastern Kentucky University for serving as critical friends and providing useful feedback in development of this analysis.

This hypothesis is supported by a range of evidence, deductions and assumptions. However, further validation would require use of other methods such as development of a computational fluid dynamics model and small or full scale fire tests.

More to Follow

My next post will examine the potential influence of positive pressure ventilation (PPV) in this incident as well as a broader look at potential hazards when PPV is used incorrectly or under inappropriate circumstances.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Contra Costa County Fire Protection District.� (2008). Investigation report: Michele drive line of duty deaths. Retrieved February 13, 2009 from http://www.cccfpd.org/press/documents/MICHELE%20LODD%20REPORT%207.17.08.pdf

National Institute for Occupational Safety and Health (2009).� Death in the line of duty report 2007-28. Retrieved May 5, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200728.pdf.

National Fire Protection Association (NFPA) (2008) NFPA 821 Standard on fire and Explosion Investigations. Quincy, MA: Author.

This post continues examination of the incident that took the lives of Captain Matthew Burton and Engineer Scott Desmond early on the morning of July 21, 2007. Captain Burton and Engineer Desmond died while conducting primary search in a small, one-story, wood frame dwelling with an attached garage at 149 Michele Drive in San Pablo (Contra Costa County), California.

This post focuses on firefighting operations, key fire behavior indicators, and firefighter rescue operations implemented after Captain Burton and Engineer Desmond were discovered after rapid fire progression in the area in which they were searching.

Firefighting Operations

Based on the report of trapped occupants, E70 immediately placed a 150′ preconnected 1-3/4″ (45 m 45 mm) line into service using apparatus tank water. The officer of E70, seeing what he believed to be E74 arriving he passed command to the E74 officer. Unfortunately, the second arriving engine was E73 (using apparatus normally assigned to Station 74 and marked E74).

Note: This incomplete passing of command resulted in loss of command, control, and coordination of tactical operations until the arrival of BC7 at 0202 and formally assumed command at 0205. All tactical operations prior to 0205 were the result of independent action by first alarm companies.

The crew of E70 (officer and firefighter) initiated fire attack through the door on Side A and advanced 3′-5′ (0.9-1.5 m) through the door and quickly knocked down flaming combustion in the living room and through dispatch, requested the first arriving truck to establish vertical ventilation. Retrieving a thermal imaging camera (TIC) from the apparatus, the crew of E70 began a left hand search (towards the bedrooms), but left the hoseline just inside the door on Side A (see Figure 1)

Figure 1. Floor Plan-149 Michelle Drive

E73 hand stretched 200′ of 5″ (127 mm) supply line to a nearby hydrant. As he returned from the hydrant the firefighter from E73 observed a large volume of smoke from Side B. E73 officer tasked E70 engineer with placing a blower at the door on Side A. E73 (officer and firefighter) entered through the door on Side A and began a right hand search (taking the opposite direction from E70). E73 encountered poor visibility, but moderate temperature. While E73 conducted the search, E73 engineer shut off the natural gas service to the house.

E69 arrived at 0157 and prepared to perform vertical ventilation. The officer performed a size-up while the engineer obtained a chain saw and the firefighter placed a 14 ladder to provide access to the roof at the A/D corner. E70 engineer, asked the E69 officer about placing a blower to the front door (as previously ordered by the officer of E73) and he answered in the affirmative. The engineers from E70 and E73 placed a blower into operation 3′ (0.9 m) from the front door due to a half wall that partially enclosed the porch.

Note: No information is provided in the report regarding air track prior to or following pressurization of the building. The only substantive exhaust opening at the time the blower was placed into operation was the window in the living room immediately adjacent to the door on Side A.

E73 located the first civilian casualty, a female occupant in the kitchen (see Figures 2 and 5). As they removed the victim, both visibility and temperature increased dramatically. As they move the victim through the living room, they observed rollover coming from the hallway leading to the bedrooms (see Figures 2 and 5). The E73 officer briefly operated the hoseline left in the living room by E70 to control flaming combustion in the upper layer. The blower was turned 90^o to permit removal of the victim, but was then returned to its original operating position. E69 officer assigned the E69 firefighter to assist E73 with patient care on Side A.

The E69 officer and engineer proceeded to the roof and began making a vertical ventilation opening on Side A roof, over the hallway. At 0159 Q76 arrived and while the officer was donning his breathing apparatus (BA), the window in Bedroom 1 failed suddenly followed by a significant increase in flaming combustion from the windows in Bedroom 1 and 2 on Sides A and B.

The firefighter from E73 who was providing emergency medical care to the civilian fire victim observed that the window in Bedroom 1 which had been cracked with some discharge of smoke, failed violently with glass blowing out onto the lawn and a large volume of flames venting from the window for a period of 10 to 15 seconds (see Figure 2).

Figure 2. Extreme Fire Behavior

Note: Adapted from eight seconds of video was shot by Q76 firefighter from in front of Exposure D, looking towards the A/D corner of the fire building.

Figure 3. Post Fire Photo from in Front of Exposure D

Note: This screenshot from Google Maps Street View is from a similar angle as the video taken by Q76 firefighter and is provided to provide a point of reference and perspective for the video.

The E73 officer reentered the building and initiated fire attack using the hoseline left in the living room. E70 engineer stretched a second 150′ 1-3/4″ (45 m 45 mm) line to the front door. The second line was stretched into the building by Q76. Immediately after entering through the door on Side A, the Q76 met E73 officer who was exiting with low air alarm activation. Q76 took over the initial hoseline and worked their way down the hallway leading to the bedrooms, leaving the second line in the living room (see Figure 2) Q76 encountered poor visibility and high temperature with flames extending out of Bedrooms 1 and 2 and rollover in the hallway.

Shortly after exiting the building E73 officer advised E73 engineer that he was “out of air” [he was likely in a low air condition with low air alarm sounding rather than completely out of air] and expressed concern regarding E70’s air status.

Battalion 7 (BC7) arrived at 0202 and attempted to make face-to-face contact with Command (E70) as he had not heard E70 attempt to pass command to E74. At 0203, BC7 confirmed that a medic unit was responding and requested that the medic upgrade from Code 2 to Code 3. (Code 2 is a non-life threatening medical emergency requiring immediate response without the use of red lights or siren. Code 3 is a a medical emergency requiring immediate response with red lights and siren.) BC7 then attempted to contact E70 on the tactical channel and asked other crews operating at the incident about the status of E70. At 0205, BC7 ordered a second alarm and attempted to contact E70 on non-assigned tactical channels (in the event that their radios were inadvertently on the wrong channel). The second alarm added three engines (E74, E75, and E73) and a battalion chief (BC71) to the incident.

While BC7 was attempting to locate E70, Q76 was operating in the hallway and bedrooms in an effort to control the fire. They knocked the fire down in Bedroom 2 and controlled the rollover extending from Bedroom 1 down the hall. Q76 officer scanned Bedroom 2 with a TIC, but did not observe any victims. Q76 then advanced to Bedroom 1.

E69 completed a 6′ x 6′ (1.8 m x 1.8 m) ventilation opening in the roof on Side A, two thirds of the way from their access point at the A/D corner to Side B. Immediately after making the opening, they observed minimal smoke discharge (and were able to see items stored in the attic and the attic floor (original roof). They attempted to breach the attic floor, but were unable to do so (as it was constructed of 2″ x 6″ (51 mm x 152 mm) tongue and groove planks).

At 0206, after repeated unsuccessful attempts to contact E70, BC7 transmitted a report of a missing firefighter and assumed Command. Command requested an additional engine (E68) be added to the second alarm assignment. Battalion 64 (BC64) added himself to the incident and advised dispatch.

As E69 exited the roof they heard a loud pop and observed flames exiting the roof ventilation opening a distance of 8′-10′ (2.4-3.0 m). After knocking down the fire in Bedroom 1 Q76 moved back to Bedroom 2. Failure of the gypsum board on the wall between Bedrooms 1 and 2 allowed operation of the stream from their hoseline into both bedrooms.

While at the doorway of Bedroom 2, Q76 observed a substantial volume of fire in the attic through a small hole in the hallway ceiling (see Figure 4) and attempted to apply water into the attic. However, their stream was ineffective.

Figure 4. Hallway Ceiling.

Note: Adapted from Contra Costa Fire Protection District Photos, Investigation Report: Michele Drive Line of Duty Deaths. Brightness and contrast adjusted to increase clarity.

After exiting the roof, E69 proceeded counter clockwise around the building to Side C where they removed window screens and broke out several panes of glass, but did not observe an appreciable discharge of smoke. Continuing around the B/C corner, E69 observed flames from the window of Bedroom 2 and the attic.

At 0208 Command (BC7) repeatedly attempted to contact E70 by radio on the tactical channel. Unsuccessful, he requested an additional Code 3 ambulance and advised that the status of the missing firefighters was unknown.

E69 met with Command (BC7) and was assigned to continue primary search for the second reported occupant. E69 firefighter and engineer began the search while the officer replaced his SCBA cylinder. As they entered, they picked up a hoseline (second 1-3/4″ (45 mm) hoseline) and used it to extinguish small areas of fire as they moved towards the kitchen. Q76 handed off their TIC to E69 as they exited the building with low air alarms sounding.

Q76 replaced SCBA cylinders and was tasked with search for E70 on the exterior. While conducting this search, they observed flames 10′-15′ (3.0-4.6 m) in length issuing from the gable vent on Side B.

After E69 officer rejoined his crew in the kitchen, they located the second civilian casualty who was determined to be diseased (see Figure 2). Command (BC7) ordered E69 to defer removing the victim and continue searching for E70.

Firefighter Rescue Operations

E69 walked through the interior of the dwelling looking for E70 and used a hoseline to knock down fire still burning in the closet of Bedroom 2. E69 advised command that E70 was not inside, but was instructed to conduct a second search of the interior.

At 0127, Command (BC7) asked dispatch to conduct a “head count” [personnel accountability report (PAR)]. Second alarm resources arrived between 0218 and 0221.

E69 reentered the building and conducted a thorough search for E70. At 0221, Command (BC7) ordered companies to “evacuate” [withdraw from] the building. Based on the urgency of his assignment to locate E70, E69 officer decided to continue the search into Bedroom 2. At approximately 0222, E69 located Captain Burton (fire service casualty 1) under debris on the right side of the bed (see Figure 2). His facepiece was still in place and his low air alarm was ringing slowly. E69 attempted to remove the Captain, but were only able to move him to the doorway to Bedroom 2 before smoke conditions worsened and visibility decreased. Near exhaustion, one member of the crew experience low air alarm activation and became disoriented requiring assistance to exit to the door on Side A.

Command (BC7) assigned Q76 to assist with the search. As E69 exited, they advised Q76 that they had located one member of E70 in the bedroom. After exiting, E69 advised Command (BC7) that they had located one member of E70 and that he appeared to be diseased and that they were having difficulty in removing him. Q76 quickly located Captain Burton inside the doorway of Bedroom 2 and removed him to Side A at 0228. E73 attempted resuscitation, but quickly determined that the Captain’s injuries were fatal.

BC64 and E76 officer continued the search in Bedroom 2 and located Engineer Desmond (fire service casualty 2) on the left side of the bed (see Figure 2). E72 assisted in controlling the fire in Bedroom 2 and the removal of the second member of E70 on a backboard. Engineer Desmond was removed from the building at approximately 0224. After both members of E70 were removed, crews removed the deceased civilian occupant.

Timeline

Review the Michelle Drive Timeline (PDF format) to gain perspective of sequence and the relationship between tactical operations and fire behavior.

Questions

The following questions focus on fire behavior, influence of tactical operations, and related factors involved in this incident.

1. The E73 officer tasked E70 engineer with placement of a blower at the door on Side A (use of this tactic was reaffirmed by the E69 officer). What air track did this use of positive pressure create and what effect did this have on 1) conditions in the living room and kitchen and 2) in the hallway and bedrooms? Why do you think that this was the case?
2. What type of extreme fire behavior phenomena occurred in this incident? Do you agree with the Contra Costa County Fire Protection District report conclusion that this was a fire gas ignition or do you suspect that some other phenomenon was involved?
3. How did the conditions necessary for this extreme fire behavior event develop (address both the fuel and ventilation sides of the equation)?
4. What was the initiating event(s) that lead to the occurrence of the extreme fire behavior that trapped Captain Burton and Engineer Desmond? How did the use of positive pressure ventilation influence the occurrence of the extreme fire behavior (if in fact it did)?
5. What action could have been taken to reduce the potential for extreme fire behavior and maintain tenable conditions during primary search operations?
6. How did building design and construction impact on fire behavior and tactical operations during this incident?

Ed Hartin, MS, EFO, MIFireE, CFO

References

Contra Costa County Fire Protection District.� (2008). Investigation Report: Michele Drive Line of Duty Deaths. Retrieved February 13, 2009 from http://www.cccfpd.org/press/documents/MICHELE%20LODD%20REPORT%207.17.08.pdf

National Institute for Occupational Safety and Health (2009).� Death in the Line of Duty Report 2007-28. Retrieved May 5, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200728.pdf.

As discussed in previous posts, developing mastery of the craft of firefighting requires experience. However, it is unlikely that we will develop the base of knowledge required simply by responding to incidents. Case studies provide an effective means to build our knowledge base using incidents experienced by others.

Introduction

The deaths of Captain Matthew Burton and Engineer Scott Desmond in a residential fire were the result of a complex web of circumstances, actions, and events. This case study was developed using the Contra Costa County Fire Protection District Investigative Report and NIOSH Death in the Line of Duty Report 2007-28 and video taken by a Firefighter assigned to Quint 76 (Q76), the first alarm truck company. This case study focuses on the fire behavior and related tactical operations involved in this incident. However, there are a number of other lessons that may be learned from this incident and readers are encouraged to review both the fire district’s investigation and NIOSH report for additional information.

The Case

Early on the morning of July 21, 2007, Captain Matthew Burton and Engineer Scott Desmond were performing primary search of a single family dwelling in San Pablo, California. During their search, they were trapped by rapidly deteriorating conditions and died as a result of thermal injuries and smoke inhalation. Two civilian occupants also perished in the fire.

Figure 1. 149 Michele Drive-Alpha/Delta Corner

Note: Contra Costa Fire Protection District (Firefighter Q76) Photo, Investigation Report: Michele Drive Line of Duty Deaths. This photo illustrates conditions shortly after 0159 (Q76 time of arrival).

Building Information

The fire occurred in a 1,224 ft² (113.7 M2), one-story, wood frame dwelling with an attached garage at 149 Michele Drive in San Pablo (Contra Costa County), California. The house was originally built in 1953 and remodeled in 1991 with the addition of a pitched rain roof over the original (flat) roof.

This single story structure was of Type V, platform frame construction. The building was originally constructed with 4″ x 8″ (102 mm x 203 mm) beams supporting a flat roof with 2″ x 6″ (51 mm x 152 mm) tongue and groove planking with a built-up overlay consisting of several layers of tar and gravel. The pitched roof was constructed of 2″ x 8″ (51 mm x 203 mm) rafters covered with plywood and asphalt composite shingles. The ridge of the pitched roof was parallel to Side A. The gable ends on Sides B and D were constructed of plywood and fitted with a small gable vent.

Figure 2. Floor Plan-149 Michelle Drive

Note: This floor plan is based on data provided in the Contra Costa Fire Protection District Investigation Report and is not drawn to scale. The position of exterior doors and condition of windows as illustrated is based on the narrative or photographic evidence. Interior doors are shown as open as illustrated in the report. Fire service casualties are designated as follows: 1) Captain Burton, 2) Engineer Desmond.

All windows with the exception of the Living Room and Bedroom 1 (see Figure 2) were fitted with security bars (see Figure 3). The front door was the primary exit. In addition, an additional exit was provided from the kitchen through the garage to the exterior on Side D. The exterior door on Side D was fitted with a security grate.

Figure 3. View of Side C from the B/C Corner

Figure 4. Hallway and Bedroom 2

Note: Figures 3 & 4 adapted from Contra Costa Fire Protection District Photos (brightness and contrast adjusted to provide increased clarity).

Interior walls were gypsum board with wood veneer paneling on some of the walls (e.g., living room). All ceilings with the exception of the kitchen were exposed 2″ x 6″ (51 mm x 152 mm) tongue and groove planking (see Figure 4). The kitchen ceiling was covered with gypsum board. Ceiling height was 8′ (2.4 M).

Figure 5. Living Room

Note: Adapted from Contra Costa Fire Protection District Photos, Investigation Report: Michele Drive Line of Duty Deaths.

The Fire

Investigators determined that the fire likely originated on or near the east end of the bed in Bedroom 2 (see Figures 2 & 3). The likely source of ignition was improper discard of smoking materials. Developing into growth stage, the fire progressed from Bedroom 2 into the hallway (see Figures 2 & 4) leading to the living room, dining area, and kitchen (see Figures 2 & 5). It is likely that the door on Side A was closed at the time of ignition, but was opened by an occupant exiting some time after discovery of the fire.

Dispatch Information

Occupants discovered the fire and notified a private alarm company via two-way intercom at 0134. The alarm company notified the Contra Costa Regional Fire Communications Center of receipt of a fire alarm from 149 Michelle Drive at 0136 using the non-emergency telephone number. The alarm company did not indicate that they had talked to the resident who had reported a fire, but simply that they had received a fire alarm. The caller was placed on hold due to a higher priority 911 call. The dispatcher returned to the call from the alarm company at 0142 to obtain the address and callback information. Two attempts were made to call the incident location prior to dispatch of Engine 70 at 0144 to investigate the alarm. Contra Costa County Fire Protection District (CCCFPD) Engine 70 responded at 0145.

Shortly after Engine 70 responded, the communications center received a cell phone call from the female occupant at 149 Michelle Drive. This call was originally received by the California Highway Patrol and transferred to Contra Costa County Regional Fire Communications Center. The caller reported a residential fire and indicated that she had not been able to get her husband out of the building. Between the time that she spoke to the dispatcher and arrival of Engine 70, the female occupant reentered the building to attempt to rescue her husband (leaving the door on Side A open).

At 0146, the dispatcher upgraded the response to a residential fire and added two additional engines, a quint (as the truck company), and a battalion chief. Subsequent to the upgrade to a residential fire, additional 911 calls were received reporting a residential fire at 149 Michelle Drive.

Resources dispatched on the first alarm were as follows: Engine 70 (already responding on the initial dispatch for a residential alarm), Engine 69 (CCCFPD) as well as Rodeo-Hercules Fire Protection District Quint 76, and Battalion 7.� Richmond Fire Department Engine 68 was requested for automatic aid response through the Richmond Communications Center to fill out the first alarm assignment. Pinole Fire Department Engine 73 cleared a medical call a short distance away from the incident location and added themselves to the first alarm assignment. With the addition of Engine 73, the dispatcher canceled response of Engine 68 through Richmond Dispatch.

Note: Engine 73 was using an apparatus normally assigned at Station 74 which was marked with the designation Engine 74. This created some confusion during initial incident operations.

Weather Conditions

Conditions were clear, temperature was approximately 61^o F (16^o C), with a south to southeast (Side D to Side B) wind at between 2 and 6 mph (3.2 and 9.7 kph).

Conditions on Arrival

Shortly prior to arrival, Engine 70 reported “smoke showing a block out” and was advised by the dispatcher that the female occupant had been trying to get her husband out of the house and that it was uncertain if she had been successful. Engine 70 arrived at 0150, reported heavy smoke and fire from a single-story residential structure (flames and smoke were exiting from the open front door and large living room window on Side A), and established Command. Due to delays in the dispatch process, the time from the initial auomatic alarm until the arrival of E70 was approximately 16 minutes.(Refer to Contra Costa Fire Protection District, Investigation Report: Michele Drive Line of Duty Deaths for additional information regarding factors influencing the dispatch delay.

Questions

The following questions provide a basis for examining the first segment of this case study. You have an advantage that Captain Burton did not in that you are provided with a floor plan, photographs of Side C and the interior, and have knowledge of the eventual outcome. However, it is important that you place yourself in the situation encountered on arrival.

1. What stage(s) of fire and burning regime(s) were present in the building when E70 arrived? Consider potential differences in conditions in the living room, hallway, and bedrooms?
2. If you suspect that fire conditions in the living room were different than the hallway and bedrooms, why might this be the case? What evidence supports your position? What are your assumptions?
3. While limited information is available about the fire behavior indicators present during this incident, what Building, Smoke, Air Track, Heat, and Flame (B-SAHF) indictors did E70 observe when they arrived?
4. What B-SAHF indicators would you anticipate could have been observed on Sides B and C had this reconnaissance been conducted prior to making entry?
5. If you were faced with this situation, fire showing from the front door and window of a single family dwelling with persons reported, what actions would you take?
6. How do you think your selection of tactics would have influenced fire behavior and interior conditions?

Tactical Operations & Fire Behavior

My next post will examine tactical operations conducted by the first arriving companies and fire behavior encountered inside the building.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Contra Costa County Fire Protection District.� (2008). Investigation Report: Michele Drive Line of Duty Deaths. Retrieved February 13, 2009 from http://www.cccfpd.org/press/documents/MICHELE%20LODD%20REPORT%207.17.08.pdf

National Institute for Occupational Safety and Health (2009). �Death in the Line of Duty Report 2007-28. Retrieved May 5, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200728.pdf.

The deaths of Captain Matthew Burton and Engineer Scott Desmond in a residential fire on July 27, 2001 were the result of a complex web of circumstances, actions, and events. The Contra Costa County Fire Protection District and National Institute for Occupational Safety and Health (NIOSH) both investigated this incident and have published reports that outline the sequence of events, contributing factors, lessons learned, and recommendations. Readers are encouraged to read the Contra Costa County Fire Protection District Report and National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Report F2007-28. Also have a look at Tim Sendelbach’s post In Their Honor at Firefighter Nation.

Incident Overview

Early on the morning of July 21, 2007, Captain Matthew Burton and Engineer Scott Desmond were performing primary search of a small, one-story, single family dwelling in San Pablo, California. During their search, they were trapped by rapidly deteriorating conditions and died as a result of thermal injuries and smoke inhalation. Two civilian occupants also perished in the fire.

The crews of the first arriving companies (two engines arrived almost simultaneously) faced significant challenges with a report of civilian occupants trapped in the building, flames from the door and a large window on Side Alpha and smoke throughout the structure. The two engines rapidly initiated fire attack, primary search, and placed a blower for positive pressure ventilation. During interior firefighting operations, Captain Burton and Engineer Desmond were trapped extremely rapid fire development in the hallway and bedrooms while conducting search without a hoseline.

Contributing Factors

NIOSH Report F2007-28 identifies eight factors that contributed to the tragic outcome of this incident.

• Failure by the alarm company to report a confirmed fire
• Inadequate staffing to effectively and safely respond to a structure fire
• The failure to conduct a size-up and transfer incident command
• Conducting a search without protection from a hoseline
• Failure to deploy a back-up hoseline
• Improper/inadequate ventilation
• Lack of comprehensive training on fire behavior
• Failure to initiate/deploy a Rapid Intervention Crew

NIOSH identified these factors as contributing, not causal factors. This reflects the complex and interrelated relationship between the factors that resulted in the occurrence of extreme fire behavior during primary search operations and inability of the search crew to escape from the building.

As you read the reports on this incident consider the contributing factors identified by NIOSH. Do you agree that these factors were contributory; if so, in what way; if not, why not?

NIOSH Recommendations

Based on analysis of this incident and the contributing factors, NIOSH made nine recommendations [emphasis added]:

• Ensure that fire and emergency alarm notification is enhanced to prevent delays in the alarm and response of emergency units
• Ensure that adequate numbers of staff are available to immediately respond to emergency incidents
• Ensure that interior search crews are protected by a staffed hose line
• Ensure that firefighters understand the influence of positive pressure ventilation on fire behavior and can effectively apply ventilation tactics
• Develop and implement standard operating procedures (S.O.P.’s) regarding the use of backup hose lines to protect the primary attack crew from the hazards of deteriorating fire conditions
• Develop and implement (S.O.P.’s) to ensure that incident command is properly established, transferred and maintained
• Ensure that a Rapid Intervention Crew is established to respond to fire fighters in emergency situations
• Implement joint training on response protocols with mutual aid departments

Additionally standard setting agencies, states, municipalities, and authorities having jurisdiction should:

• Consider developing more comprehensive training requirements for fire behavior to be required in NFPA 1001 Standard for Fire Fighter Professional Qualifications and NFPA102 1 Standard for Fire Officer Professional Qualifications and states, municipalities, and authorities having jurisdiction should ensure that fire fighters within their district are trained to these requirements

This final recommendation is extremely significant in that this is the first time that NIOSH has indicated that lack of effective fire behavior training in the US fire service is a systems problem. Fire training is often driven by the need to meet (rather than exceed) minimum standards. This is understandable, given the wide range of competencies required of today’s firefighters and fire officers. However, the need to develop a sound understanding of fire behavior and practical fire dynamics is critical. While this issue needs to be addressed in the professional qualification standards, we should not wait until this is accomplished. Firefighters and fire officers must become (or continue to be) students of fire behavior and develop proficiency in reading the fire and mitigation of the hazards presented by extreme fire behavior phenomena such as flashover, backdraft, smoke explosion, and flash fire.

Ed Hartin, MS, EFO, MIFireE, CFO

In Fire Gas Ignitions and Language & Understanding: Extreme Fire Behavior, I pointed out the ambiguity in definition of terms related to extreme fire behavior. In the structural firefighting context, the term extreme fire behavior is used to identify phenomena that result in rapid fire progression and present a significant threat to firefighters. Rapid fire progression may involve transition to a fully developed fire (e.g., flashover) or it may involve a brief, but significant increase in energy release (e.g., backdraft, flash fire, smoke explosion).

One way to begin the process of reducing the ambiguity surrounding extreme fire behavior phenomena is to establish a framework for organizing and classifying extreme fire behavior phenomena.

Organizing Concepts

The organization and classification framework presented in this post is based on the following general concepts:

• Extreme fire behavior involves a rapid increase in heat release rate (HRR).
• The increase in HRR can be sustained or it may be relatively brief.
• Brief increases in HRR may or may not result in overpressure inside a compartment or building.
• Extreme fire behavior may occur in a fuel or ventilation controlled burning regime
• Concentration (mass fraction) of fuel in the gas phase influences the nature of extreme fire behavior.
• Depending on existing or developing conditions, extreme fire behavior may be initiated by reaching critical HRR, an increase in ventilation, or a source of ignition.

It is likely that there are additional concepts or criteria that may prove useful in the process of organizing and classifying extreme fire behavior. However, these concepts provide a starting point for this process and discussion.

Classification by Outcome

At the highest level, extreme fire behavior phenomena are classified on the basis of the duration of increased HRR. If increased HRR is sustained and the fire enters a (relatively) steady state of combustion, the phenomena would be classified as a Step Event. However, if the increase in HRR is brief and not sustained, the phenomena would be classified as a Transient Event.

A rapid increase in HRR results in increased temperature of the atmosphere inside the compartment. As temperature increases, the gas (i.e., air and smoke) volume within the compartment will expand. If the gas volume inside the compartment is confined and cannot expand, pressure will increase, in some cases significantly! Transient events are classified as Explosive (resulting in a significant overpressure) or Non-Explosive (not resulting in a significant overpressure). Explosiveness is in part a result of the mixture of gas phase fuel and air present in the compartment and the extent to which combustion is confined.

Classification of extreme fire behavior phenomena on the basis of outcome are illustrated graphically in Figure 1.

Figure 1. Outcome Classification

Classification by Conditions

Additional clarity can be obtained by examining extreme fire behavior phenomena on the basis of requisite conditions for occurrence. However, it is important to keep in mind that conditions are rarely uniform in structure fires. Different compartments (e.g., habitable spaces, voids) can have dramatically different conditions in burning regime, fuel concentration, oxygen concentration, and temperature.

In a compartment with sufficient openings, flashover can occur prior to fire growth becoming significantly limited by available ventilation. However, a majority of extreme fire behavior phenomena occur when the fire is in a ventilation controlled burning regime. As compartment fire development becomes limited by ventilation, not all of the gas phase fuel resulting from pyrolysis is burned. This excess pyrolizate increases both the mass and concentration of fuel within the compartment (and other compartments as smoke spreads through the building). Concurrently, with increased fuel concentration, oxygen concentration decreases.

Provided a source of ignition with sufficient energy, gas phase fuel/air mixtures within the flammable range can be ignited. However, if the fuel/air mixture is too rich, additional air must be introduced and mixed with the fuel in order for combustion to occur.

For extreme fire behavior phenomena occurring within a ventilation controlled burning regime, the following factors can be used to further define the nature of the phenomena:

• Fuel Concentration
• Oxygen Concentration
• Extent of Confinement

The combination of fuel/air mixture and extent of confinement define what type of initiating event (contact with source of ignition, increase in ventilation, or both) will be necessary for the extreme fire behavior to occur.

Graphical Representation

It is often easier to see how things are organized using a visual model or diagram. However, it is not so simple to capture a high level of complexity in a simple drawing. Figure 2 illustrates the concepts presented in this post regarding classification of extreme fire behavior phenomena.

This is a work in progress and feedback is greatly appreciated!

Ed Hartin, MS, EFO, MIFireE, CFO

Language is Important

Language has a substantial influence on what and how we think. “What a man cannot state he does not perfectly know, and conversely the inability to put his thoughts into words sets a boundary to his thought” (Newbolt, Bailey, Baines, Boas, Davies, Enright, et al., 1921, p. 20).

While the authors of this statement were focused on English language education in English schools in the 1920’s, the underlying concept applies equally well today. Language is the foundation of understanding. While this is true in day-to-day life, it is equally (or even more) important when dealing with scientific concepts and phenomena related to firefighting.

While construction and fuel loading vary to some extent, fire services around the world are challenged by similar fire problems in the built environment. Each of us faces the same processes of compartment fire development and extreme fire behavior phenomena such as flashover, backdraft, and smoke explosion. However, our understanding and communication about these important processes and phenomena are limited by lack of a common language. In many cases terms have more than one definition. In addition, definitions are often unclear and imprecise.

Shared Concepts

In philosophy, ontology is the study of the nature of reality, categories of being, and their relations; what entities can exist and how they can be grouped, related within a hierarchy, and divided based on their similarities and differences. Ontology is a system of concepts that provides a shared vocabulary that can be used to describe and think about a particular domain.

We do not really have an ontology that encompasses fire behavior phenomena such as flashover, backdraft, smoke explosion, and the like. As Dr. Stefan Svennson so astutely observes, it is complicated and there may not always be a clearly defined differences between phenomena. However, going back to the opening paragraph of this post, I contend that a shared language is necessary for us to understand and mitigate the hazards we face as a result of rapid fire progress. Hopefully this post will engage you in this ongoing effort.

Extreme Fire Behavior

Terms such as flashover, backdraft, and smoke explosion are often used to describe phenomena involving rapid fire progression in compartment fires. Currently accepted definitions provide a starting point for developing improved clarity. As a starting point, I have examined definitions of extreme fire behavior phenomena from the following sources:

1. International Standards Organization (ISO)
2. National consensus standards organizations (e.g., National Fire Protection Association, Fire Protection Association)
3. International or national professional associations (e.g., Institution of Fire Engineers, Society of Fire Protection Engineers)
4. Recognized texts

Consider the similarities and differences in the following definitions and give some thought to the questions that follow.

Flashover: 1) Stage of fire transition to a state of total surface involvement in a fire of combustible materials within an enclosure’ (ISO 13943, 2008, 4.156). 2) A transitional phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space resulting in full room involvement or total involvement of the compartment or enclosed area (NFPA 921-2007).

Discussion: This transition is often assumed to take place between the growth and fully developed stages. However, neither the ISO nor NFPA definition specifies this. In addition, while the NFPA definition indicates that this transition is extremely rapid (i.e., more or less simultaneously), the ISO definition does not describe the speed with which the transition to total surface involvement occurs.

• Is the occurrence of flashover limited to the transition between growth and fully developed stages of fire development?
• Can flashover result from increasing ventilation to a ventilation controlled fire (vent induced flashover)? If yes, how does this differ from backdraft?
• Can a fire reach the fully developed stage without transitioning through flashover?

Backdraft: 1) Rapid flaming combustion caused by the sudden introduction of air into a confined oxygen-deficient space that contains hot products of incomplete combustion. In some cases, these conditions can result in an explosion (ISO 13943, 2008, 4.21). 2) A deflagration resulting from the sudden introduction of air into a confined space containing oxygen-deficient products of incomplete combustion (NFPA 921, 2008, 3.3.14).� 3) A phenomenon that occurs when a fire takes place in a confined area such as a sealed aircraft fuselage and burns undetected until most of the oxygen within is consumed. The heat continues to produce flammable gases, mostly in the form of carbon monoxide. These gases are heated above their ignition temperature and when a supply of oxygen is introduced, as when normal entry points are opened, the gases could ignite with explosive force (NFPA 402, 2008).

Discussion: The ISO definition is considerably more broad than that specified in NFPA 921 and as such would be inclusive of phenomena such as ventilation induced flashover as well deflagration resulting from introduction of air to an extremely ventilation controlled fire. The definition of backdraft in NFPA 402, Guide for Aircraft Rescue and Firefighting Operations illustrates the common misconception that carbon monoxide is the primary gas phase fuel in a backdraft. There is no scientific evidence that this is the case. Both NFPA definitions indicate that backdraft is explosive in nature (e.g., deflagration) while the ISO definition indicates that this is a possibility, but not a requisite outcome.

• How does backdraft differ from a vent induced flashover? This is essentially the same question as before, but this time, think about it from the backdraft perspective.
• If there is a difference between vent induced flashover and backdraft, what is different (about the nature of the phenomena, requisite conditions, and initiating event(s))?
• Many firefighters believe that backdraft requires high temperature (resulting in auto-ignition following an increase in ventilation), yet this is not mentioned in any of the definitions. Is this the case?
• Is a backdraft always an explosive event?

Fire Gas Ignition: Ignition of accumulated unburned pyrolysis products and flammable products of incomplete combustion existing in or transported into a flammable state (Grimwood, Hartin, McDonough, & Raffel, 2005)

Discussion: In 3D Firefighting, Grimwood uses the term Fire Gas Ignition as a broad category of phenomena including smoke (fire gas) explosion, flash fire, and a number of other fire behavior phenomena.

• What differentiates phenomena classified as fire gas ignitions from backdraft, or for that matter flashover?
• If there is a common theme, is it useful to have an overarching category such as fire gas ignition?

Smoke Explosion: 1) See Backdraft (NFPA 921, 2008). 2) When unburnt gases from an under-ventilated fire flow through leakages into a closed space connected to the fire room, the gases there can mix very well with air to form a combustible gas mixture. A small spark is then enough to cause a smoke gas explosion (Karlsson & Quintiere, 2000). 3) A smoke gas explosion results from ignition of a confined mass of smoke gases and air that fall within the flammable range. This may result in a significant increase in pressure within the compartment (paraphrased from Bengtsson, 2001).

Discussion: In the past, the terms smoke explosion and backdraft were frequently used synonymously (and still used this way within NFPA 921). However, smoke explosion is a substantively different phenomenon as evidenced by the definitions provided by Karlsson & Quintiere (2000) and Bengtsson (2001). Drysdale (1998) also discusses this phenomenon, and while not providing a definition per say, delineates the difference between smoke explosion and backdraft as different phenomena.

• How are smoke explosion and backdraft different?
• What differentiates smoke explosion from flash fire?
• The phenomenon of smoke explosion as defined in various texts requires a mixture of fuel and air within the flammable range. If this flammable mixture is achieved by an increase in ventilation (adding air to a rich mixture of air and fuel), would piloted ignition result in a smoke explosion or backdraft?

Flash Fire: A fire that spreads rapidly through a diffuse fuel, such as dust, gas, or the vapors of an ignitable liquid, without the production of damaging pressure (NFPA 921, 2008, 3.3.72)

Discussion: While this definition appears reasonably clear when taken by itself, how does this differ from rollover, or for that matter flashover?

• What differentiates flash fire from other phenomena such as rollover (flameover) where fire spread rapidly through gas phase fuel in the upper layer?
• While the term “flash” infers a brief occurrence, the definition does not clearly define the duration of this phenomenon. Is this different from the rapid transition to a fully developed fire that results from flashover?
• What differentiates flash fire from a smoke explosion (the NFPA definition of flash fire provides a fuzzy hint, but is this clear enough)?

For a longer and more detailed examination of the definitions of flashover and backdraft, see The Current Knowledge and Training Regarding Flashover, Backdraft, and Other Rapid Fire Progression Phenomenon (Gorbett & Hopkins, 2007).

What Next?

Over the next couple of months, I will be working to develop a discussion (in a variety of formats) to develop a common framework and working definitions that will aid us in talking about fire behavior phenomena that present a significant threat to firefighters (i.e., extreme fire behavior). I invite you to be part of this process! More information will be provided in subsequent posts.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Bengtsson, L. (2001). Enclosure Fires. Karlstad, Sweden: R�ddnings Verket.

Drysdale, D. (2000). An introduction to fire dynamics. Chichester, England: John Wiley & Sons.

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.pdf.

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

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

National Fire Protection Association. (2008) NFPA 402 Guide for aircraft rescue and fire-fighting operations. Quincy, MA: Author.

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

Newbolt, H., Bailey, J., Baines, K., Boas, F., Davies, H., Enright, D., et al. (1921). Teaching of English in England.� Retrieved March 17, 2009 from http://ia340921.us.archive.org/2/items/teachingofenglis00greaiala/teachingofenglis00greaiala.pdf

What is Extreme?

There is some debate about the use of the term extreme fire behavior (some of my colleagues indicate that processes such as flashover is not “extreme” but simply “normal” fire behavior). I contend that flashover would potentially be a normal part of fire development, but is also extreme, at least in the context that we are using the word. As defined in the wildland firefighting community:

“Extreme” implies a level of fire behavior characteristics that ordinarily precludes methods of direct control action. One or more of the following is usually involved: high rate of spread, prolific crowning and/or spotting, presence of fire whirls, strong convection column. Predictability is difficult because such fires often exercise some degree of influence on their environment and behave erratically, sometimes dangerously (National Wildfire Coordinating Group Glossary)

In the structural firefighting environment, occurrence of flashover (particularly while firefighters are operating inside the compartment) fits substantially with the description of extreme used by wildland firefighters.

Classification and Understanding

Ontology may be described as definition of a formal representation of concepts and the relationships between those concepts. An ontology provides a shared vocabulary. Unfortunately we do not have a well developed ontology of fire behavior phenomenon and many types of phenomena have more than one definition. As with the use of the word extreme, there is some debate about the need to classify phenomena as being this or that (e.g., flashover or backdraft). I take the position that it is useful (but difficult as we do not have a common classification scheme or ontology). But, I think that it is still worth the effort.

This is a substantive topic for a later post. This post will examine a type of fire gas ignition phenomena that has been involved in a number of incidents in recent years resulting in near misses, injuries, and fatalities.

Fire Gas Ignitions

In a previous post, I posed the question: Backdraft or Smoke Explosion?. This post used a video clip to open a discussion of the difference between these two phenomena. A smoke (or fire gas) explosion is a type of fire gas ignition, but there are a number of other types of fire gas ignition that present a hazard during firefighting operations.

All fire gas ignitions (FGI) involve combustion of accumulated unburned pyrolysis products and flammable products of incomplete combustion existing in or transported into a flammable state (Grimwood, Hartin, McDonough, & Raffel, 2005). In a smoke explosion, ignition of a confined mass of smoke gases and air that fall within the flammable range results in extremely rapid combustion (deflagration), producing an significant overpressure which can result in structural damage. However, what happens if the mass of gas phase fuel is not pre-mixed within its flammable range and does not burn explosively?

The general term Fire Gas Ignition, encompasses a number of phenomena that are related by the common characteristic that they involve rapid combustion of gas phase fuel consisting of pyrolizate and unburned products of incomplete combustion that are in or are transported into a flammable state. For now, let’s differentiate these phenomena from backdraft on the basis of the concentration of gas phase fuel (backdraft involving a higher concentration than fire gas ignition).

Fire gas ignition can involve explosive combustion (as in a smoke explosion) or rapid combustion that does not produce the same type of overpressure as an explosion. One such phenomenon is a flash fire. In this case, gas phase fuel ignites and burns for short duration, but does not release sufficient energy for the fire to transition to a fully developed stage (as occurs in flashover). While a flash fire may not result in flashover, the energy release is still significant and heat flux (energy transferred) can be sufficient result in damage to personal protective equipment, injury and death. This post uses a case study to examine the flash fire phenomenon.

Residential Fire

This case study is based on a near-miss incident involving extreme fire behavior during a residential fire that occurred on October 9, 2007 at 1119 William Street in Omaha, Nebraska. Special thanks to Captain Shane Hunter (Omaha Fire Department Training Officer) for sharing this post incident analysis and lessons learned.

Unlike many of the incidents used as case studies, no one died or was injured during incident operations. In this near miss incident, the firefighters and officers involved escaped without injury, but the outcome could easily have been quite different.

Weather Conditions

Weather was typical for early fall with a light breeze from the south (blowing towards Side C of the fire building).

Building Information

The fire building was a one and a half story, wood frame dwelling with a basement (see Figure 1). The attic space had been renovated into three separate compartments to provide additional living space.

Figure 1. Exterior View Side A

Figure 2. Floor 2 Layout

Conditions on Arrival

When the first company arrived they observed fire and smoke from the second floor window (see Figure 1) and reported a working fire. The doors and windows on the first floor were closed.

Firefighting Operations

What initial actions were taken? A 200′ hoseline was extended through the door located on Side A and through the living room and kitchen to the stairway to the second floor, which was located at the C/D corner of the structure (Figures 2 and 3).

Figure 5 & 6. Kitchen (view from Floor 1) and Stairwell (view from Floor 2)

What did the fire attack crew observe? The living room and kitchen were clear of smoke and the door to the second floor stairway was closed. When this door was opened and the line was advanced up the stairway to the second floor, the company assigned to fire attack encountered smoke down to floor level on the second floor. Making a left turn at the top of the stairs (see Figure 4) the Captain noted high temperature at the floor level and observed rollover at the ceiling level.

• How did the ventilation profile change when the door to second floor stairway was opened? How might this have changed fire behavior?
• What did the depth of the hot gas layer (from ceiling to floor) indicate about the ventilation profile?
• What did rollover in the center compartment indicate?

The Captain instructed the nozzle operator to apply water to the ceiling. The firefighter on the nozzle applied water in a 30^o fog pattern (continuous application). Simultaneously, a crew working on the exterior vented the second floor window on Side C (see Figures 4 and 6).

How did conditions change? The engine company working on floor 2 heard an audible, whoosh as the hot gas layer ignited producing flames down to floor level. Operation of the hoseline (30^o fog pattern) had no immediate effect. The Captain ordered the crew to retreat into the stairwell and continue water application.

• What extreme fire behavior phenomena occurred?
• What were the initiating events that caused this rapid fire progression?

Figure 4. Floor 2 Side A (Looking Towards Side A)

Figure 5. Floor 2 Side C (Looking Towards Side C)

What action was taken? While the engine company operated from the stairwell, vertical ventilation was completed over the center compartment (see Figures 4 and 5). After the creation of an exhaust opening in the roof, conditions on floor 2 became tenable and the engine crew was able to knock the fire down within several minutes.

• Why did conditions improve quickly after the creation of a vertical exhaust opening?
• What tactical options might have prevented this near miss?

Observations and Analysis

Captain Shane Hunter observed that the initial fire attack crew viewed this incident as an easy job. They thought that an attack from the unburned side would simply push the fire out the window where fire was initially showing on Side A. Why did things turn out so differently than anticipated?

In his analysis of this incident, Captain Hunter points out that there is a considerable difference between a “self-vented” fire and an adequately ventilated fire. As discussed in the April 2008 Officer’s Corner (GFES), horizontally ventilated fires are likely to remain ventilation-controlled. It is important to read the Building, Smoke, Air Track, Heat, and Flame (B-SAHF) indicators to determine the current burning regime (fuel or ventilation-controlled) and anticipate the effect of changes to the ventilation profile.

The fire in the compartment of origin reached flashover resulting in the extension of flames into the center compartment as evidenced by the observation of rollover by the Captain of the engine company performing fire attack. However, the center compartment and the compartment on Side C did not experience flashover (note the condition of contents in the center compartment in Figure 6.). If flashover did not occur in these two compartments, what happened?

In this incident, the fire gases ignited in a flash fire, but combustion did not rapidly transition to a fully developed state in the two compartments adjacent to the compartment of origin.

A flash fire rapidly increases heat release rate, temperature within the compartment and heat flux (as experienced by the fire attack crew in this incident). Like rollover, this phenomenon should not be confused with flashover as fuel in the lower region of the compartment may or may not ignite and sustain combustion. However, fire gas ignition can precede and precipitate flashover (should the fire quickly transition to the fully developed stage).

The concentration of fuel within the hot gas layer varies considerably, with higher concentrations at the ceiling. Concentrations within the flammable range most commonly develop at the interface between the hot gas layer and the cooler air below. Isolated flames (an indicator of a ventilation-controlled fire) are most commonly seen in the lower region of the hot gas layer (as there may be insufficient oxygen concentration in the upper level of the hot gas layer to support flaming combustion). Mixing of the hot gas layer and air due to turbulence increases the likelihood of a significant fire gas ignition.

• What was the ventilation profile and air track when the engine company reached the top of the stairs to begin their attack on the fire?
• How did the tactical ventilation performed from the exterior (removal of the window on floor 2, Side C) influence the ventilation profile and air track?
• What effect do you think that continuous operation of the 30^o fog stream had on conditions on floor 2?
• What combination of factors likely resulting in mixing of air and smoke (fuel) leading to the fire gas ignition that drove the fire attack crew off floor 2 and into the stairwell?

Key Considerations and Lessons Learned

This incident points to a number of key considerations and lessons learned.

• Beware the routine incident! Even what appears to be a simple fire in a small residential structure can present significant challenges and threats to your safety.
• Use the B-SAHF indicators to read the fire and consider both the stage of fire development and burning regime (fuel or ventilation-controlled) in strategic and tactical decision making.
• Flame showing is just that. Do not be lulled into a false sense of security by thinking that the fire is adequately ventilated. Read the air track indicators!
• Continue to read the fire after making entry. Smoke is fuel and hot gases overhead are a threat. Observation of isolated flames indicates a ventilation-controlled fire. Rollover often precedes flashover. Take proactive steps to mitigate the threat of extreme fire behavior.
• Recognize that ventilation-controlled fires will increase in heat release rate if additional air is introduced. Manage the ventilation profile using tactical ventilation and tactical anti-ventilation. Anticipate unplanned ventilation due to fire effects.
• Recognize that both horizontal and vertical ventilation are effective when used appropriately and coordinated with fire control. Consider the influence of inlet and exhaust opening location and size when anticipating the influence of tactical ventilation on fire behavior and conditions within the building.

Again special thanks to Captain Shane Hunter and the Omaha Fire Department for sharing the information about this incident and their work to improve firefighter safety.

Ed Hartin, MS, EFO, MIFireE, CFO