It has been a busy six weeks since my last post with several trips to Chile and around the United States delivering seminars on Practical Fire Dynamics and Reading the Fire along with finalizing the fire district’s budget for 2014. Spending a full-day on B-SAHF and reading the fire at the Springfield Professional Firefighters IAFF Local 333 professional development seminar and working with our fire district’s members on our adaptation of First Due Questions (see FDQ on Facebook and First Due Tactics on the web) provided inspiration to get back to the Reading the Fire series of blog posts.
Fireground photos and video can be used to aid in developing and maintaining proficiency in reading the Fire using the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme for fire behavior indicators. This post provides an opportunity to exercise your skills using a video segment shot during a live fire training. While live fire training is a considerably different context than an actual incident, this video provides an opportunity to focus on each of the elements of B-SAHF somewhat more closely than in typical incident video.
In this exercise, the focus will be on identifying specific indicators related to stages of fire development and burning regime (rather than anticipating fire development).
In this video, the fire has been ignited in a room (likely a bedroom) on the Bravo/Charlie corner of the building and the video is being taken from the exterior on the same corner. The ventilation profile is uncertain, but there is likely an opening/entry point on Side Alpha.
As you watch the first 0:43 of the video, identify the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators that can be observed and how they change over time.
What are the first visible indicators?
What indicators are visible on and through the window between 0:43 and 0:56? How do condensation of water or pyrolysis products on window glazing aid in determining burning regime and stages of fire development? How might these indicators differ at locations more remote from the fire?
How do the B-SAHF indicators change between 0:56 and 2:40? Why might this be the case?
After 2:40 flaming combustion appears to increase. What might have influenced this change?
By 3:37, the window on the Bravo/Charlie corner is dark and little flaming combustion can be observed. What might this indicate about burning regime and stages of fire development?
At approximately 3:41, how do smoke and air track indicators change. What might this indicate? If there is no change in ventilation profile, how might the smoke and air track indicators change next?
At 4:10 crews on Side Alpha report fire in a front (Side Alpha) room. Why might fire conditions be significantly different on this side of the building than in the original fire compartment? How might extinguishment of the fire in a room on Side Alpha influence fire development in the original fire compartment (Bravo/Charlie corner)?
The lower portion of a window in the fire compartment on the Bravo/Charlie corner is broken out at 4:24. How does this change the B-SAHF indicators observed from this location? What may be inferred from these observations?
Immediately after the lower portion of the window is broken out, a narrow fog stream is applied in a rotating manner through the window. What effect does this have on fire conditions in the room? How did smoke and air track indicators change during the brief water application? What did these changes indicate?
How did smoke and air track indicators change after the brief application of water into the fire compartment?
After the brief application of water through the window, how long did it take for the fire to resume significant growth in the fire compartment (crews operating from Side Alpha delayed fire attack intentionally).
At 7:09, the upper portion of the window on the Bravo/Charlie corner is removed. How does this change in ventilation influence visible B-SAHF indicators and fire behavior?
How do the B-SAHF indicators change as interior crews begin fire attack?
How might taking the glass in the window(s) on the Charlie side of the building have influenced visible B-SAHF indicators and fire behavior?
Had the window in the fire compartment located on Side Charlie (Charlie/Bravo Corner) failed first, what impact would this have had on flow path? How might this have influenced conditions encountered by the fire attack crew entering from Side Alpha?
At approximately 8:40, interior crews begin hydraulic (negative pressure) ventilation through a window in the fire compartment on the Charlie/Bravo corner. How does this tactic integrate with the natural pressure differences created by the wind? What might be a more effective alternative?
Developing world class knowledge and skill takes approximately 10,000 hours of deliberate practice. This equates to almost three hours every day, 365 days per year, for 10 years. If you only practice every third day achieving 10,000 hours in 10 years would require just over eight hours per day and if you only spend 2 hours every third day, it would take over 40 hours to achieve 10,000 hours of deliberate practice.
How are you coming on your 10,000 hours? Keep at it!
A pre-arrival video of a July 23, 2013 residential fire posted on YouTube illustrates the impact of ventilation (making an entry opening) in advance of having a hoseline in place to initiate fire attack. The outcome of increased ventilation mirrors the full scale fire tests conducted by Underwriters Laboratories (UL) during their Horizontal Ventilation Study (see The Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction or the On-Line Learning Module).
Residential Fire
63 seconds after the front door is opened, the fire transitions to a fully developed fire in the compartment on the Alpha/Bravo Corner of the building and the fire extends beyond the compartment initially involved and presents a significant thermal insult to the firefighters on the hoseline while they are waiting for water.
A More Fine Grained Look
Take a few minutes to go back through the video and examine the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) Indicators, tactical actions, and transitions in fire behavior.
0:00 Flames are visible through a window on Side Bravo (Alpha Bravo/Corner), burning material is visible on the front porch, and moderate smoke is issuing from Side Alpha at low velocity.
0:30 Flames have diminished in the room on the Alpha/Bravo Corner.
1:18 An engine arrives and reports a “working fire”. At this point no flames are visible in the room on the Alpha/Bravo Corner, small amount of burning material on the front porch, moderate smoke is issuing at low velocity from Side Alpha and from window on Side Bravo
1:52 A firefighter kicks in the door on Side Alpha
2:02 The firefighter who opened the door, enters the building through the Door on Side Alpha alone.
2:08 Other members of the engine company are stretching a dry hoseline to Side Bravo.
2:15 Increased in flaming combustion becomes visible through the windows on Sides A and B (Alpha/Bravo Corner).
2:31 The firefighter exits through door on Side Alpha and flaming combustion is now visible in upper area of windows on Sides A and B (Alpha/Bravo Corner).
2:49 Flames completely fill the window on Side Alpha and increased flaming combustion is visible at the upper area of the window on Side Bravo. The engine company is now repositioning the dry hoseline to the front porch
2:55 The fire in the compartment on the Alpha/Bravo Corner is now fully developed, flames completely fill the window on Side Alpha and a majority of the window on Side Bravo. Flames also begin to exit the upper area of the door on Side Alpha.
3:07 Steam or vapors are visible from the turnout coat and helmet of the firefighter working in front of the window on Side Alpha (indicating significant heat flux resulting from the flames exiting the window)
3:25 Steam or vapors are visible from the turnout coat and helmet of the firefighter on the nozzle of the dry line positioned on the front porch (also indicating significant heat flux from flaming combustion from the door, window, and under the porch roof).
3:26 The hoseline on the front porch is charged and the firefighter on the nozzle that is positioned on the front porch begins water application through the front door.
Things to Think About
There are a number of lessons that can be drawn from this video, but from a ventilation and fire control perspective, consider the following:
Limited discharge of smoke and flames (even when the fire has self-vented) may indicate a ventilation controlled fire.
Ventilation controlled fires that have already self-vented will react quickly to additional ventilation.
Control the door (before and after entry) until a hoseline is in place and ready to apply water on the fire
Application of water into the fire compartment from the exterior prior to entry reduces heat release rate and buys additional time to advance the hoseline to the seat of the fire.
Use of the reach of the stream from the nozzle reduces the thermal insult to firefighters and their personal protective equipment.
Also see Situational Awareness is Criticalfor another example of the importance of understanding practical fire dynamics and being able to apply this knowledge on the fireground.
As discussed in my last post, doctrine is a guide to action rather than a set of rigid rules. Clear and effective doctrine provides a common frame of reference, helps standardize operations, and improves readiness by establishing a common approach to tactics and tasks. Doctrine should link theory, history, experimentation, and practice to foster initiative and creative thinking.
One way to frame the discussion necessary to develop doctrine that is applicable to a range of circumstances, is to use a series of scenarios presenting different conditions and examine what is similar and what is different. Ideally, firefighters will work together to integrate this theoretical discussion with their experience to develop sound doctrine based on their own context (e.g., staffing, building and occupancy types).
Fireground Scenarios
Important! Not all of the tactics presented in the questions are appropriate and others may be appropriate in one context, but not necessarily in another. For example, a lightly staffed engine may not have the option of offensive operations until the arrival of additional resources (barring a known imminent life threat), where a company with greater staffing may have greater strategic and tactical flexibility. These questions focus on the impact of strategic (offensive or defensive) tactical options on fire dynamics.
Scenario 1: The first arriving company arrives to find a small volume of smoke showing from around windows and doors and from the eaves on Side Alpha with low velocity, no air inlet is obvious. Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows are closed. Several windows on Side Alpha (Alpha Bravo Corner) are darkened with condensed pyrolysis products and the home appears to have smoke throughout (smoke logged).
How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
The fire is likely in a ventilation controlled, decay stage. If the ventilation profile does not change prior to entry (e.g., doors are kept closed, windows remain intact), the heat release rate (HRR) from the fire will continue to decline and temperatures within the building will drop (but may still be fairly high when entry is made).
How would opening the front door prior to having a charged line at the doorway on Side Alpha impact fire development?
Increased ventilation will result in a significant and potentially rapid increase in HRR. The proximity of the door to the fire compartment and temperature in the fire compartment at the time that ventilation is increased will have a direct impact on the speed with which the fire returns to the growth stage (but still remaining ventilation controlled). The closer the air inlet to the fire and the higher the temperature, the more rapidly the fire will return to the growth stage.
How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the (still closed) doorway on Side Alpha?
As noted in the answer to question 2, increased ventilation will result in an increase in HRR. As windows in the fire compartment are in closer proximity to the fire, taking the windows potentially will result in a more rapid return to the growth (but still ventilation controlled) stage. It is also important to consider that a window cannot be unbroken; selecting this ventilation option does not provide an option for changing you mind if you do not like the result.
What would be the impact on fire behavior if the engine company advanced the first hoseline to the windows; took the glass and applied water to the burning fuel inside the fire compartment prior to making entry through the door? How might this change if offensive fire attack was delayed (e.g., insufficient staffing for offensive operations)?
This is an interesting question! Research by UL, NIST, and FDNY has shown the positive impact of exterior application of water into the fire compartment in reducing heat release rate. However, as noted in the answer to the preceding question, a window cannot be unbroken. If this is simply a contents fire in the compartment where the window is broken and water is applied, the result is likely to be favorable with a temporary reduction in HRR due water applied on burning fuel. However, if the fire extended to other areas of the building which shielded from direct attack at this point of application, effectiveness of exterior application from this single location is likely to be limited.
How would opening the front door and horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the doorway on Side Alpha?
Advice on coordination of tactical ventilation and fire attack has typically stated, don’t vent until a charged hoseline is in place. This is good advice, but requires a bit of clarification.
“As soon as the hoseline is deployed to the doorway” may simply mean that a dry line has been stretched and firefighters are donning their self-contained breathing apparatus (SCBA) facepieces while waiting for water. The fire will begin transition back to the growth stage as soon as tactical ventilation is performed. Depending on the time required for the firefighters to mask up, the line to be charged, air bled off, pattern checked, and the charged line advanced to the fire compartment(s), the HRR may increase significantly and conditions are likely to be quite a bit worse than if the door and window had remained closed until the hoseline was in place to begin offensive fire attack from the interior.
If tactical ventilation is performed after the line is charged and firefighters are ready to immediately make entry and quickly advance to the fire compartment, it is likely that the effect of increased ventilation will be positive. There may be some increase in HRR, but it is likely to be minimal due to the short distance and simple stretch from the front door to the fire compartment(s). Once direct attack has begun to control the fire, the increased ventilation will improve conditions inside the building.
Assuming that sufficient resources are on-scene to permit an offensive attack, when should the entry point be opened? Assuming that the door is unlocked, how should the fire attack crew approach this task?
Tactical size-up is critical for the crew assigned to offensive fire attack. This includes assessment of B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators, forcible entry requirements, and assessment of fire attack requirements (e.g., flow rate, length of line, and complexity of the stretch).
The door should remain closed until the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. Check to see if the door is unlocked, but control the door (closed) and check conditions inside (visible fire, level of the hot upper layer, presence of victims inside the doorway) by opening the door slightly. The firefighter on the nozzle should do this check while the tools firefighter opens and controls the door. If hot smoke or flames are evident, the nozzle firefighter should cool the upper layer with one or more pulses of water fog (depending on conditions). The door should be closed while the crew assesses the risk of entry (e.g., floor is intact and fire conditions will permit entry from this location). If OK for entry; the crew can open the door and advance the line inside, while cooling the upper layer as necessary.
Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
Ideally, the door will be closed after the hoseline is advanced through the doorway to limit the air supplied to the fire. How this is accomplished will depend on staffing. The door may be controlled by the fire attack crew or it may be controlled by the standby crew (two-out).
As discussed in the prior post Influence of Ventilation in Residential Structures: Tactical Implications Part 2, when the door is open, the clock is ticking! In the ventilation controlled burning regime, increased ventilation results in an increasing HRR as the fire returns to the growth stage. The timeframe for increased HRR is dependent on the proximity of the inlet to the fire, configuration of the building, and temperature in the fire area (higher temperature results in faster increase in HRR). Closing the door (even partially) slows the increase in HRR. Once the attack line begins direct attack, the door can be opened as part of planned, systematic, and coordinated tactical ventilation.
Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?
As with most questions, the answer here is “it depends”. There are a few missing bits of information that are important to horizontal tactical ventilation. Wind direction and the location of potential openings. To keep things simple, assume that there is no wind and that the only potential openings in the fire compartment are two windows on Side Alpha at the Alpha/Bravo Corner.
Once direct attack has commenced, horizontal tactical ventilation can be performed from Alpha (doorway) to Alpha (windows in the fire compartment). As the top of the door and tops of the windows are likely to be approximately at the same level, there a bi-directional flow path (smoke out at the top and air in at the bottom) is likely to develop. However, the bottom of the door is lower than the windows which will provide increased air movement from the door to the fire compartment.
In discussing this question (and the entire topic of door control for that matter), some firefighters will undoubtedly raise the question of positive pressure attack (PPA) or positive pressure ventilation (PPV). These tactics may provide an effective approach in this scenario, but developing comprehensive tactical ventilation doctrine requires examination of all of the options to control both smoke and air movement, so we are starting with a look at anti-ventilation and tactical ventilation using natural means.
Scenario 2: The first arriving company arrives to find smoke showing with moderate velocity and a bi-directional air track (smoke out the top and air in the bottom) from an open door on Side Alpha. A moderate volume of smoke is also pushing from around windows and from the eaves on Side Alpha. Several windows on Side Alpha (Alpha Bravo Corner) are darkened with condensed pyrolysis products and a glow is visible inside in the room behind these windows. Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. The home appears to have smoke throughout (smoke logged).
How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
The fire is in a ventilation controlled burning regime (indicators include the limited ventilation provided by the single opening at the front door and flames at the interface between the smoke and air at the door). The open door will likely provide sufficient ventilation for the fire to continue its growth and extension from the compartment of origin along the flowpath to the front door.
How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?
Based on the reported observations during 360o reconnaissance, the only significant ventilation opening is the front door. The bi-directional air track indicates that this opening is serving as both an inlet and outlet. Closing the door will reduce the air supply to the fire and will reduce the HRR and slow worsening conditions outside the fire compartment. Ideally this would be done prior to starting the 360o reconnaissance.
Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?
As in Scenario 1, the door should be opened only when the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. The same door entry procedure described in Scenario 1 should be used as if the door had been closed on arrival.
How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development is performed as soon as the hoseline is deployed to the open doorway on Side Alpha?
The outcome of tactical ventilation of the fire compartment will depend on sequence and timing. If the door remained open during initial size-up and while the line was being stretched, he fire would have continued to grow (limited by ventilation provided by the doorway and interior configuration of the building). Additional ventilation in this case would result in a rapid increase in HRR. If the door had been closed during the 360, the increase in HRR on ventilation of the windows would likely be somewhat slower as the HRR and temperature in the fire compartment would have dropped once the door was closed. In either case, HRR will increase while the charged line is being stretched from the entry point to the fire compartment. This is not necessarily a problem if the stretch is quick and the flow rate of the hoseline is adequate. It is essential that the crews stretching the line and performing ventilation understand the influence of their actions on fire behavior and are not surprised at the result.
Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
As noted in Scenario 1, closing the door to the greatest extent possible after the line is inside will slow fire development until the hoseline is in place to begin a direct attack.
Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?
The same basic approach would be taken as in Scenario 1. Once direct attack has commenced, horizontal tactical ventilation can be performed from Alpha (doorway) to Alpha (windows in the fire compartment).
Scenario 3: The first arriving company arrives to find smoke showing with moderate velocity and a bi-directional air track (smoke out the top and air in the bottom) from an open door on Side Alpha. A moderate volume of smoke is also pushing from around windows and from the eaves on Side Alpha. Flames are visible from several windows on Side Alpha (Alpha Bravo Corner) with a bi-directional air track (flames from the upper ¾ of the window with air entering the lower ¼). Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the two windows and door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. Flames from the windows on Side Alpha are similar to when first observed. The home appears to have smoke throughout (smoke logged).
How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
The fire is likely in a ventilation controlled burning regime (indicators include the limited ventilation provided by the openings at the front door and windows. Existing ventilation will likely be sufficient for the fire to continue its growth and extension from the compartment of origin along the flowpath to the front door. As there are multiple ventilation openings (more cross sectional area), HRR is greater and as a result fire development and spread will be much more rapid than in Scenario 2.
How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?
As the windows in the fire compartment have failed and are serving as ventilation openings (in addition to the front door), the fire will likely remain in a ventilation controlled growth stage even if the door is closed. However, closing the door will still reduce the air supply to the fire and will slow fire growth. In addition, elimination of the flow path between the fire compartment and front door will reduce heat transfer along this flow path.
Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?
As in Scenarios 1 and 2, the door should be opened only when the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. The same door entry procedure described in the prior scenarios should be used.
How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the open doorway on Side Alpha?
As the windows in the fire compartment have already failed, some ventilation of the fire compartment has already occurred. In that the fire is ventilation controlled, any additional ventilation will significantly increase HRR. With a ventilation controlled growth stage fire and high temperature in the fire compartment, the HRR will increase rapidly.
Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
As in the previous two scenarios, the door should be closed to as great an extent possible after the hoseline is advanced inside the building. This will limit air to the fire, slow fire development, an reduce the flow path between the fire and the front door.
Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?
As the windows in the fire compartment have already failed, they will continue to provide ventilation. Once a direct attack has been initiated, the front door may be opened to increase air flow and the efficiency of the horizontal ventilation from Side Alpha to Side Alpha.
As noted in the previous post, these questions were all based on a similar fire (different development based on the ventilation profile at the time of the first company’s arrival) in the same, simple building, a one story, wood frame dwelling. It is important to examine other levels of involvement and ventilation profiles in this building as well as other types of buildings and fire conditions with similar questions. Also give some thought to the impact of door control when using vertical ventilation in coordination with fire attack.
Additional Examples
The following video of pre-arrival conditions and initial fireground operations provides an additional opportunity to consider the impact of ventilation and the importance of door control.
Video 1: In the first video, the door is closed when the fire department arrives, but the fire has self-vented through a window on Side Delta.
How might effective door control have influenced fire development and the safety of companies operating at this incident?
Video 2: In this video, the front door is open when the fire department arrives and it appears that the fire may have self-vented on Side Charlie.
How might effective door control have influenced fire development and the safety of companies operating at this incident?
Video 3: In the last video, the front door is partially open and existing ventilation includes a window on Side Alpha and one or more openings on Side Charlie.
How might effective door control have influenced fire development and the safety of companies operating at this incident?
There has been an increasing awareness that smoke is fuel and that hot smoke overhead results in thermal insult (due to radiant heat transfer) and potential for ignition. However, the hazard presented by smoke as gas phase fuel can extend a considerable distance from the current area of fire involvement.
Reading the Fire
Print a copy of the B-SAHF Worksheet. Use the worksheet to document observed fire behavior indicators as you watch the first six minutes of the following video of an apartment fire that occurred on May 10, 2013 at the corner of Park Creek Lane and Hill Park Court in Churchville, NY. In particular, focus on fire behavior indicators that may point to changes in conditions. Don’t focus too much on the flame indicators presenting from the area involved, but pay particular attention to Building, Smoke, and Air Track indicators.
The following satellite photo and view of the Alpha/Delta Corner prior to the fire are provided to help orient you to the incident location. You can also go to Google Maps Street View and do a walk around on Sides Alpha (Hill Park Court) and Delta (Park Creek Lane) to view all four sides of the building.
The following time sequence from the video of this incident illustrates the conditions immediately prior to and during the explosion. The extremely rapid increase in heat release rate during the explosion was not sustained (a transient event) as evidenced by conditions illustrated at 06:25.
Building Factors
This building is of Type V construction with a wood truss roof system. In a large apartment building such as this, the trussloft is typically subdivided with draft stops comprised of gypsum board applied to one (or both) sides of a truss to stop rapid spread of fire within the trussloft. Draft stops should be thought of as speed bumps rather than a barrier (such as a firewall that extends through the roofline). While draft stops slow fire and smoke spread, they do not stop it completely and it is common for smoke to spread beyond the fire area despite the presence of draft stops.
The small dimension framing materials used in truss construction have a high surface to mass ratio, increasing the speed with which they can be heated and increasing pyrolysis products in the smoke when heated under ventilation limited conditions.
Note: The possible location of the draft stops is speculative as specific information regarding the construction of this building was not available at the time of this post. However, draft stops may be provided between the trussloft between units or based on the size of the trussloft without regard to the location of walls between units. Preplan inspections provide an opportunity to examine building factors that may be critical during an incident!
Smoke and Air Track Indicators
An important air track indicator in this incident was the strong wind blowing from the Alpha/Bravo Corner towards the Charlie/Delta Corner. The wind may have had some influence on ventilation in the trussloft above Exposures Bravo and Bravo 2, and definitively influenced other Smoke and Air Track indicators.
From the start of the video light colored smoke is visible at the peak of the roof above Exposure Bravo and Bravo 2, indicating that smoke had infiltrated areas of the trussloft that had not yet become involved in fire. Smoke that is light in color may be comprised of pyrolysis products and air and may be to lean or too rich to burn or it may be explosive See the video Smoke on the Firegear website for a good discussion of the characteristics of smoke (note that this video is currently undergoing validation).
The volume and color (smoke indicators), velocity and direction (air track indicators) above exposure Bravo 2 vary considerably from the start of the video until shortly before the explosion that occurred at 06:12 in the video. At 02:52 a firefighter entered Exposure Bravo 2 and a short time later at 03:47 a hoseline (dry) was stretched into this exposure and charged. It is unknown from watching the video if the firefighters on this line advanced to Floor 2 or if they took any action to change the ventilation profile (other than opening the door on Floor 1, Side Alpha). The exited after the explosion, but without haste, so it is likely that they were not on Floor 2 at the time of the explosion.
Smoke Explosion
Smoke explosion is described in a number of fire dynamics texts including Enclosure Fire Dynamics (Karlsson and Quintiere) and An Introduction to Fire Dynamics (Drysdale). However, Enclosure Fires by Swedish Fire Protection Engineer Lars-Göran Bengtsson (2001) provides the most detailed explanation of this phenomenon. Paraphrasing this explanation:
A smoke or fire gas explosion occurs when unburned pyrolysis products and flammable products of combustion 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.
In some cases, the fire serves as a source of ignition as it extends into the void or compartment containing the flammable mixture of smoke (fuel) and air.
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. Smoke explosion creates a significant overpressure as the fuel and air are premixed and ignition results in a very large energy release. 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 within the flammable range (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)
Potential Smoke Explosion Indicators
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 600o C or 1112o F) smoke
Presence of void spaces, particularly if they are interconnected
Combustible structural elements
Infiltration of significant amounts of smoke into uninvolved compartments in the fire building or into exposures
Preventing a Smoke Explosion
As it is difficult to predict a smoke explosion, there are challenges to preventing their occurrence as well. However, general strategies would include 1) preventing smoke from accumulating in uninvolved spaces or 2) removing smoke that has accumulated remote from the fire (e.g., in attached exposures), or 3) a combination of the first two approaches.
Tactics to implement these strategies may include:
Pressurizing uninvolved spaces with a blower to prevent infiltration of smoke. This involves use of a blower for anti-ventilation by applying pressure without creating an exhaust, similar to what is done to pressurize a highrise stairwell. It is essential to check for extension prior to implementing this tactic!.
Horizontal ventilation of attached exposures to remove smoke, checking for extension, and then pressurization with a blower to prevent continued infiltration of smoke. If fire extension is found, pressurization without an exhaust opening must not be implemented!
Additional Resources
The following previous posts on the CFBT-US Blog may also be of interest in exploring the smoke explosion phenomena.
On March 10, 2013 five Harrison, New Jersey firefighters were injured in an explosion while working at a commercial fireat 600-602 Frank E. Rodgers Boulevard. The fire originated in a two-story commercial building at the corner of Frank E. Rodgers Boulevard North and Davis Street and extended into Exposures Charlie and Delta, two-story residential buildings.
Figure 1. Alpha/Bravo Corner and Exposure Charlie
Image from Google Maps, click on the link to walk around using Street View.
Reading the Fire
Before watching the video (or watching it again if you have already seen it), download and print the B-SAHF Worksheet. Using the pre-fire photo (figure 1) and observations during the video, identify key B-SHAF indicators that may have pointed to potential for extreme fire behavior in this incident.
Important! Keep in mind that there is a significant difference between focusing on the B-SAHF indicators in this context and observing them on the fireground. Here you know that an explosion will occur, so we have primed the pump so you can focus (and are not distracted by other activity).
Backdraft or Smoke Explosion
While smoke explosion and backdraft are often confused, there are fairly straightforward differences between these two extreme fire behavior phenomena. A smoke explosion involves ignition of pre-mixed fuel (smoke) and air that is within its flammable range and does not require mixing with air (increased ventilation) for ignition and deflagration. A backdraft on the other hand, requires a higher concentration of fuel that requires mixing with air (increased ventilation) in order for it to ignite and deflagration to occur. While the explanation is simple, it may be considerably more difficult to differentiate these two phenomena on the fireground as both involve explosive combustion.
Did you observe any indicators of potential backdraft prior to the explosion?
Do you think that this was a backdraft?
What leads you to the conclusion that this was or was not a backdraft?
If you do not think this was a backdraft, what might have been the cause of the explosion?
For more information in Backdraft, Smoke Explosion, and other explosive phenomena on the fireground, see:
I would like to say thanks to all of you who have sent e-mail or contacted me on Facebook inquiring about the status of the CFBT-US blog. The last several years have been extremely busy at Central Whidbey Island Fire & Rescue and my focus has been almost exclusively on the fire district. However, I am renewing my commitment to developing knowledge of practical fire dynamics throughout the fire service and will endeavor to return to posting on a regular basis. In addition, I am working on a series of short (10-minute) drills on fire dynamics that will be cross posted on the CFBT Blog and the Fire Training Toolbox.
Video of several incidents involving explosions during structural firefighting operations have been posted to YouTube in the last several weeks. Two of these videos, one from New Chicago, IN and the other from Olathe, KS involve residential fires. The other is of a commercial fire in Wichita, KS.
When a video shows some sort of spectacular fire behavior there is generally a great deal of speculation amongst the viewers about what happened. Was it a smoke (fire gas) explosion, backdraft, flashover, or did something else happen? Such speculation is useful if placed in the framework of the conditions required for these phenomena to occur and the Building, Smoke, Air Track, Heat, and Flame (B-SAHF) indicators that provide cues of to current fire conditions and potential fire behavior.
Occasionally, what happened is fairly obvious such as flashover resulting from increased ventilation under ventilation controlled conditions. However, the phenomena and its causal factors are often much more of a puzzle.
Limited information was posted along with this pre-arrival video of a residential fire in Olathe, KS. The home was unoccupied when the fire occurred.
Watch the thirty seconds (0:30) of the video. First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions (based only on what you observe during the first thirty seconds of the video)?
What additional information would you like to have? How could you obtain it?
What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
What burning regime is the fire in (fuel controlled or ventilation controlled)?
What conditions would you expect to find inside this building?
How would you expect the fire to develop over the next two to three minutes
Watch remainder of the video and consider the following questions:
Did fire conditions progress as you anticipated?
What changes in the B-SAHF indicators did you observe?
What may have caused the explosion (consider all of the possibilities)?
Were there any indications that may have given warning of this change in conditions?
Residential Fire-New Chicago, IN
Companies from New Chicago and Hobart were dispatched to a reported house fire at 402 Madison in New Chicago, IN on February 17, 2012.
Watch the thirty seconds (0:30) of the video. First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions (based only on what you observe during the first thirty seconds of the video)?
What additional information would you like to have? How could you obtain it?
What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
What burning regime is the fire in (fuel controlled or ventilation controlled)?
What conditions would you expect to find inside this building?
How would you expect the fire to develop over the next two to three minutes
Watch remainder of the video and consider the following questions:
Did fire conditions progress as you anticipated?
What changes in the B-SAHF indicators did you observe?
What may have caused the explosion (consider all of the possibilities)?
Were there any indications that may have given warning of this change in conditions?
Commercial Fire-Wichita, KS
Wichita Fire Department on scene of a working building fire in large, non-combustible commercial building. Extreme heat and fire conditions cause an unknown cylinder to explode.
Keep in mind that gas cylinders and other closed containers can result in explosions during structural firefighting operations. Unlike backdraft and smoke explosion, the only clue may be building factors related to occupancy (and this may not be a good indicator when operating at a residential fire).
Wichita Fire Department on scene of a working building fire in a large metal structure. Extreme heat and fire conditions cause an unknown cylinder to explode. If you listen close, you can hear it vent before it goes off. Concussion actually cuts out my audio for just a couple seconds. No one was injured.
Potential for explosions related to extreme fire behavior such as backdraft and smoke explosion may be recognized based on assessment and understanding the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators. Other types of explosions such as those resulting from failure of closed containers (e.g., containing liquids or gases) may be a bit more difficult as this potential is likely to be present in most types of occupancies. However, commercial and industrial occupancies present greater risks.
Recognizing that even with sound experienced judgment, there may be undetected hazards on the fireground. Managing the risk requires developing a solid knowledge base and skills and operating within sound rules of engagement such as the IAFC Rules of Engagement for Structural Firefighting. However, considering the hazards presented by rapid fire progression and potential for changes in conditions following explosive events, I would add the following:
Base your strategies and tactics on current and anticipated fire behavior and structural stability.
Ensure that members correctly wear complete structural firefighting clothing and SCBA when working in the hazard zone and practice good air management. Buddy check before entry!
Crews operating on the interior should have a hoseline or be directly supported by a crew with a hoseline. If conditions deteriorate, a hoseline allows self-protection and provides a defined egress path.
My next post will address the impact of a closed door on tenability during a residential fire as the ninth tactical implication identified in the UL study on the Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction.
Subsequent posts will come back to the Olathe, KS and New Chicago, IN residential fires to examine potential impacts on fire behavior and explosions that resulted during these incidents.
Watch the first minute and thirty seconds (1:30) of the video. First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions?
What additional information would you like to have? How could you obtain it?
What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
What burning regime is the fire in (fuel controlled or ventilation controlled)?
What conditions would you expect to find inside this building?
How would you expect the fire to develop over the next two to three minutes
In addition, consider how the answers to these questions impact your assessment of the potential for survival of possible occupants.
Now watch the video clip from 1:30 until 2:00. Now answer the following questions:
Did fire conditions progress as you anticipated?
What changes in the B-SAHF indicators did you observe?
What indications of fire stream effectiveness did you observe?
What potential avenues of fire extension would you consider based on the type of construction and building design?
As you watch the remainder of the video, consider the changes in observed conditions and what information this might provide the Incident Commander. What information should interior crews report to Command during this stage of incident operations.
More on Reading the Fire
See the following posts for more information on reading the fire:
The eighth and tenth tactical implications identified in the Underwriters Laboratories study of the Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2011) are the answer to the question, can you vent enough and the influence of pre-existing openings or openings caused by fire effects on the speed of progression to flashover.
The ninth implication; the effects of closed doors on tenability for victims and firefighters, will be addressed in the next post.
Photo Credit: Captain Jacob Brod, Pineville (NC) Fire Department
Kerber (2011) indicates that firefighters presume that if you create enough ventilation openings that the fire will return to a fuel controlled burning regime. I am not so sure that this is the case. Until fairly recently, the concept of burning regime and influence of increased ventilation on ventilation controlled fires was not well recognized in the US fire service. However, there has been a commonly held belief that increased ventilation will improve interior conditions and reduce the potential for extreme fire behavior phenomena such as flashover. In either case, the results of the experiments conducted by UL on the influence of horizontal ventilation cast considerable doubt on the ability to accomplish either of these outcomes using horizontal, natural ventilation.
The Experiments
In order to determine the impact of increased ventilation, Kerber (2011) compared changes in temperature with varied numbers and sizes of ventilation openings. The smallest ventilation opening in the experiments conducted in both the one and two story houses was when the door on Side A was used to provide the only opening. The largest number and size of ventilation openings was in the experiments where the front door and four windows were used (see Figures 1 and 3)
The area of ventilation openings in experiments conducted in the one-story house ranged from 1.77 m2 (19.1 ft2) using the front door only to 9.51 m2 (102.4 ft2) with the front door and four windows. In the two-story house the area of ventilation openings ranged from 1.77 m2 (19.1 ft2) with front door only to 14.75 m2 (158.8 ft2) using the front door and four windows.
The most dramatic comparison is between Experiments 1 and 2 where a single opening was used (front door) and Experiments 14 and 15 where five openings were used (door and four windows).
One Story House
Experiment 1 was conducted in the one-story house using the door on Side A as the only ventilation opening. The door was opened eight minutes after ignition (480 seconds). Experiment 14 was also conducted in the one-story house, but in this case the door on Side A and four windows were used as ventilation openings. Windows in the living room and bedrooms one, two, and three were opened sequentially immediately after the door was opened, providing more than five times the ventilation area as in Experiment 1 (door only).
Figure 1. Ventilation Openings in the One-Story House
In both Experiment 1 (door only) and Experiment 14 (door and four windows), increased ventilation resulted in transition to a fully developed fire in the compartment of origin (see Figure 2). In Experiment 1, a bi-directional air track developed at the door on Side A (flames out the top and air in the bottom). In Experiment 14, a bi-directional air track is visible at all ventilation openings, with flames visible from the door and window in the Living Room on Side A and flames visible through the window in Bedroom 3. No flames extended out the ventilation openings in Bedrooms 1, 2, and 3. The upper layer in Bedroom 3 is not deep, as such there is little smoke visible exiting the window, and it appears to be serving predominantly as an inlet. On the other hand, upper layer in Bedroom 2 is considerably deeper and a large volume of thick (optically dense) smoke is pushing from the window with moderate velocity. While a bi-directional air track is evident, this window is serving predominantly as an exhaust opening.
Figure 2. Fire Conditions at 600 seconds (10:00)
As illustrated in Figure 3, increased ventilation resulted in a increase in heat release rate and subsequent increase in temperature. It is important to note that the peak temperature in Experiment 14 (door and four windows) is more than 60% higher than in Experiment 1 (door only).
Figure 3. Living Room Temperature 0.30 m(1’) Above the Floor One-Story House
Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 298), by Steve Kerber, 2011, Northbrook, IL: Underwriters Laboratories.
Based on observed conditions and temperature measurement within the one-story house, it is evident that increasing the ventilation from 1.77 m2 (19.1 ft2) using the front door to 9.51 m2 (102.4 ft2) with the front door and four windows did not return the fire to a fuel controlled burning regime and further, did not improve interior conditions.
It is important to note that these experiments were conducted without coordinated fire control operations in order to study the effects of ventilation on fire behavior. Conditions changed quickly in both experiments, but the speed with which the fire transitioned from decay to growth and reached flashover was dramatically more rapid with a larger ventilation area (i.e., door and four windows).
Two Story House
Experiment 2 was conducted in the two-story house using the door on Side A as the only ventilation opening. The door was opened ten minutes after ignition (600 seconds). Experiment 15 was also conducted in the two-story house, but in this case the door on Side A and four windows were used as ventilation openings. One window in the Living Room (Floor 1, Side A, below Bedroom 3) Den (Floor 1, Side C, below Bedroom 2) and two windows in the Family Room (Side C) were opened sequentially immediately after the door was opened, providing more than eight times the ventilation area as in Experiment 2 (door only).
Figure 4. Ventilation Openings in the Two-Story House
In both Experiment 2 (door only) and Experiment 15 (door and four windows), increased ventilation resulted in transition to a fully developed fire in the compartment of origin. Flames were seen from the family room windows in Experiment 15 (see Figure 5). However, in Experiment 2, no flames were visible on the exterior (due to the distance between the fire compartment and ventilation opening) and a bi-directional air track developed at the door on Side A (smoke out the top and air in the bottom). In Experiment 15, a bi-directional air track is visible at all ventilation openings, with flames visible from the windows in the family room on Side C. No flames extended out the ventilation openings on Side A or from the Den on Side C (see Figure 5). The upper layer is extremely deep (particularly considering the ceiling height of 16’ in the family room and foyer atrium. The velocity of smoke discharge from ventilation openings is moderate.
Figure 5. Fire Conditions at 780 seconds (13:00)
As illustrated in Figure 6, increased ventilation resulted in a increase in heat release rate and subsequent increase in temperature. It is important to note that the peak temperature in Experiment 15 (door and four windows) is approximately 50% higher than in Experiment 2 (door only).
Figure 6. Living Room Temperature 0.30 m(1’) Above the Floor One-Story House
Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 299), by Steven Kerber, 2011, Northbrook, IL: Underwriters Laboratories.
Another Consideration
Comparison of these experiments answers the questions if increased horizontal ventilation would 1) return the fire to a fuel controlled state or 2) improve interior conditions. In a word, no, increased horizontal ventilation without concurrent fire control simply increased the heat release rate (sufficient for the fire to transition through flashover to a fully developed stage) in the involved compartment.
Examining thermal conditions in other areas of the building also provides an interesting perspective on these two sets of experiments. Figure 7 illustrates temperatures at 0.91 m (3’) during Experiment 1 (door only) and Experiment 14 (door and four windows) in the one-story house.
Figure 7. Temperatures at 0.91 m (3’) during Experiments 1 and 14
Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 99, p. 162), by Steven Kerber, 2011, Northbrook, IL: Underwriters Laboratories.
Thermal conditions not only worsened in the fire compartment, but also along the flow path (for a more detailed discussion of flow path, see UL Tactical Implications Part 7) and in downstream compartments. Temperature in the hallway increased from a peak of just over 200o C to approximately 900o C when ventilation was increased by opening the four additional windows.
Unplanned Ventilation
Each of the experiments in this study were designed to examine the impact of tactical ventilation when building ventilation was limited to normal leakage and fire conditions are ventilation controlled (decay stage). In each of these experiments, increased ventilation resulted in a rapid increase in heat release rate and temperature. Even when ventilation was increased substantially (as in Experiments 14 and 15), it was not possible to return the fire to a fuel controlled burning regime.
It is also possible that a door or window will be left open by an exiting occupant or that the fire may cause window glazing to fail. The impact of these types of unplanned ventilation will have an effect on fire development. Creation of an opening prior to the fire reaching a ventilation controlled burning regime will potentially slow fire progression. However, on the flip side, providing an increased oxygen supply will allow the fire to continue to grow, potentially reaching a heat release rate that will result in flashover. If the opening is created after the fire is ventilation controlled, the results would be similar to those observed in each of these experiments. When the fire is ventilation controlled, increased ventilation results in a significant and dramatic increase in heat release rate and worsening of thermal conditions inside the building.
If the fire has self-ventilated or an opening has been created by an exiting occupant, the increased ventilation provided by creating further openings without concurrent fire control will result in a higher heat release rate than if the openings were not present and will likely result in rapid fire progression.
What’s Next?
I will be at UL the week after next and my next post will provide an update on UL’s latest research project examining the influence of vertical ventilation on fire behavior in legacy and contemporary residential construction.
Two tactical implications from the horizontal ventilation study remain to be examined in this series of posts: the impact of closed doors on tenability and the interesting question can you push fire with stream from a hoseline?
The last year has presented a challenge to maintaining frequency of posts to the CFBT Blog. However, I am renewing my commitment to post regularly and will be bringing back Reading the Fire, continuing examination of fundamental scientific concepts, and integration of fire control and ventilation tactics.
In the experiments conducted by UL, both the single and two story dwellings filled rapidly with smoke with the smoke layer reaching the floor prior to ventilation. This resulted in zero visibility throughout the interior (with the exception of the one bedroom with a closed door). After ventilation, the smoke layer did not lift (as many firefighters might anticipate) as the rapid inward movement of air simply produced a tunnel of clear space just inside the doorway.
Put in the context of the Building, Smoke, Air Track, Heat, and Flame (B-SAHF) fire behavior indicators, these phenomena fit in the categories of smoke and air track. Why did these phenomena occur and what can firefighters infer based on observation of these fire behavior indicators?
Smoke Versus Air Track
There are a number of interrelationships between Smoke and Air Track. However, in the B-SAHF organizing scheme they are considered separately. As we begin to develop or refine the map of Smoke Indicators it is useful to revisit the difference between these two categories in the B-SAHF scheme.
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.
Smoke Indicators
There are a number of smoke characteristics and observations that provide important indications of current and potential fire behavior. These include:
Location: Where can you see smoke (exterior and interior)?
Optical Density (Thickness): How dense is the smoke? Can you see through it? Does it appear to have texture like velvet (indicating high particulate content)?
Color: What color is the smoke? Don’t read too much into this, but consider color in context with the other indicators.
Physical Density (Buoyancy): Is the smoke rising, sinking, or staying at the same level?
Thickness of the Upper Layer: How thick is the upper layer (distance from the ceiling to the bottom of the hot gas layer)?
As discussed in Reading the Fire: Smoke Indicators Part 2, these indicators can be displayed in a concept map to show greater detail and their interrelationships (Figure 1).
Figure 1. Smoke Indicators Concept Map
Air Track
Air track includes factors related to the movement of smoke out of the compartment or building and the movement of air into the fire. Air track is caused by pressure differentials inside and outside the compartment and by gravity current (differences in density between the hot smoke and cooler air). Air track indicators include velocity, turbulence, direction, and movement of the hot gas layer.
Direction: What direction is the smoke and air moving at specific openings? Is it moving in, out, both directions (bi-directional), or is it pulsing in and out?
Wind: What is the wind direction and velocity? Wind is a critical indicator as it can mask other smoke and air track indicators as well as serving as a potentially hazardous influence on fire behavior (particularly when the fire is in a ventilation controlled burning regime).
Velocity & Flow: High velocity, turbulent smoke discharge is indicative of high temperature. However, it is essential to consider the size of the opening as velocity is determined by the area of the discharge opening and the pressure. Velocity of air is also an important indicator. Under ventilation controlled conditions, rapid intake of air will be followed by a significant increase in heat release rate.
Discharge of smoke at openings and potential openings (Building Factors) is likely the most obvious indicator of air track while lack of smoke discharge may be a less obvious, but equally important sign of inward movement of air. Observation and interpretation of smoke and air movement at openings is an essential part of air track assessment, but it must not stop there. Movement of smoke and air on the interior can also provide important information regarding fire behavior.
An Ongoing Process
Reading the fire is an ongoing process, beginning with reading the buildings in your response area prior to the incident and continuing throughout firefighting operations. It is essential to not only recognize key indicators, but to also note changing conditions. This can be difficult when firefighters and officer are focused on the task at hand.
UL Experiment 13
This experiment examined the impact of horizontal ventilation through the door on Side A and one window as high as possible on Side C near the seat of the fire. The family room was the fire compartment. This room had a high (two-story) ceiling with windows at ground level and the second floor level (see Figure 3).
Figure 3. Two-Story Dwelling
In this experiment, the fire was allowed to progress for 10:00 after ignition, at which point the front door (see Figure 3) was opened to simulate firefighters making entry. Fifteen seconds after the front door was opened (10:15), an upper window in the family room (see Figure 3) was opened. No suppression action was taken until 12:28, at which point a 10 second application of water was made through the window on Side C using a straight stream from a combination nozzle.
As with all the other experiments in this series fire development followed a consistent path. The fire quickly consumed much of the available oxygen inside the building and became ventilation controlled. At oxygen concentration was reduced, heat release rate and temperature within the building also dropped. Concurrently, smoke and air track indicators visible from the exterior were diminished. Just prior to opening the door on Side A, there was little visible smoke from the structure (see Figure 4).
Figure 4. Experiment 13 at 00:09:56 (Prior to Ventilation)
As illustrated in Figure 5, a bi-directional air track was created when the front door was opened. Hot smoke flowed out the upper area of the doorway while air pushed in the bottom creating a tunnel of clear space inside the doorway (but no generalized lifting of the upper layer.
Figure 5. Experiment 13 at 00:10:14 (Door Open)
As illustrated in Figure 6, opening the upper level window in the family room resulted in a unidirectional air track flowing from the front door to the upper level window in the family room. No significant exhaust of smoke can be seen at the front door, while a large volume of smoke is exiting the window. However, while the tunneling effect at floor level was more pronounced (visibility extended from the front door to the family room), there was no generalized lifting of the upper layer throughout the remainder of the building.
Figure 6. Experiment 13 at 00:10:21 (Door and Window Open)
With the increased air flow provided by ventilation through the door on Side A and Window at the upper level on Side C, the fire quickly transitioned to a fully developed stage in the family room. The heat release rate (HRR) and smoke production quickly exceeded the limited ventilation provided by these two openings and the air track at the front door returned to bi-directional (smoke out at the upper level and air in at the lower level) as shown in Figure 7.
Figure 7. Experiment 13 at 00:11:22 (Door and Window Open)
What is the significance of this observation? Movement of smoke out the door (likely the entry point for firefighters entering for fire attack, search, and other interior operations) points to significant potential for flame spread through the upper layer towards this opening. The temperature of the upper layer is hot, but flame temperature is even higher, increasing the radiant heat flux (transfer) to crews working below. Flame spread towards the entry point also has the potential to trap, and injure firefighters working inside.
Gas Velocity and Air Track
A great deal can be learned by examining both the visual indicators illustrated in Figures 4-7 and measurements taken of gas velocity at the front door. During the ventilation experiments conducted by UL, gas velocities were measured at the front door and at the window used for ventilation (see Figure 3). Five bidirectional probes were placed in the doorway at 0.33 m (1’) intervals. Positive values show gas movement out of the building while negative values show inward gas movement. In order to provide a simplified view of gas movement at the doorway, Figure 8 illustrates gas velocity 0.33 m (1’) below the top of the door, 0.33 m (1’) from the bottom of the door, and 0.66 m (2’) above the bottom of the door.
A bidirectional (out at the top and in at the bottom) air track developed at the doorway before the door was opened (see Figure 8) as a result of leakage at this opening. It is interesting to note variations in the velocity of inward movement of air from the exterior of the building, likely a result of changes in combustion as the fire became ventilation controlled. The outward flow at the upper level resulted in visible smoke on the exterior of the building. While not visible, inward movement of air was also occurring (as shown by measurement of gas velocity at lower levels in the doorway.
Creation of the initial ventilation opening by opening the front door created a strong bidirectional air track with smoke pushing out the top of the door while air rapidly moved in the bottom. Had the door remained the only ventilation opening, this bidirectional flow would have been sustained (as it was in all experiments where the door was the only ventilation opening).
Opening the upper window in the family room resulted in a unidirectional flow inward through the doorway. However, this phenomenon was short lived, with the bidirectional flow reoccurring in less than 60 seconds. This change in air track resulted from increased heat release rate as additional air supply was provided to the fire in the family room.
While not the central focus of the UL research, these experiments also examined the effects of exterior fire stream application on fire conditions and tenability. Each experiment included a 10 second application with a straight stream and a 10 second application of a 30o fog pattern. Between these two applications, fire growth was allowed to resume for approximately 60 seconds.
The straight stream application resulted in a reduction of temperature in the fire compartment and adjacent compartments (where there was an opening to the family room or hallway) as water applied through the upper window on Side C (ventilation opening) cooled the compartment linings (ceiling and opposite wall) and water deflected off the ceiling dropped onto the burning fuel. As the stream was applied, air track at the door on Side A changed from bidirectional to unidirectional (inward). This is likely due to the reduction of heat release rate achieved by application of water onto the burning fuel with limited steam production.
When the fog pattern was applied, there was also a reduction of temperature in the fire compartment and adjacent compartments (where there was an opening in the family room or hallway) as water was applied through the upper window on Side C (ventilation opening) cooled the upper layer, compartment linings, and water deflected off the ceiling dropped onto the burning fuel. The only interconnected area that showed a brief increase in temperature was the ceiling level in the dining room. However, lower levels in this room showed an appreciable drop in temperature. Air track at the door on Side A changed from bidirectional to unidirectional (outward) when the fog stream was applied. This effect is likely due to air movement inward at the window on Side C and the larger volume of steam produced on contact with compartment linings as a result of the larger surface area of the fog stream.
The effect of exterior streams will be examined in more detail in a subsequent post.
Important Lessons
The fifth tactical implication identified in the Underwriters Laboratories study of the Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2011) is described as failure of the smoke layer to lift following horizontal natural ventilation and smoke tunneling and rapid air movement in through the front door.
Additional lessons that can be learned from this experiment include:
Ventilating horizontally at a high point results in higher flow of both air and smoke.
Increased inward air flow results in a rapid increase in heat release rate.
The rate of fire growth quickly outpaced the capability of the desired exhaust opening, returning the intended inlet to a bi-directional air track (potentially placing firefighters entering for fire attack or search at risk due to rapid fire spread towards their entry point).
Tactical applications of this information include:
Ensure that the attack team is in place with a charged line and ready to (or has already) attack the fire (not simply ready to enter the building) before initiating horizontal ventilation.
Cool the upper layer any time that it is above 100o C (212o F) to reduce radiant and convective heat flux and to limit potential for ignition and flaming combustion in the upper layer.
Note that this research project did not examine the impact of gas cooling, but examination of the temperatures at the upper levels in this experiment (and others in this series) point to the need to cool hot gases overhead.
What’s Next?
I am on the hunt for videos that will allow readers to apply the tactical implications of the UL study that have been examined to this point in conjunction with the B-SAHF fire behavior indicators. My next post will likely provide an expanded series of exercises in Reading the Fire.
The next tactical implication identified in the UL study (Kerber, 2011) examines the hazards encountered during Vent Enter Search (VES) tactical operations. A subsequent post will examine this tactic in some detail and explore this tactical implication in greater depth.
Developing and maintaining proficiency in reading the Fire using the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme for fire behavior indicators, requires practice. This post provides an opportunity to exercise your skills using a video segment shot during a commercial fire.
Residential Fire
This post examines fire development during a residential fire in New Chicago, Indiana.
Watch the first 30 seconds (0:30) of the video. First, describe what you observe in terms of the Building, Smoke, Air Track, Heat, and Flame Indicators; then answer the following five standard questions?
What additional information would you like to have? How could you obtain it?
What stage(s) of development is the fire likely to be in (incipient, growth, fully developed, or decay)?
What burning regime is the fire in (fuel controlled or ventilation controlled)?
What conditions would you expect to find inside this building?
How would you expect the fire to develop over the next two to three minutes
In addition, consider how the answers to these questions impact your assessment of the potential for survival of possible occupants.
Now watch the video clip from 0:30 until firefighters make entry at 3:05. Now answer the following questions:
Did fire conditions progress as you anticipated?
What changes in the B-SAHF indicators did you observe?
How do you think that the stage(s) of fire development and burning regime will change over the next few minutes?
What conditions would you expect to find inside this building now?
How would you expect the fire to develop over the next two to three minutes
The crews working in this video appeared to achieve fire control fairly quickly and without incident. However, consider the following tactical and task related questions:
It did not appear that any member of the first arriving companies performed a 360o recon and size-up (they may have, but this was not visible in the video). Why might this be a critical step in size-up at a residential fire?
It appeared that two lines were run simultaneously (the first line to the door ended up as the back-up line, possibly due to a slight delay in charging the line). How should fire attack and backup roles be coordinated?
Fire attack was initiated from the interior (unburned side). What would have been the impact of the first line darkening the fire from the exterior (prior to entry)?
Were there any indicators of potential collapse (partial) of the roof? How would you manage this risk when working in a lightweight wood frame residence with observed extension into the trussloft? What factors would influence your decision-making and actions?
Reading the Fire
See the following posts for more information on reading the fire:
Note: Adapted from