Archive for the ‘Tactical Ventilation’ Category

Fire Rescue magazine Editor in Chief Tim Sendelbach recently raised a number of questions related to door control in his recent on-line article, Becoming Better Informed on the Fireground(2014). This article, has generated a fair bit of on-line discussion around the following issue: Which is a better tactic to provide a more tenable environment for the occupants; closing the door to limit inward air flow and reducing heat release rate (HRR) or leaving it open to reduce smoke logging of the space and provide an inward flow of air to aid in occupant survivability?

The debate may be broken down into a number of more specific question that frame the larger issue in a simpler way (or a more complex way, depending on your perspective):

• Will reducing the oxygen concentration to limit the HRR also have a negative effect on survivability of occupants due to the oxygen deficient atmosphere?
• Which results in a more toxic atmosphere, closing the door or leaving the door open?
• Which presents the larger and most significant threat, fire development or the toxicity of the atmosphere?

As always there are no simple answers to these questions. The answers depend on a number of variables that are unlikely to be known during fireground operations. However, we cannot be paralyzed by this complexity as strategic and tactical decisions must be made in a timely manner.

Place the Questions in Context

In order to frame the questions, consider a fire scenario which could result in serious injury or fatality to one or more building occupants: A fire in a one story, three bedroom, single family dwelling, occurring in the late evening or early morning hours, resulting from ignition of bedding as the result of contact with a cigarette (USFA, 2013a, 2013b). Bedroom 1 is the room of origin and has an open door to a hallway leading to the remainder of the house. Bedroom 2 is immediately adjacent to Bedroom 1 and has a closed door. Bedroom 3 is slightly further away from Bedroom 1 (than Bedroom 2) and has an open door. The home has functioning smoke alarms and the occupant of Bedroom 3 was alerted to the fire by alarm activation and was able to escape. The occupants of Bedrooms 1 and 2 were not alerted by the smoke alarm and remained in their respective bedrooms.

Scenario 1: The occupant of Bedroom 3 exited the home, leaving the front door open. Bedroom windows are closed and remain intact. These conditions remain constant until the arrival of the first fire company.

Scenario 2: The occupant of Bedroom 3 exited the home, closing the front door. Bedroom windows are closed and remain intact. These conditions remain constant until the arrival of the first fire company.

In both of these scenarios, companies arrive to find one occupant who has exited the building, and two occupants reported with a last known location in Bedrooms 1 and 2.

Fire Development in Scenario 1

In this scenario, the open bedroom door provides an adequate supply of oxygen to allow the fire to quickly progress from the incipient to the growth stage and transition through flashover. This results in untenable conditions in the fire compartment. A bi-directional air track exists in the flow path between the front door and the fire. Hot gases will exit the fire compartment and flow towards the front door at the upper level. Prior to flashover the fire will become ventilation limited and will continue in this state as the fire becomes fully developed in Bedroom 1 and flames extend into the hallway.

Conditions will vary considerably throughout the dwelling depending on location and height above the floor. Close to the fire, the hot upper layer will be well defined, but radiant heat flux at floor level will likely make conditions thermally untenable. Smoke production will be substantial and will likely fill any areas open to the fire (e.g., living spaces open to the hallway and bedroom with an open door). As distance from the fire increases, smoke will cool somewhat and smoke will be present in both the hot upper layer and the cooler layer below. Air moving from the open front door to the fire, will provide some cooling and a higher oxygen concentration along the flow path. However, continued fire development will result in increased smoke production and will likely overwhelm the ventilation provided by the open front door, causing increased velocity of smoke discharge and lowering of the upper layer. Flames will extend down the hallway and towards the front door, increasing radiant heat flux, pyrolizing fuel, and will likely result in a growth stage fire along the flow path.

Conditions at the lower levels remote from the fire may remain tenable for some time and even with close proximity to the fire compartment, Bedroom 2 with the closed door is also likely to provide tenable conditions for some time.

Fire Development in Scenario 2

In Scenario 2, the basic conditions at the start of the fire are the same. However, in this case, the exiting occupant closes the front door. Initially, there will be little difference in fire development as oxygen from throughout interconnected compartments will sustain fire growth. A bi-directional air track exists in the flow path between uninvolved spaces and the fire compartment. Hot gases will exit the fire compartment and flow into the hallway, filling areas open to the fire compartment at the upper level. Prior to flashover the fire will become ventilation limited and become more ventilation limited as the fire becomes fully developed in Bedroom 1 and flames extend into the hallway. As oxygen inside the house is used by the fire and oxygen concentration decreases, HRR and flaming combustion will be reduced. However, combustion will continue in the fire compartment and heat transfer in adjacent areas will result in continued pyrolysis, increasing the concentration of gas phase fuel in the smoke.

As in Scenario 1, conditions will vary considerably throughout the dwelling depending on location and height above the floor. However, areas open to the fire compartment are likely to be smoke logged (filled with smoke). Temperatures will be lower and oxygen concentration will likely be higher in areas remote from the fire. As the HRR continues to decrease, temperatures will slowly begin to drop throughout the building.

Conditions at the lower levels remote from the fire may remain tenable for some time and even with close proximity to the fire compartment, Bedroom 2 with the closed door is also likely to provide tenable conditions for some time.

Alternate Scenarios

The two scenarios presented are but a small fraction of possible conditions that could exist in this building. Failure of a window, partial closing of a door (or doors), fuel type, the specific location of the occupants (on the bed versus on the floor) can all impact on potential fire conditions and survivability. All of which are not fully known to responding firefighters (who simply know that they have persons reported, and their observation of B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators.

Tactical Options

This tactical discussion will focus on the issue of door control, and as such the variable of fire control tactics will be held constant by stating that given building configuration and access, the fastest approach to getting water into the fire compartment is by making access through the front door.

There are two basic decision points related to door control. Should the position of the door be changed immediately (e.g., during 360^o reconnaissance) and should the door be open or controlled (partially closed) from the time the hoseline is stretched to the interior until water is effectively applied to the fire.

Each of these decisions must be made in a timely manner and knowing when and if you will control the door should be a key element of your firefighting doctrine. In making this decision, it is essential to recognize that tenable conditions for trapped occupants and control of the fire environment to permit entry for fire control and primary search are both important considerations.

Close the Door: If the door is open, closing it will have several impacts on fire behavior. HRR will diminish and temperature within the building will be reduced. However, the smoke level will likely drop lower to the floor, but this effect will vary with location.

Open the Door: If the door is closed, opening it prior to a charged hoseline being in place will introduce fresh air (and oxygen). However, the effects of this action will occur primarily along the flow path between the opening and the fire (having limited effect on occupants in any other location). In addition, the additional air will increase the HRR from the fire. Increased HRR will likely overwhelm the limited ventilation provided by the opening, causing the upper layer to drop, with a small area of clear air at floor level just inside the door.

Door Control After Entry: If the door is controlled (partially closed) after entry, the flow of both hot smoke and air in the flow path between the fire and the front door will be reduced, limiting the increase in HRR and slowing fire progression in the upper layer between the fire and the entry point. Controlling the door after entry generally requires commitment of at least one member to door control and aiding in movement of hose through the controlled opening.

Door Open After Entry: If the door is open after entry, flow of hot smoke and air between the fire and the front door will increase as the fire receives additional oxygen and HRR increases. Extension of flames and ignition of gas phase fuel in the upper layer between the fire and the entry point is likely and should be anticipated. Access and egress through the door and for advancement of hose is unimpeded if the door remains in an open position.

The outcome of each of these choices is impacted by the distance between the entry point/ventilation opening and the fire (this influences both the speed with which the fire reacts to additional air and the time that it will take to advance the hoseline into a position where a direct attack can be made on the fire).

Unanswered Questions

Research conducted by the Underwriters Laboratories Firefighter Safety Research Institute (UL FSRI) and others have measured temperature, heat flux oxygen concentration, carbon monoxide, and carbon dioxide in the fire environment during full scale experiments (Kerber, 2011, 2013). Other tests have examined the range of toxic products in the fire environment and determined that carbon monoxide is not an effective proxy measure for overall risk of exposure to toxic products (Fabian, Baxter, & Dalton, 2010; Regional Hazardous Materials Team HM 09-Tualatin Valley Fire & Rescue Office of State Fire Marshal, 2011; Bolstad-Johnson, D., Burgess, J., Crutchfield, C., Storment, S., Gerkin, R., &Wilson, J., 2000).

Toxic effects resulting from exposure to products of combustion and pyrolysis are dependent on the dose (concentration x time) and the time over which that dose is received. However, potential survival is also impacted by potential thermal insult which depends on temperature, heat flux, and time. The potential variations in specific combustion and pyrolysis products present and thermal conditions in the fire environment is not limitless, but is nearly so. So what actions can be taken to reduce the risk to occupants who have been unable to egress the building prior to the arrival of fire companies?

Proactive Action Steps

While this post examines tactical options, the ideal outcomes is to prevent the fire from occurring in the first place, to increase the potential for occupants to escape prior to the development of untenable conditions, or for occupants to take refuge in a manner that will provide a tenable environment until the fire service can remove the threat or aid the occupants in their escape. Proactive steps would include the following:

• Home safety surveys to identify fire hazards and reduce the risk of fire occurrence as well as ensuring that homes have working smoke detectors and a home fire escape plan.
• Public education and fire code requirements to encourage or require residential sprinklers to increase the potential time for occupants to escape.
• Public education on the value of sleeping with your door closed and closing doors when escaping from a fire.
• Dispatch protocols to prompt occupants to close doors as they exit or to take refuge behind a closed door if they cannot escape.
• Train other emergency response personnel such as law enforcement and emergency medical services regarding the importance of not increasing ventilation to vent limited fires.

However, once a fire occurs and the fire department responds, our actions can have a significant impact on the outcome.

Firefighting Doctrine

The starting point for defining doctrine is to first, recognize that there is no single answer or silver bullet that will provide an optimal outcome under all circumstances. A second consideration is that you will never (this is one of the only absolutes) have enough information to clearly and definitively know exactly what is happening, what will happen next, and what impact your actions will have (you should have a good idea, but will not know with complete certainty). Starting points for thinking about integrating door control and anti-ventilation into your firefighting doctrine include:

• Research (Kerber, 2011, 2013) has provided solid evidence that when water cannot be immediately applied to the fire, closing the door will generally improve conditions on the interior. That said, there may be times when door control may not be necessary or may be contraindicated.
• If water can immediately be applied to the fire from the point of entry or within close proximity to the point of entry (e.g., the fire is not shielded), door control may not be needed prior to direct attack (but likely will not make things worse if it is performed).
• Control of doors in the flow path to confine hot smoke and fire gases may make operations safer and improve tenability for both trapped occupants and firefighters (think about the Isolate in Vent, Enter, Isolate, and Search (VEIS)).

Doctrine should be based on evidence provided by research and fireground experience. Both are necessary, but neither is sufficient.

The purpose of research is not to choose sides; it’s simply to provide data to help validate the debatable points of a chosen tactic and provide a greater degree of certainty for a recommended tactic. Keep in mind, with facts in hand, the fireground remains a dynamic situation and no tactic can or should ever be considered absolute. The goal is to provide as much factual information as possible so we can make informed decisions before, during and after the fire (Sendelbach, 2014).

Understanding the evidence provided by fire dynamics research cannot be developed by simply reading the Tactical Considerations or Executive Summary of a research report. Dig a bit deeper and examine the research questions and how the research was conducted. Consider the evidence, as research continues additional questions will be answered and our understanding of the fire environment and impact of tactical operations will continue to improve and likely have further impact on what we do on the fireground.

References

Sendelbach, T.(2014). Becoming better informed on the fireground. Retrieved July 5, 2015 from http://www.firefighternation.com/article/command-and-leadership/becoming-better-informed-fireground.

United States Fire Administration (USFA). (2013a). Civilian fire fatalities in residential buildings (2009–2011). Retrieved July 5, 2014 from http://www.usfa.fema.gov/downloads/pdf/statistics/v14i2.pdf

United States Fire Administration (USFA). (2013b) One- and two-family residential building fires (2009-2011). Retrieved July 5, 2014 from http://www.usfa.fema.gov/downloads/pdf/statistics/v14i10.pdf

Kerber, S. (2011). Impact of ventilation on fire behavior in legacy and contemporary residential construction. Retrieved July 5, 2014 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf

Kerber, S. (2013). Study of the effectiveness of fire service vertical ventilation and suppression tactics in single family homes. Retrieved July 17, 2013 from http://ulfirefightersafety.com/wp-content/uploads/2013/06/UL-FSRI-2010-DHS-Report_Comp.pdf

Fabian, T., Baxter, C., & Dalton, J. (2010). Firefighter exposure to smoke particulates. Retrieved July 5, 2014 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/WEBDOCUMENTS/EMW-2007-FP-02093.pdf

Regional Hazardous Materials Team HM 09-Tualatin Valley Fire & Rescue Office of State Fire Marshal (2011). A study on chemicals found in the overhaul phase of structure fires using advanced portable air monitoring available for chemical speciation. Retrieved July 5, 2014 from http://www.oregon.gov/osp/sfm/documents/airMonitoringreport.pdf

Bolstad-Johnson, D., Burgess, J., Crutchfield, C., Storment, S., Gerkin, R., &Wilson, J. (2000). Characterization of firefighter exposures during fire overhaul. Retrieved July 5, 2014 from http://www.firefightercoexposure.com/CO-Risks/

Social Learning

Last week, at the Underwriters Laboratories (UL) Firefighter Safety Research Institute (FSRI) Advisory Board Meeting, we discussed changes in the fire environment over the last 40 years and also explored how to effectively roll out the new UL Vertical Ventilation on-line course. On my flight home, was checking Facebook and found several interesting questions from Colin Patrick Kelley and Scott Corrigan related to my blog post titled Integration which encouraged readers to integrate the tactical considerations and lessons learned from the UL Horizontal and Vertical Ventilation Studies (Kerber, 2010, 2013). Scott had reposted a link to Integration on Facebook and after having a look at the Tactical Integration Worksheet, Colin commented with an interesting question for Scott and I. The fire environment is not the only thing that has changed in the last 40 years! Almost every day, I interact with firefighters from around the world through my blog, social media, VOIP telephone or video, e-mail, and a host of other technological innovations. The tools that allow us to interact with a worldwide network have also changed dramatically (likely as much as the fire environment) in the same timeframe.

Social learning can occur as either a formal, organization-driven process or as an informal employee-driven process…networks of people belonging to all professions, working across time and space, can make informed decisions and solve complex problems in ways they couldn’t dream of years ago. By bringing together people who share interests, no matter their location or time zone, social media has the potential to transform the workplace into an environment where learning is as natural as it is powerful (ASTD, 2011, p. 1-2)

It is important for us to consider how we use formal (e.g., training and education), informal (e.g., company drills and discussions), and social (e.g., use of social media, blogs) learning as part of our professional development as firefighters and fire officers. Take advantage of opportunities for learning in each of these areas. Be curious, think critically, and learn continuously!

The Questions

Collin explains his perspective and poses a question. Scott replies and redirects the question to me. This type of dialog is an excellent example of how we can use social learning to deepen our understanding and learn from the experience of others.

Colin Patrick Kelley writes: This is great stuff & memory aids are always appreciated by a numbskull like me. But I’m having some trouble. Scott Corrigan or Chief Ed Hartin, can you help me out with one of the categories listed on the Tactical Integration Worksheet? It reads as follows:

Large Vertical Vents are Good, But…. A 4’ x 8’ ventilation opening removed a large amount of hot smoke and fire gases. However, without water on the fire, the increased air supply caused more products of combustion to be released than could be removed through the opening, overpowering the vertical vent and worsening conditions on the interior. Once fire attack returned the fire to a fuel controlled regime, the large opening was effective and conditions improved (Hartin, 2013)

Collin Patrick Kelly continues: I feel like this tactical tidbit is missing a vital piece of info. Hear me out. If we know that horizontal openings (doors & windows) begin as bi-directional ventilation openings or flow paths (high side exhaust and low side inlets )that can and will eventually become almost all exhaust if left alone to burn and track long enough and we also know that vertical openings (cut holes, skylights, scuttles) are always going to start off as Unidirectional Flow paths or ventilation openings ( all exhaust) and will stay this way throughout the fire. Then how did the vertical opening aid in the fires growth? It aided in fire growth because the vertical vent studies were all done with the front door open and therein lies the problem. This front door was the low air inlet that the fire needed for growth. And in fact, during the Governors Island scuttle (vertical vent) test, when they opened the scuttle at the top of the stairs and closed the front door conditions began to get better and this was before a drop of water was sprayed. Temps began to decrease because as Steve Kerber put it “we are releasing more energy than the fire can produce”, in effect, stopping the “wood stove” scenario (another Kerber quote), which is the perfect scenario for fire growth. Low horizontal inlet and then up and out vertically. It stated above that “the increased air supply caused the fire to grow and overpower the vent opening”. I think it is critical to state that door control coupled with vertical vent can be a winning combination and in many instances the least risky and most effective means of ventilation. Was this either of your understandings of the study vs. the Governors Island tests and if so should that one listing contain a bit more specificity in its definition and understanding?

Scott Corrigan replied: Great input and shows you are closely watching [and] not [simply] relying on the footnotes of others. Door control to avoid the intake is key to all entry, when you are not going to apply water. It becomes part of a synchronized intake with you open it with the attack team advancing on the fire, not waiting to see flames, but comfortable flowing the line into smoke. Any tactical ventilation (PPA, Horizontal and Vertical) that is conducted without water application will produce ill results. The key is to continue to understand the cohesion of all the elements and the true coordination of fire attack and tactical ventilation. Sometimes putting a couple of sentences together can lead others see things as less than positive. I have had some great discussions with brilliant people about the “perceived” negatives of vertical ventilation. I think to frame it properly when discussing tactical ventilation is that we all agree (at least we should) that it needs to be in support of fire attack. Kevin Story from Houston says, “Engine work without truck work can suck, Truck work without Engine work can be disastrous.”. Ed Hartin what do you think regarding the Vertical Vent information Colin poses above?

Ian Bolton added to the conversation: You mentioned ‘It aided in fire growth because the vertical vent studies were all done with the front door open and therein lies the problem’ I think what you may be referring to is the possibility of providing an outlet, but without an inlet, perhaps by keeping the front door closed. Well, one thing that is sometimes not considered regarding ventilation is that for smoke/hot fire gases to be able to leave an environment, an equal amount/mass of air needs to replace it. It all goes back to the good old Law of Conservation of Mass from the mid-1700s. Stating that the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. And of course when we are relating this to ventilation, the mass we are considering is our air/smoke/fire gases etc. So for us to be able to release those hot gases, they will need to be replaced by fresh air, either via a door, window, building leakage or some other means.

The Integration Worksheet accomplished its task as it stimulated thought and discussion about how these various tactical considerations should be integrated. Steve Kerber and I discussed the varied and in some cases misguided interpretation of the study results last week. Both studies presented data that support the effectiveness of coordinated fire attack and ventilation with vertical ventilation being generally more effective than horizontal, but not always necessary for effective operations in private dwellings. Both studies also supported the concept that uncoordinated horizontal or vertical ventilation of a ventilation controlled fire would result in increased heat release rate and worsening fire conditions.

Collin’s post includes a number of statements that frame his question:

• Horizontal openings (doors & windows) begin as bi-directional ventilation openings or flow paths ( high side exhaust and low side inlets )that can and will eventually become almost all exhaust if left alone to burn and track long enough.
• Vertical openings (cut holes, skylights, scuttles) are always going to start off as Unidirectional Flow paths or ventilation openings (all exhaust) and will stay this way throughout the fire.
• [The vertical ventilation opening] aided in fire growth because the vertical vent studies were all done with the front door open… This front door was the low air inlet that the fire needed for growth.

Question: Was this either of your understandings of the [vertical ventilation] study vs. the Governors Island tests and if so should that one listing contain a bit more specificity in its definition and understanding?

The Foundation

It is important to ensure that we share a common understanding of terminology and concepts. The following are important to this discussion of practical fire dynamics and tactical ventilation:

Ventilation: The exchange of the atmosphere inside a compartment or building with that outside the compartment or building. Ventilation is going on all the time, even when there is no fire. Under fire conditions, ventilation may be changed by creation of openings by exiting occupants, fire effects, or by other human action.

Tactical Ventilation: Planned, systematic, and coordinated removal of hot smoke and fire gases and their replacement with fresh air. Actions ranging from opening a door to make entry, breaking or opening a window, or cutting an opening in the roof can all be part of tactical ventilation.

Tactical Anti-Ventilation: Planned, systematic, and coordinated confinement of hot smoke and fire gases and exclusion of fresh air. Closing or controlling the door to limit inflow of air is an anti-ventilation tactic.

Conservation of Mass: The mass of air entering a compartment (single compartment or building) must equal the mass of smoke and air exiting the building. This means that other than in the extremely short term, if smoke is exiting the building, air must be entering. This may be through one or more openings functioning solely as inlets or openings may be functioning as both inlets and outlets (with either a bi-directional flow or alternating (pulsating) flow). However, the mass of the inflow must equal that of the outflow.

Flow Path: The flow path is the volume between inlet(s), the fire, and outlet(s).

Air Track: While not used extensively in the scientific literature, the term air track as used in 3D Firefighting: Training, Techniques, and Tactics (Grimwood, Hartin, McDonough, & Raffel, 2005) may be used to describe the movement of smoke and air within the flow path. If the flow path is thought of as a road (path), movement of vehicles along the road would be the air track.

Bidirectional Air Track: A bi-directional air track is movement of smoke out and air in along the same flow path or at an opening.

Unidirectional Air Track: A unidirectional air track is movement of air or smoke in a single direction along a flow path or at an opening.

Impact of Differences in Elevation of Openings: As demonstrated in both the horizontal and vertical ventilation tests conducted by UL, the greater the difference in height between the inlet and the outlet, the more effective the ventilation. Given the buoyancy of hot smoke, making an exhaust opening above the height of the inlet increases effectiveness of both horizontal and vertical ventilation. Vertical ventilation resulted in greater gas movement (smoke out and air in) under similar conditions.

Exhaust and Inlet Openings: The relationship of the size of the exhaust opening(s) and inlet opening(s) has a significant effect on the efficiency of tactical ventilation. With natural ventilation, the total area of the inlet(s) should be larger than that of the exhaust opening(s). With equal sized openings, efficiency will vary depending on the temperature of the gases, but at 500^o C, efficiency is likely to be approximately 70%. Higher temperatures result in increased efficiency, while lower temperatures result in decreased efficiency. Increasing the size of the inlet to twice that of the exhaust will increase efficiency to approximately 90%. Further increases in inlet size result in diminishing increases in efficiency (Svensson, 2000).

Tactical Considerations: As used in the UL reports on Horizontal and Vertical Ventilation and their accompanying on-line training programs, tactical considerations are things to think about in application of firefighting strategies and tactics based on the results of experimental research in. The tactical considerations are not rules or procedures, but serve to inform our practice and also to raise additional questions to be answered (e.g., do these same considerations apply in other types of buildings or with different building geometry?).

Discussion

The following section addresses Colin’s statements and question.

Bi-Directional Air Track from Horizontal Openings: Collin indicated that horizontal openings begin with a bi-directional air track and as the fire develops transition to almost all exhaust. Horizontal Openings may present a bi-directional air track (smoke out the top and air in the bottom), this is common (but not exclusively) when the opening is at the same level as the fire and is a typical indicator of a ventilation controlled fire. Under these conditions, the area of opening serving as an exhaust increases as the fire develops and temperature of the hot gases exiting through the opening increase. As a result the area of the opening serving as an inlet will decrease. Mass balance is maintained as the cooler outside air is more dense (greater mass per unit volume) than the hot gases that are exiting. So far so good, this is consistent with Colin’s first assumption.

However, several conditions may result in a unidirectional, outward flow of smoke from a horizontal opening. First, if the opening is above the fire and another (lower) inlet is present, the opening may have a unidirectional, outward flow. Second, if the opening is on the leeward (downwind) side and an inlet is present on the windward (upwind) side of the building, a unidirectional, outward flow of smoke may be present. Conversely, these conditions also may result in a unidirectional, inward flow at the inlet opening.

Horizontal openings may also present with a pulsing (inward and outward flow) under extremely ventilation controlled conditions. This air track is an indicator of potential for a ventilation induced flashover or backdraft.

The following video is an excellent illustration of B-SAHF (building, smoke, air track, heat, and flame) indicators, the concept of flow path, anti-ventilation, tactical ventilation, door control, and a host of other interesting things. This test was conducted by the National Institute of Standards and Technology (NIST) in Bensenville, IL. The building is a wood frame townhouse with a fire ignited on the first floor. The door on Floor 1, Side Alpha is closed and the window on Side 1, Alpha is open. The door to the second floor room where the open window is located is also open, providing a flow path between the window and the first floor fire. While the second floor window is not a vertical vent, it is above the fire and at different points in the test showed a bi-directional and unidirectional air track.

At the start of the video, the air track is bi-directional and while continuing in this mode, becomes substantially and exhaust opening. Pay close attention at 03:36 as the fire becomes more ventilation controlled and the air tack begins to pulse, alternating between inlet and exhaust. At 03:46, smoke discharge from the window ceases as the opening becomes an inlet (or at least not an exhaust). This condition continues until the door is opened at 04:06. Once the door is opened, the window becomes an exhaust while the door maintains a bidirectional air track, serving as both an exhaust and inlet for the remainder of the test.

Important! Changes in air track are as (or likely even more) important as the direction (in, out, bidirectional, or pulsing (in and out)).

Unidirectional, Outward Air Track from Vertical Openings: Collin states that vertical openings will always going to start off and remain unidirectional (all exhaust) throughout the fire. Two factors influence movement of smoke (and air), differences in density (mass per unit volume) and pressure. Increased temperature (in comparison with ambient temperature of the outside air) reduces the density of smoke, making it buoyant. The same increased temperature in combination with the confinement provided by the building results in (slightly) increased pressure. Both of these factors influence movement of smoke and the tendency of vertical (or the upper area of horizontal) openings to serve as an exhaust.

I agree with Colin that vertical openings generally will serve as an exhaust point throughout the incident. However, the extent to which they do so is dependent on the presence of one or more inlet openings as well as the buoyancy and pressure resulting from the fire’s heat release rate.

The following video was taken as part of a NIST (2003) research project examining structural collapse. While focused on building performance, this video clearly demonstrates another one of the UL tactical considerations; nothing showing means exactly that, nothing. In particular, note conditions at 2:30, 4:40, and 5:30 in the video.

Changes in discharge from existing vertical building openings continues to be an exhaust, but at a significantly diminished flow. Additional detail is provided in the prior CFBT-US blog post Influence of Ventilation in Residential Structures: Tactical Implications Part 3 (Hartin, 2011). For more information on these tests, see Structural Collapse Fire tests: Single Story, Ordinary Construction Warehouse (Stroup, Madrzykowski, Walton, & Twilley, 2003) and additional video on the NIST web site.

It is also important to consider the impact of wind and fire conditions on the function of vertical openings, wind effects or cooling of smoke due to severely ventilation limited conditions may impact on smoke movement and the function of vertical openings as an exhaust.

Integration

Integration of the tactical considerations presented in the Horizontal and Vertical Ventilation Studies requires a deeper look. Each of the considerations must be framed in context. Both studies were experimental in nature, meaning that as many variables as possible were controlled to allow data directly related to ventilation to be collected. In that the fires needed to be extinguished to preserve the structures for subsequent experiments, data on the interrelationships between fire attack and ventilation were also collected. However, tactical operations were not conducted in exactly the same manner as they would on the fireground. Ventilation openings were precut, durable materials were used for window coverings rather than glass, and fire attack was limited to exterior streams. These variations from the typical fireground provided consistency from experiment to experiment and between series of tests (e.g., horizontal and vertical) that allowed valid and reliable analysis of data related to ventilation and exterior fire attack.

There are a number of tactical considerations identified in the Horizontal and Vertical Ventilation Studies that are interrelated (see the Tactical Integration Worksheet):

You Can’t Vent Enough (Horizontal) & Large Vertical Vents are Good, But…(Vertical): Ventilation (either horizontal or vertical) presents a bit of a paradox. Hot smoke and fire gases are removed from the building, but the fresh air introduced provides oxygen to the fire resulting in increased heat release rate.  In the horizontal ventilation study, each successive increase in horizontal ventilation released additional smoke, but also provided an increased air supply to the fire. In the vertical ventilation study, a 4’ x 8’ ventilation opening removed an even larger amount of hot smoke and fire gases. However, without water on the fire to reduce the heat release rate and return the fire to a fuel controlled regime, the increased air supply caused more products of combustion to be released than could be removed through the opening, overpowering the ventilation openings and worsening conditions on the interior. Once fire attack returned the fire to a fuel controlled regime, the large opening was effective and conditions improved. This held true in all experiments in both studies!

Coordination (Horizontal) & Coordinated Attack Includes Vertical Ventilation (Vertical): The Horizontal Ventilation Study identified that the window of time between increased ventilation and transition to conditions that were untenable for both building occupants and firefighters was extremely short. This held true with vertical ventilation as well. Vertical ventilation is the most efficient type of natural ventilation, it not only removes a large amount of smoke, but it also introduces a large amount of air into the building (the mass of smoke and air out must equal the mass of air introduced). If uncoordinated with fire attack, the increase in oxygen will result in increased fire development and heat release. However, once fire attack is making progress, vertical ventilation will work as intended, with effective and efficient removal of smoke and replacement with fresh air.

Gaining Access is Ventilation (Horizontal) & Control the Access Door (Vertical): If a fire is ventilation limited, additional oxygen will increase the heat release rate. The entry point is a ventilation opening that not only allows smoke to exit, but also provides additional atmospheric oxygen to the fire, increasing heat release rate and speeding fire development. Keep in mind that the entry point is a ventilation opening and don’t open it until ready to initiate fire attack. Controlling the door after entry (closed as much as possible while allowing the hose to pass) slows fire development and limits heat release rate. Once the fire attack crew has water on the fire and is limiting heat release by cooling the door can and should be opened as part of planned, systematic, and coordinated tactical ventilation.

Expanded Tactical Considerations

Colin was correct in his assertion that the statement “Large Vertical Vents are Good, But…” needs a bit more detail. Each of the tactical considerations presented in the UL Horizontal and Vertical Ventilation studies needs to be integrated with one another along the operational context of your department. Some of the considerations will be the same, regardless of if you are a member of FDNY or Central Whidbey Island Fire & Rescue, others will be different. Large organizations with substantial resources will be challenged by coordination (what must be done concurrently or in close sequence) while smaller organizations with fewer resources are challenged to a greater extent by sequence (what comes first, second, and third). However, regardless of the context, the fire dynamics remains the same.

The following tactical considerations related to vertical ventilation are based in part on the research results and tactical considerations developed by the UL Firefighter Safety Research Institute, ongoing study of practical fire dynamics, and fireground operations, over the last 40 years.

• The air track from vertical ventilation openings in or directly connected to the involved area of the building is most likely to be unidirectional, and outward.
• The air track from horizontal ventilation openings above the fire is likely to be unidirectional, outward, may be bidirectional (out at the top and in at the bottom), or may be pulsing (in and out).
• The air track from horizontal openings on the same level as the fire is likely to be bidirectional, but may be unidirectional, outward or inward or it may be pulsing (in and out).
• The air track from horizontal openings below the level of the fire is likely to be unidirectional, inward, but may present differently depending conditions.
• Air track is influenced by the location and size of openings, the distance of the opening from the fire, wind conditions, the burning regime (fuel or ventilation controlled), and if ventilation controlled, the extent to which ventilation is limited. As with all of the B-SAHF (building, air track, heat, smoke, and flame), air track must always be considered on context.
• Larger vertical ventilation openings will release a larger amount of smoke and a correspondingly large volume of air will be introduced into the building.
• With natural tactical ventilation, if the area of the inlet or inlets is small in relation to the exhaust opening, the movement of both smoke and air will be constrained and ventilation will be less efficient. Correspondingly if the area of the inlet or inlets is large movement of smoke and air will be more efficient.
• When using natural tactical ventilation, the inlet area should whenever possible be two or three times the size of the exhaust opening (note that this is reversed when using positive pressure ventilation).
• If the fire is in a fuel controlled burning regime, effective vertical tactical ventilation will provide a lift in the smoke level and slow fire development even if fire attack is delayed. This was commonly seen in the legacy fire environment, but is unlikely in the modern fire environment due to the high heat release rate of modern fuels and fuel loads found in today’s buildings.
• If the fire is ventilation controlled (most likely in the modern fire environment) and either horizontal or vertical tactical ventilation is performed absent fire attack, the lift (if it occurs) will be momentary as increased heat release rate and smoke production will likely overwhelm the size of the ventilation opening.
• If the fire is ventilation controlled, the effectiveness of vertical tactical ventilation on improving conditions is dependent on concurrent application of water onto the fire. Note that this requires effective fire attack, not simply a charged line at the door or being advanced into the building. Once ventilation openings are created, the clock is ticking on increased heat release rate.
• Coordinating fire attack and vertical tactical ventilation requires close communication between companies assigned to fire attack and those assigned to ventilation. Communication when water is being applied to the fire is critical. However, it is also important to evaluate observed conditions in conjunction with reports from the interior.
• If using existing vertical openings such as skylights, scuttles, or roof bulkheads, it may be necessary to delay opening until the hoseline is in place and operating.
• Vertical ventilation through cut openings takes longer than using existing openings and as such hoselines may be in place and operating before the hole is completely cut. However, it is important for company or team performing ventilation to verify that this is the case before opening the cut hole.
• Effective coordination between fire attack and ventilation requires that command and company officers have a good idea of how long specific tactical operations take in different types of buildings and with varied construction types. If you don’t know, it is time to get dirty and find out!

Closing Thoughts

Remember that “training and learning are not the same thing… Training is an outside in approach to providing quantifiable content” (ASTD, 2011, p. 3) many firefighters and firefighters correctly perceive that training is what is done to you. Learning on the other hand; “is an inside out process that originates with the learner’s desire to know” (ASTD, 2011, p. 3). Training and learning are both important! Social learning does not replace training, it may overlap and reinforce training, but it can also enable the transfer of knowledge in a way that training cannot.

I would like to thank Colin Patrick Kelley, Scott Corrigan, and Ian Bolton for engaging in a bit of Social Learning and helping me do the same! Be curious (but not simply in a passive way, ask questions), think critically (ask questions and probe, consider “so what”, “now what”, and why as critical tools in your toolbox), and learn continuously (learning is an inside out process that starts with you).

Stay up to date with the latest UL research with the fire service by connecting with the Firefighter Safety Research Institute on the web or liking them on Facebook. Integrate this information with what you currently know and engage in deliberate practice to master your craft!

References

American Society of Training and Development. (2011) Social learning. Retrieved August 24, 2013 from http://www.astd.org/Certification/For-Candidates/~/media/Files/Certification/Competency%20Model/SocialLearning1.ashx

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

Hartin, E. (2013) Integration [blog post]. Retrieved August 24, 2013 from https://cfbt-us.com/wordpress/?p=1926

Hartin, E. (2011) Influence of Ventilation in Residential Structures: Tactical Implications Part 3. Retrieved August 25, 2013 from https://cfbt-us.com/wordpress/?p=1666

Kerber, S. (2010). Impact of ventilation on fire behavior in legacy and contemporary residential construction. Retrieved July 17, 2013 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf.

Kerber, S. (2013). Study of the effectiveness of fire service vertical ventilation and suppression tactics in single family homes. Retrieved July 17, 2013 from http://ulfirefightersafety.com/wp-content/uploads/2013/06/UL-FSRI-2010-DHS-Report_Comp.pdf

Stroup, D. Madrzykowski, D., Walton, W., & Twilley, W. (2003) Structural collapse fire tests: Single story, ordinary construction warehouse. Retrieved August 25, 2013 from http://www.nist.gov/customcf/get_pdf.cfm?pub_id=861215

Each of the UL ventilation studies has generated a list of tactical considerations, many of which overlap or reinforce one another. It is useful to revisit the tactical considerations developed in the horizontal ventilation study and to integrate these with those resulting from the vertical ventilation research project.

Download the Tactical Integration Poster as an 11″ x 17″ PDF document and post it to stimulate discussion of the concept of tactical integration and how research with the fire service can be integrated into our standard operating guidelines, work practices, and fireground operations.

Download the Tactical Integration Worksheet provided as an 11” x 17” PDF document and work through the commonalities and differences in these two sets of tactical considerations. Also take a few minutes to think about how this information has (or should) inform your operations on the fireground.

Stay up to date with the UL Firefighter Safety Research Institute and the latest research being conducted with the fire service by connecting with the Firefighter Safety Research Institute on the web or liking them on Facebook.

Update

I am currently in Jackson Hole, Wyoming attending a Underwriters Laboratories Firefighter Safety Research Institute Advisory Board meeting and yesterday had a preview of the on-line training program focused on the results of the Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes. The on-line training materials produced by the institute continue to improve, providing a higher level of interactivity and multiple paths through the curriculum. Learners can choose a short overview, the full program, or the full program with additional information for instructors that can be used to enhance training programs integrating the on-line program with classroom and hands-on instruction.

UL hopes to have the on-line vertical ventilation training program up and running within the week and I will update this post with information on how to access the course as soon as it becomes available.

Stay up to date with the UL Firefighter Safety Research Institute and the latest research being conducted with the fire service by connecting with the Firefighter Safety Research Institute on the web or liking them on Facebook.

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 Critical for another example of the importance of understanding practical fire dynamics and being able to apply this knowledge on the fireground.

Ed Hartin, MS, EFO, MIFireE, CFO

Even as a member of the technical panel on the UL Vertical Ventilation Study, it will take some time to fully digest all of the data presented in the Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes (Kerber, 2013). However, the tactical implications presented in this report provide an excellent starting point to understanding the influence of vertical ventilation on fire behavior and other important findings in this research project. UL will also be releasing an on-line training program in the near future that will provide a user friendly approach to exploring this information.

Read the Report and Stay up to date with the latest UL research with the fire service by connecting with the Firefighter Safety Research Institute on the web or liking them on Facebook.

Tactical Implications

A number of the tactical implications identified in the vertical ventilation study replicate and reinforce those identified when UL studied the effect of horizontal ventilation. Other implications are specifically focused on vertical ventilation. The following summary examines and expands slightly on the tactical implications presented in Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes (Kerber, 2013).

The Fire Environment Has Changed: While many firefighters, particularly those who have less than 15 or 20 years of service have never known a fire environment fueled by synthetic materials with rapid fire development and ventilation limited fire conditions. However, many of the tactics in use today were developed when the fire environment was quite different. Decades ago the fire environment was predominantly fueled by natural materials; fires had a lower potential heat release rate, and remained fuel controlled much longer. Changes in the fire environment require reevaluation and shift of tactics to meet these changes.

Control the Access Door: If a fire is ventilation limited, additional oxygen will increase the heat release rate. The entry point is a ventilation opening that not only allows smoke to exit, but also provides additional atmospheric oxygen to the fire, increasing heat release rate and speeding fire development. Controlling the door slows fire development and limits heat release rate. Once the fire attack crew has water on the fire and is limiting heat release by cooling the door can and should be opened as part of planned, systematic, and coordinated tactical ventilation.

Coordinated Attack Includes Vertical Ventilation: While vertical ventilation is the most efficient type of natural ventilation, it not only removes a large amount of smoke, it also introduces a large amount of air into the building (the mass of smoke and air out must equal the mass of air introduced). If uncoordinated with fire attack, the increase in oxygen will result in increased fire development and heat release. However, once fire attack is making progress, vertical ventilation will work as intended, with effective and efficient removal of smoke and replacement with fresh air.

Large Vertical Vents are Good, But… Ventilation (either horizontal or vertical) presents a bit of a paradox. Hot smoke and fire gases are removed from the building, but the fresh air introduced provides oxygen to the fire resulting in increased heat release rate. A 4’ x 8’ ventilation opening removed a large amount of hot smoke and fire gases. However, without water on the fire to reduce the heat release rate and return the fire to a fuel controlled regime, the increased air supply caused more products of combustion to be released than could be removed through the opening, overpowering the vertical vent and worsening conditions on the interior. Once fire attack returned the fire to a fuel controlled regime, the large opening was effective and conditions improved.

Location of the Vertical Vent? It Depends! The best location for a vertical ventilation opening depends on building geometry, location of the inlet(s) and resulting flow path. Often this is not known with certainty. If ventilation and fire attack are coordinated, venting over the fire provides the most efficient flow of hot smoke, fire gases, and air. However, while not mentioned in this report on vertical ventilation, working above engineered wood roof supports that are involved in fire or may have been damaged by the fire presents considerable risk. Surprisingly vertical ventilation remote from the fire provided some positive effects, but this was dependent on geometry. One of the important lessons in this tactical implication is that the effects of vertical ventilation are not only dependent on the location of the exhaust opening, but also on the location of the inlet and resulting flow paths created within the building.

Operations in the Flow Path Present Significant Risk: In UL’s tactical implication titled Stages of Fire Growth and Flow Path, Steve Kerber states “the stage of the fire (i.e. ventilation or fuel limited)”. This may be a bit confusing as the stages of fire development are typically described as ignition or incipient, growth, fully developed, and decay. Burning regime may be used to describe the conditions of fuel or ventilation controlled (although this term is used in the text 3D Firefighting, it is not as commonly used in fire dynamics literature). The location of the inlet and exhaust openings, distance between the inlet opening and the fire, shape of the inlet and exhaust openings, the interior geometry of the building and its contents all impact on flow path and the availability of oxygen for fire growth. Firefighters must consider both the upstream (between the inlet and the fire) and downstream (between the fire and the exhaust) elements of the flow path. Operations in the downstream segment of the flow path are hazardous due to the flow of hot gases and smoke, increasing convective heat transfer and potential for fire spread in this space.

Timing is (Almost) Everything: Why do we perform tactical ventilation? While firefighters can typically provide a list of potential benefits, one of the most important is to improve interior conditions for both firefighters and victims who may still be in the building. When effective tactical ventilation is coordinated with fire attack, the fire environment becomes cooler, visibility is increased, and useful flow paths are created that remove hot smoke, fire gases, and steam ahead of hoselines. However, tactical ventilation completed significantly before fire attack is having an effect on the fire can result in increased heat release rate and fire growth. Additional considerations that impact or are impacted on by timing of tactical ventilation include:

• The fire does not react to additional air (oxygen) instantaneously
• The higher the interior temperatures the faster the fire reacts
• The closer the inlet opening is to the fire the faster it reacts
• The higher the exhaust opening the faster the fire reacts
• The more smoke exhausted from the building the more air that is introduced (the mass of air in must equal the mass of smoke and air that is exhausted)
• The more air (oxygen) the faster the fire reacts

Reading The Fire: The UL report on vertical ventilation refers to “Reading Smoke”. While smoke is a critical category of fire behavior indicators, firefighters must consider all of the B-SAHF indicators (Building, Smoke, Air Track, Heat, and Flame) when reading the fire. The key point made in the UL vertical and horizontal ventilation reports is that nothing showing means exactly that. Nothing! As a fire becomes ventilation controlled, temperature decreases, reducing pressure in the building and as a result visible smoke indicators on the exterior often are substantially diminished or absent. When little or no smoke are observed, the fire should be treated as if it is in the ventilation limited, decay stage until proven otherwise.

Closed Doors=Increased Potential for Survival: As with UL’s horizontal ventilation experiments, the vertical ventilation experiments further demonstrated that closed doors increase victim survivability. . In each experiment a victim in the closed bedroom would have had survivable conditions and would have been able to function well through every experiment and well after the arrival of fire companies. In the bedrooms with open doors, potential victims would be unconscious if not deceased prior to fire department arrival or as a result of fire ventilation actions.

Softening the Target: In many cases, the fire has self-vented prior to the arrival of the first company (note that self-vented should not be confused with adequate, planned, systematic, and coordinated tactical ventilation). Tactical implications presented in Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2010) indicated that a self-vented fire most likely will most likely be ventilation controlled and will respond quickly to any increase in ventilation.

Even with a ventilation location open the fire is still ventilation limited and will respond just as fast or faster to any additional air [oxygen]. It is more likely that the fire will respond faster because the already open ventilation location is allowing the fire to maintain a higher temperature than if everything was closed. In these cases rapid fire progression is highly probable and coordination of fire attack with ventilation becomes even more important (Kerber, 2010, p. 301).

Data on the effects of water application from the exterior during the vertical ventilation experiments reinforced the conclusions drawn from those conducted during the horizontal ventilation study. Regardless of the point of application, water quickly applied into the fire compartment improved conditions throughout the entire building. In the vertical ventilation experiments water applied from the exterior for approximately 15 seconds had a significant impact on interior conditions increasing potential for victim survivability and firefighter safety. During size-up consider the fastest and safest way to apply water to the fire. This could be by applying water through a window, through a door, from the exterior or from the interior.

You Can’t Push Fire with Water: During the vertical ventilation study, UL continued examination of the question; can water applied from a hoseline push fire? Data from this study continues to support the position that application of water does not push fire. However, discussion during the study pointed to several situations that may give the appearance of fire being pushed.

• A flow path is changed with ventilation and not water application
• A flow path is changed with water application
• Turnout gear becomes saturated with energy and passes through to the firefighter
• One room is extinguished, which allows air to entrain into another room, causing the second room to ignite or increase in burning (see Contra Costa LODD: What Happened? for an example of this phenomena)

Direct Attack is Important on Fires in Large Spaces: While large open floor plans in many modern homes presents a fire suppression challenge, open floor plans also permit application of water to burning fuel from a distance. This tactical recommendation points to the importance of using the reach of a hose stream to advantage. It is not necessary to be in the fire compartment to begin effective suppression. If an involved room is in line of sight, water can be applied to burning fuel with good effect.

Important! While not addressed in this tactical implication, the emphasis on direct attack does not diminish the importance of cooling the hot smoke and gases (fuel) in the upper layer as a control (not fire extinguishment) measure, particularly when the fire is shielded and not accessible for direct attack.

Ventilation Doctrine

Just as with door control (an anti-ventilation tactic) it is important to extend the concept of consistent doctrine to the broader context of tactical ventilation and anti-ventilation strategies and tactics. This doctrine is likely to differ based on context (e.g., building sizes and types and firefighting resources), but the fire dynamics framework will likely be quite similar. Future posts will work to examine the vertical ventilation study in more detail and to also integrate the tactical implications from this study with those from the earlier vertical ventilation study. These two important studies don’t answer all of the questions, but provide a good start.

References

Kerber, S. (2010). Impact of ventilation on fire behavior in legacy and contemporary residential construction. Retrieved July 17, 2013 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf.

Kerber, S. (2013). Study of the effectiveness of fire service vertical ventilation and suppression tactics in single family homes. Retrieved July 17, 2013 from http://ulfirefightersafety.com/wp-content/uploads/2013/06/UL-FSRI-2010-DHS-Report_Comp.pdf

Door Control Doctrine

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 360^o 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.

See Nozzle Techniques & Hose Handling: Part 3 for additional information on door entry procedure.

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 360^o 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 360^o 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 360^o 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 360^o 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?

My next post will come back to the final set of questions regarding door control doctrine posed in Close the Door! Where You Born in a Barn?

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 600^o C or 1112^o F) smoke
• Presence of void spaces, particularly if they are interconnected
• Combustible structural elements
• Infiltration of significant amounts of smoke into uninvolved 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.

• Smoke Explosion or Backdraft
• Fire Gas Ignitions
• Language and Understanding: Extreme Fire Behavior
• Extreme Fire Behavior: An Organizational Scheme (Ontology)
• Gas Explosions
• Sudden Blast
• Explosions During Structural Firefighting

References

Bengtsson, L. (2001). Enclosure Fires. Retrieved May 12, 2013 from https://www.msb.se/RibData/Filer/pdf/20782.pdf .

This post will finish up with Captain Mike Sullivan’s Fire Attack Questions. In the coming weeks I will explore the research conducted by UL, NIST, and FDNY on Governors Island last summer (see the video of a presentation on this research at FDIC later in this post). If you have questions or topics that you would like to see addressed in the CFBT-US Blog, please comment on the post or send me an e-mail.

In your Blog about gas cooling you mention combustion products and pyrolysis products. Combustion products being light heat and smoke but can you elaborate on pyrolysis products, are they just the gasses that are off gassing from the fuel?

Smoke is a complex aerosol comprised of gases, vapors, and particulates resulting from pyrolysis and incomplete combustion along with entrained air. So, smoke is comprised of both chemical products of pyrolysis (thermal decomposition of fuel) and combustion products. The chemical composition of smoke is extremely complex and depends on both the type(s) of fuel and conditions under which it is burning, predominantly limitations on ventilation and oxygen concentration.

Smoke is toxic, with incomplete combustion of organic fuels producing substantial amounts of carbon monoxide and nitrogen containing materials producing hydrogen cyanide. As smoke is a product of pyrolysis and incomplete combustion, it also contains a substantial percentage of unburned fuel, as such, smoke is fuel.

I have read that if smoke is venting from a building then there will be air entering from somewhere. During basement fires where the fire is below the neutral pressure plane you will often see smoke exiting from the front door from top to bottom of the doorway with no apparent entry of air (no neutral pressure plane) and no other vent opening. Could you comment on this?

The mass of smoke exiting from the building must equal the mass of the oxidized fuel and the mass of air entering the building as mass can neither be created or destroyed (law of conservation of mass) as illustrated below.

If you see smoke exiting from an opening with a unidirectional air track (out), air is entering somewhere else. Likely, air is entering from multiple locations without presenting an obvious indicator as to the flow paths involved.

Controlling the flow path in this case, involves closing the door. This acts in the same manner as closing the damper in a wood stove. Restricting the exhaust will slow intake of air and reduce the heat release rate until water can be applied (preferably making access through an exterior doorway at the basement level or applying water through a window to further reduce heat release prior to an interior attack.

Recent research by Underwriters Laboratories (UL), National Institute of Standards and Technology (NIST), and the Fire Department of the City of New York on Governors Island showed that closing an open front door reduced the heat release rate from a basement fire. Battalion Chief George Healey, Dan Madryzkowski, Steve Kerber, and Lieutenant John Ceriello provided an excellent presentation on this research at the 2013 Fire Department Instructors Conference. I strongly recommend viewing the presentation (embedded below)!

Scientific Research for the Development of More Effective Tactics

The following video recording provides an excellent overview of research conducted by UL, NIST, and FDNY on Governors Island to develop an understanding of fire dynamics in the modern fire environment and the influence of firefighting tactics on firefighter safety and effective fire control and ventilation operations.

This presentation was a seminal event in the US Fire Service that emphasized the importance of understanding fire behavior and the connection between solid research (both in the lab and in the field) with operational strategies and tactics. The research is solid, but it is important that all of us understand that it does not answer all of the questions and we should consider context when attempting to apply specific findings in general terms. For example:

• The suppression elements of the Governors Island tests were conducted using solid stream nozzles as that is the predominant type of nozzle used by FDNY. Tests showed that positive impact can be had using this type of nozzle. An important finding, but it was not intended to address the question of where are solid streams more effective than fog patterns (and where fog patterns are more effective).
• Tests were conducted on the Vent, Enter, Isolate, and Search (VEIS) tactic. Evidence points to the importance of controlling the flow path by closing the door. This does not mean that this is or is not an appropriate tactic under all circumstances or in all contexts, it simply addresses the importance of controlling the flow path.

The fire service owes a tremendous debt to UL, NIST, and FDNY (and in particular George, Dan, Steve, and John) for their commitment to improving firefighter safety and the effectiveness of firefighting operations. In order to maximize the value of this critically important research, it is essential that we explore the findings and underlying data and make sense of how this information can improve firefighting operations in our communities. More on this in subsequent posts!

Ed Hartin

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 200^o C to approximately 900^o 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.

References

Kerber, S. (2011). Impact of ventilation on fire behavior in legacy and contemporary residential construction. Retrieved July 16, 2011 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf

The seventh 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 the influence of changes in ventilation on flow path.

“Every new ventilation opening provides a new flow path to the fire and vice versa. This could create very dangerous conditions when there is a ventilation limited fire” (Kerber, 2011).

Air Track and Flow Path

Air track and flow path are closely related and provide an excellent framework for understanding the influence of changes in ventilation on fire development and flow path.

Air Track: Closely related to flow path, air track is the movement of air and smoke as observed from the exterior and inside the structure. Air track is used to describe a group of fire behavior indicators that includes direction of smoke movement at openings (e.g., outward, inward, pulsing), velocity and turbulence, and movement of the lower boundary of the upper layer (e.g., up, down, pulsing).

Observation of air track indicators may provide clues as to the potential flow path of air and hot gases inside the fire building. As discussed in previous posts in this series (Part 1, Part 2, Part 3, Part 4, Part 5, Part 6), movement of air to the fire has a major impact on fire development. Movement of hot gases away from the fire is equally important!

Flow Path: In a compartment fire, flow path is the course of movement hot gases between the fire and exhaust openings and the movement of air towards the fire.

Both of these components of flow path are important! Movement of hot gases between the fire an exhaust openings is a major factor in heat transfer outside the compartment of origin and presents a significant thermal threat to occupants and firefighters. When the fire is in a ventilation controlled burning regime, movement of air from to the fire provides the oxygen necessary for fire growth and increased heat release rate (impacting on conditions in the flow path downstream from the fire.

Flow path can significantly influence fire spread and the hazard presented to occupants and firefighters.

Reading the Fire

Before engaging in the meat of this UL Tactical Implication, quickly review essential air track indicators used in the Building, Smoke, Air Track, Heat, and Flame (B-SAHF) fire behavior indicators organizing scheme.

Figure 1. Air Track Indicators

As illustrated in Figure 1, key indicators include wind direction and velocity (consider this before you even arrive on-scene), directions in which the air and smoke are moving, and the velocity and flow of smoke and air movement.

Take a look at Figure 2. Consider all of the B-SAHF indicators, but pay particular attention to Air Track. What is the current flow path? How might the flow path change if one or more windows on Floor 2 Side A are opened prior to establishing fire control?

Figure 2. Residential Fire in a 1 ½ Story Wood Frame Dwelling

Photo courtesy of Curt Isakson, County Fire Tactics

UL Focus on Flow Path

Tactical implications related to flow path identified in Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2011) focus on creation of additional openings and changes in flow path as a result of “crews venting as the go” (p. 296). This is only one issue related to flow path!

The UL experiments showed that increasing the number of flow paths resulted in higher peak temperatures, a faster transition from decay to growth stage and more rapid transition to flashover. However, this is not the only hazard!

As previously discussed in the series of posts examining the fire in a Washington DC townhouse that took the lives of Firefighters Anthony Phillips and Louis Matthews, operating in the flow path presents potential for significant thermal hazard.

In this incident, the initial attack crew was operating on the first floor of a two-story townhouse with a daylight basement. When crews opened the sliding glass doors in the basement (on Side C), a flow path was created between the opening at the basement level on Side C, up an open interior stairway to the first floor, and out the first floor doorway (on Side A). Firefighters working in this flow path were subjected to extreme thermal stress, resulting in burns that took the lives of Firefighters Phillips and Mathews and serious injuries to another firefighter.

Figure 1. Perspective View of 3146 Cherry Road and Location of Slices

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

Figure XX illustrates thermal conditions, velocity and oxygen concentration at various locations within the flow path.

Figure 10. Perspective Cutaway, Flow/Temperature, Velocity, and O₂ Concentration

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

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

For a more detailed discussion of this incident and the influence of radiative and convective heat transfer in the flow path, see the prior posts on the Washington DC Townhouse Fire Case Study.

• Fire Behavior Case Study Townhouse Fire: Washington, DC
• Townhouse Fire: Washington DC-What Happened
• Townhouse Fire: Washington DC-Extreme Fire Behavior
• Townhouse Fire: Washington DC-Computer Modeling
• Townhouse Fire: Washington DC-Computer Modeling Part 2

Wind Driven Fires & Flow Path

While operating in the flow path presents serious risk, when fire behavior is influenced by wind, conditions in the flow path can be even more severe. In experiments conducted by the National Institute of Standards and Technology (NIST) demonstrated that under wind driven conditions, both temperature and heat flux, which were twice as high in the “flow” portion of the corridor as opposed to the “static” portion of the corridor (where there was no flow path). See the previous posts on Wind Driven Fires for more information on flow path hazards under wind driven conditions:

• Wind Driven Fires
• NIST Wind Driven Fire Experiments: Establishing a Baseline
• NIST Wind Driven Fire Experiments: Anti-Ventilation and Wind Control Devices
• NIST Wind Driven Fire Experiments: Anti-Ventilation and Wind Control Devices Part 2

Discussion

The sixth and seventh tactical implications identified in the UL Horizontal Ventilation Study are interrelated and can be expanded to include the following key points:

• Heat transfer (convective and radiative) is greatest along the flow path between the fire and exhaust opening.
• Exhaust openings located higher than the fire will increase the velocity of gases along the flow path (further increasing convective heat transfer).
• Flow of hot gases from the fire to an exhaust opening is significantly influenced by air flow from inlet openings to the fire (the greater the inflow of air, the higher the heat release rate and flow of hot gases to the exhaust opening).
• Flow path can be created by a single opening that serves as both inlet and exhaust (such as an open door or window).
• Thermal conditions in the flow path can quickly become untenable for both civilian occupants and firefighters. As noted in an earlier NIST Study examining wind driven fires, under wind driven conditions this change can be extremely rapid.
• Closing an inlet, exhaust opening, or introducing a barrier (such as a closed door) in the flow path slows gas flow and reduces the hazard downstream from the barrier.
• When the fire is ventilation controlled, limiting inflow of air (e.g., door control) can slow the increase in heat release rate and progression to a growth stage fire.
• Multiple openings results in multiple flow paths and increased air flow to the fire, resulting in more rapid fire development and increased heat release rate.

What’s Next?

The next tactical implication identified in the UL Horizontal Ventilation study examines an interesting question: Can you vent enough (to return the fire to a fuel controlled burning regime)? This question may also be restated as can you perform sufficient natural horizontal ventilation to improve internal conditions. The answer to this question will likely be extended through the Vertical Ventilation Study that will be conducted by UL in early 2012!

References

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

Kerber, S. (2011). Impact of ventilation on fire behavior in legacy and contemporary residential construction. Retrieved July 16, 2011 from http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/ventilation/DHS%202008%20Grant%20Report%20Final.pdf

Madrzykowski, D. & Kerber, S. (2009). Fire Fighting Tactics Under Wind Driven Conditions. Retrieved (in four parts) February 28, 2009 from http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part1.pdf; http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part2.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part3.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part4.pdf.

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

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