Posts Tagged ‘vent controlled fire’

Mass and Energy Balance in Fire Ventilation

Sunday, March 16th, 2014

Milestone! As I was preparing to upload this post, I realized that this is the 200th CFBT-US Blog Post since its inception in August of 2008. Quite a lot has happened since then. In 2008 there were few people in the fire service focused on the importance of fire dynamics to firefighting operations. Today it is a significant research focus and an ongoing topic of discussion throughout the US fire service. Progress is being made, but much remains to be done.

This post focuses on questions posed by firefighters in Europe and North America. Art Arnalich, a Fire Officer from Spain recently sent me a message asking for clarification and further explanation of the application of conservation of mass as it relates to fire ventilation. As always, questions form an excellent basis to examine what we think we know and how it applies in a practical context.

In my previous post, Large Vertical Vents are Good, But…, I stated:

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.

Art writes: The first condition for the Principle of Conservation of Mass to be applied is that the physical system must be closed to all transfers of matter and energy. While a closed compartment could be considered as a nearly “closed system”, a venting structure suffers important transfers of matter and energy. If we were to consider a bigger system (let’s say the 100x100x100m cube in which the house and all of its fire gases are included) the PCM [principle of conservation of mass] applies… Being the structure volume constant, any exiting gases will create an interior drop of pressure that will instantly drag an equal volume of gases to enter. Inlets with the bigger pressure differentials (lower side) will observe the larger flows. Outflow volume must equal inflow volume unless significant pressure changes can take place (not likely). Since there is an important difference between inflow/outflow temperatures (and densities), inflow mass (mass=density x volume) does not equal outflow mass.

The amount of gases coming out of combustion as a result of the new oxygen flow has been disregarded. In an actual fire, outflow volume should be larger than inflow volume because combustion of products generates new gases in within the interior.

But that doesn’t mean that mass in = mass out if we just consider the house. Total mass of unburned air + mass of fuel + mass of all combustion products = constant. But to measure this we can’t consider the volume of the structure itself but the volume that contains all fire gases, unburned gases and the house.

Art Asks: Could you please explain the implications of Principle of Conservation of Mass applies at a molecular level…If Mass-in=Mass-out then there is no mass variation over time (dm/dt=0). This would mean that the total mass of the house before the fire equals its mass after the fire. That doesn’t make sense.

Conservation of Mass and Energy

Mass is neither created nor destroyed in chemical reactions. The mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. If we account for all reactants and products in a chemical reaction, the total mass will be the same at any point in time in any closed system.

In combustion, if you consider the mass of the fuel and atmospheric oxygen before combustion, this must be the same as the mass of unburned fuel, unused oxygen, plus the products of combustion (this leaves out nitrogen and other thermal ballast that are not part of the combustion reaction). This is a bit different than the balance of the mass of smoke exiting the compartment and the mass of air entering.

I posed a similar question to Dr. Stefan Svensson from Lund University concerning the difference in the volume of products of combustion discharged and air intake from a single opening with a bi-directional air track. I discussed Art’s question with Stefan to ensure that my answer was clear and as accurate as possible (while maintaining a practical context).

In actuality, I should have stated that mass and energy must be balanced. Application of the principle of conservation of mass and energy in practical fire dynamics is an estimate and it applies on the molecular level (i.e. molecular mass). Usually we look at the building as a system in which the principle of conservation of mass and energy works as a rough estimate. If you define the system as a large cube that contains the building, the cube becomes the system.

In considering mass balance in a compartment fire it is important to keep in mind that solid fuel in the compartment is undergoing pyrolysis; thermally decomposing into gas phase fuel. Some of the fuel burns producing a range of combustion products and some remains unburned. Smoke is comprised of air, products of combustion, and unburned pyrolizate.

As air, products of combustion, and pyrolizate are heated, the volume increases (but mass stays the same), cooler outside air flowing into the building is more dense (smaller volume, but the same mass). This results in approximate balance between of the mass of hot air and products of combustion exiting the building and the mass of cooler external air entering the building.

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As smoke is a complex aerosol and its content varies considerably based the fuel that is burning and combustion efficiency, its density cannot be specified as a single value (at a given temperature). However, since air is a large constituent of smoke, I will use density of air for this example:

Density of Dry Air at 20o C: 1.205 kg/m3 (at Sea Level)

Density of Dry Air at 300o C: 0.616 kg/m3 (at Sea Level)

The implications of this difference in density is that if 1 m3 of hot air and products of combustion exit the building at 300o C, they will be replaced by approximately 0.5 m3 of cooler air (which will have the same mass as the exiting smoke and hot air. This differential will increase further if the temperature of the smoke is higher (resulting in lower density). It is important to note that the volume of air is not the same as the products of combustion and air that exit the compartment, but the mass is the same.

Pressure Differential and Flow

Smoke movement is due to both pressure and differences in density (gravity current). However, in general, the pressure differential between the interior of the building and the exterior is what causes smoke discharge. However, this pressure differential is not uniform and will be higher in the hot upper layer than in cooler air below (if a two layer environment exists inside the building). This is fairly simple to visualize when considering a single compartment. As shown in the following four photographs, hot smoke exits at the top of the door (above the neutral plane) and air enters at the bottom of the door (below the neutral plane). Movement of smoke in this case is the result of both the pressure resulting from increased temperature of the gases in the upper layer and the difference in density between the hot smoke (less dense) and the cooler air (more dense).

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Pressure is also influenced by building geometry, compartmentation, and external effects such as wind. Velocity, length of the flow path, and the size of the exhaust opening(s) will all influence flow in much the same manner as velocity, length of a hoseline, and nozzle size influence flow rate in a hoseline.

More Questions

Mike Sullivan from Canada posed several related questions, focusing on a video included in the Large Vertical Vents are Good, But… post. Just to get everyone back up to speed on the video, 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.

 

Mike Asks: Although the Law of Conservation of Mass can be used to explain that for a mass of smoke to exit an equal amount of mass of oxygen must enter. But in reality is the mass of smoke inside the townhouse not an artificial mass—meaning—-typically all things in life are trying to reach an equilibrium. In this case I would think that the interior mass of smoke also elevates interior pressures and should continue exiting until an equilibrium with the exterior is met.

In the video the smoke does exit the window for quite a while. In this case if we were to discuss the Law of Conservation of Mass, would it be the mass of oxygen entering the lower part of the window that allows the smoke to exit OR with the fire burning in the living room is the mass of smoke being produced by the fire acting as a replacement for the mass of smoke exiting the window?

Both good questions! As previously discussed, smoke discharge (as well as movement on the interior) is the result of both differences in pressure and density. If considered simply from the perspective of higher pressure on the interior, smoke would discharge from the building until pressure equilibrium is reached (with the same pressure inside the building as outside). This is related to exchange of mass and energy, but only indirectly. If you opened a cylinder of compressed air, air would be discharged out of the cylinder into the atmosphere (no exchange). However, with a fire burning in the building, air must flow inward to sustain release of thermal energy, which in turn maintains (or increases) the temperature that causes the pressure increase.

Mike also had a question related to cooling of the upper layer with a solid stream, but that will be the focus of another post.

UL/NIST Video Series

Have a look at the seven part video series of Battalion Chief Derik Alkonis, LA County Fire Department; Steve Kerber, Underwriters Laboratories Firefighter Safety Research Institute, and Dan Madrzykowski, National Institute presenting on Fire Dynamics at the IAFF Redmond Firefighter Safety Symposium.

Upcoming Events

Taking Scientific Research to the Street, 2014 Fire Department Instructors Conference, April 9, 2014 at 13:30

3D Firefighting Workshop, Winkler, MB April 25 & 26, Call (204) 325-8151 to register or for more information

NIOSH Report 2012-28
Thought & Observations

Wednesday, November 27th, 2013

After reading National Institute for Occupational Safety and Health (NIOSH) Death in the line of duty…2012-28, I was left scratching my head. For many years I have been a supporter of the Firefighter Fatality Investigation and Prevention Program and have served as an expert reviewer for several reports involving fatalities resulting from extreme fire behavior. As a friendly critic I have encouraged the NIOSH staff to improve their investigation and analysis of fire behavior related fatalities. Over the last several years there has been considerable improvement However, this latest report leaves a great deal to be desired. That said, there are a number of important lessons that can be drawn from this incident.

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Discussion of Fire Behavior

The Fire Behavior section of the report identified the attic as the origin of the fire and that the fire burning in the attic was ventilation limited. The report also identified that the enclosed rear porch was substantially involved. However, the report failed to discuss how the fire may have extended from the attic to the lower area of the porch (other than a statement that the BC notices “fire raining down in the enclosed porch area”.

The report correctly described the influence of the addition of air to a ventilation limited fire; increased heat release rate and potential to transition through flashover to a fully developed stage. However, the report failed to clearly articulate that there are two sides to the ventilation equation, air in and hot smoke and fire gases out. Flow path is critical to fire development and extension, and in this incident was likely one of the most significant factors in creating untenable conditions in the 2nd floor hallway.

It would have been useful to examine how the changes in ventilation resulting from opening of doors at the first floor level, existing openings in the attic (windows at the front and rear), opening of the door at the 2nd floor to extend the hoseline, and failure of the rear door may have influenced the flow path. While, the National Institute of Standards and Technology (NIST) modeling of this incident will shed considerable light on this subject, the physical evidence present at the fire scene could have informed discussion of flow path in the report.

Recommendation #1 states “Fire departments should ensure that fireground operations are coordinated with consideration given to the effects of horizontal ventilation on ventilation-limited fires”. This is a reasonable recommendation, but fails to speak to the importance of understanding flow path and the thermal effects of operating in the flow path downstream from the fire. In addition, while speaking to the importance of coordination, the report neglects to define exactly what that means; water on the fire concurrent with or prior to performing tactical ventilation.

Failure of the rear door established a flow path through the narrow, question mark shaped hallway and kitchen to the front stairway. Given the narrow width of this hall and its complex configuration, it is likely that there would be considerable mixing of hot smoke (fuel) and air providing conditions necessary for combustion. The dimensions of the space may also have influenced the velocity of the hot gases, increasing convective heat transfer.

The report did not speak to conditions initially observed in the kitchen and hallway or observed changes in conditions by members of other companies or the Engine 123 firefighter, prior to Captain Johnson’s collapse.

Things to Think About: Conditions on floor 2 were quite tenable prior to failure of the 2nd floor rear door, but changed extremely quickly in the hallway when the door failed. It is important to consider potential changes in flow path resulting from tactical operations and fire effects. It is unclear if the crews working on the 2nd floor were aware of the extent or level of the fire in the rear porches (having observed conditions indicating an attic fire on approach). The BC addressed the fire in the rear, but the it is uncertain if the line stretched to the back of the building was in operation before door failed or if application through the attic window would have significantly impacted the fire in the lower areas of the porch.

Structure

The section of the report addressing the Structure provided a reasonably good overview of the construction of this building and identified that the 2nd floor ceiling had multiple layers. However, there was no discussion of what influence these multiple layers may have had (e.g., reducing the thermal signature of the fire burning above). One significant element missing from discussion of the structure was the open access between the rear porch and the attic that allowed ready extension of fire to the rear porches.

The report also failed to discuss the type of door between the 2nd floor living area and the rear porch, other than to mention in passing that it was metal. Closed doors frequently provide a reasonable barrier to fire spread, but in this case, the door failed following an undetermined period of fire exposure. This was likely a significant factor in changing the flow path and creation of untenable conditions on the 2nd floor.

Things to Think About: Closed doors can provide a significant fire barrier in the short term. However, it would be useful to examine door performance in greater depth to understand what happened in this incident.

Training and Experience

The section of the report addressing training and experience is exhaustive, providing an overview of state training requirements implemented in 2010 (well after the Captain would have attended recruit training). It was unclear if these requirements were implemented on a retroactive basis. The number of hours of training for various personnel involved in the incident were provided, but with little specificity as to content of that training.

These observations are not intended to infer that the training of the members involved was or may have been inadequate, but simply that if NIOSH is investigating a fire behavior related incident, it would be useful to speak to training focused on fire behavior, rather than a generic discussion of training.

It was also interesting to note that while the report spoke well of the Chicago Fire Department training program, it failed to mention that the CFD has been heavily involved in fire dynamics research with both NIST and Underwriters Laboratories (UL) for many years.

Things to Think About: If you are reading this, you likely are plugged into current research in fire dynamics and tactical operations. Share the knowledge and build a strong connection between theory and practical application on the fireground.

Other Observations

While the floor plan of the 2nd floor is useful in understanding the layout of that space, it does not provide a good basis to visualize the flow paths and changes in flow paths that influenced the tragic outcome of this incident. Providing a simple three dimensional drawing with ventilation openings would have significantly increased the clarity of the information provided.

Things to Think About: Don’t be a passive user of NIOSH reports. For a host of reasons, NIOSH does not include the names of Firefighters who have died in the line of duty, the agency they worked for, or the location of the incident (other than the state). However, this information is readily available and can provide additional information to help you understand the incident. In this case accessing the address of this incident (2315 W 50th Place, Chicago) allows the use of Google Maps satellite photos and street view to gain a better perspective of the exterior layout of the building and configuration of openings.

Final Thoughts

The NIOSH Firefighter Fatality Investigation and Prevention Program is an important and valuable resource to the fire service. Developing an understanding of causal factors related to firefighter fatalities is an important element in extending our knowledge and reducing the potential for future line of duty deaths. Firefighters often observe that NIOSH reports simply say the same thing over and over again. To some extent this is true, likely because Firefighters continue to die from the same things over and over again.

The fire service across the United States is making progress towards developing improved understanding of fire dynamics and the influence of tactical operations on fire behavior. This is in no small part due to the efforts of the UL Firefighter Safety Research Institute, NIST, and agencies such as the Chicago Fire Department and Fire Department of the City of New York (FDNY). However, we need to look closely at near miss incidents, those involving injury, and fatalities resulting from rapid fire progression and seek to develop a deeper understanding of the contributing and causal factors. The NIOSH Firefighter Fatality Investigation and Prevention Program can be a tremendous asset in this process, but more work needs to be done.

What’s Next

I just spent the last two days at UL’s Large Fire Lab for the latest round of Attic Fire Tests and will be headed to Lima, Peru the first week of December. While on the road I will be working on my thoughts and observations related to attic fire tactics. The simple answer is that there is no single answer, but these recent tests presented a few surprises and have given me a great deal to think about.

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Ed Hartin, MS, EFO, MIFireE, CFO

Large Vertical Vents are Good, But…

Tuesday, August 27th, 2013

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!

large_vents_social_learning

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.

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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 500o 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!

Deliberate Practice

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 http://cfbt-us.com/wordpress/?p=1926

Hartin, E. (2011) Influence of Ventilation in Residential Structures: Tactical Implications Part 3. Retrieved August 25, 2013 from http://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

Tactical Integration

Tuesday, August 20th, 2013

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.

tactical_integration

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.

ISFSI Single Family Dwelling Fire Attack

Saturday, August 3rd, 2013

The International Society of Fire Service Instructors (ISFSI) in conjunction with the South Carolina Fire Academy and National Institute of Standards and Technology (NIST) have released an on-line training program addressing firefighting operations in single family dwellings.

isfsi_course

This training program is comprised of five modules examining current research on fire dynamics and firefighting tactics and its application to operations in single family dwellings.

  • Module 1: Introduction
  • Module 2: Current Conditions
  • Module 3: Ventilation
  • Module 4: Suppression
  • Module 5: Size-Up and Decision Making

ISFSI did an effective job of integrating their own research conducted in South Carolina along with current research from NIST, FDNY, and UL in developing and for the most part have provided an effective learning experience that is well worth the four hours needed to complete the training. Visit the ISFSI learning management system (LMS) at http://learn.isfsi.org/ to complete this course (and ISFIS’s building construction course as well).

Important lessons emphasized in Single Family Dwelling Fire Attack include:

  • The fire environment has changed, resulting in faster fire development and transition to ventilation controlled conditions.
  • Under ventilation controlled conditions, increased ventilation will result in increased heat release rate and temperature.
  • In the modern fire environment, ventilation and fire attack must be closely coordinated. Particularly if resources are limited fire attack should often precede ventilation to minimize the adverse impact of ventilation without concurrent fire attack.
  • Exterior attack can speed application of water into the fire compartment and frequently will have a positive impact on conditions.
  • Speedy exterior attack can be an effective element of offensive operations.
  • Smoke is fuel and presents a significant hazard, particularly at elevated temperatures. Hot smoke overhead should be cooled to minimize potential for ignition.
  • Ongoing size-up needs to consider current and projected fire behavior as well as structural conditions.

While a solid training program, Single Family Dwelling Fire Attack could do a better job of explaining the differences between direct and indirect fire attack and how gas cooling impacts the fire environment to reduce the flammability and thermal hazards by the hot upper layer. The following posts expand on the challenges presented by shielded fires and application of gas cooling:

Single Family Dwelling Fire Attack does a solid job of addressing size-up and decision making, but firefighters and fire officers need to develop a more in-depth understanding of reading the fire. The following posts provide an expanded look at this important topic:

One great feature in Modules 3, 5 and 5 of Single Family Dwelling Fire Attack are brief video presentations by Dan Madrzykowski on Ventilation, Suppression, Size-Up and Decision Making which are also available on YouTube. The video on Ventilation is embedded below as a preview:

Control the Door and Control the Fire

Thursday, July 25th, 2013

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.

sequence_0000_to_0320

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

UL Vertical Ventilation Study
Tactical Implications

Wednesday, July 17th, 2013

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.

vertical_quad

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

Sunday, July 7th, 2013

The last several weeks have brought a number of interesting things in the area of fire dynamics and firefighting operations. Before getting back to the question of Door Control Doctrine, take a few minutes to have a look at the ALIVE on-line interactive training program by the NYU Poly Fire Research Group and the recently released research report Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes

ALIVE On-Line Interactive Training

NYU Poly Fire Research Group has teamed up with the FDNY, Chicago Fire Department (CFD) the Bloomington Fire Department (BFD), the Eagan Fire Department (EFD), and the Eden Prairie Fire Department (EPFD) to develop a web-based, interactive firefighter training program – ALIVE (Advanced Learning through Integrated Visual Environments).

nyu_poly_fire_research

A recently released training module addresses the implications of fire dynamics and lightweight/engineered construction on firefighting operations in residential occupancies. Narrated by FDNY Lieutenant John Ceriello, this training program provides an excellent integrated review of current research conducted by UL, NIST, FDNY & the CFD and its application to fireground operations. The on-line training is available for use on a PC as well as an iOS and Android app. Have a look and share this important training with others!

UL Vertical Ventilation

Underwriters Laboratories Fire Service Research Institute (UL FSRI) recently released the research report Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes.

ul_vertical

In conjunction with with the previous study on horizontal ventilation, this report provides a solid look at the capabilities and limitations of tactical ventilation in a residential context. Download a copy of the report and review the tactical implications (or read the entire report if you are extremely ambitious). The outcomes of this research will be explored in detail in upcoming CFBT-US blog posts.

Visit the UL FSRI web site and Facebook Page for regular updates on UL’s ongoing research with the fire service!

Door Control Doctrine

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.

Given what we know about the modern fire environment and the influence of both existing and increased ventilation on ventilation controlled fires, what guidance should we provide to firefighters regarding door control? The following questions are posed in the context of a residential occupancy (one or two-family home, garden apartment unit, townhouse, etc.).

door_entry_drill

If the door to the fire occupancy is open when the first company arrives, should it be (immediately) closed by the member performing the 360o reconnaissance? If so why? If not, why not?

In general, if the door is open it should be closed as soon as possible. In the modern fire environment, most fires beyond the incipient stage will be ventilation controlled when the first company arrives. Closing the door until the first line is ready to enter will limit air flow to the fire and reduce heat release rate.

If the door should be closed immediately there any circumstances under which it should not? If there are circumstances under which the door should not be closed, what are they and why?

If the fire is not ventilation controlled, closing the door will not have a positive impact. However, it is unlikely to have a negative effect as well. If occupants remain inside (or have gone back in through the open door in an effort to rescue others), an argument could be made that closing the door might make it more difficult for them to find the exit. However, under ventilation controlled conditions, the increased air supply will quickly make conditions untenable and the flow path between the open door and the fire will result in fire spread along this path, further reducing tenability and potential for safe occupant egress. The short answer is no. If the door is open, close it.

If the door is closed on arrival (or you closed the door during the 360o reconnaissance) when and how should it be opened for entry? Think about tactical size-up at the door, forcible entry requirements, and the actual process of opening the door and making entry? How might this differ based on conditions?

When the door is opened, the clock is ticking on increased heat release rate (HRR). The door should remain closed until a charged hoseline is in place and the crew on the hoseline is ready to make entry for fire attack.

The door entry procedure should include assessment of B-SAHF indicators and forcible entry requirements (if the door is closed and locked). If forcible entry is required, it may be forced before the crew is ready to enter, but should be controlled in a closed position after it is forced. The door may be opened briefly and partially to assess conditions and if necessary to cool the hot upper layer prior to entry, but should generally remain closed until the crew on the hoseline enters the building.

After making entry should the door be closed to the greatest extent possible (i.e., leaving room for the hoseline to pass)? If so why? If not, why not?

If the fire is shielded from direct attack from the door, it should be closed after entry to limit air flow to the fire and reduce the flow path between the entry point and the fire. Limiting air flow will slow the increase in HRR. Limiting the flow path (it cannot be eliminated by closing the door completely due to the space required to pass the hoseline) will reduce the risk of fire spread towards the entry point.

If the door should be closed to the greatest extent possible, who will maintain door control and aid in advancement of the line? How might this be accomplished with limited staffing?

This is a significant question! As always, it depends. With a four person crew, one member may control the door with a two person team working inside. With smaller crew sizes, the standby team (two-out) may be able to control the door. If operating with limited staffing (three) in rescue mode, the apparatus operator may need to add door control to their rather substantial list of critical tasks after charging the attack and standby lines).

If you are performing search, should doors to the rooms being searched be closed while searching? If so why? If not, why not? Are there conditions which would influence this decision? If so, what are they?

In the past, firefighters may have been trained to “vent as you go” when searching. The concept was that venting the rooms being searched would improve tenability and increase visibility. However, horizontal ventilation also creates a flow path between the fire and the ventilation opening. If the opening serves as an inlet (due to vertical position in relation to the fire or wind effects), it may improve conditions in the room, but has the potential to worsen fire conditions due to increased HRR. If the opening serves as an outlet, a flow path for fire spread is created, which will potentially worsen conditions in the room being searched.

Closing the door to the room being searched allows the searcher to tactically ventilate the room if necessary while preventing a flow path between the fire and the room being searched.

Should the doors to rooms which have been searched be closed after completing the primary search? If so why? If not, why not? Are there conditions which would influence this decision? If so, what are they?

As with closing the door, it depends. Tactical ventilation must be planned, systematic, and coordinated. If the fire is being controlled (water on the fire) and the location of the opening in the compartment which has been searched is advantageous and part of the ventilation plan, leaving the door open is necessary. If the location is not advantageous and part of the plan, it should be closed.

How else can doors be used to aid in fire control or the protection of occupants and firefighters? Give this some thought!

As seen in the UL horizontal and vertical ventilation research projects, a closed door provides an area of refuge for both building occupants and if necessary for firefighters. Be mindful of potential areas of refuge while working inside, particularly if you are not on a hoseline, or in the event that water supply in your hoseline is compromised.

LA County Fire Department adopts door control doctrine! In a recent video posted on the LA County Fire Department Training Division web site, Battalion Chief Derek Alkonis explains the department’s door control doctrine and how this integrates into residential fire attack with three and four person engine companies. While the use of straight streams in an effort to cool hot gases overhead differs considerably than the use of pulsed water fog advocated by CFBT-US, this video provides an excellent example of effective door control and integration of tactical anti-ventilation, fire control, and tactical ventilation.

Developing Door Control Doctrine

Monday, June 17th, 2013

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.

contro_the_door

One way to frame the discussion necessary to develop doctrine that is applicable to a range of circumstances, is to use a series of scenarios presenting different conditions and examine what is similar and what is different. Ideally, firefighters will work together to integrate this theoretical discussion with their experience to develop sound doctrine based on their own context (e.g., staffing, building and occupancy types).

Fireground Scenarios

Important! Not all of the tactics presented in the questions are appropriate and others may be appropriate in one context, but not necessarily in another. For example, a lightly staffed engine may not have the option of offensive operations until the arrival of additional resources (barring a known imminent life threat), where a company with greater staffing may have greater strategic and tactical flexibility. These questions focus on the impact of strategic (offensive or defensive) tactical options on fire dynamics.

Scenario 1: The first arriving company arrives to find a small volume of smoke showing from around windows and doors and from the eaves on Side Alpha with low velocity, no air inlet is obvious. Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows are closed. Several windows on Side Alpha (Alpha Bravo Corner) are darkened with condensed pyrolysis products and the home appears to have smoke throughout (smoke logged).

How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.

The fire is likely in a ventilation controlled, decay stage. If the ventilation profile does not change prior to entry (e.g., doors are kept closed, windows remain intact), the heat release rate (HRR) from the fire will continue to decline and temperatures within the building will drop (but may still be fairly high when entry is made).

How would opening the front door prior to having a charged line at the doorway on Side Alpha impact fire development?

Increased ventilation will result in a significant and potentially rapid increase in HRR. The proximity of the door to the fire compartment and temperature in the fire compartment at the time that ventilation is increased will have a direct impact on the speed with which the fire returns to the growth stage (but still remaining ventilation controlled). The closer the air inlet to the fire and the higher the temperature, the more rapidly the fire will return to the growth stage.

How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the (still closed) doorway on Side Alpha?

As noted in the answer to question 2, increased ventilation will result in an increase in HRR. As windows in the fire compartment are in closer proximity to the fire, taking the windows potentially will result in a more rapid return to the growth (but still ventilation controlled) stage. It is also important to consider that a window cannot be unbroken; selecting this ventilation option does not provide an option for changing you mind if you do not like the result.

What would be the impact on fire behavior if the engine company advanced the first hoseline to the windows; took the glass and applied water to the burning fuel inside the fire compartment prior to making entry through the door? How might this change if offensive fire attack was delayed (e.g., insufficient staffing for offensive operations)?

This is an interesting question! Research by UL, NIST, and FDNY has shown the positive impact of exterior application of water into the fire compartment in reducing heat release rate. However, as noted in the answer to the preceding question, a window cannot be unbroken. If this is simply a contents fire in the compartment where the window is broken and water is applied, the result is likely to be favorable with a temporary reduction in HRR due water applied on burning fuel. However, if the fire extended to other areas of the building which shielded from direct attack at this point of application, effectiveness of exterior application from this single location is likely to be limited.

How would opening the front door and horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the doorway on Side Alpha?

Advice on coordination of tactical ventilation and fire attack has typically stated, don’t vent until a charged hoseline is in place. This is good advice, but requires a bit of clarification.

“As soon as the hoseline is deployed to the doorway” may simply mean that a dry line has been stretched and firefighters are donning their self-contained breathing apparatus (SCBA) facepieces while waiting for water. The fire will begin transition back to the growth stage as soon as tactical ventilation is performed. Depending on the time required for the firefighters to mask up, the line to be charged, air bled off, pattern checked, and the charged line advanced to the fire compartment(s), the HRR may increase significantly and conditions are likely to be quite a bit worse than if the door and window had remained closed until the hoseline was in place to begin offensive fire attack from the interior.

If tactical ventilation is performed after the line is charged and firefighters are ready to immediately make entry and quickly advance to the fire compartment, it is likely that the effect of increased ventilation will be positive. There may be some increase in HRR, but it is likely to be minimal due to the short distance and simple stretch from the front door to the fire compartment(s). Once direct attack has begun to control the fire, the increased ventilation will improve conditions inside the building.

Assuming that sufficient resources are on-scene to permit an offensive attack, when should the entry point be opened? Assuming that the door is unlocked, how should the fire attack crew approach this task?

Tactical size-up is critical for the crew assigned to offensive fire attack. This includes assessment of B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators, forcible entry requirements, and assessment of fire attack requirements (e.g., flow rate, length of line, and complexity of the stretch).

The door should remain closed until the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. Check to see if the door is unlocked, but control the door (closed) and check conditions inside (visible fire, level of the hot upper layer, presence of victims inside the doorway) by opening the door slightly. The firefighter on the nozzle should do this check while the tools firefighter opens and controls the door. If hot smoke or flames are evident, the nozzle firefighter should cool the upper layer with one or more pulses of water fog (depending on conditions). The door should be closed while the crew assesses the risk of entry (e.g., floor is intact and fire conditions will permit entry from this location). If OK for entry; the crew can open the door and advance the line inside, while cooling the upper layer as necessary.

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 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. The home appears to have smoke throughout (smoke logged).

How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.

The fire is in a ventilation controlled burning regime (indicators include the limited ventilation provided by the single opening at the front door and flames at the interface between the smoke and air at the door). The open door will likely provide sufficient ventilation for the fire to continue its growth and extension from the compartment of origin along the flowpath to the front door.

How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?

Based on the reported observations during 360o reconnaissance, the only significant ventilation opening is the front door. The bi-directional air track indicates that this opening is serving as both an inlet and outlet. Closing the door will reduce the air supply to the fire and will reduce the HRR and slow worsening conditions outside the fire compartment. Ideally this would be done prior to starting the 360o reconnaissance.

Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?

As in Scenario 1, the door should be opened only when the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. The same door entry procedure described in Scenario 1 should be used as if the door had been closed on arrival.

How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development is performed as soon as the hoseline is deployed to the open doorway on Side Alpha?

The outcome of tactical ventilation of the fire compartment will depend on sequence and timing. If the door remained open during initial size-up and while the line was being stretched, he fire would have continued to grow (limited by ventilation provided by the doorway and interior configuration of the building). Additional ventilation in this case would result in a rapid increase in HRR. If the door had been closed during the 360, the increase in HRR on ventilation of the windows would likely be somewhat slower as the HRR and temperature in the fire compartment would have dropped once the door was closed. In either case, HRR will increase while the charged line is being stretched from the entry point to the fire compartment. This is not necessarily a problem if the stretch is quick and the flow rate of the hoseline is adequate. It is essential that the crews stretching the line and performing ventilation understand the influence of their actions on fire behavior and are not surprised at the result.

Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?

As noted in Scenario 1, closing the door to the greatest extent possible after the line is inside will slow fire development until the hoseline is in place to begin a direct attack.

Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?

The same basic approach would be taken as in Scenario 1. Once direct attack has commenced, horizontal tactical ventilation can be performed from Alpha (doorway) to Alpha (windows in the fire compartment).

Scenario 3: The first arriving company arrives to find smoke showing with moderate velocity and a bi-directional air track (smoke out the top and air in the bottom) from an open door on Side Alpha. A moderate volume of smoke is also pushing from around windows and from the eaves on Side Alpha. Flames are visible from several windows on Side Alpha (Alpha Bravo Corner) with a bi-directional air track (flames from the upper ¾ of the window with air entering the lower ¼). Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the two windows and door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. Flames from the windows on Side Alpha are similar to when first observed. The home appears to have smoke throughout (smoke logged).

How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.

The fire is likely in a ventilation controlled burning regime (indicators include the limited ventilation provided by the openings at the front door and windows. Existing ventilation will likely be sufficient for the fire to continue its growth and extension from the compartment of origin along the flowpath to the front door. As there are multiple ventilation openings (more cross sectional area), HRR is greater and as a result fire development and spread will be much more rapid than in Scenario 2.

How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?

As the windows in the fire compartment have failed and are serving as ventilation openings (in addition to the front door), the fire will likely remain in a ventilation controlled growth stage even if the door is closed. However, closing the door will still reduce the air supply to the fire and will slow fire growth. In addition, elimination of the flow path between the fire compartment and front door will reduce heat transfer along this flow path.

Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?

As in Scenarios 1 and 2, the door should be opened only when the crew on the hoseline is ready to make entry; hoseline charged, air bled off, nozzle function and pattern checked, SCBA facepeices on, on-air. The same door entry procedure described in the prior scenarios should be used.

How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the open doorway on Side Alpha?

As the windows in the fire compartment have already failed, some ventilation of the fire compartment has already occurred. In that the fire is ventilation controlled, any additional ventilation will significantly increase HRR. With a ventilation controlled growth stage fire and high temperature in the fire compartment, the HRR will increase rapidly.

Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?

As in the previous two scenarios, the door should be closed to as great an extent possible after the hoseline is advanced inside the building. This will limit air to the fire, slow fire development, an reduce the flow path between the fire and the front door.

Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?

As the windows in the fire compartment have already failed, they will continue to provide ventilation. Once a direct attack has been initiated, the front door may be opened to increase air flow and the efficiency of the horizontal ventilation from Side Alpha to Side Alpha.

As noted in the previous post, these questions were all based on a similar fire (different development based on the ventilation profile at the time of the first company’s arrival) in the same, simple building, a one story, wood frame dwelling. It is important to examine other levels of involvement and ventilation profiles in this building as well as other types of buildings and fire conditions with similar questions. Also give some thought to the impact of door control when using vertical ventilation in coordination with fire attack.

Additional Examples

The following video of pre-arrival conditions and initial fireground operations provides an additional opportunity to consider the impact of ventilation and the importance of door control.

Video 1: In the first video, the door is closed when the fire department arrives, but the fire has self-vented through a window on Side Delta.

 

How might effective door control have influenced fire development and the safety of companies operating at this incident?

Video 2: In this video, the front door is open when the fire department arrives and it appears that the fire may have self-vented on Side Charlie.

How might effective door control have influenced fire development and the safety of companies operating at this incident?

Video 3: In the last video, the front door is partially open and existing ventilation includes a window on Side Alpha and one or more openings on Side Charlie.

 

How might effective door control have influenced fire development and the safety of companies operating at this incident?

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?

Close the Door!
Were You Born in a Barn?

Thursday, May 30th, 2013

Coming and going as a little kid, I frequently would forget to close the door to the house and my mother would say; close the door! Were you born in a barn? What does this have to do with firefighting operations? As it turns out, it has significant impact!

close_the_door

Research conducted by Underwriters Laboratories (UL), National Institute of Standards and Technology (NIST), and the Fire Department of the City of New York (FDNY) points to the importance of close coordination of tactical ventilation (including opening a door to gain access) and fire attack. While doors are not ordinarily considered a firefighting tool, this post examines door control as an essential element in firefighting operations.

The Fire Environment-A Quick Review

Modern homes have a high fire load (both in mass and heat of combustion of common building contents), are better insulated and more energy efficient, and are larger and have large open, undivided living spaces.

These conditions often result in rapid fire development and transition from a growth stage, fuel controlled burning regime to decay stage, ventilation controlled burning regime prior to the arrival of the fire department. Increased ventilation (without concurrent fire control) will result in increased heat release rate, returning the fire to the growth stage and rapid transition through flashover to a fully developed stage of fire development.

A number of factors influence the speed with which heat release rate accelerates when the air supplied to a ventilation controlled fire increases. These include building and compartment size and geometry, thermal conditions, and size and location of the ventilation openings.

  • In general, fires in smaller compartments will react more quickly, but compartmentation and complex geometry will slow air movement from the inlet to the fire, and resulting increase in HRR.
  • Introduction of air close to the fire will influence HRR more quickly than air introduced at a distance.
  • Exhaust openings that are above the fire (horizontal or vertical) will increase HRR more quickly and to a greater extent than those at the same level (but may be more effective in improving conditions when fire control is established)
  • Larger openings (or multiple smaller openings) will increase HRR to a greater extent and more quickly than smaller (or fewer) openings.

Conditions on Arrival

A critical element of size-up is identification of the current ventilation profile of the building. Remember that ventilation (exchange of the atmosphere inside the building and that outside the building) is always going on to one extent or another. Assessment of the ventilation profile is based on the Building, Smoke and Air Track elements of B-SAHF (Building, Smoke, Air Track, Heat, and Flame) Fire Behavior Indicators (FBI). Starting with Building factors, consider the nature of current ventilation openings:

  • No significant ventilation openings (normal building leakage only)
  • One or more doors may be open
  • One or more windows may be open
  • Some combination of door(s) and window(s) may be open

In addition to the ventilation openings, it is important to consider if they are exhaust openings, inlets, both exhaust and inlet, and what is visible; flames or smoke:

  • Nothing showing (remember that this means nothing, the fire may be ventilation controlled and in the decay stage, but interior temperatures may be above 425o C (800o F) even when little or nothing is showing from the exterior.
  • Smoke showing from ventilation openings (consider the direction of the air track at each opening, in, out, bi-directional, or pulsing)
  • Smoke and flames showing from ventilation openings (as with smoke, consider the direction of the air track)

Structural Firefighting is Simple

OK this is a bit of an overstatement (actually more than a bit). Generally, there are only two things that firefighters can do to influence fire behavior; change the ventilation or absorb the energy being released by the fire. Read each of the following three scenarios and consider the questions posed. While examining door control, this anti-ventilation tactic is not used alone so there are a few questions that address fire control tactics (which will be the subject of a subsequent post).

Scenario 1: The first arriving company arrives to find a small volume of smoke showing from around windows and doors and from the eaves on Side Alpha with low velocity, no air inlet is obvious. Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows are closed. Several windows on Side Alpha (Alpha Bravo Corner) are darkened with condensed pyrolysis products and the home appears to have smoke throughout (smoke logged).

  1. 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.
  2. How would opening the front door prior to having a charged line at the doorway on Side Alpha impact fire development?
  3. 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?
  4. 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)?
  5. 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?
  6. 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 this task be approached?
  7. 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?
  8. 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)?

Scenario 2: The first arriving company arrives to find smoke showing with moderate velocity and a bi-directional air track (smoke out the top and air in the bottom) from an open door on Side Alpha. A moderate volume of smoke is also pushing from around windows and from the eaves on Side Alpha. Several windows on Side Alpha (Alpha Bravo Corner) are darkened with condensed pyrolysis products and a glow is visible inside in the room behind these windows. Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. The home appears to have smoke throughout (smoke logged).

  1. 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.
  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?
  3. 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?
  4. 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?
  5. 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?
  6. 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)?

Scenario 3: The first arriving company arrives to find smoke showing with moderate velocity and a bi-directional air track (smoke out the top and air in the bottom) from an open door on Side Alpha. A moderate volume of smoke is also pushing from around windows and from the eaves on Side Alpha. Flames are visible from several windows on Side Alpha (Alpha Bravo Corner) with a bi-directional air track (flames from the upper ¾ of the window with air entering the lower ¼). Performing a 360o reconnaissance, the officer observes similar smoke and air track indicators on other sides of the building and that all doors and windows with the exception of the two windows and door on Side Alpha are closed. Returning to Side Alpha, the officer observes that the velocity of smoke from the open door has increased and flames at the interface between the smoke and air as it exits the doorway. Flames from the windows on Side Alpha are similar to when first observed. The home appears to have smoke throughout (smoke logged).

  1. 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.
  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?
  3. 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?
  4. 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?
  5. 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?
  6. 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)?
  7. Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed?

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.

Door Control Doctrine

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.

Given what we know about the modern fire environment and the influence of both existing and increased ventilation on ventilation controlled fires, what guidance should we provide to firefighters regarding door control? The following questions are posed in the context of a residential occupancy (one or two-family home, garden apartment unit, townhouse, etc.).

  1. If the door to the fire occupancy is open when the first company arrives, should it be (immediately) closed by the member performing the 360o reconnaissance? If so why? If not, why not?
  2. If the door should be closed immediately there any circumstances under which it should not? If there are circumstances under which the door should not be closed, what are they and why?
  3. If the door is closed on arrival (or you closed the door during the 360o reconnaissance) when and how should it be opened for entry? Think about tactical size-up at the door, forcible entry requirements, and the actual process of opening the door and making entry? How might this differ based on conditions?
  4. After making entry should the door be closed to the greatest extent possible (i.e., leaving room for the hoseline to pass)? If so why? If not, why not?
  5. If the door should be closed to the greatest extent possible, who will maintain door control and aid in advancement of the line? How might this be accomplished with limited staffing?
  6. If you are performing search, should doors to the rooms being searched be closed while searching? If so why? If not, why not? Are there conditions which would influence this decision? If so, what are they?
  7. Should the doors to rooms which have been searched be closed after completing the primary search? If so why? If not, why not? Are there conditions which would influence this decision? If so, what are they?
  8. How else can doors be used to aid in fire control or the protection of occupants and firefighters? Give this some thought!

Review The Influence of Ventilation in Residential Structures Part 2 for additional information on the influence of ventilation and door control as an  anti-ventilation tactic.

I plan on posting my thoughts on the questions posed in this post next week. However, it would likely make this much more interesting if you post your perspectives (or additional questions) as a comment!

Ed Hartin, MS, EFO, MIFireE, CFO