Posts Tagged ‘underwriters laboratories’

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

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

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

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

Place the Questions in Context

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

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

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

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

Fire Development in Scenario 1

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

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

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

Fire Development in Scenario 2

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

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

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

Alternate Scenarios

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

Tactical Options

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

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

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

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

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

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

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

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

Unanswered Questions

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

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

Proactive Action Steps

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

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

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

Firefighting Doctrine

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

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

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

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

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

References

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

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

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

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

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

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

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

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

Social Learning

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

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

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

The Questions

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

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

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

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

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

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

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

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

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

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

The Foundation

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

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

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

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

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

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

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

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

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

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

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

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

Discussion

The following section addresses Colin’s statements and question.

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

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

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

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

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

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

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

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

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

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

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

Integration

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

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

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

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

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

Expanded Tactical Considerations

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

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

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

Closing Thoughts

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

Update

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

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

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

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

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

Tactical Implications

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Ventilation Doctrine

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

References

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

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

The eighth and tenth tactical implications identified in the Underwriters Laboratories study of the Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2011) are the answer to the question, can you vent enough and the influence of pre-existing openings or openings caused by fire effects on the speed of progression to flashover.

The ninth implication; the effects of closed doors on tenability for victims and firefighters, will be addressed in the next post.

Photo Credit: Captain Jacob Brod, Pineville (NC) Fire Department

Kerber (2011) indicates that firefighters presume that if you create enough ventilation openings that the fire will return to a fuel controlled burning regime. I am not so sure that this is the case. Until fairly recently, the concept of burning regime and influence of increased ventilation on ventilation controlled fires was not well recognized in the US fire service. However, there has been a commonly held belief that increased ventilation will improve interior conditions and reduce the potential for extreme fire behavior phenomena such as flashover. In either case, the results of the experiments conducted by UL on the influence of horizontal ventilation cast considerable doubt on the ability to accomplish either of these outcomes using horizontal, natural ventilation.

The Experiments

In order to determine the impact of increased ventilation, Kerber (2011) compared changes in temperature with varied numbers and sizes of ventilation openings. The smallest ventilation opening in the experiments conducted in both the one and two story houses was when the door on Side A was used to provide the only opening. The largest number and size of ventilation openings was in the experiments where the front door and four windows were used (see Figures 1 and 3)

The area of ventilation openings in experiments conducted in the one-story house ranged from 1.77 m² (19.1 ft²) using the front door only to 9.51 m² (102.4 ft²) with the front door and four windows. In the two-story house the area of ventilation openings ranged from 1.77 m² (19.1 ft²) with front door only to 14.75 m² (158.8 ft²) using the front door and four windows.

The most dramatic comparison is between Experiments 1 and 2 where a single opening was used (front door) and Experiments 14 and 15 where five openings were used (door and four windows).

One Story House

Experiment 1 was conducted in the one-story house using the door on Side A as the only ventilation opening. The door was opened eight minutes after ignition (480 seconds). Experiment 14 was also conducted in the one-story house, but in this case the door on Side A and four windows were used as ventilation openings. Windows in the living room and bedrooms one, two, and three were opened sequentially immediately after the door was opened, providing more than five times the ventilation area as in Experiment 1 (door only).

Figure 1. Ventilation Openings in the One-Story House

In both Experiment 1 (door only) and Experiment 14 (door and four windows), increased ventilation resulted in transition to a fully developed fire in the compartment of origin (see Figure 2). In Experiment 1, a bi-directional air track developed at the door on Side A (flames out the top and air in the bottom). In Experiment 14, a bi-directional air track is visible at all ventilation openings, with flames visible from the door and window in the Living Room on Side A and flames visible through the window in Bedroom 3. No flames extended out the ventilation openings in Bedrooms 1, 2, and 3. The upper layer in Bedroom 3 is not deep, as such there is little smoke visible exiting the window, and it appears to be serving predominantly as an inlet. On the other hand, upper layer in Bedroom 2 is considerably deeper and a large volume of thick (optically dense) smoke is pushing from the window with moderate velocity. While a bi-directional air track is evident, this window is serving predominantly as an exhaust opening.

Figure 2. Fire Conditions at 600 seconds (10:00)

As illustrated in Figure 3, increased ventilation resulted in a increase in heat release rate and subsequent increase in temperature. It is important to note that the peak temperature in Experiment 14 (door and four windows) is more than 60% higher than in Experiment 1 (door only).

Figure 3. Living Room Temperature 0.30 m(1’) Above the Floor One-Story House

Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 298), by Steve Kerber, 2011, Northbrook, IL: Underwriters Laboratories.

Based on observed conditions and temperature measurement within the one-story house, it is evident that increasing the ventilation from 1.77 m² (19.1 ft²) using the front door to 9.51 m² (102.4 ft²) with the front door and four windows did not return the fire to a fuel controlled burning regime and further, did not improve interior conditions.

It is important to note that these experiments were conducted without coordinated fire control operations in order to study the effects of ventilation on fire behavior. Conditions changed quickly in both experiments, but the speed with which the fire transitioned from decay to growth and reached flashover was dramatically more rapid with a larger ventilation area (i.e., door and four windows).

Two Story House

Experiment 2 was conducted in the two-story house using the door on Side A as the only ventilation opening. The door was opened ten minutes after ignition (600 seconds). Experiment 15 was also conducted in the two-story house, but in this case the door on Side A and four windows were used as ventilation openings. One window in the Living Room (Floor 1, Side A, below Bedroom 3) Den (Floor 1, Side C, below Bedroom 2) and two windows in the Family Room (Side C) were opened sequentially immediately after the door was opened, providing more than eight times the ventilation area as in Experiment 2 (door only).

Figure 4. Ventilation Openings in the Two-Story House

In both Experiment 2 (door only) and Experiment 15 (door and four windows), increased ventilation resulted in transition to a fully developed fire in the compartment of origin. Flames were seen from the family room windows in Experiment 15 (see Figure 5). However, in Experiment 2, no flames were visible on the exterior (due to the distance between the fire compartment and ventilation opening) and a bi-directional air track developed at the door on Side A (smoke out the top and air in the bottom). In Experiment 15, a bi-directional air track is visible at all ventilation openings, with flames visible from the windows in the family room on Side C. No flames extended out the ventilation openings on Side A or from the Den on Side C (see Figure 5). The upper layer is extremely deep (particularly considering the ceiling height of 16’ in the family room and foyer atrium. The velocity of smoke discharge from ventilation openings is moderate.

Figure 5. Fire Conditions at 780 seconds (13:00)

As illustrated in Figure 6, increased ventilation resulted in a increase in heat release rate and subsequent increase in temperature. It is important to note that the peak temperature in Experiment 15 (door and four windows) is approximately 50% higher than in Experiment 2 (door only).

Figure 6. Living Room Temperature 0.30 m(1’) Above the Floor One-Story House

Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 299), by Steven Kerber, 2011, Northbrook, IL: Underwriters Laboratories.

Another Consideration

Comparison of these experiments answers the questions if increased horizontal ventilation would 1) return the fire to a fuel controlled state or 2) improve interior conditions. In a word, no, increased horizontal ventilation without concurrent fire control simply increased the heat release rate (sufficient for the fire to transition through flashover to a fully developed stage) in the involved compartment.

Examining thermal conditions in other areas of the building also provides an interesting perspective on these two sets of experiments. Figure 7 illustrates temperatures at 0.91 m (3’) during Experiment 1 (door only) and Experiment 14 (door and four windows) in the one-story house.

Figure 7. Temperatures at 0.91 m (3’) during Experiments 1 and 14

Note. Adapted from Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (p. 99, p. 162), by Steven Kerber, 2011, Northbrook, IL: Underwriters Laboratories.

Thermal conditions not only worsened in the fire compartment, but also along the flow path (for a more detailed discussion of flow path, see UL Tactical Implications Part 7) and in downstream compartments. Temperature in the hallway increased from a peak of just over 200^o C to approximately 900^o C when ventilation was increased by opening the four additional windows.

Unplanned Ventilation

Each of the experiments in this study were designed to examine the impact of tactical ventilation when building ventilation was limited to normal leakage and fire conditions are ventilation controlled (decay stage). In each of these experiments, increased ventilation resulted in a rapid increase in heat release rate and temperature. Even when ventilation was increased substantially (as in Experiments 14 and 15), it was not possible to return the fire to a fuel controlled burning regime.

It is also possible that a door or window will be left open by an exiting occupant or that the fire may cause window glazing to fail. The impact of these types of unplanned ventilation will have an effect on fire development. Creation of an opening prior to the fire reaching a ventilation controlled burning regime will potentially slow fire progression. However, on the flip side, providing an increased oxygen supply will allow the fire to continue to grow, potentially reaching a heat release rate that will result in flashover. If the opening is created after the fire is ventilation controlled, the results would be similar to those observed in each of these experiments. When the fire is ventilation controlled, increased ventilation results in a significant and dramatic increase in heat release rate and worsening of thermal conditions inside the building.

If the fire has self-ventilated or an opening has been created by an exiting occupant, the increased ventilation provided by creating further openings without concurrent fire control will result in a higher heat release rate than if the openings were not present and will likely result in rapid fire progression.

What’s Next?

I will be at UL the week after next and my next post will provide an update on UL’s latest research project examining the influence of vertical ventilation on fire behavior in legacy and contemporary residential construction.

Two tactical implications from the horizontal ventilation study remain to be examined in this series of posts: the impact of closed doors on tenability and the interesting question can you push fire with stream from a hoseline?

The last year has presented a challenge to maintaining frequency of posts to the CFBT Blog. However, I am renewing my commitment to post regularly and will be bringing back Reading the Fire, continuing examination of fundamental scientific concepts, and integration of fire control and ventilation tactics.

References

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

The fourth tactical implication identified in the Underwriters Laboratories study of the Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction (Kerber, 2011) is that fire attack and (tactical) ventilation must be coordinated. This recommendation has been repeated in National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Reports for many years. In fact, most reports on firefighter fatalities related to rapid fire progression contain this recommendation.

Importance of Coordination

Coordination of (tactical) ventilation and fire attack as a tactical implication is closely related to the first two tactical implications identified in the UL study; potential changes in fire behavior based on stages of fire development, burning regime, and changes in ventilation profile that increase oxygen supplied to the fire.

If air is added to the fire and water is not applied in the appropriate time frame the fire gets larger and the hazards to firefighters increase. Examining the times to untenability provides the best case scenario of how coordinated the attack needs to be. Taking the average time for every experiment from the time of ventilation to the time of the onset of firefighter untenability conditions yields 100 seconds for the one-story house and 200 seconds for the two-story house. In many of the experiments from the onset of firefighter untenability until flashover was less than 10 seconds. These times should be treated as very conservative. If a vent location already exists because the homeowner left a window or door open then the fire is going to respond faster to additional ventilation openings because the temperatures in the house are going to be higher at the time of the additional openings (Kerber, 2011, p. 289-290)

The Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction Underwriters Laboratories (UL) on-line course and report provide an example of firefighters are at risk when ventilation is performed prior to entry, fire attack is delayed, and other tactical operations such as primary search are initiated.

In UL’s hypothetical example, the firefighters make entry into the one-story house, search the living room (fire compartment), the kitchen, and dining room shortly after forcing the door and ventilating a large window in the fire compartment. Consider a somewhat different scenario, with the same fire conditions.

Companies respond to a residential fire with persons reported during the early morning hours. A truck and engine arrive almost simultaneously and while the engine lays a supply line from a nearby hydrant, the truck company forces entry, ventilates a window on Side A, and begins primary search (anticipating that the engine crew will be right behind them to attack the fire). The engine completes a forward lay and begins to stretch an attack line after the search team has made entry.

Figure 1. Timeline and Progression of Primary Search

Figure 2. View of the Living Room (Fire Compartment) from the Door on Side A

As illustrated in Figure 3, visible flaming combustion when the door is opened at 08:00 is limited to a small flame from the top of the couch just inside the door on Side A. However, in the 30 seconds that it takes for the search team to make entry, flaming combustion has resumed and flames are near or at the ceiling above the couch. The search team may estimate that they have time to complete a quick search of the bedrooms (likely location of the reported persons). However, fire development progresses to untenable conditions within a minute, trapping the crew on Side D of the house.

Figure 3. Fire Progression in the Living Room 00:08:00 to 00:10:00

As the search team completes primary search of Bedroom 2 and moves towards Bedroom 3 in the hallway, conditions have deteriorated to an untenable level. Figure 4 illustrates the change in temperature at the 3’ level in the Living Room (fire compartment). Shortly before the search team reached Bedroom 2, fire conditions in the living room began to change dramatically, with temperature at the 3’ level transitioning from ordinary to extreme, quickly becoming untenable in the living room, hallway and adjacent compartments. In addition to this significant change in temperature, flames (with temperatures higher than the gas temperature at the 3’ level) significantly increase radiant heat transfer (flux) to the surface of both fuel packages and firefighters protective equipment.

Figure 4. Temperature at the 3’ Level

Note: Figure 4 illustrates temperature conditions starting eight minutes after ignition. The fire previously progressed through incipient and growth stages before beginning to decay due to lack of ventilation.

Why the Dramatic Change in Conditions?

As discussed in UL Tactical Implications Part 1, Fires in the contemporary environment progress from ignition and incipient stage to growth, but often become ventilation controlled and begin to decay, rather than continuing to grow into a fully developed fire. This ventilation induced decay continues until the ventilation profile changes (e.g., window failure due to fire effects, opening a door for entry or egress, or intentional creation of ventilation openings by firefighters. When ventilation is increased, heat release rate again rises and temperature climbs with the fire potentially transitioning through flashover to the fully developed stage (see Figure 4 and 5).

Figure 5. Fire Development in a Compartment

Captain James Mendoza of the San Jose (CA) Fire Department and CFBT-US Lead Instructor demonstrates the influence of ventilation on fire development using a small scale prop developed by Dr. Stefan Svensson of the Swedish Civil Contingencies Agency.

The prop used in this demonstration is a small, single compartment with a limited ventilation opening on the right side (which in a full size building could be represented by normal building leakage or a compartment opening that is restricted such as a partially open door or window). The front wall of the prop is ceramic glass to permit direct observation of fire conditions within the compartment.

As you watch this demonstration, pay particular attention to how conditions change as the fire develops and then enters the decay stage. In addition, observe how quickly the fire returns to the growth stage and develops conditions that would be untenable after the window is opened at 12:17.

Download Doll’s House Plans (or Doll’s House Plans: Metric) for directions on how to construct a similar small scale prop.

Fire development and changes in conditions following ventilation in this demonstration mirror those seen in the full scale experiments conducted by UL. Increasing ventilation to a ventilation controlled fire, results in increased heat release rate and transition from decay to the growth stage of fire development.

The same phenomena can be observed under fireground conditions in the following video clip of a residential fire in Dolton, Illinois (this is a long video, watch the first several minutes to observe the changes in fire behavior).

It appears that the front door was open at the start of the video clip and the large picture window on Side A was ventilated at approximately 00:47. Fire conditions quickly transition to the growth stage with flames exiting the window and door, causing firefighters on an uncharged hoseline that had been advanced into Floor 1, to quickly withdraw.

As discussed in UL Tactical Implications: Part 1:

• Fires that have progressed beyond the incipient stage are likely to be ventilation controlled when the fire department arrives.
• Ventilation controlled fires may be in the growth, decay, or fully developed stage.
• Regardless of the stage of fire development, when a fire is ventilation controlled, increased ventilation will always result in increased HRR.
• Firefighters and fire officers must recognize that the ventilation profile can change (e.g., increasing ventilation) as a result of tactical action or fire effects on the building (e.g., window failure).
• Firefighters and fire officers must anticipate potential changes in fire behavior related to changes in the ventilation profile and ensure that fire attack and ventilation are closely coordinated.

Coordinated Tactical Operations

Understanding how fire behavior can be influenced by changes in ventilation is essential. But how can firefighters put this knowledge to use on the fireground and what exactly does coordination of tactical ventilation and fire attack really mean?

Tactical ventilation can be defined as the planned, systematic, and coordinated removal of hot smoke and fire gases and their replacement with fresh air. Each of the elements of this definition is important to safe and effective tactical operations.

Ventilation (both tactical and unplanned) not only removes hot smoke, but it also introduces fresh air which can have a significant effect on fire behavior.

Tactical ventilation must be planned; these two elements speak to the intentional nature of tactical ventilation. Tactics to change the ventilation profile must be intended to influence the fire environment or fire behavior in some way (e.g., raise the level of the upper layer to increase visibility and tenability). The ventilation plan must also consider the flow path (e.g., vent ahead of, not behind, the attack team; vent in the immediate area of the fire, not at a remote location).

Tactical ventilation must be systematic, exhaust openings should generally be made before inlet openings (particularly when working with positive pressure ventilation or when taking advantage of wind effects).

And as pointed out in the UL Study (Kerber, 2011), tactical ventilation must be coordinated. Coordination of ventilation and other tactical operations requires consideration of sequence and timing:

Sequence: Ventilation may be completed before, during, or after fire attack has been initiated. Sequence will likely depend on the stage of fire development, burning regime, time required to reach the fire.

If the fire is small and staffing is limited, it may be appropriate to control the fire and then effect ventilation (e.g., hydraulic ventilation performed by the attack team). This approach minimizes potential fire growth,

In general, when the fire is ventilation controlled (as those beyond the incipient stage are likely to be), ventilation should not be completed unless the attack line(s) can quickly apply water to the seat of the fire. In a small, single family dwelling this may mean that the attack team is on-air, the line is charged, and the entry door is unlocked or has been forced and is being controlled (held closed). In a larger building, this may mean that the attack line has entered the structure and is in position to move onto the fire floor or into the fire area.

The key questions that must be answered prior to implementing tactical ventilation are:

1. What influence will these ventilation tactics have on fire behavior?
2. Are charged and staffed attack line(s) in place?
3. Will the attack team(s) be able to quickly reach the fire?
4. How will this impact crews operating on the interior of the building?

Coordination requires clear, direct communication between companies or crews assigned to ventilation, fire attack, and other tactical functions that are or will be taking place inside the building.

Important: While not a tactical implication directly raised by the UL study, another important consideration is the hazard of working without or ahead of the hoseline. While a controversial topic in the US fire service (where truck company personnel generally work on the interior without a hoseline), searching with a hoseline provides a means of protection and a defined exit path. Staffing is another key element of the operational context. If you do not have enough personnel to control the fire and search; in most cases it is likely the best course of action to control the fire and ensure a safer operating environment for search operations.

What’s Next?

The next tactical implication identified in the UL study (Kerber, 2011) examines information that may be obtained by reading the air track at the entry point opening. This implication will be expanded with a broader discussion of air track indicators and how related hazards can be mitigated to improve firefighter safety.

References

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

Impact of Ventilation on Fire Behavior

Earlier this year, Underwriters Laboratories (UL) conducted a series of full-scale experiments to determine the influence of ventilation on fire behavior in legacy and contemporary residential construction (see Did You Ever Wonder?).

UL University recently releases an on-line training program based on this research. Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction is an excellent examination of the influence of ventilation on fire behavior and discussion of the tactical implications of the lessons learned through this research.

Every Firefighter and Fire Officer should complete
this training program within the next 30 days!

Completion of this on-line program could be the most important 90 minutes of training that you complete in the next year! I do not make this statement lightly. Understanding the relationship between ventilation and fire behavior is a critical competency for firefighters and fire officers.

After completing this on-line training program, consider the following questions and discuss them with the firefighters and fire officers you work with:

• What are the indicators of a ventilation controlled fire?
• How do your forcible entry and door entry procedures influence fire behavior?
• How do you (or do you) coordinate fire attack and ventilation? How can tactical coordination be improved in your department?
• What hazards are presented when performing VES (Vent, Enter, & Search) under ventilation controlled conditions? How can these hazards be mitigated?
• What influence do closed doors have on the survivability profile (for either civilian occupants or trapped firefighters)?
• What other lessons can you draw from this important research?

Research Report

In addition to the on-line course, UL has published a comprehensive report on this important research projects: Impact of Ventilation on Fire Behavior in Legacy and Contemporary Residential Construction.

Video

You can also download an excellent video illustrating the difference between fuel characteristics and loading in legacy and contemporary residential occupancies. This video is a tremendous tool to illustrate changes in the built environment to both firefighters and civilian audiences.

High Resolution Video

Low Resolution Video

Lima Backdraft

I am still working the report on my staff ride to the site of the 1997 backdraft at Luis Giribaldi Street and 28 de Julio Street in the Victoria section of Lima, Peru and should have it posted within the next week.

Ed Hartin, MS, EFO, MIFireE, CFO

The ability to read the fire and predict likely fire behavior is a critical skill for both firefighters and fire officers. Previous posts have examined how to use the B-SAHF scheme to recognize critical fire behavior indicators and identify the stage of fire development, burning regime, and potential for extreme fire behavior such as flashover or backdraft. However, there is something missing!

Experience is critical to adapting standard procedures and practices to a complex and dynamic operational environment. However, learning about fire behavior and changes in fire conditions based on fireground observations are a bit like a black box test. Black box testing is a technique for testing computer software in which the internal workings of the item being tested are not known by the tester. This is not entirely true in the case of fire behavior, but there is much that we don�t know when assessing conditions on the fireground. How long has the fire been burning? What are the specific characteristics of the fuel? What sort of internal compartmentation is present? What exactly is the ventilation profile? Some of these factors can be determined during fire investigation and it is also possible to determine (with some degree of uncertainty) what influence these factors had on the outcome of the incident. Did you ever wonder how fire behavior would have changed if you had used different tactics? Unfortunately, in real life there are no �do overs�!

UL Tactical Ventilation Research Project

One of the people who has asked himself the question of what would have changed if different tactics were used is Underwriters Laboratories Fire Protection Engineer Steve Kerber.

Underwriters Laboratories (UL) has received a Firefighter Safety Research and Development Grant from the Department of Homeland Security (DHS). This research project will investigate and analyze the impact of natural horizontal ventilation on fire development and conditions in legacy (older, more highly compartmented) and contemporary (multi-level, open floor plan) residential structures.

Preliminary work has included review of literature related to horizontal ventilation and incidents in which ventilation had a significant influence on firefighter injuries and fatalities. In addition, UL has done preliminary work on the performance of various structural components such as single and multi-pane windows as preliminary input for design of full scale residential fire experiments.

In mid-December 2009, Steve Kerber met with the project advisory panel comprised of Captain Charles Bailey, Montgomery County (MD) Fire Department; Lieutenant John Ceriello New York City Fire Department, Firefighter James Dalton and Director of Training Richard Edgeworth, Chicago Fire Department, Chief Ed Hartin, Central Whidbey Island (WA) Fire & Rescue, Chief Otto Huber Loveland-Symmes (OH) Fire Department, and Chief Mark Nolan, Northbrook (IL) Fire Department. In addition, the advisory panel includes Fire Protection Engineers Dan Madrzykowski from the National Institute of Standards and Technology (NIST) and Dr. Stefan Svensson, a research and development engineer from the Swedish Civil Contingencies Agency.

Figure 1. Defining Experiment Parameters for the Contemporary Structure

The main task presented to the advisory panel at the first meeting was to aid in defining the parameters for the experiment; including fire location, changes in ventilation profile, timing of these changes, and instrumentation to measure effects on fire development and conditions.

UL Large Fire Research Facility

The ventilation experiments will be conducted at the UL Large Fire Research Facility in Northbrook, IL. From the exterior, this facility simply looks like a large industrial building (see Figure 2). However, the interior of the structure includes a unique facility for fire research.

Figure 2. UL Large Fire Research Facility

One of the facilities inside this building is a 100� x 120� (30.48 m x 36.58 m) with a ceiling height that is adjustable up to 50� (15.24 m) (see Figure 3). All of the smoke resulting from tests in this facility is exhausted through a system designed to oxidize unburned fuel and scrub hazardous products from the effluent prior to discharge to the atmosphere. Tests are monitored from a control room that overlooks the large burn room.

Figure 3. Large Burn Room

Over the next month, the two residential structures to be used for the ventilation experiments will be constructed inside the large burn room at the UL Large Fire Test Facility. After construction is complete, a series of 16 full scale fire experiments is planned to evaluate a range of different horizontal ventilation scenarios.

Research with the Fire Service

Steve Kerber has often stated that it is essential that scientists and engineers conduct research with, not for, the fire service. Engagement between researchers and firefighters on the street is essential in advancement of our profession. With this ventilation research project, Underwriters Laboratories is actively engaged in this process.

The outcome of this project will not simply be an academic paper (but there might be one or more of those as well). As part of the DHS grant, UL will be developing an on-line course to present the results of the experiments and their practical application on the fireground.

Happy Holidays,

Ed Hartin, MS, EFO, MIFireE, CFO