Posts Tagged ‘fire behavior’

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/

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

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

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

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

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

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

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

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

Conservation of Mass and Energy

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

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

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

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

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

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

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

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

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

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

Pressure Differential and Flow

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

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

More Questions

Mike Sullivan from Canada posed several related questions, focusing on a video included in the Large Vertical Vents are Good, But… post. Just to get everyone back up to speed on the video, this test was conducted by the National Institute of Standards and Technology (NIST) in Bensenville, IL. The building is a wood frame townhouse with a fire ignited on the first floor. The door on Floor 1, Side Alpha is closed and the window on Side 1, Alpha is open. The door to the second floor room where the open window is located is also open, providing a flow path between the window and the first floor fire.

 

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

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

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

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

UL/NIST Video Series

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

• Part 1-Introduction
• Part 2-The Fire Environment
• Part 3-Fire Dynamics
• Part 4-Case Studies
• Part 5-Fire Behavior Training
• Part 6-Live Fire Tests
• Part 7-Organizational Change

Upcoming Events

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

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

It has been a busy six weeks since my last post with several trips to Chile and around the United States delivering seminars on Practical Fire Dynamics and Reading the Fire along with finalizing the fire district’s budget for 2014. Spending a full-day on B-SAHF and reading the fire at the Springfield Professional Firefighters IAFF Local 333 professional development seminar and working with our fire district’s members on our adaptation of First Due Questions (see FDQ on Facebook and First Due Tactics on the web) provided inspiration to get back to the Reading the Fire series of blog posts.

Photo by John Shafer, The Green Maltese

Fireground photos and video can be used to aid in developing and maintaining proficiency in reading the Fire using the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) organizing scheme for fire behavior indicators. This post provides an opportunity to exercise your skills using a video segment shot during a live fire training. While live fire training is a considerably different context than an actual incident, this video provides an opportunity to focus on each of the elements of B-SAHF somewhat more closely than in typical incident video.

In this exercise, the focus will be on identifying specific indicators related to stages of fire development and burning regime (rather than anticipating fire development).

In this video, the fire has been ignited in a room (likely a bedroom) on the Bravo/Charlie corner of the building and the video is being taken from the exterior on the same corner. The ventilation profile is uncertain, but there is likely an opening/entry point on Side Alpha.

1. As you watch the first 0:43 of the video, identify the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators that can be observed and how they change over time.
2. What are the first visible indicators?
3. What indicators are visible on and through the window between 0:43 and 0:56? How do condensation of water or pyrolysis products on window glazing aid in determining burning regime and stages of fire development? How might these indicators differ at locations more remote from the fire?
4. How do the B-SAHF indicators change between 0:56 and 2:40? Why might this be the case?
5. After 2:40 flaming combustion appears to increase. What might have influenced this change?
6. By 3:37, the window on the Bravo/Charlie corner is dark and little flaming combustion can be observed. What might this indicate about burning regime and stages of fire development?
7. At approximately 3:41, how do smoke and air track indicators change. What might this indicate? If there is no change in ventilation profile, how might the smoke and air track indicators change next?
8. At 4:10 crews on Side Alpha report fire in a front (Side Alpha) room. Why might fire conditions be significantly different on this side of the building than in the original fire compartment? How might extinguishment of the fire in a room on Side Alpha influence fire development in the original fire compartment (Bravo/Charlie corner)?
9. The lower portion of a window in the fire compartment on the Bravo/Charlie corner is broken out at 4:24. How does this change the B-SAHF indicators observed from this location? What may be inferred from these observations?
10. Immediately after the lower portion of the window is broken out, a narrow fog stream is applied in a rotating manner through the window. What effect does this have on fire conditions in the room? How did smoke and air track indicators change during the brief water application? What did these changes indicate?
11. How did smoke and air track indicators change after the brief application of water into the fire compartment?
12. After the brief application of water through the window, how long did it take for the fire to resume significant growth in the fire compartment (crews operating from Side Alpha delayed fire attack intentionally).
13. At 7:09, the upper portion of the window on the Bravo/Charlie corner is removed. How does this change in ventilation influence visible B-SAHF indicators and fire behavior?
14. How do the B-SAHF indicators change as interior crews begin fire attack?
15. How might taking the glass in the window(s) on the Charlie side of the building have influenced visible B-SAHF indicators and fire behavior?
16. Had the window in the fire compartment located on Side Charlie (Charlie/Bravo Corner) failed first, what impact would this have had on flow path? How might this have influenced conditions encountered by the fire attack crew entering from Side Alpha?
17. At approximately 8:40, interior crews begin hydraulic (negative pressure) ventilation through a window in the fire compartment on the Charlie/Bravo corner. How does this tactic integrate with the natural pressure differences created by the wind? What might be a more effective alternative?

Developing world class knowledge and skill takes approximately 10,000 hours of deliberate practice. This equates to almost three hours every day, 365 days per year, for 10 years. If you only practice every third day achieving 10,000 hours in 10 years would require just over eight hours per day and if you only spend 2 hours every third day, it would take over 40 hours to achieve 10,000 hours of deliberate practice.

How are you coming on your 10,000 hours? Keep at it!

Ed Hartin, MS, EFO, MIFIreE, CFO

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.

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

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

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

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

Important lessons emphasized in Single Family Dwelling Fire Attack include:

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

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

• Shielded Fires
• Shielded Fires Part 2
• Gas Cooling
• Gas Cooling Part 2
• Gas Cooling Part 3
• Gas Cooling Part 4
• Gas Cooling Part 5

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

• How to Improve Your Skills
• Building Factors
• Building Factors Part 2
• Building Factors Part 3
• Smoke Indicators
• Smoke Indicators Part 2
• Air Track Indicators
• Air Track Indicators Part 2
• Heat Indicators
• Heat Indicators Part 2
• Heat Indicators Part 3
• Flame Indicators
• Flame Indicators Part 2
• Putting it All Together

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

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

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

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

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

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

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

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

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

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

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

Scientific Research for the Development of More Effective Tactics

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

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

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

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

Ed Hartin

Captain Mike Sullivan with the Mississauga Ontario Fire Department and I are continuing our dialog with another series of questions related to the science behind fire attack and fire control methods.

The first several questions pertain to the video produced by the Kill the Flashover project illustrating the impact of anti-ventilation on heat release rate and compartment temperature.

Would you happen to know what type of building this was done in (house or concrete burn building) and what fuel was used?

KTF 2011 and 2012 were conducted  in acquired structures and KTF 2013 was conducted in a purpose built burn building. Each of the KTF burns used normal types of building contents to provide realistic fire conditions for the demonstrations/experiments. The first burn in KTF 2011 use a fuel load consisting of a chair, small amount of wood, carpet and carpet pad (as illustrated below).

You mentioned in the “Kill the Flashover” video about the key to heat reduction is the lack of oxygen for the heat release. I understand this but still wonder where all this heat goes, does it not have to dissipate somewhere?

The following video was shot during the first burn in KTF 2011. As previously discussed, the fuel load was comprised of a chair, carpet, carpet pad, and a small amount of wood. At the start of the burn the only opening to the compartment was a typical sized residential doorway. After the fire became well developed the door was closed.

You are absolutely correct! A compartment fire is an open thermodynamic system in which there is an ongoing transfer of mass (e.g., smoke out and air in) and energy between the system and its environment. This leads to another excellent question.

We often speak about fire and how the box “can’t absorb any more heat” and this is usually the point where we start to near flashover, this is what we thought was occurring, the box was simply continuing to absorb heat.

The phrase “can’t absorb any more heat” is scientifically incorrect, unless the “box” and the flames or hot gases are all of equal temperature. If any portion of the compartment or fuel packages within the compartment are lower than the temperature of flames or hot gases, the temperature of this matter will continue to increase (until thermal equilibrium is reached). The oversimplified explanation likely relates to the endothermic (heat absorbing) process of pyrolysis and transition to the exothermic (heat releasing) process of combustion.

Any object with a temperature above absolute zero transfers thermal energy to objects having a lower temperature. In a compartment fire energy released by the combustion reaction is transferred to materials within the thermodynamic system through radiation, conduction, and convection (as illustrated below).

Under fire conditions, increasing temperature in the compartment is the result conversion of chemical potential energy in the fuel to thermal energy through combustion. When the rate of energy released exceeds losses of thermal energy to the thermodynamic surroundings, temperature increases. When heat release rate is reduced by limiting the oxygen available for combustion (i.e. closing the door), continued transfer of energy to the thermodynamic surroundings results in a drop in temperature.

This is somewhat like bringing a pot of water on the stove to a boil and then removing it from the burner. Once off the burner, the water continues to transfer energy to its surroundings and will begin to cool.

 

FAQ-Fire Attack Questions will continue next week with a discussion of gas cooling, fog patterns and solid or straight streams, and limitations encountered when working in large volume spaces!.

Seven Firefighters Injured

Seven firefighters were tragically injured in Prince George’s County Maryland on Friday, February 24, 2012. The fire broke out in the basement of a single-family, one-story house located at 6404 57^th Avenue in Riverdale, MD shortly after 21:00 hours.

Note: View from Alpha-Bravo Corner street side. Photo by Billy McNeel.

On arrival, Engine 807B reported a two-story, single family dwelling with fire showing from the basement level on Side Bravo. Seven members from Companies 807 (Riverdale) and 809 (Bladensburg) entered Floor 1 of the building on Side A (East Side) and within eight seconds were enveloped by untenable, wind driven fire conditions. Preliminary reports indicate that firefighters had initiated an interior attack on the fire when a sudden rush of air, fanned by high winds, entered from the rear of the house either from a door or window being opened or broken out. (Brady, 2012). A report on Monday, February 27 indicated that some of the firefighters ran to the back of the one-story home, then entered through a basement door while other members of their company opened the front door in search of a victim (FirefighterNation, 2012).

In a statement to Washington Post reporter J. Freedom du Lac (2012), Chief Marc Bashoor indicated that strong winds were gusting out of the west at up to 40, 45 mph, blowing directly into the burning basement, which had a west-facing door. “As soon as the guys opened the front door and advanced, it blew from the basement, up the steps and right out the front door,” Bashoor said. “It was like a blowtorch coming up the steps and out the door… Without that wind, the hot air and gases would have been venting out of the rear of the house,” he said. “The current of air essentially produced a chimney right up the steps and out the front door.” (Washington Post, 2012).

Firefighters Ethan Sorrell and Kevin O’Toole from Bladensburg Volunteer Fire Department remain in critical condition at Washington Hospital Center. Riverdale Volunteer, Michael McLary also remains hospitalized for injuries. The other injured firefighters were released and sent home Saturday evening according to the latest reports.

The wind-fueled fireball that injured seven Prince George’s County firefighters when it blew through the burning house they had just entered was “a freak occurrence,” a department spokesman, Mark Brady, said Saturday (du Lac, 2012).

Chris Naum at Command Safety has an excellent post examining the fire building and weather conditions at the time of the incident. See Residential Fire Injures Seven Firefighters: Wind Driven Conditions Suspected.

Freak Occurrence?

Dealing with an accident involving a serious injury or fatality is extremely difficult, particularly when the complete circumstances and eventual outcome is unknown. What may appear to be obvious in retrospect may also have been not so clear to the individuals engaged in emergency operations. However, one might ask if the fire behavior encountered at 6404 57^th Avenue in Riverdale, MD was in fact a freak occurrence. A freak is defined as a thing or occurrence that is abnormal, markedly unusual or irregular.

The conditions encountered were markedly different than usually encountered in fires occurring in single family dwellings. However, the conditions described in this incident are not unusual when considered in light of the building configuration and wind conditions at the time of the incident. Wind, flow path, and burning regime (fuel or ventilation controlled) have a tremendous impact on fire behavior and potential for rapid fire progression resulting in untenable conditions.

Wind Driven Fires

On April 16, 2007 Technician Kyle Wilson of the Prince William Fire & Rescue lost his life in a wind driven fire occurring in a large, single family dwelling. In the introduction to the investigative report produced by Prince William Fire & Rescue examining this incident, Chief Kevin J. McGee states:

First, the impact the wind had on this event was significant. While weather conditions, and specifically wind, are often discussed in the firefighting environment of wildland fires, it does not receive the same attention and consideration in structure fires. This incident showed the dramatic and devastating effect the wind can have on the spread of fire in a building. The wind forced the fire into the building and caused the sudden change in fire conditions inside, including the “blowtorch” effect witnessed by the crews on the scene (Prince William County Fire Rescue, 2008)

In January, the National Institute of Standards and Technology (NIST) released Simulation of the Dynamics of a Wind-Driven Fire in a Ranch-Style House-Texas (Barowy & Madrzykowski, 2012) examining fire behavior in the incident that took the lives of Houston Fire Department Captain James Harlow and Firefighter Damion Hobbs on April 12, 2009 while engaged in firefighting operations in a single family dwelling. This report emphasized that potential for wind driven fire conditions can occur in all types of buildings, including single-family residential structures.

NIST research (Madrzykowski & Kerber.(2009a, 2009b) has identified that wind driven fire conditions can be created with wind speeds as low as 4.5 m/s (10 mph) and that while structural fire departments have recognized the impact of wind on fire behavior, in general, standard operating guidelines (SOG) have not changed to address the risk of wind driven fires (Barowy & Madrzykowski, 2012).

Previous posts have examined NISTs research on the issue of wind driven fires:

• Wind Driven Fires
• NIST Wind Driven Fire Experiments: Establishing a Baseline
  
• NIST Wind Driven Fire Experiments: Anti-Ventilation-Wind Control Devices
  
• NIST Wind Driven Fire Experiments: Wind Control Devices & Fire Suppression

Flow Path

On May 30, 1999, Firefighters Anthony Phillips and Louis Matthews of the District of Columbia Fire Department (DCFD) died and two others were severely injured as a result of rapid fire progression while engaged in firefighting operations at 3146 Cherry Road, NE. The fire occurred in the basement of a two-story, middle of building, townhouse apartment. Crews entered on Floor 1, Side A and were caught in the flow path of hot smoke and flames when a sliding glass door was opened at the Basement Level on Side C. Previous posts examined this incident in detail:

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

More recently, the City of San Francisco Fire Department released an investigative report examining the circumstances surrounding the deaths of Lieutenant Vincent Perez and Firefighter/Paramedic Anthony Valerio on June 2, 2011 while operating at a fire in the basement of a two story home with two levels below grade. Failure of a basement window placed the Lieutenant and Firefighter in the flow path between the basement window and their entry point on Floor 1. The investigative report produced by the San Francisco Fire Department details their findings and recommendations related to this incident.

Safety Investigation Report Line-of-Duty Deaths, 133 Berkley Way, June 2, 2011, Box 8155, Incident #11050532

Structural Firefighting Under Wind Conditions

Research and fireground experience point to the following:

• Building configuration including windows, doors, and open interior stairways can have a significant impact on development of a flow path from the fire to one or more exhaust points.
• Introduction of additional air to a ventilation controlled fire (without concurrent fire suppression) will quickly result in increased heat release rate.
• Creation of openings at and above the fire level which result in a flow path with an exhaust opening above the inlet will result in a rapid increase in heat release rate.
• Thermal conditions in the flow path above the fire and/or downstream from the fire location or will quickly become untenable.
• Even limited wind conditions can result in wind driven fire conditions.
• These factors in combination are even more likely to result in rapid fire progression and untenable conditions in the downstream flow path.

It is essential that Firefighters and Fire Officers recognize the influence of ventilation on fire behavior and potential for wind driven fire conditions and adjust their strategies and tactics accordingly. The following guidance is based on recommendations developed through the NIST wind driven fires research as well as data from National Institute for Occupational Safety and Health (NIOSH) death in the line of duty reports and incident investigative reports by the Texas State Fire Marshals Office.

Potential for wind driven conditions increases directly with wind speed. When wind speeds exceed a gentle breeze (8-12 mph) consider the potential for wind driven fire conditions and apply the following strategic and tactical considerations (CWIFR District Board, 2011):

• If potential for wind driven fire conditions is identified, this should be communicated to all companies and members working at the incident as a safety message.
• When possible, operate from the exterior and apply water from upwind directly into the involved compartments prior to interior attack. Even low flow exterior streams applied from upwind can have a significant impact on controlling the fire prior to interior operations).
• In a wind-driven fire, it is most important to use the wind to your advantage and attack the fire from the upwind side of the structure, especially if the upwind side is the burned side. Note that this may be contrary to conventional offensive tactics that place hoselines between the hazard presented by the fire and potential occupants and uninvolved property.
• Avoid pressurization of the building without first establishing adequate exhaust openings (2-3 times larger than the inlet). Remember that wind can create the same (or greater) positive pressure as a blower used in positive pressure ventilation (PPV). Pressurization without adequate exhaust can result in extreme fire behavior. Note: This is particularly important when the fire is on the leeward (downwind) side of the building and entry is made from the windward (upwind) side of the building.
• Consider controlling the flow path by using anti-ventilation such as door control and limiting the use of (horizontal and vertical) tactical ventilation prior to fire control. However, it is essential to remember that unplanned ventilation resulting from fire effects can have a significant impact on the ventilation profile and subsequent flow path(s).
• Avoid working in the exhaust portion of the flow path (between the fire and exhaust opening) or potential flow paths (between the fire and potential exhaust openings). Unplanned ventilation from fire effects can suddenly change the interior thermal conditions.
• Identify potential refuge areas, escape routes, and safety zones prior to and during interior operations. Taking refuge in a compartment with an intact and closed door may temporarily provide tenable conditions and a place of refuge until the fire can be controlled or another avenue of egress established.

References & Additional Reading

Brady, M. (2012). Seven firefighters injured battling Riverdale house fire. Retrieved February 26, 2012 from http://pgfdpio.blogspot.com/2012/02/seven-firefighters-injured-battling.html

Central Whidbey Island Fire & Rescue (CWIFR) District Board. (2011). Board minutes February 9, 2012. Coupeville, WA: Author. [Adoption of Purpose, Policy, and Scope of SOG 4.3.6 Structural Firefighting Under Wind Conditions]

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

du Lac, J. (2012). Blaze that injured 7 Prince George’s firefighters called ‘freak occurrence’. Retrieved February 26, 2012 from http://www.washingtonpost.com/local/blaze-that-injured-7-prince-georges-firefighters-called-freak-occurrence/2012/02/25/gIQAdGJMaR_story.html?hpid=z3

FirefighterNation. (2012). Critically burned in Maryland house fire, firefighters face long recovery. Retrieved February 28, 2012, from http://www.firefighternation.com/article/news-2/critically-burned-maryland-house-fire-firefighters-face-lengthy-recovery.

Madrzykowski , D. &  Barowy, A. (2012). Simulation of the dynamics of a wind-driven fire in a ranch-style house – Texas, TN 1729. Retrieved February 8, 2012 from http://www.nist.gov/customcf/get_pdf.cfm?pub_id=909779

Madrzykowski, D & Kerber, S. (2009a). Fire fighting tactics under wind driven conditions: Laboratory experiments, TN 1618. Retrieved February 8, 2012 from http://fire.nist.gov/bfrlpubs/fire09/PDF/f09002.pdf

Madrzykowski, D & Kerber, S. (2009b). Fire fighting tactics under wind driven fire conditions: 7-story building experiments, TN 1629. Retrieved February 8, 2012 from http://fire.nist.gov/bfrlpubs/fire09/PDF/f09015.pdf

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

National Institute for Occpational Safety and Health (NIOSH). (2008). Death in the line of duty…2007-12. Retrieved February 9, 2012 from http://www.cdc.gov/niosh/fire/pdfs/face200712.pdf

National Institute for Occpational Safety and Health (NIOSH). (2009). Death in the line of duty…2009-11. Retrieved February 9, 2012 from http://www.cdc.gov/niosh/fire/pdfs/face200911.pdf

National Institute for Occpational Safety and Health (NIOSH). (2009). Death in the line of duty…2007-29. Retrieved February 9, 2012 from http://www.cdc.gov/niosh/fire/reports/face200729.html

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

Prince William County Department of Fire & Rescue. (2007). Line of duty death investigative report. Retrieved February 9, 2012 from http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCgQFjAB&url=http%3A%2F%2Fwww.iaff.org%2Fhs%2FLODD_Manual%2FLODD%2520Reports%2FPrince%2520William%2520County%2C%2520VA%2520-%2520Wilson.pdf&ei=b3dKT8LyGfHSiALt5tnrDQ&usg=AFQjCNFBBTfVkWIREXw0-wbd978fWSoP8w&sig2=y6_OEeJvhFSggiKioMESaw

San Francisco Fire Department. (2012). Safety Investigation Report Line-of-Duty Deaths, 133 Berkley Way, June 2, 2011, Box 8155, Incident #11050532 Retrieved February 26, 2012 from http://statter911.com/files/2012/02/Safety-Investigation-133-Berkeley-Way-Printable.pdf

Texas State Fire Marshal’s Office. (2007). Firefighter fatality investigation, Investigation Number FY 07-02. http://www.tdi.texas.gov/reports/fire/documents/fmloddnoonday.pdf

Texas State Fire Marshal’s Office. (2009). Firefighter fatality investigation, Investigation Number FY 09- http://www.tdi.texas.gov/reports/fire/documents/fmloddhouston09.pdf

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 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