Archive for the ‘Practical Fire Dynamics’ Category

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

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

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

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

Place the Questions in Context

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

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

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

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

Fire Development in Scenario 1

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

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

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

Fire Development in Scenario 2

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

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

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

Alternate Scenarios

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

Tactical Options

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

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

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

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

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

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

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

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

Unanswered Questions

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

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

Proactive Action Steps

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

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

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

Firefighting Doctrine

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

English scientist Michael Faraday initiated The Royal Institution Christmas Lectures in 1825. These lectures which have been held at the Royal Institution in London each year since 1825, with the exception of 1939-1942 are an entertaining and informative presentation of scientific subjects. In 1848, Faraday conducted a series of lectures titles The Chemical History of a Candle (read on-line here).

Faraday conducted a series of demonstrations during this lecture series that are still used by fire behavior instructors today. As Christmas approaches, I spent some time reading The Chemical History of a Candle and thinking about how we develop Firefighters understanding of fire behavior. Poking about   on YouTube, I came across a more recent Christmas lecture at the Royal Institution in which Ian Russell examined Faraday’s lecture on The Chemical History of a Candle and the creative tension between explanation and exploration in hands on science. I suspect that we spend far too much effort on explanation and too little on exploration. Developing Firefighters knowledge of fire behavior and their curiosity about the underlying science might be better served with a larger dose of exploration… If you teach fire behavior, take an hour and watch Ian Russell’s lecture.

Thanks to Ian Bolton for reminding me of another great resource on the topic: Understanding Fire Through the Candle Experiments on the International Association of Arson Investigators CFITrainer.net website (which also has other excellent fire dynamics resources).

In 2014, I will be working on the concept of a learning laboratory which will allow development of Firefighters understanding of practical fire dynamics by shifting the balance from explanation to exploration and encourage all of you to contribute to this process! Have a Happy Holiday season, remain curious, and keep learning! Ed Hartin

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

ALIVE On-Line Interactive Training

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

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

UL Vertical Ventilation

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

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

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

Door Control Doctrine

Doctrine is a guide to action rather than a set of rigid rules. Clear and effective doctrine provides a common frame of reference, helps standardize operations, and improves readiness by establishing a common approach to tactics and tasks. Doctrine should link theory, history, experimentation, and practice to foster initiative and creative thinking.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Door Control Doctrine

As discussed in my last post, doctrine is a guide to action rather than a set of rigid rules. Clear and effective doctrine provides a common frame of reference, helps standardize operations, and improves readiness by establishing a common approach to tactics and tasks. Doctrine should link theory, history, experimentation, and practice to foster initiative and creative thinking.

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

Fireground Scenarios

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Ideally, the door will be closed after the hoseline is advanced through the doorway to limit the air supplied to the fire. How this is accomplished will depend on staffing. The door may be controlled by the fire attack crew or it may be controlled by the standby crew (two-out).

As discussed in the prior post Influence of Ventilation in Residential Structures: Tactical Implications Part 2, when the door is open, the clock is ticking! In the ventilation controlled burning regime, increased ventilation results in an increasing HRR as the fire returns to the growth stage. The timeframe for increased HRR is dependent on the proximity of the inlet to the fire, configuration of the building, and temperature in the fire area (higher temperature results in faster increase in HRR). Closing the door (even partially) slows the increase in HRR. Once the attack line begins direct attack, the door can be opened as part of planned, systematic, and coordinated tactical ventilation.

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

As with most questions, the answer here is “it depends”. There are a few missing bits of information that are important to horizontal tactical ventilation. Wind direction and the location of potential openings. To keep things simple, assume that there is no wind and that the only potential openings in the fire compartment are two windows on Side Alpha at the Alpha/Bravo Corner.

Once direct attack has commenced, horizontal tactical ventilation can be performed from Alpha (doorway) to Alpha (windows in the fire compartment). As the top of the door and tops of the windows are likely to be approximately at the same level, there a bi-directional flow path (smoke out at the top and air in at the bottom) is likely to develop. However, the bottom of the door is lower than the windows which will provide increased air movement from the door to the fire compartment.

In discussing this question (and the entire topic of door control for that matter), some firefighters will undoubtedly raise the question of positive pressure attack (PPA) or positive pressure ventilation (PPV). These tactics may provide an effective approach in this scenario, but developing comprehensive tactical ventilation doctrine requires examination of all of the options to control both smoke and air movement, so we are starting with a look at anti-ventilation and tactical ventilation using natural means.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Additional Examples

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

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

 

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

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

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

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

 

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

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

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

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

The Fire Environment-A Quick Review

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

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

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

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

Conditions on Arrival

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

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

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

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

Structural Firefighting is Simple

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

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

1. How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
2. How would opening the front door prior to having a charged line at the doorway on Side Alpha impact fire development?
3. How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the (still closed) doorway on Side Alpha?
4. What would be the impact on fire behavior if the engine company advanced the first hoseline to the windows; took the glass and applied water to the burning fuel inside the fire compartment prior to making entry through the door? How might this change if offensive fire attack was delayed (e.g., insufficient staffing for offensive operations)?
5. How would opening the front door and horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the doorway on Side Alpha?
6. Assuming that sufficient resources are on-scene to permit an offensive attack, when should the entry point be opened? Assuming that the door is unlocked, how should this task be approached?
7. Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
8. Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?

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

1. How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
2. How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?
3. Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?
4. How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the open doorway on Side Alpha?
5. Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
6. Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?

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

1. How do you think the fire will develop between arrival and initiation of offensive fire attack (assuming that adequate resources are on-scene for offensive operations) assuming no change in ventilation prior to fire attack.
2. How would the officer closing the front door prior to having a charged line at the doorway on Side Alpha (e.g., when performing the 360) impact fire development?
3. Assuming that sufficient resources are on-scene to permit an offensive attack and the door was closed during the 360, when should the entry point be opened? How should this task be approached?
4. How would horizontal ventilation of the fire compartment (Alpha/Bravo Corner) impact fire development if performed as soon as the hoseline is deployed to the open doorway on Side Alpha?
5. Once the hoseline is deployed into the building through the door on Side Alpha for offensive fire attack, should the door remain fully open or closed to the greatest extent possible? Why?
6. Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed (describe the flow path from inlet to exhaust)?
7. Assuming that this is a contents fire and horizontal ventilation will be appropriate, when and where should it be performed?

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

Door Control Doctrine

Doctrine is a guide to action rather than a set of rigid rules. Clear and effective doctrine provides a common frame of reference, helps standardize operations, and improves readiness by establishing a common approach to tactics and tasks. Doctrine should link theory, history, experimentation, and practice to foster initiative and creative thinking.

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

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

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

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

Ed Hartin, MS, EFO, MIFireE, CFO

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

Amazing!

Thursday morning saw a sea change in perspectives on fire behavior in the United States! Over 2500 people were in the big room at FDIC to hear BC George Healey (FDNY), Dan Madryzkowski (NIST), Steve Kerber (UL), and LT John Ceriello (FDNY) talk about fire research conducted on Governors Island in New York.

This excellent presentation emphasized the importance of understanding fire behavior and the influence of flow path and provided several key tactical lessons, including:

• Importance of control, coordination, and communication between crews performing fire attack and those performing tactical ventilation
• The effectiveness of anti-ventilation such as closing the door (even partially) on slowing fire development
• Effectiveness of water quickly applied into the fire compartment (from any location, but in particular from the exterior) in slowing fire progression
• The demonstrated fact that flow path influences fire spread and not application of water. You can’t push fire with water applied into the fire compartment.
• Importance of cooling the hot smoke (fuel) in the upper layer

Several years ago, who would have thought that a presentation on fire dynamics and research would have drawn this number of people to a presentation at FDIC. Kudos to FDNY, NIST, and UL for their ongoing work in developing an improved understanding of fire dynamics and firefighter safety.

FAQ (Fire Attack Questions) Continued

I had the opportunity to visit with Captain Mike Sullivan with the Mississauga Ontario Fire Department while at FDIC and we are continuing our dialog with another series of questions related to the characteristics of water fog and its use of a fog pattern for self-protection when faced with rapid fire progression in a structure fire.

The next three questions deal with using a fog stream for protection. In the IFSTA Essentials of Firefighting 5th edition it states that “wide fog patterns can also protect firefighters from radiant heat”, however in the IFSTA Essentials of Firefighting 3rd edition it states “In the past, water curtain broken stream nozzles were commonly used for exposure protection. However, research has indicated that these nozzles are only effective if the water is sprayed directly against the exposure being protected”. This tells me that fog patterns cannot protect from radiant heat.

Another question for which the answer is “it depends”. Both statements are correct (in context). Water droplets reduce radiant heat by absorbing energy and scattering the radiant energy. The effectiveness of these mechanisms depends on droplet size, wavelength of the radiation, geometric dimensions of the water spray, and density of the fog pattern. To put this in context, firefighters use a water spray for protection when approaching a flammable gas fire. In this context, the high density of the spray in proximity of the nozzle is quite effective. In contrast, application of a water spray between a fire and exposure is likely to be much less dense, and thus less effective in protecting the exposure than simply applying water to the exposure to keep its temperature <100^o C.

In the past there was a belief (which some still believe) that if you find yourself in a bad situation in a house fire you can simply switch to a wide fog and it develops an “umbrella of protection from the heat and fire”. I believe this to be false. What I do think has happened in the past is that firefighters have found themselves in a room with extreme rollover or even had pockets of unburned gas igniting around them. When they used this technique they didn’t protect themselves with an umbrella of fog protection but they cooled the smoke layer and made the situation better.

This also is an interesting question, there are incidents where firefighters have opened the nozzle when caught in rapid fire progression and have survived (not necessarily uninjured), likely due to the cooling effects of the water spray. However, I would agree that this does not provide “an umbrella of protection” like a force field that provides complete protection. The benefit is likely by cooling of the hot gases above and potentially controlling some of the flaming combustion in the immediate area. However, as continuous application will likely not only cool the hot upper layer, but also generate a tremendous amount of steam on contact with compartment linings, the environment will not be tenable in the long term. However, this environment is likely more survivable than post-flashover, fully developed fire conditions.

Much the same as in driving or riding in fire apparatus, the best way to avoid death and injury in a crash is to not crash in the first place. If firefighters recognize worsening fire conditions, they should cool the upper layer to mitigate the hazards presented, if this is ineffective, withdrawing while continuing to cool the upper layer is an essential response.

My last comment on this; and this is where I am not really sure. If you are in a situation where you need to back out quickly, would it work to use a fog stream to push the heat away as you are reversing out of the structure? You would only do this for a short time while you retreat.

If you cannot put water on the fire to achieve control (shielded fire) or the heat release rate (HRR) of the fire exceeds the cooling capacity of your stream you are in a losing position. When faced with rapidly deteriorating thermal conditions, it is essential to cool the upper layer. It is important to note that cooling, not simply “pushing the heat away” is what needs to happen in this situation. This action reduces heat flux from both convective and radiant transfer. Adequate water must be applied to accomplish this task, as temperature increases so too does the water required. Long pulses provide a starting point, but the pulses need to be long enough to deliver the required water. If needed, flow could be continuous or near continuous while the crew withdraws. In much the same manner a crew working with a solid stream nozzle would operate the nozzle in a continuous or near continuous manner and rotate the stream to provide some cooling to the upper layer while withdrawing.

There are those who believe that you can use a fog stream to protect yourself in a house fire by pushing the heat away from you as you advance on the fire. I believe you can push heat away from you and it happens in 2 distinct ways,  the wide fog with the entrained air is literally pushing the heat away from you and you have now created high pressure in an area that was low pressure (typically you are near an open door) so you have effectively changed the flow path. Having said this, I feel the benefits are short lived. With this fog pattern you will also be creating a lot of steam which will continue expanding until it’s temperature reaches equilibrium with the rest of the fire compartment (expansion could be as high as 4000 times). With all this pushing and expansion you are now creating high pressure in an area down stream from you that had previously been a low pressure area. As we know, everything is trying to move from high to low pressure, now the low pressure area is directly behind the nozzle. Now you are in a situation where not only is the heat coming back behind the nozzle but there is an enormous amount of steam being created and heading your way. The confusion here is most likely with the techniques we use when practicing for gas fires, we do this outside where there is an endless amount of space to push the heat away (I read this part in a good article in Fire Engineering).

The impact of continuous application of a fog stream (or any stream for that matter) as you advance is dependent on a number of factors, principal among which are the flow path and where steam is produced (in the hot gas layer versus on contact with surfaces). Continuous application is likely to result in vaporization of a significant amount of water on contact with surfaces; this will result in addition of steam to the hot upper layer without corresponding contraction of the hot gases that results from vaporization of water while it is in the gases. Without ventilation in front of the fog stream (or any stream for that matter), this can result in a reduction in tenability. However, when ventilation in front of the stream is provided, a combination attack (using a fog pattern, straight, or solid stream) can be quite effective for fully developed fire conditions.

I was hoping you could elaborate on the term “painting”. It is defined as a “gentle application of water to cool without excess steam production”. The hard part as a firefighter is the word “gentle” as this word doesn’t register in firefighter lingo. I can see this during overhaul but was hoping you could elaborate.

The way that I typically explain the concept of “gentle” is using a fire in a small trash can or other incipient fire inside of a building. If you use a hoseline to extinguish this fire, it is unlikely that you will need a high flow rate or application of the stream with the bail of the nozzle fully open. It would be appropriate to simply open the nozzle slightly on a straight stream and apply a small amount of water to the burning fuel.

Surface cooling can be done using a vigorous application from a distance when faced with a well involved compartment. In this situation, the reach of the stream is appropriately used to extinguish the fire and cool hot surfaces from a distance to minimize thermal insult to firefighters while quickly achieving control. However when faced with hot and pyrolizing compartment linings or contents, it may be useful or necessary to cool these surfaces from closer proximity. In this case applying water with force will result in much of the water bouncing off the surfaces and ending up on the floor. Painting involves using a straight stream or narrow fog pattern with the nozzle gated back to provide a gentle application resulting in a thin layer of water on the hot surface. As you note, this is most commonly used during overhaul, but could be used anytime that there is a need to cool hot, pyrolizing, but unignited surfaces.

Next week Mike and I will conclude this series of FAQ with a look at pyrolysis and flow path.

 

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. Mike’s next several question deal with gas and surface cooling.

I know the best way to extinguish a fire is to put water on it but my questions below deal with a situation of large, open concept homes where you can see the entire main floor except the kitchen cooking area, in many cases this area is not separate from the open floor plan but around the corner so we can’t hit the fire until we get around that corner. My questions are all geared around how to cool the environment as you make your way to the fire (if you need to go to the very back of the house to get to the fire, fire can’t be seen).

When you answered the question about the effects of flowing a straight/solid stream across the ceiling it sounds as if this is really only surface cooling and not effectively gas cooling. If this is true then I was wondering what the value of doing this is, what are the main benefits of cooling the ceiling, walls and floor (and any furniture etc. the water lands on)? Also, what do you recommend to those departments that only use solid bore nozzles?

Use of a solid (or straight) stream off the ceiling has some effect on cooling the gases, but this is limited as the droplets produced are quite large and do not readily vaporize in the hot upper layer (great for direct attack, but not so much for gas cooling). The value of doing this is that any energy taken out of the hot upper layer (buy cooling the gases or by cooling surfaces and subsequent transfer of energy from hot gases to the cooler surfaces) will have some positive effect. In addition, hot combustible surfaces, depending on temperature are likely pyrolizing and adding hot, gas phase fuel to the upper layer. Cooling reduces pyrolysis and the fuel content of the smoke overhead.

The following video of the “Nozzle Forward”, Aaron Fields, Seattle Fire Department demonstrates some excellent hose handling techniques and also provides an illustration of how a solid stream nozzle can be used to cool hot gases by breaking up the stream on contact with compartment linings. Have a look at the video between 2:00 and 2:30 where the nozzle is being rotated as in a combination attack while advancing down a hallway. Note that the stream breaks up on contact with the ceiling and walls, providing a distribution of large droplets in the overhead area.

This technique can be quite effective when faced with a large volume of fire and ventilation is provided in front of the fire attack. However, if the hallway is not involved in fire, but there is a hot layer of smoke overhead, this approach is less effective as large droplets are less efficient in cooling the hot gases and much of the water will end up on the floor, not having done appreciable work.

While this will likely generate some hate and discontent, I would recommend that departments using only solid stream nozzles reconsider their choice. This type of nozzle has a number of great characteristics, but also has a number of significant limitations, principal among which is limited ability to cool the hot upper layer when dealing with shielded fires. That said, the firefighter riding backwards or company officer in the right front seat may have limited impact on this decision (at least in the short term). If all you have to work with is a solid stream nozzle, directing the stream off the ceiling to break up the pattern and provide limited gas cooling when dealing with extremely hot gases overhead are likely a reasonable option.

I understand how penciling a fog stream in the hot gas layer is the best way to cool the gases. My concern is this, where I work there are many new homes with open concept, large rooms and little compartmentation. I like the idea of cooling the gases above my head but I still have a large room full of gases that could still flash. Sure I’m cooling the gases around me but if the gases at the other end of the open space flash, I am still in the same room and in trouble. I would prefer to cool that area before I get there. What are your recommendations for this situation?

As a point of clarification, we use the term “penciling” in reference to an intermittent straight stream application. Gas cooling is most effectively accomplished with pulsed or intermittent application of water fog. We refer to this technique as “pulses” (to differentiate this from penciling with a straight or solid stream)

We also have quite a few large residential occupancies with open floor plans. The issue of large area or volume compartments also applies in commercial and industrial building as well. Gas cooling simply provides a buffer zone around the hose team, but other than in a small compartment does not change conditions in the upper layer throughout the space. Gas cooling must be a continuous process while progressing towards a shielded fire. The upper limit of area (or more appropriately volume) is an unanswered question. My friend Paul Grimwood, Principal Fire Safety Engineer with the Kent Fire and Rescue Service in the UK holds that the upper limit with a relatively normal ceiling height is approximately 70 m² (753 ft²). Paul’s perspective is anecdotal and not based on specific scientific research. However, this is not unreasonable, given the reach of a narrow fog pattern and vaporization of water as it passes through the upper layer. Given the higher flow rates used by the North American fire service, it may be possible to control a somewhat larger area than Paul suggests, but this remains to be determined.

As to an answer to this problem, pulsed application does not always mean short pulses, multiple long pulses with a narrow pattern or a sweeping long pulse may be used to cover a larger area. In addition, large area compartments or open floor plan spaces may require multiple lines to adequately control the environment. The purpose of the backup line is to protect the means of egress for the attack line and this is of paramount importance in an open plan building.

The following two videos demonstrate the difference between short and long pulses. At 115 lpm (30 gpm) the flow rates in these two videos are low by North American standards, but are fairly typical for gas cooling applications in many parts of the world. Short pulses can be used effectively up to approximately 570 lpm (150 gpm) with minimal water hammer, for higher flow rates, long pulses are more appropriate.

When we do these quick bursts of fog to cool the gases we are not using much water compared to the feeling that the best way to handle this is to flow a large amount of water and basically soak the entire area down before you advance through it. I was hoping you could comment on this.

As noted in the answer to your previous question, pulses are sometimes, but not always quick. In a typical legacy residence (small compartments) short pulses are generally adequate to cool hot gases overhead. When accessing a shielded fire, and cooling the hot gases overhead it is not generally necessary to cool hot surfaces and fuel packages such as furniture (it may be a different story in the fire compartment). Water remaining on the floor or soaked into contents did not do significant work and simply added to fire control damage. We should not hesitate to use an adequate amount of water for fear of water damage, but tactical operations should focus on protecting property once (or while) we are acting to ensure the safety of occupants and firefighters.

We often enter house fires where the house is full of smoke but the smoke is not necessarily very hot. In these cases we would not normally cool the gases. From what we understand now, smoke is fuel and with open concept homes this smoke could ignite close to the fire therefore igniting the smoke nearer to us. What I was wondering is what are you teaching in regards to cooling the smoke, do you do it only when you feel a lot of heat or start cooling regardless?

As the temperature of the upper layer drops, the effectiveness of application of pulsed water fog diminishes. That said, if the upper layer is hot enough to vaporize some of the water (i.e. above 100^o C), application of water will further cool the gases and provide some thermal ballast (the water will have to be heated along with the gases for ignition to occur).

When presented with cold (< 100^o C) smoke, firefighters still face a hazard as gas phase fuel can still be ignited resulting in a flash fire (if relatively unconfined) or smoke explosion. The only real solution to this hazard is to create a safe zone by removing the smoke through tactical ventilation.

Mike and I will continue this dialog next week with a discussion of the protective capabilities of fog streams.