The importance of the initial Incident Commander conducting 360^o reconnaissance (or quickly obtaining information about conditions on sides of the building that are not visible) has been repeatedly emphasized in National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty reports. This is important to assess both building and fire conditions. However, the building was there prior to the alarm of fire. Situational awareness (SA) does not only apply on the fireground, it must begin well before response. In structural firefighting, the built environment (including the building, its contents, and surroundings) are the ground we fight on and in. Situational assessment and size-up must be ongoing.

View from the Street

The Knead & Feed (see photo below), is an excellent restaurant in Coupeville, WA that serves breakfast and lunch. At first glance this building appears to be an older, one-story, wood frame, commercial with the Delta Exposure being a two-story building of similar construction. Given the age of the buildings, it would be reasonable to assume that they are of balloon frame construction. Looking beyond the building you can see Penn Cove, which provides an excellent view from the back of the restaurant.

Reconnaissance on Side C

However, the view in this photo begs the question, what’s on Side C? Access to Side C is via an exterior stairway on Side Bravo. Descending this stairway provides access to another kitchen and dining area in the Basement which is not accessible from the interior of the restaurant on Floor 1. Continuing down the stairway, provides access to a bakery at the Basement 2 level. The stairway then continues down to the beach, providing access to Side C…provided that it is low tide.

Obviously you get a considerably different picture from Side C! However, this is only the beginning of the story.

The Rest of the Story

It may appear that the small, one-story section of building between the Kneed and Feed restaurant and Exposure Delta is part of the exposure due to the color of the building on Side Alpha and the roof line on Side Charlie. However, this assumption would be incorrect as this is the main kitchen for the Kneed and Feed Restaurant.

There is no interior access between Floor 1 and the Basement (in either the Kneed and Feed or Exposure Delta). The Basement and Basement 2 levels of the Kneed and Feed are accessed from the exterior on Side Bravo. The Basement of Exposure Delta (apartment unit) is accessed from the exterior on Side Delta. The second floor of Exposure Delta is accessed from the interior.

Continuing down to the Basement level, the section of the building below the main kitchen contains an unprotected stairwell that is open to the underside of the Basement of Exposure Delta and the void space under the wood sidewalk that runs in front of the restaurant and Exposure Delta. The Basement and Basement 2 levels are interconnected this stairway (non-fire rated doors provide access between the stairway and the Basement and Basement 2. This stairway is framed in at the Basement level, but simply enclosed by wood slats at the Basement 2 level.

Strategic and Tactical Implications

This building presents considerable challenges due to its construction, configuration, attached exposure on Side Delta, and limited access. The following questions provide a starting point for discussion of strategic and tactical implications for this building and its most significant exposure:

1. How might the construction and configuration of this building and exposure impact on the B-SAHF (building, smoke, air track, heat, and flame) indicators presented during a fire? How might this vary based on location (Floor 1, Basement, Basement 2)?
2. How might the open stairwell between the Kneed and Feed and Exposure Delta impact on fire development and spread if the fire originated at one of the basement levels, or within the stairwell itself? How might communication between the stairwell and the wooden sidewalk on Side A impact firefighting operations (note that the sidewalk and void space below extends beyond the access points for Sides Bravo and Delta).
3. How would the open framing under the Basement of Exposure Delta impact on potential for fire spread from the Kneed and Feed to Exposure Delta (particularly if a fire originated on the Basement or Basement 2 level)
4. How would tidal conditions impact on access to Side Charlie for firefighting operations or placement of ladders for rescue or secondary egress from the Kneed and Feed or Exposure Delta (particularly the apartment unit in the Basement of Exposure Delta).
5. What strategies and tactics would provide the safest and most effective approach to confining and extinguishing a fire in each level of this building?
6. Given the significant threat to Exposure Delta should a fire occur in the Kneed and Feed, what strategies and tactics would be most effective in evacuating the occupants of this building and preventing extension?
7. Given the multiple occupancies (restaurant, retail, and residential), how would time of day impact on firefighting operations in this building and exposure?

While this building is in my response area, you have challenging buildings in yours as well. Time to find out what’s in your patch! When on a medical response, automatic alarm, performing fire inspections, or just eating breakfast, take the time to look around and ask yourself what if…. Building Factors are the first element in B-SAHF and they are present prior to the fire. Pre-incident planning either on a formal basis (best choice) or informally as an individual or company is essential to safe and effective incident operations.

Thanks!

I would like to extend a special thank you to the owners and staff of the Kneed and Feed for providing the opportunity to learn about their building. While challenging from a firefighting perspective, this is one of the best places to have breakfast or lunch (but particularly breakfast) in our District! If you are on Whidbey Island, stop in for a meal, but bring your appetite.

There has been an increasing awareness that smoke is fuel and that hot smoke overhead results in thermal insult (due to radiant heat transfer) and potential for ignition. However, the hazard presented by smoke as gas phase fuel can extend a considerable distance from the current area of fire involvement.

Reading the Fire

Print a copy of the B-SAHF Worksheet. Use the worksheet to document observed fire behavior indicators as you watch the first six minutes of the following video of an apartment fire that occurred on May 10, 2013 at the corner of Park Creek Lane and Hill Park Court in Churchville, NY. In particular, focus on fire behavior indicators that may point to changes in conditions. Don’t focus too much on the flame indicators presenting from the area involved, but pay particular attention to Building, Smoke, and Air Track indicators.

The following satellite photo and view of the Alpha/Delta Corner prior to the fire are provided to help orient you to the incident location. You can also go to Google Maps Street View and do a walk around on Sides Alpha (Hill Park Court) and Delta (Park Creek Lane) to view all four sides of the building.

The following time sequence from the video of this incident illustrates the conditions immediately prior to and during the explosion. The extremely rapid increase in heat release rate during the explosion was not sustained (a transient event) as evidenced by conditions illustrated at 06:25.

Building Factors

This building is of Type V construction with a wood truss roof system. In a large apartment building such as this, the trussloft is typically subdivided with draft stops comprised of gypsum board applied to one (or both) sides of a truss to stop rapid spread of fire within the trussloft. Draft stops should be thought of as speed bumps rather than a barrier (such as a firewall that extends through the roofline). While draft stops slow fire and smoke spread, they do not stop it completely and it is common for smoke to spread beyond the fire area despite the presence of draft stops.

The small dimension framing materials used in truss construction have a high surface to mass ratio, increasing the speed with which they can be heated and increasing pyrolysis products in the smoke when heated under ventilation limited conditions.

Note: The possible location of the draft stops is speculative as specific information regarding the construction of this building was not available at the time of this post. However, draft stops may be provided between the trussloft between units or based on the size of the trussloft without regard to the location of walls between units. Preplan inspections provide an opportunity to examine building factors that may be critical during an incident!

Smoke and Air Track Indicators

An important air track indicator in this incident was the strong wind blowing from the Alpha/Bravo Corner towards the Charlie/Delta Corner. The wind may have had some influence on ventilation in the trussloft above Exposures Bravo and Bravo 2, and definitively influenced other Smoke and Air Track indicators.

From the start of the video light colored smoke is visible at the peak of the roof above Exposure Bravo and Bravo 2, indicating that smoke had infiltrated areas of the trussloft that had not yet become involved in fire. Smoke that is light in color may be comprised of pyrolysis products and air and may be to lean or too rich to burn or it may be explosive See the video Smoke on the Firegear website for a good discussion of the characteristics of smoke (note that this video is currently undergoing validation).

The volume and color (smoke indicators), velocity and direction (air track indicators) above exposure Bravo 2 vary considerably from the start of the video until shortly before the explosion that occurred at 06:12 in the video. At 02:52 a firefighter entered Exposure Bravo 2 and a short time later at 03:47 a hoseline (dry) was stretched into this exposure and charged. It is unknown from watching the video if the firefighters on this line advanced to Floor 2 or if they took any action to change the ventilation profile (other than opening the door on Floor 1, Side Alpha). The exited after the explosion, but without haste, so it is likely that they were not on Floor 2 at the time of the explosion.

Smoke Explosion

Smoke explosion is described in a number of fire dynamics texts including Enclosure Fire Dynamics (Karlsson and Quintiere) and An Introduction to Fire Dynamics (Drysdale). However, Enclosure Fires by Swedish Fire Protection Engineer Lars-Göran Bengtsson (2001) provides the most detailed explanation of this phenomenon. Paraphrasing this explanation:

A smoke or fire gas explosion occurs when unburned pyrolysis products and flammable products of combustion accumulate and mix with air, forming a flammable mixture and introduction of a source of ignition results in a violent explosion of the pre-mixed fuel gases and air. This phenomenon generally occurs remote from the fire (as in an attached exposure) or after fire control.

In some cases, the fire serves as a source of ignition as it extends into the void or compartment containing the flammable mixture of smoke (fuel) and air.

Conditions Required for a Smoke Explosion

The risk of a smoke explosion is greatest in compartments or void spaces adjacent to, but not yet involved in fire. Infiltration of smoke through void spaces or other conduits can result in a well-mixed volume of smoke (fuel) and air. Smoke explosion creates a significant overpressure as the fuel and air are premixed and ignition results in a very large energy release. Several factors influence the violence of this type of explosion:

• The degree of confinement (more confinement results in increased overpressure)
• Mass of premixed fuel and air within the flammable range (more premixed fuel results in a larger energy release)
• How close the mixture is to a stoichiometric concentration (the closer to an ideal mixture the faster the deflagration)

Potential Smoke Explosion Indicators

It is very difficult to predict a smoke explosion. However, the following indicators point to the potential for this phenomenon to occur:

• Ventilation controlled fire (inefficient combustion producing substantial amounts of unburned pyrolysis products and flammable products of incomplete combustion)
• Relatively cool (generally less than 600^o C or 1112^o F) smoke
• Presence of void spaces, particularly if they are interconnected
• Combustible structural elements
• Infiltration of significant amounts of smoke into uninvolved compartments in the fire building or into exposures

Preventing a Smoke Explosion

As it is difficult to predict a smoke explosion, there are challenges to preventing their occurrence as well. However, general strategies would include 1) preventing smoke from accumulating in uninvolved spaces or 2) removing smoke that has accumulated remote from the fire (e.g., in attached exposures), or 3) a combination of the first two approaches.

Tactics to implement these strategies may include:

• Pressurizing uninvolved spaces with a blower to prevent infiltration of smoke. This involves use of a blower for anti-ventilation by applying pressure without creating an exhaust, similar to what is done to pressurize a highrise stairwell. It is essential to check for extension prior to implementing this tactic!.
• Horizontal ventilation of attached exposures to remove smoke, checking for extension, and then pressurization with a blower to prevent continued infiltration of smoke. If fire extension is found, pressurization without an exhaust opening must not be implemented!

Additional Resources

The following previous posts on the CFBT-US Blog may also be of interest in exploring the smoke explosion phenomena.

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

References

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

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

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

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

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

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

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

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

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

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

Scientific Research for the Development of More Effective Tactics

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

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

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

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

Ed Hartin

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

This week’s questions focus on training firefighters to recognize, prevent, and if necessary react appropriately to flashover conditions. Casey Lindsay of the Garland, Texas Fire Department sent an e-mail to a number of fire behavior instructors regarding how they conduct “flashover training”

One of the challenges we face in discussing fire behavior training, particularly live fire training is the result of variations in terminology. Differences exist in the way that live fire training props are described and in fire control techniques. For this discussion, CFBT-US defines the type of prop pictured below as a “split level demo cell”. This terminology is derived from the original purpose of this design as conceived by the Swedish Fire Service in the 1980s. The split level cell is intended for initial fire behavior training focused on observation of fire development. As used in the United States (and some other parts of the world) it is described as a “flashover simulator” or “flashover chamber”. This provides a disconnect in context as this prop is not intended and does not subject the participants in training to flashover conditions, but simply provides an opportunity to observe fire development through the growth stage and recognize some potential cues of impending flashover.

Note: The prop illustrated above is a Split level cell at the Palm Beach County Fire Training Center.

Container based props can be configured in a variety of ways for both demonstration and fire attack training. Most commonly single compartment cells are single level or split level design. Multiple compartment cells are arranged in a variety of ways with containers placed in an “L”, “H” or other configuration.

Do you currently teach firefighters that “Penciling control techniques can be used to give firefighters additional time to escape a flashover”?

We define penciling as an intermittent application using a straight stream as compared to pulsing which uses a fog pattern or painting which is a gentle application of water to hot surfaces. We do not teach penciling, pulsing, or painting as a technique to give firefighters additional time to escape flashover. We use gas cooling (short or long pulses) and coordination of fire attack and ventilation to control the environment and prevent or reduce the potential for firefighters to encounter flashover. However, long pulses (or continuous application) while withdrawing is taught as a method of self-protection if fire conditions exceed the capability of the crew engaged in fire attack.

In response to Casey’s questions, Jim Hester, with the United States Air Force (USAF) presents an alternative perspective:

No! We do not teach penciling or 3D Fog attack anymore. We did temporarily after receiving our training as instructors in the flashover trainer. We gave the technique an honest look and conducted research using Paul Grimwood’s theories. We decided there are too many variables. For example; what works in a room and contents [fire] will not work in heavy fire conditions inside a commercial. The last thing we want is someone penciling any fire, inside any structure, that requires constant water application until the fire is darkened down. That’s what we teach.  Open the nozzle for as long as it takes to get knock down and then shut the nozzle down. [It is as] simple as that. If you take that approach, even in the flashover trainer you will alleviate confusion or misapplication of your fire stream.

While I have a considerably different perspective, Jim raises several good points. I agree that there are many variables related to fire conditions and room geometry. If firefighters are trained in lock step manner that short pulses are used to control the temperature overhead, there will definitely be a challenge in transitioning from the container to a residential fire and even more so when confronted with a commercial fire. However, if firefighters are introduced to the container as a laboratory where small fires are used to develop understanding of nozzle technique, rather than a reflection of real world conditions, this presents less of an issue.

As Jim describes, fire conditions requiring constant application in a combination attack with coordinated tactical ventilation, may not be controlled by short pulses. However, when cooling hot smoke on approach to a shielded fire, constant application of water will likely result in over application and less tenable conditions (too much water may not be as bad as too little, but it presents its own problems).

Most firefighters, even those that advocate continuous application, recognize that a small fire in a trash can or smoldering fire in a upholstered chair or bed does not require a high flow rate and can easily be controlled and extinguished with a small amount of water. On the other hand, a fully developed fire in a large commercial compartment cannot be controlled by a low flow handline. To some extent this defines the continuum of offensive fire attack, small fires easily controlled by direct application of a small amount of water and large fires that are difficult to control without high flow handlines (or multiple smaller handlines). There is not a single answer to what is the best application for offensive fire attack. Shielded fires require control of the environment (e.g., cooling of the hot upper layer) to permit approach and application of direct or combination attack. Fires that are not shielded present a simpler challenge as water can be brought to bear on the seat of the fire with less difficulty.

Nozzle operators must be trained to read conditions and select nozzle technique (pulsed application to cool hot gases versus penciling or painting to cool hot surfaces) and fire control methods (gas cooling, direct attack, indirect attack, or combination attack) based on an assessment of both the building and fire conditions.

What flashover warning signs do you cover during the classroom portion of flashover training?

We frame this discussion in terms of the B-SAHF (Building, Smoke, Air Track, Heat, and Flame) indicators used in reading the fire (generally, not just in relation to flashover).

Building: Flashover can occur in all types of buildings. Consider compartmentation, fuel type, and configuration, ventilation profile, and thermal properties of the structure. Anticipate potential for increased ventilation (without coordinated fire control) to result in flashover when the fire is burning in a ventilation controlled regime (most fires beyond the incipient stage are ventilation controlled). Note that these indicators are not all read during the incident, but are considered as part of knowing the buildings in your response area and assessing the building as part of size-up.

Smoke: Increasing volume, darkening color and thickness (optical density), lowing of the level of the hot gas layer.

Air Track: Strong bi-directional (in at the bottom and out at the top of an opening), turbulent smoke discharge at openings, pulsing air track (may be an indicator of ventilation induced flashover or backdraft), and any air track that shows air movement with increasing velocity and turbulence.

Heat: Pronounced heat signature from the exterior (thermal imager), darkened windows, hot surfaces, hot interior temperatures, observation of pyrolysis, and feeling a rapid increase in temperature while working inside (note that this may not provide sufficient warning in and of itself as it is a late indicator).

Flame: Ignition of gases escaping from the fire compartment, flames at the ceiling level of the compartment, isolated flames in the upper layer (strong indicator of a ventilation controlled fire) and rollover (a late indicator).

How do you incorporate the thermal imaging camera into your flashover class?

We do not teach a “flashover” class. We incorporate learning about flashover (a single fire behavior phenomena) in the context of comprehensive training in practical fire dynamics, fire control, and ventilation (inclusive of tactical ventilation and tactical anti-ventilation). Thermal imagers (TI) are used in a variety of ways beginning with observation of small scale models (live fire), observation of fire development (with and without the TI) and observation of the effects of fire control and ventilation.

Do you allow students to operate the nozzle in the flashover chamber?

We use a sequence of evolutions and in the first, the students are simply observers watching fire development and to a lesser extent the effects of water application by the instructor. In this evolution, the instructor limits nozzle use and predominantly sets conditions by controlling ventilation. If necessary the instructor will cool the upper layer to prevent flames from extending over the heads of the participants or to reduce the burning rate of the fuel to extend the evolution. Students practice nozzle technique (short and long pulses, painting, and penciling) outside in a non-fire environment prior to application in a live fire context. After the initial demonstration burn, students develop proficiency by practicing their nozzle technique in a live fire context.

When working in a single level cell rather than a split level cell (commonly, but inaccurately referred to as a “flashover chamber” or “flashover simulator”) we expand on development of students proficiency in nozzle technique by having them practice cooling the upper layer while advancing and importantly, while retreating. In addition, students practice door entry procedures that integrate a tactical size-up, door control, and cooling hot gases at the entry point.

Do you maintain two-in/two-out during flashover chamber classes?

We comply with the provisions of NFPA 1403 and provide for two-in/two-out by staffing a Rapid Intervention Crew/Company during all live fire training.

What is your fuel of choice for the 4×8 sheets (OSB, Particleboard or Masonite)?

We have used a variety of fuel types, but commonly use particle board. OSB tends to burn quickly, but can be used if this characteristic is recognized. We have also used a low density fiberboard product (with less glue) which performs reasonably well. The key with fuel is understanding its characteristics and using the minimum quantity of fuel that will provide sufficient context for the training to be conducted. I recommend that instructors conduct test burns (without students) when evaluating fuel packages that will be used in a specific burn building or purpose built prop (such as a demo or attack cell).

Do you have benches or seating in the flashover chamber?

No, firefighters are expected to be in the same position that they would on the fireground, kneeling or in a tripod position. When we work in a demo cell (“flashover chamber”) with benches, we keep the students on the floor.

Do you teach any flashover survival techniques, other than retreat/evacuate?

We focus first on staying out of trouble by controlling the environment. Second, we teach firefighters the skill of retreating while operating the hoseline (generally long pulses to control flames overhead). There are not really any options other than control the fire of leave the environment (quickly)! This is similar to James Hester’s answer of continuous flow, with a sweeping motion (long pulses can be applied in a sweeping manner, particularly in a large compartment). It is important to understand that a short pulse is extremely short (as fast as you can open the nozzle) and a long pulse is anything else (from several seconds to near continuous application, depending on conditions).

Refer to the series of CFBT Blog on Battle Drills for additional discussion developing proficiency in reaction to deteriorating conditions.

Additional Thoughts

Our perspective is that discussion of flashover should be framed in the context of comprehensive fire behavior training, rather than as a “special” topic. Practical fire dynamics must be integrated into all types of structural firefighting training, in particular: Hose Handling, Fire Control, and Tactical Ventilation (but the list goes on). When working with charged hoselines, take the time to practice good nozzle technique as well as moving forward and backward (do not simply stand up and flow water when performing hose evolutions). In fire control training (live fire or not), practice door control, tactical size-up, and door entry procedures. When training on the task activity of tactical ventilation (e.g., taking glass or cutting roof openings), make the decision process explicit and consider the critical elements of coordination and anticipated outcome of you actions.

FDIC

Plan on attending Wind Driven Fires in Private Dwellings at Fire Department Instructors Conference, Indianapolis, IN on Wednesday April 24, 2013 in Wabash 3. Representing Central Whidbey Island Fire & Rescue, Chief Ed Hartin will examine the application of NIST research on wind driven fires to fires in private dwellings. This workshop is a must if the wind blows where you fight fires!

This post continues the discussion with Captain Mike Sullivan with the Mississauga Ontario Fire Department regarding fire attack methods. Captain Sullivan refined his definitions and explanation of direct, indirect, and combination fire attack, stating:

Direct Attack: Water droplets put out the fire (droplets land directly on the burning fuel and cool this fuel to put out the fire).

This is essentially correct, water applied directly to the burning fuel absorb energy as the water is heated and considerably more when vaporized into steam, this reduces the temperature of the fuel and extinguishes the fire. In the end, this is generally necessary regardless of what method of fire attack or fire control you begin with.

Indirect Attack: Steam puts out the fire (water droplets turn to steam and this expanded steam eventually makes its way to the area where the burning fuel is and continues to absorb heat from this burning fuel until the fire goes out. All this steam also reduces oxygen concentration which results in a reduced heat release rate).

This is close, but the process of steam production absorbs a tremendous amount of energy. So it might be more accurate to state that production of steam and that heating of the steam as the hot gases and steam reach a thermal equilibrium cool the fire environment. In addition, steam production reduces oxygen concentration that reduces heat release rate. These processes in combination control and in fewer cases may achieve extinguishment. Indirect attack almost always must be followed up with aggressive overhaul and direct attack to achieve extinguishment. This does not diminish the utility of indirect attack for control of fully developed fires or decay stage fires resulting from limited ventilation (where high temperatures exist).

Combination Attack: Water droplets put out the fire (the droplets act the same way here as in the direct attack).

As with direct attack this is essentially correct. The application of water to burning fuel results in extinguishment through cooling. With the combination attack, some of the water is vaporized in the upper layer, assisting with control of the fire environment as well as the process of extinguishment. However, this is often at the expense of disrupting thermal layering (less of an issue when well-coordinated tactical ventilation is provided in front of fire attack.

This discussion gave rise to several other questions from Captain Sullivan:

In the combination attack, although the hose stream is directed at the ceiling (indirect part of the combination attack) and creates steam it is not as effective at cooling the fuel as the direct part of the combination attack is (wow is that wordy), Therefore,the main purpose of the indirect part of the combination attack is to cool the overhead gases so the entire environment is cooler when firefighters enter and really doesn’t have much to do with extinguishing the fire. So would you say in this case the “indirect” part of the combination attack really isn’t a key contributor to extinguishment?

This would depend (another way of saying “it depends”). The indirect component of the combination attack is important in controlling flaming combustion in the upper layer (such as rollover). While control of the burning gases overhead alone will not achieve extinguishment (same as with gas cooling), it is an important component of the extinguishment process as the heat flux from burning gases overhead is significant both as a threat to firefighters and also as a mechanism for heating unignited fuel and continuing the combustion process of fuel that is already burning. However, in the end, it is the direct element of the combination attack that achieves extinguishment. As with indirect attack, combination attack is followed up with direct attack to achieve complete extinguishment.

If what I have said above is true then, although both the indirect and combination attack produce large amounts of steam, is the purpose of the steam production actually different (put out the fire vs. cool the overhead gases)?

The purpose of steam production in both cases is to take advantage of the high latent heat of vaporization of water to achieve cooling. In addition, indirect attack reinforces the cooling effects of steam production by reducing oxygen concentration and thus reducing heat release rate from the fire.

In his comments Stefan Svensson stated that “in order to put out the fire we need to hit it with water”, but from what we have discussed here, with an indirect attack it is not water putting out the fire but steam.

In the indirect attack, production of steam and related effects on oxygen concentration result in fire control, but not necessarily extinguishment. Consider the potential outcome if you used an indirect attack on a fire in a building an did not follow up with direct attack and thorough overhaul. Likely a return visit to the same building some time later for a rekindle. In the end, when dealing with Class A fuels typically found in buildings, it is necessary to put water on fuel that is burning.

When Nelson and Royer were doing their research on the Iowa Rate of Flow, did they use a combination attack or did they use and indirect attack and then develop the combination attack after their experiments?

The combination attack was developed during their experiments. Initial application of water was done using an indirect attack (similar to that described by Lloyd Layman in Attacking an Extinguishing Interior Fires (1955). The Iowa State Story: The Iowa Rate of Flow Formula and Other Contributions of Floyd W. (Bill) Nelson and Keith Royer to the Fire Service – 1951 to 1988 (Wiesman, J., 1998) provides an excellent overview of Nelson’s and Royer’s work (but their discussion of fire behavior is inconsistent with current theory and terminology). While out of print it is available (used) through Amazon and a number of other used book outlets.

There are many departments that will flow a straight steam ahead of them across the ceiling to cool the room as they make their way to the fire. I have read that this would be considered surface cooling and not gas cooling because a straight stream will pass right through the gas layer without cooling it and only cool the ceiling, upper wall and floor surfaces as the stream bounces off the ceiling and land on the floor. I have a few questions about this.

When straight stream from a combination nozzle or a stream from a solid bore nozzle deflects off the ceiling, does the stream get broken up enough that the droplets become reduced in size enough that they will cool the hot gas layer on the way down to the floor or are they still too large and therefore pass right through the hot gas layer without cooling it?

There is some cooling, but it is less efficient than when a fog pattern is used as the large droplets will be more difficult to vaporize. If temperature is extremely high, some cooling will occur as even large droplets may be vaporized. If the stream can reach the seat of the fire, this inefficiency may be less significant as the fire will likely be controlled by the direct element of the combination attack. When faced with hot gases or flaming combustion overhead with a fire that is shielded from direct attack, cooling the gases with pulsed water fog will be considerably more effective and efficient than use of a solid or straight stream.

When the stream cools the ceiling and upper walls are the ceiling and walls now able to absorb more heat from the upper gas layer ( so this actually would be gas cooling) and if so how effective is it at cooling these gases (how much heat can these cooled surfaces now absorb from the hot gas layer)?

As discussed in my last post, gypsum board (a typical compartment lining material) which has a specific heat of 1.017 kJ/kg (Manzello, Park, Mizukami, & Bentz, 2008). This is one quarter the specific heat of water and half the specific heat of steam. So the indirect cooling effect of removing energy from compartment linings is quite inefficient at cooling the fire environment.

Once you have created steam from applying water to the ceiling and upper walls—-does that steam not now effectively cool the gases? I know you need smaller droplets suspended in the gases to absorb heat from the upper gas layer and steam would certainly meet that criteria.

The specific heat of steam is 2.0 kJ/kg  as compared to the combined theoretical cooling capacity of 2.6 MJ/kg when water is heated from 20^o C to 100^o C and vaporized into steam. While steam will cool the hot gases until they reach thermal equilibrium, but to a lesser extent than water fog applied into the hot upper layer.

Stefan Svensson mentioned in his comments that “sometimes fog nozzles are the best way to apply water to fire and sometimes it’s straight streams”. You often hear blanket statements being made about straight streams producing less steam and only fog streams can cool the gas layer. I was wondering if you could expand on the misconceptions and highlight some of the better practices we need to know about using the different streams from a more scientific point of view? When approaching a fire are we better to use both straight and fog patterns to cool the room as we make our way to find the base of the fire?

In a conversation with John Wiseman, Keith Royer stated that “there is not just one tool that will solve all fire problems”. The perspective that there is only one way to approach structural firefighting is dogmatic. Dogma is a point of view or tenet put forth as authoritative without adequate grounds. The simplest answer to your question is that when cooling gases, a fog pattern is more effective and when applying water to surfaces, the pattern selected may depend on the distance from the surface. When far away and the stream must be applied through a hot atmosphere, a solid or straight stream will likely be most effective, when close, a straight stream or fog pattern may be equally effective.

A question unrelated to this discussion but I am sure you can help me with. I am sure you are quite aware (or involved with) that excellent video called “kill the flashover” that shows the effects of closing a door. I know that the temperature stops increasing due to the lack of oxygen for heat release. But,  not only does the temperature not increase but it actually quickly decreases. This decrease is due to the fact that the walls and ceiling are absorbing the heat causing it to drastically reduce so my question is this; if that fire was allowed to burn for long enough that the walls could no longer hold any more heat, then the door was closed, would the temperature drop have been less and would it have lowered more slowly?

The reason the temperature dropped so quickly was not due to the absorption of energy by compartment linings, but by reduction of heat release rate (HRR) due to consumption of oxygen within the compartment. So, it would not make a significant difference if the fire had been burning longer. The higher the HRR, the more quickly you would see an impact. This also influences the visible fire behavior indicators (smoke and air track) on the exterior. As demonstrated in the UL ventilation experiments and previous work by NIST, visible smoke and air track indicators decrease dramatically as the fire becomes ventilation controlled due to a reduction in temperature (and resulting reduction in pressure inside the building).

Thanks for the great questions, let’s keep the discussion going! The next set of questions comes from Garland TX regarding “Flashover Training”. A bit of controversy here in a number of areas!

References

Layman, L. (1955) Attacking and extinguishing interior fires. Boston: National Fire Protection Association (NFPA).

Wiesman, J. (1998).The Iowa state story: The Iowa rate of flow formula and other contributions of Floyd W. (Bill) Nelson and Keith Royer to the fire Service – 1951 to 1988. Stillwater, OK: Fire Protection Publications.

As I was beginning work on a post focusing on fire attack methods and fire stream effectiveness, I received an e-mail from Captain Mike Sullivan with the Mississauga Ontario Fire Department asking for help in clarifying indirect and combination fire attack methods and their impact on the fire environment.

Mike is particularly interested in how to explain the method of extinguishment in the various methods of fire attack discussed in the International Fire Service Training Association (IFSTA) Essentials of Firefighting.

As Mike’s current perspectives and explanation of the methods of fire attack are quite good, they serve as a good starting point for our examination of this topic:

 Direct Attack: This is fairly straight forward; water is applied directly to the burning fuel to cool it to the point where there is no longer pyrolysis (below its ignition temperature).

 As Mike explains, the concept and mechanism of direct attack application of water to burning fuel to cool it. However, it is important to remember that combustion does not necessarily cease when flaming combustion is no longer visible, surface combustion can continue unless sufficient cooling is accomplished to not only extinguish flaming and surface combustion, but also to cool the fuel to the point where it is no longer pyrolizing.

 Indirect Attack: Here is how I would like to explain it. This is used when the seat of the fire cannot be readily accessed. Water is applied from the exterior of a very hot compartment (1000 degrees [F]+ at the ceiling) with limited ventilation. The goal is to create as much steam as possible. To do so you can begin with a fog stream since it is the most effective at cooling therefore creates more steam. The fog stream should be directed at the ceiling where it is hottest. Due to the fact that the stream has limited reach you will then want to narrow your stream eventually using straight stream. The idea is to reach as much of the room as possible. When a straight stream hits the superheated walls and ceilings it will also create a huge amount of steam as it cools the surfaces (most people don’t consider that a straight stream can create a lot of steam). The goal is to do this very quickly then close the door or window and let the steam do its work. There is one main question I was hoping you could help me with here since I have read different theories. What is the main mechanism of extinguishment here, does the steam continue to absorb heat to cool the room down and extinguish the fire or is there so much steam created that it excludes the oxygen therefore smothering and not cooling the fire (I realize both are actually happening), basically does this technique mainly cool or smother the fire.

 This is a complex question in need of a simple answer. The simplest answer is that the primary method of extinguishment is cooling. The complexity is in that the cooling is accomplished by several mechanisms. First, water heated from 20^o C to 100^o C and vaporized into steam absorbs a tremendous amount of energy based on its specific heat (energy required to raise the temperature of a specific mass of water by one degree) and latent heat of vaporization (energy required to change a substance from liquid to gas phase with no increase in temperature).

Water has a specific heat of 4.2 kJ/kg and a latent heat of vaporization of 2260 kJ/kg. Heating a single kilogram of water from 20^o C to 100^o C and vaporized it into steam, requires 2.6 MJ of energy. In addition (and contrary to common belief in the fire service) steam produced in an environment above 100^o C continues to absorb energy and increase in temperature until the temperature of the steam and the surrounding environment is equalized. Steam has a specific heat of 2.0 kJ/kg. This compares to the specific heat of smoke of approximately 1.0 kJ/kg (Särdqvist, 2002) and gypsum board (a typical compartment lining material) which has a specific heat of 1.017 kJ/kg (Manzello, Park, Mizukami, & Bentz, 2008). Water converted to steam in an indirect attack absorbs a tremendous amount of energy and the steam continues to absorb energy as the temperature in the compartment moves towards equilibrium. As with gas cooling or direct attack, some of the water is vaporized in the hot upper layer and some is vaporized in contact with hot surfaces (compartment linings, burning fuel, etc.). As the specific heat of smoke and compartment lining materials are lower than the specific heat of water (as a liquid or steam) and considerably lower than the latent heat of vaporization of water, the temperature of the smoke and compartment linings will drop to a greater extent than the temperature of the steam will increase (for a more detailed discussion of the cooling effects of water along with a bit of math, see Gas Cooling Parts 1-5).

Steam produced in and enclosed space also reduces oxygen concentration. As oxygen is required for release of energy from fuel, this can also be considered an extinguishing method. Reduction in oxygen concentration results in decreased heat release rate (HRR), which correspondingly results in a decrease in temperature. So in reality it is all about cooling (largely accomplished by vaporization of water into steam along with reduction of oxygen concentration).

 Combination Attack: We seem to have a real problem with this one. When I ask for an explanation of this technique I usually get “T”, “O”, and “Z” pattern as an answer. As a matter of fact a neighbouring fire department has these 3 letters painted on their walls to practice the pattern, again we are dealing more with technique instead of method of extinguishment. My explanation is that these patterns are merely a way of creating steam by cooling all surfaces in the room as well as allowing the water land on the burning fuel to cool it. What is the main mechanism of extinguishment here is it the creation of steam (and again what is the steam doing, cooling or smothering) or is it the water on the fuel cooling it. Also, would you recommend using a fog stream to create steam as it cools the gases and nearby surfaces then switch to a straight stream to create steam as it hits more distant surfaces (walls ceilings).

 The combination attack is intended to both cool the hot upper layer and apply water to burning fuel (less so to cool compartment linings, although this is accomplished as well). The term “combination” refers to the combination of direct and indirect attack. As indirect attack is not applied in an occupied compartment due to steam production (on contact with compartment linings), it is critical ventilation be provided in front of and closely coordinated with fire attack. As with the other methods of fire attack, the principle method is cooling.

As to your second question regarding use of a fog stream to create steam as it cools the gases and nearby surfaces and then switch to a straight stream to cool more distance surfaces. A combination attack may be done with a narrow fog pattern, straight stream, or solid stream. Reach in this case is a good thing. Cooling of hot gases overhead (with a little cooling of compartment linings) is the basic concept used in gas cooling. This technique is most commonly used to control the fire environment when the fire is shielded from direct attack and is not an extinguishing method. This approach does not result in an increased volume of steam and smoke and related lowering of the upper layer. In fact if approximately 35% or more of the water is vaporized in the upper layer, the total volume will be reduced (see Gas Cooling Parts 1-5 for a more detailed explanation of why). This technique can be effectively combined with direct attack on burning fuel and painting of compartment linings to lower their temperature. Painting is a gentle application of water to cool without excess steam production.

I believe that the Fire Streams and Fire Control Chapters in the 6^th Edition of the International Fire Service Training Association (IFSTA) Essentials of Firefighting provide a more clear discussion of fire attack methods inclusive of direct, indirect, combination, and the technique of gas cooling.

References

International Fire Service Training Association (IFSTA). (2013). Essentials of firefighting (6^th ed). Stillwater, OK: Fire Protection Publications.

Manzello, S., Park¸S, Mizukami, T., & Bentz, D. (2008) Measurement of thermal properties of gypsum board at elevated temperatures. Retrieved March 23, 2013 from http://fire.nist.gov/bfrlpubs/fire08/PDF/f08023.pdf

Särdqvist, S. (2002) Water and other extinguishing agents. Karlstad, Sweden: Räddnings Verket

Upcoming Events

April 19-20, 2013 – Seminar and Workshop on Practical Fire Dynamics & 3D Firefighting in Winkler, MB

April 23-27, 2013 – Wind Driven Fires in Private Dwellings at Fire Department Instructors Conference, Indianapolis, IN

May 25-26, 2013 – Compartment Fire Behavior Training Workshop at the British Columbia Training Officers Conference, Penticton, BC

Updated with Additional Video

On March 10, 2013 five Harrison, New Jersey firefighters were injured in an explosion while working at a commercial fire at 600-602 Frank E. Rodgers Boulevard. The fire originated in a two-story commercial building at the corner of Frank E. Rodgers Boulevard North and Davis Street and extended into Exposures Charlie and Delta, two-story residential buildings.

Figure 1. Alpha/Bravo Corner and Exposure Charlie

Image from Google Maps, click on the link to walk around using Street View.

Reading the Fire

Before watching the video (or watching it again if you have already seen it), download and print the B-SAHF Worksheet. Using the pre-fire photo (figure 1) and observations during the video, identify key B-SHAF indicators that may have pointed to potential for extreme fire behavior in this incident.

Important! Keep in mind that there is a significant difference between focusing on the B-SAHF indicators in this context and observing them on the fireground. Here you know that an explosion will occur, so we have primed the pump so you can focus (and are not distracted by other activity).

Backdraft or Smoke Explosion

While smoke explosion and backdraft are often confused, there are fairly straightforward differences between these two extreme fire behavior phenomena. A smoke explosion involves ignition of pre-mixed fuel (smoke) and air that is within its flammable range and does not require mixing with air (increased ventilation) for ignition and deflagration. A backdraft on the other hand, requires a higher concentration of fuel that requires mixing with air (increased ventilation) in order for it to ignite and deflagration to occur. While the explanation is simple, it may be considerably more difficult to differentiate these two phenomena on the fireground as both involve explosive combustion.

1. Did you observe any indicators of potential backdraft prior to the explosion?
2. Do you think that this was a backdraft?
3. What leads you to the conclusion that this was or was not a backdraft?
4. If you do not think this was a backdraft, what might have been the cause of the explosion?

For more information in Backdraft, Smoke Explosion, and other explosive phenomena on the fireground, see:

• Smoke Explosion and Backdraft
• Explosions During Structural Firefighting
• Lima, Peru: Backdraft
• Chicago Extreme Fire Behavior: Analysis of Fire Behavior Indicators
• Sudden Blast
• Gas Explosions
• Extreme Fire Behavior: An Organizing Scheme
• Backdraft at 62 Watts Street
• Fire Gas Ignitions

Back at it!

I would like to say thanks to all of you who have sent e-mail or contacted me on Facebook inquiring about the status of the CFBT-US blog. The last several years have been extremely busy at Central Whidbey Island Fire & Rescue and my focus has been almost exclusively on the fire district. However, I am renewing my commitment to developing knowledge of practical fire dynamics throughout the fire service and will endeavor to return to posting on a regular basis. In addition, I am working on a series of short (10-minute) drills on fire dynamics that will be cross posted on the CFBT Blog and the Fire Training Toolbox.

Ed Hartin, MS, EFO, MIFIreE, CFO