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By Author(s): Jeff Diederich
Published Wednesday, August 13, 2014

By now most of the American fire service has worked a building fire where the call was made to put water through a self-vented window or door rather than stick to the principles of traditional interior firefighting and extend the first line to the interior. Recently my crew worked such a fire in a bi-level single family Home (SFH) with fire venting from a rear kitchen window. The resident was outside reporting everyone was out of the home and there were no exterior exposures. The first arriving crew pulled a 1-3/4 around the back of the home and played water into the fire window as my company stepped off the rig. The order for us was to enter through the front door and start a search.

The collective question: enter opposite the attack line?

As ordered we made our way to the front door and as I entered I was greeted with hot dense smoke banked down to the floor with a cloud of steam that violently pushed over top of me. Only one foot inside I quickly backed out of the front door and gave the steam time to dissipate. Even though I had the protection of a hood, that experience was not a pleasant one.

My crew in tow, we made the stairs to the second level bedrooms and completed the search. More confusion was audible as the attack crew finished extinguishing the kitchen and then started to search the first floor and sub-level. Complications arose as the nozzle team ran into other search crews also ordered to enter opposite the hose line. This strategy of multiple points of entry is not our standard procedure and neither is a transitional attack on a single room fire. In this situation, one could argue that the confusion was an incident command issue. I believe this is a symptom of the Underwriter Laboratory (UL) studies and the miss-understanding and/or miss-application of that work. The fire service is quick to jump on the bandwagon of “hitting it hard from the yard”. At this bread and butter fire, all would have been smoothly completed if the initial order was to enter from the front door, use the reach of the stream and push into the kitchen with an open nozzle. This would have protected the stairs for search crews, all but eliminated the steam condition, and promoted better communications and accountability.

My experience in the fire service includes 20 years working for a single engine fire department which is a close suburb of Cleveland, Ohio. My fire duty could be summed up as typical of a suburban firefighter. My fire department worked around 50 fires in 2013. When compared to five-year veteran of my nearby metropolitan city, I need more training and off the job experiences to fill in the experience gap. Throughout my career I have looked for every live fire training opportunity and even engaged in ride along programs, all with the goal of gaining relevant experience. This personal development has provided the author great opportunities to learn from the best firemen I could find, and in turn, pass that wisdom on as a fire service instructor for the last 10 years. On my journey through the fire service I have come to believe wholeheartedly that we must jealously guard our profession as we investigate and learn about the evolving strategy of fighting fire. This evolution must occur without sacrificing traditional lifesaving principles for modern fire ground management.

Since 2011 UL has provided the fire service with more practical science than has been published in many years. They have tirelessly studied and conducted experiments using several scenarios relating to residential fires. The missing piece is the perspective of those of us that are not scientists who want to ask some questions. First, if the definition of science is the observation, identification, description, experimental investigation, and theoretical explanation of phenomena, then all possible variables must be accounted for. Is it possible to account for every possible variable in residential structural firefighting in a laboratory setting? If not, is interior firefighting in an occupied structure a science?

The accumulated data from hundreds of years of interior firefighting is the bedrock of our profession’s strategy and tactics. The first of which is to protect human lives. The fire service must remain focused on what does that. We make the building and the byproducts of combustion behave the way we want them to; e.g. pushing them away from interior exposures and occupants. Unwittingly, the UL studies have put the fire service on a path opposite these core principals. There are scenarios when “softening the target”, “transitional attack”, or “hitting it hard from the yard” can be applied, but that tactic should not be the first applied at every fire that is venting. Do not miss-interpret, I am not dismissing the great information and scientific facts that are coming from the UL work. I am concerned that no one is talking about the variables that have not or can not be tested and the push to move away from strategy and tactics that we know saves lives.

My intent is to bring your attention to the limited association these studies have on the real dynamic world of the fire ground. I’m referencing the long list of unknowns at a “real” fire; the difference in water application, the relationship between suppression efforts and the harmful effects of steam. What follows are some excerpts from the UL study UL FSRI 2010 DHS Report that grabbed my attention. The highlighted lines are this author’s emphasis.

The second two pictures were captured 10 seconds later and the gases from the water application are forced into the bedroom in the flow path with the open window. This did not occur with the use of the straight stream water application but the fog stream was more effective at cooling during these experiments. While steam was “pushed” along the flow path there was no fire “pushed”.
A common argument against flowing water onto the fire prior to entry is the belief that conditions beyond the fire would be made worse. Data from this experiment showed otherwise. Temperatures ONLY! (author’s added emphasis) were measured in the hallway just outside the room and in the other bedrooms on the second floor, (Figure 6.29). As shown in Figure 6.29, 25 gallons of water directed off of the ceiling of the fire room decreased fire room temperatures from 1792 °F to 632 °F in 10 seconds and the hallway temperature decreased from 273°F to 104°F in 10 seconds.

There are dramatic reductions in temperature and I appreciate these as fact. The tradition of the American fire service is to fight these fires - whenever possible - from the inside out. Why? Because our value as a service is directly related to our ability and willingness to position ourselves between the fire and the people trapped. The conversation surrounding “transitional attack” is an over simplification of the art of interior firefighting. As with compressed air foam attack and positive pressure fire attack, there is value and a place to apply these tactics. Depending on each individual fire department’s manpower, training, and staffing I would argue that these tactics, as well as transitional attack, have a limited application in an occupied building. Essentially, water is the answer! If we all agree, and UL has proven, that today’s fires develop faster, then why are we not talking about getting inside between the fire and the people? Why are we not talking about getting inside faster, via deploying efficient hose loads that are practiced to perfection so as to move the byproducts of combustion away from interior exposures and any trapped occupants? Some have argued that an interior hose team cannot be as fast as water from the outside. My rebuttal is that the steam production caused by water from the outside is faster at controlling fire but there is a consequence we must account for. That is the production of steam in a space that may or may not be compartmentalized. This is surely impacting interior firefighting crews and may be negatively affecting those we are sworn to protect.

A discussion about steam conversion

For the sake of clarity and for discussion here, let’s define; heat, temperature, and latent heat of condensation.

Heat Energy is a form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state. – NFPA 921

Temperature is a measure of the degree of molecular activity of a material compared to a reference point (degrees). NFPA 921

Latent Heat of Condensation is defined as the quantity of heat needed to be transferred to convert a unit mass of a substance in gaseous phase into liquid phase at its condensation point at one atmosphere pressure.

When energy is transferred to a substance, usually, temperature of the substance increases. If the substance is at a higher temperature than its surroundings, temperature of the substance decreases as heat is transferred from the substance to its surroundings. Thus we can conclude that a substance undergoes a change in temperature whenever flow of energy transfer between a substance and its surroundings takes place.

Let’s investigate the science behind a statement many of us have heard: Dry heat is not as harmful as a wet heat?

The answers I’ve found:

There’s more energy (heat) in the steam. To raise the temperature of one gram of water from 37ºC (temperature of skin) to 100ºC (boiling point) requires 63 calories (one calorie per degree). To convert that gram of water to steam requires another 540 calories. So the energy (heat) in the steam is nine-fold greater than the energy in the same weight of water at the boiling point. This energy (as heat) is released when the steam condenses to water and the water cools to the temperature of skin. Steam will be substantially more injurious. - David Kessel, Ph.D., Professor, Wayne State University, Detroit

Let’s discuss the physics of steam injuries. Steam burns have the potential to cause more damage (to human skin) than scalding. The reason has to do with the latent heat of vaporization. This is the amount of heat energy necessary to change the phase or state of matter from liquid to gas. This energy is absorbed by the liquid, but does not change the temperature. Conversely, when a gas condenses, it must release this latent heat and become a liquid before it can cool below its boiling temperature. The latent heat of vaporization for water at sea level is about 2250 J/g, as compared to the specific heat of water of about 4 J/g•°C. All that extra heat has to go somewhere, mostly to the surrounding air. If, however, you place your hand into a jet of steam, much of that heat will be absorbed by your skin - very unhealthy. And what’s worse, as the steam condenses onto your skin, it will still be at 100°C! - Grant Coble, B.S., Physics Teacher, Hollywood High, Hollywood California.

In summary, steam has a very high latent heat capacity. Steam filled air transmits the energy as the gas turns to water (boiling temperature), and continues to burn human flesh. Dry air is much more breathable because air is a very efficient insulator. My conclusion is that moist air conducts the energy (heat) to the respiratory tract and exposed skin rapidly and with long lasting, destructive duration.

It is reasonable to deduce that steam is hotter in smaller areas of confinement like hallways and stairways, as well as “exhaust” openings like a windows or doors. Steam temperature is a direct result of its pressure (density). This assumption further underpins the fact that we must control not only the air current (flow path) to and from the fire as UL has demonstrated, but we must also control the steam production from our hose stream. We are there for the people and their property, not the fire. If we suppress the fire by quickly darkening the fire from a “safe location” yet by doing so, expose victims to deadly amounts of steam, we have failed in our mission. The American fire service cannot become teams of exterior sprinkler systems that are not thinking critically of our actions.

A further investigation of the properties of steam and how steam affects the survivability of victims trapped inside a structure fire is in order (as UL has noted). UL has documented that their studies have provided data that is only starting the conversation regarding fighting fires in occupied buildings. In the future perhaps they will be able to qualify the physics of steam and its impacts to victims in a fire building. Most firefighters I know are not looking at the words clearly written in these reports. Examples: “the experiments did not simulate water being applied from inside the structure by an advancing hoseline. It is understood that this happens on most fires.”

The second two pictures were captured 10 seconds later and the gases from the water application are forced into the bedroom in the flow path with the open window. This did not occur with the use of the straight stream water application but the fog stream was more effective at cooling during these experiments. While steam was “pushed” along the flow path there was no fire “pushed”.

These statements clearly illustrate a few points lost on many of us. First, most firefighters know what it is like to be “steamed” while working a fire. We are forgetting to think about that experience and how our tactics may be doing that to our citizens that don’t have the benefit of PPE and self-contained breathing apparatus. Second, we must consider the fact that the UL studies are only one side of the fire ground operation. Until a study is completed where water is bring applied inside of a structure by an advancing hose line team, we will only have half of the story. Third, we must rediscover the principles and experiences of those that have applied their life to pursuit of this art; William Clark, Andy Frederics, David Fornell, Jeff Shupe, and recently Aaron Fields. Each one standing on the shoulders of those that came before them, to build the knowledge needed to maintain and develop the specific skillset known as interior firefighting.

Pushing Fire

The main casualty of the mis-interpretation of these 400+ page studies has been the downgrading of the importance of interior hand lines in an occupied structure, and the importance of vertical ventilation. The UL study excerpt cited below leads firefighters away from these core tactics by contradicting itself and not advocating what, in the authors opinion, clearly helps victims in a building fire; that is the placement of interior handlines that push smoke, heat and fire gasses away from victims and the protection of survivable space. This contraindication is evident in Section 6.11 paragraphs 1 and 2 of UL-FSRI-2010-DHS-Report

6.11. You Can’t Push Fire

You cannot push fire with water. The previous UL ventilation study included the concept of pushing fire in the data analysis. That study generated a lot of discussion, and stories surfaced from well-respected fire service members who had experienced the phenomenon of pushing fire, or had perceived that it had happened. The specific fires recalled by the firefighters were discussed in detail. In many of these situations, the firefighters were in the structure and in the flow path opposite the hoseline. In most cases, the event described occurred while fire attack crews were advancing on the inside, and not while applying water from the outside into a fully developed fire. All of the experiments in this study were designed to examine the operations and the impact of the initial arriving fire service units. It is not suggested that firefighters position themselves in a flow path opposite the hoseline. However, there are times when this may happen so the experience of these firefighters should not be discounted. Also, the experiments did not simulate water being applied from inside the structure by an advancing hoseline. It is understood that this happens on most fires.

1) A flow path is changed with ventilation and not water application. When the firefighters are opposite the hoseline, in many cases they entered from a different point than the hoseline and left the door or window open behind them. This flow path is entraining air low, where they are crawling, and hot gases are exiting over their heads. As the fire reacts to the added air, the burning moving over their heads increases and conditions could deteriorate quickly. If an attack crew is preparing to move in or is inside, the experience of the firefighters opposite the hoseline could be blamed on the hoseline. However, the fire was just responding to the air and the added flow path and not to water flow. Often this occurs in close timing of water application and occurs without coordination (Figure 6.34).

A flow path is changed with water. Opening a wide fog changes the flow path or plugs a flow path (Figure 6.35 and Figure 6.36); this can also be accomplished with a straight stream when whipped in a circular pattern (Figure 6.37 through Figure 6.39). This can disrupt the thermal layer and move steam ahead of the line, which is why firefighters do it. If a firefighter is downstream, they may get the impression of pushing fire or elevated heat, especially if they are in the cool inflow of another vent location.

These sections leave the interpretation of the study to the reader, who may not consider the consequences of flowing water into an occupied building fire that has self-vented because there is no data from a UL study available on the effects of super-heated moist air filling the survivable space. We need to know how much steam is created from “10 seconds of water directed at the ceiling from outside of the window”. We need to have a UL study that uses realistic handline flow rates, current UL studies have handlines flowing at 100GPM.

Another disconnect between the fire service and the information from the UL studies is the definition of “fire”. When most firefighters hear the word fire we instantly picture not just the orange and red stuff but the super-hot gasses that burn and kill, including steam. If you are suffering from a burn, the delivery of the energy may have varied (convection, conduction, radiation) but the results are still tissue damage. The summarization from UL that we cannot push fire with our hose streams is therefore incorrect, if you look at it in an injury causing definition. We cannot push fire with our hose stream to ignite a different area within the building, but we DO push steam and hot gasses, which the UL makes note of in their study.

Nozzle Forward instructor Aaron fields also poses a pertinent question. He asks, “How much air does your nozzle move?” Of course, most of us cannot qualify that with an answer, but it is a legitimate question when considering the impact that air has on the atmosphere inside the building (not just the temperature but the gasses that actually kill our victims). Aaron Fields states that a smooth bore nozzle at 150 gpm, can move up to 800 cubic feet of air per minute with an aggressive “O” pattern. These deductions are sited from an earlier fire service mentor named David Fornell in his book Fire Stream Management Handbook. UL has also confirmed that all nozzles move air as was demonstrated in the Horizontal Ventilation Study “firefighters can close off the exhaust with a fog or circular patterned straight stream”.

It’s clear that our hoselines aid to influencing the movement of air inside a fire building (flow path, air tract, etc.). The hose team is the “weather front” or the high pressure moving into the building and pushing air with open nozzles. As Fields has said “an open nozzle is the truest form of positive pressure attack.” We should be concentrating on moving the by-products of destruction out of the building from an opening of our choosing. We do this by flowing water while moving towards the fire putting water on what is burning as we go. This action is coupled with coordinated opening of an exterior window or ceiling/roof or other vent to allow an exhaust for the products of combustion, including steam.

Steam production and its impact on survivable space

If a fire has self-vented to the outside and an interior door from the fire compartment to the rest of the structure is open, there is no question in my mind that water applied from the outside will produce steam and that steam will move into and throughout the structure. Steam will absorb energy (heat) snuffing out some of the fire but it will also push into survivable spaces, replacing the breathable air with energy transmitting steam.

There has been much study and computer mapping done on the subject of breathable air. In this research it was established that “A person can ideally inhale air under 358 Kelvin (185 degrees F) for 20 seconds without sustaining significant tracheal tissue damage.”

“Certain gasses may burn the trachea quicker than others and some gasses may react with itself or upon contact with the trachea, causing further deterioration of tissue. Also, the model does not include the effects of densely hot wet air, such as water vapor, where phase change heat transfer must be considered.” - Tracheal burning from hot air inhalation; Christina Cossell, Jan Ma, Samantha Spindel, and Yang Wang. Cornell University, Ithaca, NY May 4, 2007.

In the common scenario of a trapped victim, just adjacent to a fire compartment, who is lying on the floor, clinging to life breathing nearly 200 degree, dry air. It is this author’s belief that the application of water from the exterior without knowing that a barrier (door) is closed between the victim and the fire, will be catastrophic to the interior exposure or “the unprotected respiratory tract of the fire victim” – A. Fields FDIC 2014. Just as we train our firefighters not to get caught opposite the nozzle, for obvious reasons. The Fire service needs to know, why are we not making the same argument for trapped civilians? Are we not in agreement to risk a lot to save a lot? How much would our risk assessment change in our favor (the citizen’s favor) if we know we can advance a flowing handline?

Vertical Ventilation

The lost art of principled truck work needs to be addressed. Below is a UL excerpt that brings the point to bare. We are charged with making the survivable space bigger for them and us.

There was not a ventilation hole size used (4 ft. by 4 ft. or 4 ft. by 8 ft.) in these experiments that slowed the growth of the fire. All vertical ventilation holes created flashover and fully developed fire conditions more quickly. Once water was applied to the fire, however, the larger the hole was, and the closer it was to the fire, allowed more products of combustion to exhaust out of the structure, causing temperatures to decrease and visibility to improve.

Ventilating over the fire is the best choice if your fire attack is coordinated.

If a ventilation limited fire receives air, it will increase in size.

Additionally, the closer the source of the air to the seat of the fire, the quicker it will increase in size. If you ventilate in coordination with fire attack (the hose stream is removing more energy than is being created), it does not matter where you ventilate, but the closer to the seat of the fire, the more efficient the vent will be in removing heat and smoke, which will improve conditions for the remainder of the operations taking place on the fire ground.


I would like you to consider the impact of super-heated moist air pressurizing the inside of the building and the effect that has on the breathable air in survivable spaces and egress routes within the structure.

I do not believe that the UL is misleading or omitting or miss-representing data. It is our brothers and sisters in the fire service that are only reading the highlights, who are not spending adequate time to truly understand the data coming from the UL and apply it in a smart way on the fireground. We can’t just put an emphasis on “hitting it hard from the yard” without a complete understanding of that tactic and the impact it has on the interior of a structure. My academy instructor Jeff Shupe said; “Fire departments always need to look at the changes in tools and equipment from the past to the present.” but, he never mentioned changing our values and principles! Second, vertical ventilation can be difficult and dangerous, but the benefits to those without breathing apparatus in the building are clear. UL continues to illustrate how critical it is to coordinate ventilation. The concept of coordination is where our emphasis should be. Teaching patience to the outside horizontal vent crew and speed and efficiency to the roof crew. Third, and the most important lesson, is that we must be able to apply overwhelming pressure (volume of water) to the fire and have an exit in mind for the super-heated gasses.

More questions for the fire service. Are we changing the way we protect lives for the right reasons? Does transitional attack on smaller fires make the atmosphere more survivable for our citizens? What does the transitional attack mindset do to our argument for staffing levels and training? Are we moving towards a priority of stopping the fire versus saving lives?

How do we balance the old tactical truth of interior firefighting (an art form), with the new science of fire suppression in a modern furnished building? It is my opinion that we as a service must re-dedicate ourselves to mastering the basics of applying water from an advancing hose line. We must have the ability to advance a flowing hose line using a smoothbore tip from an entry point to the room of origin and change the “weather” inside of the building. Moving while flowing water is the “new science”! So save the transitional attack for the scenarios that call for it. Namely when you arrive to a 40%-90% involved structure, two or more floors with fire, Only 1 or 2 firefighters on the scene, or supporting an in-progress VES operation, or if there is an unavoidable delay in getting an interior attack line in service.

Wisdom is defined as truth from all perspectives. A truth of firefighting is that the first well placed interior hose line saves more lives than any other tactic we can deploy (in most cases). The variables of interior fighting in occupied structures are endless. Beware of “new truths” as they are not truly proven without real world application that validate their efficacy. I insist we maintain our profession to be result based and value driven with all evolution and advancement aimed at helping those we all sworn to protect on day one.

References and Acknowledgements

Underwriters Laboratory FSRI 2010 The study of effectiveness of fire service vertical ventilation and suppression tactics in a single family home

Underwriters Laboratory DHS 2008 Report The impact of ventilation on fire behavior in legacy and contemporary furnished residential construction

NFPA 921


Fornell, David. Fire Stream Management Handbook. 1991. (Saddle Brook, NJ: Fire Engineering-Pennwell Publishing Company, 1991), 78.

Aaron Fields, Nozzle Forward. 2014 FDIC.

Jeff Shupe. Fire academy class of 94-01 Cuyahoga Community College.

Jeff Shupe. Fire Engineering October 2013,

Christina Cossell, Jan Ma, Samantha Spindel, Yang Wang. Tracheal burning from hot air inhalation

About the Author

Lt. Jeff Diederich has been a professional firefighter since 1994 working for a suburban fire department in northern Ohio. He has been a fire instructor at the Cuyahoga Community College for the last 10 years, as well as being a rescue and hazmat technician for the local technical rescue and hazmat response teams.