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Water Rules: Summary of the recent UL Studies Part 3: Full Scale Experiments - Findings

We have come to the point in this series that we will be looking at the results of the type of experiments the fire service has been clamoring for since UL and NIST first began releasing findings from their fire dynamics research that challenged longstanding practices. (To be fair, only some members of the fire service wanted these additional studies, in large part to address the concerns of other members who didn’t think the previous tests were valid. Regardless, both groups hope their positions are confirmed, resulting in a lot of us anxious for their completion, whether with excitement or dread.) Beginning with the surprises from Analysis of One and Two-Story Single Family Home Fire Dynamics and the Impact of Firefighter Horizontal Ventilation ( and Study of the Effectiveness of Fire Service Vertical Ventilation and Suppression Tactics in Single Family Homes (, which demonstrated how much ventilation before fire control can worsen interior conditions, and continuing with the Governors Island tests ( that demonstrated how well water application from the exterior can improve interior conditions, we have been attempting to comprehend and incorporate a steady flow of information that often contradicts our previous understanding of the effects of our actions.

Despite the consistency and repeatability of the research findings, and the success of the tactical recommendations that were synthesized from those new insights and operationalized in the Principles of Modern Fire Attack/SLICE-RS approach, these groundbreaking experiments have been criticized as not being representative of "real firefighting" practices. Admittedly, prior studies were limited to the use of exterior streams (although a few tests were performed with fixed interior monitors); sequential tactics were not performed, such as knocking a fire down with exterior streams then transitioning to an interior attack; and there was no direct comparison of the exterior and interior approach. In this study, for the first time that this writer is aware of, firefighting teams performed a variety of different evolutions on the same fire scenarios, including entering a burning structure and operating a charged hoseline, and with even more robust monitoring and measurement than for any previous attempt at analyzing the dynamics of the extinguishment process.

“Impact of Fire Attack Utilizing Interior and Exterior Streams on Firefighter Safety and Occupant Survival” ( is the official moniker for this study, and indicates that the focus was on the water application portion of our tactics, and its effects on both those of us who serve, and those whom we serve. All research naturally inspires more research, with the need to further investigate any findings being a consistent and predictable requirement, whether undertaken to better define, expand upon, or just confirm those results. The first two posts in my series on these studies reviewed the experiments that preceded this set of instrumented burns. The Water Mapping ( and Air Entrainment ( tests, in which the effects of water alone were observed and measured, served to guide the design and focus of the live-fire, live-firefighter scenarios in these Full Scale Experiments. Taking the effort to perform preliminary experiments in order to better inform an already-planned project demonstrates the dedication and thoroughness of the UL researchers, and their commitment to its goals. The volume of information from the comparative experiments in this, the major component of the series, will require at least two installments to even begin to review, with this one covering the general findings, and the next discussing the resulting tactical recommendations.

First, though, a disclaimer: The following opinions and assessments are this author's alone, and anyone who plans to operate in the uniquely dynamic and dangerous environment found inside burning buildings should review this data personally. Not only will such an examination provide additional and necessary understanding of the information, but it will likely instill an appreciation for the researchers and their methods. As with the earlier experiments, there is also an interactive, web-based training program available ( covering this material, though viewing this would still be less informative than actually reading the reports. This summary is just that: an attempt to condense the mass of material and information available into a more easily digested portion, and not a substitute for individual effort.

The study writers listed twelve categories of findings, ranging from Repeatability (the consistency of the fire environments created, which serves to ensure that results are not “flukes” or "one-offs") to Thermal Imaging Camera (TIC) Limitations (explained as the inconsistency of readings from these devices when temperatures were highest, which is why other instruments were utilized for those measurements), each of which is sufficiently interesting and complex to justify individual attention, but far too much material to cover in a format such as this blog. Instead, I will utilize a more condensed framework that describes the overall experiments, comparisons of the different extinguishment methods, effects on the interior environment, and the potential impacts to victims, or “Project, Process, Products, and People”. Keep in mind that this is just an organizational tool for our collective benefit (i.e., easier for me to write and for you all to read), and in no way suggests that any of these components can be considered independent of any others. Still, you should know that my earlier drafts that followed the study’s format were almost as long at the report itself!

Study Description (Project)

Rather than attempt to write a condensed description of the methods, I found an even better summary here in its Abstract:

"This report evaluates fire attack in residential structures through twenty-six full-scale structure fire experiments. Two fire attack methods, interior and transitional, were preformed at UL’s large fire lab in Northbrook, IL, in a single-story 1,600 ft2 ranch test structure utilizing three different ventilation configurations. To determine conditions within the test structure it was instrumented for temperature, pressure, gas velocity, heat flux, gas concentration, and moisture content. Additionally, to provide information on occupant burn injuries, five sets of instrumented pig skin were located in pre-determined locations in the structure. The results were analyzed to determine consistent themes in the data. These themes were evaluated in conjunction with a panel of fire service experts to develop 18 tactical considerations for fire ground operations."

Except for the random collection of "fire service experts" at your typical structure fire, the observations and measurements conducted were far beyond those available to us as we actually perform these functions inside or around a burning building, and even surpassed the array of instruments employed in previous fire dynamics experiments, so the information obtained had the potential to be uniquely enlightening. The stated intent of searching for "consistent themes" bears emphasis, as it indicates that the goal was to identify findings that were confirmed in multiple formats, rather than sporadically; and which represent predictable, rather than random, events. That is, they were looking for lessons.

The researchers created a standard environment (single story, 4-bedroom, furnished residence); set fires in the same areas (end of hall bedroom[s]); kept certain bedroom doors open or closed throughout; and let all of the fires become fully developed before intervening. They then varied the ventilation profiles (none, window[s], entry door), water application direction (exterior, interior, both, neither), nozzle types (smooth bore, combination), stream type (straight, fog), sequence and timing of interventions, and even hoseline movement (flow while moving [F&M], shut down and move [S&M]). All the while they were measuring the very factors that are of concern to firefighters: heat (temperature, heat flux), “steam” (moisture content), toxic gas (carbon monoxide level), flow path (gas velocity), and water usage, analyzing how the different combinations of these elements might affect firefighters and any occupants. Where possible, each tactic was conducted with various combinations of fire and ventilation (single room of fire with no ventilation, single room of fire with a single window vent, two rooms of fire with two window vents, and with and without door control), as well as assorted nozzle types (smooth bore and combination).

Despite securing the agreement of researchers (who are, as a rule, an extremely careful bunch) to allow human subjects to operate in a potentially lethal environment (which had been created by those same researchers), two interventions that were not attempted were the interior use of wide fog streams and entry without water application. In another example of experimentation informing further experimentation, these maneuvers were avoided because of insight obtained through prior studies. For the fog nozzle issue, Jerry Knapp, who was a member of the expert panel for this study, and his associates had shown ( that the interior use of wide fog resulted in significant "blow back" of products of combustion onto the hose crew when used indoors, even with a door-way sized exhaust beyond the nozzle. Regarding the consistent application of water while advancing interior hoselines, analysis of the temperature and ingredients of interior smoke, which consists in large part of pre-heated and aerosolized petroleum products, mandated cooling overhead with hose streams during the approach to the fire room, even if this action has not yet become "standard" practice on the non-laboratory fireground.

Comparisons of Extinguishment Methods (Process)

As mentioned previously, a variety of different nozzle maneuvers were compared. These included those that might be considered "standard", with exterior streams in a solid/straight pattern directed steeply inward to deflect off the ceiling, sometimes called “steep, straight, and still (SSS)”; and interior solid/straight and narrow fog patterns intermittently sprayed as the hoseline was maneuvered down the hallway toward the involved room, termed "shutdown and move (S&M)". Variations included following up on the exterior knockdown by placing the nozzle inside the window and applying water directly to the burning contents; or continuously spraying water as the interior hoseline progressed toward the fire, termed "flow and move (F&M)".

While the focus of this study was on water application, and one of its unique features was the ability to compare various extinguishment approaches on the same fire, this was not a "which method is better" contest. For one thing, the consistent scenario - a ground-story fire, without such typical outdoor obstructions as plants, fences, or even windows; and the involved compartments located at the end of a long corridor, distant from the entryway - was inherently, and unrealistically, easier and faster to attack from the exterior. Also, since every fire presents unique factors that must be weighed when determining the ideal direction of fire attack, and interior vs. exterior are merely two general categories, creating a true “head-to-head” comparison of every possible approach would be both impossible and meaningless.

For instance, the exterior approach used the least amount of water for fire knockdown - about 50 to 60 gallons per room - compared to about 80 to 90 gallons per room when using interior streams. Except, the difference in water usage was not due so much to the direction of the attack, but by the need for crews stretching down the hallway to flow water to cool as they proceeded to the involved area. When the amount of water used during the approach to the fire via the interior route was discounted, the volume used for extinguishment was virtually identical for all approaches. The real value and purpose of these experiments were the opportunity they provided to evaluate the effects (temperature reduction, steam production, air movement, etc.) of different interventions on the same situation, not necessarily their relative ease or speed. From these experiments, we now have been shown the comprehensive effects of attacking the same type of fire using either exterior or interior hose streams. Let’s look at what was learned about how we put the wet stuff on the red stuff:

Exterior Streams

As expected, spraying water through the window was the most rapid way to reduce temperatures, with reduction to beneath 400F - roughly corresponding to the thermal protection limits of firefighter PPE - occurring within about 15 seconds of initiating water flow. This cooling persisted long enough to accomplish an interior attack, and was more prolonged when the initial straight, still, and steep (SSS) flow was followed by actually placing the nozzle into the window to apply water to the burning contents directly, with the bail partially closed to create a coarser stream. If there were two rooms involved, persistent and significant cooling in the other room did not occur until water could also be applied into that compartment, either by repositioning the exterior line to that window, or by attacking via the interior. Despite the lack of sustained cooling in a second involved room when water was flowed only into the first, though, temperatures did decrease in the intervening hallway below 400F, which would facilitate an interior attack via that route.

While the benefits of exterior streams were clearly demonstrated, so were its lack of ill effects. Critics of that approach have long warned: ”Of course it’s easier and faster to apply water from the exterior, but it’s also bad for any occupants!” The inaccuracy, or at least incompleteness, of that view had been suggested in earlier experiments, and these tests provide further evidence to debunk that myth. Specifically, applying water into the window of a burning compartment correctly (SSS) was shown to cause no increase in steam or temperature in the other areas of the home. Given the right circumstances, you certainly can push a lot of products of combustion with a fog stream, but we now know that’s only appropriate when performed from the inside out.

Interior Streams

As mentioned above, hoselines stretched into the structure generally took longer and used more water and time to reduce temperatures but, as with the performance of the exterior streams, these findings were not unexpected. The more important results of the experiments were the lack of differences in the effects of the direction of water application: the fire went out when the water reached the burning compartment, and the effects on the remainder of the interior conditions were similar. Even when comparing the two different interior nozzle operation techniques, with F&M more consistently propelling products of combustion ahead of the hose team due to continuous flow, but S&M extinguishing the fire slightly faster due to better control of water flow direction, the differences were, at least in the opinion of this reviewer, inconsequential. S&M showed a rebound of overhead temperatures in the few seconds after the water flow was stopped while the hoseline was advanced, but the interior crews utilizing that method would likely not even have noticed, and the temperatures again fell as water flow resumed. Operating a narrow fog stream in the interior hallway was even more successful than either of the straight/solid maneuvers in both measures - extinguishing the fire more quickly and propelling products of combustion ahead of the advancing hose crew more forcefully. Long story short, every method was effective at extinguishing the fire and moving of products of combustion away from the advancing hose team.

Effects on interior environment (Products)

One of the earliest enlightenments produced by fire dynamics research, performed by NIST while investigating LODDs, was the significant contribution to fire scene fatalities of products of combustion, even without direct fire exposure. Those studies introduced the previously-unappreciated concept of “Flow Paths”, which are the routes that heat and smoke travel within a burning structure as they inexorably seek an exit. This study examined the effects of several different tactics on this movement, with comparisons provided between a variety of interior and exterior flow types, including straight, solid, and narrow fog. There are many products of combustion that are affected by extinguishment efforts, but the ones we firefighters are most concerned about, and which the researchers measured, are heat, water vapor (steam), and smoke. The first was consistently lowered by water application, regardless of direction (exterior or interior); the second was essentially unaffected; and, as noted above in the discussion of interior streams, the third did what we intended.

More specifically, temperatures were universally reduced by the application of water, without a corresponding increase in adjacent areas. (That is, there was no “pushing” of high temperatures deeper into the structure by an expanding cloud of steam.) In fact, applying water into a burning bedroom from the exterior actually caused airflow into the fire room from the interior corridor opposite the window, and even the initially bidirectional airflow at the window converted to complete inflow. This was due to the contraction of hot gases occurring as the interior cooled, though it was aided - or at least not negated - by proper nozzle technique (SSS).

Looking at the issue of "steam" created by firefighting operations, the researchers also analyzed the amount of water suspended in the smoke. (This was described as a "technically difficult" process, given that many of the conventional methods utilize the effects on a light source, which is significantly hampered by the presence of smoke; or are adversely affected by high temperature, as is common in a burning building.) Data was collected in Bedroom 4, the one with an open door, but in which there was no fire set nor water flowed, in an effort to measure the effects of steam beyond the areas involved with fire. Here was one of the many unexpected findings of these experiments: the concentration of water in the atmosphere of the interior compartment was essentially unaffected by the application of additional water for extinguishment. Instruments showed that the water content of the smoke was increased more by the process of combustion itself than by firefighting crews, rising from the time of ignition to the time of extinguishment at a greater rate before than after the hose line was opened. So, once again, the long-taught, and even logical, concern amongst firefighters regarding the creation of steam from the use of water to extinguish fires was not supported by the data.

Consistent with the findings from earlier studies, and traditional teaching, hose streams had the ability to "push" smoke (though "drag" might be a more accurate term when straight/solid streams are involved), generally in the direction of water flow, but movement was minimal, and only persisted as long as water flow continued. This was both predictable and controllable. (It was surprising to this commentator that interior hose crews could propel smoke away even if there was no ventilation opening ahead, though this action was much more effective if an exhaust were present.) Front door control had its greatest effect when the fire room was vented via a window. In the case of an unvented fire, the airflow was minimal if the front door were kept open as crews entered with a hoseline. If vented, though, the flow path thus created between the open door and the open window caused a significant increase in combustion and smoke movement.

Effects on Occupants (People)

Carbon monoxide and heat flux levels were measured at various areas in the structure, corresponding to victims on the floor, on a bed in rooms with an both an open or closed door, and assorted distances from the fire. The lethality of these two components, which increase with intensity and duration, but vary due to victim age, baseline health, and other individual factors, were calculated using a method called "Fraction of Effective Dose" (FED), a probability measurement where an FED of 1 indicates half of persons exposed to this level will die, and an FED of 3 is lethal to almost everyone. The researchers noted that statistics indicate about half of fatalities in residential fires had both smoke inhalation and thermal burns as cause, with smoke inhalation alone killing a third more, for a total of 85% of fatalities in those settings being caused in whole or part by asphyxiation. Heat alone kills “just” 6 percent, while the remainder succumb to variety of other maladies, to include even occasional blunt or penetrating trauma.

For carbon monoxide, the victim on the bed in the room with the open door fared the worst, with lethal levels reached in 2 to 4 minutes, corresponding to when the smoke level descended to that height. For the duration of these tests, anyone lying on floor would probably be just coughing from the smoke or, if within a closed room, completely unaffected. Heat, on the other hand, would likely kill the victim lying on the floor outside the fire room first, and more quickly if the fire were better supplied with oxygen (i.e., it occurred most rapidly when two rooms were involved and the windows in each were open). Unsurprisingly, those victims located furthest away from the fire would likely survive, and the simple protection of a closed door was again proven sufficient to prevent harm from both smoke and heat.

The use of instrumented pig skin was a unique attempt to quantify the potential for damage to skin within the environment of a burning structure. While the temperatures required to cause pain and destruction of human flesh are well known (about 110F and 160F, respectively), the amount of heat that is actually transmitted to, absorbed by, and retained in skin is much more complex and difficult to measure. While this entire question may seem pointless, as we know high temperatures are harmful to unprotected persons in a burning building, there have also been lingering concerns amongst many in the fire service regarding the effect of steam on victims, and the potential for extinguishment efforts to pose dangers above and beyond that from the fire itself.

Pigs, whose skin is close to the structure and thickness of human's, were chosen as an acceptable surrogate for gauging the depth of burn damage. The fact that the skin was no longer attached to a pig, therefore eliminating the effects of underlying blood flow and deeper structures, is an obvious limitation of this model, and was compensated for by placing the skin above a water bath that allowed heat to be conducted through the skin. The experiments found no difference in the extent of burn damage between those exposed to an interior or a transitional attack, while the worse effects were found when no intervention was performed (duh!). More to the point, there was no evidence that applying water to a fire would increase the severity of burns to an occupant.

In summary, all of the various water application tactics - from the exterior, interior, or combinations thereof; and with numerous nozzle types and maneuvers - resulted in prompt fire extinguishment, and did so with similar effects on the interior environment. All in all, the findings were refreshingly consistent with prior studies, and provided further evidence of the benefits of many of our "novel" tactics.

So much of what we do occurs right in front of us, but we cannot see it. Thankfully, the folks at UL have, once again, given us a clearer view of the inside of burning structures.


The author can be reached at

Next: Water Rules #4: Tactical Recommendations

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