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Engine company ops: What the research tells us about our tactics

Understand the power of flowing a steep, straight and steady stream


If we understand the basic principles and truly want to do what is best for the potential victim, then flowing water from the interior or exterior should no longer be a debate.


Battalion Chief Chad Christensen presents “Evidence-Based Engine Operations” at FDIC 2024 on Wednesday, April 17.

LA - Engine 9 on scene. We have fire showing from the second floor of a two-story single-family dwelling on the Alpha side. Now what?

This is the question we should all be asking ourselves. Some will say the answer is simple: Stretch a preconnect to the front door and go get it. But in today’s ever-changing fire environment, it might be that simple and it might not. Furthermore, fire dynamics, building construction, air entrainment and water-mapping principles of our hose streams can make that decision more complex.

The easy decision is to get a line stretched and flowing water. Consider this, though: If you have fire venting from the A-side window on the second floor, do you flow from the exterior or not? Is the front door open or is there a forcible entry issue? The decision can be simple but really only if you understand the fundamentals of fire dynamics in relation to building construction and water application.

If I have a charged hoseline, fire venting from an A-side window on the second floor and people masking up or forcing entry, then why not flow some water into those windows? A good company officer will have done a 360-degree size-up, and with the fire venting from a single window, the officer knows the fire location. If we flow from the exterior, we can get the search team in ahead of the hoseline. If we choose to wait to force entry, mask up, make entry and flow upon making the second floor, the time spent delaying water application to the seat of the fire could be the difference between a grab and a body recovery.

The better we understand the fundamentals, the easier our decisions can be made. This doesn’t mean that every fire should be looked at the same way nor should we always flow from the exterior. Understanding how and when is part of the decision-making process, and you have a few seconds to make the right decision for the people we took an oath to protect.

Research makes the case

Thanks to years of research, we can now understand the residential fireground far better than we did in the past. When we (the members of the technical panel) embarked on the research project with FSRI for the residential fire attack study, we knew that water flowed from 1¾-inch hoselines, and that combination nozzles were the tool of the West Coast, with the smoothbore being the tool of the East Coast. We also had a good idea that flowing from the exterior of a building could have positive and negative implications on the fireground, but we didn’t know why or how.

We now understand that the American fire service nozzle, regardless of your choice a combination or smoothbore, perform equally as well on the fireground. When it comes to reach of stream, air entrained in the stream, and how water coats surface to cool and contract gases, the nozzles perform equally well.

It is up to you to do the research to ensure that you have the right hose and nozzle combination to meet the needs of your organization and built environment. What works for me on the West Coast may not be what works for you in your department and built environment. It is critical that you understand how both nozzles work. Every hose and nozzle combination needs to be tested to ensure that it will get you what you’re looking for on your fireground. What we do understand is that every nozzle has air entrained in the stream, and when we move the stream, it entrains more air.

You might be wondering, “Why do we care about air entrainment?” We care because it is the foundational piece of what we do. We flow water, cool and contract gases, and need to bring in replacement air to improve visibility with coordinated ventilation. It goes back to understanding the fireground and its basic physical principles of high pressure and low pressure. As we cool gases on the approach, we begin to reduce temps and lower pressures in the entire structure. As we reduce the pressures and temperatures, we need to bring in replacement air to improve visibility and exhaust the toxic gasses with ventilation. With this knowledge of cooling equals contraction and not expansion, as once believed, we can improve our extinguishment culture and understanding. As gases cool and contract, we need replacement air to be brought in to allow the smoke to be replaced by lower pressure cool air. This tactic, in coordination with ventilation, can improve conditions for the victims and search crews in a more efficient manner.

We do this on our approach by flowing and moving down the hallway and bringing air with us. An open nozzle moving on any pattern can bring 6,000 cfm of air with it on the approach to the fire room. We seal off the flow path from the fire room and the rest of the structure as we flow and move down the hallway. We are immediately having a global impact on the structure by reducing temperatures throughout. As the nozzle firefighter is flowing on the approach, search crews can take a more global approach to searching. Knowing the flow of water is positively impacting the structure, we can turn our search focus to being more targeted and improve our ability to save more lives.

We were wrong about water

The other key factor to understand is how water travels across surfaces. We once were taught that if we flowed a straight stream against a flat residential ceiling, water would rain down into the center of the room. We were wrong. Water will ride the surface and coat the entire ceiling before it rains down the walls of the space. The steeper angle you take with the stream, the better surface coverage of a room you can get. We must coat the surfaces to cool them and contract the gases that are burning to allow us to get into the room and extinguish the surface fire in the compartment.

One concern has been what about the steam we are creating – a great question and significant concern of the fire service. What we found is the fire environment is wet prior to extinguishment. The byproduct of fire is water, and our application of water reduces the moisture in the compartment as opposed to adding to it. If we are putting water into a flashed-over compartment that is over 1,500 degrees, we are getting 100% contraction in our extinguishment efforts. Thus, we need to use these findings to improve our tactical choices on the fireground.

Steep, straight and steady

What tactical choices can we employ on the fireground together? The research has given us the tools to work with and allows us to develop our own process and application of the tactical considerations.

If you are presented upon arrival with the ability to flow from the exterior as crews are making their way to the second floor, can both happen simultaneously? Absolutely they can! If the firefighter on the exterior understands that they can flow steep, straight and steady into the second-floor window, then they will have no negative impact on the interior crew or potential victims. They will have a positive impact on the entire floor all at once.

Again, as we understand how water travels, it is important to remember that a steep, straight and steady stream into a window focused on the inside of the windowsill or lentil will travel the surfaces and rain down the walls. The worst thing that could happen to the search crew entering that room is they get wet from the water raining down the walls. We have found that the power of cooling and getting water into the fire compartment has a greater return on investment than not doing anything at all.

This same concept can be used while crews are advancing a hoseline down a hallway or up to the second floor. One NFPA requirement is to have a backup line. Just because we know that proper water application (mapping the space) and quick water will result in less water than we think to extinguish the fire doesn’t mean we don’t need a backup line. If you have fire venting on the “B” side of a structure and the best access is the front door, should we be pulling the initial line to the B side window? It depends on your staffing, apparatus arrival and your built environment. What I will say is if you pull that line to the “B” side first, consider leaving it in place and pulling another line. Re-positioning hoselines can be time consuming and staffing-intensive. If we leave or pull a second line to the “B” side, we accomplish the backup line and can flow from the exterior again if needed.

Know that your hose stream is a line-of-sight tool. If we can’t get water into the compartment, we need to consider alternative methods to get water where it needs to go. One method we have found to be very effective is following up an exterior water application to a second-floor window with banking the stream off the lintel or windowsill. We have also seen positive effects in banking the stream off the door jamb on your approach down the hallway. Being creative in how you get water into the fire compartment is up to you and your response model.

Mission-first mindset

The ultimate focus needs to be on the potential victim. If we understand the basic principles and truly want to do what is best for the potential victim, then flowing water from the interior or exterior should no longer be a debate. We should understand that if we employ good fireground discipline and good tactical choices, then we can search ahead of the hoselines. We can flow from the interior and exterior at the same time.

Good communication and coordination are key concepts to allowing us to be even more aggressive with our approach on the fireground. Some will debate that we can’t have opposing hoselines or crews operating opposite of a hoseline. This may have been true prior to our understanding of how to appropriately flow our hose streams into a compartment fire, but now more than ever, we need to be willing to employ tactics that work to save lives and property. This goes for exposures as well! If we put water on the fire, the problem goes away. If I decide to flow on the exposure building, we are not addressing the problem at hand. Water on the fire is the best tactical choice we can make.

Final thoughts

Today, we should approach the fireground with a view of how we can improve the fireground we are faced with quickly and most efficiently with the resources you have responding. Are we pulling one line and going inside? Are we pulling multiple lines and flowing from the interior and exterior? These options are just that – options. The better you understand the research and the modern fireground, the better firefighter, company officer or chief officer you will be.

Even though it seems like a simple decision, the fireground is a challenging place to make life-saving decisions in split seconds. The self-study required to be the most efficient fireground operator is the foundation to providing the best decisions for your people and those you serve. FSRI has provided the fire service with amazing tools to continue that self-study and allow you to pair it with your fireground experience to make the best decisions for them.

About the Author

Chad Christensen is a battalion chief with the Los Angeles County Fire Department where he has served since 2002. Christensen is a founding member of the LACoFD Fire Behavior Cadre and is the lead fire dynamics instructor for the department. He helped implement fireground tactical changes in Los Angeles County starting in 2012 based on UL Fire Safety Research Institute research and continues to update department tactics based on new research. Christensen previously served as a technical panel member for the FSRI Fire Attack Study and the Coordinated Fire Attack study and is a current member of the FSRI Fire Dynamics Boot Camp Instructor Cadre. Christensen assisted in the roll out of NFPA 1700 with FSRI’s online training program and ISFSI’s regional training and has helped agencies across the country in developing live-fire training programs.