In a 4-month period during 2007, 54 firefighters lost their lives in the line of duty. Eighteen of those firefighters were killed after becoming lost, caught or trapped in structures. Numbers like these should motivate us to ask why our current fire attack tactics aren’t sufficient to allow us to fight structure fires in a way that gets the job done, protects occupants and prevents us from getting killed in the process.
One major element of structural firefighting that’s changed in recent years: building construction. By now you’ve heard about how lightweight construction changes the way fires burn. But in many cases, we’re still approaching fires the same way we did 30 years ago.
In this article, I’ll share some suggestions for how to understand fire behavior in lightweight structures, and for how crews can modify fire attack to be successful in lightweight structures. Specifically, I’ll discuss hose and nozzle selection for fighting fires in lightweight structures. In a future article, I’ll address ventilation and search-and-rescue (SAR) tactics.
Fire Behavior
Let’s start with the basics: Lightweight, wood-frame buildings burn extremely fast and hot. If the fire breaks out of the container (or room of origin), then it’s “off to the races.” As fire exits a container and vents to the outside of the structure, it will spread upward very rapidly, involving everything combustible in its path. Fire venting from a window or door will quickly burn into combustible truss voids. Once fire has entered the void, the roof decking will burn through and the truss may collapse in less than 5 minutes. The fire will also enter the overhead and/or floor void from within the container. A post-flashover fire will not be contained, and the fire and super-heated fire gases will penetrate through numerous pathways into combustible void spaces.
Fire in lightweight steel (non-combustible) buildings also spreads quickly. The rapidly growing contents fire will quickly heat the lightweight steel trusses and structural members, causing rapid collapse. These lightweight structural systems are often not protected by any fire-rated membrane or sprinkler system. (Note: The best time to discover this situation is while conducting inspections and preplanning.)
So why is fire behavior in lightweight structures so unique and deadly? Since the late 50s and early 60s, structures built of wood and steel, or any combination of the two, have utilized lightweight building design and lightweight structural building components, such as gusset plate trusses, plywood, wood I-beams, OSB sheeting and other engineered systems. Gone are the days of solid-sawn dimensional lumber joists and decking.
In addition, as structures get lighter in structural weight, they’re loaded with contents and furnishings that burn hotter and more quickly than ever before–a deadly combination for building occupants and firefighters.
What does this mean for us? We have NO time! Once the fire has flashed in the container, the container can no longer hold, absorb or contain the heat. As fire enters combustible lightweight voids, collapse is imminent.
Change Things Up
The tactics I learned more than 30 years ago were developed by firefighters who fought fires in conventionally built structures. Clearly, these tactics will not work in lightweight structures and, as such, we must modify our tactics.
Modifying tactics means operating from protected positions until we can control the fire and verify that fire is not in the combustible voids above and below us. We should not enter a structure without clearing the overhead void and the floor void.
Fighting fires from the interior, being aggressive with advancing the nozzle, search and rescue, ventilation, opening voids, and chasing down the fire until we get to clean wood–these are all sound tactics that are still applicable today. The difference for lightweight structures is in how we employ these tactics, how we access the voids, how and where we vent, the time and ability to enter and search, and the time and ability to attack from the interior. For example, although we must be aggressive in our actions to save lives and property, we need to be smart with our aggressiveness. We need to look at every situation from an intelligent and calculating position before engaging in a course of action.
Hoseline Selection
The initial hoseline should deliver enough water to overwhelm the fire, knock it down and gain control. It is crucial to escape the 1 ¾” hoseline mindset. You will not overwhelm the fire with a fire stream from a control or fog nozzle flowing 150 gpm or less. Thus, hose size and nozzle selection are critical to your ability to overwhelm the fire and quickly gain control.
An example: Several years ago we had a fire in a three-story center hallway apartment complex. The structure was built of lightweight, wood-frame construction with a flat roof. The fire originated on the wooden porch or balcony of a second-floor apartment. The fire broke through the sliding glass door and extended into the apartment. Typical to this type of construction, a wood porch for the third-floor apartment was located directly above. The fire spread upward and involved the wooden porch, then spread into the third floor apartment. The fire also began to burn into the flat roof mansard void.
On arrival, fire crews were confronted with an exterior flame front from the second- and third-floor apartments that were totally involved. The fire had not yet extended into the center hallway; however, the hallway was full of dense smoke, preventing the occupants from exiting the building. Residents of adjoining apartments required immediate ladder rescues.
As ladders were being placed for exterior rescue and crews were entering the building to begin search-and-rescue (SAR) efforts and stretch hoselines into the center hallways, a lone firefighter stretched a pre-connected 2 ½” hose with a 1 ¼” solid stream nozzle to the fire extending on the exterior of the building. The firefighter lined up with the burning apartments, sat on the hoseline and called for water. The line loaded with water and the firefighter opened the nozzle, directing the stream into the second-floor apartment. That apartment blackened down and the stream was raised to the third-floor apartment. With the third-floor apartment blackened down, the stream was directed to the roof mansard, and that fire was blackened down.
In 60 seconds, enough water was delivered from the initial line to overwhelm the fire and bring it under control. This action prevented the fire from extending into the interior hallway and allowed the interior crews to enter and search uninvolved apartments. Several occupants were rescued over ladders, and the remaining occupants were removed through the interior. Crews were able to enter both of the involved apartments, complete extinguishment and begin overhaul operations.
So why was the exterior line so effective? Let’s take a closer look. And don’t freak out that this was an exterior line. The firefighters were still aggressively stretching interior lines to gain control of the center hallway to support SAR efforts and control the fire if it extended.
The initial line was deployed from a protected (in this case, exterior) position and able to overwhelm the developing fire. A 1 ¼” tip delivers 325 gpm at 50 psi nozzle pressure with an effective reach of 50 feet. Clearly, 325 gallons per minute is a lot of water, and the solid stream has incredible reach and penetration capabilities.
This line can be deployed within seconds of arrival, making it a very effective tool for bringing a rapidly extending fire under control until you can reinforce your positions for rescue and interior extinguishment. We’re talking about stopping the runaway train by taking the steam out of it. This action will buy you time to rescue threatened occupants and get interior lines into position. It’s effective and fast.
Know the Numbers
Is your department set up to deliver the knock-out punch with an initial fire stream that can be deployed within seconds of arrival? Does your crew drill on this evolution so you’re proficient? Are you maximizing the flow potential from hoselines by using solid-stream nozzles? Control or fog nozzles will not give you the same reach and penetration capabilities as a solid stream. It’s a fact.
Do you realize you can flow 400 gpm through your 2 ½” hoseline? How? Bump the nozzle pressure to 80 psi on a handline that’s anchored on the ground by you sitting on it and another firefighter backing you up. If you don’t believe me, try it out. If you thought 325 gallons was a lot of water and an effective stream, try 400 gallons at 80 psi. Remember, your effective reach increases to 80 feet.
If you’re thinking about buying one of those fancy lightweight ground monitors (blitz monitor), a cheap alternative is to line up on your target using a 2 ½” line with a smooth-bore nozzle, sit on the line, lift the nozzle into position and open it up. You’ll be able to elevate and sweep the nozzle without any problem, because the back pressure is being directed into the ground. Obviously, if you lower the nozzle you will begin to feel the hoseline slide from the back pressure. And, of course, safety is always paramount. The key to success is to practice and understand your capabilities and limitations.
Note: With a solid-stream nozzle, flowing 325 gpm at 50 psi produces a back pressure of approximately 120 lbs. The back pressure at 80 psi, flowing 400 gpm, is approximately 195 lbs. For comparison purposes, a fog nozzle in a straight stream flowing 325 gpm has a back pressure of 162 lbs.; at 400 gpm, it is 200 lbs.
You might be wondering: “Can you put the line into operation with tank water while you wait for your supply line?” This is a risky venture. It takes 50 gallons of tank water to load a 200′ pre-connected 2 ½” hose. With a 500-gallon tank, once the hose is loaded, you’ll have a maximum of 400 gallons for flow through the nozzle. That’s approximately 1 minute of flow from the 1 ¼” solid stream tip at 325 gpm. That’s enough time to knock down a lot of fire, but can you secure an uninterrupted supply to the pump in 1 minute? Bottom line: It is always preferable to establish a supply line to the pump when pumping 2 ½” hoselines. Circumstances will dictate. If you’re drilling and practicing these evolutions, then you’ll know what to expect and how much time it may take.
The firefighter on the nozzle can always buy more tank time by controlling the time of flow. If your nozzle has a 1 ?” tip, you would flow 250 gpm. At this flow you would buy some more tank time and still have an effective fire stream. Once the supply was secured, you could bump up to the bigger tip or increase your nozzle pressure. The 1 ?” tip at 80 psi will flow 300 gpm–not bad!
Tactical Adjustments
So how do we apply this hoseline and nozzle selection to fire attack? The age-old method of aggressive interior attack may not be the best initial deployment option with lightweight construction. Consider the following scenario:
You roll up on a single-family dwelling of lightweight construction. The dwelling is approximately 1,600 square feet with light-colored, low-volume smoke showing from the soffit and eaves.
As you make entry, there’s no perceptible heat at the point of entry; you observe smoke beginning to build at the ceiling level, and visibility is still fairly clear. Odds are you can get the primary search completed, vent the structure, locate the fire quickly and extinguish it.
Although I would agree with the initial size-up, I will suggest some tactical adjustments. Before entering the structure, did you complete a 360-degree walk-around and add information to your size-up? Did you determine where and how to vent the structure? Are there any indications of heat build-up from the exterior? What do you see through the windows? Any indications of a basement fire? Did you run into an occupant? Any cars parked in the driveway? Did you determine the fire location?
As you enter the structure, open the ceiling above your head and take a quick look. Is the void clear of smoke? What is the roof construction? Based on what you see, are you comfortable proceeding under the void? Note: It’s possible to have significant fire in an overhead void and not know it.
As you develop the answers to these and other questions, you may well decide to go for an aggressive interior attack, or not. How long does this process take and how much valuable information can you obtain? The answer: It takes only moments, and the information gained will allow you to make intelligent decisions on how aggressive you can be in solving the problem from the interior. The primary search can be completed quickly, vents made, positive pressure ventilation (PPV) blowers set at the entrance point, the fire extinguished, the void opened and cleared. It’s a bread-and-butter operation.
But what if I change the scenario a bit? Let’s keep the same structure, but this time, on arrival, you have pressurized dark brown smoke coming from the eaves and soffit. On your walk-around, you note a failed bedroom window with fire venting from it. As you gain access, you encounter high heat and a thick blanket of black-boiling smoke banking down at the ceiling level. What are you going to do?
- Do you still need to complete a primary search? Yes.
- If there is an occupant in the structure, are they still viable? The answer depends on fire severity, time, location and our ability to enter. Obviously, if there is heavy involvement, then occupant viability in the fire area is doubtful. An occupant could still be viable if they’re far from the fire, in a closed room, or in a basement. But now firefighters’ lives could be at risk. This is wholly situational and will be a difficult and courageous decision on the part of the incident commander and/or company officer.
- How will you vent this fire? Can you pressurize the structure to assist the natural ventilation process? Large truss voids can and will fill with super-heated fire gasses (black-fire) that are laden with carbon monoxide and other combustible fire gasses. Experience has taught us that we can have void-space backdrafts that will blow down ceilings and cause fire to be driven down into the occupied space, causing conditions to deteriorate very quickly. These backdrafts can be caused by structural failure, allowing fresh air into the void, or from firefighters pulling ceiling and admitting fresh air. This reinforces the fact that we should open the void from a protected position to assess conditions before we commit ourselves underneath the void. If the fire is in the overhead void, our ability to vertically vent is eliminated. The quickest way to vent this structure is to take out windows (if they have not already failed) nearest the fire and pressurize the entry or air-in point. The fire in our scenario had already vented. Pressurization will only enhance the movement of heat and fire gasses toward the vent and following the path of least resistance. Pressurization should also clear the entry point, making it easier to open the ceiling and assess conditions overhead prior to entry.
- Can you access the overhead void from your protected position at the door to assess conditions in the void? As in the first scenario, you should assess the overhead void before entering the structure. Firefighters moving in under a lightweight void that’s involved in fire or charged with super-heated fire gases have placed themselves in a very risky position. With a pike pole and hoseline at the entrance point, water can be directed into the involved void, gaining control of the fire in the overhead, cooling and inerting the void prior to making entry.
- Could you bring a second line around to where the fire is venting and take some steam out of the fire while you assess the void from your entry point? An exterior line can knock down the room fire and the stream can be directed up into the soffit or punch through the ceiling of the room to get water into the involved overhead. Solid stream nozzles will not push fire and smoke toward the crews entering the building. The stream from the outside is directed toward and deflected off of the ceiling and into the truss void if necessary. This does not create an opposing fire stream situation. Note: The officer and/or firefighter monitoring the exterior line can and should communicate with the line being brought into the interior.
- Once inside the structure, where are protected positions? A protected position is one that gives the firefighter protection from collapse of ceilings, roofs and floors: the hallway, standing inside door openings, against walls, or in an entry vestibule. An attack line operated from a protected position can control the void fire.
- Once the void is cleared, can you enter for the primary search and final extinguishment? It’s critical that you rule out a basement fire or fire in the floor void space before you enter. There is no protected position inside the structure when the floor you are on is burning out from underneath you.
Lightweight structural steel systems (roll-bar joists and metal decking) will heat rapidly when exposed to super-heated fire gasses. Again, the most effective tactic is to cool the steel with a fire stream that has adequate volume, reach and penetration. Cooling the steel will prevent collapse. Operate from protected positions and open voids and clear them and/or cool them before and as you enter. These lightweight steel roof systems are typical to commercial structures, and many commercial structures have very high ceilings and roofs. Firefighters entering the building may not see the large volumes of black fire at ceiling level or in voids. Always check the overhead before you enter; if it’s hot, gain control by opening and cooling it.
What tools do we have that can help get water on the fire while in a protected position? Void space fires can be extinguished in a traditional way: Open it up and put water on it. Or they can be extinguished from a protected position with special application nozzles, such as distributors (cellar nozzles/Bresnan distributor, etc.), wand nozzles and piercing nozzles. These special application nozzles can be supplied by 1 ¾” hose and have flow rates between 100 and 150 gpm.
Practice deploying these devices from the tip of aerial, platform and ground ladders. Our department has had tremendous success using special application nozzles while training on live-fire conditions in attic and basement fires. We’ve also had great success opening the gable end of a roof with a chainsaw and directing a fire stream into the involved attic void. All of this is done from a protected position.
At a recent dwelling fire, firefighters moved aggressively to horizontally vent the structure, enter the interior to complete a primary search and extinguish a room-and-contents fire. The ladder engineer placed the aerial at the roof and had deployed a chainsaw and wand nozzle in anticipation of the fire breaking out of the container or room of origin and entering the lightweight truss void. This is a result of practice and drill.
In Sum
There are many protected positions to operate from in a lightweight structure. The primary point is to assess your conditions prior to making entry. Experience shows that an unchecked void fire will cause conditions on the interior to deteriorate so quickly that firefighters operating underneath the void can become caught and trapped. Plus, you can have substantial fire in an overhead void and not be aware of it until structural failure occurs and/or the fire breaks out into your space. This scenario has happened many times and killed numerous firefighters.
Remember: Be calculating in how aggressively you attack fires in lightweight structures. The fundamentals we were taught many years ago still hold true, but we must adjust our tactics for the new construction types. Failure to do so will only result in more firefighter deaths.
The Solid Stream
When it comes to large flows, solid-stream nozzles are key
When fighting fires in lightweight structures, consider maximizing fire flow from 1 ¾” hoselines by using solid-stream nozzles.
A 1″ solid-stream tip at 50 psi will allow you to flow 200 gpm through a 1 ¾” hoseline with a friction loss of 50 psi for each 100 feet. A 15?16” inch tip will flow 180 gpm at 50 psi nozzle pressure, with a friction loss of 40 psi in 100 feet of hose. These are highly effective fire streams that carry a solid punch in terms of reach and penetration for interior fire attack.
Two hundred feet of 1 ¾” hoseline with a 1″ solid-stream tip flowing 200 gpm will require a pump discharge pressure (PDP) of 150 psi. An automatic control nozzle on the same hose line will flow 150 gallons for that same PDP. Which line do you think will be the most effective firefighting tool?
