By Eric Wahlberg
Plano, Texas, is a large, suburban city north of Dallas with a population approaching 300k. Easily more than half of the homes have been built in the last 30 years. Modern one- and two-story homes with attached garages make up the bulk of these homes. For the purposes of ventilation, they can be divided into three boxes: interior, garage, and attic. These homes range from 1,500 to more than 4,000 square feet, and present significant challenges when on fire, even for a large department like Plano Fire Rescue.
- Flow Paths and Fire Behavior
- Fire Ventilation and Flow Path Control
- Searching in the Flow Path
- Ventilation-Limited Fire: Keeping it Rich and Other Tactics Based Off Science
According to our data, 80 percent of the working fires in these modern homes in the City of Plano start in the garage and extend into the attic or are exterior fires that extend into the attic. We also see several working fires that originate in the attic every year. This means that in most fires we have in these modern homes, we have no active fire conditions “inside the box’ (the interior living area of the home), even though heavy smoke conditions and moderate heat are normal. This allows for rapid horizontal ventilation to clear the conditions that have pushed into the box. I think firefighters are conditioned to believe that when we have a house on fire, all the space inside the exterior walls is directly connected and subject to the effects of any ventilation we initiate. This is not the case. In fact, since most of the fires that our department responds to in modern homes are in the garage and/or attic, the interior box can probably be opened up indiscriminately without making conditions worse, especially if you have effective water on the main body of fire (provided that the garage or attic areas are still isolated from the interior box).
My goal in this article is to simplify the process of ventilating modern homes using data from UL Fire Safety Research Institute (FSRI) construction features of the modern home, and provide a model or best practice approach for mitigating these fires by quickly gaining control of the interior of the home using horizontal ventilation to facilitate search and rescue and fire attack. Subsequent articles in this series will consider tactical approaches for single-story and two-story homes.
FSRI Data
The concept of ventilation is easy—make an opening in the structure to let the heat and smoke out. However, horizontal ventilation is rarely used and because of roof pitch or access issues in modern homes, vertical ventilation can be delayed or impossible. FSRI’s Governors Island findings were published in 2013 and included some critical information for firefighters. First, when you provide ventilation to ventilation-limited fires through doors, windows, or the roof, you can rapidly transition to flashover. Second, they coined the term “flow path” to describe the physical movement of air into the structure through an opening, and the movement of gases and other products of combustion out the same path. Third, water applied to the seat of the fire, whether from inside or outside the structure, rapidly improved conditions throughout the interior. Further, FSRI’s “Residential Home Size-Up and Search and Rescue Operations,” published in May of 2022, found that isolating spaces prior to suppression and rapidly ventilating the interior horizontally after suppression starts will quickly reestablish a survivable atmosphere in ventilated areas.
I suspect that the FSRI concept of how horizontal ventilation creates flow paths that cause the fire to grow and move toward that new opening has greatly reduced the use of horizontal ventilation over the last decade. Controlling the door to limit the fire’s access to oxygen became standard operating procedure in many fire departments. Unfortunately, the act of controlling the door started to be applied to windows, too, with no consideration for the location of the fire or progress of the fire attack, thus delaying the ventilation of the structure. I have spoken with many firefighters who say they don’t like to make any openings they can’t control, which has translated into opening windows instead of breaking them. While there is some benefit in opening a window, breaking it lets the heat and smoke out from the top of the room, which is more effective and faster. Additionally, in most cases, firefighters must access the windows from the interior to open them, since they are usually locked. Locating the windows from the inside, under zero-visibility conditions, takes considerably longer and extends the completion of the primary search. Even for room-and-contents fires that are quickly under control, horizontal ventilation anywhere other than the seat of the fire has become increasingly rare. “Thinking Inside the Box” simply applies data from FSRI depending on which “box” the fire is located in.
Modern Homes
When you break down modern homes into separate spaces or “boxes,” understanding how to ventilate them becomes easier and fire operations become more effective. First, let’s define the modern home. I’m generally referring to homes that were built in the last 30 years. They are 2,000 to 5,000 square feet and have large attic spaces, hip-style roofs, and, in the City of Plano, mostly attached-rear garages. Ceilings of up to 12 feet are also common, and the two-story open concept will have 20-foot ceilings in the foyer and great room. These are large to very large homes that, when charged with smoke, are very difficult to search completely and often make coordinated operations ineffective if there is no ventilation.
The modern home can be separated into three boxes: The interior box or living space, the garage box, and the attic box. The key to quickly and effectively ventilating these homes centers on identifying which box or boxes the fire is in during your 360 size-up and whether an effective fire attack is in place. The FSRI findings provided above give clear direction for the ventilation of these structures. We all know that if the door to a bedroom is closed with fire in another part of the house, that room will be much less affected by heat and smoke. In the May 2022 release of FSRI’s “Residential Home Size-Up and Search and Rescue Operations,” one of the main findings was that isolating a bedroom by closing the door during vent-enter-search (VES) operations improves the conditions within that room rapidly. Truck companies searching for victims and fire ahead of the line are taught to close the door to the room that is on fire, when possible, to reduce the spread of fire and products of combustion throughout the rest of the space. These examples are small versions of the “box” method of ventilation for modern homes. Stated more simply, if there is a fire in a bedroom and the door to the bedroom is closed, only ventilating the window or opening the door to that bedroom will affect fire growth.
A fire in the garage or attic space is usually effectively compartmented from the interior box. The smoke and heat have been pushed into the interior mainly from the attic space through vents and lights, etc. This means that you can rapidly open up the house by taking windows and doors if the fire is in the garage or attic box, in most cases. This will allow the rapid completion of primary search and provide visibility for interior crews. It is important that garage and large exterior fires be attacked from the outside (our department generally employs a 2 ½-inch blitz line). The goal is to knock down these large fires as quickly as possible. Handlines can then be stretched inside to address the remaining fire in the attic once the truck company has ventilated the interior and, optimally, completed the primary search.
FSRI data also shows that once suppression begins, ventilating the house as quickly as possible to remove heat and toxic gases is the best course of action when the fire originates in the interior box. In other words, you can’t spread the fire to uninvolved spaces or cause hostile fire events once you have effective water on the main body of fire. Effective water from the first attack line removes the energy from the fire and cools the atmosphere, allowing horizontal ventilation without negative results.
Effective water means enough water to knock down the main body of fire. Knocking down the main body of fire removes any active flow path. FSRI data shows that with knockdown, all areas of the home improve rapidly with reduced heat and levels of toxic gases. Since most of the fires in modern homes start in the garage or attic, I strongly recommend large lines and blitz-style attacks to gain control of the fire as quickly as possible. The garage and attic in modern homes are large spaces that respond well to heavy streams. The good news is that even when fire has penetrated the interior box from the garage, horizontal ventilation can be initiated almost simultaneously with attack resulting in no negative effects on the interior. I will usually wait to open the main body of the house if there is significant extension from the garage or certainly the exterior into the living space. The fire doesn’t have to be out; I just look for a change in conditions indicating that the fire attack is effective on the main body of the fire affecting the interior.
The Three Boxes
The FSRI studies looked at interior fires for obvious reasons: these are the most dangerous for occupants and require firefighters to access the interior space for search and rescue operations and fire attack, making it dangerous for us as well. I know there are many departments that have primarily interior, or room and contents fires, but with close to three decades of service with the Plano Fire Rescue, I can tell you that our most likely working fire is the attached garage fire. We also get a good number of attic fires from exterior fires that burned into the attic or lightning strikes. As with most jurisdictions, cooking fires are the most prevalent in the interior box, but those are mostly incipient in nature and controlled with the can or extinguisher. Kitchen fires are rarely fully developed, have not created an active flow path, and haven’t progressed to zero-visibility conditions. Garage and attic fires sometimes will gain the interior box if a hollow-core wood door to the garage burns through, or a large backyard deck space is involved on the exterior that auto-exposes through a door or window. However, most of the time these fires are compartmented to the garage, garage and attic, or just the attic space.
Interior Box
Anytime the living space of the home is involved in fire, the risk of fire victims is higher. The 2022 UL “Study of Fire Service Residential Home Size-up and Search and Rescue” looks at this problem and provides great data on what is happening inside. Since the experiments looked specifically at the relationship between the effects of ventilation pre- and post-suppression on interior fires and the adjoining spaces, the data developed allowed FSRI to make best practice recommendations for ventilation and search and rescue. FSRI also confirmed the things we all know from operating inside the box: the upper atmosphere is hotter than the floor, conditions behind a closed door are much better than if the door was open, and either closing a door behind you and venting the space or entering from the window and closing the door to the room prevents the conditions in the space from getting worse. Also, when water is applied to the seat of the fire, things get better immediately.
Because our objective is to gain control of this box for search and rescue and to confine and extinguish the fire, understanding when you have fire in the interior box will determine how you horizontally ventilate the space and initiate the search.
Garage Box
In modern homes, garages are built to keep fire out of the living space of the home, provided the interior door to the garage is closed. Although the International Residential Code (IRC) does not require a fire-rated assembly, ½-inch drywall walls and ceilings (ceilings are ⅝ sheetrock when there is living space above the garage) provide good fire protection. Doors between the living area and garage are required to be 1⅜ solid wood, a full metal door, or an actual 20-minute rated fire door. These doors are very good at preventing fire from entering the living space. In many cases, there is an attic scuttle or drop stairs so garage fires rapidly extend to the attic. Whether or not these fires are through the roof on arrival, we normally find heavy smoke in the living area and moderate heat conditions even when the fire has not extended through the door to the living space.
Attic Box
The attic is the third box, and although there are penetrations to the living space through HVAC vents and can lights, fires do not burn down readily. Garage and exterior fires that involve the attic space must be dealt with before accessing the attic space from the interior. Until the main body of fire is addressed, you will probably not have very good results attacking an attic fire from the interior. Attic fires can present completely clear inside to zero-visibility conditions. Whether you are on the truck or engine, anytime you find clear conditions inside, get a run through primary search prior to attic access. Even when interior conditions are clear initially, conditions usually go to zero visibility or close to that once interior crews breach the drywall to access and attack the attic fire. Horizontally ventilate prior to opening the ceiling, including “vent as you go” for search personnel. Use positive pressure fans, if needed, to maintain a clear space or some visibility from the front door to back door or exhaust opening. Vertical ventilation is definitely indicated for ventilation-limited attic fires, but due to the size and fire load in these large attics, water in the attic is a must before opening the roof. The coordination of ventilation and attack is essential for successful operations.
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Horizontal ventilation may have become something of a lost art, but it remains an effective tactic. If you understand how fire in the modern home is compartmented and the location and extent of the fire, these large structures can be rapidly ventilated. Additionally, FSRI data clearly shows ventilation through VES and horizontal ventilation promotes the improvement of interior conditions, facilitating primary search, returning survivable atmospheres in the living space, and visibility for ongoing interior operations.
Eric Wahlberg is a 28-year veteran of Plano (TX) Fire Rescue and is a captain/paramedic assigned to Truck 2 on C Shift. He is a Master Firefighter with the state of Texas and holds numerous other certifications with the state. As a firefighter he has served on the special rescue and hazmat teams and was a flight medic for almost two years.
References
Governors Island Experiments: Research for the Development of More Effective Tactics https://fsri.org/research/governors-island-experiments
Analysis of Search and Rescue Tactics in Single-Story Single-Family Homes Part III: Tactical Considerations. C. Weinschenk and K. Stakes, UL’s Fire Safety Research Institute, Columbia, MD 21045, May 17, 2022.
https://fsri.org/research/study-fire-service-residential-home-size-and-search-rescue-operations
