Much of the energy expended in promoting, discussing, and opposing Modern Fire Attack (MFA) methods regards the use of exterior streams for controlling fires in structures, an understandable focus given the rather revolutionary, and therefore controversial, nature of the research findings. (In a nutshell, applying water from the outside was found to be a whole lot more useful, and a whole lot less harmful, than we had believed.) Drowned out in the noise of this debate, so to speak, have been several more specific, but no less remarkable, water application directional recommendations that were also supported by the results of these studies. This post will focus on circumstances that benefit from an alternative approach – literally – for fire extinguishment.
Attics, basements, and the outsides of structures are settings in which fires demonstrate some unique, but predictable, behaviors, requiring appropriately unique, but logical, tactics for their control. Not surprisingly, given that I am including this topic in the Modern Fire Attack (MFA) series, the fire dynamics studies have produced guidelines that are not necessarily those we have been taught and practiced for decades. Also, unlike the use of exterior streams for interior fires on the ground, second, and, occasionally, higher floors, which are being offered merely as an option for initiating fire attack, to be utilized when that route is quickest, the recommendations for these settings are intended to be the default approaches, to be followed in most cases. That’s right: When presented with fires in one of these areas, researchers haven’t merely found us another way; they’ve determined the ideal way. Though deviations from these new tactics are appropriate when circumstances dictate, they represent water application best practices. Not only did the studies point out that our previous tactics did not necessarily provide the effects we expected or believed, but new insights were provided that supported a shift to methods that are more likely to result in improved effects. (Please note that the following discussions and recommendations are applicable when a fire is in an advanced state. Incipient blazes in these or any settings can almost always be managed via whatever approach offers the most direct access.)
The space beneath the roof of a dwelling, regardless of its volume, is typically engineered for natural ventilation, with cooler air flowing in through the soffits, warming after entering the interior space, rising up along the underside of the roof deck, and exhausting out the ridge, roof, or gable vents. This circulation is designed to remove water vapor from within the living space and prevent its condensation, but also unintentionally promotes fire extension into the attic, especially from an outside fire. Still, this baseline air flow is insufficient to support unlimited combustion of the structural members in that enclosed compartment, much less any contents, even if the gable and roof vents fail. Fires in attics therefore typically and quickly become ventilation-limited, even more so than lower levels of a structure that have more windows and doors. Opening the roof or gables will merely increase the rate of combustion, and subsequent heat production and structural deterioration, while providing no benefit. (As I have noted previously, the impressive ball of fire that erupts from a ventilation h*** represents a worsening of conditions, not an improvement. What is occurring in those instances is that heated, over-rich gases are suddenly being introduced to a sufficient supply of fresh air, resulting in almost explosive combustion. Firefighters who ventilate burning compartments are not releasing heat; they are creating more.)
Not only is tactical ventilation a challenge in these settings, but so is extinguishment. It was noted by researchers that the underside of the roof deck can represent over 50% of the surface area of combustibles in a typical attic, and that wetting the entirety of these surfaces is a necessity to ensure complete extinguishment. But, even if water can be played in from the gable ends of an attic, rafters usually block it from reaching all of the burning areas, necessitating a different approach. On a more positive note, our previous fears of fire extending downward if the upper floor ceiling/attic floor was breached were debunked, at least partially, in that it was found that heat, fire, and smoke will remain in the attic unless a flow path is created in a downward direction, usually requiring the addition of wind entering from above and forcing products of combustion out of a lower floor opening. (Yet another reason to avoid cutting roofs.)
Putting all of this new knowledge to practical use, from a water application point of view, the recommendation is that the extinguishment of attic fires should be undertaken from below, either from the interior through the top floor ceiling/attic floor, or from the exterior by playing streams into the soffits. Through ceilings, piercing nozzles can be used for initial knockdown, but punching through a small h*** and introducing a straight or solid stream will have a similarly beneficial effect. Once the compartment is cooled, all burning surfaces must then be wetted, a tedious, but necessary, chore. From inside the structure, one technique is to remove a longitudinal section of the top ceiling/attic floor, creating a “trough” from which streams can be directed into each of the rafter spaces. When possible, this access should be parallel to, and directly beneath, the ridge line, which frequently coincides with the location of the upper floor hallway. Opening the attic in this manner also expedites the removal of any combustible insulation or other contents, which can be shoveled/swept from the attic floor and down into the hallway below. Alternatively, and somewhat more painstakingly, sections of the ceiling can be removed along the outer walls, parallel to the ridge line, to allow access for streams to play into each rafter space.
From the outside of a structure, playing water into the soffits allows it to follow the path of that space’s passive ventilation, along the bottom of the roof deck to the ridge. Streams so directed will also rain down upon any burning contents and other structural members. Accessing the soffits can be a challenge, whether due to distance from the ground on anything but a one-story structure, or the use of solid wood coverings in older construction, but, once achieved, offers a route for wetting between each rafter. Modern construction, with lightweight, perforated coverings, can be more easily removed, if they have not melted away already.
So, for attic fires, the “new direction” provided by researchers is to apply water from below, via an existing or newly-created opening through the top ceiling or soffit, and then to methodically wet the entire underside of the roof deck and any burning contents. While a painstaking process, the elimination of the need for opening the roof or gables has the potential benefit of freeing up crews who would previously have been committed to those efforts. The result is a process that has demonstrated benefits and reduced hazards, a winning combination.
Next installment: Basements and Exterior Fires
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