Commentary

Commentary: Changing Directions II: Basements and Exteriors

Commentary by Mark J. Cotter

Photo courtesy of UL Firefighter Safety Research Institute

Firefighters have been provided with new extinguishment strategies that offer better speed, effectiveness, and safety. A triple win! Continuing on the theme introduced with my last post regarding the new fire attack vectors recommended by fire dynamics research, first addressing Attic fires, now we will cover the practical application of those findings to enhance our ability to control fires in the subsurface level and the outside of structures. Again, the scientific analysis of the burning environment found that, in at least these three locations, the nontraditional approaches to fire control that were suggested were not merely optional, but actually optimal. Fortunately, any fire department can readily implement these improvements basically by reading this article and following the advice within (though readers are encouraged to review for themselves the technical reports that can be accessed via the links below).

Basements

Fires in the below-ground level of a structure present, in many aspects, challenges that are both similar to and the opposite of those faced in attics, and which are no less daunting. Access is just as, if not more, limited, and fires also become ventilation-controlled quickly. Regarding attack paths, though, that setting is much more challenging. The traditional tactic of stretching the hoseline down the basement stairs places firefighters in the exhaust side of a potential flow path, while often requiring that they first traverse the potentially fire-weakened floor overlying the burning compartment. Furthermore, it has been shown that directing water streams down the stairs into an involved basement provides limited cooling, and therefore limited protection for firefighters. Finally, there is no reliable method for assessing the stability of a floor structure above a basement fire, short of the development of visible sagging or flame penetration, with both traditional (“sounding” the floor with a tool) and modern (use of a Thermal Imaging Camera [TIC]) methods to detect structural deterioration found to be lacking.

The availability of a ground-level “BILCO” door avoids much of these difficulties and should be utilized when available. (Such access also renders the burning compartment, essentially, a poorly-ventilated space with a collapse-proof floor.) Regardless of the presence of a same-level entryway, cooling of the basement should be initiated as soon as possible to interrupt combustion and reduce temperatures to a level tenable for firefighters. This can often be accomplished by spraying water into one or more basement windows or, if none are available or compartmentation limits stream penetration, through penetrations firefighters make for that purpose. Access for water streams into the basement space can be cut into the floor just inside a door or window, the location of which allows firefighters to remain off of the potentially-weakened floor while creating the access; or along the lower edge of the outside wall, providing a path for water application beneath the first floor sill.

Unlike attics, which can be almost completely wet down from below, without the need for entry, fires below grade will eventually require firefighters to enter that space in order to complete extinguishment, particularly to control any burning that remains in the ceiling structure. The dangers of descending fire-weakened stairways are well-known, and not always avoided by merely going down quickly. The placement of ladders over the stairs, or creating a larger breach in the floor or wall to provide access, may be necessary. Of course, extension to the floors above is also a concern. It is worth noting that the Governors Island burn tests (https://ulfirefightersafety.org/resources.html#training/scientific-…) found that fires in those basements most often spread upward along pipe chases into the kitchen cabinets, there leading to collapse of the kitchen floor, rather than traveling up the open basement stairways, which would previously have been considered the more likely path.

Exterior

Fires that initiate on the outside of a structure (PDF) can be much more rapidly invasive and destructive than those that start from within (a distinction that, in my opinion, is not appreciated by many in the fire service). Not only is fire spread over an exterior wall amazingly rapid, depending upon the material used in its construction (the presence of rigid foam insulation being the worst), but the natural ventilation engineered into attics, as discussed in the previous post, promotes the extension of fire into that compartment. At the same time, while flames race upwards and are virtually drawn into the soffits, entry into the lower levels of a structure is slower, and typically limited to sites of existing penetrations in the wall. Windows are the largest and most obvious of these potential fire paths, while electrical switches and outlets, especially those made of plastic that can quickly melt away, will also admit flames. Conversely, research showed that surprisingly little heat is transmitted to the interior through an intact, gypsum-covered wall, even with a raging blaze right behind.

The findings that fires on the outside of structures propagate and enter attic spaces rapidly, while extending into lower levels much more slowly, drives the change in strategy for these blazes. This translates into prioritizing the control of the exterior blaze, and even initiating control of any spread, from the outside. That is, not only knockdown, but extinguishment is best performed from the exterior. While interior lines will need to be stretched to extinguish any areas of extension, this might best be considered as overhaul, as it is virtually impossible to effectively control a fire from the inside if it started on the outside. Also, with the primary spread being into the attic, and fires in that space controllable by streams directed into the soffits (again, see the discussion of Attics in the previous post), exterior streams are ideal choices to control both the seat of the fire and its extension. On the other hand, entering the interior of a structure that is burning on its outside, and hoping to push back and extinguish flames that are, for the most part, shielded by walls as they extend into building voids, often on multiple levels, is a futile effort. First extinguish the fire outside, then move inside for “mop-up”.

Thanks to knowledge gleaned from fire dynamics research, we now have better information regarding the ideal methods for controlling fires inside the tops and bottoms, and on the outsides, of structures. While these new recommendations call for a change in directions from those with which we had all been familiar, their basis is sound, and the resulting tactics have proven effective. Implementation requires training and practice in these principles and techniques, but can be accomplished using existing tools and equipment. These new insights, once understood and acted upon, will assist us in our ongoing mission to protect life and property from fire.

Mark J. Cotter has more than 40 years experience in emergency services and is currently a volunteer captain with the Salisbury (MD) Fire Department. He can be reached at [email protected]


This commentary reflects the opinion of the author and does not necessarily reflect the opinions of Fire Engineering. It has not undergone Fire Engineering‘s peer-review process.