I'm going to steal the words from my brainiac kids here - "Science doesn't care what you think." So I'm going to apply science to some of my earlier writing regarding heavyweight tactics on lightweight apartment "externally-ignited" fires.
In the June, 2014 edition of Fire Engineering Magazine I wrote about the critical need for heavyweight tactics when faced with a lightweight apartment building fire, especially when the fire starts on the exterior (http://www.fireengineering.com/articles/print/volume-167/issue-6/fe...). These externally-ignited fires are becoming very common with changes in human smoking habits and lightweight building materials.
In the article I referenced several recent apartment building fires in Omaha which started on the exterior, were caused by careless smoking, resulted in Maydays, near-miss incidents, several firefighter injuries, and millions of dollars in property damage.
The challenges behind extinguishment of these fires lie in their exterior nature, vinyl siding and soffits not protecting the exterior surfaces from ignition and fire spread, rapid growth and spread into the lightweight attics under a lightweight roof, which is an supported by pre-engineered truss systems. Occupants are generally not aware of the fires until someone on the exterior notifies them verbally or by pulling a manual pull-station. Wind is almost always a factor and also plays a large role in the intensity and speed of these fires. Congestion of parking and travel routes around the buildings is also a detriment to apparatus placement and water supply.
However, the American fire service has come to adopt two popular fire flow formulas to successfully extinguish structure fires. First, the Iowa State Fire Flow Formula (Royer, Nelson) which simply put, is length x width x height / 100. Second the National Fire Academy (NFA) Fire Flow Formula which is length x width / 3.
Using these formulas for the sake of argument on a recent apartment building fire, the building was 165’ x 65’, and approximately 30’ in height to the eave of the gable roof. By the time of arrival, like is often the case, the fire involved a 20 – 30’ wide area of the siding from the second floor balcony upward, and approximately 30% of the attic/roof. The Iowa State formula would be applied as follows:
165 x 65 x 30 = 321,750
321750 / 100 = 3,200 GPM (rounded)
For a single floor of involvement of a three story building, you could take the 3,200 GPM times 1/3 (1,070 GPM), plus half of that (535 GPM) for exposure of the next floor, giving you around 1,600 GPM total. Since the fires I am referring to are usually on a vertical exterior surface upon arrival, and progressing quickly toward the attic by melting through the eave material, the roof is also an exposure or actually on fire. A gable roof mathematically requires 50% of a standard floor, so add another 535 GPM. These fires may or may not have progressed to the interior and will result extensive fire damage to the top floor, while burning the roof off. Adding these requirements up, we get around 2,100 GPM fire flow using the Iowa State formula. Extinguishment would come in the form of a multi-pronged attack, involving 300-plus GPM handlines, ground-based and aerial master streams, followed by an interior attack and mop-up as soon as possible.
Using the NFA formula, we would simply have 165 x 65 = 10,725. Then 10,725 / 3 = 3,600 GPM (rounded). In actuality, while rolling up to this fire, I would have rounded the dimensions significantly from the get-go to make the math possible in my head. With the percentages of involvement and exposures being the same, following the NFA formula, you would end up with approximately 2,400 GPM. A person could argue this number based on much of the early fire being exterior, but we don’t know if it will stay that way, and we must anticipate that it won’t. Surprisingly, the two formulas end up being only 300 GPM apart (or one 2 ½ inch handline). Also, not surprisingly, these large flows were eventually required in every actual fire referenced above to achieve extinguishment.
We have grown accustomed to fighting Type-I and older type III and V apartments from the interior very successfully over and over again. We cut our teeth on those fires and get lulled to sleep by the sheer numbers of manageable interior fires. As a matter of fact, in a new lightweight wood apartment building, conventional tactics are still applicable along with flow path control and closely-timed ventilation for most interior fires. But if the fire is on the exterior upon arrival, this fire is an entirely different animal, with a different mindset, strategy, and tactics required.
The point is, scientifically, we won’t fight these large “outside-in” fires effectively with conventional interior handline attack. On an exterior and roof assembly fire that is difficult to access from the interior, with such a large GPM requirement, the best chance to have an impact on the fire is initially from the exterior.
How will you know if it is interior or exterior? First, there will be smoke on approach from a significant distance on an exterior fire, so you will at least know the fire is large – Get those resources coming. Second, a quick interior size-up will reveal little heat and smoke as compared to the exterior. Direct attack on the visible exterior and roof assembly fire at this point will remove a lot of energy, and make interior operations feasible.
In my 30-plus year career, I was trained to save lives and ensure life safety, put the fire out and reduce fire loss, all while preventing fire service casualties. Fighting the fire from the interior with the easiest stretching crosslay just because “that’s how we’ve always done it here” doesn’t work in this situation. A thorough size-up will save you time, energy, and resources needed to successfully apply the correct tactics.
For apartment buildings, hotels, and the like sized buildings constructed of lightweight wood, call extra resources early to achieve and apply the required GPM, and be prepared to mount a successful multi-pronged fire attack, up to and including the use of aerial master streams early in the attack. The longer it takes to apply the scientifically required GPM, the larger the fire will be, and the more dangerous the fire will become.