Horizontal vs Vertical Ventilation
One of the most common questions we receive regarding a fire officer simulator or actual fire ground tactics is, “when should vertical ventilation be performed on a single family dwelling”?
Finding the right balance of safety, efficiency and customer service often makes for a difficult decision. In something as dynamic as firefighting, there can never be a pre-determined answer for every possible situation.
Let’s first talk about smoke conditions. If you see lazy white, gray or even light black smoke at ceiling height only -you’re probably leaning toward horizontal ventilation. Conversely, if you encounter dense black or black/gray smoke, it’s turbulent or pressurized, at chest level or lower and especially if rollover is present-going to the roof is justifiable.
If you observe a lazy, slow burning fire confined to one room or the engine company has quickly knocked the fire down, horizontal ventilation is appropriate. However, if the fire is blowing out of openings on two sides, extending down the hallway or you suspect it has breached the attic, going to the roof is a good call.
Building construction is another important component that has to be factored in. To make things simple let’s utilize two categories; lightweight construction and conventional construction. If the dwelling was built prior to the late 1960’s, its framework was probably “full dimensional” lumber and held together with nails (conventional). The decking was usually 1×6 boards. If was built after the late 60’s, its framework is more likely smaller than advertised and held together with metal gusset plates or gang nails . The decking found is likely plywood, particle board or OSB (lightweight). As we all know, lightweight construction doesn’t hold up for very long in fire conditions. It has shown to fail in as little as 5 minutes with direct flame impingement. If you suspect the fire has penetrated the attic & you’ve determined that you’re standing on a lightweight roof, cutting a hole over the fire is not a smart move.
Another construction feature that can cause you problems are tiles-especially on a lightweight roof. Their added weight can accelerate failure and it’s nearly impossible to safely and efficiently “sound” a roof covered with tiles.
When you are confronted with these “no go” situations and still believe vertical ventilation is needed, what should you do? One viable option is to open up the attic vents. These are typically 1’x2’ openings located under the eaves-at opposite ends of the house. After removing them, it is relatively easy work to expand them with a chain saw from the safety of a ground ladder.